Computer quantitation of saturation impairment time as an index of oxygenation during sleep

The measurement of oxygenation during sleep has become a standard procedure in the assessment of hypoxemia in patients with various disorders. However, an accepted method for quantitating this hypoxemia is not available. This study describes the development of computerized data acquisition and analysis programs to quantitate nocturnal hypoxemia in patients with sleep and breathing disorders. The acquisition program samples the voltage output from pulse oximeters used to measure oxyhemoglobin saturation (SpO2) and stores this on an IBM PC or compatible computer. The analysis program integrates the SpO2 over time below the patient's pretest baseline as well as the integral below 90, 80, 70, 60 and 50% saturation. We refer to each integral as Saturation Impairment Time or SIT. In order to compare these integrals between patients or between the same patient but different studies, the integral is divided by the total sleep study time. We refer to each of these integrals, corrected for sleep study time, as the SIT index. Evaluation of the SIT index in 10 consecutive patients referred for various sleep disorders revealed acquisition program detection and deletion of 48 of 57 (86%) oximeter probe artifacts (mean duration of 3 seconds for undetected artifacts). There were no significant artifacts in the analysis program calculation of the SIT index in these same patients. In conclusion, computer programs were developed to measure and quantitate oxygen saturation measured by oximeters. Preliminary results reveal an accuracy of measurement which should prove acceptable in further clinical evaluations.