UPPER AIRWAY DILATING MUSCLE HYPERACTIVITY DURING NONRAPID EYE-MOVEMENT SLEEP IN ENGLISH BULLDOGS

Sleep-disordered breathing (SDB) is seen during rapid eye movement (RE M) sleep in English bulldogs, but it is absent during non-REM sleep. T he SDB during REM sleep is associated with changes in neural drive to the diaphragm (DIA) and to an upper airway dilator, the sternohyoid (S H). In the present study, the EMG activity of the DIA was recorded in unrestrained, naturally sleeping, English bulldogs (n = 6) and in cont rol dogs (n = 5). The EMG of the SH was recorded in five of these bull dogs and in four of the control dogs. The activity of the DIA was simi lar in the two groups of dogs throughout sleep, with the normal increa sed variability and altered recruitment patterns during REM sleep in a ll dogs. However, in the presence of the narrowed upper airway of bull dogs, the pattern of the upper airway dilator was dramatically differe nt. In bulldogs, SH activity was virtually always related to inspirati on (96 to 100% of breaths during both waking and non-REM sleep). In co ntrast, SH activity showed inspiratory-related increases in only a min ority of breaths during non-REM sleep (32%) in control dogs (p < 0.05) . Furthermore, SH drive, as measured by the plateau amplitude, fell du ring REM sleep in bulldogs, whereas it increased in control dogs (p < 0.05). In control dogs without SDB, we found that central respiratory drive to the SH was highest but variable during waking and minimal dur ing non-REM sleep and that it fluctuated with phasic events during REM sleep. In bulldogs, however, high levels of SH activity occurred duri ng waking and throughout non-REM sleep, apparently preventing SDB in t hese states. Episodic decreases in SH drive were observed during REM, and they were associated with SDB. These data support the proposition that compensatory pharyngeal dilator hyperactivity is necessary to mai ntain airway patency and normal breathing in bulldogs, a canine breed with an anatomically compromised upper airway.