Better sleep quality could reinforce the relationship between sleep posture and kidney stone laterality in obstructive sleep apnea patients.

Urolithiasis is a common urologic problem among adults worldwide. It is interesting that urinary stones tend to recur on the same side and the pathophysiology of unilateral stone formation is not clearly understood. Researchers found that sleep posture could alter renal perfusion, and subsequent vascular injury may lead to urolithiasis formation. The aim of this study is to retrospectively evaluate the correlations between the specific sleep postures recorded in polysomnography (PSG) and the stone laterality in unilateral urinary stone formers with obstructive sleep apnea (OSA). We retrospectively reviewed patients receiving PSG for the diagnosis of OSA in our institutes between January 1st 2002 and September 30th 2016. Those had a history of unilateral urinary stones which surgical intervention was warranted were included. Supine, prone, right decubitus, and left decubitus sleep postures were determined as patients remained specific postures for more than 50% of their sleep time. The laterality of stones with sleep posture was analyzed with Chi-square test. A student t test was used to assess factors that influenced the ipsilateral stone formation. IBM SPSS Statistics 21 software was adopted to analyze the data, and p value less than 0.05 was considered statistically significant. 117 patients were enrolled in this study, among which 105 (89.7%) were male and 12 were female. The mean age at PSG examination was 53.5 ± 11.5 years. 66 patients were diagnosed as left-side urolithiasis, and 51 patients had urinary stones at right side. 58 (49.6%) patients slept predominantly in supine posture, while 53 (45.3%) patients, in decubitus posture, and no patient, in prone posture. A total of 51 patients' stones appeared at the same side as their decubitus posture (p < 0.0001). Shorter sleep stage I ratio (24.3 ± 15.5% versus 52.4 ± 24.7%, p = 0.017), longer sleep stage II + III + IV ratio (66.2 ± 21.9% versus 30.9 ± 2.8, p = 0.049), and less sleep stage change (176.6 ± 69.6 times versus 282.5 ± 91.2 times, p = 0.041) were correlated with stone formation on the same side. Age, gender, body mass index, and other polysomnographic parameters failed to demonstrate associations between the sides of urinary calculi and sleep postures. We discovered that sleep posture is associated with unilateral urolithiasis formation. Favorable sleep quality and less sleep stage changes could consolidate the correlations. Further prospective study is warranted to evaluate the effect of sleep posture and quality on non-OSA patients as well as the preventive effect of sleep posture modification on repeated unilateral stone formers.