Factors influencing sleep time with oxygen saturation below 90% in sleep-disordered breathing

To determine factors influencing sleep time with oxygen saturation below 90% (ST₉₀) in a population referred to a tertiary sleep center for assessment of possible sleep-disordered breathing (SDB).

Retrospective review of demographic and polysomnographic data of 731 consecutive patients with suspected SDB.

Bivariate correlation analyses were performed, and Spearman rho coefficients were calculated. Variables with a marginal association with ST₉₀ (P < .05) in the bivariate analysis were included into the multiple regression analysis.

The distributions of SDB were as follows: normal/simple snoring, 18.2%; mild obstructive sleep apnea (OSA), 25.6%; moderate OSA, 17.4%; and severe OSA, 38.9%. The univariate analysis revealed a significant correlation between ST₉₀ and age (r = 0.204), body mass index (BMI) (r = 0.440), arousal index (r = 0.754), apnea-hypopnea index (AHI) (r = 0.761), mean oxygen saturation (SaO₂) (r = -0.506), and mean O₂ desaturation (r = 0.858) (P < .001 for all parameters). In multiple regression analysis, age (P < .001), BMI (P = .040), male gender (P = .001), AHI (P < .001), mean SaO₂ (P < .001), and mean O₂ desaturation (P < .001) were found to be independent parameters influencing ST₉₀. Furthermore, these parameters explained a significant proportion of variance in ST₉₀ (R(2)  = 0.794, F (6, 729) = 464.65, P < .001). Although there was a strong correlation between AHI and ST₉₀ (r = 0.76, P < .001), a large variation of ST₉₀ values was observed, especially within the severe OSA group.

The study results provide supporting evidence that patients with similar AHI may have quite different values of ST₉₀, and thereby hypoxia. The stratification of patients with OSA according to AHI combined with ST₉₀ may allow better identification of prognostic information.