THE EFFECT OF EXERCISE ON THE RENAL PLASMA FLOW AND FILTRATION RATE OF NORMAL AND CARDIAC SUBJECTS 1

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Abstract
Patients with heart failure who form edema at rest usually have a low resting cardiac output and a correlatively low resting renal plasma flow with a filtration rate below 70-80 ml. per minute. Since tubular reabsorption is almost complete, the low filtration of salt and water results in retention to salt and water, i.e., edema. The operation of other factors in Na reabsorption is appreciated. Cardiac subjects who form edema only while exercising usually have filtration rates above 70 ml./-min. In order to determine why they form edema it was necessary to study them under the conditions in which the edema was formed[long dash]in the exercising state. With various forms of mild exercise, the filtration rates of 6 of 10 cardiac subjects approached or fell well below the "critical" level of 70 ml./min. None of the control subjects showed a comparable change in filtration rate, though a few had a definite fall in renal plasma flow. Thus there seems to be a mechanism for reducing the renal plasma flow when the cardiac output is insufficient for tissue demands, perhaps in order to supply tissues such as the brain, the metabolic needs of which are greater than those of the kidney in proportion to blood supply. The possible mechanisms of this are mentioned.