Figure 1. EMG_GG remains elevated after a CPAP drop beyond the return of ventilation to baseline.

Example of a CPAP drop and calculation of the genioglossus AD duration. After a CPAP drop lasting five breaths, the CPAP is increased back to the optimum pressure. At this pressure, the ventilation matches the ventilatory drive because the airways are completely open. The increased ventilatory drive in the first breaths after the CPAP dial‐up is considered as the response to transient hypoxia/hypercapnia (with a possible contribution from diaphragmatic AD) (Jordan et al. 2002). In this example, the ventilation returned to baseline (pre‐drop) values after four breaths (right of shaded region). After this time, the genioglossus activity remained elevated above baseline (pre‐drop) levels for multiple breaths (orange horizontal box); note that the tonic (i.e. minimum value in expiration) in particular is increased, suggesting that a neural memory specific to the genioglossus (independent of the diaphragm and phasic/respiratory‐related activity) is at play at this time. Genioglossus AD was measured from the time in which ventilatory drive (ventilation) was back to eupnoea after the CPAP drop to the time in which the genioglossus was back to baseline (pre‐drop) levels. From top to bottom: EMG_GG moving time average (arbitrary units, A.U.), EMG_GG raw data (μV), ventilatory flow (L s^–1) and continuous positive airway pressure level (mask pressure, cmH₂O). [Color figure can be viewed at http://wileyonlinelibrary.com]