Nocturnal blood pressure fluctuations measured by using pulse transit time in patients with severe obstructive sleep apnea syndrome

Background Obstructive sleep apnea syndrome (OSAS) is related to arterial hypertension. In the present study, we test the hypothesis that patients with severe OSAS have excessive apnea induced blood pressure (BP). Methods We investigated 97 patients with an apnea/hypopnea index (AHI) greater than 30. Systolic BP (SBP) was continuously determined by using the pulse transit time (PTT). Apnea/hypopnea induced nocturnal BP fluctuations (NBPFs) were detected and showed phenomena of continuous increases of the SBP baseline. Such periods of SBP baseline elevations >= 10 mmHg were called superposition. Respiratory and cardiac parameters were obtained from the polysomnographic investigation. Results Eighty-four periods of superposition were detected in 48 patients. They occurred mainly during REM sleep (76%). Apnea duration was increased and the time in respiration was reduced in periods of superposition compared to nonsuperposition periods. In superposition periods mean oxygen saturation (SpO(2)) and the minimal SpO(2) were lower, desaturations were more pronounced, and the mean heart rate (HR) was increased. The maximum SBP during superposition was significantly increased (204 +/- 32 vs. 171 +/- 28 mmHg). The clinic BP was higher in patients with superposition (SBP 149.2 +/- 17.5 vs. 140 +/- 19.1, DBP 91.5 +/- 11.5 vs. 86.3 +/- 11.8). Conclusions The study reveals that patients with severe OSAS can have periods of BP superposition during night with extremely high SBP and very low oxygen saturation, which may add to a high risk for cardiovascular events during the night.