WO2015040548A1

WO2015040548A1 - Spirometer

Info

Publication number: WO2015040548A1
Application number: PCT/IB2014/064577
Authority: WO
Inventors: Cornelius Scheffer; Johan Smith; Jacobus Charles Bender Kotze; Raphael V. SMITH
Original assignee: Stellenbosch University
Priority date: 2013-09-19
Filing date: 2014-09-17
Publication date: 2015-03-26

Abstract

A portable spirometer is provided for positioning in an airflow path between a patient and a positive pressure ventilation source and is configured to measure actual lung function details of the patient during inspiration and expiration. An electronic user interface receives user input including at least one physical characteristic of the patient. A processor is in data communication with the user interface and a memory on which is stored reference criteria matching physical patient characteristics to target lung function parameters. A display is in data communication with the processor. The processor is configured to determine target lung function details for the patient based on at least one physical characteristic and to compare actual lung function details to the target lung function details. The display shows if the patient details are above or below the retrieved target values. The spirometer is preferably made as a non-disposable unit and a disposable unit.

Description

SPIROMETER

FIELD OF THE INVENTION

This invention relates to a spirometer of the type capable of providing feedback as to the volume and rate at which air is being inspired and expired by a patient. In particular, the invention relates to such a spirometer that may be used during resuscitation of a patient and that may be referred to as a flow volume monitor. It is recorded that a spirometer is an apparatus that determines the amount of air and the flow rate of air that is expired over a specified time period; and also, in some instances, the amount of air and the flow rate of air that is inspired. Medical spirometers are used for testing/measuring respiratory functions of humans, including instant flow rate during respiration (peak-flow meters) and total volume discharge or vital capacity. The term thus includes devices referred to as flow volume monitors.

BACKGROUND TO THE INVENTION During the delivery of air to a patient during resuscitation procedures, there is a danger of damage to the patient's lungs due to the delivery of too small or too large a volume of air to the patient's lungs, in a specified period of time.

In a ventilated child, for example, atelectasis or ventilation-perfusion mismatch may occur when inappropriately small air volumes are delivered to the lungs. Structural disruption generated during repetitive opening and collapse of the atelectatic regions may initiate or exacerbate significant lung injury. In any ventilated patient, excess air delivery can result in ventilator-induced injury which in turn can result in possible permanent lung damage, hypoxia, and even mortality. Excess air delivery often leads to further complications such as respiratory distress syndrome, dependency on ventilators and neurological deficiencies. The mortality rate of patients who develop ventilator-associated lung injury as a complication of mechanical ventilation may, according to the applicant's knowledge, be as high as 13% to 35%.

It is thus important to know the approximate amount of air that a patient requires, and to deliver that amount of air at an appropriate pressure. Sufficient monitoring of the amount of air that is inspired or expired by a patient during resuscitation is desirable to at least partially prevent some of the abovementioned problems. Current methods for monitoring air flow include ultrasonic pneumotachometers, pressure transducers, turbines and thermal convection pneumotachometers. These devices are, however, bulky, expensive and difficult to use, especially in sparsely equipped locations such as in emergency field scenarios or in some rural areas.

In what follows it will be understood that the term "actual" means the value insofar as it is a measured value.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a portable spirometer adapted to be positioned in an airflow path between a patient and a positive pressure ventilation source in a resuscitation system and configured to measure actual lung function details of the patient during inspiration and expiration, comprising an electronic user interface configured to receive user input including at least one physical characteristic of the patient; a processor in data communication with the user interface; and a display in data communication with the processor, wherein the processor is configured to determine target lung function details for the patient based on the at least one physical characteristic and to compare actual lung function details of the patient to the target lung function details; and transmit control signals to the display causing it to indicate whether the actual lung function details exceed or deceed the target lung function details.

Further features of the invention provide for the spirometer to include a memory that may either be a memory of the processor itself or a separate memory module on which is stored reference criteria matching physical patient characteristics to target lung function parameters; for the at least one physical characteristic of the patient to be one or more of the patient's estimated or actual age, weight and sex; and for the processor to be further configured to determine target lung function details by comparing them with the target lung function details in the memory module which match the physical characteristics of the patient received by means of the electronic user interface.

