there is individual variation in the difference of blood pressure estimates from
simultaneous full frequency and audible frequency assessments (Blank et al. 1988 ).
Moreover, in examining the energy spectrum, it was also found that during the
re-establishment of bloodflow, there can befluctuation in the signal which will lead
to gaps (auscultatory gaps) in the Korotkoff sounds heard by the listener (Blank
et al. 1991 , 1995). These gaps, depending upon when they occur during cuff
deflation, can influence either or both recorded systolic and diastolic pressure
(Blank et al. 1991 ). Thus, because Korotkoff’s method relies on audible sound,
there are hidden, inherent biases in the recorded values.
Ambulatory Blood Pressure Variation and Health
Even though there are methodological issues, ausculted blood pressures taken by
Korotkoff’s technique have been used as an indicator of cardiovascular health for
over a century. A condition, hypertension, has been defined as a resting, seated
Fig. 8.2 Comparison of simultaneous blood pressures taken by two observers using a
double-headed stethoscope in a validation study, showing the average difference between
observers at four different sites and the standard deviation of those measurement differences. Note
that the average difference at the various sites varies and is never zero, and that there is substantial
variation in the differences (modified from White et al.1991)
8 Continuous Blood Pressure Variation: Hidden Adaptability 147