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Claims  |
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What is claimed is:
1. A method for the noninvasive measurement of cardiac output of a
mammalian patient on a real time, beat-by-beat basis as a combined
function of the cross-sectional area of the ascending aorta and the
systolic velocity of blood flow therethrough, comprising the steps of:
a. pulsedly insonifying the ascending aorta of said patient with
repetitive, intermittent ultrasonic energy propagating along a line
generally transverse with respect to the axis of said ascending aorta to
define a first insonification zone;
b. receiving pulses of ultrasonic energy reflected from anatomical
structure within said first insonification zone, including energy
reflected from the anterior and posterior walls of said ascending aorta
characteristic of the separation thereof along the transverse line of
propagation;
c. discriminating said pulses of received ultrasonic energy to detect the
transverse dimension of said ascending aorta between said anterior and
posterior walls thereof;
d. developing an aortic diameter signal proportional to and indicative of
said transverse dimension;
e. computing the cross-sectional area of said ascending aorta in the plane
of said transverse line of propagation of pulsed energy;
f. continuously insonifying said ascending aorta with uninterrupted
ultrasonic energy propagating along a line generally axial with respect to
the axis of said ascending aorta to define a second insonification zone;
g. receiving Doppler-shifted ultrasonic energy reflected from pulsatile
blood flow through said ascending aorta, frequency-shifted from said
uninterrupted ultrasonic energy by values characteristic of systolic
velocity of said blood flow;
h. developing a systolic velocity energy signal proportional to and
indicative of said systolic velocity;
i. subjecting said systolic velocity energy signal to frequency spectrum
analysis at a predetermined signal sampling rate to yield a velocity
component profile signal;
j. integrating said velocity component profile signal over time for each
period of said pulsatile flow to calculate a systolic velocity integral;
k. computing systolic volume as a combined function of said cross-sectional
area and said systolic velocity integral;
l. computing cardiac output as the sum of said systolic volumes for n
periods and dividing the sum by the time duration thereof.
2. The method of claim 1, wherein said step of subjecting said systolic
velocity energy signal to frequency spectrum analysis includes the steps
of:
a. establishing a plurality of signal sampling rates;
b. establishing a plurality of statistically anticipated systolic velocity
ranges for pulsatile blood flow;
c. selecting high and low threshold values for said ranges;
d. monitoring systolic velocity to determine its value within a given one
of said ranges relative to said threshold values; and,
e. adjusting said signal sampling rate to a predetermined one of said
plurality corresponding to the value of said systolic velocity within the
high and low threshold values for said predetermined range.
3. The method of claim 2, further comprising the step of providing an
operator-interactive visual display for presenting a visual sequence of
procedural operator options, including the step of measuring said aortic
diameter by:
a. locating a pulse-echo ultrasonic transducer probe to establish said
first insonification zone through said patient's cardiac window;
b. presenting a scaled visual display of said received ultrasonic energy
indicative of the anatomical structure within said insonification zone
including said anterior and posterior walls of said ascending aorta;
c. measuring the scaled dimension between said walls to develop said
transverse aortic signal; and
d. delivering said transverse aortic signal to processor means for
computing said cross-sectional area in accordance with an adaptive
algorithm stored therein.
4. The method of claim 3, further comprising the step of manipulating said
probe to minimize the scaled distance between said walls and returns from
structure other than said walls appearing on said visual display.
5. The method of claim 4, wherein said measuring step includes:
a. visually discriminating the returns corresponding respectively to said
anterior and posterior walls for the correct cross section of said aorta;
b. positioning a first moveable visual marker over said return for said
anterior wall;
c. positioning a second moveable visual marker over said return for said
posterior wall; and,
d. measuring the scaled distance between said first and second markers.
6. The method of claim 5, wherein said display is a cathode ray tube
display and said presenting step includes:
a. amplifying received pulse-echo signals indicative of returned ultrasonic
energy from said first insonification zone;
b. selectively attenuating said pulse-echo signals inversely proportional
to the propagation distance between said probe and the structure within
said first insonification zone responsible for a given return to spatially
normalize said pulse-echo signals;
c. digitizing the normalized pulse-echo signals to develop digital raster
scan signals; and,
d. controlling raster scan of said cathode ray tube with said digital
raster scan signals to present said visual display.
