Breathing-metabolic simulator was developed to be used for evaluation of life support equipment. Apparatus simulates human breathing rate and controls temperature and humidity of exhaled air as well as its chemical composition. All functions are designed to correspond to various degrees of human response

Bartlett, R. G.

Hendricks, C. M.

Morison, W. B.

English

The development of a breathing metabolic simulator (BMS) is reported. This BMS simulates all of the breathing and metabolic parameters required for complete evaluation and test of life support and resuscitation equipment. It is also useful for calibrating and validating mechanical and gaseous pulmonary function test procedures. Breathing rate, breathing depth, breath velocity contour, oxygen uptake, and carbon dioxide release are all variable over wide ranges simulating conditions from sleep to hard work with respiratory exchange ratios covering the range from hypoventilation. In addition, all of these parameters are remotely controllable to facilitate use of the device in hostile or remote environments. The exhaled breath is also maintained at body temperature and a high humidity. The simulation is accurate to the extent of having a variable functional residual capacity independent of other parameters

NASA Technical Reports Server

BREATHING METABOLIC SIMULATOR 
R .  G. Bartlett, C. M. Hendricks, and W. B. Morison 
Federal Systems Division 
International Business Machines Corporation 
Gaithersburg, Md. 
INTRODUCTION 
I The NASA Office of Advanced Research and Technology and the Bureau of Mines have jointly 
funded the development of a breathing metabolic simulator (BMS) under contract NASW-2032. 
This BMS simulates all of the breathing and metabolic parameters required for complete evaluation 
and test of life support and resuscitation equipment. It is also useful for calibrating and validating 
mechanical and gaseous pulmonary function test procedures. Breathing rate, breathing depth, 
~ + breath velocity contour, oxygen uptake, and carbon dioxide release are all variable over wide ranges 
simulating conditions from sleep to  hard work with respiratory exchange ratios (R) covering the 
range from hypoventiliation to  hyperventilation. In addition, all of these parameters are remotely 
controllable to  facilitate use of the device in hostile or remote environments. The exhaled breath is 
also maintained at body temperature and a high humidity. The simulation is accurate to the extent 
of having a variable functional residual capacity (FRC) independent of other parameters. 
I SIMULATION DESIGN CONSIDERATIONS 
1 The following breathing characteristics were considered in implementing the BMS design. 
I 
I Breathing Rate 
The breathing rate adjustment provided by the BMS covers the rates that occur in the human, 
ranging from rest to  hard work conditions, Although this wide range is available, most subjects 
would fall into a much narrower range. 
! Breathing Depth 
I The breathing depth adjustment provided by the BMS covers a wide range up  to 3 literslbreath. 
Although an individual breath may exceed 3 liters under some conditions, the depth under 
continuous hard exercise should not exceed simulator capacity. Individual breath (tidal volume) is 
normally on the order of 0.5-0.6 liter under rest conditions, and it increases with activity. The 
I 
minimum simulator capacity includes this normal rest capacity. Selection of the appropriate 
combination of breathing rate and depth will allow the simulation of a wide range of breathing 
1 activity. 
I For special applications the breathing depth can be made greater than 3 liters. i t  can be made to 
i simulate a full vital capacity (e.g., 6 liters). 
Velocity-Time Waveform 
The breath velocity pattern in the human is not generally represented by a true sinewave. It may 
vary from a slightly blunted sinewave under some conditions to a drastic variation under conditions 
https://ntrs.nasa.gov/search.jsp?R=19720019479 2020-03-23T12:32:59+00:00Z
encountered during forced exhalation. To provide a faithful simulation, a waveform control is 
provided, allowing a wide range of variations from a basic sinewave. 
Functional Residual Capacity 
The FRC is the volume of air remaining in the lungs at the end of normal exhalation. To obtain 
