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REVIEW OF ANIMAL INSTRUMENTATION: 
TRANSDUCER CAPABILITY 
W. S. Topham' 
In almost all animal experiments designed lor evalua- 
tion of the cardiovascular system, the measurement of 
flow, pressure, electrical activity of the heart (ECG), 
and blood gasses, including oxygen saturation and pH, 
are important. While the electrocardiogram is the most 
frequently measured variable, it is somewhat more 
difficult to obtain in animals. Experience has shown 
that externally applied electrodes are more reliable 
than needle electrodes. Accurate and calibrated in 
vivo flow has been difficult to obtain, particularly if 
instantaneous flow measurement is desired. However, 
the electromagnetic flowmeter now has pre-calibrated 
probes available and an accurate electrical zero which 
allows zero flow to be determined at any time. This 
adds a new dimension to in vivo flow measurement. To 
accurately measure pressure, a catheter tip transducer 
is required ; but because of the temperature sensitivity of 
the transducer, it is difficult to calibrate the transducer 
after implantation. A method for reducing the tempera- 
ture drift is described, and accurate venous pressure 
measurements obtained while a dog is exercising are 
possible, using a pulsed excitation source for the cath- 
eter tip transducer. Frequent oxygen saturation meas- 
urements are difficult and somewhat tedious to perform 
when blood has to be drawn for each measurement. A 
fiberoptics oximeter using a 5-French catheter with a 
center lumen can give continuous oxygen saturation 
measurement, as well as pressure measurement. One 
catheter provides hemodynamic and blood gas measure- 
ment. 
INTRODUCTION 
To evaluate the function of the cardiovascu- 
lar system or the effects that circulatory assist 
devices have on this system, measurement of 
pressure, flow, electrical activity of the heart 
(ECG), blood gas content, and pH are of great 
importance. The particular flows and pressures 
measured are dependent upon the experiment 
being conducted or the device being evaluated. 
For instance, if the device under test is to in- 
crease or maintain the cardiac output and coro- 
* Manager, Dept. of Biophysics, Utah Biomedical Test Laboiatoiy, 
Salt Lake City, Utah. 
nary perfusion while at the same time reducing 
the workload on the heart, then coronary blood 
flow, aortic pressure, and total flov^^ in the aorta 
become of particular importance. The ECG is a 
good indicator of the rhythm and electrical tim- 
ing of the heart. This information is particu- 
larly important if the heai-t has been insulted or 
if it is necessary that an assist device function 
synchronously with the heart beat. Blood gas 
measurements provide information as to 
vi^hether the circulatory system is carrying out 
its function of oxygen transport and CO2 re- 
moval. Oxygen saturation measurements give 
indication of the effectiveness of the circulatory 
system in performing these functions, but 
measurement of the partial pressure of oxygen, 
CO2 and pH provide added insight. Since one or 
more of these measurements, flow, pressure, 
ECG, or blood gas, is basic to cardiovascular ex- 
perimentation, it will be the purpose of this 
paper to describe some methods and limitations 
in obtaining accurate measurement of these 
variables. 
ECG MEASUREMENT 
The ECG is probably the most frequently 
measured parameter because it can be obtained 
with non-invasive techniques. However, its sim- 
plicity of measurement is reduced in animal 
work because of the difficulty in obtaining good 
electro-contact through the fur of the animal. 
While subcutaneous electrodes are suggested, 
obvious and simple surface electrode methods 
have provided good ECGs in our animal experi- 
ments. In exercising dogs, it was found neces- 
sary to shave the contact area very closely, ei- 
ther with a safety razor or a fine set of clippers, 
and clean the area with a surgical scrubbing 
brush, scrubbing not only to clean the area, but 
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