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

This study tested the hypotheses that 1) spleen volume increases during head-out-of-water immersion (HOWI) and returns to preHOWI values postdiuresis, and 2) the magnitude of apnea-induced spleen contraction increases when preapnea spleen volume is elevated. Spleen volume was measured before and after a set of five apneas in 12 healthy adults (28 +/- 5 yr, 3 females) before, during (at 30 and 150 min), and 20 min after temperate temperature (36 +/- 1 degrees C) HOWI. At each time point, spleen length, width, and thickness were measured via ultrasound, and spleen volume was calculated using the Pilstrom equation. Compared with 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 postapnea bouts at each time point (P < 0.01). The magnitude of reduction in spleen volume from pre- to postapneas was elevated at 30 min of HOWI ( 69 +/- 24 mL) compared with pre-HOWI ( 52 +/- 20 mL, P = 0.04) but did not differ from pre-HOWI at 150 min of HOWI ( 54 +/- 16 mL, P = 0.99) and post-HOWI (-50 +/- 18 mL, P = 0.87). Thus, spleen volume is increased throughout 180 min of HOWI, and whereas apnea-induced spleen contraction is augmented after 30 min of HOWI, the magnitude of spleen contraction is unaffected by HOW! thereafter.

Automated summary

This study found that spleen volume increases during head-out-of-water immersion and returns to pre-immersion levels after the process. Additionally, apnea-induced spleen contraction is enhanced when spleen volume is elevated before the apnea.