WO2017036500A1

WO2017036500A1 - Breathing circuit for use in a respiratory system

Info

Publication number: WO2017036500A1
Application number: PCT/EP2015/069780
Authority: WO
Inventors: Jeno Kurja; Frédéric ARIEN
Original assignee: Plastiflex Group
Priority date: 2015-08-28
Filing date: 2015-08-28
Publication date: 2017-03-09

Abstract

A breathing circuit (10) for use in a respiratory system comprising a heated conduit (12) comprising a breathing tube, a tube heating system (17) associated with the breathing tube (18) configured for heating the breathable gas travelling through the breathing tube (18) to a target temperature and a connector element (15) arranged for supplying a source voltage to the tube heating system (17) so as to heat the breathable gas to the target temperature. The tube heating system (17) is a variable resistance heating system arranged for receiving at least one control signal by which the electrical resistance of the tube heating system (17) can be altered. The breathing circuit (10) comprises a temperature controller (21) arranged for receiving ambient temperature information and for generating, based on the ambient temperature, the at least one control signal.

Description

BREATHING CIRCUIT FOR USE IN A RESPIRATORY SYSTEM

Technical field

The present invention relates to a breathing circuit for use in a respiratory system and more specifically to a breathing circuit comprising a temperature controller arranged for adjusting the temperature of the breathable gas supplied to the patient based on at least the ambient temperature detected so as to minimise the risk of condensation in the breathing tube.

Background art

Respiratory systems are widely used in medical application for delivering a breathable gas to a patient. As the breathable gas is delivered to the patient and due to the high air flow of the breathable gas, the patient airways are not able to deliver sufficient heat and moisture. As a result, the patient airways lose moisture and eventually will show symptoms of drying, which may lead to undesirable side effects such as dry nose, dry throat, headache, painful chest, damage of weak tissue around nose entry, bleeding nose, dry and damaged lips, and infections of nose, throat and sinus. In order to avoid these side effects the breathable gas is usually heated and humidified before being delivered to the patient.

As the heated and humidifier air travels along the conduit, some heat is lost to the air outside of the conduit resulting in condensation of the breathable gas. In order to avoid condensation within the breathing tube of the conduit, the breathing tube usually comprises a heating element provided for heating the breathable gas, counteracting the heat lost along the length of the tube. Conventional electrically heated breathing tubes make use of a heating element in the form of a resistance wire. In order to provide the heating element with the right heating, the breathing tube usually comprises one or more sensors to measure the temperature of the breathable gas, this information being provided back to a controller which is associated with the heating element.

WO2014077706 describes a zone heating system for use in a breathing circuit arranged for delivering a breathable gas to a patient interface. In the zone heating system of the prior art, an inspiration limb of the breathing circuit is provided with a first segment that comprises a first heater wire circuit and a second segment that comprises a second heater wire circuit. The inspiratory limb includes an intermediate connector that includes a connection circuit that electrically couples the first heater wire circuit to the second heater wire circuit. The inspiratory limb is configured to operate in two modes wherein, in a first mode, electrical power passes through the first electrical connection to provide power to the first heater wire circuit without providing power to the second heater wire circuit, and in a second mode, wherein electrical power pass through the first electrical connection to provide power to both the first heater wire circuit and the second heater wire circuit. By providing the inspiration limb with a first and a second heating segment, a zone heating system can be provided for controlling over heating of the breathable gas in a specific segment of the respiratory limb. However, the system of the prior art can only operate between two heating modes, as previously described, thereby providing a limited control over the condensation in the breathing tube. This is because, the heater wire circuits of the first and second segment of the inspiration limb are connected in series, thereby allowing the system to be operated in only two modes, whereby power is provided either to the first heater circuit or to both the first and second heater wire circuits. As a result, the temperature adjustments required for controlling the condensation in the tube can only be affected by continuously switching between the two modes.

US201 10023874 describes a system for use in a respiratory system arranged for delivering a breathable gas to a patient interface. The system comprises a breathing tube for delivering the breathable gas to the patient interface and a tube heating system associated with the breathing tube arranged for heating the breathable gas at a target temperature. The tube heating system comprises a sensor for measuring the temperature of the breathable gas. The sensor output is connected to a control unit, which is arranged for monitoring the temperature detected by the sensor so as to determine if the temperature is within an acceptable target temperature range and accordingly switch-on or switch-off the power supply to the tube heating system. For example, in the case where the temperature of the breathable gas is above an acceptable target temperature range, the control unit switches-off the power supply to the tube heating system. The control unit continuously monitors the temperature detected by the sensor and accordingly switches-on or switches-off the power supply to the tube heating system so as to control the temperature provided by the tube heating system to the breathable gas. However, with the system the prior art, the switching of the power supply occurs only after there is a temperature deviation in the sensor output from the target temperature. As a result, there is a temperature adjustment time-lag between detecting the temperature deviation and switching the power supply so as to correct the deviation. This may have as an effect, that during the temperature adjustment time-lag the temperature of the breathable gas will be outside the target temperature range, which may lead to condensation in the breathing tube thereby limiting the level of humidity delivered to the patient. Moreover, due to the continuous switching of the power supply of the system of the prior art it is extremely difficult to maintain the breathable gas at a constant target temperature.

Disclosure of the invention

It is an aim of the present invention to provide a breathing circuit for use in a respiratory system arranged for tracking the ambient temperature and accordingly adjust the temperature of the breathable gas flowing in the breathable tube so as control the condensation in the breathing tube. This aim is achieved according to the invention with a breathing circuit showing the technical characteristics of the first claim.

