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.

No abstract

No abstract

S=m=Y1. The effects of acute intravenous infusion of 2 litres of saline/l20 min on pulmonary capillary blood flow (Oc), diffusing capacity per unit of alveolar volume @L/VA), functional residual capacity (FRC), and pulmonary tissue plus capillary blood volume (VTPC) were compared with the changes induced by water immersion to the neck for 4 h. Serial measurements were made at 30 min intervals in five normal subjects, utilizing a non-invasive rebreathing method with a gas mixture containing 0 5 % acetylene, 0.3% C"0, 10% He, 21% O2 and 68.2% N2.2. Infusion of saline produced a rise in & which was similar to that induced by immersion. This increment in Oc persisted for the 3 h of observation after stopping the infusion, in contrast to the prompt decrease in Qc to pre-study values after cessation of immersion.3. DLIVA was unaffected by saline administration in contrast to the marked and prompt increment induced by immersion.4. Pulmonary tissue plus capillary blood volume was unchanged during both saline administration and immersion, suggesting that neither gradual saline administration nor immersion induces major extravasation of fluid into the pulmonary interstitial space.5. The present data indicate that the 'volume stimulus' of immersion is similar to that of saline-induced extracellular fluid volume ex-