Renal plasma flow (RPF) and glomerular filtration rate (GFR) are decreased in patients with heat stroke. Heat stroke after prolonged exercise under high temperatures is usually associated with hypotension and dehydration, leading to decreased RPF. However, whether renal blood flow (RBF), RPF, and GFR are increased or decreased during immersion in mild warm water remains unknown.
Para-aminohippurate clearance (C_PAH), sodium thiosulfate clearance (C_thio), and creatinine clearance (C_cr) were determined in 14 healthy men aged 19 to 27 years old (mean±SD, 22±2), 161 to 181cm (171.5±6.3) tall, and weighing 52 to 78kg (64.2±7.4) without immersion at about 25°C (room temperature) and during immersion in water at 41±0.5°C.
C_PAH, C_thio, and RBF significantly increased during immersion compared with those without immersion (P<0.0001, P<0.03, P<0.0001, respectively). C_cr did not change (P=0.108). The filtration fraction (FF) was significantly decreased (P<0.001). Levels of plasma atrial natriuretic peptide, aldosterone, anti-diuretic hormone and renin did not significantly differ between these two conditions.
This investigation suggests that daily immersion at 41°C is beneficial for renal function.