Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2000-05-22
2001-07-03
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C606S131000
Reexamination Certificate
active
06254544
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heart-function monitor apparatus which monitors a function of the heart of a living subject by evaluating a cardiac mechanical efficiency, i.e., a mechanical efficiency of the heart.
2. Related Art Statement
When a characteristic of the left ventricle of the heart as an elastic tube, that is, an elastic coefficient of the same, at a telesystolic time immediately before the aortic valve is closed, is defined as a left-ventricle telesystolic elastance E
es
, and a characteristic of the aorta as an effective elastic tube, that is, an elastic coefficient of the aorta is defined as an aorta effective elastance E
a
, the ratio, E
es
/E
a
, of the left-ventricle telesystolic elastance E
es
to the aorta effective elastance E
a
indicates a degree of balance of the connection of the left ventricle and the aorta, that is, a mechanical efficiency of the left ventricle. Accordingly, this ratio E
es
/E
a
can be used as an important index of the function of the heart. It has been theoretically and experimentally elucidated that the ratio E
es
/E
a
changes depending upon the current state of the cardiac function, such as at rest, under stress, or in heart failure, and that the ratio E
es
/E
a
reflects cardiac metabolic rate (i.e., the ratio of the amount of work of the heart to the amount of consumption of oxygen by the cardiac muscle).
However, determination of the above left-ventricle telesystolic elastance E
es
, which is also known as the maximum pressure-volume ratio, or the left-ventricle telesystolic pressure-volume ratio, needs (a) detecting continuously respective changes of the inner pressure and inner volume of the left ventricle, (b) obtaining, in a two-dimensional coordinate system having a volume axis indicative of the inner volume of the left ventricle and a pressure axis indicative of the inner pressure of the same, a plurality of pressure-volume loops before and after preload or afterload is applied to the cardiac muscle, (c) estimating, based on the plurality of pressure-volume loops, a left-ventricle unstressed volume, V
0
, taken when the inner pressure would take zero, and (d) determining the telesystolic elastance E
es
by dividing a telesystolic pressure, P
es
, by the difference of a telesystolic volume, V
es
, and the unstressed volume V
0
. Thus, the determination of the telesystolic elastance E
es
needs measuring simultaneously the inner pressure and inner volume of the left ventricle. Conventionally, this determination has been carried out by an invasive method in which a cutting operation or a catheter insertion is employed. Thus, it has been very difficult to monitor the cardiac function. In addition, determination of the aorta effective elastance E
a
needs (e) determining, in the above-indicated two-dimensional coordinate system, the effective elastance E
a
by dividing the telesystolic pressure P
es
by the difference of a telediastolic volume, V
ed
, and the telesystolic volume V
es
. Thus, conventionally, this determination also needs measuring invasively the inner pressure and inner volume of the left ventricle, and it has been very difficult to monitor the cardiac function.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a heart-function monitor apparatus which can non-invasively and easily monitor a cardiac mechanical efficiency E
es
/E
a
of a living subject.
The Inventor has carried out extensive studies in the above-mentioned background, and has found the fact that when (a) a pressure-volume ratio, i.e., an elastance, E(t), is obtained by dividing a continuously obtained left-ventricle inner pressure, P(t), by the difference, (V(t)−V
0
), of a continuously obtained left-ventricle inner volume, V(t), and the above-indicated unstressed volume V
0
, (b) a time-elastance curve is drawn, as shown in
FIG. 8
, in a two-dimensional coordinate system having a time axis and an elastance axis, (c) a first portion of a length of the time-elastance curve between its start end and a maximum elastance, E
max
, i.e., a telesystolic elastance E
es
(the first portion corresponds to a pre-ejection period, PEP) is approximated by a straight line, L
1
, as shown in
FIG. 9
, and a second portion of the length (the second portion corresponds to an ejection period, ET) is approximated by a straight line, L
2
, and (d) k is defined to be equal to the ratio, k
2
/k
1
, of a slope, k
2
, of the straight line L
2
to a slope, k
1
, of the straight line L
1
, the ratio of the left-ventricle telesystolic elastance E
es
to the aorta effective elastance E
a
, i.e., the cardiac mechanical efficiency E
es
/E
a
can be expressed by using a telediastolic aorta (blood) pressure, P
ad
, i.e., an aorta inner pressure at the telediastolic time of the left ventricle; a telesystolic aorta pressure P
es
, i.e., an aorta inner pressure at the telesystolic time of the left ventricle; the ejection period ET and the pre-ejection period PEP of the left ventricle; and the ratio k. The present invention has been developed based on this finding.
(1) According to a first feature of the present invention, there is provided an apparatus for monitoring a function of a heart of a living subject, comprising a pre-ejection period measuring device which non-invasively measures a pre-ejection period from a time when contraction of a cardiac muscle of a left ventricle of the heart starts, to a time when ejection of blood from the left ventricle starts; an ejection-period measuring device which non-invasively measures an ejection period during which the blood is ejected from the left ventricle; an aorta-pressure estimating means for estimating blood pressure values in an aorta of the subject; a telediastolic-aorta-pressure determining means for determining, based on the aorta blood pressure values estimated by the aorta-pressure estimating means, a telediastolic blood pressure in the aorta at a telediastolic time of the heart; a telesystolic-aorta-pressure determining means for determining, based on the aorta blood pressure values estimated by the aorta-pressure estimating means, a telesystolic blood pressure in the aorta at a telesystolic time of the heart; and a cardiac-mechanical-efficiency determining means for determining, based on the measured pre-ejection period, the measured ejection period, the determined telediastolic aorta blood pressure, and the determined telesystolic aorta blood pressure, a cardiac mechanical efficiency of the subject according a predetermined relationship between (A) cardiac mechanical efficiency and (B) (b1) pre-ejection period, (b2) ejection period, (b3) telediastolic aorta blood pressure and (b4) telesystolic aorta blood pressure.
According to this feature, the cardiac-mechanical-efficiency determining means determines, based on the non-invasively measured pre-ejection period, the non-invasively measured ejection period, the determined telediastolic aorta blood pressure, and the determined telesystolic aorta blood pressure, a cardiac mechanical efficiency of the subject as the ratio of left-ventricle telesystolic elastance to aorta effective elastance, according the predetermined relationship. Thus, the present heart-function monitor apparatus can non-invasively and easily monitor the cardiac mechanical efficiency corresponding to the cardiac function of the subject.
(2) According to a second feature of the present invention that includes the first feature (1), the predetermined relationship is defined by a following expression:
E
es
/E
a
=(P
ad
/P
es
){1
+k
(
ET/PEP
)}−1
where E
es
/E
a
is the cardiac mechanical efficiency,
P
ad
is the telediastolic aorta blood pressure,
P
es
is the telesystolic aorta blood pressure,
ET is the ejection period,
PEP is the pre-ejection period, and
k is a coefficient.
The above expression is obtained based on the fact that when a portion of the time-elastance curve, shown in
FIG. 8
, between its start end and the maximum elastance E
max
, i.e., the telesystolic elastance E
Colin Corporation
Mallari Patricia C.
Nasser Robert L.
Oliff & Berridg,e PLC
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