INTRODUCTION This study focuses on endothelial function in obstructive sleep apnea (OSA) and its possible improvement with continuous positive airway pressure (CPAP) treatment. We report preliminary data from an ongoing study on evening and morning endothelial function in OSA patients before and after 3 months on CPAP treatment.

METHODS Evening (18:00) and morning (08:00) measurements of blood pressure and endothelial function were performed after <greater-or-equal-to> 4 hours of fasting by measuring reactive hyperemia peripheral arterial tone index (RH-PAT index) (Itamar Medical Ltd, Caesarea, Israel). Patients underwent a full polysomnography. Data evaluation was done in a standard manner, i.e. sleep scoring and apnea-hypopnea index (AHI) calculation.

RESULTS Altogether twenty otherwise healthy male OSA patients, with mean age 49, (range 2561) and mean AHI 42 (range 19-64), have been studied before treatment. There was not a significant difference between evening RH-PAT index (mean 2.13 ±  SD 0.47) and morning index (1.95 ± 0.39). Five patients (mean age 50, range 25-61) have been measured again after 3 months on CPAP. Mean AHI went from 46 (range 33-64) to 4 (range 1-10) after treatment. The average increase in evening index was from 1.82 ± 0.35 to 1.97 ± 0.44 (p = 0,04), and in morning index from 1.77 ± 0.15 to 2.09 ± 0.28 (p = 0,04). Compared to pre-treatment values, diastolic blood pressure was reduced in the morning (82 ± 10 mmHg to 76 ± 8 mmHg, p = 0.02).

DISCUSSION The first results from this ongoing study show that endothelial function is improved with treatment of OSA. This improvement is greatest in the morning.