Experiences With Radiosulfate in the Estimation of Physiologic Extracellular Water in Healthy and Abnormal Man 12

We have been interested in studying the changes in extracellular fluid volume in patients undergoing acute heat stress.Attempts to apply the inulin method to our needs were fruitless because of the prolonged time period required for equilibrium.Walser's radiosulfate method (1, 2) had appeal since it appeared suitable for repeated determina- tions within a short period of time.Walser has suggested that within 15 to 20 min- utes following ai single intravenous injection, radio- sulfate reached an apparent equilibrium between the vascular and interstitial spaces (1,2).He showed that the calculated volume of distribution of radiosulfate increased with time (1, 2) and that this increase could not be accounted for by urinary excretion (1, 2), fecal loss (3), or penetration of the muscle chloride space (4).He proposed that the 18-minute volume of distribution of radiosul- fate could be used as an index of functioning extra- cellular fluid volume (1, 2).The present report, dealing with the radiosul- fate method, confirms and extends many of Walser's observations.In addition, it points out the desirability of calculating a "zero time" rather than an 18-minute volume of distribution, and pro- poses a modification of existing ways of calculating the "zero time" space. METHODSA. Subjects: Radiosulfate spaces were determined on 33 healthy individuals: eleven (Nos.1-11) young, mus- cular soldiers; nine (Nos.12-20) young, male medical students and physicians; five (Nos.21-25) ambulatory, elderly males; and eight (Nos.26-33) ambulatory, elderly females.Four patients with abnormalities of water metabolism were studied: two (Nos.34, 35) were de- 1 Supported in part by a grant from the U. S. Public Health Service.2The opinions expressed in this paper are those of the authors and do not necessarily represent the official views of any government agency.hydrated and two (Nos.36, 37) had ascites without peripheral edema.In five subjects the radiosulfate space was redetermined at various intervals, ranging from 1 to 30 days, during which they continued their usual daily activities.Each of the eleven soldiers had a second determination following a three-week period of paratroop training.B. Procedure: All subjects were studied in the morn- ing after a twelve-hour fast.They were allowed water ad libitum during the preceding day and were given 200 ml. of water every two hours during the course of the test.Approximately 100 microcuries of S5 as carrier-free sodium sulfateB were injected intravenously, from a cali- brated syringe, over a period of one minute.An aliquot