【Abstract】 Objective To study the effects of obstructive sleep apnea hypopnea syndrome ( OSAHS) on blood pressure variations, and explore the possible mechanism. Methods 84 adult patients ( mean age 50. 1 ±14. 8 years, male /female 67 /17) were recruited for polysomnography ( PSG) and ambulatory blood pressure monitoring. Four groups were identified based on apnea hyponea index ( AHI) ,ie. non-OSAHS group ( n=9) ,mild group ( n=19) , moderate group ( n=23) , and severe group ( n =33) .The blood pressure levels were compared among the four groups. Correlations between PSG indexes,variations of systolic blood pressure ( SBP) and diastolic blood pressure ( DBP) were analyzed. Results Inter-group blood pressure comparison showed significant differences in SBP and DBP( P lt;0. 05) , except forthe mild and the moderate OSAHS patients. As compared with the non-OSAHS patients, SBP for those with severe OSAHS was about 15 mm Hg higher, and DBP 10 mm Hg higher. Observation on SBP non-dipping rate indicated that, except for the mild and the moderate OSAHS patients where no significant differences were found, SBP non-dipping rate increased with the severity of OSAHS( the rates were 78. 3%, 57. 1% ,54. 5%, and 32. 6% , respectively for the four groups) , whereas DBP non-dipping rate significantly increased in the severe OSAHS patients( 54. 3% ) ( P lt;0. 05) . For the mild OSAHS patients, blood pressure was found to be correlated positively with the body mass index ( correlation coefficient for day time SBP was 0. 26, and for DBP was 0. 22) , the arousal index ( correlation coefficient for day time SBP was 0. 25, and for DBP was 0. 17) , and heart rate variation ( correlation coefficient for night time SBP was 0. 18, and for DBP was 0. 17) . For the moderate OSAHS patients, a positive correlation was also found between blood pressure and AHI ( correlation coefficient for day time SBP was 0. 31, and for DBP was 0. 22, correlation coefficient fornight time SBP was 0. 26) , and between blood pressure and the longest hypopnea time during sleep ( LH) ( correlation coefficient for night time DBP was 0. 2) . For the severe OSAHS patients, blood pressure was correlated positively with apnea index ( AI) ( correlation coefficient for day time SBP was 0. 61, and for DBP was 0. 5, correlation coefficient for night time SBP was 0. 57 and for night time DBP was 0. 48) . Conclusions OSAHS has ber impact on SBP than on DBP. DBP hypertension and SBP non-dipping are usually found in early OSAHS-affected patients. Factors affecting blood pressure differ with the severity of the OSAHS.