CA1331209C - Continuous cardiac output by impedance measurements in the heart - Google Patents

Abstract

CONTINUOUS CARDIAC OUTPUT BY
IMPEDANCE MEASUREMENTS IN THE HEART
Abstract of the Disclosure A diagnostic catheter for use in measuring cardiac output in the right ventricular chamber of a heart includes a catheter body having an outer periphery and a distal section terminating in a distal end and a proximal section terminating in a proximal end. A plurality of spaced electrodes are secured to the body outer periphery along the body distal section. A plurality of electrical leads extend in the catheter body from a respective one of the electrodes to the proximal end of the catheter body. An elongated rigid member is provided for stiffening a portion of the catheter body. One end of the rigid member is located adjacent a proximal most one of a plurality of electrodes. The rigid member so locates the plurality of electrodes as to space them away from endocardial tissue.
The catheter is used with a cardiac output monitoring system. Signals from the catheter are acquired by a signal conditioning and catheter control unit and, are thereafter fed to a microcomputer. The catheter and the system are used in a method for determining the instantaneous volume of blood in a heart chamber.

Description

1~312d9 CCL 2 1~)4 CONTINUOUS C~RDIAC OUTPUT BY
IME'EDI~NCE PIEASUR~EN~S IN THE HEART
Backqround of the Invention This invention generally relates to medical apparatus for measuring characteristics of a heart. More particularly, the invention relates to a balloon Elotation electrode catheter which can be used with appropriate equipment to monitor cardiac outputs on a beat-by-beat basis over a prolonged period of time.
While the invention is particularly applicable to the measurement of cardiac -output in the right ventricular chamber of a human heart, it should be appreciated that the measurement of cardiac output in another chamber of a heart, such as the left ventricular chamber and of a non-human heart such as a suitable mammalian heart can also be - performed by the present invention.
Several parameters are routinely monitored in patients having heart problems or those undergoing cardiovascular surgery. These include the electrocardiogram (ECG), the arterial blood pressure (ART), the central venuous pressure (CVP), the pulmonary artery pressure (PAP), and the cardiac output (CO). With the - 20 exception of cardiac output, technology now exists which permits these time varying parameters to be monitored continuously. However~ all present techniques for clinically obtaining cardiac output involve indirect methods with sample intervals of several minutes. In addition, these techniques require either the injection of an indicator substance or the gathering of significant respiratory and blood gas patient data.
Cardiac output is generally measured in terms of liters per minute which corresponds to the heart's stroke volume multiplied by heart rate. Cardiac output values change depending on the activity level of the body, the :
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level o~ metabolic demand, the condition of the heart and ¦ many other factors. During major operations, cardiac output is clinically significant because it is an indicator of how well the heart itself is performing and it S demonstrates whether a sufficient supply of blood is being circulated to maintain metabolic demands.
one of the indirect methods of measuring cardiac output is the Fick method which determines such output by examining both the oxygen consumption of the lungs and the difference between arterial and venuous oxygen concentrations. A second method involves indicator dilution. Early indicator techniques used injectates such as cardio green dye which was in;ected as a bolus into the vascular system and allowed to mix with the venuous blood.
An arterial sampling through a densitometer was then used to measure the time varying concentration levels of dye.
I The concentrations recorded were directly related to the I flow rate o~ the dya mixed blood through the circulatory system.
1 20 The currently accepted clinical indicator method is a technique known as thermodilution. This method relies on thermal changes as a flow indicator. A bolus of cold fluid, at least 10C less than the patient's core temperature, is in;ected into a venuous site. After mixing in the right ventricle, the adjacent cooled blood and fluid pass a small thermistor temperature sensor which has been placed via a catheter in the patient's pulmonary artery.
The time varying temperature changes are directly related I ; tolthe flow rate of the mixed ~luid through the right side of the heart. Since the circulatory system is a series ~- circuit, the right side value is also reflective o~ the left side ejections. Thus, a cardiac output can be calculated from the indicator dilution curve using a known eguation.

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""i.' ""'': ~.' ' ' ' ' ' '~',: ', ' ' " '. ' ' , , ' ' ' ~ 3 ~ ~3312~3 Non-invasive techniques for obtaining cardiac output have been recently developed. Echocardiographic instruments can be used to measure aortic sizes and ventricular volumes at specific times during the cardiac cycle. Stroke volumes can then be derived Prom this information. In this connection, flow doppler instruments have been developed to measure blood velocity via external probes which are placed on the skin of the patient and aimed at a major arterial vessel such as the ascending or descending aorta. Cardiac output is then derived by estimating the vessel diameter in determining blood flow.
Further calculations can convert the flow determinations to cardiac output by multiplying tha heart rate and the flow per beat. Also, instruments which attempt to measure transthoracic impedance have also been developed in an attempt to determine non-invasive cardiac output. Finally, a non-invasive technique known as the pulse wave contour technique has been developed which makes use of the concept that the area under the arterial waveform curve is related to the stroke volume and the aortic compliance.
Each of the above recited methods has deficiencies which greatly limit either its use and/or functionality for clinical applications, especially during surgery. The Fick principle requires special equipment and careful attention in collecting the required samples and present technology ¦ does not allow all of the required patient data to be continuously monitored and analyzed. Non-invasive methods have also demonstrated severe limitations with regard to , the size and expense of equipment, the requirement for highly trained personnel and may lead to inaccurate ~- information in patients with cardiac diseases. Finally, the thermodilution technique is not capable of providing real time data on a beat-by-beat basis.

