Subjects
Ten normal subjects and six renal transplant patients were studied. 			 All participants were male. Each subject gave informed consent and the hospital 			 ethics committee approved the study. The normal subjects were recruited from 			 the medical staff with a mean ± SD age of 24 ± 1.56 years and none of 			 them were on medication. Six male patients with renal allografts for treatment 			 of chronic renal failure were randomly recruited from the nephrology outpatient 			 department. They were at least 18 months post renal transplantation (mean 30 			 months) with an average age of 37.7 ± 4.27 years. Each patient had a stable 			 renal function, with serum creatinine level < 200mmol/l and no recent renal 			 complications. All patients were on immunosuppressive therapy which included 			 prednisolone, azothioprine and cyclosporin. Seven of the patients were on 			 antihypertensive medication, consisting of a beta-blocker in five cases and 			 nitrates in two. None of them had a history of cardiac or respiratory 			 disease.
Each subject was studied at a similar time each day. CPAP was 			 delivered via tight-fitting full-face mask by a continuous-flow system using a 			 Downs flow generator (Vital Signs, Boston, Massachusetts, USA). CPAP was 			 started at a level of 2.5 cmH2O and increased by increments of 			 2.5 cmH2O to a maximum of 7.5 cmH2O. CPAP was applied for 			 20 min at each of the three sequential pressure settings.