Cumulative brain desaturation: Time to consider brain derived parameters to measure daytime sleepiness in obstructive sleep apnea

Objective: /Background: The change in cerebral hemodynamics induced by sleep apneas and hypopneas may contribute to the daytime sleepiness in patients with obstructive sleep apnea (OSA). However, previous studies failed to discovery their relationship. We propose and test a new parameter, the cumulative brain oxygen desaturation, which may contribute to OSA patient's daytime sleepiness. Patients/methods: 22 patients with severe OSA (apnea-hypopnea index (AHI) at diagnosis [mean +/- standard deviation, std.]: 52.1 +/- 21.6/h, median: 45.1/h, interquartile range: 34.4-60.2/h) were monitored by poly-somnography during routine continuous positive airway pressure titration. The reductions of brain tissue oxygen saturation (StO2) in all respiratory events at baseline sleep were measured by frequency-domain near-infrared spectroscopy (NIRS). The cumulative brain desaturation was calculated as AHI times the mean StO2 desaturation (i.e., AHI x Delta StO2). Similarly, cumulative peripheral desaturation was also calculated, i.e., AHIx Delta SpO2 where Delta SpO2 was the mean reduction of peripheral arterial oxygen saturation (SpO2). The correlations between Epworth sleepiness scale (ESS) and AHI, Delta StO2, AHI x Delta StO2, and AHIx Delta SpO2 were tested, respectively. Linear regression was applied to predict ESS using AHIx Delta StO2 and AHI x Delta SpO2, with age and BMI as covariates. Results: ESS significantly correlates to the cumulative brain desaturation (Pearson's correlation coefficient: 0.68, p = 0.00056), not the other parameters. Regression analysis only finds significant association between ESS and the cumulative cerebral desaturation (p = 0.00195) but not the cumulative peripheral desaturation (p = 0.71). Conclusions: The cumulative brain oxygen desaturation, which comprehensively combines total sleep time, the frequency of apnea and hypopnea events, and the severity of cerebral oxygen desaturation, is a new indicator for daytime sleepiness in severe OSA.