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BLOOD PRESSURES IN MAN, NORMAL ANI> PATHOLOGICAL 315 



height of the blood pressure response to exertion. The extent and 

 course of this response varies much in different types and degrees of 

 muscular activity — whether the latter be 1, strong or maximal effort 

 with fixation of the thoracic walls, etc., bringing in the factors concerned 

 in Valsalva's experiment; 2, exercises of endurance as in walking, long 

 distance running, cycling, etc.; 3, execution of difficult, though not neces- 

 sarily strong, movements involving much mental concentration; 4, 

 static contraction of muscles. 



A direct relation of the blood pressure rise (associated with exertion) 

 to the amount of work, rather than to its rate, has been affirmed. This 

 is applicable in a general way to certain types of exercise where the 

 mental factor remains tolerably constant, but it is not applicable for 

 comparison between different types involving variable degrees of mental 

 concentration, emotional accompaniments, etc.; in these very different 

 amounts of blood pressure change may be associated with the per- 

 formance of equivalent amounts of muscular work. 



Blood pressures in sleep. That there is a lowered blood pressure 

 during sleep has been found by various observers, often amounting to 

 15 to 30 mm. at the end of two hours' sleep, then gradually rising to- 

 ward the time of waking. Such falls of general arterial pressure 

 obviously mean only a relatively limited reduction in the brain vessels 

 — the hydrostatic factor being largely taken off the head vessels in the 

 recumbent posture. Greater reductions have been noted in persons 

 with high pressures in the daytime, e.g., 44 mm. by Brooks and Car- 

 roll (22) in hypertonic subjects. 



Muller (100) found the systolic pressure to be down to 94 mm. in 

 men and 88 mm. in women during sleep, after a small dose of veronal. 

 In persons with moderate day pressures Blume (15) recorded falls of 

 15 mm. and 21 mm. in men and women respectively while in subjects 

 with high day pressures the lowering averaged 31 mm. and 39 mm. 

 These observers describe a remarkable constancy of pressures during 

 sleep (rarely more than 5 mm. variation in sleep), even in high 

 pressure cases, in contrast to the great variability seen in the waking 

 pressures. Katsch and Pansdorf (72) while confirming the fall of 

 systolic pressure in sleep — parallel to the depth of the sleep — found 

 that the diastolic pressure sinks little if at all, but on the contrary 

 often rises during the deepest sleep, so that the pulse pressure is di- 

 minished. In essential hypertension they observed an abnormal 

 range of systolic lowering; in other hypertensions little or no lowering. 



The present writer (88) finds that there are two entirely different 



