O039 A Novel Approach to Quantify Breathing effort in Obstructive Sleep Apnoea

INTRODUCTION: Breathing effort is an important component of obstructed breathing and determinant of arousal in obstructive sleep apnoea (OSA). However, relative effects of hypopnoea versus apnoea on effort and work of breathing (WOB) are largely unknown. This study applied a novel modelling approach to quantify breathing effort, WOB and obstruction severity to evaluate differences between hypopnoea and apnoea events in OSA. METHODS: 1659 apnoea and hypopnea events from six obese males (BMI: 30-41 kg/m2; age: 34-56 years; AHI: 31-114 events/hr) with severe OSA were evaluated using conventional sleep measures and a 3-compartment (nasal, collapsible upper airway and lungs) respiratory mechanics model using mask airflow and pressure, and oesophageal and epiglottic pressures. Attempted airflow and WOB, and WOB loss to obstruction (attempted minus measured WOB), were estimated breath-by-breath via the model for comparisons between hypopnoea and apnoea events and sleep stages. RESULTS: The model explained most of the variance in attempted flow (Pearson r= 0.91 [95% CI 0.71 to 0.98]). Compared to hypopnoea events, WOB loss during obstructive apnoeas was 3.5 [95%CI 1.7 to 5.4] times higher. WOB losses were also higher during deep versus N2 sleep. Visualising breath-by-breath WOB loss revealed a significant number of flow- limited breaths not detected using traditional human scoring. Over 30% of breaths not classified as hypopnoeas or apnoeas exhibited WOB loss higher than for hypopnoea events. CONCLUSIONS: Respiratory mechanics modelling is useful to assess breathing effort and upper airway obstruction severity and could provide novel mechanistic insights into sleep-related breathing problems and treatment outcomes.