U.S. patent application number 10/077179 was filed with the patent office on 2003-08-14 for non-invasive determination of left-ventricular pressure.
Invention is credited to McIntyre, Kevin M..
Application Number | 20030153837 10/077179 |
Document ID | / |
Family ID | 27660269 |
Filed Date | 2003-08-14 |
United States Patent
Application |
20030153837 |
Kind Code |
A1 |
McIntyre, Kevin M. |
August 14, 2003 |
NON-INVASIVE DETERMINATION OF LEFT-VENTRICULAR PRESSURE
Abstract
A left-ventricular pressure waveform is obtained non-invasively
by obtaining pressure waveforms from first and second pressure
measurements and selecting a segment from each of the first and
second pressure waveforms. Each segment is associated with a
different interval of a cardiac cycle. The segments are then
time-shifted by an amount indicative of a relative time of
occurrence of each of the first and second segments.
Inventors: |
McIntyre, Kevin M.; (Boston,
MA) |
Correspondence
Address: |
FISH & RICHARDSON PC
225 FRANKLIN ST
BOSTON
MA
02110
US
|
Family ID: |
27660269 |
Appl. No.: |
10/077179 |
Filed: |
February 14, 2002 |
Current U.S.
Class: |
600/485 |
Current CPC
Class: |
A61B 7/04 20130101; A61B
5/02125 20130101; A61B 5/021 20130101; A61B 5/352 20210101 |
Class at
Publication: |
600/485 |
International
Class: |
A61B 005/02 |
Claims
1. A method for non-invasively constructing a left-ventricular
pressure waveform, the method comprising: obtaining a first
pressure waveform from a first non-invasive pressure measurement;
obtaining a second pressure waveform from a second non-invasive
pressure measurement; selecting a first segment from said first
pressure waveform, said first segment being associated with a first
interval of a cardiac cycle; selecting a second segment from said
second waveform, said second segment being associated with a second
interval of said cardiac cycle; and time-shifting said first and
second segments relative to each other by an amount indicative of a
relative time of occurrence of each of said first and second
segments.
2. The method of claim 1, wherein obtaining a first pressure
waveform comprises obtaining a signal indicative of a left-atrial
pressure.
3. The method of claim 2 wherein obtaining a signal indicative of a
left-atrial pressure waveform comprises obtaining a shape of said
signal from an apex cardiogram and adjusting an amplitude of said
signal on the basis of an early diastolic pressure.
4. The method of claim 1, wherein obtaining a second pressure
waveform comprises obtaining a signal indicative of an arterial
pressure.
5. The method of claim 1, wherein selecting a first segment
comprises determining an occurrence of an event indicative of said
first interval of said cardiac cycle.
6. The method of claim 5, wherein determining an occurrence of an
event comprises detecting a signal indicative of activity of a
heart valve.
7. The method of claim 6, further comprising selecting said heart
valve from the group consisting of a mitral valve and an aortic
valve.
8. The method of claim 6 wherein detecting a signal indicative of
activity of a heart valve comprises detecting a signal indicative
of a transition between an open state of said heart valve and a
closed state of said heart valve.
9. The method of claim 6, wherein detecting a signal indicative of
activity of a heart valve comprises detecting an acoustic signature
indicative of valve activity.
10. The method of claim 6, wherein detecting a signal indicative of
activity of a heart valve comprises detecting signature indicative
of valve activity, said signature being selected from the group
consisting of an electrical signature and a mechanical
signature.
11. The method of claim 1, wherein time-shifting said first and
second segments relative to each other comprises connecting an end
point of said first segment to a start point of said second
segment.
12. The method of claim 11, wherein connecting an end point to a
start point comprises defining a line connecting said end point and
said start point.
13. A system for non-invasively constructing a left-ventricular
pressure waveform, said system comprising: a first amplitude sensor
for non-invasively obtaining a first pressure waveform; a second
amplitude sensor for non-invasively obtaining a second pressure
waveform; an event sensor for detecting a time of occurrence of an
event in a cardiac cycle; and a processor in communication with
said first and second amplitude sensors and with said event sensor,
said processor being configured to select a segment from each of
said first and second waveforms and to connect said segments on the
basis of said time of occurrence of said event.
