Relationship of daytime blood pressure and severity of obstructive sleep apnea among Chinese： a multi-center investigation in China

Background Epidemiologic studies have shown an independent and definite association between obstructive sleep apnea （OSA） and hypertension. This study aimed to define the association between daytime blood pressure and severity of OSA in Chinese population in mainland of China. Methods Twenty university hospital sleep centers in mainland of China were invited by the Chinese Medical Association （CMA） to participate in this epidemiologic study and 2297 consecutive patients （aged 18-85 years; 1981 males and 316 females） referred to these twenty sleep centers for evaluation of OSA between January 2004 and April 2006 were prospectively enrolled. Nocturnal polysomnography was performed in each patient, and disease severity was assessed based on the apnea-hypopnea index （AHI）. These patients were classfied into four groups： non-apneic control （control, n=257） with AHI 〈5 episodes/hour; mild sleep apnea （mild, n=402） with AHI 〉5 and 〈15 episodes/hour; moderate sleep apnea （moderate, n=460） with AHI 〉15 and 〈30 episodes/hour and severe sleep apnea （severe, n=1178） with AHI 〉30 episodes/hour. Daytime blood pressure measurements were performed under standardized conditions in each patient at 10 a.m. in office on the day of referring to sleep centers for getting average value. All the patients were requested to quit medications related to blood pressure for three days before the day of assessing. Results Both daytime systolic blood pressure and diastolic blood pressure values were significantly related to AHI positively （r = 0.201 and 0.276, respectively; both P values 〈0.001） and to nadir nocturnal oxygen saturation negatively （r = -0.215 and -0.277, respectively; both P values 〈0.001）, which were the parameters of OSA severity. In two special designed mean plots, means of daytime systolic and diastolic blood pressure increased gradually with increasing AHI. Beyond AHI of 61-65, this increasing trend reached a plateau. Conclusions The results showed that OSA severity was associated with daytime blood pressure until AHI of 61-65, providing evidence for early OSA management, especially in OSA patients with concomitant hypertension.

Elevated nocturnal and morning blood pressure in patients with obstructive sleep apnea syndrome

Background The nocturnal nondipping and elevated morning blood pressure （BP） in patients with obstructive sleep apnea syndrome （OSAS） have not yet been well investigated in Chinese patients. This study aimed to describe the BP profile, and to elucidate the relationships between daytime BP and nighttime BP, and between evening BP and morning BP in patients with OSAS. Methods Twenty teaching hospital sleep centers in China were organized by the Chinese Medical Association to participate in this study and 2297 patients were recruited between January 2004 and April 2006. BP assessments were made at four time points （daytime, evening, nighttime and morning） and polysomnography （PSG） was performed and subjects were classified into four groups by their apnea-hypopnea index （AHI）： control, n=213 with AHI 〈5; mild, n=420 with AHI -〉5 and 〈15; moderate, n=460 with AHI -〉15 and 〈30; and severe, n=1204 with AHI -〉30. SPSS 11.5 software package was used for statistical analysis and figure drawing. Results All the average daytime, nighttime, evening and morning BPs were positively correlated with AHI and negatively correlated with nadir nocturnal oxygen saturation. The ratios of nighttime/daytime and morning/evening average BP were positively correlated with AHI. The ratio of nighttime/daytime systolic BP became a ＂reversed BP dipping＂ pattern until the classification reached severe, while the ratio of nighttime/daytime diastolic BP became reversed at moderate. Similarly, the ratio of morning/evening diastolic BP becomes reversed even at mild. Conclusions OSAS may result in higher BP levels at all four time points. The ratios of nighttime/daytime and morning/evening BP increase with increased AHI. The increasing of diastolic BP, which is inclined to rise more quickly, is not parallel with increasing systolic BP.