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It would be very desirable to provide the clinician with the ability to evaluate cardiac function in certain circumstances, such as with critically ill patients or ~ during surgery, on a continual basis since all other i 5 hemodynamic information except cardiac output is ;~ currently gatherad on a beat-to-beat basis. By obtaining beat-to-beat cardiac output, a hemodynamic assessment of the patient could be performed continuously by the attending staff.
Accordingly, it has been considered desirable to develop a new and improved catheter for measuring cardiac output together with a method for determining the instantaneous volume of blood in a chamber of a heart and ~i a cardiac output monitoring system with which the catheter can be used which would overcome the foregoing ' difficulties and others while providing better and more advantageous overall results.
Brief 8u~m~ry of th0 Invention In accordance with the present invention, a new and improved diagnostic catheter is provided for measuring cardiac output in the right ventricular chamber.
More particularly, this invention provides a diagnostic catheter for use in measuring cardiac output in the right ventricular chamber comprising:
(a) an elongated, multi-lumen, flexible member having a distal end and a proximal end, a first lumen extending the entire length of said member and terminating in a distal port, a second port extending through the side wall of said member at a location immediat~ly proximate of said distal end of said flexible member and a second lumen extending from said proximal end of said member to said second port;
(b) an expandable sleeve surrounding said member and spanning said second port, said sleeve inflatable by a fluid introduced into the proximal end of said second lumen;

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1~ 5 ~3~12~9 (c) a plurality of ring electrodes secured to the j outer surface of said member at predetermined axial I spacing including a distal ring electrode located a first predetermined distance proximal of said distal end of said flexible member, a proximal ring electrode located a second predetermined distance greater than said first predetermined distance from said distal end of said flexible member and a further plurality of intermediate ring electrodes disposed betwaen said distal ring 1 10 electrod~ and said proximal ring electrode;
(d) a plurality of electrical conductors extending longitudinally through a third lumen in said flexible member from said proximal end of said flexible member and individually connected to separate ones of said plurality of ring electrodes; and, (e) a first stiffening member disposed in a fourth lumen in said flexible member and extending from a third predetermined distance to a fourth predetermined distance proximal of said distal end of said flexible member, said third and fourth distances being greater than said second predetermined distance.
Further, invention provides, a catheter for measuring cardiac output, comprising:
. a catheter body having an outer periphery and a 25 distal section terminating in a distal end and a proximal ,.
section terminating in a proximal end;
a plurality of spaced electrodes secured to said body outer periphery along said body distal section;
a plurality of electrical leads, each one extending in said catheter body from a respective one of said ~ ~ electrodes to said proximal end of said catheter body:
I and an elongated rigid means for stiffening a portion of said catheter body, a distal end of said rigid means ~: 35 being located proximally of a proximal-most of one said plurality of electrodes, said rigid means being located proximally of said plurality of electrodes in order to .,~ i;.. , ; ' .,~

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', 6 1331209 allow them to be spaced away from endocardial tissue when said cathater body is correctly located in a haart.
Finally, this invention provides a catheter for measuring cardiac output, comprising:
an elongated flexible multi-lumen catheter body ~ having an outer periphery and a distal section ! terminating in a distal end and a proximal section ~ terminating in a proximal end;
¦ a balloon attached to said distal end of said body;
1 10 a first lumen extending the entire length of said catheter body and terminating in a first port which communicates with an interior surface of said balloon;
a plurality of spàced elactrodes secured to said . body outer periphery along said body distal section proximal of said balloon;
a second lumen extending from a distal most one of said plurality of spaced electrodes to said proximal end of said body;
a plurality of electrical leads, each one extending through said second lumen from a respective one of said electrodes to said proximal end of said catheter body;
and, .
a means for taking blood pressure measurements in a ~:~ right ventricle of a heart when the catheter is fully -; 25 inserted in the heart, said means comprising a third lumen which extends longitudinally in said catheter body from said proximal end to a second port intermediate said plurality of spaced electrodes, wherein said second port is adapted to take blood pressure measurements as the port passes through a tricuspid valve and becomes ~:, stationary in the right ventricle of the heart.
one advantage of the present invention is the provision of a new and improved catheter for use in 1~ : monitoring stroke volume.
Another advantage of the present invention is the .
: provision of a method and apparatus for measuring stroke volume and cardiac output with an accuracy greater than :
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Still another advantage of the present invention is the provision of a method and apparatus for measuring stroke volume and cardiac output on a beat-to-beat basis in a continuous manner.

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Yet another advantage of the present invention is the provision of a catheter which, together with apparatus for mea~uring stroke voluma facilitates the measurement of cardiac output on a beat-to-beat basis. The catheter can also be used in ventricular pacing and the diagnosis of ¦ complex arrhythmias.
Still yat another advantage of ~he present invention is the provision of a balloon catheter having a series o~
axially aligned electrodes extending over a predetermined lo length proximally of the balloon such that when th~ balloon is guided into the pulmonary outflow trac~ of the heart, the portion of the catheter bearing the electrodes extends I between the tricuspid valva and the pulmonary valve of a ¦ right ventricle of the heart.
A further advantaqe o~ the present invention is the provision of a flow diracted catheter having a stiffening member contained in a lumen thereof for causing the catheter to assume the correct orientation in a right ventricle of the heart.
A still further still advantage of the present invention is the provision of a method and apparatus for measuring ventricular volume of a heart wherein the cathetar is capable of conducting stroke volume measurements us~ng two different techniques so that a comparison or a calibration can be performed.
A yet further advantage of the present invention is the provision of a ventricular volume measuring system including a catheter having electrode~, a signal conditioning and cath~ter control unit and a microcomputer.
The system allows any electrode pair to be selacted for use as either sensing electrodes or drive elsctrodes as desired and the electrods~ can be scanned to determine cathet~r position.
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- 9 - 13~209 ~ Still other benefits and advantages of the ! invention will b~come apparent to those skilled in the art upon reading and understanding of the following detailed speci~ication.