14. The system of claim 13 wherein said first amplitude sensor
comprises an atrial pressure sensor.
15. The system of claim 14, wherein said atrial pressure sensor
comprises an apex cardiograph in communication with an
atrial-pressure acquisition-unit.
16. The system of claim 13 wherein said second amplitude sensor
comprises an arterial pressure sensor.
17. The system of claim 13 wherein said event detector is selected
from the group consisting of an electrocardiograph and a
phonocardiograph.
18. A method of non-invasively obtaining a left-ventricular
pressure waveform, said method comprising: selecting, from a first
signal, a first signal portion that corresponds to a first phase of
a cardiac cycle; selecting, from a second signal, a second signal
portion that corresponds to a second phase of said cardiac cycle;
determining a temporal relationship between said first and second
signal portions; and time-shifting said first and second signal
portions consistent with said temporal relationship.
19. A system for non-invasively generating a ventricular pressure
waveform, said system comprising: a non-invasive barograph for
obtaining first data and second data indicative of first and second
pressures within a ventricle, said first and second pressures being
temporally separated from each other; a non-invasive event detector
for obtaining third data indicative of an occurrence of an event in
the cardiac cycle; and a data processor configured to receive said
first, second and third data and to combine said first and second
data on the basis of said third data to construct therefrom, a
ventricular pressure waveform.
20. The system of claim 19, wherein said data processor comprises a
shifting process, said shifting process configured to temporally
shift said first data on the basis of said second data.
21. The system of claim 20, wherein said data processor further
comprises a calibration process, said calibration process
configured to assign corresponding pressures to said first and
second data.
22. The system of claim 19, wherein said non-invasive barograph
comprises an atrial barograph.
23. The system of claim 22, wherein said atrial barograph comprises
an apex cardiograph.
24. The system of claim 19, wherein said non-invasive barograph
comprises an arterial barograph.
25. The system of claim 19 wherein said non-invasive event detector
is selected from the group consisting of a phonocardiogram, a
venous pulse acquisition unit, and an apex cardiograph.
26. The system of claim 19, wherein said non-invasive event
detector comprises a venous pulse acquisition unit.
27. The system of claim 19, wherein said non-invasive event
detector comprises an apex cardiograph.
Description
FIELD OF INVENTION
[0001] This invention relates to medical diagnostic devices, and in
particular, to devices for measurement of pressure within the
heart.
BACKGROUND
[0002] The pressure within the left ventricle of the heart is an
important parameter in the treatment of heart disease. However, the
measurement of that pressure is hampered by the need to insert a
probe into the left ventricle. Such invasive measurements are
costly, time-consuming, and potentially dangerous to the patient.
As a result, despite its importance, the pressure within the left
ventricle is only rarely measured directly.
[0003] There exist systems for non-invasively measuring
left-ventricular pressure during limited portions of the cardiac
cycle. For example, during the ejection phase, and in the absence
of aortic valve disease, the left-ventricular pressure corresponds
to the arterial pressure. During that portion of the cardiac cycle
characterized by an open mitral valve, the left-ventricular
pressure is (to the extent that the mitral valve is normal)
virtually the same as the left-atrial pressure. This left-atrial
pressure is in turn related to PCWP (pulmonary capillary wedge
pressure), which can be measured non-invasively by using a device
and methods described in McIntyre, U.S. Pat. No. 5,291,895, the
contents of which are herein incorporated by reference.
SUMMARY
[0004] The invention provides software for extracting segments from
the outputs of two or more non-invasive diagnostic devices, each of
which provides data that is indicative of left-ventricular pressure
over at least a portion of the cardiac cycle. As used herein, data
indicative of left-ventricular pressure includes absolute and
relative pressure data, as well as data showing a contour of a
pressure waveform. The software of the invention then time-shifts
the extracted segments to inscribe a continuous curve indicative of
the left-ventricular pressure waveform.
[0005] In one practice of the invention, a left-ventricular
pressure waveform is assembled by obtaining a first pressure
waveform from a first non-invasive pressure measurement and a
second pressure waveform from a second non-invasive pressure
measurement. First and second segments are then selected from the
first and second waveforms respectively. These segments are
associated with first and second intervals of the cardiac cycle.
