 |
Description  |
|
|
BACKGROUND OF THE INVENTION
This invention generally relates to medical apparatus for measuring
characteristics of a heart. More particularly, the invention relates to a
balloon flotation 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 nonhuman
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 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
level of 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 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
injected 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. The
concentrations recorded were directly related to the flow rate of the dye
mixed blood through the circulatory system.
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 10.degree. C. less than the patient's core
temperature, is injected 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 to the flow rate of the mixed fluid through the right side of the
heart. Since the circulatory system is a series circuit, the right side
value is also reflective of the left side ejections. Thus, a cardiac
output can be calculated from the indicator dilution curve using a known
equation.
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 from 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 the 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.
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 hemodynamic information except cardiac output is currently gathered
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
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 SUMMARY OF THE 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 in accordance with this aspect of the invention, the
catheter comprises an elongated multilumen flexible member having a distal
end and a proximal end. A first lumen extends the entire length of the
member and terminates in a distal port. A second port extends through the
side wall of the member at a location immediately proximate of the distal
end of the flexible member and a second lumen extends from the proximal
end of the member to the second port. An expandable sleeve surrounds the
member and spans the second port. The sleeve is inflatable by a fluid
introduced into the proximal end of the second lumen. A plurality of ring
electrodes are secured to the outer surface of the member at a
predetermined axial spacing. The electrodes include a distal ring
electrode located at a first predetermined distance proximal of the distal
end of the flexible member and a proximal ring electrode located a second
predetermined distance greater than the first predetermined distance from
the distal end of the flexible member. The electrodes further include a
plurality of intermediate ring electrodes disposed between the distal ring
electrode and the proximal ring electrode. A plurality of electrical
conductors extend longitudinally through a third lumen in the flexible
member from the proximal end of the flexible member and are individually
connected to separate ones of a plurality of ring electrodes. A first
stiffening member is disposed in a fourth lumen in the flexible member and
extends from a third predetermined distance to a fourth predetermined
distance.
According to another aspect of the invention, a catheter is provided for
measuring cardiac output.
More particularly in accordance with this aspect of the invention, the
catheter comprises 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 are provided each one of which extends in the catheter body from a
respective one of the electrodes to the proximal end of the catheter body.
An elongated rigid means is provided for stiffening a portion of the
catheter body. One end of the rigid means is located adjacent a proximal
most one of the plurality of electrodes. The rigid means so locates the
plurality of electrodes as to space them away from endocardial tissue.
In accordance with still another aspect of the invention, a catheter is
provided for measuring cardiac output.
More particularly in accordance with this aspect of the invention, the
catheter comprises 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 is attached to
the distal end of the body. A first lumen extends the entire length of the
catheter body and terminates in a first port which communicates with an
interior surface of the balloon. A plurality of spaced electrodes are
secured to the body outer periphery along the body distal section proximal
of the balloon. A second lumen extends from a distal most one of the
plurality of spaced electrodes to the proximal end of the body. A
plurality of electrical leads are provided each one of which extends
through the second lumen from a respective one of the electrodes to the
proximal end of the catheter body. A third lumen is provided which extends
longitudinally in the catheter body from the proximal end to a port which
is intermediate to the plurality of spaced electrodes.
According to a further aspect of the invention, a method is provided for
determining the instantaneous volume of blood in a chamber of an animal
heart.
More particularly, the method comprises the steps of inserting an elongated
tubular catheter percutaneously into the heart chamber. The catheter has a
plurality of longitudinally spaced electrodes on the surface thereof which
electrodes are individually connected to a corresponding plurality of
terminals at the proximal end of the catheter by conductors passing
through the tubular catheter. The longitudinal spacing of the electrodes
are such that a distal electrode and a proximal electrode are located at
the pulmonic valve and the tricuspid valve of the heart, respectively. The
distal electrode and the proximal electrode are driven with a constant
current source. The potential signal developed between pairs of sensing
electrodes located intermediate the pair of driving electrodes and
attributable to the application of the driving constant current source to
the pair of driving electrodes is selectively and sequentially detected.