5Brlef_~escription of_the ~ra~inqs Th~ invention may take phy~ical form in certain parts and arrangements of parts, a preferred embodimant of which will ba described ~n detail in this specification and illustrated in the accompanying drawings which form a part 10hereof and wherein:
FIG. 1 is a plan vi8W of a catheter according to the preferred embodiment of the pre~ent invention:
FIG. 2 i3 an enlarged cross-sectional view along ~- line 2-2 of the catheter of FIG. 1;
15FIG. 3 is a block diagram of a continuous cardiac :: output measuring system according to the present invention;
FIG. 4 is a front elevational view of a signal conditioning and control unit housing of the system of FIGURE 3 according to the present invention;
20FIG. 5 is a block diagram of the electronic modules .~ within the signal conditioning and control unit of FIG. 4;
~IG. 6 iB a block diagram at the input isolation unit of FIG. 5.
FIG. 7 i~ a block diagram of the signal processing 25unit of FIG. 5.
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oscillator unit of FIG. 5.
FIG. 9 iq a block diagram of th~ ma~or Yections of the signal conditioning and catheter control unit of FIG.

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~- FIG. 10 i~ a block diagram o~ a microcomputer of .the systsm of FIG. 3;

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FIG. 1~ i~ a ~low di~gram o~ th~ software routines in modul~ 1 o~ the module~ illustratad in FIG. 11;
FIG. 13 18 a ~low dlagram o~ the soft~are routines ln module 2 o~ the modula~ illu~trated in F~G. 11:
FIG. 14 la ~ ~low dlngr~m of tha 80~tw~re routlneq in module 3 D~ th~ m~dules lllu~trated in FIG. 11:
FIG~ 15 i~ a ~ectional view of a heart ~howing the ~ 10 catheter o~ FIGURE 1 in~rt~d in the right ventricle;
¦ FIG. 16 i~ a perspective view of a removed section I of the right v-ntrlcl~ o~ the haart of FIG~ 15 ' ~e~El~tlon o~ th~ PreferrQd_Em~odi~n~
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Referring now to the drawing3, wherein the showings are for purposea of lllu~trat~ng a preferred embodiment of thi~ invention only and not for purposec o~ limiting same, FIG. 1 show~ th~ ~ub~ect n~w diagnostlc catheter A which 18 ~: adspt~d to be positlonsd in A heart B a~ i8 illu6trated in ~-~ FIG. 15 and i~ adapted to convey information to the ~: 2~ continuou~ cardlac output measuring system C illu~trated in FIGo 3~ While the catheter will be described ~or use in monitorlng cardiac output in the right ventricl2 o~ a human heart, it should be appraclated that th~ cathQter can be used ~or monitoring cardia¢ oUtput elsewherQ in the heart, ~uch as ln ttlo ~e~t v~ntr~cle, and can al~o ~e u~d to ~:~
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monitor cardiac output in hearts other than human hearts, ~¦ such a~ suitable mammalian hearts and others.
More specifically, the catheter A is a balloon flotation catheter of the type known as a Swan-Ganz catheter. The catheter A compri~es an elongated tubular member 10 which~can be approximately 110 cm long if desired and which can be made from a plasticized PVC extrus1on~ if de~ired. The member 10 i~ extruded so a~ to have a predetermined outer diameter which, for purposes of illustration only, may be about a French 7.5 diameter t2.475 mm) and which is preferably formed from silicone rubber, polyurethane or some other suitable plastic that tends to be non-thrombogenic. It should be appreciated, however, that the tubular member could have a diameter between about French 4 (1.32 mm), fox pediatric applications, and French 8 ~2.64 mm). The tubular mem~er 10 includes a distal section 12 having a distal end 14 and a proximal section 16 having a proximal end 18 which terminates in a pigtail sheath 20.
Extending from the pigtail sheath are a first inlet tube 22, a second inlet tube 24, a third inlet tube 26, and a fourth inlet tube 28. Al~o extending from the sheath is a first electrical conduit 30 and a second electrical conduit 32~ Secured on a free end of the first inlet tube 22 1~ a connector terminal 34. Similarly secured on the free end~ of the second and third inlet tubes 24 and 26 are suitable second and third connector terminals 36 and 38.
To a free end of the fourth inlet tube 28 is secured a fluid connector terminal 40 known as a Luer valve~ ~ first electrical terminal 42, which is for the thermistor and can be a three pin Edwards type connector if desired, is connected to a free end of the first electrical conduit ..i,~
30. Similarly, secured to the free end of the second ~i ~ .
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electrical conduit 32 i8 a suitable second electrical terminal 44, which i8 for the electrodes and can include ten pins, if desired.
The distal end 14 of the cathater is provided with a first outlet port 50 which is in fluid communication with the first inlet tube 22 through a first or distal lumen 52 as shown in the cro~s-sectional view of FIG. 2. Similarly, second and third outlet ports 54, 56 are in fluid communication with a respective one of the second and third inlet tubes 24, 26, throu~h suitable lumens only one of which, 58, is illustrated in FIG. 2 since the port 56 can terminate the other lumen before the cross-sectional view of FIG. 2. A balloon section 60 is in fluid communication with the fourth ~nlet tube 28 through a third lumen 62 as is illustrated in FIG. 2.
Formed through the side wall of the tubular member 10 in tha zono spanned by the balloon 60, is a port, not visible in FIG. 1, which communicates with the third lumen 62. Thus, when fluid under pressure is ~ntroduced throuqh the open fluid terminal 40, it flows through the lumen 62 and out the mentioned port so as to inflate the balloon.
By then closing the valve 40, the balloon can be retained in its inflated state.
Secured on an outer periphery of the tubular member 10 are a plurality of spaced ring type surface electrodes 70, which can be made from Elgiloy. The electrodes are spaced apart by approximately .8 to 1.0 cm and can be approximately 2 mm ~ide. The most proximal electrode is identi~ied by ths numeral 70P and the most distal electrode is identified by the numeral 70D. Preferably, ten electrodes are provided with each of the electrodes being connec~ed to a separate insulated conductor 72 which is -~ positioned in a fourth or electrical lumen 74 as is . illustrated in FIG. 2. If desired, the distal-most ~:
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Such an elactrode spacing may be advantageous for patients with small ventricles. The conductors 72 axtend in th~
fourth lumen proximally to the second electrical terminal 44 and terminate in indivldual connector pins 76 contained in the terminal or housing 44. The terminal is adapted to be connected to a control unit as described hereinbelow.
Located on the tubular member 10 is a port 80 adjacent the balloon section S0 for holding a conventional thermistor element 82 which is normalized for blood temperature measurement and is disposed within the tubular membar. As i~ well known in the art, a suitable plastic such as polyurethane haviny good heat conducting properties covers the thermistor in the port 80 in order to prevent th~ ingress of blood and other body fluids. The thermistor 82 is in electrical contact with the thermistor terminal 42 through a suitable insulated conductor 84 (FIG. 2) which for the sake of convenisnce, can also extend through the fourth lumen 74 if de~ired.
As illustrated in FIG. 2, a metallic stiffening member or stylet 90 is suitably disposed in a lumen 92 proximally of ths proximal most electrode 70P. If desired, the lumen 92 can be a continuation of the lumen which leads also to the third port or proximal port 56. In order to prev~nt fluid from flowing further down this lumen, a suitable adhesive plug (not visible) is suitably injected into the lumen at a location distal of the port 56, as i~
.; well known in tha art.
As i~ evident from FIG. 2, the tubular member can be a five lumen cathe~er. However, it should bs ., ë'~
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The stif~ening stylet 90 can comprise a suitable stainless steel wire which is encapsulated in an insulating material such as nylon. In order to give the wire considerable stiffness, it can ba made out of a suitable conventional spring wire if desired. The stylet 90 can be positioned lmmediately proximally of the proximal most electrode 70P and can extend approximately 10 cm proximally therafrom as-is illustrated in FIGURE 1. During insertion, the stiffening stylet 90 aids in the proper positioning of the catheter to locate the electrodes away from the heart chambar wall~ thereby allowing the cathater to be placed in a poRition which per~its impedance measurement3.
