Increased spleen volume provoked by temperate head-out-of-water immersion

Abstract

This study tested the hypotheses that (1) spleen volume increases during head out water immersion (HOWI) and returns to pre HOWI values post diuresis, and (2) the magnitude of apneas induced spleen contraction increases when pre apneas spleen volume is elevated. Spleen volume was measured pre- and post- a set of five apneas in twelve healthy adults (28 ± 5 y, 3 females) before, during (at 30 and 150 min) and 20 min following temperate temperature (36 ± 1°C) HOWI. At each timepoint, spleen length, width, and thickness were measured via ultrasound and spleen volume was calculated using the Pilström equation. Compared to pre HOWI (276±88 ml), spleen volume was elevated at 30 (353±94 ml, p<0.01) and 150 (322±87 ml, p<0.01) min of HOWI, but returned to pre HOWI volume at post HOWI (281±90 ml, p = 0.58). Spleen volume decreased from pre to post apnea bouts at each timepoint (p < 0.01). The magnitude of reduction in spleen volume from pre to post apneas was elevated at 30 minutes of HOWI (-69±24 mL) compared to pre HOWI (-52±20 mL, p = 0.04) but did not differ from pre HOWI at 150 min HOWI (-54±16 mL, p = 0.99) and post HOWI (-50±18 mL, p = 0.87). Thus, spleen volume is increased throughout 180 minutes of HOWI, and while apneas induced spleen contraction is augmented after 30 minutes of HOWI, the magnitude of spleen contraction is unaffected by HOWI thereafter.