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A device for measuring oxygen consumption in the dog
A DEVICE FOR CONSUMPTION ROBERT
BOONE
MEASURING IN THE AND
THE determination of oxygen consumption during experimental and clinical stress has attracted renewed interest [ 1, 31. Traditionally, oxygen consumption has been measured with a spirometer, but this method requires continuous attention, and monitoring the experiment becomes laborious. Guyton et al. [2] has designed an excellent automatic device for measuring and computing both oxygen consumption and cardiac output, but despite many desirable features it is so elaborate that it is not available to many laboratories. However, we have devised a simple modification of the Collins spirometer which has been helpful to us in monitoring oxygen consumption over long periods. It is described below.
MATERIALS
AND
METHODS
The components required are: three microswitches (0.5 A., 110 V., single-pole, singlethrow); one solenoid (Square-D AG8); one Collins 13.5liter spirometer; one potentiometer (Fairchild 554); one Synchromotor timer (2 rph). The assembly of the components is illustrated in Figure 1. The axle of the potentiometer and the axle of the chain-wheel of From the Department of Surgery, University of Kentucky College of Medicine, Lexington, Ky. This work was supported by National Institutes of Health Grant AM 06956-05 and Office of the Surgeon General Grant DA49-193-MD-2348. Submitted for publication Sept. 21, 1966.
418
B.
F.
RUSH,
OXYGEN DOG JR.,
M.D.
the spirometer are directly connected. As the wheel turns with the rise or fall of the spirometer bell, the potentiometer is turned directly without hazard of slippage. The potentiometer must tolerate long wear. Our current unit is of resistant plastic and is still giving noise-free service after three years. An ordinary wirewound potentiometer previously used in this fashion had a service life of lessthan 8 months. Two microswitches are placed above and below the original pen mounting of the spirometer, separated by a distance equivalent to I3 liters of volume in the spirometer. A third microswitch is mounted on the timer. Oxygen is emptied from the spirometer by the experimental animal. Every 30 minutes the timer activates a microswitch which opens a solenoid acting as a valve between the pressure regulator of a cylinder of oxygen and the intake of the spirometer. Oxygen rushing in from the open solenoid enters the spirometer and the pen mounting drops until it touches the lower microswitch, which closes the solenoid and stops the intake of oxygen. The spirometer is now refilled to 13 liters. The potentiometer leads are connected directly to the galvanometers of a Honeywell polygraph, the current being great enough so that no amplification is required. The recording indicates the gradual change in potential as the spirometer is emptied and the sudden change produced by refilling. Each refill is equivalent to 30 minutes of oxygen consumption. In the unlikely event that the animal
BOONE
AND
RUSH:
A
DEVICE
FOR
MEASURING
OXYGEN
CONSUMPTION
IN
THE
DOG
The entire system, including spirometer, potentiometer, and galvanometer, is linear, and calibration is simple. A known excursion of the spirometer is equivalent with a known volume of gas, and the equivalent excursion of the recorder is directly obtained. A schematic diagram of the electrical system of this device is shown in Figure 2. A leak-free system is essential, and all components of the spirometer system must be carefully tested. The use of a mechanical respirator especially fabricated to eliminate leaks is of great help. The ordinary flutter valves often used in directing the flow of gaseshave some back leak and if used will cause an accumulation of CO, in the spirometer. An airtight pumping system acts not only to control respiration but also as a foolproof valve system. We originally designed a modification of the Harvard Model 607 pump for this use. Since that time an excellent pump has been devised which, in our hands, has been completely leakproof in a total of more than 500 experiments.* RESULTS Fig. 1.
Modified spirometerfor continuousmonitoring of oxygen consumption. consumes 13 liters in less than 30 minutes, the upper microswitch is tripped and the spirometer refills without interruption of the timer. This change is easily detected on the polygraph.
A polygraph record of the tracing obtained with this device is shown in Figure 3. Change in the slope of the tracing introduced by severe hemorrhagic shock can be detected directly, but the integration of the entire 30minute period of oxygen consumption is most accurately derived by measuring the sudden * Developed Mass.
by
Harvard
,4pparatus
Co.,
Dover,
OXYGEN TANK SOLENOID VALVE NORMALLY CLOSED
Electrical system of spirometer (schematic). SW 1: on-off toggle switch; SW 2: microswitch tripped by clock, normally open; SW 3: microswitch tripped by empty spirometer, normally open; SW 4: microswitch tripped at end of spirometerrefill, normally closed. Fig. 2.
419
JOURNAL
OF
SURGICAL
RESEARCH
VOL.
7
NO.
9,
SEPTEMBER
1967
150B P (MEAN) lnm Hg o-
Fig. 3. minutes.
Tracing Second
of oxygen consumption at top. First vertical change equals normal consumption vertical change equals oxygen consumption during 30 minutes of hemorrhagic
change in height of the tracing at the end of the time period.
REFERENCES 1.
SUMMARY
A simple modification of a Collins 13.5liter spirometer is described whereby oxygen consumption in dogs can be continuously monitored.
for 30 shock.
2.
3.
Crowell, J. W., and Smith, E. E. Oxygen deficit and irreversible hemorrhacic shock. Amer. J. Physiol. 206:313, 1964. Guyton, A. C., Farish, C. A., and Abernathy, J. B. A continuous cardiac output recorder employing the Fick principle. Circ. I&s. 7:661, 1959. ^ Rush, B. F., Rosenberg, J., and Spencer, F. Changes in oxygen consumption in shock: Correlation with other known parameters. J. Surg. Aes. 5~252, 1965.