While the stylet 90 is shown in FIG. 1 as being substantially straight, it should be appreciated that curved, bent, or looped stylets might prove advantageous for certain catheter uses as well. The stylet could be fixed or adju~tabls as may be required. While the stylet has been illu~trated as being made of stainless steel, other types of material, such as for example fiber-reinforced composites may be used instead.
The first lumen s2 which terminates in the first port ~0 at the tip of the catheter is useful for monitoring blood pressures during insertion of the catheter.
Additionally, blood samples can also be drawn from the first port 50. The third port or proximal port 56 with which the lumen 92 can communicate as explained above, can terminate approximately 30 cm from the dista} end o~ the catheter. When the cathetar is correctly inserted in the heart, the port 56 will be located in the right atrium.
This port can be used to monitor central venuous pressures ~:
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I and can also be employed as an injection site for fluids ¦ and medication~. Blood samples can also be obtained ¦ through this port.
f As mentioned previously, it is advantageou-~ to ¦ 5 provide a second port 54 which is located between the I serias o~ spaced elactrod2s 70. The lumen 58 communicating i with port 54 can terminate at approximately the 15 cm mark ¦ as measurad from the distal end locating the port between the ei~hth and ninth electrodes 70~ The port 54 can be ¦ 10 used for measuring right ventricular pre~sures as well as I determining catheter location by examining the changes in ¦ the pressure wave-form as the port passes through the tricuspid valve and into the right ventricle.
! In another embodiment of the invention, ten electrodes can be spaced apart at 1 cm intervals b~ginning 9 cm from the distal tip of the catheter and terminating 20 ~ cm from the distal tip. A calibrated thermistor bead can ¦ be located approximately 4 cm from the distal tip. The catheter can have a balloon of approximately 1.5 cc volume located between the thermistor and the distal tip. A
~¦ stiffening or stabilizing stylet 10 cm in length can be provided in the catheter between 20 cm and 30 cm from the 1 di~tal tip of the catheter, that is proximally from the proximal-most electrode. The stylet can be made of ~tainles~ sti~el which is encapulated in nylon.
¦~ This catheter can include four lumens, namely, a proximal lumen which terminates 30 cm from the di~tal end ~1 of th~ catheter for monitoring central venuous pressures, injecting fluids and medications and drawing blood samples:
an electrical lumen which contains the leads for the thermistor and each of the ten electrodes; a balloon lumen which is used to control the inflation and deflation of the 3~
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balloon; and a distal lumen which terminates at the tip of the cathQter, for monitorlng blood pressures and drawing blood samples.
With referenca now to FIG. 15, the catheter A can, i~ desired, be inserted via the superior vena cava. The site of entry can be an internal jugular, subclavian or antecubital vein. Insertion and final catheter positioning are guided by pressure waveforms and EKG signals obtained from the catheter. The methods employed for introducing the catheter are identical to those used for the insertion of a conventional Swan-Ganz catheter, and, a~cordingly, no further description of them is considered necessary. Once the distal tip of the catheter has been routed through a right atrium 100 of the heart B, and a tricuspid valve 102 thereof and into the right ventricle 104, an in~lating - fluid is applied under pressure to the balloon lumen 62 to inflate the balloon 60. As blood is pumped from the right ventricle, the balloon 60 tends to be carried by blood flow through the pulmonary valve 106 and into the pulmonary outflow tract. Once the tip -of the catheter has been located in the pulmonary artery, it is advanced until a wedge condition exi~ts, i.e., the inflated balloon lodges in a branch o~ the pulmonary artery 108.
When correctly located, the proximal electrode 70P
is located adjacent the tricuspid valve 102 and ~he distal electrode 70D is located at the entrance to the pulmonary outflow tract and preferably adjacent the pulmonic valve 106. once the catheter is installed, stroke volume ; measurements can be taken using the techniques set out hereinbelow.
on advantage of the pentamerous lumen embodiment of the invention illustrated in FIGURE 1, i8 that the port 54 can be used to in~ect medications directly into the cardiovascular system even when ~lood pressure measurements ~: .
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are being taXen through the ports 50 and 56. Also, the port 54 will be posltioned in the right ventricle (as shown in FIGURE 15) which is advantageous for obtaining a good mixing of th~ medication with the blood.
on the other hand, the port 56 can also be used to inject medication. Thi~ port, since it will be positioned in the right atrium (see FIGURE 15~ will also assure a good mixing o~ medication with the blood.
Turning now to FIGURE 3, a block diagram of a continuous cardiac output measuring system C of the present invention will be described. The entire monitoring system C is contained in the portable cart D. The - monitoring system c receives electrical power from a power source connection 110. Power entering through connection 110 passes through an isolation transformer 112, and then to a power distr~bution network 114 which functions to condition power to appropriate levels and distribute it throughout the system. The power isolation transformer 112 functions to provide a level of patient safety for the equipment when operating in a critical environment.
Signals received from the multi-electrode catheter A
into the continuous monitoring system C are acquired by a - signal conditioning and catheter control unit 118 ("SCCCU"), the user interface of which is illustrated more fully by FIGURE 4. The SCCCU 118 provides a user interface ; to control operation parameters of the system. Included is user selected auto position control; pacer balancing controls; input channel gain select; electronic filtration;
position control; signal gain; and a master power control.
It will be recalled that analog signals are received by the continuous monitoring system C. Signals received by the unit 118 are passed through a gain select 120 which functions to isolate a desired signal level. Analog outputs frcm the gain select 120 are fed to a four channel ' :
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~, ¦ analog recorder 122, which in turn interfaces a patient monitor through an interface adapter 124. Analog signals from the gain select 120 are also fed to a microcomputer 130 via an analog to digital t"A to D") interface 132. In $ 5 this fashion, a digital signal representative o~ the analog values obtained ~rom the multi-catheter electrode A is obtained for use in the microcomputar 130 which, in the preferred embodiment, is digital. The microcomputer 130 will be dascribed more fully in conjunction with FIGURE 10, below.
¦ The microcomputer 130 is also in data communication with a hard-copy data recorder illustrated by printer 134.
The microcomputer 130 is also similarly in data communication with an external display such as that illustrated by display 6creen 136 which is suitably comprised of a conventional cathode ray tube ~"CRT") display. The microcomputer 130 is also shown as including a contiguous CRT monltor 138, a data entry device such as key board 140, and a ma~s storage medium 142 which is illustrated as a pair of disk drives 142a and 142b. The mass storage medium 142 i8 suitably comprised of a hard disk, a floppy disk, a CD-MEMORY (compact disk memory), or the like, or any combination thereof. A data port 146, .
which is suitably comprised of a parallel port or a serial port, proYides a means for communicating data to an exterior of the microcomputer 130. As illustrated, t~e -~ data port 146 communicates data back to the signal conditioning and cathetQr control unit 118 in a f~ed-back manner.
Turning n~w to FIGURE 5, a block diagram of the signal conditioning and catheter control unit 118 is ` presented. Power is received into the SCCCU unit 118 via - interconnect 150 which is in turn connected to the power distribution network 114 (FIGURE 3). The power network ,~ .