A still further feature of the invention provides for the lung function details to include one or both of expired and/or inspired air volume, and expired and/or inspired air flow rate.

A yet further feature of the invention provides for the display to include a series of warning lights configured to indicate if the measured lung function details exceed or deceed the target lung volume details.

A further feature of the invention provides for the spirometer to include an audible alarm such as a speaker, buzzer, siren or the like, which is configured to provide an audible warning to a user if the measured lung function details exceed or deceed the target lung volume details by a predetermined amount. A still further feature of the invention provides for the user interface to be configured to request the at least one physical characteristic from the user when the spirometer is activated. A yet further feature of the invention provides for the spirometer to be adapted to be connected in the airflow path, proximate the patient's lungs, preferably to a mouthpiece, tracheal tube or the like.

Additional features of the invention provide for the spirometer to comprise a non-disposable unit in which the processor and associated electronic circuits are located and a disposable unit comprising a tubular unit that attaches to the non-disposable unit in a releasable manner; for the attachment to be by way of cooperating formations on the non-disposable unit and the disposable unit wherein separation of the two units causes the disposable unit to become damaged to an extent that it cannot be reused; and for the spirometer to include a paddlewheel flow sensor whereof the paddle extends partly into the flow path and partly into the non-disposable unit with the paddlewheel forming part of the disposable unit. The invention also provides a method for monitoring expired or inspired airflow by a patient during a resuscitation process, the method being performed on a portable spirometer and including the steps of receiving, at a user interface, at least one physical characteristic of the patient; determining, by means of a processor, target lung function details based on the at least one physical characteristic of the patient; measuring actual lung function details of the patient; comparing, by means of the processor, the actual lung function details to the target lung function details; and indicating on a display whether the actual lung function details exceed or deceed the target lung function details.

Further features of the invention provide for the step of receiving the at least on physical characteristic of the patient to include receiving one or more of the patient's estimated or actual age, weight and sex; for the step of determining the target lung function details to include looking up the at least one physical characteristic of the patient in a memory on which is stored reference criteria matching physical patient characteristics to target lung function parameters; and for the steps of measuring and determining the actual and target lung function details to include measuring and determining, as the case may be, one or both of expired and/or inspired air volume, and expired and/or inspired air flow rate. In order that the above and other features of the invention may be more fully understood one embodiment of the invention will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-

Figure 1 is a diagrammatic elevation showing a portable spirometer in accordance with the general principles of the invention;

Figure 2 shows the spirometer illustrated in Figure 1 attached in an air flow path between a resuscitation bag and a face mask;

Figure 3 is a flow diagram of a method for monitoring expired or inspired airflow of a patient during a resuscitation process;

Figure 4 is a three dimensional view from one side showing a second and more fully developed embodiment of portable spirometer in accordance with the invention with a disposable unit attached to a non-disposable unit;

Figure 5 is the same as Figure 4 but showing the non-disposable unit rotated through 90^Q as would be the case when positioning the display for ease of visibility;

Figure 6 is a three dimensional view from the other side of the assembled unit illustrated in Figure 4;

Figure 7 shows the spirometer of Figure 4 with a cut-away portion so as to show certain internal components; Figure 8 is an enlarged view of the paddle and detectors shown in

Figure 7;

Figure 9 shows the spirometer illustrated in Figure 4 attached in an air flow path between a resuscitation bag and an intubation tube; and,

Figure 10 is a block diagram of the spirometer electronics of the embodiment illustrated in Figures 4 to 9 that are contained within the non-disposable unit.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

Referring firstly to Figures 1 to 3 of the drawings, a basic embodiment of portable spirometer (1 ) in accordance with of the invention may have standard sized fittings (10) at respective ends of an airflow channel (1 1 ) through the spirometer, which allows the spirometer to be positioned in an air flow path of a resuscitation system without the requirement of additional fittings. The spirometer (1 ) includes a user interface (12) which includes a plurality of input buttons (14), a display (16), a speaker (18) and a plurality of warning lights (20, 22, 24, 26, 28), in the present embodiment five warning lights. The spirometer also houses a processor (13), a memory module (15) and an air flow monitor (17). In the instance that of the particular processor has adequate memory for the purpose, the memory module may be omitted. The air flow monitor may be a turbine air flow monitor. It should be noted that such a turbine air flow monitor should be located in the air flow channel between the fittings (10) in such a way so as not to obstruct the air flow in an airflow path of a resuscitation system between the lungs of a patient and a positive pressure ventilation source of the resuscitation system.