faithful simulation, the FRC must remain constant for breathing rate or depth changes or both. It is 
also necessary t o  have the FRC variable so that individuals with different FRCs can be simulated. 
Both of the conditions are provided by the BMS. 
Exhaled Breath Temperature and Humidity 
In the human the exhaled breath is at body temperature and, except for conditions of extremely 
hard breathing, is at 100 percent relative humidity. Both of these conditions are provided by the 
BMS. 
Oxygen Consumption 
The simulation of the metabolic range between sleep and medium hard work requires a variable 
oxygen consumption rate. The range of the adjustable consumption rate of the BMS includes these 
conditions. For special applications the BMS can be made to simulate maximum oxygen 
consumption rates for the human undergoing maximum physical work. 
Carbon Dioxide Production 
The amount of carbon dioxide produced in the human is related to  the amount of oxygen 
consumed. This ratio os 0.707 if the fuel is fat and is 1.0 if the fuel is carbohydrates. This ratio, 
when referenced to tissue metabolic activity, is referred to as the respiratory quotient (RQ). When 
referenced to the ratio of gases in the exhaled breath (as in the BMS), it is referred to  as the 
respiratory exchange ratio (R). (This differentiation is made because an individual may be 
underbreathing or overbreathing, markedly affecting the amount of carbon dioxide removed from 
the body and thus the value of R.)  To simulate these conditions, the BMS provides a range of 
carbon dioxide/oxygen (R) wider than the normal range of 0.7 t o  1 .O. 
HARDWARE FUNCTIONAL DESCRIPTION 
The BMS has been implemented in a configuration that may be described as consisting of three 
subsystems: temperature/hurnidity, breathing, and metabolism. These subsystems are shown in the 
simplified system schematic (fig. 23.1 ) and are then described individually. Performance 
specifications are shown in table 23.1. 
TemperatureIHumid ity Subsystem (fig. 23.2) 
Functions. Incoming air from the artificial trachea is fed into an exchange box, where it is 
blocked from entering the humidity chamber by a check valve. The air then passes through another 
check valve and enters the main connection to the top of the bellows during bellows expansion. 
Outgoing (exhaled) air comes from the main connection to  the top of the bellows during bellows 
contraction. The air passes through a check valve and enters the input end of the humidity chamber. 
The air entering the chamber displaces air from the output end of the chamber through a check 
valve, where it enters the exchange box and exits to  the artificial trachea. 
Features. The check valves and exchange box are used to  control air flow direction and to permit 
a single connection to  the artificial trachea. 
TEMPERATURE,/HUWIDITY 
- 1 
METABOLISM 
- - - -- - - - - - - - - - - - - - - - - - - 
FLU\': METER 
- - - -  1 
I 
I 
ELLOVJS POSITION I I 
I 
1 
I 
I 
I 
I 
- - - - - - - - - - - - -  J 
BREATHING 
1 Figure 23.1 Simplified system schematic. 
I 
I Table 23.1 Performance specifications. 
I 
Breathing Simulation Subsystem 
Rate adjustment 
Depth adjustment 
FRC adjustment 
Velocity-time waveform 
5-60 breathslminute 
400-3000 mllbreath (up to  6000 ml for special 
applications 
1,7 - 4.0 liters, constant with rate, depth and wave- 
form changes 
Variable, from sinewave t o  other shapes as obtained 
via 12 separately controllable velocity regions 
within a breath cycle 
1 HumiditylTemperature Subsystem 
Humidity Gas exhaled with a humidity between 96 percent and 
100 percent through medium high volumes, t o  90 
percent for extreme high volumes 
Temperature Gas exhaled with a temperature controlled t o  98.6" F 
within 2 2" F for all volumes 
Metabolic Simulation Subsystem 
O2 consumption rate Adjustable within the range of 250 to  2000 ml/min 
(up t o  3000 ml/min for special applications) 
C02  production rate Adjustable within a range to  produce a respiratory 
exchange ratio of 0.6 to  1.5. 
To/Frorn Bellows  
1 Water Reservoor 
e a r  T e r m o r  3 Imp 
Wet & Dry EiulbY 
Thermistors 
c 
H u m ~ d ~ t v  Chamber & Hedter 
Sample 
0 2  & C 0 2  Output  
Sampl~ng 
0 2  Level Safety 
Mor i~ to r  
0753IAB 
Figure 23.2 Temperature/humidity subsystem. 
