Orthopnoea and the Effect of Posture upon the Rate of Blood Flow.

Lindhard (1) has noted that, of seven subjects, three, all of them females, had a slower rate of blood flow in the sitting than in the recumbent posture while the four male subjects showed practically no change. As far as we know these are the only direct observations in the literature concerning the effect of posture on blood flow. We have made thirteen determinations of the circulatory rate with the subjects sitting and nine determinations with the subjects standing, each one compared with a preceding determination made while the subject was recumbent. A rest period of about an hour preceded the first determination in each experiment. Change of position was accompanied by as little exertion as possible and a further rest period of fifteen to twenty minutes preceded each determination in the new position. The method used is a gasometric one, based on the Fick principle, which we have previously described (2). The subjects were young, healthy, adult males except the last two who were females and G. R. who has a rheumatic cardiac lesion which is well compensated. None of the subjects were athletic. Our results, shown in table 1 are even more striking than those of Lindhard. In no case did we fail to observe a diminution in the rate of blood flow on changing from the recumbent to the sitting position. Only once was the reduction less than 500 cc. per minute, while another observation on the same individual showed a greater change. The slowing of the circulation was more marked in the standing than in the sitting position. The average rate of blood flow while sitting was 76 per cent and while standing it was 50 per cent of the