Apnoea-Hypopnoea Index: Variability During a Short-term Follow-up

Objectives: The apnoea-hypopnoea index (AHI) is frequently used to classify the severity of obstructive sleep apnea (OSA), and to evaluate therapeutic success. Although significant AHI variability over consecutive nights has been reported, variability over a longer period, which corresponds better with the “clinical situation” of therapy evaluation, has not been reported before. Knowledge of AHI variability is necessary to estimate the smallest significant change in AHI, using the so-called smallest detectable difference (SDD; Kropmans TJ et al, 1999). The aim of the present study, that is part of a controlled RCT in which a mandibular advancement device is compared with both nasal continuous positive airway pressure and a placebo appliance, was to determine the SDD of AHI in a placebo group during a short-term follow-up. Methods: So far, four mild-to-moderate OSA patients (mean age = 40.0 ± 7.8 years) underwent four polysomnographic (PSG) recordings after delivery of the placebo appliance with an interval of four weeks between the recordings. The recordings were performed at home, using ambulatory equipment. The PSG recordings were manually analysed by a single observer. Results: The intra-examiner reliability for the AHI scores was excellent (ICC = 0.96). The mean AHI values of the four patients were not significantly changed throughout the study period (ANOVA; F = 1.80; P = 0.218); the SDD in AHI was 6.6. Conclusion: These preliminary results suggest that a change in AHI of about 7 in individual OSA patients may be considered statistically significant. As a consequence, a therapy for OSA can only be qualified as having an effect when a decrease in AHI of at least 6.6 has been achieved. (Supported by the IOT.)