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~33~ 2~ -lg ~, interface~ c-rouit breakers 152 and a powsr trans~ormer 154, which steps down the voltage therethrough to suitable ~ levels for operation of the remaining circuitry. The ;~ con~rol unit 118 includes primary circuit modules comprising an input isolation untt 158, a ~ignal processing unit 160, and interface/oscillator/filter unit 162, a power supply filter unit 164, and a power supply unit 166. All I devices are interfaced via a common signal bus 170. The i signal bus 170 also interfaces the control panel of FIGUR~
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¦ The power supply unit 166 receives power from the power transformer 154, stappinq it down to appropriate i values for use throughout the control unit 118. The voltage levels obtained from the power supply unit 166 are filtered, prior to distribution to the remaining circuitry of the unit, by power supply filter unit 164.
Use of the common connector bus 170 provides a means by which any or all o~ the above units may be implemented by "plug-in" modules which facilitates selective replacement, enhancement, or modification. Implementation of this bus structure al80 provides for minimization of noise proble~s.
The signal bu~ 170 also interconnects the multi-electrode catheter A via an input protection circuit 174.
The input protection circuit 174 isolates the signal bus 170, and accordingly the remaining components interfaced thereto, from voltage levels which may otherwise damage circuitry within the control unit 118.
Turning to FIGURE 6, tha input isolation unit 158 will be described in detail. The input isolation unit 158 contains circuitry which provides five channels of input isolation, a constant current source, electrode select control, and ground isolation. All signal~, as well as . power entering or leaving this module, are isolated via '~

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opto-isolators or transformer coupling. Blocks within the q dash lins of FIGURE 6 are isolated. Blocks through which the dash line passes are providing the isolation. Block 180 illustrates a series of six high impedance voltage follower amplifiers which function as buffers between the multi-electrode catheter and the remaining circuitry.
Outputs from the input buf~ers 180 are in turn fed to a series of five channals of differential input amplifiers illustrated by block 182. Signals resultant from the amplifiers 182 are in turn fed outward, again through the signal bus 170 (FIGURE 5) via a group of opto-isolators 184. The opto-isolators isolate the signals passed therethrough from the next stage via optic coupling. This circuitry is powered via a transformer coupled with non-earth ground re~erence6. This forms ths iso-power input 190. The iso-power used is referenced to a potential known as isolated ground. I~olated ground is not tied to earth ground. This feature provides a level of patient isolation preventing currents which are flowing due to ground reference potentials from passing into this circuitry. Each optical coupler provides a signal isolation well above several thousand volts.
Turning to FIGURE 7, fabrication of the signal - processing unit 160 of FIGURE 5 will be described. The signal procea~ing unit 160 contains oircuitry which provides AC buffering, bandpass filtering, amplitude demodulation, signal smoothing, signal in~ersion, and waveform isolation. FIGURE 7 depicts a signal flow and control related to this module. The board is connected, via the signal bus 170, to two external devices. These external devices include a circulating fan (not sho~n) via an interconnect 192, and an o~fset control (not shown) via an offs2t control interconnect 194. Unlike the circuitry o~ FIGURE 5A the signal processing unit 160 includes no ~'~" " , `' 7 ~ ~

