Flextube reflectometry and pressure-recordings for level diagnosis in obstructive sleep apnoea

The objective of this study was to compare sound reflections in a flexible tube (flextube reflectometry) with pressure-catheter recordings (ApneaGraph) for identifying the predominant obstructive level of the upper airway during sleep. Seventeen males with suspected obstructive sleep apnoea syndrome (OSAS) were included in the study. The mean (standard deviation = SD) number of flextube narrowings per hour recording was 50.2 (20.4) and the mean (SD) RDI (respiratory disturbance index = apnoeas and hypopnoeas per hour recording) determined by the ApneaGraph was 45.7 (20.2). The mean difference (SD) between the number of flextube narrowings per hour recording and the RDIs determined by the ApneaGraph was not statistically significantly different from 0. There was no statistically significant correlation between the percentage of retropalatal narrowing of the total narrowing (retropalatal and retrolingual narrowing) measured by flextube reflectometry and the percentage of retropalatal ("upper") obstructive apnoeas and hypopnoeas of the total number ("upper", "intermediate" and "lower") measured by ApneaGraph (Spearman's correlation coefficient r = 0.24, p = 0.36, N = 17). In conclusion diverging results were found in flextube reflectometry studies and pressure-recordings performed on different nights regarding the level distribution of obstructions during sleep. Possible explanations of this discrepancy are discussed.