Figure 2 shows the mobile spirometer (1 ) of Figure 1 attached in an airflow path of a bag valve mask. In the present embodiment, the positive pressure ventilation source is a resuscitation bag (30). The spirometer is positioned between the resuscitation bag (30) and a mask (32). As mentioned before, the fittings (10) of the spirometer (1 ) are of a standard size so that they attach to the fittings which normally allow the mask (32) and the bag (30) to be connected to one another.

Research has shown that lung volume should be measured close to a tracheal tube, mouthpiece or the like in a resuscitation system to obtain as accurate as possible lung function details, which typically includes both the volume of air being inspired or expired by a patient, as well as the rate at which such expiration or inspiration takes place. Techniques which measure the amount of air being displaced by the positive pressure ventilation source have been found to be ineffective. Positioning the spirometer in the airflow path of a resuscitation system as shown in Figure 2 enables measurement of the volume of air being inspired or expired by a patient to be taken sufficiently close to a tracheal tube, mouthpiece or the like in a resuscitation system. The user interface (12) is configured to receive, in use, input from a user, the input relating to one or more physical characteristics of a patient. The input buttons (14) are used to input these physical characteristics. Although only three buttons (14) are shown on the user interface, any sufficient number may be provided.

The physical characteristics may be observed or estimated by the user; may be presented to the user by a bystander who is familiar with the patient; may be obtained from a medical information bracelet, card, or the like on the patient's person; or may be obtained in any other sufficient manner. Possible physical characteristics which may be accepted by the user interface include the sex of the patient, the approximate weight of the patient, the approximate age of the patient, and whether or not the patient suffers from any illness which may influence their lung capacity, such as asthma or the like. It has been found that all of the above characteristics influence lung function, including the lung volume, of an individual. Other possible physical characteristics may also be included, such as, for example, whether or not the patient has had a lobectomy of a lung performed.

The processor is in data communication with the memory which may be the module where same is present; user interface; display (16); and flow rate monitor. The memory is preloaded with reference criteria including lists or tables of physical characteristics and corresponding target lung function details of patients with such physical characteristics. After the processor receives the physical characteristics from the user interface (16), it determines target lung function details by looking up the target lung function details corresponding to the input physical characteristics as stored in the memory.

During the movement of air in the airflow channel of the resuscitation system, the flow rate monitor measures the airflow rate and volume and transmits the measurements to the processor. In the present embodiment, the airflow monitor may be a disposable turbine airflow monitor, such as a FlowMir^® turbine airflow monitor from Medical International Research. The use of a disposable air flow monitor allows it to be replaced between uses of the spirometer in order to improve the hygiene of a resuscitation system equipped with such a spirometer.

It should be noted that the processor may be configured to determine the volume of air which has passed through the airflow path from the airflow rate, or the flow rate monitor may be capable of determining this on its own. If the flow rate monitor cannot determine the volume of air itself, it will at least be able to measure the airflow rate in volumetric units per second. Multiplying the airflow rate by the time for which that airflow rate has occurred will indicate the volume of air which has passed through the airflow path. Measurements taken at small intervals should account for small changes in airflow rate, which in turn will result in a more accurate calculation of volume.

The processor is configured to compare the measured, actual volume and/or rate of air which has passed through the airflow path, in whichever way it has been obtained, with the previously determined target lung function details. The result of this comparison is indicated to a user on the display (20). If the measured lung function details are too high or too low, the user is alerted to this on the display (16) by means of a "high" alert, or a "low" alert signal. The warning lights (20 - 28) may assist in alerting the user of this fact.

The warning lights may be positioned linearly along an operatively bottom region of the display, as is shown in Figure 1 . If the measured lung function details are too high, the rightmost light (28) is activated. If the measured volume is too low, the leftmost light (20) is activated. The speaker (18) will accompany the activation of the leftmost and rightmost warning lights with an audible signal. This may assist in drawing a user's attention to the display and lights so as to determine what is wrong in the current resuscitation procedure.

