. Medical studies in aviation . udden fainting at low altitudes. For if therewere a momentary failure of coronary circulation dueperhaps primarily to a wholly neurotic influence on thevasomotors, a condition of undernourishment of theheart would be started that would be rapidly cumulative. The elements of strength in meeting the situationare a strong heart muscle, efficient and accuratelyadjustable coronary circulation, and the ability of theperipheral vasomotors to allow increase of blood flowto the parts that need it without undue strain on theheart by increased blood pressure. These arteria
. Medical studies in aviation . udden fainting at low altitudes. For if therewere a momentary failure of coronary circulation dueperhaps primarily to a wholly neurotic influence on thevasomotors, a condition of undernourishment of theheart would be started that would be rapidly cumulative. The elements of strength in meeting the situationare a strong heart muscle, efficient and accuratelyadjustable coronary circulation, and the ability of theperipheral vasomotors to allow increase of blood flowto the parts that need it without undue strain on theheart by increased blood pressure. These arterial reac-tions demand in the first line perfect anatomic condition 33 of the vascular walls and perfect vasomotor a consequence, two classes of cases are found thatare most likely to react badly to lowered oxygen ten-sion : men who have any arterial change in the way ofsclerosis, and those with poor vasomotor control. The latter class includes numerous individuals whoare either overvigorous in their reactions and run a. Fig. 1.—Dilatation of the heart under deficiency of oxygen beyondthe individuals power of compensation: solid line, percussion outlineof heart before and after experiment; broken line, outline at 19,800feet elevation in low pressure chamber. high blood pressure (often high strung, efficient people)or who have fluctuations of vasomotor tone which aremanifested in a variety of ways but eventually lead toan identical result, namely, circulatory collapse andfainting, usually following marked dilatation of theheart. 34 The optimum type of individual will go to extremeheights with practically no signs of circulatory diffi-culty, and will at the end become unconscious fromdirect effect of oxygen want on the cortical centers,giving quite a different picture from that of circulatorycollapse. FAILURE TO COMPENSATE Paradoxically enough, the poorer types of organismsalso fail to show heart strain and dilatation. Personsof poor physical and sluggish reactions, whe
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