INFLUENCE OF HYDROSTATIC-PRESSURE GRADIENTS ON REGULATION OF PLASMA-VOLUME AFTER EXERCISE

The impact of posture on the immediate recovery of intravascular fluid and protein after intense exercise was determined in 14 volunteers. F orces which govern fluid and protein movement in muscle interstitial f luid pressure (P-ISF), interstitial colloid osmotic pressure (COPi), a nd plasma colloid osmotic pressure (COPi) were measured before and aft er exercise in the supine or upright position. During exercise, plasma volume (PV) decreased by 5.7 +/- 0.7 and 7.0 +/- 0.5 ml/kg body weigh t in the supine and upright posture, respectively. During recovery, PV returned to its baseline value within 30 min regardless of posture. P V fell below this level by 60 and 120 min in the supine and upright po sture, respectively (P < 0.05). Maintenance of PV in the upright posit ion was associated with a decrease in systolic blood pressure, an incr ease in COPp (from 25 +/- 1 to 27 +/- 1 mmHg; P < 0.05), and an increa se in P-ISF (from 5 +/- 1 to 6 +/-: 2 mmHg), whereas COPi was unchange d. Increased PISF indicates that the hydrostatic pressure gradient fav ors fluid movement into the vascular space. However, retention of the recaptured fluid in the plasma is promoted only in the upright posture because of increased COPi.