1092 
MONITORING 
cathode ray tube outputs.^ These facilities are 
used for a number of projects simultaneously.'' 
In addition, the system has made it easy for us 
to have a stream of ideas which can be tested 
in series expeditiously. One does not get tied up 
in the generation of new hardware configura- 
tions, nor in the retraining of programmers 
as the experiments vary and progress (Figure 
2). 
Table I lists the major projects carried out 
as part of heart research by the Division of 
Cardiovascular Surgery at Stanford and shows 
the features of the system which were required. 
The bulk of this presentation consists of a 
description of the steps used by our group in 
studying the heart rate response to vagal stimu- 
lation and the role this system played in the 
development and understanding of these con- 
cepts. In particular, we were interested in deter- 
mining a mathematical theory which relates 
the arterial pressure to heart rate for possible 
Figure 2. — Laboratory equipment and computer inter- 
face. 
use in a controller for an artificial heart device. 
We reviewed the theory on vagal heart rate 
control. The generally accepted hypothesis that 
physiologists have taught for a considerable 
period of time is based on the concept that 
stimulation of the vagus nerve results in release 
of acetylcholine, which, by causing an increase 
in permeability of the cell membrane of the 
pacemaker, results in inhibition of the heart 
rate. The heart rate is assumed to be propor- 
tional to the concentration of acetylcholine. This 
is summarized by Homer Warner and his col- 
leagues. We set out to confirm this formulation. 
EXPERIMENT CONTROL 
The design of the experiment was to evaluate 
first the effect of vagal stimulation on heart 
rate, followed by the effect of sympathetic 
stimulation, and then to develop our own ex- 
periments relating heart rate to arterial pres- 
sure in an open loop test model. 
We used the normal dog anesthetized with 
morphine, chloralose and urethane, and pre- 
medicated with propranolol to block sympathetic 
activity. We then carried out bilateral vagal 
transections, and stimulated the cardiac branch 
of the vagus nerve with a Grass stimulator. The 
timing and the number of the stimuli were de- 
termined by digital computer. 
The appendix provides a listing of a program 
used, and we will make reference to the line 
numbers of the program where pertinent. This 
program was written by one of us (E.D.) and 
expanded by Mrs. Margaret Miller. Several pro- 
grams and program revisions were used and 
the one chosen may be considered typical. An 
array of values were generated based on param- 
Table I. — Cardiac Surgery Utilization of the Acme Computer System 
Facilities used 
Large 
Long 
Analog 
On-line 
Links to 
Year 
Project 
On-line 
memory 
term 
Alphabetic 
input and 
graphic 
small 
interaction 
available 
files 
data 
outpiit 
output 
computers 
Bloodvolume calc 
X 
1966 
Tabular results - 
X 
X 
X 
1967 
Physiologic data-reduction 
X 
X 
1967 
Storage of data from PDP-8 
X 
X 
1967 
Graphical analysis of M-waves 
X 
X 
X 
1968 
Vagus nerve control 
x 
X 
X 
1969 
Interactive modelling 
X 
X 
X 
1970 
Patient data files 
X 
X 
1970 
M-wave data analysis _ 
X 
X 
X 
X 
1971 
Ultrasound data processing 
X 
X 
X 
X 
1972 