The middle lights (22, 24, 26) located between the leftmost and rightmost lights may be activated when an acceptable or correct volume and/or rate of air is inspired or expired by a patient. For example, the middle light (24) may be activated when the volume of air being inspired of expired is exactly right. The light (22) between the leftmost light (20) and middle light (24) may be activated when the volume is slightly low, but still acceptable. Similarly, the light between the middle light (24) and rightmost light (28) may be activated when the volume is slightly high, but still acceptable. This may assist a user in at least slightly modifying the volume of air they are displacing by means of the resuscitation bag (30). In this embodiment of the invention it is assumed that, in use, the first direction of airflow in the airflow passage will be from the positive pressure source to the patient's lungs, as a non-breathing patient will typically not have air in their lungs. Therefore, the processor is configured to set the first direction of airflow as being inspired by a patient, while the subsequent direction of travel will be from the lungs of the patient, and therefore as being expired by the patient. Further directions of airflow travel will, naturally, alter between the two possible directions of flow. It will be apparent to those skilled in the art that every sudden reduction in flow rate, and subsequent sudden increase in flow rate, will indicate that the flow rate of air has reversed, and that inspiration has changed to expiration, or vice versa. The processor will be configured to detect this change in flow rate, and to start a new measurement either for expiration or inspiration, depending on the direction of flow at the moment of change of flow direction. Figure 3 shows a flow diagram for a method for monitoring inspired and expired airflow by a patient during a resuscitation process and for indicating whether an adequate amount of air is being expired or inspired by the patient, the method being performed by the mobile spirometer such as that described above with reference to Figures 1 and 2.

In a first step (300), the spirometer receives physical characteristics relating to the patient. The physical characteristics are input by the user of the spirometer on the user interface (12), by means of the input buttons (14).

At a next step (310), the processor of the spirometer determines target lung function details, which may include one or both of target airflow volume and rate, which are applicable to the patient based on the physical characteristics input by the user. The input physical characteristics are compared to a list of physical characteristics stored in a memory module of the spirometer and which are associated with expected target lung volume details. At a next step (320), the process of resuscitation is commenced by the user. Since the spirometer is included in the airflow channel of the resuscitation system, the air flow sensor is able to measure the airflow rate in the airflow system, and the processor of the spirometer can use this to determine the actual volume and/or rate of air being inspired and/or expired by the patient. This is compared to the target lung function details determined in the previous step (310).

The next step depends on a comparison of the determined volume of air being inspired or expired by the patient, and the target volume of air. If the actual value is lower than the target value, a next step (330) follows. In this step, a "low" alert is activated. This alert will activate the leftmost light (20) on the display. The display will include a warning text which indicates this fact, and the speaker will transmit a warning sound to attempt to attract a user's attention to the display.

If the actual value is acceptable or correct, the middle lights (22, 24, 26) will be activated in a further step (340), as explained earlier with reference to Figure 1 . If the actual value is too high, a next step (350) follows, in which a "high" alert is activated. This alert will activate the rightmost light (28) on the display. The display will include a warning text which indicates this fact, and the speaker will transmit a warning sound to attempt to attract a user's attention to the display. After each alert step (330, 340 or 350), the method returns to the step (320) where the comparison is performed, and a new measurement is initiated. This method thus provides feedback to a user after every inhalation or exhalation, allowing the user to adjust the resuscitation procedure as required. This may improve resuscitation procedures to at least partially reduce the risks involved with a too high or too low volume of air being provided to a patient.

Turning now to the second and somewhat more developed embodiment of the invention that is illustrated in Figures 4 to 9, the spirometer has, other than those specifically described below, the same external controls, display and lights as described above and consequently the same reference numerals are used to denote the same components as may be appropriate.

In this embodiment of the invention the spirometer comprises a non- disposable unit (35) and disposable unit (36). The non-disposable unit (35) can rotate through 90 ° so as to orientate the display (16) forming part of the non-disposable unit at an ergonomic angle, as will be appreciated from a reference to Figures 4 and 5. It will be understood that the purpose of the disposable unit is that hygiene is greatly enhanced by disposing of the disposable unit once it has been used and may have become contaminated by a patient that used it. The attachment of the non-disposable unit (35) to the disposable unit (36) will preferably be such that it ensures that the non-disposable unit is clipped onto the disposable unit in a manner such that when the two units are separated, the disposable unit becomes damaged to an extent that it cannot be reused typically consequent on the fact that attachment formations may be rendered inoperative. This may optionally be the result of breaking at least a part of cooperating clipping formations on the disposable unit (36) that are engaged by formations on the non-disposable unit (35) when the two units are separated.