More specifically, according to embodiments of the present invention, a breathing circuit for use in a respiratory system is provided. The breathing circuit is arranged for supplying a breathable gas from a breathable gas supply system to a patient interface. The breathing circuit comprises a heated conduit system comprising a breathing tube connectable between the breathable gas supply system and the patient interface. The breathing tube is arranged for supplying the breathable gas from the breathable gas supply system to the patient interface. The heated conduit system is provided with a tube heating system associated with the breathing tube configured for heating the breathable gas travelling through the breathing tube to a target temperature so as to minimise condensation inside the tube. The tube heating system is provided with an electrical resistance and arranged, when a supply voltage is applied, for generating an amount of heating power for heating the wall of the breathing tube along its entire length such that the breathable gas travelling through the breathing tube is heated to a target temperature for minimising condensation inside the breathing tube. A connector element is provided in the heated conduit system, which is arranged for interfacing the breathing tube with the breathable gas supply system. The connector element is further arranged for applying the supply voltage to the tube heating system. For example, the connector element may be provided with electrical conductive contact points, via which the supply voltage is applied to the tube heating system. The tube heating system is a variable resistance heating system arranged for receiving at least one control signal by which the electrical resistance of the tube heating system can be altered. The breathing circuit is provided with a temperature controller arranged for receiving ambient temperature information and for generating, based on the ambient temperature, the at least one control signal. It has been found that by providing the tube heating system with a variable resistance that can be altered via at least one control signal generated from a temperature controller, the temperature of the breathable gas can be quickly adjusted in response to an ambient temperature change, thereby providing a better control of condensation inside the breathing tube. For example, in the case where a change in the ambient temperature is detected, the temperature controller in order to minimise the risk of condensation in the breathing tube may generate at least one control signal for adjusting the electrical resistance of the tube heating system, thereby altering the temperature of the breathable gas so as to compensate for the ambient temperature change. In other words, the amount of heating power generated by the tube heating system can be quickly adapted to ambient conditions, thereby allowing for better control of the condensation in the breathing tube. Moreover, with the system of the present invention, the temperature of the breathable gas can be easily maintained at a near-constant target temperature since there is no need for constantly switching the power supply on and off so as to maintain the breathable gas at the target temperature, as it is the case with the system of the prior art. As a result, the temperature adjustment time-lag during which the temperature of the breathable gas is outside the target temperature may be significantly reduced thereby minimising the risk of condensation in the breathing tube.

According to embodiments of the present invention, the tube heating system is provided with a plurality of heating elements that are connected in parallel, each provided with a predetermined electrical resistance.

It has been found that by providing the tube heating element with a plurality of heating elements that are connected in parallel, the electrical resistance of the tube heating system may be easily adjusted by selecting the heating elements to which the supply voltage is to be applied. Each of the heating elements may be provided with a predetermined electrical resistance arranged when a supply voltage is applied for generating a predeternnined amount of heating power so as to heat the breathable gas towards a predetermined temperature. As a result, by selecting the heating elements to which the supply voltage is to be applied, the electrical resistance of the tube heating system can be easily adjusted according to ambient temperature changes so as to minimise the risk of condensation in the tube.

According to embodiments of the present invention, the temperature controller may be provided with a switching mechanism arranged, based on the at least one control signal, for applying the supply voltage to at least one of the heating elements. For example, the switching mechanism may be provided with a number of switches each connected at one end to a supply voltage and to the other end to a heating element. The switching mechanism may be arranged for operating the switches according to the at least one control signals generated by the temperature controller, so as to select the heating elements to which the supply voltage is to be applied. For example, the switches may comprise transistors arranged, based on the voltage level of the control signal for respectively switching-on, thereby applying the supply voltage to the heating elements selected, or switch ing-off, thereby disconnecting the supply voltage from the heating elements selected. The switching mechanism may be provided with other types of switches known in the art. For example, the switching mechanism may be provided with bimetallic strips arranged, in response to ambient temperature changes for reversibly applying the supply voltage to at least one of the heating elements. For example, the bimetallic strip may be provided with two strips of metal each having a different coefficient of thermal expansion. For example, each of the bimetallic strips may be adapted for responding to a predetermined ambient temperature, such that for each predetermined ambient temperature detected the supply voltage may be arranged for being reversibly applied to a predetermined heating element or number of heating elements. According to embodiments of the present invention, the heating elements may be heating wires each provided with a predetermined electrical resistance. The heating wires may be in the form of electrically conductive strips, which may be inject printed on a surface of the breathing tube wall in the form of layers. For example, the heating wire may be provided with identical resistances or with different resistances, or any combination thereof. In this way, the heating of the breathable gas may be adjusted by switching between the different heating elements, based on the ambient temperature detected. The switching mechanism may be arranged for applying the supply voltage to more than one heating element so that the breathable gas is heated towards a predetermined target temperature. So according to embodiments of the present invention, the heating elements may have identical resistances or different resistances, and the switching mechanism may be arranged to connect one or more of the heating elements to adjust the heating of the breathable gas.

According to embodiments of the present invention, the temperature controller may be provided with a temperature tracking system arranged for generating the at least one control signal for operating the switching mechanism. The temperature tracking system may be arranged for evaluating the ambient temperature information and accordingly generate at least one control signal for adjusting the electrical resistance of the tube heating system, e.g by operating the switching mechanism so as to select to which of the heating elements the supply voltage is to be applied. As a result, the temperature of the breathable gas can be quickly adjusted so as to compensate for changes in the ambient temperature, thereby minimising the risk of condensation in the breathing tube.

According to embodiments of the present invention, the tube heating system may be provided with a variable resistance heating element, such a variable resistance heating wire. For example, the heating element may be a coaxial wire provided with a first electrical conductive element, a variable resistance material surrounding the first electrical conductive element, and a second electrically conductive element electrically surrounding the variable resistance material. The electrical resistance of the variable resistance material may depend upon the potential difference created across the material. For example the temperature controller may be arranged for generating a potential difference across the variable resistance material, which can be altered by means of the at least one control signal. For example and without any limitation, the variable resistance material may be made from a photoresistive material, the electrical resistance of which depends on the light intensity detected. In this case, in order to adjust the electrical resistance of the variable resistance wire, the temperature controller may be arranged for generating an optical control signal, the light intensity of which can be changed based on the electrical resistance required, so as to generate across the variable resistance material a required potential difference. The temperature controller may be further arranged for applying to the first and second electrical conductive elements a predetermined supply voltage, e.g. through the switching mechanism. As a result, the electrical resistance of the variable resistor may be easily adjusted by providing at least one control signal arranged for altering the potential difference across the variable resistance material, thereby altering the amount of heat generated by the tube heating system.

According to embodiments of the present invention, the temperature tracking system may be provided with a processing unit arranged for processing the ambient temperature information received from the at least one temperature sensor and accordingly generating at least one control signal for operating the switching mechanism. The processing unit may be provided with a comparator arranged for comparing the ambient temperature detected to at least one predetermined threshold temperature. The at least one predetermined threshold temperature may be adjustable, so that a different threshold temperature may be set according to the application where the breathing circuit is used. The processor unit may be arranged for generating at least one control signal for operating at least the switching mechanism, which can be either analogue or digital depending on the application. For example, the processor may generate a set of control signals for operating at least the switching mechanism according to the comparator output, as discussed previously.