7. The method of claim 6, wherein said display includes a touch-sensitive
overlay for operator interaction, whereby said sequence of procedural
operator options are elected upon a manual touch of active field areas of
said overlay.
8. The method of claim 3, further comprising the steps of providing a
continuous wave transducer probe having a transmitter crystal for
developing said uninterrupted ultrasonic energy at a transmitter frequency
and a receiver crystal for detecting received, Doppler-shifted energy from
said second insonification zone having a frequency shift proportional to
said systolic velocity, and converting said received energy to a Doppler
signal, wherein said step of developing said systolic velocity energy
signal comprises the steps of:
a. amplifying said Doppler signal;
b. mixing said Doppler signal with at least one reference signal having a
reference frequency selected to develop an audio frequency Doppler signal;
and,
c. digitizing said audio frequency Doppler signal and applying same to said
frequency spectrum analysis.
9. The method of claim 8, wherein said mixing step includes the steps of:
a. selectively attenuating said Doppler signal to develop an amplitude
normalized RF Doppler signal;
b. mixing said normalized RF Doppler signal with a first reference
frequency signal having a frequency different from said transmitter
frequency by a frequency f to develop an intermediate frequency Doppler
signal;
c. selectively attenuating said intermediate frequency Doppler signal to
develop an amplitude normalized intermediate frequency Doppler signal;
and,
d. mixing said normalized intermediate frequency Doppler signal with a
second reference frequency signal having a frequency f to develop an audio
frequency Doppler signal having a frequency directly proportional to
systolic velocity, constituting said systolic velocity energy signal.
10. The method of claim 9, wherein said step of subjecting said systolic
velocity energy signal to frequency spectrum analysis includes:
a. sampling said systolic velocity energy signal at a first of said signal
sampling rates to develop a sampled systolic velocity energy signal;
b. digitizing said sampled systolic velocity energy signal;
c. subjecting the digitized systolic velocity energy signals to fast
Fourier transformation; and,
d. selecting the peak component frequency in each sampling period to
develop said velocity component profile signal.
11. The method of claim 10, wherein said step of establishing a plurality
of signal sampling rates includes establishing a first range for systolic
velocities up to about 82 cm/s, a second range for systolic velocities up
to about 165 cm/s and a third range for systolic velocities up to about
330 cm/sec.; and further wherein said step of adjusting said signal
sampling rate comprises:
a. initially sampling at a first rate corresponding to said first range;
b. monitoring said velocity component profile signal for a predetermined
number of cardiac cycles to determine systolic velocity;
c. comparing systolic velocity to a high threshold value for said first
range;
d. adjusting said sampling rate to a second rate corresponding to said
second range upon the occurrence of systolic velocities in excess of the
high threshold value for said first range;
e. comparing systolic velocity ot a high and low threshold values for said
second range;
f. adjusting said sampling rate to said first rate upon the occurrence of
systolic velocities lower than the low threshold value for said second
range or to said third rate upon the occurrence of systolic velocities in
excess of said high threshold value for said second range;
g. comparing systolic velocity to a low threshold value for said third
range; and,
h. adjusting said sampling rate to said second rate upon the occurrence of
systolic velocities lower than said low threshold value for said third
range.
12. The method of claim 11, wherein said velocity component profile signal
is applied to processor means for computing the time integral of each of
said signals over the corresponding cardiac period to yield said systolic
velocity integral and for computing cardiac stroke volume as the product
of said systolic velocity integral and said aortic cross-sectional area.
13. The method of claim 12, further comprising the step of visually
displaying said systolic velocity integral on a cathode ray tube display.
14. The method of claim 13, further comprising the steps of manipulating
said continuous wave transducer probe to maximize the value of the
displayed systolic velocity integral.
15. The method of claim 14, wherein said cardiac output is calculated as
the average of the sum of discrete stroke volume values based on the sum
of cardiac cycle periods.
16. The method of claim 15, further comprising the steps of calculating
cardiac index as the ratio of cardiac output to body surface area of said
patient and stroke index as the ratio of stroke volume to said body
surface area.
