invented microscope showed that there was a capillary network that joined the two
structures (Magner 1992 ).
As with most discoveries during this time, acceptance of the new physiology
was slow, and it took more than 100 years (1733) before thefirst measurements of
the pressure of the circulating blood were made in a horse by Stephen Hales (1677–
- (O’Rourke 1990 ; Pickering 1991 ). Hales actually made measurements of
blood pressure in several animal species by insertingfine tubes (cannula) into
arteries and measuring the height to which the column of blood rose. Hales also
noted that the pressure of blood as it circulated was variable and depended upon the
circumstance of the animal, such as feeding, exercise, and rest (Pickering 1991 ).
Subsequent to Hales’work, blood pressure began to be recognized as an
important medical measurement and indicator, but because direct cannulation of
arteries in man was not feasible, various methods were investigated to determine
arterial pressure from the peripheral pressure pulse (O’Rourke 1990 ). Several
techniques were developed through the nineteenth century, but none proved to be
reproducible and reliable. Finally, Nikolai Korotkoff, using the arterial occlusion
method of Riva-Rocci and a stethoscope, discovered the auscultatory technique of
blood pressure measurement, reporting on the sounds that bear his name to the
Imperial Military Medical Academy in St. Petersburg, Russia, in 1905 (Paskalev
et al. 2005 ). Korotkoff was afield surgeon during the Russo-Japanese war and
stumbled upon the sounds as he was trying to devise a method to determine whether
severely injured limbs still had circulation (Paskalev et al. 2005 ). Since that time,
other methods of blood pressure assessment have been added, including oscillo-
metric, plethysmographic, and ultrasound techniques (Pickering 1991 ; Pickering
and Blank 1995 ), but the quantitation of blood pressure as a ratio of the maximum
(systolic) and minimum (diastolic) of the pressure pulse wave based on Korotkoff
sounds is still the standard for describing blood pressure (James 2013 ).
Blood Pressure Measurement by Auscultation
As the pressure pulse wave circulates through the arterial system to smaller and
smaller branching arteries and ultimately to the capillaries, the shape of the pulse
wave changes, and hence the values of systolic and diastolic blood pressure also
change (O’Rourke 1990 ). Thus, by convention, for medical and most epidemio-
logical andfield purposes, systolic and diastolic pressures are estimated from the
brachial artery, usually in the non-dominant arm (i.e., left arm for right dominant
people) (James2007a). Following Korotkoff’s method, values are determined in a
process where bloodflow isfirst blocked and then re-established in the artery using
an air-inflated bladder inside a cuff that is wrapped around the upper arm. The
bladder is also attached to a mercury column or gauge, and a listener, using a
stethoscope placed at the distal end of the bladder-cuff assembly, slowly releases
the pressure inside the bladder using a stopcock valve (at a rate of approximately
2 mmHg per second), recording systolic pressure as the value registered on the
8 Continuous Blood Pressure Variation: Hidden Adaptability 145