Apparatus for the diagnosis of heart conditions

An apparatus for analyzing the biomechanical behaviour of the cardiac muscle and for diagnosing pathological conditions of the heart. The apparatus measures and records the rise and fall of intra-ventricular pressure monitored by a transducer installed in a cardiac catheter or in an arterial probe. The pressure versus time recordings during both the systolic and diastolic phases are mathematically analyzed, and two parameters indicative of the biomechanical conditions of the muscle are derived. The parameters are then plotted against each other on a map in which diagnostic zones of various normal and pathological heart conditions are delineated.

FIELD OF THE INVENTION 
This invention relates to medical apparatuses such as instruments used in 
the diagnosis of pathological disorders through recording and analysis of 
signals representing physiological activities. More specifically, the 
invention relates to instruments designed to analyze the behaviour of the 
cardiac muscle. 
BACKGROUND OF THE INVENTION 
In-vitro studies of muscular tissue and, in particular cardiac muscle 
bundles have been directed toward the understanding of the mechanical 
characteristics of the contracting phenomenon. 
It was thought that once these characteristics had been defined, the 
mechanical behavior of a healthy organ could be represented in 
mathematical terms. Some of these terms could then be used as criteria in 
the diagnostic of pathological conditions. 
The inventor focused his study on the analysis of the inotropy (from the 
Greek is, inos fiber; and tropos, behaviour) of the cardiac muscle, i.e. 
its contractibility. 
Traditionally, the behaviour of the cardiac muscle has been analyzed by 
measuring the absolute values of the systolic and diastolic blood 
pressures and of the pulse rate; and by listening to auditory 
manifestations of the muscle valve activity. Electrocardiography provides 
only a gross inferential tool for the diagnosis of pathological heart 
conditions. Studies of time and displacement dependency in the behaviour 
of the cardiac organ have mainly been directed to the interpretation of 
force-versus-velocity curves, and the potential use of a theoretical 
maximum velocity parameter (obtained by converging extrapolations of a 
family of force-velocity curves) as an indicator of organ health. None of 
the previous time-dependence studies have suggested a practical 
interpretation of the consistent parameters around which this invention is 
implemented. 
SUMMARY OF THE INVENTION 
A simple phenomenological model of the contracting cardiac muscle has been 
developed which is capable of simulating most major mechanical attributes 
of the contraction phenomenon. From this model two critical parameters 
have been isolated. The first, y is indicative of the delayed time 
response of the cardiac muscle to the signal initializing contraction or 
relaxation. The second, x represents the inotropic state of the muscle, 
i.e. its ability to respond to the and the excitation and the particular 
mechano-chemical characteristic of that response. 
These parameters can be derived from the continuous measurement of the 
intra-ventricular pressure during both the systolic and diastolic phases 
of the heart movement, according to the formula: 
EQU P(V,t)=B(V)t.sup.y e.sup.-xt 
wherein P, is the intra-ventricular pressure as a function of the volume 
(V) and time (t); B represents the influence of the muscle length as a 
function of the volume (V) on the force of contraction; y is the 
excitation-contraction coupling parameter; and x is the inotropic 
coefficient. 
It can be shown that the time Tmax necessary to reach peak pressure is 
equal to the ratio of y over x. 
It is the principal object of the invention to provide an apparatus for 
analyzing the biomechanical behaviour of the cardiac muscle and for 
diagnosing its pathological conditions. 
It is also an object of the invention to provide an apparatus for 
conducting clinical studies of the heart organ on live subjects, and 
in-vitro studies of muscular tissue samples. 
A further object of the invention is to provide such an apparatus which 
calculates the y and x parameters for a particular muscle contracting 
phenomenon, and which uses them as criteria for the diagnosis of 
pathological conditions. 
Another object of this invention is to provide a cardiac muscle analyzing 
apparatus which relies strictly on pressure-time dependency observations 
and uses only simple and reliable measurement of time and relative 
pressure variation. 
These and other valuable objects are achieved by means of a simple 
monitoring device which records samples of intraventricular or arterial 
pressures during the systolic and diastolic phases of the heart movement; 
then, conducts a analytical study of the pressure-versus-time variations 
in order to extract the parameters characteristic of the muscle inotropy.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
Referring now to the drawing, there is shown in FIG. 1 a general block 
diagram of the cardiac inotropy analyzing apparatus 1 which is divided 
into three major components. The sensor and signal-conditioning unit 2 
comprises a pressure monitoring probe 3 which is applied to the radial 
artery 4, or inserted into the heart by means of a catheter (not shown). 
