CIRCULATION I27 



(tighten up) or dilate (open wider). They tighten up when you are all 

 keyed up with joy, fear, anger, worry, or working under tension. When 

 they constrict, less blood can get into them from the arteries, and so the 

 pressure of blood in the arteries goes up. When the excitement is over 

 they dilate (open wider), and the pressure goes down. 



Hyperte?]sion, or high blood pressure, weans simply that through some 

 nervous or toxic influence the arterioles throughout the body — and there 

 are miles of them — are kept more or less constantly in a constricted, or 

 tightened-up, state. 



Hypotension, or loiv blood pressure, means that the blood pressure re- 

 mains more or less constantly within or below the lower limits of normal 

 pressure. Unlike high blood pressure, it does not cause heart disease. In- 

 deed, low blood pressure seldom causes real illness of any kind, and definite 

 diseases in which it occurs are very rare. Individuals who are physically 

 below par, especially if they are underweight, may have hypotension. 

 However, the blood pressure of many healthy individuals tends to be 

 lower than the average for their age. If your doctor concludes that you 

 are one of these "low-normal" individuals, you may consider yourself 

 fortunate because you may expect to live longer than other people. 



H01V High Blood Pressure Affects the Heart and Arteries. The effect 

 of hypertension on the heart is what you might expect if you screwed 

 down the nozzle of a hose connected with a water pump. Just as the pump 

 would have to work harder against increased resistance in the hose to keep 

 water spraying out of the nozzle in the same volume as before, so the heart 

 must work harder against increased resistance in the arteries to keep blood 

 flowing through the constricted arterioles at nearly the normal rate. To 

 take care of this extra work the heart muscle is forced to enlarge. And 

 often, but not always, the walls of the arteries become scarred and thick- 

 ened — a process called sclerosis, or hardening, of the arteries (arterioscle- 

 rosis). 



A strong heart and wear-resistant arteries may be able to cope with high 

 blood pressure for years without much trouble. In some cases there may be 

 no symptoms at all; in others, there may be headaches, dizziness, general 

 aches and pains, and possible shortness of breath. These symptoms also 

 appear in other common conditions. Instead of wondering whether you 

 have high blood pressure the sensible thing to do is to see your doctor. 



Sometimes high blood pressure clears up of itself before it has a chance 

 to damage the heart and blood vessels, or it may be lowered to a safe level 

 by drugs or diet or surgery if it is discovered in time. Even malignant hy- 

 pertension, a severe form of high blood pressure which often progresses 

 very rapidly, has recently been treated with good results in some cases. 



Persistent high blood pressure, however, nearly always results in en- 

 largement of the heart muscle — the first step in the development of hyper- 

 tensive heart disease. The progress of hypertensive heart disease to the 



