Determinants of respiratory disturbance and oxygen saturation drop indices in obstructive sleep apnoea syndrome.

Although chronic sleep fragmentation and oxygen saturation (Sao2) drops alone do not induce obstructive sleep apnoea (OSA), both are part of the feedback loop leading to obstructive sleep apnoea syndrome (OSAS). To determine factors in respiratory disturbance and Sao2 drops, we used polysomnographic and cephalometric data from 120 OSAS patients to construct a model which we then applied prospectively to 25 new OSAS patients, calculating the correlation between observed and predicted values. We found body mass index and the amount of stage 1 non-rapid eye movement sleep to be significant variables when considering both the respiratory disturbance index (RDI) and Sao2 drops. Posterior airway space was also a significant variable for RDI. Forced expiratory volume in one second, expressed as the percentage of forced vital capacity (FEV1/FVC), was significant when considering Sao2 drops. Upper airway abnormalities were also significant variables in the models and must be considered when treating OSAS patients.