Table 2.

Drive-Related Event Pathophysiology

Characteristic	All Subjects	Classic	Drive-Dependent
Individual Events
N events	4747	2094	2653
Reduction in drive (%baseline)	20[3,42]	12[12,32]	27[4,53]
Reduction in flow (%baseline)	68[38,100]	70[39,100]	66[38,96]
Δdrive/Δflow (%)	34[−2,70]	20[−16,50]	47[10,83]
Proportion of events with falling drive (%)	74	66	80
Ensemble-Averaged Events
N patients	50	20	30
Reduction in drive (%baseline)	16[9,28]	5[12,−5]	23[16,37]
Reduction in flow (%baseline)	59[48,73]	65[46,79]	59[49,68]
Δdrive/Δflow (%)	26[16,46]	10[−10,18]	44[27,59]
Flow-drive correlation, R	0.78[0.24,0.94]	0.18[−0.38,0.30]	0.92[0.81,0.96]
Flow-drive nadir time difference (s)	4[2,8]	8[6.5,9.5]	2[1,5]

Continuous data shown are median[IQR]. Drive denotes diaphragm EMG (calibrated to units of ventilation, L/min). Flow denotes ventilation (tidal volume × respiratory rate). Reduction in drive denotes change in drive from baseline (below) to that measured during events (at nadir flow, see Methods). Reduction in flow denotes the change in flow during events (i.e. a 30% reduction is the theoretical minimum for a hypopnea; a value of 100% represents apnea). Baseline (pre-event) drive is measured at the time when flow is closest to eupneic levels. The fall in drive represented by Δdrive/Δflow seeks to quantify an aspect of the central nature of events: a value of 100% indicates that the fall in drive (Δdrive) is of equal magnitude to the fall in Δflow (and no exacerbation of obstruction). Flow-drive correlation (R) indicates the synchrony between flow and drive during events; a high value indicates that falling drive potentially explains (directly or indirectly) the reduction in flow.