17. A system for the noninvasive measurement of cardiac output of a
mammalian patient on a real time, beat-by-beat basis as a combined
function of the cross-sectional area of the ascending aorta and the
systolic velocity of blood flow therethrough, comprising:
a. pulse-echo transducer means for developing repetitive, intermittent
bursts of ultrasonic energy and applying same to said patient to define a
first insonification zone enveloping the region of the ascending aorta of
said patient and for detecting energy reflected from the anatomical
structure within said first insonification zone, including the anterior
and posterior walls of said ascending aorta;
b. pulse transmitter means for exciting said pulse-echo transducer to
develop said bursts of energy;
c. pulse receiver means for developing an echo signal proportional to and
indicative of detected energy;
d. operator-interactive visual display means for presenting control and
display capabilities, including a graphic, scaled display of echo signals
representative of the spatial conformation of said anatomical structure
and signal strength representative of pulsatile blood flow therethrough;
e. measurement means in operative association with said visual display
means for determining the spatial separation between anterior and
posterior walls represented on said scaled display, to develop an aortic
diameter signal,
f. area processor means receiving said aortic diameter signal for
determining the cross-sectional area of said ascending aorta;
g. continuous wave transducer means for developing uninterrupted ultrasonic
energy and applying same to define a second insonification zone within
said region of said ascending aorta and for detecting Doppler-shifted
energy reflected from pulsatile blood flow therethrough;
h. continuous wave transmitter means for exciting said continuous wave
transducer to develop said uninterrupted ultrasonic energy at a continuous
wave transmitter frequency;
i. continuous wave receiver means for developing a Doppler signal having a
frequency shift from said continuous wave transmitter frequency
proportional to and indicative of the systolic velocity of said pulsatile
blood flow;
j. converter means for processing said Doppler signal to an audio frequency
systolic velocity energy signal;
k. spectrum analyzer means receiving said systolic velocity energy signal
for developing a frequency domain velocity component profile signal
characteristic of the velocity profile of systolic flow over an observed
cardiac cycle;
l. velocity processor means receiving said velocity component profile
signal for computing the time integral thereof over the period of said
caridac cycle, in accordance with an adaptive algorithm stored therein, to
yield a systolic velocity integral signal and a stroke volume signal as a
function of said cross-sectional area and said stroke volume; and,
m. cardiac output processor means receiving said stroke volume signal and a
heart rate signal for determining cardiac output as the time-averaged sum
of a plurality of cyclic stroke volumes.
18. The system of claim 17, wherein said pulse receiver means comprises:
a. echo amplifier means for developing an amplitude-conditioned radio
frequency echo signal;
b. controlled attenuator means for amplitude alteration of said
amplitude-conditioned radio frequency echo signal inversely proportional
to the propagation distance between said pulse-echo transducer means and
the anatomical structure within said first insonification zone responsible
for a given return to develop a spatially normalized echo signal;
c. detector means for rectifying and filtering said spatially normalized
echo signal to yield an envelope signal proportional to and indicative of
said detected energy; and,
d. analog-to-digital converter means receiving said envelope signal for
developing a digital echo signal output.
19. The system of claim 18, wherein said visual display is a cathode ray
tube display; said system further comprising raster scan driving and
storage means receiving said digital echo signal for visual presentation
of said detected energy on a scaled video display representing said
anatomical structure.
20. The system of claim 19, wherein said measurement means is comprised of
moveable markers appearing on said display for operator registration with
the video display at returns representative of said anterior and posterior
walls respectively.
21. The system of claim 20, further comprising touch-sensitive overlay
means in operative association with said visual display, wherein said
markers are moveable in response to a manual touch of an active field area
on said display and said aortic diameter signal is developed as a signal
proportional to the distance between said markers when registered with
said returns.
22. The system of claim 21, wherein said continuous wave receiver means
includes:
a. Doppler signal amplifier means for developing an amplitude-conditioned
radio frequency Doppler signal; and,
b. mixer means for frequency translation of said Doppler signal to yield a
frequency normalized Doppler signal.
23. The system of claim 22, wherein said receiver means includes first and
second mixer stages preceded respectively by first and second controlled
attenuator means; and further wherein said first mixer stage receives said
radio frequency Doppler signal and a beat frequency reference signal
having a frequency different from said transmitter frequency by a
frequency f to yield an intermediate frequency Doppler signal and said
second mixer stage receives said intermediate frequency Doppler signal and
a beat frequency reference signal having a frequency f to yield an audio
frequency Doppler signal having a frequency profile directly proportional
to said systolic velocity. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates, generally, to methods and means for
measuring the cardiac output of a mammalian patient, more especially to
noninvasive methods and means for measuring the cardiac output of a human
patient, and most particularly to a dual modality insonification technique
for ascertaining the cross-sectional area of the patient's ascending aorta
and the systolic velocity profile of blood flow therethrough allowing for
a determination of cardiac output, cardiac index, stroke volume and stroke
index, amongst other physiological parameters.
