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.