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jc i ~l3312~9 i circuitry which use~ isolated power. Outputs of the opto-isolators 184 from FIGURE 6 ~orm an input to AC buffering circuitry 200. Thi~ circuitry buffers analogously to the buffer~ 180 of FIGURE 6. Waveforms from the buffer circu~try 200 are pas~ed to a series of five 2Khz bandpass filters 20~. Use of multi-feedback active bandpass filters ~, permits modulatad signals of up to 40 Hertz to pass with I minimal effect. The filterq are implemented given that the ¦ modulated impedance signalq contain freguencies of up to ! lo 40 Hertz. The bandpa~s filters effectively block undesirable physiologic signals such as electrical signals ~ ganerated by the contractions of the heart.
,~, After the bandpass filters 202, the signals are ;j passed into five channels of amplitude demodulation present in demodulation circuitry 204. In this circuitry, each channel of impedance waveforms is amplitude demodulated by an absoluta value and wave smoothing circuit comprised of a pair of operational amplifiers. The output waveforms from each of these stages is a demodulated signal with some carrier frequency noise. The signals are next passed to a low pass filter 206 to further reduce carrier freguency noise. The low pass filters 206 are suitably comprised of Butterworth-type filters with a maximally flat frequency response. Attenuation i~ suitably 12 dB at twice the cut-off frequency of 100 Hertz. Signals a~ter the 100 Hertz low-pa3s filters represent real time dynamic impedance wave~orms for each of five selected pairs of electrodes from the cathetar A (FIGURE 1).
Signals are next fed to a signal inversion circuit 210. In this s~age, each impedance value is inverted to form an admittancs value. The admittance signal level is desired as it forms a signal from which volume to be measured is directly proportional. The signal inversion ~i~ . circui~ functlons by implemantation o~ ~n analoq divider .. ~ ~
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¦ chip. Impedance signals are used as denomina~or values, whila an adjustable but constant voltage is used for a numerator. With these two analog voltages, a real time quotiant (admittance) is developed for each channel which is inversely proportional measuring impedance values. One of two resistive voltage divider~ can be selected, via the front panel control of FIGUR~ 4, to determine the constant numerator voltagQ.
Output from channels are selected from the signals from the signal inver~ion circuit 210 by channel selector circuit 212. Sueh selection is accomplished by means of a signal on waveform select control lines which are obtained as described further below. These control lines determine whether a particular channel is selected. In the event a channel is not selected, no connection is made to further stages, thereby leaving th~ circuity open or at a high impedance state. Accordingly, the channel selector circuity 212 function~ an~logously to a tri-state device.
OutputR from the channel selector circuit 212 form inputs to a waveform summing amplifier 216. The summing amplifier 216 generates a composite waveform, which in turn forms an input to an offset adjust buffer 218. In the offset adding circuit 218, an externally selected DC level adds a value to the eomposite admittance waveform resultant from the ~ 25 summing amplifier 216. This functions to "window" the ; wave~orm within the range of an analog to digital convertor whieh i~ implemented in the computer 132 (FIGURE 3).
Turning now to FIGURE 8, fabrication of the interfaee/isolator/filter unit 162 will be deseribed. The ~nter~aee/isolator/fllter unit 162 provides interface - buffering, latehing eontrol, eonstant eurrant source development, eontrol level shifting, waveform filtering, paeemaker rejeetion, and auto positioning. The eomposite . admittane~ waveform developed by the signal proeessing unit ,~, .
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_ 23 -160 of FIGURE 7 is routed via interconnect 224 to circuitry which accomplishes the above-stated operations.
The interconnect 224 receivQs its signal ~rom an output 220 of the waveform summing amplifier 216 to FIGU~E 7. The ~ 5 composite waveform input obtained from interconnect 224 `j enters a signal inver~in~ stage 226 which is comprised of an inverting buffer with uni~y gain. The ou~put from the inver~er 226 forms an input for a filter selector switch ~single pole, double throw) 228 on the panel of FIGURE 4.
~l 10 The selector switch permits operator selection of an in-~, line 40 Hertz filter or a straight-through non-filtered waveform.
Tha output from the signal inverting stage 226 also , forms an input to a low-pa~s filter 230. An output of the 40 Hertz low-pass filter ls selectively ~ed to the filter selector 228 through a pacer reject module 232 prior to being additionally fed to the filter selector 228.
The pacer reject module is implemented in conjunction with the ~ignal placed on pacer reject line 234 which controls a selector switch 236. A signal on the pacer reject lina 234 is user selected by the control panel o~ FIGURE 4. The pacer reject circuitry is comprised of a slew rate limitRr ~abricated from a diode bridge circuit.
The circuitry functions by saturating if a feed-back path coupled to an ~C network is no~ at the same voltage a~ its ~input. A state o~ the feed-back path is determined by the q~slew rate of the input signals. For dynam~c values ggreater than 50 Hertz, the output of the amplifier saturates. Saturation may be positive or negative 30depend~ng on a direction of a detected signal spike. Upon activation, the clrcuit deselects the actual wave-form and connects ~he output to a high impedance source. This essentially ~orces the circuit to behave as a ~ample and ~ ~-~