SUMMARY OF THE INVENTION
The present invention advantageously provides a simple yet highly efficient
method and means for carrying out the measurement of cardiac output of a
mammalian patient, and particularly a human patient on a real time,
beat-by-beat basis. The method and means of conducting such measurement in
accordance with the present invention are especially desirable for
facilitating direct operator interaction with the apparatus over the
course of the measurement protocol via an interactive visual display which
instructs the operator at each step of the sequence and responds to an
election of operator options with certain failsafe features guarding
against the entry of invalid data and prompting the entry of maximized
physiological characteristics of the patient under examination. Still a
further advantage of the present invention is the selective, specific use
of dual modality insonification with an eye toward employing an ultrasound
mode best suited for the measurement task at hand. A related benefit is
the facility with which the operator may interact with the system to
achieve reliable, repetitive results without requiring extensive training.
As respects the system itself, the same provides the benefits of
microprocessor control for fast data computation without the need to
resort to elaborate hardware or software.
The foregoing, and other, advantages and benefits are realized in a method
wherein the diameter of a patient's ascending aorta is provided as an
input to the system, either as a known parameter or as measured via A-mode
(pulsed) insonification techniques, and the cross-sectional area computed
based on a model of the aorta as a right circular cylinder (hence, area as
that of a circle); followed by a continuous wave insonification procedure
to measure systolic velocity of blood flow through the ascending aorta
using Doppler techniques. The variable parameters of area and flow rate
provide the basis for determining cardiac output; rationalized to cardiac
index as the ratio of cardiac output to the patient's body surface area.
The system for implementing that method is comprised of circuitry for
generating the pulsed ultrasonic energy, detecting reflected returns and
processing same, cooperating with circuitry for producing continuous wave
ultrasonic energy and detecting Doppler shifted returns for processing via
spectrum analysis; both integrated through a visual or graphic display
having a touch-sensitive overlay for direct operator interaction with the
system.
A preferred method for the noninvasive measurement of cardiac output is
comprised of the steps of pulsedly insonifying the ascending aorta of the
patient with repetitive, intermittent ultrasonic energy propagating along
a line generally transverse with respect to the axis of the ascending
aorta from a position through the cardiac window of the patient to define
a first insonification zone enveloping the aortic region; receiving pulses
of ultrasonic energy reflected from the anatomical structure within the
first insonification zone, including energy reflected from the anterior
and posterior walls of the ascending aorta characteristic of the
separation thereof along the transverse line of propagation therethrough;
discriminating the pulses of received ultrasonic energy to detect the
transverse dimension of the ascending aorta between the anterior and
posterior walls; developing an aortic diameter signal proportional to and
indicative of the transverse separation between walls; computing the
cross-sectional area of the ascending aorta in the plane of the transverse
line of propagation of pulsed energy, most preferably modeling the aorta
throughout the procedure as a right circular cylinder to facilitate the
ease of computation--here the area of a circle; thence continuously
insonifying the ascending aorta with uninterrupted ultrasonic energy
propagating along a line generally axial with respect thereto from a
position within the patient's suprasternal notch to define a second
insonification zone within the aortic region; receiving Doppler-shifted
ultrasonic energy reflected from pulsatile blood flow through the
ascending aorta, and principally the red blood cells thereof, frequency
shifted from the frequency of the transmitted ultrasonic energy by values
characteristic of systolic flow velocity; developing a systolic velocity
energy signal as a time domain function proportional to and indicative of
the systolic velocity of blood flow; subjecting that systolic velocity
energy signal to frequency spectrum analysis, and most preferably to fast
Fourier transform analysis, at a predetermined signal sampling rate to
develop a velocity component profile signal as a frequency domain function
characteristic of the composite of peak frequency components in the
sampled signal; integrating the velocity component profile signal over
time for each period of pulsatile flow to calculate a systolic velocity
integral; computing stroke volume as a combined function of the
cross-sectional area of the aorta and the systolic velocity integral for
each of n periods; and computing cardiac output as the time-averaged sum
of stroke volumes for the n periods. Each stage of the overall protocol is
accompanied by a sequence of instructional steps to be followed by the
