is expelled from the heart. Since each beat-driven pulse of blood generates pressure,
the number of measureable maxima and minima in 1 day will be equal to the
number of heart beats (contractions), which will range from 100,000 to 130,000 in
an average healthy individual (James2007a). These numerous pressures are mostly
hidden from our consciousness, and they occur ceaselessly over the entire lifespan,
from the point when the heartfirst develops in the womb to the instant we die. It is
the intent of this brief discussion tofirst divulge the history and certain properties of
blood pressure and then to reveal what happens to blood pressure as people go
through their lives, revealing its hidden adaptability. The focus will be on what
happens to blood pressure over the course of a day, although I will also discuss
some specific hidden blood pressure adaptations to the menstrual cycle, having
children, and standing up.
A Brief History of Blood Pressure: Discovery
and Measurement
Physiology and human biology like much of contemporary science have roots into
antiquity, and while there were several writers, the basis of Western physiology
prior to the renaissance of the seventeenth century was the works of Galen of
Pergamum (130–200 A.D.) (Magner 1992 ). Galen’s authority in medicine and
human biology through the middle ages was generally absolute and unquestioned,
but like much of ancient thought, while some of what he observed was correct, a lot
of what he presumed as function was in error. This is particularly true in his
assessment of the movement of blood throughout the body. Galen devised a very
complex system that involved the arteries, veins, and nerves which was further tied
to respiration. Blood, he argued, was continuously synthesized from ingested foods.
The useful part of the food was transported from the intestine to the liver via the
portal vein, where it was transformed into darker, venous blood. The blood was
then pushed from the liver much like a bellows, mixed with air, and via several
processes made its way to the body’s tissues where it was consumed (Magner
1992 ). Thus, blood did not circulate; it was simply continuously produced and
consumed.
The fallacy of this explanation was demonstrated by the experimental work of
William Harvey (1578–1657) who published hisfindings in 1628 in a book entitled
An Anatomical Treatise on the Motion of the Heart and Blood in Animals(Magner
1992 ). Harvey demonstrated that all blood must go through the lungs to get from
the right to the left side of the heart, that the heart was muscular; that the heart’s
most important movement was contraction, andfinally and most importantly that it
was the rhythmic contraction of the heart that produced continuous circulation of
the blood (Magner 1992 ). The only difficulty Harvey had with his model was the
inability to identify how bloodflowed from the arteries to the veins; however, later
work by scientists such as Marcello Malpighi (1628–1694) using the newly
144 G.D. James