column or gauge when sound isfirst heard (Korotkoff phase I) and diastolic
pressure when all sound disappears (Korotkoff phase V) (James 1991 , 2007a;
Pickering and Blank 1995 ). At the above rate of bladder deflation, it will take about
20 – 30 s for sound to appear and disappear, a timeframe over which 30–50 heart
contractions will occur (James2007a). Since there is a systolic and diastolic
pressure for each contraction-related pulse, the recorded systolic and diastolic
pressures are from different pulses. Hence, they are really independent measure-
ments that are treated as an integrated pair (James and Pecker 1994 ; Pickering and
Blank 1995 ; James2007a, 2013) (see Fig.8.1 ). Why is this important to know?
Blood pressure can change by 10% or more within seconds (Pickering et al. 1986 ),
and thus the recorded diastolic pressure could be substantially increased or
decreased relative to the“same pulse”diastolic pressure. Since a significant part of
the CVD risk associated with blood pressure is the size of the pressure pulse
(difference between systolic and diastolic pressure) (e.g., Mosley et al. 2007 ), the
fact that the actual pulse pressure is not being measured could affect a patient’s
reported cardiovascular disease risk assessment and hence treatment.
Another methodological problem with the auscultatory method is the fact that it
is based on the audible sound waves produced as bloodflow is re-established during
cuff deflation. Obviously, since people have differing hearing acuity, different blood
pressures can be recorded even when two people listen at the same time (see
Fig.8.2) (modified from White et al. 1991 ).
However, it is also important to know that the spectrum of energy produced
whenflow is re-established during cuff deflation extends beyond the range of
audible sound. Specifically, the bulk of the energy during cuff deflation is in the
low-frequency range, below our ability to hear it (Blank et al. 1988 ). This was
discovered by Seymour Blank, who found that by recording the entire spectrum of
energy, a comparatively higher frequency wave (which has been called K2) that
appears and disappears during cuff deflation corresponds closely to the actual
intra-arterial pressure as measured by a sensor placed directly in the arterial blood
flow. This high-frequency signal measures, on average, 6–8 mmHg higher systolic
and 3–5 mmHg lower diastolic pressure than ausculted measurements, although
Fig. 8.1 Blood pressure
pulse wave, showing the
measure of systolic and
diastolic pressure as the
pressure in the bladder
occluding the brachial artery
is released (modified from
James and Pecker1994)
146 G.D. James