Influence of Apnea Type and Sleep Stage on Nocturnal Postapneic Desaturation

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Abstract
We examined the influence of apnea type and sleep stage on the severity of apnea-induced desaturations in 32 patients with a sleep apnea syndrome. The individual postapneic desaturations were evaluated by a desaturation curve; this curve was built by plotting the fall in SaO2 after an apnea against this apnea''s length for each apneic event during the whole night recording. We considered only apneas where the preapneic SaO2 was greater than 90% and the lowest SaO2 value after the apnea was equal to or greater than 60% (limit of linearity of our oximeter). From the desaturation curve, we determined a desaturation surface defined as the area under the curve between 10 s and a variable apnea duration. The upper bound used for the determination of the desaturation curve and the desaturation surface was the maximal length of apnea type with the shortest apnea duration between non-REM obstructive apnea and the other apnea types (i.e., obstructive and central apnea, obstructive and mixed apnea, etc.). The desaturation surface was determined separately for non-REM sleep apneas (obstructive apneas, mixed apneas, central apneas, and obstructive apneas with persistent expiratory flow) and REM sleep apnea (all obstructive in type). None-REM obstructive apneas served as reference to evaluate the severity of apnea-induced desaturations of the other apneas. We found that the desaturation surface of obstructive apnea (OA) with expiratory flow and of REM sleep OA were significantly greater than for OA in non-REM sleep (p .ltoreq. 0.005). The OA-related desaturation was significantly greater than those of central apneas (p = 0.005). Our results demonstrate that apnea type and sleep stage influence nocturnal postapneic falls in SaO2 independently of the apnea length.