In a previous communication (1) evidence was presented for a "forward failure" hypothesis of edema in patients who have low cardiac outputs at rest. These patients have a low renal blood flow, apparently accompanied by renal efferent arteriolar constriction. This seems to be directly related to the level of the cardiac output and is entirely unrelated to the height of the venous pressure. As the renal blood flow falls, a consequent reduction in filtration rate occurs. This results in a decrease in the amount of salt and water filtered, and, since the tubules continue to reabsorb salt and water almost completely, there is a net retention of the latter which produces edema. It is. recognized that other factors may be involved in the rate of reabsorption. We emphasized that the patients studied were those who formed edema at rest, since the data were collected on resting subjects. Many patients who are compensated at rest form edema with activity. The reason for this can be ascertained only by studying patients in the exercising state. This paper is a report on the effect of exercise on the renal plasma flow and filtration rate of normal and cardiac subjects. METHODSSubjects were selected most of whom, at rest in the hospital, responded readily to routine therapeutic procedures. In this way it was hoped to obtain patients with relatively normal resting filtration rates. Controls consisted primarily of patients with asymptomatic neurosyphilis who were -receiving penicillin therapy. Since other techniques are not suitable to demonstrate brief changes in renal plasma flow and filtration rate, the methods of Smith, Goldring and Chasis (2) were employed utilizing sodium para-amino hippurate for renal plasma flow and inulin for filtration rate.As accurate results necessitate maintenance of a constant blood level of these materials, forms of exercise 1 Aided by grants from the Life Insurance Medical Research Fund and Smith, Kline and French Laboratories.were used in which a constant intravenous infusion could be given. At first, studies were made on recumbent patients with simple alternate flexion of each leg. As it became obvious that so little exercise was insufficient, the patients were required to step up and down two steps, each 121/ inches high, approximately 40 times. These patients were relatively free of edema as a result of mercurial diuresis before exercise was undertaken. Still later, in the recumbent position, pedals were pushed which, through two single pulley arrangements, raised two 22-pound weights alternately through a distance of 8 inches. Finally, as indicated in the table, 22-pound weights were raised through a distance of 12 inches. After allowing 30 minutes to acquire a constant blood level, a 12-minute exercise period was preceded by two 15-minute control periods and followed by sometimes one, usually two, 15-minute control periods. In most gases the normal subjects were required to do more work than the cardiac subjects. All results are corrected to a body surface area of 1.73 square meters.In L. ...
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