Obstructive sleep apnoea (OSA) is the main cause of secondary hypertension. The main trigger mechanism for the causality is increase in sympathetic tone. Randomized controlled trials have suggested that blood pressure (BP) reduction is higher with fixed CPAP versus APAP but mechanisms are poorly established. We hypothesized a different impact of the two PAP modalities on sympathetic tone. This double blind randomized controlled trial compared sympathetic activity after 4-week of APAP versus fixed CPAP in treatment-naive OSA patients.

We included 56 adults OSA. 43 were compliant during a run-in one-week period and were randomized to APAP, (23 (53.5%)) or fixed CPAP (20 (46.51%)) arms. Muscle sympathetic nerve activity (MSNA), urinal catecholamines and 24-hour BP were obtained at baseline and intervention.

Median age, BMI, and percentage of prevalent hypertension were 57 [49;64] years, 30.5 [28.6;34.6] kg/m², 37.2%. Patients exhibited severe OSA with a median Epworth sleep Scale, AHI and ODI of 11 [9;16], 35.7/h [28.6;44.2], and 30.2/h [24.6;43.5], respectively. MSNA bursts/min reductions after APAP and CPAP were 32.7 [29.2;37] to 29.9 [22.6;37.3] and 37 [30.4;52.1] to 31.3 [18.5;39], respectively. There was a significant larger reduction of sympathetic tone in the CPAP group consistent across the different methods of assessment (i.e.: MSNA burst/min and burst/100hb, urinal epinephrin and norepinephrine, p<0.01, p<0.01, p=0.02 and p=0.02, respectively). Improvement in BP was similar between the two arms.

Higher reduction in sympathetic tone was achieved by CPAP compared to APAP, that may impact hypertension managemen in OSA.