Comparison of two methods of quantitative assessment of hypoxemia in patients with sleep disorders

Objective: To evaluate the validity of two methods of quantifying oxygen saturation during sleep: saturation impairment time (SIT) index and percentage of time spent below various levels of oxygen saturation (%T).Background: Although many methods of reporting nocturnal hypoxemia in sleep have been utilized, no 'gold standard' has been identified to report in conjunction with frequency of breathing pauses. We compare two such methods.Methods: Prospective, non-randomized, double-blind, controlled trial on 298 patients referred to a sleep-disorders center. In-laboratory recording of nocturnal polysomnography with the data from the pulse-oximetry channel stored in a computer for subsequent analysis. SIT index and %T data were compared for each patient, as were values between patient groups. Raw and logarithmic transformed data were analyzed using regression and non-parametric methods.Results: SIT index and %T data correlate well, but deviations exist between the results of these tests in individual patients and between some patient groups.Conclusion: SIT index, combining time and severity of desaturation, may provide additional useful data in the study of oxygen desaturation in sleep, compared to %T calculations. Such data may be important in future studies of physiological variables.