1238 
MONITORING 
Figure 6. — Venous pressure changes in an exercising animal as measured with pulse-driven catheter tip pressure 
transducers. 
during exercise, the waveforms look clean, and 
we can be assured that the mean level shifts 
that we see are due to actual pressure changes 
and not due to the change in zero because of 
temperature instability. The change in pressure 
due to blood temperature change is very small, 
as is shown in the Channel 3 tracing. The mean 
increase of inferior vena cava pressure at the 
onset of exercise and the mean decrease of right 
atrial pressure was typical of the responses ob- 
served in this experiment. 
This new method of pulsing catheter tip 
transducers can be used for any such transducer 
and would provide zero stability for in vivo 
applications. 
Arterial Pressure 
A single catheter inserted into the aortic arch 
can provide much information about the car- 
diovascular system. Using the method of 
Warner, 1^ stroke volume can be calculated 
from this aortic pressure waveform, and in 
turn, heart rate, cardiac output, mean pressure, 
and peripheral resistance can also be observed 
on a beat-to-beat basis. In addition, it is possible 
to determine systolic duration, stroke work, and 
obtain a measure of dP/dT. While thi • informa- 
tion can be obtained by the insertion of only one 
catheter, it does require sophisticated analysis 
of the pressure waveform which at the present 
