Objective Previous studies have shown that the changes in body posture may have effects on upper airway obstructions during sleep in obstructive sleep apnea (OSA) patients.We hypothesize that during sleep with a supine trunk posture, the head position can affect the angle of the uvula due to gravity, which can therefore affect the cross-sectional size of the upper airway.Such a change in the upper airway patency should have an important effect on the severity of OSA.We investigate the relationships between the body posture, the head position, and apnea-hypopnea index (AHI) , oxygen deprivation index (ODI) in OSA patients during overnight sleep by using experimental methods.Methods We recruit 11 participants, including 3 mild, 3 moderate, and5 severe OSA patients.Overnight polysomnography isperformed, and their AHI and ODI are calculated.The real-time changes in body posture and head position are recorded by a monitor video.We analyze the data from the video and polysomnography to obtain the values of AHI and ODI at the lateral (including left and right) trunk position, supine trunk and head position, and supine trunk with the lateral head position.The results are analyzed statistically.Results In a 95% confidence interval, the AHI value [61.5 (46.1, 76.8) ]and ODI value [61.7 (45.5, 77.9) ]in the supine trunk and head posture are greater than the AHI value [32.2 (12.7, 51.6) ]and ODI value[31.0 (9.2, 52.8) ]in the supine trunk with the head rotation, and are also greater than AHI value [22.2 (4.4, 40.1) ] and ODI value[25.2 (3.6, 46.7) ]in the lateral posture.All the above differences are statistically significant.When the patients are divided into three groups:mild, moderate and severe, we find that the effect of each sleeping posture on AHI and ODI is similar in the three patient groups.Conclusions Similar to the case with a lateral posture, a supine trunk with the lateral head position can also effectively reduce the disordered respiratory events in OSA patients.