My personal concern about hypertension dates back to ~1977 when a Caltech health center physician told me that I should keep an eye on my blood pressure, which was at that time marginally high. For a few years I lost some weight, exercised a bit, tried to relax more, and then stopped paying attention.
Around 2000 my doctor --- whom I greatly respect --- began to get concerned about those ugly systolic and diastolic readings again. She made me get a sphygmomanometer (what a word!) and gather data at home, in case the measurements at the office represented "white coat hypertension" provoked by nervousness in that environment.
As a quantitative analysis freak I was delighted to oblige. I made spreadsheets and graphs of the numbers to help her, along with N-day moving averages to smooth out some of the noise. This kept her happy for a few more years, until in early 2002 she put her foot down and gave me some antihypertensive medication to take. Those pills --- HCTZ, a cheap diuretic --- had unæsthetic side-effects and didn't really seem to do much toward reducing my blood pressure anyway. But the threat that they represented did succeed in tipping me over from a sedentary mode of existence to an order-of-magnitude more activist one: I went from less than 1 hour/week of bland exercise to ~20 miles/week of jogging and walking.
So beginning in mid-2002 I earned a reprieve from the meds. The doc felt that I was trying to do my part of the job, had no other major risk issues, and might as well continue the experiment in distance running. (I told her that it was also great fun, though that didn't seem to be a factor in her calculus.) But the ^z BP numbers just kept hanging a bit too high for her comfort. Last month she put her other foot down and prescribed a low dosage of an ACE inhibitor for me to take.
My simpleminded theory is that the body has a host of feedback loops going on constantly: little ones inside each cell that maintain a local balance of chemicals, and bigger ones that keep large-scale parameters like temperature and blood pressure in their proper zones. To quote from the product insert:
Lisinopril inhibits angiotensin converting enzyme (ACE) in human subjects and animals. ACE is a peptidyl dipeptidase that catalyzes the conversion of angiotensin I to the vasoconstrictor substance, angiotensin II. Angiotensin II also stimulates aldosterone secretion by the adrenal cortex. The beneficial effects of lisinopril in hypertension and heart failure appear to result primarily from suppression of the renin-angiotensin-aldosterone system. Inhibition of ACE results in decreased plasma angiotensin II which leads to decreased vasopressor activity and to decreased aldosterone secretion.
That's technical language to describe, in brief, one way to adjust the blood pressure's metaphorical "thermostat". Other ways include adjustments to sodium intake, weight loss, exercise, personal stress management, and various biochemical tweaks. Everybody is different; what works for one may not work for another. But there are common themes. And one thermostat can affect another; changing blood pressure may influence heart activity, potassium levels, etc.
And in a parallel way, training in all forms turns a thermostat. The muscles adapt to meet new requirements; so do the brain, and the cardio-vascular system, and other parts of the body chemistry. As ultrarunner computer scientist Paul Ammann once observed (see also UltraMan, 8 May 2002):
Your body can handle all kinds of ridiculous stresses - but only if you give it plenty of time to adapt. Many people - including me, I admit - are impatient with running goals. And many people - including me again - are often sorry about that.
And in an infinitely more serious context, Z. A. Melzak notes in Chapter 6 ("Certain Effects of Time") of InSearchOfTheFulcrum:
... the long-range Nazi policy of slow extermination rather than sudden destruction had an astounding secondary effect which ran completely counter to its intention. Simply, it gave us, or rather some of us, sufficient time in which to adapt progressively, to get tempered and annealed slowly, and to become inured gradually. And so we survived.