operator, appearing on a cathode ray tube display (CRT) having associated
therewith a touch-sensitive overlay facilitating direct operator
interaction with the system. The combination of the CRT display and the
touch-sensitive overlay provides the operator with a graphic indication of
specific optional steps throughout the measurement sequence accompanied by
active field areas allowing a given one or more options to be elected
simply upon a manual touch of the display. Data is introduced to the
system via the display upon a controlled presentation of active areas in
the form of an alphanumeric keyboard to facilitate the use of the system
by a wide range of individuals having equally diverse backgrounds. Known
physiological characteristics of the patient under examination, for
example aortic diameter and/or body surface area, may simply be introduced
to the system. Otherwise, the system will accept raw data, for example
body height and weight to compute the desired characteristic, i.e., body
surface area; or the system may be keyed to present a visual display
facilitating the measurement of the desired characteristic, e.g., aortic
diameter. Within operational limits, the system will insist upon the entry
of required data, will limit the entry of certain data to values within
statistically anticipated ranges, and will prompt the operator to maximize
the accuracy of technique in measuring unknown parameters.
Further along these summary lines of system control for maximized
efficiency and reliability, the process of the present invention most
preferably includes a self-contained procedure for enhanced data
processing, particularly in respect of the frequency spectrum analysis of
Doppler-shifted data. This procedure is comprised of the steps of
establishing a plurality of signal sampling rates based upon corresponding
ranges for statistically anticipated systolic velocities for the patient
under examination; selecting high and low threshold values for these
separate velocity ranges; monitoring systolic velocity to determine its
value within a given one of the ranges as measured with reference to the
selected threshold values; and, adjusting the signal sampling rate for
data analysis to a predetermined one of the plurality of sampling rates
corresponding to the systolic velocity within the threshold values for
that range. For example, in the most preferred embodiment of the present
invention, three anticipated velocity ranges are established--viz., 0-82
cm/s, 0-165 cm/s, and 0-330 cm/s--with correlative sampling rates for the
spectrum analysis. The system initially processes data at the first
sampling rate while monitoring the velocity signal. Upon the occurrence of
systolic velocities in excess of the high threshold value for the first
range, the system automatically adjusts the sampling rate to the second
rate for further processing. Monitoring the velocities continues, now with
reference to a high and low threshold value within the second range.
Systolic velocities lower than the low threshold causes a downward
adjustment to the first sampling rate, while velocities in excess of the
high threshold for the second range adjusts the sampling rate to the third
range. Should the third rate be selected, and subsequent monitoring
reveals systolic velocities lower than a low threshold for that range, an
adjustment in the sampling rate to the second rate is made. In this
manner, processing of data is correlated with the appropriate velocity
range, enhancing processing capabilities while simplifying system hardware
and firmware.
In those situations where the operator has elected to measure aortic
diameter, the visual display presents a graphic image showing returns
detected upon reflection of pulsed ultrasonic energy from anatomical
structure within the insonification zone (including returns from the
anterior and posterior walls thereof), scaled to the propagation distance
of the transmitted energy. The graphic display assists in proper
positioning and manipulation of the pulse transducer to insure proper
placement of the probe to direct the pulsed energy through the patient's
cardiac window at an orientation generally transverse with respect to the
ascending aorta. This is achieved by employing the highly characteristic
returns from the aortic region, and particularly the leaflets of the
aortic valve which provide a distinctive echo pattern observable by the
operator on the visual display. Manipulation of the probe results in a
corresponding alteration in the display to optimize the appearance of the
signals and allow improved operator confidence in the proper position of
the pulse transducer probe. Once that probe has properly been positioned,
the operator may freeze the graphic image and, by way of moveable cursors
operated through the touch-sensitive overlay, make a direct, scaled
measurement of the aortic diameter. In this mode, the pulse-echo portion
of the system serves principally to detect and present echo returns
through generally conventional, digital raster scan circuitry for the CRT
display while the overlay and coordinated control means serve to develop
the aortic diameter signal as the scaled separation between moveable
cursors manipulated by the operator.
