AND RADIAL SPHYGMOGRAPH TRACE. 33 
cardiac interval which is synchronous with a portion of the first arte- 
rial interval. It is therefore the interval between the commencing 
sphygmograph rise and the point of closure of the aortic valve as repre- 
sented in the cardiograph trace. 
6. The second cardio-arterial interval is that which occurs between 
the point of closure of the aortic valve and its indication at the artery 
under consideration. 
In commencing to work with the cardio-sphygmograph, measure- 
ments were made to find the duration of the first cardio-arterial interval, 
as it required but a few experiments to prove that the heart commences 
to contract before the pulse is indicated at the wrist. 
By means of compasses, or by superposing one trace on the other, 
the commencing cardiograph rise was projected on the sphygmograph 
trace ; and the interval between this event and the origin of the radial 
rise was then measured into its component beat in each pulsation of Page 321. 
the trace, from which the average of the observation was obtained. 
The results are given in Table I, Column I; and in Column III some 
of these are expressed in parts of a minute, whereby a better idea can 
be obtained as to their significance. 
Taste I. 
wl 
nly B 
4 
R 
: 
i 
002768 “002802 
-002524 “002538 
002222 “002229 
00197 “003 957 
SERSSeReesRAseS 
Ro 6 60 9 hh ei ie on on 
& Pas” apeaeeea" » oH 
From these results itis seen that the first cardio-arterial interval is 
longer in slow than in quick pulses, and that it does not increase as 
quickly as the pulse diminishes in rapidity; but that the statement 
that it varies inversely as the square root of the rapidity is correct, or 
very nearly so, is rendered evident by comparing Columns III and IV, 
in the latter of which the duration of the first cardio-arterial interval 
D 
