Chronic hypobaric hypoxia decreases intracellular and total body water in microswine

Abstract

The effects of hypobaric hypoxia on body fluid distribution were studied in five unanesthetized immature microswine (body weight 17.1 ± 1.5 kg, mean ± SEM) at sea level and after 23 days of simulated altitude exposure (427 Torr, 4600 m, 24°C, 50% RH). Total body water (TBW), extracellular fluid volume (ECF), and plasma volume (PV) were determined with D 2O, NaBr, and indocyanine green, respectively. Intracellular fluid volume (ICF = TBW − ECF) and interstitial fluid volume (ISF = ECF − PV) were calculated. Hypoxia resulted in characteristic decreases ( P < 0.05) in arterial PO 2 and PCO 2, and an increase in hemoglobin concentration. Chronic exposure to hypobaric hypoxia elicited significant ( P < 0.05) decrements in body weight gain (− 14%), TBW (− 11%, 12.5 vs 11.3 L), ICF volume (− 13%, 8.9 vs 7.8 L) and PV (− 28%, 0.82 vs 0.57 L). Although the ECF was unaffected (3.66 vs 3.57 L), the ISF was significantly increased (+ 6%, 2.83 vs 3.22 L) ( P < 0.05). Decreased TBW accounted for 51% of the expected reduction in body mass. These results suggest that the suppression in body weight gain is partially accounted for by decreases in TBW, ICF and PV. In addition the apparent elevation of ISF occurring concurrently with decreases in ICF and PV may be related to the development of edema, which can accompany exposure to high altitude.