BOONE
MEASURING IN THE AND
THE determination of oxygen consumption during experimental and clinical stress has attracted renewed interest [ 1, 31. Traditionally, oxygen consumption has been measured with a spirometer, but this method requires continuous attention, and monitoring the experiment becomes laborious. Guyton et al. [2] has designed an excellent automatic device for measuring and computing both oxygen consumption and cardiac output, but despite many desirable features it is so elaborate that it is not available to many laboratories. However, we have devised a simple modification of the Collins spirometer which has been helpful to us in monitoring oxygen consumption over long periods. It is described below.
MATERIALS
AND
METHODS
The components required are: three microswitches (0.5 A., 110 V., single-pole, singlethrow); one solenoid (Square-D AG8); one Collins 13.5liter spirometer; one potentiometer (Fairchild 554); one Synchromotor timer (2 rph). The assembly of the components is illustrated in Figure 1. The axle of the potentiometer and the axle of the chain-wheel of From the Department of Surgery, University of Kentucky College of Medicine, Lexington, Ky. This work was supported by National Institutes of Health Grant AM 06956-05 and Office of the Surgeon General Grant DA49-193-MD-2348. Submitted for publication Sept. 21, 1966.
418
B.
F.
RUSH,
OXYGEN DOG JR.,
M.D.
the spirometer are directly connected. As the wheel turns with the rise or fall of the spirometer bell, the potentiometer is turned directly without hazard of slippage. The potentiometer must tolerate long wear. Our current unit is of resistant plastic and is still giving noise-free service after three years. An ordinary wirewound potentiometer previously used in this fashion had a service life of lessthan 8 months. Two microswitches are placed above and below the original pen mounting of the spirometer, separated by a distance equivalent to I3 liters of volume in the spirometer. A third microswitch is mounted on the timer. Oxygen is emptied from the spirometer by the experimental animal. Every 30 minutes the timer activates a microswitch which opens a solenoid acting as a valve between the pressure regulator of a cylinder of oxygen and the intake of the spirometer. Oxygen rushing in from the open solenoid enters the spirometer and the pen mounting drops until it touches the lower microswitch, which closes the solenoid and stops the intake of oxygen. The spirometer is now refilled to 13 liters. The potentiometer leads are connected directly to the galvanometers of a Honeywell polygraph, the current being great enough so that no amplification is required. The recording indicates the gradual change in potential as the spirometer is emptied and the sudden change produced by refilling. Each refill is equivalent to 30 minutes of oxygen consumption. In the unlikely event that the animal
BOONE
AND
RUSH:
A
DEVICE
FOR
MEASURING
OXYGEN
CONSUMPTION
IN
THE
DOG
The entire system, including spirometer, potentiometer, and galvanometer, is linear, and calibration is simple. A known excursion of the spirometer is equivalent with a known volume of gas, and the equivalent excursion of the recorder is directly obtained. A schematic diagram of the electrical system of this device is shown in Figure 2. A leak-free system is essential, and all components of the spirometer system must be carefully tested. The use of a mechanical respirator especially fabricated to eliminate leaks is of great help. The ordinary flutter valves often used in directing the flow of gaseshave some back leak and if used will cause an accumulation of CO, in the spirometer. An airtight pumping system acts not only to control respiration but also as a foolproof valve system. We originally designed a modification of the Harvard Model 607 pump for this use. Since that time an excellent pump has been devised which, in our hands, has been completely leakproof in a total of more than 500 experiments.* RESULTS Fig. 1.
Modified spirometerfor continuousmonitoring of oxygen consumption. consumes 13 liters in less than 30 minutes, the upper microswitch is tripped and the spirometer refills without interruption of the timer. This change is easily detected on the polygraph.
A polygraph record of the tracing obtained with this device is shown in Figure 3. Change in the slope of the tracing introduced by severe hemorrhagic shock can be detected directly, but the integration of the entire 30minute period of oxygen consumption is most accurately derived by measuring the sudden * Developed Mass.
by
Harvard
,4pparatus
Co.,
Dover,
OXYGEN TANK SOLENOID VALVE NORMALLY CLOSED
Electrical system of spirometer (schematic). SW 1: on-off toggle switch; SW 2: microswitch tripped by clock, normally open; SW 3: microswitch tripped by empty spirometer, normally open; SW 4: microswitch tripped at end of spirometerrefill, normally closed. Fig. 2.
419
JOURNAL
OF
SURGICAL
RESEARCH
VOL.
7
NO.
9,
SEPTEMBER
1967
150B P (MEAN) lnm Hg o-
Fig. 3. minutes.
Tracing Second
of oxygen consumption at top. First vertical change equals normal consumption vertical change equals oxygen consumption during 30 minutes of hemorrhagic
change in height of the tracing at the end of the time period.
REFERENCES 1.
SUMMARY
A simple modification of a Collins 13.5liter spirometer is described whereby oxygen consumption in dogs can be continuously monitored.
for 30 shock.
2.
3.
Crowell, J. W., and Smith, E. E. Oxygen deficit and irreversible hemorrhacic shock. Amer. J. Physiol. 206:313, 1964. Guyton, A. C., Farish, C. A., and Abernathy, J. B. A continuous cardiac output recorder employing the Fick principle. Circ. I&s. 7:661, 1959. ^ Rush, B. F., Rosenberg, J., and Spencer, F. Changes in oxygen consumption in shock: Correlation with other known parameters. J. Surg. Aes. 5~252, 1965.