Spirometer modification to permit computer reduction of respiratory flow dat

Roman, J.

Sato, R. N.

English

NASA Technical Reports Server

NASA TECHNICAL NOTE 
A USEFUL MODIFICATION 
OF THE WRIGHT SPIROMETER 
by James Roman and Robert N. Sat0 
Flight Research Center 
Edwards, Cali$ 
N A T I O N A L  AERONAUTICS A N D  SPACE A D M I N I S T R A T I O N  W A S H I N G T O N ,  D. C.  NOVEMBER 1967 ,! 
I 
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TECH LIBRARY KAFB, NM 
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01130898 
A USEFUL MODIFICATION OF THE WRIGHT SPIROMETER 
By J a m e s  Roman 
Flight Research  Center  
Edwards,  Calif. 
and 
Robert N. Sat0 
Pro j e ct Con sult  ant 
N A T I O N A L  AERONAUT ICs AND SPACE ADM IN ISTRATION 
For sole by the Clearinghouse for Federal Scientific and Technical Information 
Springfield, Virginia 22151 - CFSTl price $3.00 
A USEFUL MODIFICATION OF THE WRIGHT SPIROMETER 
By James Roman 
NASA Flight Research Center 
and 
Robert N. Sato* 
Project Consultant 
SUMMARY 
The Wright spirometer is a useful gas flowmeter for physiological use, in that it is 
The instrument was modified 
This modification provides a digital elec- 
The power drain is 96 milliwatts, which is small 
small and reliable. 
and the calibration curve is nonlinear at low flow values. 
by fitting the output shaft with a spoked wheel that interrupts the light beam between a 
low-power light source and a photonsensor. 
trical output that can be computer-reduced, permitting correction of the data for the 
nonlinearity of the calibration curve. 
enough to be drawn from the battery supplies of most self-contained miniature tape 
recorders. 
However, data collected with this device must be reduced manually, 
INTRODUCTION 
The measurement of respiratory minute volume is of considerable interest to both 
the clinician and the physiologist. This measurement has been extended only rarely 
into the dynamic environment, usually by means of large, cumbersome spirometers. 
Smaller devices are available with which to measure mass flow; however, the conver- 
sion from mass flow to minute volume requires that pressure and temperature be avail- 
able, which significantly complicates the measurement of respiratory volume. 
The well-known Wright spirometer (fig. 1) is an excellent device for measuring 
mass flow, in that it is small and reliable; however, for measuring respiratory volumes 
and rates in the flight environment it is not entirely adequate in two respects. First, 
it does not feature an electronically recordable output, which requires that the instru- 
ment be read every minute and the reading recorded manually. Second, the calibration 
of the device is nonlinear; that is, the relationship between volume through the instru- 
ment and the reading of the instrument does not remain constant over an adequately 
large range. 
*Ph. D. candidate, Department of Electrical Engineering, University of Southern 
Calif. , employed as instrumentation consultant by the Flight Research Center for this 
project. 
- - -  - 
Because of the small size of the Wright spirometer, the advanced stage to which 
its development was carried, and its proved reliability, it was decided to circumvent 
both these deficiencies by modifying the device to provide a digital electrical output. 
Through this modification, the device provided one square wave pulse for every unit of 
volume that flowed through it. Since all the biomedical information of the flight re- 
search program (ref. 1) under which this device was developed is computer-reduced, 
it was simple to make the calibration factor of the device dependent upon instantaneous 
flow. 
This paper discusses the modifications made to the Wright spirometer and the 
performance of the modified instrument. 
DESCRIPTION OF THE BASIC INSTRUMENT 
The Wright spirometer* (fig. 1) is designed to measure gas volume. This is pre- 
sented on the dials on the face of the device. The unmodified instrument operates as 
follows: The gas entering the unit is distributed through near-tangential slots in a 
E-16851 
Figure 1.- The Wright spirometer a s  available commercially. 
*Invented by Dr. B. M. Wright of the National Institute for Medical Research 
(England). 
2 
cylindrical stator and impinges upon a flat, blade-like rotor before leaving the stator 
axially through the outlet. The flat rotor, mounted on a shaft, rotates as a result of 
the gas flow through the slots (fig. 2). The axis of these slots is not radial but is 
directed at an angle to a radius through the slot centerline. The angular velocity of 
the rotor blade is approximately proportional to the flow through the instrument. 
rotor shaft is coupled to the watch-like hands on the dial of the device through a gear 
train. The housing containing the gear train and bearings is mercury-sealed against 
moisture. The bearings are jeweled. Flow through the device is one way. The mech- 
anism is designed to minimize the angular moment of inertia of the rotor and gear train. 
The spirometer registers total volume passed through it, until reset. It can be used to 
determine mean flow rates when employed in conjunction with a stopwatch. 