-~ - 24 - 13312~
;i hold circuit, thus locking out spike potentials from the pacer and ~orcing the circuit to remain at its last detected value.
The operator selected signal from filter selec~or 228 i~ passed to a low pass filtar 242 and a fil~er selector 246. The filter selector 246 functions to selectively pass the output o~ the filter selector 228 through the 10 Hertz low-pa~s filter 242 prior to passing it to a gain select potentiometer 248 which is al50 found in FIGURE 4.
The output of gain potentiometer 248 is .celectively placed, via selector switch 250, through an auto-position circuit 252, prior to bsinq fed to a final output driver 254. Th~ auto-position circuit 252 inver~s the polarity of the signal.
~: Turning to the top portion of FIGURE 8, parallel data from the microcomputer 130 is input to the ~: interface/oscillator/filter unit 162 via a data bus 260.
Data enters control buffers 262 and 264. The buffer 262 ~ 20 holds admittance select-channel data with the buffer 264 :~ holding electrode select-line information. The lines 266 form the electrod~ select controi lines which are coupled : directly to the catheter A.
Data fro~ the bu~fer 262 is also fed to a control level translator 270 to provide for control within the interface/oscillator/filter unit 162. ThesQ ~iqnals are latched by control signal latch 272, and translated by control leval translator 274 which converts the~ to voltage levels quitable for a logic control external of the unit 162. The voltageB levels are made available on channel sRlect control lines 276.
Latch detsct clrcuitry 280 trigger~ a control pulse ~:: at ~t~ output in respsn~e to a low to high transition on -. it~ input port, which is derived from an output of the ~ B

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- 25 - ~331209 control data buffer 262. In response to an output of latch ~! detect 280, data from the select-lines control buffer 264 is made available at lines 282.
A ~ine wave generator 286 has its frequency and ~ymmetry adjusted by controls 288 and 2so, respectively.
The sina wave generated by this circuit is routed through an offset ad~ust 292 and a gain adjust potentiometer 294.
These componants form a constant current source for use elsewhere in the circuit which also includes an isolator.
10Turning to FIGURE 9, a summary o~ the interaction of all hardware components illustrated in conjunction with FIGURES 5-8 as presented.
Turning now to FIGURE 10, a more detailed description of the microcomput~r 130 as implemented in the 15preferred embodiment is pre~ented. It will be noted that the microcomputer is illustrated as based on an 8086-2 microprocessor, of Intel Corp. of Santa Clar~, California.
Suitable computers having the characteristics illustrated by FIGURE 10 are commonly available in the market.
20Turning now to FIGURES 11-13, a software routine for the microcomputer of FIGURE 10 will be disclo~ed. With particular reference to FIGUR~ 11, the three primary software module~ and their interactions will be described.
`~ FIGURE 11 shows common structural links between 25modules and how thsy are initiated. A shared or common ~ ~ memory 300 is provided to hold variables whi h are used by - all modules or units in the subject system. This provides - mean~ by which modules which may have bean programmed in ~different languages are able to change a state of a stored 30variable independently of one another. Each routine is initiated without respect to a status of any other routine.
SCCCU operation and signal analysi3 is operationally separated from other code modules, but by virtue of the ~- ~shared me~ory 300, 3hare~ common variable~ with other code ~.. O,~

-26 ~ ~ 3~ 9 ~1 sections. Activation i8 preferably not user controlled, ¦ but instQad is a function of a hardware timer and clock I circuit 302 which activate~ the module at a ~requency o~
suitably 200 tim~s per second, regardless of a state of the 1 5 remaining modules. This sectlon of code is essentially ¦ running in the background whlle all other code is running in the foreground. Because of its mode of activation, the ScCCU operation and signal analy~is module has priority over other code module~. This module is ~ermed "free-running" and raquires no operator intera~tion to begin or complete its task. The software routine implemented in module~ 1, 2, and ~304, 306, and 308 respectively), are illustrated in FIGURES 12, 13, and 14, respectively.
The computation of the volume of the right ventricular segments (one is illustrated in FI~URE 16) between selected pairs o~ sense electrodes is done accordlng to the formula Volume = (Ic x p x L2)/VEE where Ic is a known constant current source, p is the resistivity of the medium, L is the distance between electrodes and VEE 15 the measured end to end voltage.
This formula iB sub~tantially accurate although it does not take into consideration the 10B-~ of current to surrounding tissue or the varying conductivity of blood.
- If L i8 designated to be 1 cm., then each segment volume is directly proportional to P /ZEE~ whera ZEE is the i~pedance of the blood volume in the measured segment and i8 equal to Ic/VEE. Using the thermodilution technique, p can be determined as well as any signal ~ losses due to the leakage of drive current through 3 ' 30 surrounding tis~ue. Thu~, the total ventricular volume, 3 i . e. the ~um of the segments, can be determined by the for~ula VT = X ~ l/ZEE where R i5 a con~tant which repre~ent~ tha effect~ of blood resistivity and drlve signal losses.

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It should ba appreciated that the po~ential from each s~nsing electrode pair can also be used to detect the po~it~on of the catheter within the cardiovascular system.
The dynamic potential from the sensing pairs o~ electrode~
1 5 are examinad and the pair location is determined from the ¦ timing and waveform characteristics.
In the pre~ent system, the current source ~or the electrodes i8 a sinusoidal wave~orm o~ approximately 20 microamperes at a frequancy of approximately 2 KHz.
Twenty (20) microamperes has been determined to be the maximum RMS safe current at 2 KH2 by the Association for the Advancement of Medical Instrumentation.
It should also be appreciated that the construction 5~ of the inventive system allows any electrode to bs a sen~e electrode or a drive electrode as desired and selected. -~
This invention has been described with reference to ~ -a preferred embodiment, obviously modifications and alterations will occur to other~ upon the reading and understanding of this specification. It is intended that all su~h modifications and alterations be included insofar as thay come within the scop~ of the appended claims or the equlvalents thereof.
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Claims (21)

1. A diagnostic catheter for use in measuring cardiac output in the right ventricular chamber comprising:
(a) an elongated, multi-lumen, flexible member having a distal end and a proximal end, a first lumen extending the entire length of said member and terminating in a distal port, a second port extending through the side wall of said member at a location immediately proximate of said distal end of said flexible member and a second lumen extending from said proximal end of said member to said second port;
(b) an expandable sleeve surrounding said member and spanning said second port, said sleeve inflatable by a fluid introduced into the proximal end of said second lumen;
(c) a plurality of ring electrodes secured to the outer surface of said member at predetermined axial spacing including a distal ring electrode located a first predetermined distance proximal of said distal end of said flexible member, a proximal ring electrode located a second predetermined distance greater than said first predetermined distance from said distal end of said flexible member and a further plurality of intermediate ring electrodes disposed between said distal ring electrode and said proximal ring electrode;
(d) a plurality of electrical conductors extending longitudinally through a third lumen in said flexible member from said proximal end of said flexible member and individually connected to separate ones of said plurality of ring electrodes; and, (e) a first stiffening member disposed in a fourth lumen in said flexible member and extending from a third predetermined distance to a fourth predetermined distance proximal of said distal end of said flexible member, said third and fourth distances being greater than said second predetermined distance.