In a generally like vein, the cardiac output data processed as aforesaid is
presented on the visual display during the corresponding continuous wave
measurement of systolic velocity. The display thereby provides the
operator with direct visual indication of cardiac output and its changing
rate from cardiac cycle to cycle; further providing a message to the
operator when the signal level is too low, prompting manipulation for more
accurate positioning of the transducer probe. In this continuous wave
mode, the operator is also supplied with audio information indicative of
systolic velocity; developed by mixing the Doppler-shift signal downward,
preferably in two mixing stages, to yield an audio signal where frequency
is directly proportional to velocity. Thus the operator may rely upon
aural and/or visual means of perception during the diagnostic procedure.
The foregoing and other advantages of the present invention will become
more apparent, and a fuller appreciation of its construction and methods
of operation will be gained, upon an examination of the following detailed
description of preferred embodiments, taken in conjunction with the
figures of drawing, wherein:
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view illustrating an exemplary cardiac output
monitoring system embodying features of the present invention, here
mounted on casters so as to enhance the mobility of the system;
FIG. 2 is a perspective view here illustrating the cardiac output
monitoring system shown in FIG. 1 in use, and wherein a suitable medical
practitioner (for example, a doctor, nurse, technician or the like) has
positioned a pulse-type ultrasonic transducer at the cardiac window
between the second and fourth intercostal spaces of a patient's chest and
with the medical practitioner's right index finger positioned to "freeze"
the graphic image appearing on the screen of the cardiac output monitoring
system, which image is here representative of the internal diameter of the
patient's ascending aorta;
FIG. 3 is a perspective view similar to FIG. 2, but here illustrating the
patient, medical practitioner and apparatus at that stage in the process
wherein the medical practitioner has positioned a continuous wave
ultrasonic transducer within the patient's suprasternal notch with the
focused energy beam being directed substantially axially along the
patient's ascending aorta, and with the medical practitioner's right index
finger being positioned to initiate a cardiac output measuring cycle;
FIGS. 4a and 4b, when disposed in adjacent top-to-bottom relation, comprise
a block-and-line drawing here illustrating in time sequence the various
graphic images that are presented sequentially on the screen of the
cathode ray tube used with the present cardiac output monitoring system
and, illustrating further, the process that would be employed by the
medical practitioner to progressively step through a cardiac output
monitoring operation that might vary from patient to patient dependent
upon what data is known for each patient and what data must be calculated;
FIGS. 5 through and including 24 are representative illustrations depicting
the successive images that might be presented on the face of the cathode
ray tube as the medical practitioner progresses through a cardiac output
monitoring operation; and, more specifically:
FIG. 5 is a view of the master image, herein referred to as the "Menu",
which appears on the screen of the cardiac output monitoring system when
the system is first powered up;
FIG. 6 is a view illustrative of the image that appears on the face of the
CRT screen when the operator touches the appropriate active area of the
screen shown in FIG. 5 so as to enable resetting of date and/or real time
information and, illustrating also, the "keyboard" which appears on the
face of the CRT screen for enabling resetting of date and/or time;
FIG. 7 is a view of the face of the CRT screen illustrating the Menu which
reappears with corrected date and/or time information once the medical
practitioner has entered corrected date and/or real time data by touching
appropriate areas of the CRT screen shown in FIG. 6 and has touched the
active screen area in FIG. 6 labelled "Menu";
FIG. 8 is a drawing illustrating the graphic image that appears on the face
of the CRT screen when the operator activates the Menu shown in FIG. 7 for
the purpose of entering patient data with the first item of patient data
to be entered being an appropriate identification number (hrein "ID
number") and with the drawing here illustrating the CRT screen image
following entry of the first four digits of the patient's ID number;
FIG. 9 is a drawing illustrating the next successive graphic image
appearing on the face of the CRT screen following entry of the patient's
ID number, with such graphic image presenting the medical practitioner
with an option to enter either a known value for the patient's body
surface area or to calculate such value in the event that it is unknown;
FIG. 10 is a view of the graphic image appearing on the CRT screen when the
medical practitioner selects the option presented in FIG. 9 for entry of a
known value of body surface area;
FIG. 11 is a drawing illustrating the graphic image that appears on the
face of the CRT screen and which enables the medical practitioner to
calculate the patient's body surface area in the event that the value
thereof is initially unknown and that the medical practitioner had
selected that option by touching the appropriate active area of the CRT
screen shown in FIG. 9;
FIG. 12 is a view illustrating the face of the CRT screen and the image
presented thereon following entry of the patient's body surface area
either from inputting known data (FIG. 10) or from calculating such value
by inputting data representative of the patient's height and weight (FIG.