The first and second segments are then time-shifted relative to
each other by an amount indicative of a relative time of occurrence
of each of the first and second segments.
[0006] As used herein, "pressure measurement" refers to the
collection of data indicative of pressure, which, as defined
earlier, means absolute and relative pressure data, as well as data
showing or recording a contour of a pressure waveform.
[0007] The first pressure waveform can be a signal indicative of a
left-atrial pressure or one indicative of arterial pressure. When
the signal indicates left-atrial pressure, the method can include
obtaining a shape of the waveform from an apex cardiogram and
adjusting an amplitude of the waveform on the basis of a
non-invasively measured diastolic pressure.
[0008] Selecting a first segment can include determining an
occurrence of an event indicative of the first interval of the
cardiac cycle. A suitable choice of event is activity of a heart
valve, for example the mitral valve or the aortic valve. An easily
detectable event is, for example, the transition of either the
mitral valve or the aortic valve between an open state and a closed
state. Such events can be identified by detecting an acoustic
signature indicative of valve activity, by detecting an electrical
signature indicative of valve activity, or by detecting a
mechanical signature indicative of valve activity.
BRIEF DESCRIPTION OF THE FIGURES
[0009] FIG. 1 shows a system for practice of the invention;
[0010] FIG. 2 shows an arterial barogram and an atrial barogram;
and
[0011] FIG. 3 shows LV pressure during a cardiac cycle.
DETAILED DESCRIPTION
[0012] A system according to the invention synthesizes a
left-ventricular pressure waveform over a complete cardiac cycle by
piecing together segments of the left-ventricular pressure
waveform, each of which provides the left-ventricular pressure
waveform over a limited portion of the cardiac cycle. The
constituent segments of the desired waveform, the data needed to
shift those segments in time, and the data needed to calibrate the
constituent segments are obtained from a collection of non-invasive
diagnostic devises.
[0013] FIG. 1 shows a system 10 having two groups of diagnostic
devices. A first group 12 includes non-invasive pressure
measurement devices that provide signals indicative of a pressure
waveform existing in a portion of the cardiovascular system. Such
devices are collectively referred to herein as "barographs;" the
pressure waveforms that they produce are collectively referred to
as "barograms." A second group 14 includes non-invasive diagnostic
devices that detect the occurrence of particular events during the
cardiac cycle. These devices are collectively referred to as "event
detectors." It will be appreciated that, in addition to providing
data indicative of pressure, the output of one or more non-invasive
pressure measurement devices from the first group 12 can also
provide data indicative of the occurrence of particular events
during the cardiac cycle.
[0014] The barograms and the outputs of the event detectors are
provided to a software system 16 whose function is to select
portions of the barograms and to synchronize those portions to form
one continuous curve representative of the left-ventricular
pressure during the entire cardiac cycle. This synthesized curve
will be referred to herein as the "LV barogram".
[0015] One barograph from the first group 12 can be an arterial
barograph 18 in non-invasive communication (i.e. by any
non-invasive means) with a patient's arterial system. The arterial
barograph 18 generates a waveform (shown in FIG. 2 and hereafter
referred to as the "arterial barogram") that shows arterial
pressure as a function of time. For that portion of the cardiac
cycle during which the aortic valve is closed, the corresponding
portion of the arterial barogram is not closely related to the
left-ventricular pressure. However, during an ejection phase 28 of
the cardiac cycle, the aortic valve is open and the left ventricle
and aorta are (absent abnormalities of the aortic valve) in fluid
communication with each other. Consequently, for those portions of
the cardiac cycle, the arterial barogram does correspond to the LV
barogram.
[0016] As shown in FIG. 2, an arterial barogram 20 thus includes a
set of first portions 22 that are identical (absent abnormalities
of the aortic valve) to the left-ventricular pressure, and a set of
second portions 24 that are not relevant to the measurement of
left-ventricular pressure. Each first portion 22 corresponds to a
time interval during which the aortic valve is open. Each second
portion 24 corresponds to a time interval during which the aortic
valve is closed. To be of use in synthesizing the LV barogram, the
arterial barogram 20 must therefore be further processed to discard
the second portions 24 and to retain only the first portions 22.