By providing a processing unit arranged for operating the switching mechanism, the temperature adjustments may be implemented in a digital way, thereby allowing for faster and more accurate control of the condensation in the breathing tube in response to ambient temperature changes. Moreover, with the use of a processing unit other information may be used for determining the optimal resistance adjustment of the tube heating element for a given ambient temperature change. For example, and without any limitation, the processing unit may take into account the surface temperature of the breathing tube that would be generated for a given electrical resistance adjustment. For example, in the case where the tube heating system is provided with a plurality of heating elements connected in parallel, each heating element may be arranged, when the supply voltage is applied, for heating the wall of the breathing tube. As a result, each of the heating elements, when the supply voltage is applied, may change the surface temperature of the breathing tube by a predetermined amount depending on its electrical resistance. It is desired that the surface temperature of the breathing tube is maintained within a predetermined temperature range e.g. surface temperature of the breathing tube specified in the ISO 8185, which is set at 43 degrees Celsius, so as to ensure the patient comfort and safety. The surface temperature of the breathing tube generated may be experimentally derived and stored in the memory of the processor. For example the surface temperature generated by each heating element may be experimentally derived using the methods described in the ISO 8185, or any other method known to the skilled person in the art. The surface temperatures derived for each electrical resistance adjustment may be stored in a memory of the processor unit, which may be either an internal processor memory or an external processor memory. For example, the surface temperature may be stored in the memory in the form of a table. In this way, the processor unit based on the ambient temperature detected and taking into account the surface temperature information from the table, may select for adjusting the electrical resistance of the tube heating system by a predetermined amount that may be optimised for sufficiently minimising the condensation in the breathing tube while ensuring that the surface temperature of the breathing tube does not exceed the recommended value. As a result, with the system of the present invention the temperature of the breathable gas may be adjusted such that the risk of condensation in the tube is minimised while ensuring that the recommended breathing tube surface temperature is not exceeded. For example, in the case where the ambient temperature is low, e.g. due to an air conditioning unit being placed close to the patient, it can be avoided that the breathable gas will be heated by the tube heating system to a temperature exceeding the recommended surface temperature of the breathing tube. As a result, with the system of the present invention the patient safety and comfort can be enhanced, while ensuring that condensation in the breathing tube is optimally controlled.

According to embodiments of the present invention, the temperature controller is provided with at least one temperature sensor, e.g a thermistor or an infrared sensor, arranged for monitoring at least the ambient temperature. For example the at least one temperature sensor may be a thermistor, e.g. a Negative Temperature Coefficient (NTC) thermistor. In general, thermistors made from an NTC material may be considered to be less prone to permanent damage than Positive Temperature Coefficient materials. Furthermore, NTC material can detect faster a rapid increase in temperature, for instance as a result of a hot spot of the heating element, in view of the logarithmic relationship between the resistance of an NTC material and the temperature The temperature sensor may be part of the tube heating system and arranged for monitoring the temperature generated by the tube heating system. The system may be provided with further sensors arranged for monitoring different operating parameters such as gas flow sensors for monitoring the flow rate of the breathable gas in the tube, pressure sensors, humidity sensors, and the like. By integrating different type of sensors, the temperature of the breathable gas can be further optimised so as to ensure that the breathable gas remains at the optimum humidity levels. The temperature controller may be arranged based on the temperature detected from the at least one temperature sensor for operating the switching mechanism so as to select which of the heating elements is to be connected to the source voltage. In this way, the temperature of the breathable gas inside the tube can be quickly adjusted in response to ambient temperature changes detected by the at least one temperature sensor, thereby enabling a better control of the condensation inside the tube.

According to embodiments of the present invention, the tube heating system may be arranged for being at least partially in contact with a surface of the wall of the breathing tube, e.g. on the inner surface of the breathing tube, on the outer surface of the breathing tube, integrated in the wall of the breathing tube or any combination thereof. Furthermore, the tube heating system may be arranged for being helically wounded along the length of the breathing tube. For example, the tube heating system may meander on the outer or inner surface of the breathing tube. In this way, the wall of the breathing tube can be heated to a substantial equal temperature to that of the breathable gas flowing inside the breathing tube, thereby preventing the build-up of condensation in the breathing tube due to temperature differences between the tube wall surface and the breathable gas. As previously discussed, the tube heating system may be arranged for heating the surface of the breathing tube to a predetermined temperature. For example, the tube heating system may be provided on the outer surface of the wall of the breathing tube, the heating element or variable resistance heating element may be wrapped around the outer surface of the breathing tube, e.g. the heating wires are longitudinal- helical, i.e. spiralled, around the breathing tube with a pitch different from the reinforcement rib. For example, the tube heating system may be provided on the inner surface of the breathing tube, e.g. the heating elements or the variable resistance heating element may be arranged such that they are at least partially in contact with the inner surface of the wall of the breathing tube. For example, the tube heating system may be integrated in the wall of the breathing tube, e.g. heating elements or the variable resistance heating element the reinforced ribs helically wounded around the wall of the breathing tube.

According to embodiments of the present invention, the heated conduit system is formed as a single unit. For example, the heating conduit system may be provided as one piece that can be directly connected to the breathing circuit without the need for assembling the different heated conduit components, such as the breathing tube, tube heating system and connector element.

According to embodiments of the present invention, the heated conduit may be assembled from discreet components. For example, at least one of the components may need to be assembled to the heated conduit before it is connected to the breathing circuit. The connector element may be a replaceable component that can be replaced with another connector elements based on the type and brand of the breathing circuit. By providing a replaceable connector element, the breathing tube and the tube heating system may be generic elements that can be used in combination with any type/brand of breathable gas supply systems. According to embodiments of the present invention, the temperature controller may be integrated into the connector elements. The connector element may be provided with electrical contacts, which may be arranged for applying the supply voltage to the tube heating element, transferring information from the at least one sensor to the temperature controller, etc.

According to embodiments of the present invention, the target temperature of the breathable gas is in the range between 20.0 degrees and 45.0 degrees, more preferably in the range between 30.0 degrees and 40.0 degrees. For example for a non-invasive respiratory system the target temperature of the breathable gas at the patient interface may be at around 30 degrees Celsius, while for an invasive respiratory system, where the tube is inserted in the trachea, the target temperature of the breathable gas may be around 37 degrees Celsius.

Brief description of the drawings

The invention will be further elucidated by means of the following description and the appended figures.

