The activity of suprahyoid muscles during sevoflurane-induced gasping in mice.

Sevoflurane-induced gasping in mice involves an enormous increase in inspiratory effort, mandibular movement, and a marked decrease in respiratory frequency (fR). We examined differences in breathing patterns and electromyogram activity (EMG) of the suprahyoid muscles (SHMs) during eupnea under 3.2 % (1 MAC: minimum alveolar concentration) sevoflurane inhalation and sevoflurane-induced gasping under 6.5 % (2 MAC) sevoflurane inhalation in eight spontaneously breathing, tracheally intubated, adult mice. We found that the phasic EMG is obtained only during inspiration in eupnea and gasping and that integrated EMG increases more, as a percent of baseline (% baseline) than tidal volume (V) during gasping (median [interquartile range]; integrated EMG: 720 [425-1965] vs. V: 300 [238-373], P < 0.05). We also found that the onset of EMG precedes the start of airflow while maintaining a bell-shaped EMG contour, which characterizes the EMG of upper airway dilator (UAD) muscles during eupnea and gasping. Vigorous respiratory-related mandibular movements were never observed during eupnea but were observed in seven of 8 mice during sevoflurane-induced gasping. Our observations indicate that SHMs act as a preferentially activating UAD muscle, contributing to the development of mandibular respiratory movements.