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Effects of water immersion to the neck on pulmonary circulation and tissue volume in man
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1976
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The study measured pulmonary capillary blood flow, diffusing capacity, functional residual capacity, tissue volume, and oxygen consumption in five healthy subjects using a rebreathing gas mixture under three conditions—6 h sitting, 4 h sitting immersed in thermoneutral water, and 4 h lying immersed—with measurements taken every 30 min and immersion preceded and followed by 1 h rest periods. Seated immersion in thermoneutral water caused a rapid and sustained fourfold rise in sodium excretion, a 25–36 % increase in pulmonary capillary blood flow and a 45–59 % increase in diffusing capacity, while reducing functional residual capacity by 30–36 %; oxygen consumption, heart rate, and pulmonary tissue volume remained unchanged, indicating that the increased blood flow is not accompanied by interstitial fluid leakage.
Utilizing the rebreathing of a gas mixture containing C2H2, C180, He O2, and N2, we obtained serial measurements of the pulmonary capillary blood flow (Qc), diffusing capacity per unit of alveolar volume (DL/VA), functional residual capacity (FRC), pulmonary tissue plus capillary blood volume (VTPC), and O2 comsumption (VO2) in five normal subjects under the following conditions: 1) 6 h of sitting, 2) 4 h of sitting while immersed in thermoneutral water to the neck, and 3) 4 h of lying in thermoneutral water to the neck. Water immersion (NI) was preceded and followed by 1-h prestudy and 1-h recovery periods. The measurements were made at 30-min intervals. Seated NI produced a fourfold increase in sodium excretion (UNaV), a 25–36% increase in Qc, a 45–59% increase in DL/VA, and a 30–36% decrease in FRC. This occurred as early as the 1st h of NI and persisted throughout the 4-h period of study. Throughout the seated control and NI periods, VO2, heart rate, and VTPC remained constant. During supine NI, Qc, HR, DL/VA, FRC, and VO2 did not differ significantly from supine prestudy. These date demonstrate that seated NI causes a significant increase of Qc and DL/VA which persists throughout the immersion period. Furthermore, the lack of change of VTPC suggests that the central vascular engorgement induced by seated NI is not accompanied by extravasation of fluid into the pulmonary interstitial space.