The humidity chamber is used to add moisture to the exhaled air and to maintain temperature 
within specified limits. The moisture transfer media (surgical sponges) remain saturated with water 
from a separate reservoir. (Actual humidity is also affected by the dwell time of a breath inside the 
chamber.) Temperature maintenance, accomplished by a heater blanket in the bottom of the 
chamber, is controlled by a thermistor placed in the path of the chamber output. Heater power is 
remotely controlled by the appropriately labeled switch on the control unit. 
This subsystem also contains sensors for monitoring the characteristics of the air to be exhaled. 
Wet- and dry-bulb thermistors placed in the output end of the chamber can be monitored by 
positions 5 and 4, respectively, of the control unit digital voltmeter. A gas sample line connected to 
the chamber input end allows a sample pump, operating when the carbon dioxide analyzer is on, to 
extract gas samples, that are fed to the sensors of an oxygen analyzer and a carbon dioxide analyzer 
and returned to the chamber. The readout of these analyzers is accomplished on the control unit. 
(These analyzers can be calibrated from separate gas inputs, as described in detail in the operations 
manual.) 
Breathing Subsystem (Fig. 23.3) 
Functions. This subsystem controls expansion and contraction of a bellows to draw air from and 
expel air t o  the temperature/humidity subsystem. The bellows motion is independently variable in 
rate, magnitude of periodic motion and volume remaining at point of minimum periodic volume 
change. The periodic motion of the bellows is accomplished by a bellows drive motor operating a 
crankshaft/connecting rod combination through a 30: 1 gear reduction. The drive motor speed is 
I Figure 23.3 Breathing system. 
varied by means of a motor controller. Long-term variations, greater than one crankshaft revolution, 
correspond to  changes in breathing rate and are varied from the control unit by means of the 
labeled control. Short-term variations, within one crankshaft revolution, correspond to changes in 
breath waveform and are varied by the individual settings of 1 2  waveform controls on the control 
unit. Each control is effective during one-twelfth of a crankshaft revolution as determined by a 
12-position read switch. 
Connecting rod motion is transmitted to  the bellows by means of a lever arm operating on a 
movable fulcrum. Fulcrum motion along the lever arm varies the level arm ratio corresponding to 
changes in breath depth. This motion is accomplished by means of a lead screw from the fclcrum 
drive motor, which is in turn controlled by the bidirectional fulcrum switch on the control unit. 
Fulcrum driving toward minimum and maximum volume per breath is indicated on the control unit 
by the right and left limit lights illuminating, respectively. (The lights will extinguish if a limit is 
encountered while driving.) Fulcrum motion normal to the lever arm (i.e., moving the position of 
the bottom of the bellows for a fixed crank position and lever arm ratio) will change the minimum 
I bellows volume obtainable through periodic motion. This corresponds to a functional residual 
capacity adjustment and is controlled by a manual screw adjustment on the support for the fulcrum 
base. This adjustment has a scale calibrated in FRC volume in liters adjacent to  the screw. 
Features. The top of the bellows contains two separate gas lines to  provide an output to the 
compressor of the metabolism subsystem and to receive the output of this subsystem. 
Two separate magnetic flux type sensors are mounted between the bottom of the bellows and the 
adjustable support for the f~ilcrum base. These sensors measure position and velocity between 
mountings (thus sensing breath characteristics independent of FRC adjustment) and are input to the 
oscilloscope in the control unit, where either may be selected for waveform display. 
Metabolism Subsystem (fig. 23.4) 
Functions. This subsystem is used to control R .  Since R is a carbon dioxide to oxygen ratio, 
metabolism is simulated by consuming oxygen and producing carbon dioxide. This is accomplished 
by oxidizing propane and adding varying amounts of carbon dioxide in the following manner. 
Air is drawn from the top of the bellows by a compressor. The compressed air output is then fed 
