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 SH ) 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 SH is obtained only during inspiration in eupnea and gasping and that integrated EMG SH increases more, as a percent of baseline (% baseline) than tidal volume (V T ) during gasping (median [interquartile range]; integrated EMG SH : 720 [425–1965] vs. V T : 300 [238–373], P < 0.05). We also found that the onset of EMG SH precedes the start of airflow while maintaining a bell-shaped EMG SH 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. • A high concentration of sevoflurane inhalation triggers gasping respiration with distinct mandibular movements in mice. • Suprahyoid muscles behave like a single upper airway dilator muscle during sevoflurane-induced gasping in mice. • Activation of suprahyoid muscles may contribute to the generation of mandibular respiratory movements.