Figure 1 schematically shows an example of a breathing circuit according to embodiments of the present invention.

Figures 2 and 3 schematically show exemplified implementations of a heated conduit according to embodiments of the present invention.

Figures 4 to 7 schematically show exemplified implementations of the tube heating system according to embodiments of the present invention.

Figures 8 to 10 schematically show examples of how the tube heating system may be positioned on the breathing tube according to embodiments of the present invention.

Figure 1 1 to 16 schematically show examples of how the temperature controller may be interfaced with the tube heating system according to embodiments of the present invention. Modes for carrying out the invention

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the invention can operate in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances and the embodiments of the invention described herein can operate in other orientations than described or illustrated herein.

The term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B. The present invention will be elucidated by means of the example embodiments shown in figures 1 to 16, which will be described in more details below.

Figures 1 show an example of a breathing circuit 10 for use in a respiratory system according to embodiments of the present invention. The breathing circuit 10 may be either a non-invasive or an invasive breathing circuit 10. In a non-invasive breathing circuit the breathable gas may be supplied to the patient mouth or nose via a mask or another patient interface 1 1 , while in an invasive breathing circuit the breathable gas may be delivered via a patient interface 1 1 directly to the patient trachea. The breathing circuit 10 may comprise a heated conduit system 12 arranged for supplying a breathable gas to a patient interface 1 1 from a breathable gas supply system 13, in the direction indicated by the arrows. In figure 1 the breathing circuit 10 is shown as having only a single respiratory limb for providing a breathable gas to the patient interface 1 1 . However, in practise, the breathing circuit 10 may further be provided with an expiratory limb for transferring the exhaled air from the patient to the breathable gas supply system 13. Therefore, it should be understood that the present invention further applies without any limitations to breathing circuits having inspiratory and expiratory limbs. As shown in figure 1 , the breathable gas supply system 13, depending on the type and brand, may be provided with a flow generator for supplying the breathable gas and a humidifier unit arranged for heating and humidifying the breathable gas to the target humidity and temperature level. Depending on the type and/or brand of the breathable gas supply system 13, the flow generator and the humidifier unit may be integrated into a single unit or alternatively may be provided as separate units connected to one another via a tube 30, as shown in figure 1 . The breathable gas supply system 13 may be provided with a voltage source 14 arranged for supplying to the humidifier unit and/or the flow generator a predetermined source voltage, which may be derived from an external power supply. As shown in figure 2, the heated conduit system 12 may be provided with a breathing tube 18 connectable between the breathable gas supply system 13 and the patient interface 1 1 and a tube heating system 17 associated with the breathing tube 18. The tube heating system 17 may be configured for heating the breathable gas travelling through the breathing tube 18 to a target temperature so as to prevent or at least minimise condensation inside the breathing tube 18. For example, the tube heating system 17 may be provided with an electrical resistance arranged, when a supply voltage is applied, for generating an amount of heating power for heating the wall 26 of the breathing tube 18, as shown in figures 8 to 10, along its entire length such that the breathable gas travelling through the breathing tube 18 may be heated to a target temperature for minimising condensation inside the breathing tube 18. The heated conduit system 12 may be provided with a connector element 15, which may be arranged for interfacing the breathing tube 18 with the breathable gas supply system 13. The connector element 15 may be further arranged for applying a supply voltage to the tube heating system 17. For example, the connector element 15 may be provided with electrical contacts arranged for applying the supply voltage to the tube heating system 17 or other information in the form of electrical signals. The supply voltage may be directly generated from a voltage source 14a, or may be derived from the voltage source 14a. For example, the supply voltage may be generated or derived from the voltage source 14 of the breathable gas supply system 13. The connector element 15 may be arranged for applying the supply voltage generated by the voltage source 14 of the breathable tube 13 to the tube heating element 17 via a specific plug, which may be in the form of a cable, or specific contacts pads. The connector element 15 may be similar to the one described in EP2248547A, which is incorporated here in its entirety. As shown in figure 3, the voltage source 14a may be integrated into the connector element 15. In this instance the supply voltage may be derived from an external power supply, which may be the mains voltage to which the connector element 15 may be connectable by means of a standard power cable, or the supply voltage may be derived from the voltage source 14 of the breathable gas supply system 13. It should be understood and without any limitations, that the voltage source 14a may be provided in any other form known to the skilled person in the art. Connecting elements, which are not shown, may be provided for securely connecting the heated conduit 12 at one end to the breathable gas supply system 13 and on the other end to the patient interface 1 1 . For example, the connecting elements may be arranged for providing a snap-fit connection for securely connecting the heated conduit 12 to the patient interface 1 1 and to a connection point of the breathable gas supply system 13. The connecting elements may further comprise electrical connectors for applying the supply voltage to the tube heating system 17. The electrical connector pins may be for example used for transmitting information e.g. from the at least one sensor 22 to the temperature controller 21 . According to embodiments of the present invention, the heated conduit 12 may be provided as a single unit, whereby the heated conduit components, such as the breathing tube 18, the tube heating system 17 and the connector element 15 are pre- connected to one another. The heated conduit 12 may also be provided as a kit of parts, whereby at least one of the components may need to be assembled before use. For example, the connector element 15 may be provided as a loose component that needs to be assembled to the heated conduit 12. The connector element 15 may be a replaceable component that can be replaced, depending on the type and/or brand of the breathable gas supply system 13, with another connector element 15. For example, similarly to EP2248547 which is incorporated herein by reference in its entirety, the connector element may be in the form of an adapter, which may be arranged for adjusting the voltage supplied by the voltage source 14a to the tube heating system 17 from the second predetermined voltage range to a first predetermined voltage range. By providing a connector element 15 in the form of an adapter the breathing tube 18 may be a generic breathing tube, which can be used in combination with any type/brand of breathable gas supply systems 13,. For example, the system may be provided with a plurality of connector elements, each arranged for connecting the generic breathing tube 18 to a predetermined type/brand of breathable gas supply system 13 and for adjusting the voltage supplied by the power supply of the breathable gas supply system 13 to the operating voltage of the tube heating system 17. In this way, the heating power delivered by the tube heating system 17 remains independent from the type/brand of breathable gas supply system 13 used. According to embodiments of the present invention, the heated conduit 12 may further comprise features of embodiments described in WO2009022004A1 , which is incorporated herein by reference in its entirety.

