SIMPLE CARDIO-SPHYGMOGRAPH. 3l 
deepest point of this notch is always exactly synchronous with the 
point of closure of the aortic valve. This leads to the almost neces- 
sary conclusion, that the subsequent slight rise or change in direction 
of the trace is the result of the simultaneous movement of the whole 
column of blood produced by the shock of the closure of the aortic 
valve; the secondary rise at the commencement of the second arterial 
interval being the more slowly transmitted pressure wave, which 
started at the same time This explanation being correct, it is 
evident that the results obtained, by measuring the number of times 
that the interval between the origin of the main arterial rise and the 
bottom of the notch in the major fall is contained in the first arterial 
interval, ought to give the same results as those obtained by dividing Page 270. 
the calculated length of the conjugate cardio-arterial interval into the 
first arterialinterval. Such has been found to be the case very closely, 
but a sphygmograph trace must be a very good one to show the notch 
in the first arterial interval sharply defined, and the subsequent rise 
commencing abruptly. 
In all the cases above discussed it has been assumed that the 
subject from whom the traces were taken was sitting at the time, and 
as the length of the first cardiac interval changes for the same rate of 
pulse with change of position, it is evident that the equation given 
above (namely, zz = 39,/z) must be changed also; and the change 
probably consists in increasing the value of the constant for the stand- 
ing posture, as then the first cardiac interval is shorter, but still varies 
inversely as the square root of the heart’s rate. 
The explanation given above of the cause of the notch in the first 
arterial interval, might lead to the expectation that the commencing 
’ cardiac systolé indicates itself at the wrist in the same way ; but there 
is no such marked change of direction in sphygmograph traces, though 
a slight rise is generally seen just before the main ascent originates, 
especially in pulse of about 70 in a minute; and it is not improbable 
that the second rise in the extremely dicrotic pulse of adynamic pyrexia 
is caused by a combination of the slow pressure wave resulting from 
the closure of the aortic valve, and the sudden onward motion given 
to the whole mass of blood in the vessels at the moment of opening of 
the aortic valve at the commencement of the next systolé. 
The facts on which the above equations have been based are pub- 
“a lished in the “‘ Proceedings of the Royal Society,” XIX. No. 126, p-318.* 
“4 - Mr. Hawksley, of Blenheim Street, is constructing a cardio- 
sphygmograph from the model described above, with a few minor 
improvements, which can easily be applied in the study of pathological 
conditions. 
* Infra, p. 32. 
