REDISTRIBUTION OF BODY-FLUIDS DURING POSTURAL MANIPULATIONS

Inter-compartmental body-fluid distribution is contingent upon posture , exercise state and environmental temperature. This investigation aim ed at quantifying the distribution of intra- and extravascular fluid v olumes during postural manipulations. Fluid shifts were measured in ei ght males utilizing a simultaneous, radionuclide dilution technique, i n which radioiodinated serum fibrinogen, radiochromated erythrocytes, radiobromine and tritiated water were used to measure plasma, red cell , extracellular and total body water volumes. Subjects were exposed to three postural changes [seated (control), supine and standing] for 30 min at an air temperature of 22.0 degrees C, with each posture separa ted by 30 min seated rest. Total body water content remained stable th roughout postural changes (P = 0.842). Relative to seated volumes, BV increased by 89 mL when supine, and decreased by 406 mL while standing (P = 0.003), with such shifts being primarily a result of plasma move ment (P = 0.011). Red cell volume changes were not significant. Vascul ar fluid lost during standing was filtered into the interstitial compa rtment (P = 0.014), with the extracellular and intracellular volumes r emaining unaffected (P = 0.271 and P = 0.800, respectively). These obs ervations confirmed the influence of posture on inter-compartmental bo dy-fluid distribution. The intravascular fluid loss when standing was caused by the filtration of plasma into the interstitium, while, durin g supine rest, intravascular volume increased, reflecting fluid flux f rom the interstitium to the circulation.