Changes in the Suprahyoid Muscles’ Activity in Response to Increasing Concentrations of Sevoflurane in Spontaneously Breathing Mice
Authors List
Taiji Saki, Nishino Takashi, Jin Hisayo, and Isono Shiroh.
Department of Anesthesiology, Graduate School of Medicine, Chiba University, Japan
Background
Unlike common belief, some researchers have reported that volatile halogenated anesthetics such as halothane and isoflurane increase the upper airway dilator muscles’ (UADMs) activities by exciting the hypoglossal nerve in rats. Previously we found that increasing sevoflurane concentration under hyperoxia changes the breathing pattern in mice. Furthermore, a high sevoflurane concentration (2MAC; 6.5%) induces gasping breaths with visible mandibular movements, almost identical to hypoxia-induced gasping. Although the UADMs play an essential role in maintaining the patent airway, the effects of sevoflurane on the UADMs in mice have not been examined.
Since the visible mandibular movements of the sevoflurane-induced gasping indicate the strong activation of the suprahyoid muscles, the UADMs’ activities can be predicted to be augmented by sevoflurane. We hypothesize that sevoflurane inhalation increases the UADMs’ activities in mice dose-dependently.
Methods
Nine adult mice (C57BL/6) were anesthetized with sevoflurane, and the trachea of each mouse was intubated with a tracheal tube. The mice were allowed to breathe spontaneously at normothermia, and the ventilatory airflow and the subcutaneous electromyogram of the suprahyoid muscles (sEMGSHMs) were monitored continuously. The concentration of sevoflurane was changed, and the respiratory patterns were measured at defined concentrations of sevoflurane, i.e., 0.8, 1.0, 1.4, and 2.0 MACs.
Results
Increasing sevoflurane concentration caused progressive increases in tidal volume (VT), inspiratory drive (VT/TI), and sEMGSHMs’ activity (Figure). Especially at sevoflurane concentrations>1.4 MAC, VT and sEMGSHMs’ activity increased markedly with large mandibular movements. Significant correlations were obtained between VT/TI and integrated sEMGSHMs (R=0.74) and VT and integrated sEMGSHMs (R=0.75). On the other hand, minute ventilation and respiratory frequency progressively decreased. These results support our hypothesis.
Conclusion
Sevoflurane causes a progressive increase in suprahyoid muscles’ activity dose dependently, contributing to the development of mandibular respiratory movements and the maintenance of upper airway patency.
Taiji Saki, Nishino Takashi, Jin Hisayo, and Isono Shiroh.
Department of Anesthesiology, Graduate School of Medicine, Chiba University, Japan
Background
Unlike common belief, some researchers have reported that volatile halogenated anesthetics such as halothane and isoflurane increase the upper airway dilator muscles’ (UADMs) activities by exciting the hypoglossal nerve in rats. Previously we found that increasing sevoflurane concentration under hyperoxia changes the breathing pattern in mice. Furthermore, a high sevoflurane concentration (2MAC; 6.5%) induces gasping breaths with visible mandibular movements, almost identical to hypoxia-induced gasping. Although the UADMs play an essential role in maintaining the patent airway, the effects of sevoflurane on the UADMs in mice have not been examined.
Since the visible mandibular movements of the sevoflurane-induced gasping indicate the strong activation of the suprahyoid muscles, the UADMs’ activities can be predicted to be augmented by sevoflurane. We hypothesize that sevoflurane inhalation increases the UADMs’ activities in mice dose-dependently.
Methods
Nine adult mice (C57BL/6) were anesthetized with sevoflurane, and the trachea of each mouse was intubated with a tracheal tube. The mice were allowed to breathe spontaneously at normothermia, and the ventilatory airflow and the subcutaneous electromyogram of the suprahyoid muscles (sEMGSHMs) were monitored continuously. The concentration of sevoflurane was changed, and the respiratory patterns were measured at defined concentrations of sevoflurane, i.e., 0.8, 1.0, 1.4, and 2.0 MACs.
Results
Increasing sevoflurane concentration caused progressive increases in tidal volume (VT), inspiratory drive (VT/TI), and sEMGSHMs’ activity (Figure). Especially at sevoflurane concentrations>1.4 MAC, VT and sEMGSHMs’ activity increased markedly with large mandibular movements. Significant correlations were obtained between VT/TI and integrated sEMGSHMs (R=0.74) and VT and integrated sEMGSHMs (R=0.75). On the other hand, minute ventilation and respiratory frequency progressively decreased. These results support our hypothesis.
Conclusion
Sevoflurane causes a progressive increase in suprahyoid muscles’ activity dose dependently, contributing to the development of mandibular respiratory movements and the maintenance of upper airway patency.
