Many previous studies have explained about the possible mechanism of preferred sleep positions. Considering strong association between obesity and heart failure, such findings may well explain the worsening of pRDI in LLDP in patients with higher BMI. Moreover, the cardiac vagal activity is greater in RLDP.
This is believed to be associated with lung diffusion impairment or further hemodynamic compromise induced by increased heart dimensions. In some studies, patients with chronic heart failure are recommended to avoid sleep in LLDP. Patients with higher RDI may be exposed to increase in cardiac sympathetic modulation. Respiratory effort-related arousals are known to be associated with elevation of cardiac sympathetic tone. Therefore, it can be hypothesized that LLDP might induce more increased respiratory efforts than RLDP. Unlike AHI, RDI includes respiratory effort-related arousals, and thus indicates not only apneas or hypopneas but also increased respiratory effort. One study has demonstrated no correlation between BMI and AHI, although neck and abdominal fat and neck circumference were more effective in predicting AHI. There have been several studies claiming of the weak or no correlation between AHI and BMI. Interestingly, patients with higher BMI showed higher pRDI in LLDP. However, the absolute value of the difference in pAHI between RLDP and LLDP showed no association with BMI. We primarily tried to focus on the anatomical factors related to higher BMI-induced lateral obstruction in each lateral decubitus sleep position. Although the association between BMI and the severity of OSA has been proven in many previous studies, association with the lateral decubitus position was not well known. The association between BMI and various sleep parameters in each lateral decubitus position was investigated. We used WatchPAT data and patient demographics to identify variables that may influence sleep parameters in RLDP and LLDP during sleep. Several studies have tried to analyze the effect of lateral sleep positions, but very few studies have focused on specific effects of right and left lateral decubitus position (RLDP and LLDP) on sleep parameters. On the contrary, the influence of the lateral decubitus sleep positions on OSA has not been well investigated. According to the American Academy of Sleep Medicine (AASM), positional OSA is defined as a lower AHI in the non-supine position than in the supine position. Based on these findings, the concept of positional OSA was first introduced by Cartwright as apnea-hypopnea index (AHI) being at least 50% greater in supine positions than in non-supine positions. Worsening of OSA occurs in supine positions rather than non-supine positions because of more frequent upper airway collapse. Some studies have demonstrated the effects of sleep positions on the severity of OSA. Obstructive sleep apnea (OSA) is a sleep disorder characterized by repeated upper airway collapse during sleep.
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