Neural ventilatory drive decline as a predominant mechanism of obstructive sleep apnoea events.

ABSTRACT

BACKGROUND: In the classic model of obstructive sleep apnoea (OSA), respiratory events occur with sleep-related dilator muscle hypotonia, precipitating increased neural ventilatory 'drive'. By contrast, a drive-dependent model has been proposed, whereby falling drive promotes dilator muscle hypotonia to precipitate respiratory events. Here we determine the extent to which the classic versus drive-dependent models of OSA are best supported by direct physiological measurements. METHODS: In 50 OSA patients (5-91 events/hour), we recorded ventilation ('flow', oronasal mask and pneumotach) and ventilatory drive (calibrated intraoesophageal diaphragm electromyography, EMG) overnight. Flow and drive during events were ensemble averaged; patients were classified as drive dependent if flow fell/rose simultaneously with drive. Overnight effects of lower drive on flow, genioglossus muscle activity (EMGgg) and event risk were quantified (mixed models). RESULTS: On average, ventilatory drive fell (rather than rose) during events (-20 (-42 to 3)%baseline, median (IQR)) and was strongly correlated with flow (R=0.78 (0.24 to 0.94)). Most patients (30/50, 60%) were classified as exhibiting drive-dependent event pathophysiology. Lower drive during sleep was associated with lower flow (-17 (-20 to -14)%/drive) and EMGgg (-3.5 (-3.8 to -3.3)%max/drive) and greater event risk (OR 2.2 (1.8 to 2.5) per drive reduction of 100%eupnoea); associations were concentrated in patients with drive-dependent OSA (ie, flow -37 (-40 to -34)%/drive, OR 6.8 (5.3 to 8.7)). Oesophageal pressure-without tidal volume correction-falsely suggested rising drive during events (classic model). CONCLUSIONS: In contrast to the prevailing view, patients with OSA predominantly exhibit drive-dependent event pathophysiology, whereby flow is lowest at nadir drive, and lower drive raises event risk. Preventing ventilatory drive decline is therefore considered a target for OSA intervention.