Plasma volume with alternative tilting: effect of fluid ingestion.
The present study determines the effect of repeated 70 degrees head-up tilt (HUT) on plasma volume (PV) shifts by measuring blood density (BD), plasma density (PD), and hematocrit (Hct). Eight men (18-26 yr) underwent a predrink period with two supine (P1 and P3) and two HUT (P2 and P4) phases of 45 min each. At the end of P4 they drank 10 ml/kg body wt of isotonic (290 mosmol/kg) sodium chloride (Iso) or hypotonic (< 10 mosmol/kg) unsweetened tea (Hypo) or nothing [control (Con)]. The following periods continued the supine (P5, P7)/upright (P6) sequence. BD and PD were measured from ear lobe blood; they were different (P < 0.05) between Con, Hypo, and Iso P6 and P7. The density of fluid that moved between intra- and extravascular compartments was 1,008.2 +/- 0.4 g/l and did not differ with test situations. In Con (P3, P5, P7), supine PV steadily decreased compared with P1 (P < 0.05). PV in P1, P2, and P3 of all treatments averaged 120 +/- 1, 101 +/- 1, and 115 +/- 1%, respectively, of PV in P4. Tilt-induced PV shifts ranged from -9.7 to -16.7% compared with PV during the respective previous phases. After drinking, PV increased (P < 0.05) above Con values at the end of P7 by 12.9% with Iso and by 6.6% with Hypo. Progressive hemoconcentration occurred in the nondrink supine periods; isotonic saline ingestion increased supine PV to Con level but did not stop or reverse the decrease of upright hemoconcentration.(ABSTRACT TRUNCATED AT 250 WORDS)
Hinghofer-Szalkay
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HG
Institute for Adaptational and Space Flight Physiology, Austrian Society for Aerospace Medicine, Karl-Franzens-University, Graz.
Sauseng-Fellegger
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Greenleaf
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JE
D000293:Adolescent; D000328:Adult; D003627:Data Interpretation, Statistical; D004326:Drinking; D005110:Extracellular Space / Q000502:physiology*; D018495:Fluid Shifts / Q000502:physiology*; D006400:Hematocrit; D006801:Humans; D008297:Male; D008833:Microcirculation / Q000502:physiology*; D010953:Plasma Volume / Q000502:physiology*; D011187:Posture / Q000502:physiology*