The 
Shaft 
Rotor blade -Slots 
Figure 2.- Cross-section of the Wright spirometer showing how the inlet gases acquire an angular velocity 
proportional to flow rate. 
MODIFICATION OF THE INSTRUMENT 
The modifications made to the spirometer to enable it to provide a digital electrical 
output consisted of removing the dial and hands and substituting for them a spoked wheel 
that interrupts the light from a miniature lamp to a semiconductor photonsensor, and 
installing a signal-conditioning amplifier. 
On the unmodified instrument a complete revolution of the upper hand (fig. 1) is 
produced when 1 liter of gas has passed through the spirometer. A spoked wheel 
(10 spokes) was substituted for the 1-liter hand, and all gears except those necessary 
to drive the 1-liter shaft were removed along with the 100- and 10,000-liter shafts. 
3 
The miniature lamp was placed within the circumference of the spoked wheel to serve 
as a light source for a pair of photosensitive semiconductor devices (figs. 3 and 4). 
Light-interrupter wheel 
(a) Assembly drawing. 
k . 2 3  4 
(b) Side view of photonsensor, miniature 
light, and spoked-wheel assembly. 
(c) Top view of photonsensors and 
spoked-wheel assembly. 
Figure 3.- The modified Wright spirometer. Dimensions in inches unless otherwise noted. 
4 
E-15726 
Figure 4.- The modified Wright spirometer. 
- Detector and amplifier 
The passage of each spoke across the light source results in a clean square pulse at the 
output of the signal-conditioning amplifier. A simplified block diagram of the signal- 
conditioning circuitry is shown in figure 5. 
output ---J 
Housed i n  the spirometer 
I--- 
U -6 volts 
Figure 5.- Simplified block diagram of signal-conditioning circuitry. 
5 
Volume is computer-reduced by counting the number of pulses, and flow is com- 
puted by noting the number of pulses per unit time. Each pulse is equivalent to 
0.1 liter. This resolution is adequate for most respiration work in which mean values 
€or 1 minute are used. For breath-by-breath respiration work, this resolution would 
not be adequate, and a different wheel would have to be used. 
A second photonsensor was used to cancel modulated readings due to fluctuations in 
the source intensity. This second sensor also provides temperature compensation by 
forming a bridge network with the primary sensor. Because power conservation was of 
prime importance, a power converter rather than a resistor was used to drop the 
+6-volt dc battery supply voltage to that required by the lamp. The overall power re- 
quired for the modified spirometer system, including the signal conditioner, is 
96 milliwatts. Thus, use in limited power source applications such as battery-powered 
tape-recorder systems is possible. 
CALIBRATION 
The modified spirometer was calibrated to determine the response time and 
linearity of the system. 
In order to determine response time, a pressure step function was applied by first 
flaming the balloon shown on the right in figure 6 and then, as quickly as possible, 
flaming the balloon shown on the left. A square wave pressure differential was thus 
I-- 
I 
I Direct-write 
I oscillograph 
Filler 
va Ive 
I I  
Wedge 
spirometer 
W IElectrical output 
I Galvanometer 
I 
I n 
Flow I 
I 
l H i g h -  
impedance 
output 
Figure 6.- Mechanical and electrical experimental setup for determining the response time of the modified 
Wright spirometer. 
6 
I 
generated. The output pulses from the modified Wright spirometer and the output of 
the Wedge spirometer were  recorded. A typical result from this experiment is shown 
in figure 7. The modified device is seen to accelerate to essentially steady-state 
angular motion in well under 1/10 second at the impressive flow rate of 
150 liters/minute. 
rotor blade to reach steady-state rotation velocity is short with respect to the period of 
respiration. In fact, the time required for acceleration of the rotor blade to peak 
velocity was so short that, without further quantitative analysis, it is concluded that 
the response time of the system would not introduce appreciable e r ror  in volume o r  
flow measurements when this device is used for routine human respiratory studies. 
This response is sufficiently fast  that the time required for the 
Time + 
Figure 7.- Typical experimental data obtained with the setup diagramed in figure 6. 
The linearity calibration was carried out using the experimental setup shown in 
figure 8. A Wedge spirometer was used as the standard for both flow and volume cali- 
bration. Mechanical inertia effects in the Wedge spirometer were minimized by making 
all measurements in steady flow. 
for both volume and flow. In order to minimize scatter of Wright spirometer data due 
to the fact that the resolution of the modified Wright spirometer is only 0 .1  liter, 
volume measurements were made on samples of not less than 10 liters. An unmodified 
Wright spirometer was inserted in series with the modified spirometer to determine 
what effect, if any, the mechanical modifications may have had on the linearity of the 
device. 
