Electronic circuit processes arterial blood pressure waveform to produce discrete signals that coincide with beginning and end of left ventricular ejection. Output signals provide timing signals for computers that monitor cardiovascular systems. Circuit operates reliably for heart rates between 50 and 200 beats per minute

Gebben, V. D.

Webb, J. A., Jr.

English

NASA Technical Reports Server

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Differentiator
August 1972	 B72-10512 
NASA TECH BRIEF 
Lewis Research Center	
__4V 
NASA Tech Briefs announce new technology derived from the U.S. space pro g ram. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Electronic Circuit Detects Left Ventricular 
Ejection Events in Cardiovascular System 
Input 
40 	Arterial Pressure 
Waveform 
50 mV mmHg
L A
Follower 
_T	
I Pulse Adder
K 
100 
f
0.001
Po 	 Pulse At 
___________	
Begrnnin Negative 
0.001
100 
Flip . Flop 1
)(
Comparatorl 
A,...
10 
A	
Low I	 9v 
 Pass T 
1.0 
1.0	
10 
4E 100 
Comparator 2	 Flip-Flop 2 
NOTE: 
Operational Amplifiers: ±5 mA, ± 1OV Output; Input Impedance> 
1 Megohm; All Resistors Are In Kilohms 
And All Capacitors Are In Microfarads 
L^^
PULSE-WIDTH 
An electronic circuit has been developed which pro- 
cesses the arterial blood pressure waveform to produce 
discrete signals that coincide with the beginning and end 
of left ventricular ejection (LyE). The output signals 
from the circuit provide timing signals for computers 
that monitor cardiovascular systems. For a typical 
arterial pressure waveform, LVE begins at the time when 
the blood pressure rapidly increases due to the heart 
pumping blood through the aortic valve into the arteries.
-DISCRIMINATOR 
LVE ends at the waveform dicrotic notch which is a 
pressure disturbance caused by the aortic valve closure. 
By detecting these two events, the circuit provides 
timing signals to the computer. 
Openings and closures of the aortic valve are easily 
identified visually through the use of strip-chart re-
corders, but difficult to detect electronically, especially 
when the circuit (or computer) has no memory of past 
events. To cover a wide variety of situations, the de-
(continued overleaf 
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tector must operate for heart rates between 50 and 200 
beats per minute and operate reliably for the waveforms 
that can result from abnormal circulatory dynamics, 
from irregular heart beats, and from breathing pressures. 
A detection process based on slope measurements 
alone is inadequate, since it also detects extraneous 
oscillations. The approach of using a signal that is 
initiated when the pressure exceeds its average value has 
disadvantages of producing late signals and false signals 
when the pressure wave oscillates through the average 
value. 
The circuit for detecting the beginning and end of 
LVE is shown in the figure. Signal A is an electrical 
input signal proportional to the blood pressure in the 
arteries near the heart. The portion above the dashed 
line produces a positive pulse at output terminal K 
when the aortic valve opens at the beginning of LyE. 
The process below the dashed line produces a negative 
pulse at K when the valve closes at the end of LyE. 
Beginning of LVE is determined by first comparing 
signal A to signal B. The comparator switches C in a 
negative direction when A initially increases at the 
beginning of LyE. 
Signal C is quite independent of low frequency com-
ponents caused by breathing, since the cutoff frequency 
for signal B is more than two octaves above the breathing 
frequency. However, C is affected by high frequency 
components that can result from abnormal circulatory 
dynamics. Oscillations with frequency content of 6 to 
15 Hz can cause A to cross over B and result in C switch-
ing during the cardiac cycle. To avoid such problems, C 
is processed by a pulse-width-discriminator that makes E 
independent of high frequency switching in signal C. 
Signal E switches in the negative direction only once 
each cardiac cycle at the beginning of LyE. This action 
produces a positive pulse at output terminal K. 
The circuit for detecting the end of LVE is shown 
below the dashed line. The objective is to produce a 
negative pulse at terminal K coinciding in time with 
the positive inflection point that occurs at the leading 
edge of the dicrotic notch. 
Signal H is related to the second derivative of A with 
respect to time. Signal H changes polarity at the inflec-
tion points in the low frequency portion of A. Positive 
inflection points are signified by signal I switching to 
a negative voltage. Since waveform A has several inflec-
tions, signal I switches several times each cardiac cycle. 
The proper inflection point is selected by a logic 
circuit that uses two flip-flops (operational amplifiers 
dominated by positive feedback). Flip-flop 1 is switched 
positive by C and negative by E. This arrangement 
results in F switching positive only once each cardiac 
cycle just prior to the dicrotic notch. 
When signal F switches to a positive voltage, signal J 
switches to a negative voltage. The next positive inflec-
tion in A switches Ito a negative voltage, switches J to a 
positive voltage, and produces a negative pulse at output 
terminal K. This output pulse coincides with the end of 
LyE. Inflections after the dicrotic notch have no effect 
on J, since J remains latched at a positive voltage until 
F switches positive in the next cardiac cycle. 
The circuit operates reliably for heart rates between 
50 and 200 beats per minute and for the variety of wave-
forms that can result from abnormal circulatory dynam-
ics, from irregular heart beats, and from breathing 
pressures. 
Note: 
No further documentation is available. Specific ques-
tions, however, may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B72.10512 
Patent status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
Patent Counsel 
Mail Stop 500-311 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Source: Vernon D. Gebben and John A. Webb, Jr.

Lewis Research Center

(LEW-1 1581)
ON 
B72-10512	 Category 05,02


Electronic circuit detects left ventricular ejection events in cardiovascular system

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