MadSci Network: General Biology

Re: Does the height of a person affect his circulatory and respiratory system?

Date: Tue Sep 12 15:46:20 2006
Posted By: Jens Peter Bork, M.D., Internal Medicine, Erlangen University Hospital
Area of science: General Biology
ID: 1156461513.Gb


thank you for your question about the height and the gender of persons and
their heart rates. 

The answer to the first part of your question is no. Consider: Normal blood
pressure is about 120/80 mmHg, or “millimetres of Mercury”. What does that
mean: It means that if you apply that pressure to a column of Mercury (In a
glass tube, say), you can lift the column by 120mm. Now blood does not
consist of Mercury (however, older blood pressure measuring devices did,
hence the use of the unit), it consists almost exclusively of water. 1 mm
of Mercury exerts the same pressure as 1.36 cm of water. That means, the
normal human blood pressure will propel our blood to a height of  163 cm
(in systole). Since our brains are usually not more than 30 – 40 cm above
our heads, the normal pressure is able to bring blood to brains of large
and small people alike several times over. In fact, under normal
circumstances, there is a mechanism in the arteries of the brain that
dampens down the excess pressure so that the brain is not subject to
excessive blood pressures. The condition you describe is sometimes relevant
in certain diseases of the brain, but is irrelevant with respect to height. 

The second part of the question is a bit trickier. One has to ask, what
does “men” and “women” mean here? Heart rate is extremely dependent on life
stile, physical fitness, smoking or non-smoking, to name a few, so the
answer may show differences over historic times and different world
regions. In Western societies, women have a somewhat higher resting HR. For
example, in ref. [1], you’ll find this in a sample small of  age-matched,
healthy men and women – the measurements were used as baselines for the
evaluation of several physiologic parameters pertaining to blood pressure
regulation. The women came up with a resting HR of 65, the men with 52 bpm. 

[1]	Convertino A (1998) Am J Physiol (Regul Integr Comp Physiol) 275 : p
1909. The URL for access to the article online is:

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