EFFECT OF NASAL CPAP TREATMENT ON PLASMA-VOLUME, ALDOSTERONE AND 24-HBLOOD-PRESSURE IN OBSTRUCTIVE SLEEP-APNEA

Polycythaemia, peripheral oedema formation and hypertension have class ically been described in association with obstructive sleep apnoea (OS A). However, there is very limited information about blood volume in O SA and how it changes during longterm treatment with nasal continuous positive airway pressure (nCPAP). Plasma (PV) and red-cell volumes (RC V), 24-h ambulatory blood pressure (BP), 24-h natriuresis and morning plasma aldosterone, renin activity and atrial natriuretic peptide in 1 1 men with a mean age of 47 y (range 37-55), apnoea index (Al) of 55 ( 22-106), body mass index of 36 (30-43) and seated BP of greater than o r equal to 140/90 mmHg without any medication were measured. BP-measur ements were repeated after 3 weeks and all measurements after 3 mo of nCPAP treatment. Aldosterone and 24-h mean heart rates decreased durin g treatment. Twenty-four-h BP decreased after 3 weeks but that-decreas e did not persist after 3 mo of treatment. There was a relationship be tween changes in night-time mean BP and PV and aldosterone. The haemat ocrit declined in every patient. No significant changes were found in the mean PV or RCV. They were in all instances lower than has earlier been described for normal, non-obese subjects. These data also suggest that OSA causes divergent individual disturbances in blood volume hom eostasis which can be corrected by nCPAP.