CLIMATIC EFFECTS ON CARDIAC OUTPUT AND THE CIRCULATION IN MAN

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Abstract
Estimations of cardiac output (by C2H2 and also calculated from pulse pressure and pulse wave velocities) were made on subjects kept in an air-conditioned room at various temps. for 1 to 2 wks. From the relations of these values to blood pressure the effective peripheral resistances were calculated. Data were obtained both with the subjects recumbent and standing. In the recumbent position measurements were also made of the blood flow in the finger and of the size of the superficial veins. The conclusions reached are based on observations involving 87 subject-days. Cardiac output in the lying position increases in a warm, decreases in a cold environment, but returns to normal in each case after a few days. In subjects adapted to cold, cardiac outputs while standing are much below recumbent values, but in subjects adapted to warmth the difference is slight. In warm rooms blood pressures first increase, later fall. In cool rooms following warmth they first fall then rise and may attain levels which exceed control values obtained at the same temperature before exposure to warmth. Blood flow in the fingers progressively increases with adaptation to warmth; on a following exposure to cold maximal constriction may not be attained for several days. Infra-red photographs indicate that superficial veins progressively increase in size during adaptation to warmth; on a following exposure to cold they require several days to attain their maximal constriction. The differences between lying and standing pulse rates also show progressive changes with reduction of this difference during adaptation to warmth. The changes observed complicate estimates of cardiovascular fitness by criteria of this type. Many of the reactions are considered related to changes in blood vol. and heat exchange discussed in other papers.

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