This requires the ascertainment of boundaries between the first and
second portions 22, 24 of the arterial barogram 20.
[0017] FIG. 3 shows, for a patient in good cardiovascular health, a
typical arterial barogram 20 overlaid on an LV barogram 26 obtained
by direct measurement with a catheter in the left ventricle. A
typical first portion 22 overlaps the LV barogram 26 during the
ejection phase 28 of the cardiac cycle. A typical second portion 24
deviates significantly from the LV barogram 26. A time interval
associated with the first portion 22 of an arterial barogram 20
will be referred to as a "pump interval" because during this
interval, the left ventricle is pumping blood into the arterial
system.
[0018] The opening and closing of the aortic valve delineate the
extent of the pump interval. For the particular example shown in
FIG. 2, the opening and closing of the aortic valve are associated
with a sharp rise 32 in pressure and the occurrence of a dicrotic
notch 33 respectively. However, in a patient with poor
cardiovascular health, these features may not be as readily
apparent. Even in cases where these features are apparent, the
instants at which the aortic valve opens and closes cannot easily
be determined with precision because the elasticity of the
arteries, and other mechanical properties of the arterial system,
can introduce delays in the response of the arterial pressure to
the activity of the aortic valve. To some extent, these delays can
be corrected for by correlating them with the occurrence of
particular features in an electrocardiogram or phonocardiogram.
[0019] Certain events, such as the closing and opening of heart
valves, are detected by one or more event detectors from the second
group 14 of diagnostic devices shown in FIG. 1. These event
detectors determine the instants at which certain key events in the
cardiac cycle occur. These instants can then be used to identify
boundaries between first and second portions 22,24 of the arterial
barogram 20.
[0020] For example, in the illustrated system 10, an event detector
that includes a phonocardiograph 34 detects the acoustic signal
generated by the aortic and mitral valves as they close. FIG.3
shows, on the same time axis as the LV barogram 26, a
representative phonocardiogram 38 provided by the phonocardiograph
34. As is apparent from FIG. 3, the beginning of a first acoustic
pulse 40 marks the closing of the mitral valve. The beginning of a
second acoustic pulse 42 marks the closing of the aortic valve. For
event detectors that include a venous pulse acquisition unit 50,
the "V" wave of the venous pulse 52 in FIG. 3 marks the opening of
the mitral valve.
[0021] In some embodiments, an atrial barograph 54 can be used to
identify the occurrence of particular events in the cardiac cycle.
For those embodiments in which the atrial barograph 54 includes an
apex cardiograph 58, certain features of the apex cardiogram can be
used to identify the occurrence of events in the cardiac cycle. For
example, the "O" point, or nadir of the apex cardiogram can be used
to mark the opening of the mitral valve. FIG.3 shows, on the same
time axis as the LV barogram 26, a representative apex cardiogram
39 provided by the apex cardiograph 58.
[0022] Alternatively, an event detector can include an
electrocardiograph 44. In such a case, the event detector uses
selected features of an electrocardiogram to identify the
occurrence of selected events. FIG. 3 shows an electrocardiogram 46
on the same time axis as the LV barogram 26. As is apparent from
FIG. 3, the "R" spike of the QRS-wave 48 is associated with closing
of the mitral valve. The opening of the aortic valve is known to
occur after a known interval following the closing of the mitral
valve and is also marked by the up-stroke of the aortic pressure
trace.
[0023] As suggested above, an event detector can also include a
venous pulse acquisition unit 50, a representative output of which
is shown in FIG. 3 on the same time axis as the LV barogram 26. The
output 52 of the venous pulse acquisition unit 50 has a peak
associated with the opening of the mitral valve. Since the opening
of the mitral valve may not be readily discernible in the
phonocardiogram 38, the availability of data from the venous pulse
acquisition unit 50 can be useful in fixing the time at which the
mitral valve opens.