Figure 4 shows an exemplified implementation of the tube heating system 17 according to embodiments of the present invention. The tube heating system 17 may be a variable resistance heating system arranged for receiving at least one control signal by which the electrical resistance of the tube heating system 17 can be altered. For example, the tube heating system 17 may be provided with a plurality of heating elements 20, e.g. heating wires, that may be connected in parallel. Each heating element 20 may be provided with a predetermined electrical resistance arranged, when a supply voltage is applied, for drawing a predetermined amount of heating power from the voltage source thereby heating the breathable gas in the breathing tube 18. For example, the heating wires may be provided in the form of conductive strips, which may be inject printed on a surface of the breathing tube 18. Figures 5 and 6 show different heating elements configurations according to embodiments of the present invention. Figure 5 shows a tube heating system 17 provided with a plurality of heating elements 20, e.g. four heating elements, connected in parallel, each having a predetermined electrical resistance and arranged for receiving, e.g via the connector element 15, the supply voltage. With the use of parallel connected heating elements, the electrical resistance of the tube heating system may be adjusted by selecting the heating elements 20 to which the supply voltage is to be applied. For example, a temperature controller 21 by means of at least one control signal may select based on the ambient temperature detected to apply the supply voltage to none of the heating elements 20, or to some of the heating elements 20, or to all of the heating elements 20. In each case depending on the electrical resistance of the heating elements 20 a predetermined heating power will be drawn from the voltage source 14a thereby generating an amount of heat for heating the breathable gas in the breathing tube 18. The heating power drawn may be defined based on the selected heating elements 20 to which the supply voltage is to be applied, as shown in the table below:

Pin combination Total heating Heating power

resistance w+ x V²

1 and 2

Rw + Rx

Rw+Ry V²

1 and 3

Rw + Ry

1 and 4 Rw+Rz V²

Rw + Rz

V²

2 and 3 Rx+Ry

Rx + Ry

V²

2 and 4 Rx+Rz

Rx + Rz

V²

3 and 4 Ry+Rz

Ry + Rz

V²

1+2 and 3

₁ ¹ ₁ + Ry

Rw ⁺ Rx

Rw ⁺ Rx V²

1+2 and 4 1

1 1 ^{+ RZ} ^ ^ + Rz

Rw ⁺ Rx

V²

1

2+3 and 1 i i ^{+ Rw} -j + ffw

Rx ⁺ Ry

V²

1

2+3 and 4 i i ^{+ Rz}

Rx ⁺ Ry

ffx ⁺ ff

1

3+4 and 1 - γ + Rw 1

-j + Rw

Ry ⁺ Rz

1 V²

1

3+4 and 2 - γ + Rx

-j + Rx

Ry ⁺ Rz

1 1 V²

1+2 and 3+4 1 1 ' 1 , 1

Rw Rx Ry Rz 1 1 ¹ 1 , 1

Rw Rx Ry Rz

1 1 V²

1+4 and 2+3 1 1 ¹ 1 , 1 1 1 ¹ 1 1

Rw Rz Rx ⁺ Ry

i?w i?z Rx ⁺ Ry

As a result, by applying the supply voltage to different combinations of heating elements 20, the temperature of the breathable gas may be adjusted so that the condensation in the breathing tube 18 is minimised. In figure 6, a different configuration of the heating elements 20 is presented, whereby the inputs of two of the heating elements, e.g. inputs 2 and 3, are shorted, thereby leading to a different combination of heating elements 20 that can be used for adjusting the temperature of the breathable gas. Each of the heating elements 20 may be provided with a different or identical electrical resistance depending on the temperature adjustments required. According to embodiments of the present invention, the tube heating element 17 may be provided, depending on the application, with any number of heating elements 20, e.g. a higher number of heating elements 20 may lead to a higher number of possible heating power adjustments. Typically, a tube heating system 17 may be provided with 3 to 10 heating elements 20 depending on the application and electrical resistance adjustments required.

According to embodiments of the present invention, the tube heating system 17 may be provided with a variable resistance heating element 28, as shown in figure 7. The variable resistance heating element 28 may be in the form of a coaxial wire provided with an electrically conductive core 27, surrounded by a variable resistance material 26, which variable resistance material is encapsulated with an electrically conductive element 25. The variable resistance material 26 may be made from a material having an adjustable electrical resistance. For example, the electrical resistance of the variable resistance material 26 may be adjusted by creating across the variable resistance material 26 a potential difference, e.g. between pins 2 and 3. For example and without any limitation, the variable resistance material 26 may be a photoresistive material having an electrical resistance that depends on the light intensity of an optical signal received at pins 2 and 3. In this way, by providing on pins 2 and 3 of the variable resistance heating element 28 a control signal having a predetermined light intensity, a predetermined potential difference would be created across the variable resistance material 26, thereby setting the electrical resistance of the variable resistance material 26 to the required value. In this way, the electrical resistance of the variable resistor heating element 28 may be altered by adjusting the potential difference created across the variable resistance material 26. For example, in order to adjust the heating power generated by the variable resistance heating element 28, pins 1 and 4 may be connected to a predetermined voltage, while at least one control signal, e.g. an optical signal having a predetermined light intensity, may be applied respectively to pins 2 and 3, thereby creating a potential difference across the variable resistive material 26 so as to adjust the electrical resistance of the variable resistance material 26 to the required value, and thus setting the heating power generated by the variable resistance heating element 28. In essence, with the use of a variable resistance heating element 28, the electrical resistance of the tube heating element 17 may be adjusted by changing the potential difference across the variable resistance material 26.