The potentials are proportional to the instantaneous impedance of the
medium existing between the selected pairs of intermediate sensing
electrodes. The detected potential signals are then converted to digital
quantities. The digital quantities are applied to a programmed digital
computing device. A single corrected instantaneous impedance value is
generated for each of the intermediate sensing electrodes determined to
lie within the ventricle. The impedance value detected is due to the
application of the constant current source to the pair of driving
electrodes. A single corrected instantaneous impedance value is calculated
for a ventricular segment volume for each pair of the sensing electrodes.
The segment volumes for each pair of sensing electrodes are summed to
produce the total instantaneous ventricular volume.
According to a further aspect of the invention, an apparatus is provided
for measuring the instantaneous volume of blood in a chamber of a heart.
More particularly in accordance with this aspect of the invention, the
apparatus comprises an elongated tubular intravascular catheter having a
proximal end and a distal end with a pair of drive electrodes attached to
the exterior surface thereof and spaced apart from one another by a
predetermined distance D1 which is less than the length dimension of a
catheter section that is held in the chamber. A plurality of pairs of
sense electrodes are attached to the surface of the catheter and
longitudinally spaced therealong between the drive electrodes. The pair of
drive electrodes and the plurality of sense electrodes are electrically
coupled individually to a terminal at the proximal end of the catheter. A
constant current source of a frequency F.sub.1 is provided together with a
switching means which is joined to the terminals for coupling the constant
current source to a selected pair of drive electrodes. A signal detector
means is connectable through the switching means to predetermined pairs of
the plurality of pairs of sense electrodes for producing signal waves
corresponding to the impedance of the medium present between a sense
electrode pair selected by the switching means attributable to the
constant current source. A means is operatively coupled to the signal
detector means for sampling the signal waves at a predetermined rate and
converting the signal waves to digital values representative of impedance
values. A computing means is coupled to receive the digital values. The
computing means is programmed to compute the volume of the segments
between selected pairs of sense electrodes using the formula Volume
=(i.sub. c .times.p x L.sup.2)/V.sub.EE where i.sub.c is a known constant
current source, p is the resistivity of the medium, L is the distance
between electrodes and V.sub.EE is the measured end to end voltage.
According to another aspect of the invention, a continuous cardiac output
monitoring system is provided.
In accordance with this aspect of the invention, an elongated tubular
intravascular catheter is provided which is adapted for insertion into a
patient's heart. The catheter includes a plurality of spaced electrodes
positioned on a periphery of the catheter. A distal most one and a
proximal most one of the electrodes are configured as drive electrodes and
the remaining electrodes are configured as sense electrodes. Each of the
electrodes is connected to a terminal located at a proximal end of the
catheter. A signal conditioning and control unit is provided which is in
electrical contact with the catheter through the catheter terminal. The
unit comprises a constant current source, a selector means for coupling
the constant current source to drive electrodes and a signal processing
means for processing a signal received by the unit. A computing means is
electrically connected to the unit for converting signal waves from the
unit to digital values and then computing a stroke volume of the heart.
According to still another aspect of the invention, a cardiac output
monitoring system is provided.
More particularly in accordance with this aspect of the invention, the
system comprises a first signal means for sending analog data related to a
stroke volume in a right ventricle of a patient's heart. A signal
processing means is provided for processing the analog data from the first
signal means into processed analog data. A computing means is provided for
converting the processed analog data from the signal processing means to
digital values and thereafter computing the stroke volume of the patients
heart.
One advantage of the present invention is the provision of a new and
improved catheter for use in 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 has heretofore been possible using known prior art
techniques.
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.
Yet another advantage of the pr.RTM.sent invention is the provision of a
catheter which, together with apparatus for measuring stroke volume
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 yet another advantage of the present invention is the provision of a
balloon catheter having a series of axially aligned electrodes extending
over a predetermined length proximally of the balloon such that when the
balloon is guided into the pulmonary outflow tract of the heart, the
portion of the catheter bearing the electrodes extends between the
tricuspid valve and the pulmonary valve of a right ventricle of the heart.