11), and with FIG. 12 showing the two optional paths that can be selected
by the medical practitioner for entering the patient's aortic
diameter--i.e., either from known data in the patient's records or through
an ultrasonic computational mode;
FIG. 13 is the graphic image which is next presented on the face of the CRT
screen in those instances where the medical practitioner touches the
active screen area in FIG. 12 by which the option is selected for entry of
known values of the patient's aortic diameter;
FIG. 14 is illustrative of the graphic image that appears on the face of
the CRT screen in those instances where the medical practioner does not
know the patient's aortic diameter and, consequently, activitates the
ultrasonic computational mode by touching the appropriate area of the
screen depicted in FIG. 12;
FIG. 15 is a graphic image that might appear on the face of the CRT screen
had the medical practitioner elected to shift from the "Normal Scale"
shown in FIG. 14 to the "Twice Scale" shown in FIG. 15 by touching the
face of the screen in FIG. 14 in the rectangular area labeled "Normal
Scale" and, with the image shown in FIG. 15 having been frozen by the
medical practitioner and with the left and right cursors having been moved
so as to provide an accurate measurement of the inside diameter of the
patient's aorta;
FIG. 16 is a view of the graphic image next appearing on the face of the
CRT screen following entry of either known data (FIG. 13) or computed data
as measured in FIG. 15 (or in FIG. 14 had the cursors been readjusted and
the "Enter" data area touched), and illustrating particularly the option
granted to the medical practitioner either to retain the existing data or
to correct such data;
FIG. 17 is a view of the graphic image which would next appear on the face
of the CRT screen in those cases where the medical practitioner wished to
change all or certain of the data previously entered for a given patient
and which would result by touching the area labelled "No" on the screen
depicted in FIG. 16;
FIG. 18 is a view of the real time Menu that reappears on the face of the
CRT screen in those cases where the medical practitioner touches the area
labelled "Yes" on the screen shown in FIG. 16,
FIG. 19 is a view of the graphic image that first appears on the face of
the CRT screen following selection of the "Measure CO (cardiac output)"
function by touching the appropriate area of the screen depicted in FIG.
18;
FIG. 20 is a view similar to FIG. 19, but here illustrating the image that
appears on the face of the CRT screen when the ultrasonic transducer is
properly aimed but before accumulation of data representative of at least
twelve consecutive beats containing acceptable data values, it being
understood that the horizontal lines representative of successive
heartbeats are here moving across the face of the screen from right to
left with the latest heartbeat detected being at the right hand side of
the image;
FIG. 21 is representative of the graphic image that appears on the face of
the CRT screen at that point in time when at least twelve consecutive
heartbeats have been detected having data within the acceptable range;
FIG. 22 is a portrayal of the graphic image that appears on the face of the
CRT screen when the cardiac output monitoring apparatus of the present
invention has detected twenty-four consecutive heartbeats each presenting
data within acceptable limits;
FIG. 23 is a view similar to FIG. 22, but here illustrating the image
appearing on the face of the CRT screen when the medical practitioner
determines that optimum data values are being presented and enters those
values by touching the active screen area labelled "Measure C0";
FIG. 24 is a view similar to FIG. 23, but here illustrating the CRT screen
image that appears whenever the medical practitioner is not properly
aiming the ultrasonic transducer axially along the ascending aorta--for
example, after the cardiac output measurement has been completed and the
transducer has been removed from the patient's suprasternal notch;
FIGS. 25a and 25b, when disposed in adjacent side-by-side relation,
comprise a block diagram illustrating the various electronic components
that might be employed in a cardiac output monitoring system made in
accordance with the present invention;
FIG. 26 is a simplified block diagram here illustrative of the echo-ranging
signal path associated with a pulse-type ultrasonic transducer utilized to
measure a patient's aortic diameter;
FIG. 27 is a diagrammatic frontal elevational view illustrating generally a
human heart and certain of the major arterial vessels, and particularly
illustrating the relative positions of the patient's suprasternal notch
and ascending aorta with a continuous wave ultrasonic transducer
positioned in the suprasternal notch and directing a focused ultrasonic
beam substantially axially along the ascending aorta;