As shown in figures 8 to 10, the tube heating system 17 may be arranged for being at least partially in contact with the wall 26 of the breathing tube 17. For example, similarly to WO2012160524A1 or WO2012143563A1 incorporated herein by reference in their entirety, the tube heating element system 17 may be integrated in the tubular wall of the breathing tube, e.g. in the reinforced ribs 19 helically wounded around the tubular wall of the breathing tube 17, as shown in figure 8. The tube heating system 17 may be also provided on the inner surface of the wall of the breathing tube 18, e.g. in contact with the inner surface of the tubular wall 26 of the breathing tube, as shown in figure 9. The tube heating system 17 may also be provided on the outer surface of the tubular wall 26 of the breathing tube 18, e.g. the tube heating system 17 may be provided on the valleys formed between the reinforced ribs 19, as shown in figure 10. The heating wires may also be longitudinal-helical, i.e. spiralled, around the breathing tube with a pitch different from the reinforcement rib. By providing the tube heating system 17 so that it is at least partially in contact with the wall 26 of the breathing tube 18, it is ensured that wall 26 of the breathing tube 18 is also heated, thereby ensuring that temperature differences between the surface of the breathing tube 18 and the breathable gas flowing inside the breathing tube 18 are minimised, thus minimising the risk of condensation in the breathing tube 18. The tube heating system, depending on the electrical resistance adjustment, may be arranged for heating the surface of the breathing tube 18 towards a predetermined temperature. For example, in the case the tube heating system 17 is provided with a plurality of heating elements 20, each heating element may be arranged, when the supply voltage is applied, to heat the surface of the breathing tube 18 to a predetermined temperature. The surface temperature generated by the tube heating system 17 across the whole range of the electrical resistance adjustments that can be affected by means of the at least one control signal, may be experimentally derived, e.g. by using the methods disclosed in the ISO 8185 or any other method known to the skilled person in the art. The surface temperature generated by the tube heating system 17 for each electrical resistance adjustment should be within an acceptable temperature range, e.g. the temperature of 43 degrees Celsius indicated in the ISO 8185, so as to ensure the patient safety and comfort.

According to embodiments of the present invention, the tube heating system 17 may be integrated together with the breathing tube, as presented in figures 8 to 10, or may be provided as a separate unit, e.g. in the form of a sleeve stretched along the length of the breathing tube 18. According to embodiments of the present invention, the tube heating system 17 may be arranged for heating the breathable gas to a temperature in the range between 20.0 degrees and 45.0 degrees, more preferably in the range between 30.0 degrees and 40.0 degrees. For example for a non-invasive respiratory system the target temperature of the breathable gas at the patient interface may be at around 30 degrees Celsius, while for an invasive respiratory system, where the tube is inserted in the trachea, the target temperature of the breathable gas may be around 37 degrees Celsius.

According to embodiments of the present invention, the breathing circuit 10 may be provided with a temperature controller 21 arranged for receiving ambient temperature information and for generating, based on the ambient temperature, at least one control signal for adjusting the electrical resistance of the tube heating system 17, as shown in figure 1 1 . For example, in the case where the tube heating system 17 is provided with a plurality of heating elements 20, the temperature controller 21 , may receive ambient temperature information from a sensor 22 and according generate at least one control signal for selecting to which of the heating elements 20 the supply voltage is to be applied, as shown in figure 12. Similarly, in the case where the tube heating system 17 is provided with a variable resistor 28, as shown in figure 13, the temperature controller 21 may be arranged, based on the ambient temperature detected, for generating at least one control signal for creating a potential difference across the variable resistor material 26, via pins 1 and 4, so that the electrical resistance of the variable resistance heating element 28 is adjusted, thereby adjusting the temperature of the breathable gas. With the use of a temperature controller 21 , the temperature of the breathable gas can be quickly adjusted to any ambient temperature changes, thereby minimising the risk of condensation in the breathing tube 18.

As shown in figure 14, the temperature controller 21 may be provided with a temperature tracking system 24 and a switching mechanism 23 arranged for selecting the heating elements 20 to which the supply voltage is to be applied based on the ambient temperature detected. The temperature tracking system 24 may be arrange for receiving information from at least one sensor 22, e.g. ambient temperature sensor, and accordingly operate the switching mechanism 23 so as to select the heating elements 20 to which the supply voltage is to be applied. The temperature controller 21 may be arranged for receiving information regarding the ambient temperature from at least one sensor 22, which may be positioned at a desired location on the respiratory system, e.g. near the patient interface 1 1 or near the connector element 15. The temperature sensor may be of any suitable type known to the skilled person in the art, e.g. a thermistor or an infrared sensor or the like. The breathing circuit 10, although not shown, may also be provided with other type of sensors each arranged for providing information regarding a predetermined parameter, such as the flow rate of the breathable gas in the breathing tube 18, the pressure of the breathable gas, the temperature at other locations on the breathing circuit 10, humidity levels, etc. The temperature tracking system 24 may be arranged based on the information received from the temperature sensor 22 to select, via the switching mechanism 23, the heating elements 20 to which the supply voltage is to be applied, so that the temperature of the breathable gas and surface temperature of the tube 18 is adjusted according to ambient temperature changes, thereby minimising the risk of condensation in the breathing tube 18. For example, in the case where the ambient temperature is low, the temperature tracking system 24 upon receiving the temperature information from the sensor 22 may operate the switching mechanism 23 such that the supply voltage is applied to a set of predetermined heating elements 20, arranged for drawing a predetermined amount of heat power from the voltage source 14a, such that the breathable gas in the breathing tube 18 may be heated to a target temperature so as to minimise the condensation in the breathing tube 18. The temperature tracking system 20 may be arranged for determining, based on at least the ambient temperature detected and/or other information received from other sensors, the rate of heat transfer between the fluid, e.g. breathable gas, inside the breathing tube 18 and the external surface of the breathing tube 18. Based on the effective heat transfer the temperature controller may select the heating elements to which the supply voltage is to be applied so that the breathable gas inside the breathing tube 18 is heated to a target temperature so as to compensate for changes in the ambient temperature and thus minimise the risk of condensation in the breathing tube 18.

In general, heat transfer describes the exchange of thermal energy, between physical systems depending on the temperature and pressure, by dissipating heat. The fundamental modes of heat transfer are conduction or diffusion, convection and radiation. The heat transfer may be defined as the exchange of kinetic energy of particles through the boundary between two systems, which are at different temperatures from each other or from their surroundings. Heat transfer may occur from a region of high temperature to another region of lower temperature. Inside the breathing tube 18, heated and humidified air is transported to the patient or from the patient. The approximate rate of heat transfer between the bulk of the fluid inside the circuit and the circuit external surface is:

where

q = heat transfer rate (W)

h = heat transfer coefficient (W/(m2-K))

t = wall thickness (m)

k = wall thermal conductivity (W/m-K)

A = area (m2)

ΔΤ= difference in temperature.