A further advantage of the present invention is the provision of a flow
directed 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 advantage of the present invention is the provision of a
method and apparatus for measuring ventricular volume of a heart Wherein
the catheter is capable of conducting stroke volume measurements using 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
electrodes, a signal conditioning and catheter control unit and a
microcomputer. The system allows any electrode pair to be selected for use
as either sensing electrodes or drive electrodes as desired and the
electrodes can be scanned to determine catheter position.
Still other benefits and advantages of the invention will become apparent
to those skilled in the art upon reading and understanding of the
following detailed specification.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may take physical form in certain parts and arrangements of
parts, a preferred embodiment of which will be described in detail in this
specification and illustrated in the accompanying drawings which form a
part hereof and wherein:
FIG. I is a plan view of a catheter according to the preferred embodiment
of the present invention;
FIG. 2 is an enlarged cross-sectional view along line 2--2 of the catheter
of FIG. 1;
FIG. 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 FIG. 3 according to the present invention;
FIG. 5 is a block diagram of the electronic modules within the signal
conditioning and control unit of FIG. 4;
FIG. 6 is a block diagram at the input isolation unit of FIG. 5.
FIG. 7 is a block diagram of the signal processing unit of FIG. 5.
FIG. 8 is a block diagram of the interface/ oscillator unit of FIG. 5.
FIG. 9 is a block diagram of the major sections of the signal conditioning
and catheter control unit of FIG. 4;
FIG. 10 is a block diagram of a microcomputer of the system of FIG. 3;
FIG. 11 is a block diagram of the three primary software modules utilized
in the computer of FIG. 10;
FIG. 12 is a flow diagram of the software routines in module 1 of the
modules illustrated in FIG. 11;
FIG. 13 is a flow diagram of the software routines in module 2 of the
modules illustrated in FIG. 11;
FIG. 14 is a flow diagram of the software routines in module 3 of the
modules illustrated in FIG. 11;
FIG. 15 is a sectional view of a heart showing the catheter of FIGURE 1
inserted in the right ventricle;
FIG. 16 is a perspective view of a removed section of the right ventricle
of the heart of FIG. 15;
FIGS. 17A-l7I are schematics of the actual circuitry in which an embodiment
of the subject system is presented; and
FIGS. 18A-18II is a listing of the software modules with which the subject
system operates.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, wherein the showings are for purposes of
illustrating a preferred embodiment of this invention only and not for
purposes of limiting same, FIG. 1 shows the subject new diagnostic
catheter A which is adapted to be positioned in a heart B as is
illustrated in FIG. 15 and is adapted to convey information to the
continuous cardiac output measuring system C illustrated in FIG. 3. While
the catheter will be described for use in monitoring cardiac output in the
right ventricle of a human heart, it should be appreciated that the
catheter can be used for monitoring cardiac output elsewhere in the heart,
such as in the left ventricle, and can also be used to monitor cardiac
output in hearts other than human hearts, such as 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 comprises an elongated
tubular member 10 which can be approximately 110 cm long if desired and
which can be made from a plasticized PVC extrusion, if desired. The member
10 is extruded so as to have a predetermined outer diameter which, for
purposes of illustration only, may be about a French 7.5 diameter (2.475
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), for pediatric applications, and French 8
(2.64 mm). The tubular member 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. Also 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 is a
connector terminal 34. Similarly secured on the free ends 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. A 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 30. Similarly, secured to the free end of the second
electrical conduit 32 is a suitable second electrical terminal 44, which
is for the electrodes and can include ten pins, if desired.
The distal end 14 of the catheter 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 cross-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, through
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
inlet tube 28 through a third lumen 62 as is illustrated in FIG. 2.