The Wedge spirometer provided electrical outputs 
7 
It- 
loo 
90 
80- 
70 
60- 
50 
40 
30 
20 
10 
0 
n r l  
- 
- 
- 
- 
- 
- 
- 
- 
I I I I I I I I I 1 I  
.1 .2 .3 .4 .5  .6 .7 .8 . 9  1.0 1.1 
-- I I  
Air 
source 
tubing 
I 
I Volume 
I 
I Direct-write 
I oscillograph 
I 
I 
I 
I 
I 
I "Ohme 
I Flow 
I 
U 
Va Ive 
(Collins) 
P 339 
1 11 11441-1. tubing Dial face reading 
I I  
Unmodified 
sDirometer 
""## Modified Wright Wright I 
absorber spirometer 
Signal 
spirom-+-- 1 
Galvanometer High conditioner 
impedance 
electrical - 1  
- 1  /1 I I I I - . .put 
e n o m e t , ) + - e  conditioner 1-1 
Figure 8.- Mechanical and electrical experimental setup for linearity calibration of the modified Wright spirometer. 
The data obtained in this experiment are tabulated in tables I and 11 and presented 
in figures 9(a) and 9(b). As shown in the figures, nonlinear effects occur primarily at 
- d
U 
Volume ratio, Wright spirometerNedge spirometer 
(a) Unmodified. (b) Modified. 
Figure 9.- Calibration curves for the unmodified and modified Wright spirometers. 
8 
flows of less than 20 liters per minute. 
showed smaller e r ror  than the unmodified version, probably because of the decreased 
angular moment of inertia and reduction of friction in the gear train of the modified 
device, as a result of the removal of some of the moving parts. Using the calibration 
plot shown in figure 9(b), it is relatively simple to program the computer reduction of 
the electrical output of the modified flowmeter to provide automatic correction of out- 
put data, based on these instantaneous flow-rate values. 
For higher flow rates, the modified spirometer 
CONCLUDING REMARKS 
As more and more monitoring is done on active patient , the demand will increase 
for small devices that can accurately measure respiratory llow, provide an output 
suitable for computer reduction of the information, and have a power drain sufficiently 
small to be supplied by batteries of self-contained tape recorders used to record the 
information. The modified Wright spirometer should provide a useful addition to the 
sensors available to those interested in dynamic monitoring. 
Flight Research Center , 
National Aeronautics and Space Administration, 
Edwards, Calif. , September 8,  1967, 
127-49-06-02-24. 
REFERENCE 
1. Roman, James: Long-Range Program to Develop Medical Monitoring in Flight. 
The Flight Research Program-I, Aerospace Medicine, vol. 3 6 ,  no. 6,  June 1965, 
pp. 514-518. 
9 
6 
TABLE I. -UNMODIFIED SPIROMETER DATA 
Spirometer 
WC 
Flow, liters/min 
3.63 
3.70 
3.92 
4.07 
5.18 
5.40 
5.92 
6.82 
8. 15 
8.30 
12.20 
14.49 
14.82 
16.10 
17.90 
19.80 
20.75 
21.10 
22.60 
23.70 
25.30 
26.80 
26.85 
28.30 
29.30 
33.82 
41.04 
42.50 
45.60 
48.40 
50.50 
53.88 
55.00 
57.30 
57.90 
62.34 
65.04 
65.20 
70.80 
73.49 
94.56 
107.90 
128.64 
132.00 
132.00 
160.28 
171.50 
193.00 
195.50 
214.00 
216. 12 
231.36 
238.20 
241.50 
265.98 
287.00 
e 
Volume. liters 
0.915 
3.960 
4.820 
3.750 
1.840 
3.490 
2.880 
5.160 
3.220 
3.750 
3.360 
3.690 
3.450 
4.140 
4.200 
3.920 
4.140 
3.820 
4.050 
4.360 
4.370 
4.280 
4.100 
4.020 
4.340 
3.940 
4.100 
4.440 
4.100 
4.750 
4.070 
4.080 
4.660 
3.910 
3.920 
4.200 