to an accumulator used to eliminate surging caused by bellows motion. The accumulator output is 
connected to an adjustable orifice used to preset the flow rate for more than sufficient air for all 
oxidation conditions; the accumulator is then connected to a gas line input to the oxidation 
chamber. A size D tank of CP grade propane is fitted with a manual regulator (set to 1 5 psi). The 
regulator output is connected to a solenoid shutoff valve controlled by the manual switch on the 
control unit (and the series safety circuitry, discussed later). The solenoid valve output is connected 
to a remotely adjustable metering valve (controlled by valve enable and carbon dioxide adjustment 
on the control unit). The metering valve output is connected to a flow meter sensor (the flow meter 
is located on the control unit panel) and finally to the oxidation chamber input line. A size D 
carbon dioxide tank is fitted with a duplicate of the propane controls (except safety circuit not 
required) and also connected to the oxidation chamber input line. 
The oxidation chamber is an expanded line area (made of quartz) containing a probe input for a 
chamber thermocouple and surrounded by an encased insulated heating element. Power to the 
heater is manually controlled (ONIOFF only) from the control panel combustion heater switch and 
maintains the chambers temperature above that required for oxidation of propane. In operation, 
complete oxidation occurs with the chamber output having a carbon dioxide/oxygen ratio that is 
variable, dependent upon the carbon dioxide and propane flow rates into the chamber (air input is a 
constant). The chamber output is fed t o  a radiant series cooler to  reduce temperature t o  a safe level 
and then is returned to the top of the bellows. 
Features. A safety circuit (fig. 23.5) used to control propane flow will not allow the solenoid 
valve to be opened unless the proper oxidation conditions exist. The conditions monitored are the 
oxygen output level in the temperature/humidity subsystem, the compressor output pressure at the 
accumuiator, and tne chamber temperature at the output end. 
Remote  Cont ro l  
I 
O x i d ~ l l o ~ i  Chdmbr.r T tmpcrd ru re  
Manual Operdrc 
Figure 23.5 hopane safety control circuit. 
I The chamber thermocouple output can be monitored (position 3 of the digital voltmeter) to  
I determine temperature during preheating or other conditions as desired. Installation considerations 
are shown in table 23.2. Figures 23.6 and 23.7 are photographs of the device delivered under 
1 contract funded by NASA. 
I Table 23.2 Installation considerations. 
Physical Characteristics 
Control unit 
Simulator unit 
I 
Interconnection 
Electrical cables 
Size 60 in. H X 20 318 in. W X 19-718 in. D 
(including castered support cart) 
Weight approximately 200 lb 
Size 59 in. H X 18 in. W X 25-112 in. D 
Weight approximately 250 Ib 
4, with disconnects 
No other interconnections required. Length - 8 ft 
Table 23.2 Installation considerations. (Concluded) 
Electrical Input Characteristics 
Voltage 11 5 vac (60 cy) single phase, with ground 
Current Control unit input cable - less than 20 A 
Simulator unit input cable - less than 20 A 
Safety Cotzsideration 
Contains combustible gas and, for safety, should be used only in a well ventilated area. 
Output 
O 2 
Sampler  
C02 
Flow 
Propane  
Flow 
Waveform 
Displays 
Output 
C02 
Sampler  
Waveform 
Controls 
Tempera tu r e  
Sensor  
Readings 
Figure 23.6 Control unit functions. 
Breathing 
Mechanism 
Temp- 
Humidity 
Figure 23.7 Simulator unit functions. 
Metabolic 
Functions 
Output 
Sampling 
& 
Calibration 
The following expendables are required for operation: 
Carbon dioxide Air products size D tank (4 by 17 in.) 
Propane (CP) Air products size D tank (4 by 18 in.) 
Distilled water Reservoir capacity approximately 2.33 quarts 
Surgical sponge Parke-Davis gauze 4 by 8 in. approximately (one package of 100 required 
for replacement) 
BIBLIOGRAPHY 
1. Anon.: First Quarterly Progress Report BMS, April 27, 1970 to July 27, 1970 (IBM No. 
70-A95-0001) 
2. Anon.: Second Quarterly Progress Report BMS, July 27, 1970 to October 27, 1970 (IBM No. 
70-A95-000 1 ) 
3. Anon.: BMS Operations Manual, April 1 97 1 
4. Anon.: BMS Test Data Report, June 197 1 


