1096 
MONITORING 
R.M. - Intra-atrial EKG 
Figure 7. — Intra-atrial EKG. 
Figure 9 traces the course of the heart of a 
human heart transplant patient during exercise. 
The circles are the donor RR intervals and the 
XX's are the recipient P-P intervals. At the 
beginning, the P waves of the recipient and the 
R v^aves of the donor are independent in fre- 
quency and in phase. As the exercise increases 
and the donor heart rate increases, you v^^ill 
see that the two lock not only in frequency but 
in phase. The implication, therefore, is that the 
sino-atrial node of the human has the same type 
of behavior as the dog in the sense that it can 
lock to a driving arterial pressure transmitted 
through the central nervous system to the 
vagus. Besides its physiological implications, I 
feel that the data have direct application to the 
artificial heart devices. It may well be possible 
that the independent pulse generator in the 
system, under certain conditions of pressure 
and vagal transmission, forces the natural heart 
to beat in frequency with the artificial heart 
without any specific physical electrical linkage. 
DECAY OF HEART RATE 
We now wish to discuss the rate at which 
the heart period returns to the control state 
after cessation of vagal stimulation. In our 
initial discussion it was suggested that the de- 
cay of heart rate back to the control state could 
fit with a single exponential. Previous data sug- 
gested that the heart period was linearly pro- 
portional to ACH concentration. Therefore, 
during the carrying out of the previously men- 
tioned experiments in phase sensitivity, the 
logarithm of the slope of the heart period was 
also displayed, utilizing two features of ACME 
system — on-line plotting and calculations (pro- 
gram lines 14.6 to 18). Figure 9 illustrates the 
typical heart response to stimulation and cessa- 
tion of stimulation. Several trials were super- 
imposed, illustrating the reproducibility of the 
experimental data, and our confidence in the 
adequacy of the data. We were immediately 
0! CCmFDL 
a EXERCISE WITH PURSE LOCK 
n 
pT^J pT-J p/^ 
p/sJ _r~jJ _y~^ p/-^ 
r 
P TAG 
P TAG 
R THE 
P TAG 
PKG 
^ Aa rV f^/^ 
Figure 8. — Frequency relationships in transplanted hearts. 