FIG. 28 is a highly diagrammatic illustration of the various heart
structures as detected by a pulse-type ultrasonic transducer which is
directed through the cardiac window on the patient's chest and looking at
the aortic root;
FIG. 29 is a highly diagrammatic side view illustrating both proper and
improper positioning of a pulse-type transducer with respect to the
patient's aorta;
FIG. 30A is a graphic view of the image which might appear on the face of
the CRT screen in those instances where a pulse-type ultrasonic transducer
is improperly positioned as shown in FIG. 29 so as to intercept the valve
leaflets of the heart in the Sinus of Valsalva;
FIG. 30B is a view similar to that shown in FIG. 30A, but here illustrating
the image that appears on the face of the CRT screen when the pulse-type
transducer is properly positioned as shown in FIG. 29;
FIG. 31 is a highly diagrammatic top or plan view illustrating a patient's
aorta looking axially downwardly along the aorta with a pulse-type
transducer positioned properly in the solid line position and improperly
in the two phantom line positions;
FIG. 32A is a view illustrating the graphic presentation that might appear
on the face of a CRT screen in those instances where the pulse-type
transducer is improperly positioned in FIG. 31 and the ultrasonic beam is
too medial with respect to the axis of the ascending aorta;
FIG. 32B is a view similar to that shown in FIG. 32A, but here illustrating
the image that might appear on the CRT screen when the pulse-type
transducer is properly positioned in the solid line position shown in FIG.
31 with the beam cutting substantially diametrically through the ascending
aorta;
FIG. 32C is a view similar to those shown in FIG. 32A and 32B, but here
illustrating the image that might appear on the face of a CRT screen when
the pulse-type transducer is improperly positioned as shown in FIG. 31
with the energy beam being directed too lateral with respect to the
diameter of the aorta;
FIG. 33 is a simplified block diagram herein illustrating the continuous
wave Doppler signal path resulting from echo signals reflected from the
red blood cells moving vertically upward through the patient's ascending
aorta; and,
FIG. 34 is a highly diagrammatic side elevational view of the upper chest
and lower neck portion of a patient in a supine position and illustrating
particularly proper placement of the continuous wave ultrasonic transducer
within the patient's suprasternal notch with a focused ultrasonic beam
being directed substantially axially along the patient's ascending aorta
which is here illustrated diagrammatically.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates, generally, to methods and means for
measuring the cardiac output of a mammalian patient, more especially to
noninvasive methods and means for measuring the cardiac output of a human
patient, and most particularly to a dual modality insonification technique
for ascertaining the cross-sectional area of the patient's ascending aorta
and the systolic velocity profile of blood flow therethrough allowing for
a calculation of cardiac output, cardiac index, stroke volume and stroke
index, amongst other physiological parameters, on a real time,
beat-by-beat basis. Accordingly, the present invention will now be
described with reference to certain preferred embodiments within the
aforementioned contexts; albeit, those skilled in the art will appreciate
that such a description is meant to be exemplary only and should not be
deemed limitative.
The present invention employs two different ultrasonic measurement modes to
gather data used for determining stroke volume and cardiac output of the
patient. The first is an echo-ranging mode to measure the diameter of the
aorta; which involves placing an echo-transducer over the heart, obtaining
a so-called "A-mode" image of the aorta on a visual display, and measuring
the aortic diameter from the image. That measurement is then employed by
an adaptive algorithm to compute aortic cross-sectional area, modeling the
aortic structure as a right circular cylinder throughout the procedure for
ease of computation with minimal sacrifice in accuracy. The second mode is
a continuous wave mode to insonify the ascending aorta and detect
Doppler-shift caused by moving red blood cells within it. This measurement
is made by placing a Doppler ultrasound transducer in the suprasternal
notch of the patient and aiming the transducer toward the ascending aorta.
The returning signals are processed into Doppler-shift signals that are
analyzed and converted into discrete frequency components by digital fast
Fourier transform ("FFT"). Through Doppler computation, the Doppler-shift
frequencies are converted to velocities, in turn employed to calculate a
systolic velocity integral ("SVI"). Combining the SVI with aortic
cross-sectional area | | |