[0024] Following closure of the aortic valve, and the end of the
pump interval, the left ventricle continues to relax. At some
point, marked by the nadir of the apex cardiogram (indicated by "O"
in FIG. 3), the pressure within the left ventricle falls to the
point at which the mitral valve opens. This begins a fill interval,
during which the mitral valve is open, the aortic valve is closed,
and oxygenated blood flows into the left ventricle. In the absence
of mitral valve disease, the left atrium and the left ventricle are
in fluid communication during the fill interval. Hence, the
left-ventricular pressure is a function of, or correlated with, the
left-atrial pressure. Accordingly, a non-invasive measure of
left-atrial pressure during the fill interval can provide
information indicative of the atrial barogram.
[0025] Referring again to FIG. 1, in one embodiment, the first
group 12 of diagnostic devices also includes an atrial barograph 54
in non-invasive communication with the patient's left atrium. The
atrial barograph 54 provides a left-atrial pressure waveform,
hereafter referred to as the "atrial barogram," that shows the
left-atrial pressure as a function of time. The atrial barograph 54
thus provides an indication of ventricular pressure during the fill
interval.
[0026] One example of an atrial barograph 54 includes an
atrial-pressure acquisition-unit 56, such as that described in
McIntyre U.S. Pat. No. 5,291,895, used in conjunction with an apex
cardiograph 58. An atrial-pressure acquisition-unit 56 of the type
disclosed therein provides values of atrial pressure at key points
of the cardiac cycle. In particular, the atrial-pressure
acquisition-unit 56 provides the LV pre-A EDP (pre-atrial
contraction end diastolic pressure) and the LV post-A EDP
(post-atrial contraction end diastolic pressure). The apex
cardiograph 58 provides an apex cardiogram having the relative
shape of the atrial pressure waveform. The absolute values of
pressure from the atrial-pressure acquisition-unit 56 can thus be
used to calibrate the apex cardiogram. The apex cardiogram and the
pressure values provided by the atrial-pressure acquisition-unit 56
can thus be combined to provide the data needed to inscribe an
atrial barogram.
[0027] Like the arterial barogram 20, the atrial barogram includes
a set of first portions that are useful for the measurement of
left-ventricular pressure and a set of second portions that are not
relevant to the measurement of left-ventricular pressure. Each
first portion corresponds to a fill interval during which the
mitral valve is open. Each second portion corresponds to a pump
interval during which the mitral valve is closed. Like the arterial
barogram 20, the atrial barogram must be further processed to
separate the first portions from the second portions. As was the
case with the arterial barogram 20, this requires ascertainment of
the boundaries between first and second sections.
[0028] FIG. 3 also shows a representative atrial barogram 60
superimposed on the same time axis as an LV barogram 26 measured
directly by a catheter in the left ventricle. As is apparent from
FIG. 3, the atrial barogram 60 tracks the LV barogram 26 closely
during the fill interval, but deviates significantly once the
mitral valve is closed.
[0029] In general, it may not be possible to reliably determine
whether the mitral valve is closed by examining features of the
atrial barogram 60. Moreover, since disease is detected by an
improper response (pressure) to a stimulus (valve activity), it
would be illogical to use the response to identify the occurrence
of the stimulus. However, the same event detectors that were used
to separate first and second portions of the arterial barogram 20
can be used to separate first and second portions of the atrial
barogram 60.
[0030] As discussed above in connection with FIG. 3, the opening of
the mitral valve can (in the absence of mitral valve disease) be
detected on the basis of the nadir, or "O" point of the apex
cardiogram or on the basis of the venous pulse 52. Closure of the
mitral valve is associated with both the "R" spike on an
electrocardiogram and with an acoustic pulse on the phonocardiogram
38.
[0031] The cardiac cycle also includes two, relatively brief
intervals during which both the aortic valve and the mitral valve
are closed. These intervals are referred to as the upstroke and
downstroke intervals. The upstroke interval begins when, as the
left ventricle begins its contraction, the left-ventricular
pressure exceeds the left-atrial pressure. This causes the mitral
valve to close. The upstroke interval ends when, as the left
ventricle continues to contract, the pressure developed within the
left ventricle exceeds the pressure in the aorta. This change in
the sign of the pressure difference opens the aortic valve, thereby
ending the upstroke interval and beginning the pump interval. The
downstroke interval begins when, as the left ventricle relaxes,
pressure in the aorta exceeds the declining left-ventricular
pressure. The downstroke interval continues until the left
ventricle relaxes enough to cause the left-ventricular pressure to
fall below the left-atrial pressure. This change in the sign of the
pressure difference opens the mitral valve, thereby ending the
downstroke interval and beginning the fill interval.