Formed through the side wall of the tubular member 10 in the zone spanned
by the balloon 60, is a port, not visible in FIG. I, which communicates
with the third lumen 62. Thus, when fluid under pressure is introduced
through 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 wide. The most proximal electrode is identified by the
numeral 70P and the most distal electrode is identified by the numeral
70D. Preferably, ten electrodes are provided with each of the electrodes
being connected 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 electrode 70D can be located approximately 9 cm
from the distal end of the catheter with the proximal-most electrode being
located approximately 16.4 cm from the catheter distal end, when the
electrodes are spaced apart by 0.8 cm. Such an electrode spacing may be
advantageous for patients with small ventricles. The conductors 72 extend
in the fourth lumen proximally to the second electrical terminal 44 and
terminate in individual 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
60 for holding a conventional thermistor element 82 which is normalized
for blood temperature measurement and is disposed within the tubular
member. As is well known in the art, a suitable plastic such as
polyurethane having good heat conducting properties covers the thermistor
in the port 80 in order to prevent the 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 convenience, can also extend through the fourth lumen 74 if
desired.
As illustrated in FIG. 2, a metallic stiffening member or stylet 90 is
suitably disposed in a lumen 92 proximally of the 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 prevent
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 is well known in the art.
As is evident from FIG. 2, the tubular member can be a five lumen catheter.
However, it should be recognized that the member could also be provided
with six or more lumens if that was considered desirable or necessary.
The stiffening 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 be made out of a suitable
conventional spring wire if desired. The stylet 90 can be positioned
immediately proximally of the proximal most electrode 70P and can extend
approximately 10 cm proximally therefrom 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 chamber walls
thereby allowing the catheter to be placed in a position which permits
impedance measurements.
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 adjustable as may be required. While the stylet has been illustrated as
being made of stainless steel, other types of material, such as for
example fiber-reinforced composites may be used instead.
The first lumen 52 which terminates in the first port 50 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
distal end of the catheter. When the catheter 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 and can also be employed as an
injection site for fluids and medications. Blood samples can also be
obtained through this port.
As mentioned previously, it is advantageous to provide a second port 54
which is located between the series of spaced electrodes 70. The lumen 58
communicating with port 54 can terminate at approximately the 15 cm mark
as measured from the distal end locating the port between the eighth and
ninth electrodes 70. The port 54 can be used for measuring right
ventricular pressures as well as 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 beginning 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 distal tip of
the catheter, that is proximally from the proximal-most electrode. The
stylet can be made of stainless steel which is encapsulated in nylon.
This catheter can include four lumens, namely, a proximal lumen which
terminates 30 cm from the distal end of the 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 balloon; and a distal lumen
which terminates at the tip of the catheter, for monitoring blood
pressures and drawing blood samples.
With reference now to FIG. 15, the catheter A can, if 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,
accordingly, 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 inflating 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 exists, i.e., the inflated balloon lodges in a
branch of the pulmonary artery 108.
When correctly located, the proximal electrode 70P is located adjacent the
tricuspid valve 102 and the 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.
One advantage of the pentamerous lumen embodiment of the invention
illustrated in FIG. 1, is that the port 54 can be used to inject
medications directly into the cardiovascular system even when blood
pressure measurements are being taken through the ports 50 and 56. Also,
the port 54 will be positioned in the right ventricle (as shown in FIG.
15) which is advantageous for obtaining a good mixing of the medication
with the blood.
On the other hand, the port 56 can also be used to inject medication. This
port, since it will be positioned in the right atrium (see FIG. 15) will
also assure a good mixing of medication with the blood.
Turning now to FIG. 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 distribution 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 FIG. 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 from the gain select 120 are fed to a four channel 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 ("A to D") interface 132. In
this fashion, a digital signal representative of the analog values
obtained from the multi-catheter electrode A is obtained for use in the
microcomputer 130 which, in the preferred embodiment, is digital. The
microcomputer 130 will be described more fully in conjunction with FIG.
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 screen 136 which is suitably comprised of a
conventional cathode ray tube ("CRT") display. The microcomputer 130 is
also shown as including a contiguous CRT monitor 138, a data entry device
such as key board 140, and a mass storage medium 142 which is illustrated
as a pair of disk drives 142a and 142b. The mass storage medium 142 is
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, provides
a means for co | | |