2. The diagnostic catheter as in claim 1 and further including a fifth lumen extending from said proximal end of said flexible member and terminating in a third port formed through the side wall of said flexible member and located within said first predetermined distance; and a thermistor element exposed to heat conduction through said third port and having conductor means extending therefrom through said fifth lumen to the proximal end of said flexible member.

3. The diagnostic catheter as in claim 2 wherein said third port containing said thermistor includes a plastic seal covering said thermistor, said plastic having a thermal conductivity property allowing said thermistor to detect a small temperature change rapidly.

4. The diagnostic catheter as in claim 1 and further including a fourth port extending through the side wall of said flexible member-and communicating with said fourth lumen at a location proximal of said stiffening member.

5. The diagnostic catheter as in claim 1 and further including a multi-terminal electrical connector connected to said plurality of electrical conductors.

6. The diagnostic catheter as in claim 1 and further including valve means connected to the proximal end of said second lumen of said flexible member.

7. A catheter for measuring cardiac output, comprising:
a catheter body having an outer periphery and a distal section terminating in a distal end and a proximal section terminating in a proximal end;
a plurality of spaced electrodes secured to said body outer periphery along said body distal section:
a plurality of electrical leads, each one extending in said catheter body from a respective one of said electrodes to said proximal end of said catheter body;
and an elongated rigid means for stiffening a portion of said catheter body, a distal end of said rigid means being located proximally of a proximal-most of one said plurality of electrodes, said rigid means being located proximally of said plurality of electrodes in order to allow them to be spaced away from endocardial tissue when said catheter body is correctly located in a heart.

8. The catheter of claim 7 further comprising a first lumen extending longitudinally through said catheter body from said body proximal end to a distal-most one of said plurality of electrodes, wherein said plurality of electrical leads are located in said first lumen.

9. The catheter of claim 8 further comprising a second lumen which extends from a proximal end of said catheter body to a port located at approximately 15 cm from said distal end of said catheter body.

10. The catheter of claim 9 further comprising:
a balloon sleeve located adjacent a distal tip of said catheter body;
a third lumen communicating said balloon with said proximal end of said catheter body; and, a further lumen extending from said catheter body proximal end to a port located on said catheter body distal end.

11. The catheter of claim 10 further comprising a fifth lumen extending from said body proximal end and terminating in a port formed through side wall of said body and located at a predetermined distance from a proximalmost one of said plurality of electrodes.

12. The catheter of claim 7 further comprising:
a thermistor sensor secured to said catheter body and spaced distally from a distal-most one of said plurality of electrodes; and, an electrical lead extending in said catheter body from said thermistor to said proximal end of said catheter body.

13. The catheter of claim 7 wherein said plurality of electrodes comprises ten electrodes which are spaced apart from each other by approximately 0.8 to 1.0 cm and wherein a distal-most one of said plurality of electrodes is located at approximately 9 cm from said distal end of said catheter body.

14. The catheter of claim 7 wherein said stiffening means comprises an elongated stylet disposed in a lumen of the catheter, said stylet extending proximally from adjacent a proximal-most one of said plurality of electrodes.

15. The catheter of claim 7 further comprising a pair of drive electrodes, wherein a distal electrode and a proximal electrode of said plurality of electrodes serve as said pair of drive electrodes and wherein said stiffening means so locates said distal electrode and said proximal electrode as to be positioned adjacent a pulmonic valve and a tricuspid valve of the heart, respectively.

16. The catheter of claim 7 further comprising a terminal means secured to said catheter body proximal end for receiving a free end of each of said plurality of electrical leads.

17. A catheter for measuring cardiac output, comprising:
an elongated flexible multi-lumen catheter body having an outer periphery and a distal section terminating in a distal end and a proximal section terminating in a proximal end;
a balloon attached to said distal end of said body;
a first lumen extending the entire length of said catheter body and terminating in a first port which communicates with an interior surface of said balloon;
a plurality of spaced electrodes secured to said body outer periphery along said body distal section proximal of said balloon;
a second lumen extending from a distal most one of said plurality of spaced electrodes to said proximal end of said body;
a plurality of electrical leads, each one extending through said second lumen from a respective one of said electrodes to said proximal end of said catheter body;
and, a means for taking blood pressure measurements in a right ventricle of a heart when the catheter is fully inserted in the heart, said means comprising a third lumen which extends longitudinally in said catheter body from said proximal end to a second port intermediate said plurality of spaced electrodes, wherein said second port is adapted to take blood pressure measurements as the port passes through a tricuspid valve and becomes stationary in the right ventricle of the heart.

18. The catheter of claim 17 further comprising:
a fourth lumen which extends longitudinally in said catheter body from said proximal end to a third port which is located proximally of said plurality of spaced electrodes; and, a stiffening member disposed in said fourth lumen distally of said third port.

19. The catheter of claim 17 further comprising a thermistor sensor secured to said catheter body and spaced proximally from said balloon.

20. The catheter of claim 17 wherein ten ring electrodes are provided which are spaced apart from each other by approximately 0.8 to 1.0 cm and wherein a distal-most one of said plurality of electrodes is located at approximately 9 cm from said distal end of said catheter body.

21. The catheter of claim 17 further comprising a multi-terminal electrical connector connected to said plurality of electrical leads.