O057 Pressure measurement site effects on the respiratory arousal threshold

Abstract Introduction Oesophageal (Poes) and epiglottic (Pepi) pressure provide the gold-standard measures of the respiratory arousal threshold, an important pathogenic feature in obstructive sleep apnoea (OSA). Poes versus Pepi deflection-based measures of the arousal threshold have not previously been examined but should differ given the mechanical properties of the respiratory system. Aim To systematically compare Poes versus Pepi measures of the respiratory arousal threshold. It was hypothesised that Pes would be systematically more negative than Pepi, particularly during hypopnoeas. Method 164 arousal events were retrospectively analysed from 5 male OSA patients and 5 male controls who underwent polysomnography along with peak epiglottic and oesophageal pressure deflection measurements on the last obstructed breath preceding respiratory event–related arousals. Results The arousal threshold was significantly more negative in OSA patients compared with controls (mean ± SE –24.7 ± 2.2 vs –6.8 ± 2.4 cmH₂O, p<.001) and was influenced by sleep stage in OSA (p<.001), with greater effort in N2 versus N1 (p=.001), but no group by measurement site interaction (p=.838). Across all events, Poes was more negative than Pepi (–17.8 ± 1.6 vs –14.6 ± 1.6 cmH₂O, mean difference –3.2 ± 1.3, p=.012). In OSA, Poes and Pepi did not differ during apnoeas (±1.7 cmH₂O, p=.485), but Poes was significantly more negative during hypopnoeas (–4.5 ± 2.2 cmH₂O, p=.045). Conclusion These results show that Pepi underestimates the arousal threshold in the presence of airflow. Thus, measurement site selection and reporting are important considerations the interpretation of respiratory arousal thresholds and cut-off selections in OSA.