W. S. TOPHAM 
1239 
time is done on a general-purpose digital com- 
puter. 
During recent experiments/^'^^ it was de- 
sired to have the animal in as normal state as 
possible while data was being obtained. There- 
fore, a technique was developed which allowed 
the insertion of an arterial catheter without an- 
esthetizing the animal. This technique involves 
injecting a local anesthetic into the neck of the 
dog. After the anesthetic has taken effect, a 
small mid-line incision is made and the right or 
left carotid artery is disected out. Care must be 
taken not to stimulate the vagus nerve as the 
carotid sheath is cut and the artery and nerve 
are separated. In a dog, the distal portion of the 
artery can then be tied off without any ill ef- 
fects. A small incision is made in the artery and 
a catheter is inserted until a good central aortic 
pressure waveform is obtained. The insision is 
then sutured closed and the catheter tied. The 
animal can be used immediately for experimen- 
tation such as exercise runs on the treadmill. 
Since the catheter is tied in by the suture and is 
flushed daily with heparinized saline, the prepa- 
ration will last for several days, and repeated 
experiments can be performed. This technique 
was also used for the insertion of catheter tip 
transducers, thus allowing more accurate meas- 
urement of the central aortic pressure and elim- 
inating any distortion which might be caused 
by catheter movement in relation to an external 
pressure transducer. 
OXYGEN SATURATION 
The partial pressures of blood gases can be 
measured using standard clinical laboratory in- 
struments, as can pH. The per cent of hemo- 
globin saturated with oxygen (O2 saturation) 
can also be measured in the laboratory, but 
more rapid methods for on-line use have been 
developed. One of these methods requires the 
use of a cuvette oximeter, through which a sam- 
ple of blood is drawn. The intensities of trans- 
mitted IR (805 mfi) and R (630 m/x) light is 
measured from the output of selenium oxide 
photoelectric cells. The ratio of these intensities 
is logarithmically related to O2 saturation, and 
by using a two-point calibration, the saturation 
can be obtained. The logarithmic equation can 
be solved by using analog circuitry and a meter 
readout, or voltages proportional to the light in- 
tensity can be fed directly into a computer for 
on-line calculation and data storage. This latter 
method has helped in reducing the manual han- 
dling of data and provided an instantaneous 
digital readout. 
Cuvette oximetry has been used for many 
years, and while it provides a rapid method of 
determining O2 saturation, a blood sample must 
be drawn through the instrument and continu- 
ous measurement is very difficult. In many cir- 
cumstances, continuous measurement without 
withdrawing blood samples is desirable either 
because the rapid time course of saturation is 
needed or because the loss of blood is detrimen- 
tal to the experiment. This problem has been 
solved using fiberoptics and the reflection of 
light from the bloodstream.20.21,22 -y^ith the 
use of light-emitting diodes and solid-state pho- 
tosensitive devices, the method has been im- 
proved, and recently a solid-state fiberoptic oxi- 
meter was reported.2^'2* The oximeter uses a 
5-French catheter with a center lumen and the 
fiberoptics positioned around the lumen. It is 
this catheter that makes the unit particularly 
useful in experiments. With the insertion of one 
catheter in the aortic arch, not only can contin- 
uous O2 saturation be measured, but blood sam- 
ples can be drawn for blood gas and blood chem- 
istry determination. In addition, central aortic 
pressure can be measured and hemodynamic 
variables can be calculated as stated previously. 
With an additional catheter in the central 
venous system, venous saturation can be contin- 
uously monitored and an A-V difference calculat- 
ed. From this difference and an O2 consumption 
measurement, cardiac output can be calculated 
using the method of Fick. Also, the central 
venous pressure can be measured. It is possible 
to calculate cardiac output using the indicator 
dilution method if dye is injected into the ven- 
ous catheter and the arterial catheter is used to 
detect dye concentration. This would require a 
change in wave length of the IR light-emitting 
diode from 900 m^ to 805 mfi, and although 
such a diode is available, it has not been used in 
the present system. 
If this method of O2 saturation measurement 
is used in animal experiments, not only are the 
