Does the required pressure difference between REM and NREM sleep during titration polysomnography impact on the severity of complex sleep apnoea?

Background: In complex sleep apnoea (Comp SA), pressures that are effective in controlling obstructive events during REM sleep are ineffective during NREM sleep due to emergence of central apnoeas. We hypothesized the difference in required pressures beween REM and NREM sleeps affects the emergence and severity of residual central apnoeas. Methods: Comp SA was defined as central apnoea index (CAI) > 5/h and central apnoeas/total apnoeas >0.5 during titration polysomnography(PSG). PREM was considered as the effective pressure to control obstructive events, while PNREM was considered as the pressure to control as few obstructive events as possible and not to induce central apnoeas. %Pd was determined as the percent of (PREM - PNREM)/PREM. The relationship between %Pd and residual apnoea hypopnoea index (AHI) and CAI was analyzed by regression analysis. A p<0.01 was considered significant. Results: Thirty-one male patients with Comp SA (mean age 46.5 years, body mass index 27.9 kg/m2, diagnostic AHI 40.6/h, titration AHI 14.9/h, CAI 10.7/h) were recruited retrospectively. The relationship between %Pd and AHI (r2 =0.54, p< 0.0001) or CAI (r2 =0.52, p< 0.0001) was fitted significantly by 2-degree polynomial regression. Conclusion: The larger the absolute value of %Pd, the higher AHI or CAI. Upper airway neuromuscular compensation during NREM sleep might be partly involved in the mechanism of Comp SA emergence.