The probe could be applied to any other convenient arterial location, 
depending upon the diagnosis sought. In a clinical environment the radial 
artery which is often punctured for other purposes would be most 
indicated. However, it is not absolutely necessary to penetrate the 
artery, and measurement may be taken by sensing the pressure of the 
arterial walls. The associated electronic circuit converts the monitored 
pressure into a digitally-coded signal which is fed to the second major 
component, the signal processor 5. 
The signal processor analyzes the pressure signal and extracts the 
excitation-contraction coupling parameter y and the inotropic coefficient 
x from the time-response curve representing the pressure variation during 
both the systole and diastole. The signal processor 5 also creates a 
graphic interpretation of the pressure signal and parameters, then 
controls the last major component, the display 6. 
The display includes a video screen 7 and a printer 8. 
More specifically, the sensor and signal conditioning unit 2 comprises, in 
connection with the probe 3 a pressure transducer 9 such as a strain gage 
bridge connected to the input of a differential signal amplifier 10. The 
output of the amplifier is fed to an analog-to-digital converter 11 which 
produces a corresponding binary-coded signal. These circuits are energized 
by a power supply 12. 
Typically, a strain gage pressure transducer with a resolution of 2.5 
millimeters of mercury and a linearity of one percent of full scale; a 
differential amplifier with corresponding resolution and linearity; and a 
eight-bit analog-to-digital converter with a twenty microsecond conversion 
time, are suggested. 
The signal processor 5 comprises a general purpose programmable eight-bit 
microprocessor 13 equipped with sixty-four kilobytes of random-access 
memory (RAM) 14, and a read-only memory (ROM) 14a holding a standard 
operating software and common programming language interpreter or 
compiler. 
The signal processor 5 also comprises a standard user input-output 
interface 15, a keyboard input interface 16, a video screen output 
interface 17 and a serial input-output port 18. 
A keyboard 19 and disk-drive 20 complete the list of basic components of 
the system. The disk-drive 20 is used to read the application program 
recorded on diskettes, as well as some reference parameters. The 
disk-drive can also be used to record in digital form the information sent 
to the display unit 6. Alternately, the application program could be 
stored permanently in a section of the ROM 14a. 
The operation of the signal processor 5 in the analysis of the digitized 
pressure measurement data supplied by the sensor and signal-conditioning 
unit will be described in detail with reference to FIG. 2 and 3. 
The graph of FIG. 2 illustrates the blood pressure variation during the 
systolic and diastolic phases of the heart cycle. The full curve 78 
represents the theoretical function: 
EQU Pressure=(P)=Bt.sup.y e.sup.-xt 
for a particular individual based on accepted norms for his age and sex 
group. 
The dotted line 79 represents the actual measurement samples taken by the 
apparatus. The rising transient 80 at the bottom of the curve is due to 
the opening of the mitral valve and/or valvular interaction and aortic 
recoil. 
B represents a factor characteristic of the size of the particular organ 
under observation. As previously explained, the two parameters y and x 
denote the particular characteristics of the contraction phenomenon. 
Although, ideally, the actual intra-ventricular pressure-time record taken 
by means of a cardiac catheter would be preferable in order to ascertain 
the status of the heart muscle,sufficiently accurate diagnosis can be 
obtained by examination of pressure-time records obtained from the radial, 
femoral or other arterial locations (as shown in FIG. 1). This is because 
the parameters (y,x) are temporal in character and as such not greatly 
affected by amplitude attenuations occurring through the aortic tree. 
Relative measurements rather than absolute measurements are thus adequate 
in most cases. The parameters, however, should be weighted or cataloged 
according to the probing site for a given pathology. In a case of 
arterio-sclerosis for instance, the value of the parameters measured on 
the radial artery may vary from those measured at the femoral artery. 
The data obtained by means of the probe 3 and the sensor and signal 
conditioning unit 2 shown in FIG. 1 are acquired and analyzed by the 
signal processor 5 in accordance with the flow diagram of FIG. 3a and 3b. 
The data acquisition phase 21-27 is done in a series of samplings whose 
sequence and number are determined by the index I. 
As successive readings of the pressure P and time t are taken, the 
apparatus searches for a drop in the pressure 23, indicating that the 
maximum pressure Pmax has been reached. The peak pressure is noted 24, as 
well as the corresponding time Tmax 27, by multiplying the number of 
samplings taken Imax by the sample period. 
The apparatus then seeks to determine the y and x parameters of the 
theoretical function curve which most closely fits the acquired data, 
using an iterative sum of squares approximation method. 
