The Arterial Pressure in Man. 
347 
1907-8.] 
of the greatest amplitude of pulsation on the ascending curve, was 120, 
while on the descending curve it was also the same. It will be observed 
that in this tracing there are great variations in the amplitude of the 
oscillations, both in the ascending and descending curves, but more 
especially on the curve of descent. These will require more careful 
consideration afterwards. 
In the tracings which accompany this paper the lowest curve is that 
registered by the transmission sphygmograph. The abscissa is immediately 
above it, and the kymographic tracing starts from this level. Since the 
manometer has a double column of mercury, the height of the tracing above 
the abscissa must be doubled in reading the record ; if the tracing at any 
point should be 60 mm. from the abscissa, the pressure at that point must 
be recorded as 120 mm. Hg. As usually employed, the pressure is raised 
with one steady forcible expulsion of the air contained in the syringe until 
a high level is reached — 150 or 160 mm. Hg. being sufficient under 
ordinary circumstances. The valve already set at the slow escape allows 
the pressure to fall gradually. If sufficient pressure has been employed, 
the tracing from the artery, after a few oscillations due to the inertia of 
the mercury, shows an entire absence of all movements, or only very small 
pulsations, and the curve resulting from the gradual lowering of the 
column of mercury is therefore almost destitute of any fluctuations. The 
instant that the arterial pressure overcomes the resistance, small waves 
begin to appear in the arterial tracing. Sometimes, as was indeed noticed 
by von Recklinghausen (29), Jane way (4), and Masing (30), in taking 
tracings either with the sphygmograph or plethysmograph along with the 
Riva Rocci sphygmomanometer, one or two little waves show themselves 
before the appearance of definite pulsation. In most cases, however, the 
return of the pulsation is quite unmistakable. The usual appearances are 
shown in fig. 3, taken with slow revolution of the cylinder, and in fig. 4 
with quick movement. 
In the interpretation of the tracings there is one point which may 
always be depended upon with a reasonable degree of certainty : the 
point at which the pulsation returns in the vessel below the seat of com- 
pression is approximately the systolic pressure. This has been admitted 
ever since the observations of Yierordt (11), and von Basch (14). The 
middle point of the kymographic curve at this point is therefore chosen 
as the index of systolic pressure. It is perfectly true that it is not 
absolutely the end pressure. The top of the first wave which appears 
gives the maximum systolic pressure indeed, but it is the lateral and not 
the end pressure which is recorded, and therefore the method of circular 
