ALTERATIONS IN RENAL-FUNCTION IN PATIENTS WITH OBSTRUCTIVE SLEEP-APNEA SYNDROME AND EFFECTS OF CONTINUOUS POSITIVE AIRWAY PRESSURE

Objective To assess renal function in patients with obstructive sleep apnea syndrome (OSAS) during two nights when they were untreated and t reated with continuous positive airway pressure (CPAP). Methods Tubula r function was estimated on the basis of the renal lithium clearance a nd its derived formulae, urinary osmolality, osmolal clearance and fre e water clearance; while glomerular function was evaluated by endogeno us creatinine clearance. Twenty patients with OSAS and sixteen normal controls were studied. Results The untreated patients with OSAS had si gnificantly lower fractional proximal tubular sodium reabsorption (59. 1% +/- 7.1%, P < 0.001 vs controls), lower fractional distal tubular s odium reabsorption (93.8%+/-). 7%, P < 0.05 vs controls) and urinary o smolality (573.0 +/- 107.9 mosm.kg(-1), P < 0.05 vs controls). The abs olute distal tubular reabsorption rate of sodium and osmolal clearance in the untreated patients were higher 47.0 +/- 26.0 mmol.L-1 and 25.0 +/- 4.1 ml.L-1: P < 0.01 and P < 0.05 respectively vs controls). Duri ng CPAP-treated nights all abnormal renal function indexes in the OSAS patients restored to normal control values (P < 0.05). Conclusions Th e natriuresis and diuresis of OSAS patients were due to the decrease i n proximal and distal tubular sodium reabsorption and in tubular conce ntration ability during their nocturnal sleep and were returned to nor mal by CPAP therapy.