A DEVICE FOR MEASURING OXYGEN CONSUMPTION IN THE DOG

ROBERT BOONE AND B. F. RUSH, JR., M.D.

THE determination of oxygen consumption during experimental and clinical stress has at- tracted renewed interest [ 1, 31. Traditionally, oxygen consumption has been measured with a spirometer, but this method requires continu- ous attention, and monitoring the experiment becomes laborious. Guyton et al. [2] has de- signed an excellent automatic device for mea- suring and computing both oxygen consump- tion 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 micro- switches (0.5 A., 110 V., single-pole, single- throw); one solenoid (Square-D AG8); one Collins 13.5liter spirometer; one potentiom- eter (Fairchild 554); one Synchromotor timer (2 rph). The assembly of the components is illustrated in Figure 1. The axle of the poten- tiometer 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.

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the spirometer are directly connected. As the wheel turns with the rise or fall of the spirom- eter 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 wire- wound potentiometer previously used in this fashion had a service life of less than 8 months.

Two microswitches are placed above and below the original pen mounting of the spi- rometer, 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 pres- sure 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 sole- noid and stops the intake of oxygen. The spi- rometer is now refilled to 13 liters.

The potentiometer leads are connected di- rectly to the galvanometers of a Honeywell polygraph, the current being great enough so that no amplification is required. The record- ing 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 consump- tion. In the unlikely event that the animal

BOONE AND RUSH: A DEVICE FOR MEASURING OXYGEN CONSUMPTION IN THE DOG

Fig. 1. Modified spirometer for continuous mon- itoring of oxygen consumption.

consumes 13 liters in less than 30 minutes, the upper microswitch is tripped and the spirom- eter refills without interruption of the timer. This change is easily detected on the poly-

graph.

The entire system, including spirometer, po- tentiometer, 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 sche- matic diagram of the electrical system of this device is shown in Figure 2.

A leak-free system is essential, and all com- ponents of the spirometer system must be carefully tested. The use of a mechanical res- pirator especially fabricated to eliminate leaks is of great help. The ordinary flutter valves often used in directing the flow of gases have some back leak and if used will cause an ac- cumulation of CO, in the spirometer. An air- tight pumping system acts not only to control respiration but also as a foolproof valve sys- tem. 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 com- pletely leakproof in a total of more than 500 experiments.*

RESULTS

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 di- rectly, but the integration of the entire 30- minute period of oxygen consumption is most accurately derived by measuring the sudden

* Developed by Harvard ,4pparatus Co., Dover, Mass.

OXYGEN TANK SOLENOID

VALVE NORMALLY CLOSED

Fig. 2. 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 spirometer refill, normally closed.

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JOURNAL OF SURGICAL RESEARCH VOL. 7 NO. 9, SEPTEMBER 1967

150- B P (MEAN)

lnm Hg o-

Fig. 3. Tracing of oxygen consumption at top. First vertical change equals normal consumption for 30 minutes. Second vertical change equals oxygen consumption during 30 minutes of hemorrhagic shock.

change in height of the tracing at the end of the time period.

REFERENCES

1. Crowell, J. W., and Smith, E. E. Oxygen deficit and irreversible hemorrhacic shock. Amer. J.

SUMMARY - Physiol. 206:313, 1964.

2. 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. ̂ -

3. Rush, B. F., Rosenberg, J., and Spencer, F. Changes in oxygen consumption in shock: Corre- lation with other known parameters. J. Surg. Aes. 5~252, 1965.

A simple modification of a Collins 13.5- liter spirometer is described whereby oxygen consumption in dogs can be continuously monitored.