The disposable unit is preferably a short tubular unit having a protrusion in the central region thereof that carries a paddlewheel (37) rotatable about an axle having its axis "A" offset to one side of the axis "B" of the tubular unit and extending at right angles to the plane containing the axis "B" of the tubular unit. The arrangement is such that the paddles (38) of the paddlewheel project both into the flow passage on one side of the axle and outwards on the other side of the axle, as shown in Figure 7 and 8, such that the paddles, as they rotate, pass a detection arrangement associated with the non-disposable unit that also has all the electronic components of the internal components of the spirometer therein.

In operation, the paddle wheel is rotated by the flow of air through the disposable unit (36). Rotation of the paddle wheel (37) is detected by a detection arrangement comprising a plurality of light gates. In the present embodiment, two light gates are used so as to facilitate sensing the direction of rotation as well. Each light gate comprises an infrared light source (39) and a detector (41 ) located on opposite sides of the outer region of the paddle wheel. An electrical signal is generated and processed by the processor when a paddle (38) passes between the infrared source and the detector (41 ). By analysing the time between signals and the order of the signals from the two detectors (41 ), the flow rate and direction of rotation and thus a determination is made of whether the rotation is occasioned by inspiration or expiration. Also, the volume and rate of air flow may be calculated using predetermined calibration curves stored in the processor memory or memory module. The flow volume is calculated by integrating the flow rate. Figure 9 shows the mobile spirometer of Figures 4 to 8 attached in an airflow path of a ventilation tube (45). In the present embodiment, the positive pressure ventilation source is a resuscitation bag (46). The spirometer is positioned between the resuscitation bag (46) and the ventilation tube (45). As mentioned before, the fittings of the spirometer are preferably of a standard configuration so that they can attach to the fittings which normally allow the ventilation tube (45) and resuscitation bag (46) to be connected directly to one another.

Figure 10 shows a block diagram of the latter embodiment of spirometer electronics which are housed in the non-disposable unit (35). The processor is powered by a battery (50) via a battery charger module (51 ) and voltage regulator (52). The battery charger is connected to the processor (13) to facilitate low battery detection and charging control. The battery charger is powered via a USB I/O port (54). The USB I/O port is also connected to the processor to facilitate processor programming, and two-way data transfer between the processor and a USB host such as a computer.

The processor has access to the lookup tables relating the physical characteristics of the patient to the target lung volumes that may be stored on the processor's memory or may be stored on a memory module (15). The processor receives user input from the plurality of buttons (14) as described earlier. The processor also receives input from the light gate detectors (41 ) signalling the passing of a paddle (38) of the paddle wheel (37). The processor further receives input from an external crystal oscillator (56). The external oscillator satisfies the need for high speed accurate timing for the computation of the paddle wheel velocity from the light gate signals. The processor is connected to a buzzer/speaker (18) a graphical/alphanumerical display (16) and optionally an array (59) of LEDs. The LEDs may be omitted if required.

The above description of the invention is by way of example only and it should be noted that many changes may be made to the embodiments of the invention described above, without departing from the scope of the invention. For example, the positive pressure source of the resuscitation system may be any sufficient source, including that of a medical ventilator. The spirometer will then enable a user to notice if the ventilator has been incorrectly configured, allowing the user to make the necessary adjustments. Furthermore, the display may be a touch screen display by means of which the input may be obtained from the user. This may negate the need for input buttons.

It is envisaged that the spirometer will be able to operate without a memory module. The processor may be preloaded with an algorithm, which calculates the target lung volume details based in the input physical characteristics. This would negate the need for lists of stored physical characteristics and accompanying target lung volume details. Furthermore, the speaker (18) may also be a buzzer, or siren, as long as it is able to produce an audible warning sound.