[0032] During the upstroke and downstroke intervals, the fluid in
the left-ventricle is isolated from the remainder of the
circulatory system. Hence, it is not currently possible to obtain
the shape of the pressure waveform during these relatively brief
intervals. However, the upstroke and downstroke intervals are so
brief that for all practical purposes, the LV barogram 26 during
these intervals can be inscribed by connecting the known pressures
at the beginning and end of the interval by a straight line.
[0033] In some cases, the derivative of the pressure waveform,
particularly during the upstroke interval, is a useful quantitative
indicator of heart function. Under these circumstances, one can
empirically correct the pressure waveform during these intervals.
Such correction factors may be required because the closure of the
aortic valve is detected by measuring a pressure wave at a point
far from the heart. As a result, there is a time delay between the
closure of the aortic valve and the detection of that closure. This
delay causes the measured derivative of the pressure waveform
during the upstroke interval to be smaller than it should be. Such
correction factors can be empirically determined by comparing LV
measurements made directly and indirectly in a large number of
patients and using statistics derived from such measurements to
correct the measured derivative of the pressure waveform.
[0034] In other cases, the arterial barogram 20 can also provide
information about additional hemodynamic parameters, such as stroke
output and work performed by each stroke. This can be achieved by
observing the duration of the pump interval and correlating that
duration with stroke volume. A formula relating the duration of the
pump interval with the stroke volume is well-known in the medical
literature.
[0035] The area under the first portion 22 of the arterial barogram
20 can also provide information about these additional hemodynamic
parameters. This can be achieved by obtaining calibration data
using a non-invasive flow measurement technique. Such non-invasive
flow measurement techniques include echo cardiography (as described
on page 9 of vol. 6, No. 2 of a journal entitled "Congestive Heart
Failure" and published in March/April 2000) Doppler measurements
(as described in an article by Williams and Labovitz entitled
"Doppler Estimation of Cardiac Output: Principles and Pitfalls" and
published in Echocardiography 1987, pages 355-374) and non-invasive
impedance determination of cardiac output (as described by Hanley
and Stamer in "Pressure volume studies in man: an evaliation of the
duration of the phases of systole" as published in 1969 in the
Journal of Clinical Investigation, vol. 48, pp. 895-905. The
calibration data thus obtained is thereafter used to determine the
stroke volume from the integral of the arterial barogram 20 over
the first portion. Because the characteristics of a patient's
arterial system are relatively constant over time, any changes in
the value of that integral will indicate a change in stroke
output.
[0036] The software system 16 includes a first selection process 70
having inputs connected to barographs in the first group of
diagnostic devices. The first selection process 70 has an output
that corresponds to the LV barogram 26 during either the fill
interval or the pump interval. The particular input to be selected
is controlled by a control process 68 on the basis of what portion
of the barogram was last inscribed.
[0037] Similarly, the software system also includes a second
selection process 72 having inputs connected to event detectors in
the second group of diagnostic devices. The second selection
process 72, like the first, has an output that corresponds to a
selected one of its inputs. The particular input to be selected
depends on the output of the first selection process 70.
[0038] The software system 16 further includes a shift process 74
having a first and second input. The first input of the shift
process 74 is connected to the output of the first selection
process 70 and the second input of the shift process 74 is
connected to the output of the second selection process 72. The
output of the shift process 74 is its first input shifted in time
by an amount derived from its second input.
[0039] The output of the shift process 74 is provided to an
interpolation process 76 whose function is to inscribe the upstroke
and downstroke intervals on the basis of the temporal endpoints of
the pump and fill intervals and the values of the inscribed LV
barogram 26 at those endpoints. The interpolation process 76 then
provides its output to a display 78, which renders the LV barogram
on a CRT, a strip chart, or any similar display.
[0040] Having described the invention, and a preferred embodiment
thereof, what I claim as new and secured by letters patent is:
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