The program sets an initial trial value 28 for old sum of squares 
(10.sup.8) and parameter y (1.0) and .DELTA.y (0.1). These values are then 
used for the computation 29, 30 of parameter x and factor B according to 
the equations: 
##EQU1## 
The data point index I is then initialized 31 for sum squares equal to 
zero. Then the sum squares of differences between the sampled and 
theoretical pressures are computed 32-41 in iterative form until the 
detection 36 of changes in value of less than 0.005 indicates a converged 
value of y. At that point, the systolic values y, and x, of the parameters 
are noted 42. 
During this process the value of sum squares is tested 37 to assure that it 
continues to decrease as y is increased 39. If, instead, the sum square 
increases, then y is reduced 40,41; and a smaller y increment is used 
successivley if necessary, until the converged value of y is achieved. 
The analysis of the diastolic phase samplings now begins with the 
initialization 43-44 of the index. 
The samples are taken until the detection of the valve transient 80 which 
appears near the bottom end of the diastolic drop. The iterative search 
45-48 for the transient continues so long as the pressure drops 45. 
The curve fitting steps 49-63 mirror those 28-42 used during the systolic 
phase, with the difference that the index I goes from Imax at peak 
pressure to Ifinal when the valve transient is detected; instead of from 
IO to Imax as in the first phase. 
A second set of parameters y.sub.2, and x.sub.2 are then noted for the 
diastolic phase. 
The theoretical pressure curve and the sample measurements shown in FIG. 1 
may be displayed on the video screen and 7 and or the printer screen 8 as 
the data is being acquired. 
A trained operator may, upon simple observation of these graphs, draw 
various conclusions as to the condition of the organ under observation. 
The diagnosis phase of the program 64-68, however, provides a more powerful 
tool for the systematic interpretation of the parameters, leading to a 
direct formulation of diagnostic and therapeutic indications fetched from 
pre-recorded data based on accumulated experience. 
FIG. 4 illustrates the type of displayed or printed information which the 
apparatus can generate based upon the respective values of y and x. 
The final diagnostic phase begins with the display of a map 69 generated 
from data pre-stored either in the ROM 14a or read by the disk-drive 20. 
The map appears on the drawing as the background of FIG. 4. Various zones 
delineate the area indicative of various pathologies such as myocardial 
hypertrophy 70, ischemia 71, conduction blocks 72 etc. A normalized zone 
73 corresponds to the parameter values of an healthy individual in the 
patient's age and sex group. 
These various zones would be displayed as functions of the actual set of 
parameters being interpreted, the diagnosis goals as well as the patient's 
vital statistics. These various criteria can be entered according to 
well-known routines via the keyboard 19. 
Next one or more indicators 74-75 are placed 65 on the map 67 by coupling 
any two parameters y.sub.1, x.sub.1, Y.sub.2, x.sub.2 and ploting one 
against the other within each pair. 
Pathological conditions are pointed out as the indicators 74-75 appears to 
fall within the respective zones. The location and size of each zone may 
change as clinical experience accumulates in the diagnosis of various 
heart conditions. 
It should be understood that the territory of each zone 70-73 is predicated 
upon the predetermined interpretation of each pair of parameters. The 
location and size of each zone may change as various indicators are 
displayed. 
The coordinates of each indicator are then used to direct the system 66-67 
to a stored look-up table, from which printable diagnostic messages 76 or 
pharmacopoeia 77 may be extracted and printed 68. 
It should be understood that the diagnostic process is not limited to the 
illustrative examples discussed above. Various other combinations and 
subcombinations of parameters and other factors particular to the patient 
may be used to address other types of prestored diagnostic and therapeutic 
indications. For instance, the attenuation of the valve transient 80 
detected at an arterial location would indicate the presence of an 
aneurism in the arterial path. A sharpening of the transient, on the other 
hand, would reflect the conductive rigidity caused by arterio-sclerosis. 
The apparatus, thus implemented constitutes a powerful tool in the hands 
of scientists for further exploration of the cardiac muscle behaviour and 
the refinement of the diagnostic interpretations of the suggested 
parameters. As more knowledge is acquired through clinical use of the 
apparatus on live individuals, as well as applications to in-vitro studies 
of the cardiac tissues, the practice of this invention may lead to simple 
and very reliable early diagnosis of pathologies which have been 
impossible to detect in their early manifestations. 
The various hardware components of the apparatus may be selected from 
commercially available units. The system operating program, data input and 
output routine and user language assemblers do not differ from standard 
well-known processes. The implementation of the application programs in 
accordance with the instant disclosure is well within the ordinary skill 
of those knowledgeable in the arts of data processing. 
The illustrative embodiment described above could be modified and improved, 
and other related apparatuses may be devised according to the invention 
and within the scope of the appended claims.