Device monitors blood oxygen saturation, blood pressure, pulse rate, and pulse-pressure curve during conditions of high stress in simulated space flight

Smith, J. R., Jr.

English

NASA Technical Reports Server

Adjustable 
Pressure 
Source L,p
Recorder
or
Transmitter 
Recorder
or
Transmitter 
Gain	 I 
Control	 Blood 
Oxygen 
Saturation
Heart
Beat Rate 
qs--- 
Pulse Wave Form 
other measurements. As indicated in the diagram, a 
lamp illuminates the ear, and the light transmitted 
through the ear falls on two photcells, one having a 
peaked sensitivity at 790 nm (IR), and the other (R) 
peaked at 640 nm. Light absorption by the blood at 
1972	 B72-10224 
NASA TECH BRIEF 
Ames Research Center
	
_4V 
NASA Tech Briefs announce new technology derived from the U.S. space program. 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. 
Ear Oximeter-Transducer Monitors 
Four Physiological Responses 
The problem: 
To provide a device that continuously monitors 
blood oxygen saturation, blood pressure, pulse rate, 
and the pulse-pressure curve of subjects during con-
ditions of high stress in simulated space flight. The 
device must be small enough to be worn without 
discomfort; it must not interfere with activity, and it 
must also operate under conditions of severe accel-
eration and vibration.
Bracket
How it's done: 
An ear oximeter of conventional design is used to 
determine the oxygen content of the blood from 
measurements of the amount of light absorbed by 
the blood supply in the upper part of the ear; signals 
provided by the oximeter are processed to obtain 
Blood	 I Recorder 
or
	
I 
Transmitter
	
-	 Pressure 
IR 
Power	 1L_ Li	 \ Supply	 I	 Ear Lobe 
Oximeter Earpiece 
The solution: 
Utilize a conventional ear oximeter as a transducer; 
a continuous record of the in vivo blood pressure, 
pulse rate, and pulse-pressure curve can be obtained 
from calibrations of the detector output.
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the united States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000224 2020-03-17T03:33:18+00:00Z
790 nm is due essentially to the presence of hemo-
globin, regardless of whether it is oxidized or re-
duced; on the other hand, absorption at 640 i'm is 
due to oxygenated hemoglobin. Thus, the output 
from two DC amplifiers fed to a recorder or trans-
mitter gives continuous indication of oxygen content. 
The lamp source of the oximeter heats the ear to 
the extent that arterioles dilate greatly; as a result, 
the blood flow through the ear becomes so rapid 
that very little deoxygenation occurs in the capilla-
ries. Consequently, the oxygen-saturation level of 
arterial blood is measured, which in most instances 
is more important than measurement of the oxygen 
saturation in the venous blood. For initial calibration, 
a pressure capsule acts as a cuff and presses on the 
ear for 15 seconds at a maximum applied cuff pres-
sure of 250 mm so that the blood flow in arteries or 
veins is stopped; in this way the instrument "zero" 
for oxygen concentration can be obtained. 
The light falling on each photocell is, of course, 
transformed into a DC voltage that is proportional 
to the intensity of illumination transmitted by the 
ear. After amplification, the voltage signal (the blood 
saturation signal) from the infrared cell sensitive to 
790 nm can be measured directly by a recorder or 
transmitter; more importantly, however, its value 
varies inversely with blood volume, which in turn 
varies directly with blood pressure. The blood satura-
tion signal is a DC voltage that is at a minimum 
when the blood pressure is at a maximum; this cor-
responds to the systolic pressure when no ear cuff 
pressure is applied to the ear tissue. Conversely, the 
DC signal is at a maximum corresponding to diastolic 
pressure. When a plot of the blood pressure signal 
is examined on a graph or on an oscilloscope, the 
difference between the systolic and diastolic pressure 
may be obtained directly. 
The light falling on the infrared cell constantly 
fluctuates in intensity as blood pressure-pulses from 
the heart pass through the ear. Consequently, the 
output of the JR cell has an AC signal with a peak-
to-peak amplitude which is proportional to the dif-
ference between the systolic and the diastolic pressure. 
The AC signal is conveniently amplified by the AC 
amplifier indicated in. the diagram (with variable 
gain) for recording or further processing. 
The apparatus is calibrated by adjusting the gains 
of the variable-gain DC amplifier, the variable-gain 
AC amplifier, and the adjustable voltage source bias 
as follows: The pressure capsule is pressurized to 
about 200 mm of Hg (c27 kN/m 2 ), sufficiently high 
to cut off all circulation through the ear tissue so that 
no blood flows under the earcuff and there is no 
B72-10224
absorption of light due to blood. 
The earcuff pressure is then allowed to decrease 
slowly; as it becomes equal to systolic pressure, some 
circulation commences as noted by a decrease in the 
blood-pressure signal and the appearance of some 
pulse-pressure wave forms. The earcuff pressure is 
noted (since it is the systolic pressure of the sub-
ject) and at the same time a pressure-pulse signal 
is obtained. 
As the earcuff pressure continues to decrease, the 
blood-pressure signal decreases (indicating absorp-
tion of light due to flow of blood) and the amplitude 
of the pressure-pulse signal continues to increase, 
showing that more and more flow due to the heart's 
pressure pulse passes through the illuminated tissue. 
As soon as the earcuff pressure is equal to the dias-
tolic pressure, the total amplitude of the pressure 
pulse is utilized to pump blood through the tissues 
and the amplitude becomes constant; at this point, the 
earcuff pressure, that is, diastolic pressure, is noted. 
After the earcuff pressure has been allowed to 
bleed off completely, the gain of the variable-gain 
DC amplifier is adjusted in accordance with some 
convenient scale. For example, the gain may be de-
creased so that the blood-pressure signal becomes 
—1.0 volt. 
The difference between the systolic and the 
diastolic pressure may be read from a graph in a 
continuous manner. Additionally, the pressure-curve 
signal provided on a time scale affords a ready means 
of determining the pulse rate. 
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B72-10224 
Patent status: 
This invention has been patented by NASA U.S. 
Patent No. 3,412,729) and royalty-free license rights 
will be granted for its commercial development. 
Inquiries about obtaining a license should be ad-
dressed to: 
Patent Counsel 
Mail Code 200-1A 
Ames Research Center 
Moffett Field, California 94035 
Source: Joseph R. Smith, Jr. 
Ames Research Center 
(XAC-05422) 
Category 05


Ear oximeter-transducer monitors four physiological responses

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