ABSTRACT
OBJECTIVE: The mechanisms involved in the development and maintenance of hypertension in obstructive sleep apnoea (OSA) are not clear. We hypothesized that OSA patients have an abnormal renal handling of sodium and water during the night. MATERIAL AND METHODS: We studied 29 OSA patients and 19 healthy controls at night with serial determinations of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), arginine vasopressin (AVP), aldosterone (Aldo), fractional urinary excretion of sodium (FE(Na)), free water clearance (C(H2O)), urinary excretion of aquaporin 2 (u-AQP2), systolic blood pressure (SBP), diastolic blood pressure (DBP) and oxygen saturation. RESULTS: OSA patients had a higher FE(Na) (0.6 (0.4-1.0) versus 0.4 (0.3-0.6) %; p = 0.017), SBP (129 (114-145) versus 114 (106-122) mmHg; p = 0.001) and DBP (81 (72-87) versus 71 (65-74) mmHg; p<0.001) than healthy controls at night. In hypertensive OSA patients, the FE(Na) correlated significantly with the change in nocturnal DBP (r (2) = 0.411; p = 0.010). Mean level of AVP during the night was higher in OSA patients compared with healthy controls (1.1 (0.8-1.4) versus 0.8 (0.6-1.1) pmol/L; p = 0.033) and correlated with SBP. ANP, BNP, Aldo, C(H2O) and u-AQP2 were the same in OSA and controls. CONCLUSIONS: We conclude that the higher fractional excretion of sodium in OSA is most likely attributable to pressure natriuresis. The correlation between mean AVP and blood pressure suggests that AVP may be part of the pathogenetic mechanism underlying hypertension in these patients.