As indicated in the equation above the heat transfer rate (q) will become bigger as ΔΤ increases. ΔΤ will increase when the temperature of the surroundings drops. So the lower the surrounding temperature the more heat will be exchanged with the surrounding. This heat loss increases the risk of condensation inside the breathing tube 18. In order to compensate for the heat loss to the surroundings and prevent condensation, additional heat is added to the breathable gas via the tube heating system 17. The additional heat supplied to breathable gas may lead to a certain surface temperature of the breathing tube 18, as previously discussed, which may not exceed a recommended limit so as to ensure patient safety and comfort, e.g. the surface temperature limit of 43 degrees Celsius as specified in ISO 8185. In order to ensure that the risk of the condensation in the breathing tube is minimised, while ensuring the patient safety and comfort, the temperature tracking system 24 may be provided with a processing unit 25, as shown in figure 15, arranged for processing the information received from the sensors and/or information stored in a processor accessible memory in order to optimise the selection of heating elements to which the supply voltage is to be applied. The processing unit 25 may be arranged for processing the ambient temperature detected in combination with other information that may be provided from other sensors or stored in a processor accessible memory and accordingly generate at least one control signal 30, either analogue or digital, arranged for operating the switches 29 of the switching mechanism 23. The switches 29 may comprise, transistors or other means of switching known to the skilled person in the art, which in response to an electrical signal, they are arranged for switching-on, thereby allowing the supply voltage to be applied to the respective heating elements 20, or switch ing-off, thereby disconnecting the source voltage from the respective elements 20. For example, the processing unit 25 may generate a set of control signals 30 by taking into account the ambient temperature detected and the surface temperatures generated by the tube heating system for each electrical resistance adjustment that can be affected, which surface temperatures may be stored in a processor accessible memory, e.g in the form of a table. For example, in the case where the tube heating system 17 is provided with a plurality of heating elements 20, the surface temperature generated by each heating element, when the supply voltage is applied, may be stored in the processor memory, e.g. in the form of a table. In this way, the processor unit 25 based on the ambient temperature detected and taking into account the surface temperature information stored in a processor accessible memory, may adjust the electrical resistance of the tube heating system such that the heating power generated is optimised to control the condensation in the breathing tube 18 while ensuring that the surface temperature of the breathing tube 18 does not exceed a recommended value. As a result, with the system of the present invention the temperature of the breathable gas can be adjusted such that the risk of condensation in the tube 18 is minimised while ensuring that the recommended breathing tube surface temperature is not exceeded. For example, in the case where the ambient temperature is low, e.g. due to an air conditioning unit being placed close to the patient, it can be avoided that the breathable gas will be heated by the tube heating system 17 to a temperature exceeding the recommended surface temperature of the breathing tube 18. As a result, with the system of the present invention the patient safety and comfort can be enhanced, while ensuring that condensation in the breathing tube is optimally controlled. The processing unit 23 may be provided with a comparator unit arranged for comparing the ambient temperature detected to at least one or more predetermined thresholds. The comparator may further take into account other information that may be stored in the processor unit memory or received by sensors in order to generate at least one control signal for at least operating the switches 29 of the switching mechanism 23. For example, the comparator may compare the ambient temperature detected to a predetermined ambient temperature threshold, so as to decide whether the temperature of the breathable gas needs to be adjusted. The processor prior to generating the control signals 30 may check the surface temperature table to determine whether the surface temperature generated by the electrical resistance adjustment is within the acceptable temperature range. Based on this assessment, the processor unit may optimise the electrical resistance adjustment of the tube heating system 17, such that the risk of condensation is minimised while ensuring that the patient safety and comfort is compromised by exceed the recommended surface temperature. For example, the temperature tracking system 24 may be arranged for selecting the appropriate heating element 20 or combination of heating elements 20 to which the supply voltage is to be applied such that the temperature of the breathable gas in the breathing tube 18 is adjusted, thereby minimising the risk of condensation in the breathing tube 18, while ensuring the surface temperature of the breathing tube 18 does not exceed the recommended surface temperature.

According to embodiments of the present invention, the temperature controller 21 may be provided with at least one bimetallic strip. For example, the switching mechanism 23 may be provided with a plurality of bimetallic strips each configured, in response to a predetermined ambient temperature, for applying the supply voltage to at least one heating element 20. The bimetallic strip may be made from two strips of metal, each having a different coefficient of thermal expansion. The metals used in each of the bimetallic strips may be selected for responding to a predetermined ambient temperature. In this way, each bimetallic strip may be configured, in response to a predetermined ambient temperature change, for applying the supply voltage to a predetermine number of heating elements 20, so as to control the condensation in the breathing tube 18. For example, a bimetallic strip having a predetermined coefficient of thermal expansion may be provided between each heating element 20 and the voltage source 14a. In this way, in response to a predetermined ambient temperature at least one of the heating elements 20 may be selected to be connected to the source voltage 14a, thereby adjusting the temperature of the breathable gas so as to control condensation in the tube without the need of an external temperature sensor, which may lead to the simplification of the design of the temperature controlled switching mechanism 21 . The bimetallic strip may be further used in combination with the temperature tracking system 24. For example, the temperature tracking system 24 may be arranged, in response to the ambient temperature detected and/or taking into account other information, e.g. tube surface temperature generated by each heating element 20, for generating control signals 30 arranged for operating the bimetallic strip, e.g. by generating a hot spot in the vicinity of the selected bimetallic strips, thereby causing the bimetallic strip to expand so as to make contact with the corresponding heating elements 20.

According to embodiments of the present invention, the temperature controller 21 may be arranged, based on the ambient temperature detected, for adjusting the supply voltage supplied by the voltage source 14a, thereby adjusting the heating power drawn by the tube heating system 17. The voltage source adjustment can be effected instead or in combination with the adjustment of the electrical resistance of the tube heating system 17. The source voltage supplied by the voltage source 14a may be adjusted by any known methods known to the person skilled in the art. For example, a variable resistance heating element 28 may be used for adjusting the supply voltage supplied to the tube heating system 17 based on the ambient temperature detected by temperature sensor 21 .

Similarly to figure 14, the temperature controller 21 may be arranged for adjusting the electrical resistance of the variable resistance heating element 28, as shown in figure 16. For example, the temperature tracking system 24 may be arranged for generating a plurality of control signal 30, a first set of which may be used for operating the switching mechanism 23, so that a predetermined supply voltage is applied to pins 2 and 3, while a second set of control signals may be supplied directly to pins 1 and 4 so that a predetermined potential difference is crated across the variable resistance material 26 of the variable resistance heating element 28. For example, the second set of control signals may comprise optical signals each having a predetermined light intensity, such that when they are received by a variable resistive material 26 made from a photoresistive material, a potential difference may be created between pins 1 and 4, thereby setting the electrical resistance of the variable resistance material 26 to the required value. In this way, the heating power generated by the variable resistance heating element 28 may be quickly adjusted based on ambient temperature changes detected by a sensor. According to embodiments of the present invention, the temperature tracking system 24 may be arranged for deriving from a voltage source 14a the supply voltages to be applied to the tube heating system 17 so that the electrical resistance of the tube heating system can be adjusted based on the ambient temperature changes.