4.510 
4.380 
4.180 
4.210 
4.220 
5.360 
3.770 
4.070 
4.040 
4.000 
5.600 
5.370 
4.590 
5.900 
4.520 
4.250 
5.050 
5.930 
4.490 
6.760 
Wright 
Volume. liters 
~~ ~ ~ 
0.550 
2.160 
2.870 
2.300 
1.340 
2.640 
2.160 
4.200 
2.780 
3.130 
3.180 
3.610 
3.360 
4.030 
4.130 
3.950 
4.180 
3.890 
4.140 
4.440 
4.530 
4.440 
4.230 
4.170 
4.570 
4.210 
4.420 
4.830 
4.440 
5.125 
4.470 
4.500 
5.120 
4.290 
4.400 
4.680 
4.950 
4.820 
4.630 
4.680 
4.730 
6.070 
4.290 
4.630 
5.050 
4.600 
6.530 
6.170 
5.300 
6.760 
5.160 
4.870 
5.340 
6.850 
4.820 
7.710 
~ ~~ ~~~ 
~ - - 
Volume ratio 
Wright spirometer/Wedge spirometer 
0.600 
.546 
.596 
.613 
.727 
.756 
.750 
.814 
,864 
.835 
.947 
.978 
.974 
.974 
.983 
1.010 
1.010 
1.020 
1.024 
1.020 
1.037 
1.038 
1.032 
1.038 
1.050 
1.067 
1.078 
1.089 
1.080 
1.079 
1.100 
1.100 
1.099 
1.100 
1.120 
1.110 
1.100 
1.090 
1.110 
1.110 
1.120 
1.134 
1.130 
1.130 
1.130 
1.150 
1.166 
1.150 
1.150 
1.146 
1.140 
1.140 
1.060 
1.165 
1.075 
1.140 
~ ~~ ~~ ~~ 
~~ 
~ 
10 
TABLE II. - MODIFIED SPIROMETER DATA 
u 
Flow, liters/m 
3.92 
4.07 
5.03 
5.18 
5.40 
5.92 
6.82 
8. 15 
8.30 
10.31 
10.80 
12.20 
12.85 
13.75 
13.92 
14.82 
16.10 
17.90 
19.80 
20.30 
20.75 
21.10 
22.60 
23.70 
25.00 
25.30 
26.80 
28.30 
29.30 
41.04 
45.60 
50.50 
53.88 
57.30 
57.90 
62.34 
45.04 
AS. 50 
70.80 
73.49 
75.80 
82.50 
89.10 
94.56 
102.00 
105.10 
106. 50 
128.20 
128.64 
132.00 
132.00 
154.50 
160.28 
164.00 
170.10 
180.00 
187.50 
195.50 
200.00 
216. 12 
230.50 
231.36 
234.20 
238.20 
255.00 
265.98 
NASA-Langley, 1967 
Spirometer-- 
Volume. liters 
4.820 
3.750 
1.300 
1.840 
3.490 
2.880 
5.160 
3.220 
3.750 
2.020 
1.970 
3.360 
2.310 
3.360 
2.380 
3.450 
4.140 
4.200 
3.920 
3.210 
4.140 
3.820 
4.050 
4.360 
3.990 
4.370 
4.280 
4.020 
4.340 
4.100 
4.100 
4.070 
4.080 
3.910 
3.920 
4.200 
4.510 
4.470 
4.180 
4.210 
4.410 
4.780 
4.730 
4.220 
5.250 
5.110 
5.080 
6.360 
3.770 
4.070 
4.440 
5.550 
4.000 
5.140 
4.830 
4.560 
4.580 
4.590 
5.130 
4.520 
5.740 
4.250 
5.400 
5.050 
5.340 
4.490 
14 H-494 
Wright ~ 
irolume. liters 
~ 
- 
-
1.600 
1.620 
.eo0 
1.160 
2.400 
1.970 
3.900 
2: 600 
2.930 
1.700 
1.700 
3.000 
2.110 
3.100 
2.300 
3.200 
3.900 
4.000 
3.800 
3.100 
4.000 
3.170 
4.000 
4.300 
3.900 
4.400 
4.300 
4.000 
4.400 
4.300 
4.300 
4.200 
4.300 
4.100 
4.200 
4.500 
4.800 
4.800 
4.500 
4.500 
4.600 
5.100 
5.100 
4.500 
5.600 
5.500 
5.400 
6.900 
4.100 
4.400 
4.800 
6.000 
4.400 
5.500 
5.200 
5.000 
5.100 
5.200 
5.800 
5.100 
6.500 
4.800 
6.100 
5.700 
6.000 
5.000 
Volume ratio 
Wright spirometer/Wedge spirometer 
0.332 
.460 
.615 
.730 
.688 
.685 
.760 
.813 
.780 
.e32 
.E64 
.e92 
.908 
.923 
.966 
.918 
.944 
.970 
.966 
.966 
.970 
.990 
.987 
.978 
1.005 
1.003 
.997 
1.012 
1.050 
1.050 
1.030 
1.050 
1.050 
1.070 
1.070 
1.060 
1.075 
1.080 
1.070 
1.043 
1.066 
1.077 
1.070 
1.067 
1.077 
1.064 
1.090 
1.080 
1.080 
1.090 
1.080 
1.100 
1.070 
1.076 
1.097 
1.110 
1.130 
1.130 
1.130 
1.130 
1.130 
1.130 
1.130 
1.124 
1.110 
.955 
11 
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A useful modification of the Wright spirometer

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