Breathing metabolic simulator

October 1972	 B72-10657 
•	 NASA TECH BRIEF 
NASA Headquarters
	 4r 
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. 
Breathing - Metabolic Simulator 
The problem: 
Thorough evaluation of life support and resuscitation 
equipment requires the use of human subjects. Such a 
requirement, however, is not practical because no two 
humans provide an identical load to the equipment and no 
single individual is capable of supplying consistent load 
requirements. Thus, the only way to obtain meaningful 
evaluation of life support and resuscitation equipment is 
to use an apparatus which simulates human breathing. 
The solution: 
A breathing-metabolic simulator has been developed to 
be used for evaluation of life support equipment.
How it's done: 
The apparatus, as shown in the figure, simulates human 
breathing rate and controls temperature and humidity of 
exhaled air as well as its chemical composition. All of 
these functions are designed to correspond to various 
degrees of human response. 
The breathing rate in this system is maintained by 
bellows which are driven by a motor operating through 
the simulated breath mechanism. The motor speed is 
controlled by the simulated breath waveform control, 
which independently determines the rate and waveform 
pattern. Breath depth changes may be implemented 
remotely by energizing the fulcrum drive motor to vary 
TEMPERATURE/HUMIDITY
1 
'Fulcrum 
BREATHING 
Propane
(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=19720000656 2020-03-17T03:42:54+00:00Z
the lever arm ratio in the drive mechanism. In addition, 
functional residual capacity (FRC) adjustment is accom-
plished by moving the fulcrum normal to the lever arm 
(i.e., moving the position of the bottom of the bellows for 
a fixed crank position and lever arm ratio). 
Temperature and humidity of the breath exhaled from 
the bellows are adjusted by a humidification chamber 
where the temperature of exhaled air is raised to that of 
the human and moisture is added to obtain near satura-
tion of the chamber output upon succeeding breaths. The 
temperature is provided by a heat sheet located in the 
bottom of the chamber. It is controlled by sensor at the 
chamber output. Humidification is accomplished by pas-
sing the breath to be exhaled over a large area of surgical 
sponge which wicks moisture from water covering the 
heater. 
Exhaled breath composition corresponding to various 
metabolic rates is simulated by varying the output breath 
CO2 /02
 ratio (R). Oxygen is consumed and CO 2 pro-
duced to obtain various ratios by oxidizing propane gas 
fed from a storage cylinder after combination with 
compressed air gathered from the bellows. (Addition of 
CO2
 from storage allows rate changes.) This oxidation 
process occurs in a combustion chamber where the 
propane is heated above its ignition temperature. The gas 
is then cooled and returned to the bellows where it mixes 
with incoming air to form the proper output "R" value. 
The breathing metabolic simulator has several unique 
features: 
The combination of breathing and metabolic simula-
tion in the same simulator permits more comprehensive
testing of breathing equipment in that the simulation is 
much more realistic than could be obtained before. 
2. Separate packaging for the control unit and for the 
simulator unit itself permits testing of breathing 
devices in hostile environments and allows changes in 
value of test parameters to be accomplished without 
interruption of the test conditions. 
3. Continuously and independently variable rates for both 
breathing and metabolic parameters permit selection of 
an infinite number of simulated loadings within the 
wide range of the simulator capabilities. 
Notes: 
1. Additional information is contained in the following 
Tech Briefs: B72-10658 HQN-10776), B72-10659 
(HQN-10777), B72-10660 (HQN-10778), and 
B72-10661 (HQN-10779). 
2. Requests for further information may be directed to: 
Technology Utilization Officer 
NASA Headquarters 
Code KT 
Washington, D. C. 20546 
Reference: B72-10657 
Patent status: 
NASA has decided not to apply for a patent. 
Source: R. G. Bartlett, C. M. Hendricks, 
and W. B. Morison of
IBM Corp.
under contract to
NASA Headquarters
(HQN- 10766)
. 
B72-10657	 Category 05


Breathing-metabolic simulator

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