Figure 2.

Sec-by-sec averages (19 patients) of the change in heart rate after upper airway opening with five different interventions (see insert and Table 2). Brief events (no hypopnea, minimal, mild/moderage, and severe) were terminated deliberately by increasing continuous positive airway pressure (CPAP) after three breaths and were not associated with arousal. Long events terminated spontaneously with an associated arousal. Note that the response increases with event severity in observations without cortical arousal and that the pattern of increase is very similar. Response after severe long events (with arousal) was greater than after brief severe events and extended beyond 12 sec. Bars are standard error of the mean. Asterisks in brief dial-downs denote significant difference from heart rate just before increasing CPAP. Asterisks in the long dial-downs denote significant difference from heart rate just before airway opening. *P < 0.05; **P < 0.005; ***P < 0.0005.