It will be apparent to persons skilled in the art that changes may also be made to the method as shown in Figure 3 without departing from the scope of the invention. The mobile spirometer as disclosed in this specification is reusable and is suitable for use in especially emergency field situations, however, the device may also be used in resuscitation rooms, theatres, ambulances, delivery rooms, intensive care units, or in fact in any location where a patient requires resuscitation or assisted breathing, whether long-term or short-term. The user interface is located so that a user of the spirometer is easily able to determine whether resuscitation of a patient is performed adequately. Warning lights, messages or sirens will alert the user if the resuscitation process is not performed adequately. The positioning of the spirometer near a patient's lungs ensures that the measurements taken by the spirometer are sufficiently accurate.

Claims

A portable spirometer adapted to be positioned in an airflow path between a patient and a positive pressure ventilation source in a resuscitation system and configured to measure actual lung function details of the patient during inspiration and expiration, comprising an electronic user interface configured to receive user input including at least one physical characteristic of the patient; a processor in data communication with the user interface and, in use, with a memory on which is stored reference criteria matching physical patient characteristics to target lung function parameters; and a display in data communication with the processor, wherein the processor is configured to determine target lung function details for the patient based on the at least one physical characteristic; to compare actual lung function details of the patient to the target lung function details; and to transmit control signals to the display causing it to indicate whether the actual lung function details exceed or deceed the target lung function details.

A portable spirometer as claimed in claim 1 in which the spirometer includes a memory module on which is stored reference criteria matching physical patient characteristics to target lung function parameters.

A portable spirometer as claimed in either one of claims 1 or 2 in which the at least one physical characteristic of the patient is at least one of the patient's estimated or actual age, weight, and sex.

A portable spirometer as claimed in any one of the preceding claims in which the processor is configured to determine target lung function details by comparing them with the target lung function details in the memory module which match the physical characteristics of the patient received by means of the electronic user interface.

A portable spirometer as claimed in any one of the preceding claims in which the lung function details include one or both of expired and/or inspired air volume, and expired and/or inspired air flow rate.

A portable spirometer as claimed in any one of the preceding claims in which the display include a series of warning lights configured to indicate if the measured lung function details exceed or deceed the target lung volume details.

A portable spirometer as claimed in any one of the preceding claims in which the spirometer includes an audible alarm configured to provide an audible warning to a user if the measured lung function details exceed or deceed the target lung volume details by a predetermined amount.

A portable spirometer as claimed in any one of the preceding claims in which the spirometer is adapted to be connected in the airflow path, proximate the patient's lungs, and selected from a mouthpiece and a tracheal tube.

A portable spirometer as claimed in any one of the preceding claims in which the spirometer comprises a non-disposable unit in which the processor and associated electronic circuits are located and a disposable unit comprising a tubular unit that attaches to the non- disposable unit in releasable manner.

A portable spirometer as claimed in claim 9 in which releasable attachment of the non-disposable unit to the disposable unit is by way of cooperating formations on the non-disposable unit and the disposable unit. A portable spirometer as claimed in claim 10 in which releasable attachment of the non-disposable unit to the disposable unit is configured such that separation of the two units causes the disposable unit to become damaged to an extent that it cannot be reused.

A portable spirometer as claimed in any one of claims 9 to 1 1 in which spirometer includes a paddlewheel flow sensor whereof the paddle extends partly into the flow path and partly into the non-disposable unit with the paddlewheel forming part of the disposable unit.

A method for monitoring expired or inspired airflow by a patient during a resuscitation process, the method being performed on a portable spirometer and including the steps of receiving, at a user interface, at least one physical characteristic of the patient; determining, by means of a processor, target lung function details based on the at least one physical characteristic of the patient; measuring actual lung function details of the patient; comparing, by means of the processor, the actual lung function details with the target lung function details; and indicating on a display whether the actual lung function details exceed or deceed the target lung function details.

A method as claimed in claim 13 in which the step of receiving the at least on physical characteristic of the patient includes receiving one or more of the patient's estimated or actual age, weight and sex.

A method as claimed in either one of claims 13 or 14 in which the step of determining the target lung function details include looking up the at least one physical characteristic of the patient in a memory on which is stored reference criteria matching physical patient characteristics to target lung function parameters.