According to embodiments of the present invention, the temperature controller 21 may be provided at an appropriate location in the breathing circuit 10. For example, the temperature controller 21 may integrated in the breathable gas supply system 13. In another example, the temperature controller 21 may be integrated in the connector element 15. In an alternative configuration, each component of the temperature controller 21 may be positioned at a different location in the breathing circuit, e.g. the temperature tracking system 24 may be positioned in the breathable gas supply system 13 while the switching mechanism 23 may be positioned in the connector element 15. It should be noted that the temperature controller 21 may be positioned at any desirable location and it is not limited to the ones mentioned above.

Claims

1 . A breathing circuit (10) for use in a respiratory system arranged for supplying a breathable gas from a breathable gas supply system (13) to a patient interface (1 1 ), the breathing circuit (10) comprising a heated conduit system (12) comprising:

a breathing tube (18) connectable between the breathable gas supply system (13) and the patient interface (1 1 ), the breathing tube being arranged for delivering the breathable gas from the breathable gas supply system (13) to the patient interface (1 1 );

a tube heating system (17) associated with the breathing tube (18), the tube heating system (17) having an electrical resistance and arranged, when a supply voltage is applied, for generating an amount of heating power for heating a wall (26) of the breathing tube (18) along its entire length such that the breathable gas travelling through the breathing tube (18) is heated to a target temperature for minimising condensation inside the breathing tube (18); and

a connector element (15) arranged for interfacing the breathing tube (18) with the breathable gas supply system (13) and for applying the supply voltage to the tube heating system (17);

characterised in that the tube heating system (17) is a variable resistance heating system arranged for receiving at least one control signal by which the electrical resistance of the tube heating system (17) can be altered;

and in that the breathing circuit (10) comprises a temperature controller (21 ) arranged for receiving ambient temperature information and for generating, based on the ambient temperature information, the at least one control signal.

2. A breathing circuit (10) according to claim 1 , wherein the tube heating system (17) comprises a plurality of heating elements (20) connected in parallel, each provided with a predetermined electrical resistance.

3. A breathing circuit (10) according to claim 2, wherein the temperature controller (21 ) comprises a switching mechanism (23) arranged, based on the at least one control signal, for applying the supply voltage to at least one heating element (20).

4. A breathing circuit (10) according to any one of the preceding claims, wherein the temperature controller (21 ) comprises a temperature tracking system (24) arranged for generating the at least one control signal for operating the switching mechanism (23).

5. A breathing circuit (10) according to any one of the preceding claims, wherein the tube heating system (17) comprises a variable resistance heating element (28).

6. A breathing circuit (10) according to claim 5, wherein the variable resistance heating element (28) comprises a first electrical conductive element (27), a variable resistance material (26) surrounding the first electrical conductive element, and a second electrically conductive element (25) electrically surrounding the variable resistance material (26).

7. A breathing circuit (10) according to claim 5 or 6, wherein the temperature controller (21 ) is arranged for generating across the variable resistance material (26) a potential difference, which can be altered by means of the at least one control signal so as to adjust the resistance of the variable resistance material (26).

8. A breathing circuit (10) according to any one preceding claims, wherein the at least one control signal is an optical signal.

9. A breathing circuit (10) according to any one of claims 5 to 8, wherein the temperature controller (21 ) is arranged for applying to the first and second electrical conductive elements (25, 27) a predetermined supply voltage.

10. A breathing circuit (10) according to any one of claims 5 to 9, wherein the variable resistance material (26) is made from a photoresistive material.

1 1 . A breathing circuit (10) according to any one of the preceding claims, wherein the temperature tracking system (24) comprises a processing unit (25) arranged for processing the ambient temperature information received from the at least one sensor (22) and accordingly generating a set of control signals (30) for at least operating the switching mechanism (23).

12. A breathing circuit (10) according to claim 1 1 , wherein the processing unit (25) comprises a comparator arranged for comparing the ambient temperature detected to at least one predetermined threshold temperature.

13. A breathing circuit (10) according to any one of the preceding claims, wherein the temperature controller (21 ) comprises at least one sensor (22) arranged for monitoring the ambient temperature.

14. A breathing circuit (10) according to claim 13, wherein the at least one sensor (22) comprises a thermistor.

15. A breathing circuit (10) according to claim 13, wherein the at least one sensor (22) is an infrared temperature sensor

16. A breathing circuit (10) according to any one of the preceding claims, wherein the tube heating system (17) is arranged for being at least partially in contact with a surface of the wall (26) of the breathing tube (18).

17. A breathing circuit (10) according to any one of the preceding claims, wherein the tube heating system (17) is helically wounded along the breathing tube (18).

18. A breathing circuit (10) according to any one of the preceding claims, wherein the tube heating system (17) is arranged for being at least partially in contact with an outer surface of the breathing tube wall (26).

19. A breathing circuit (10) according to any one of the preceding claims, wherein the tube heating system (17) is arranged for being at least partially in contact with an inner surface of the breathing tube wall (26).

20. A breathing circuit (10) according to any one of the preceding claims, wherein the tube heating system (17) is integrated in the wall (26) of the breathing tube.

21 . A breathing circuit (10) according to claim 20, wherein the tube heating system (20) is integrated in the reinforced ribs (19) helically wounded around the wall (26) of the breathing tube (18).

22. A breathing circuit (10) according to any one of the preceding claims, wherein the heating elements (20) are resistance heating wires.

23. A breathing circuit (10) according to claim 22, wherein the heating wires are provided in the form of conductive strips.

24. A breathing circuit (10) according to claim 23 wherein the conductive strips are inject printed on a surface of the wall (26) of the breathing tube (18).

25. A breathing circuit (10) according to any one of the preceding claims, wherein the heated conduit system (12) is formed as a single unit.

26. A breathing circuit (10) according to claims 1 to 24, wherein the heated conduit system (12) is assembled from discreet components.

27. A breathing circuit (10) according to any one of the preceding claims, wherein the temperature controller (21 ) is integrated into the connector element (15).

28. A breathing circuit (10) according to any one of the preceding claims, wherein the target temperature of the breathable gas is in the range between 20.0 degrees and 45.0 degrees, more preferably in the range between 30.0 degrees and 40.0 degrees.