Mechanisms of oronasal airflow partitioning in dogs

We examined the integrated (MTA) electromyographic activity (EMG) of the hyoepiglotticus (HE) muscle and the soft palate muscles (SPM) during CO2 administration in 6 anaesthetised prone, mouth open dogs. As ventilation increased nasal flow (Vn) as a percentage of total flow (Vt), i.e. Vn/Vt%, decreased. Breath-by-breath peak inspiratory and peak expiratory HE EMG activity was strongly and inversely correlated with Vn/Vt% (both r > 0.8, p < 0.001), whereas the correlation between SPM MTA EMG activity and Vn/Vt% was highly variable. Severing of the HE muscles halved the rate at which Vn/Vt% was reduced with respect to increasing ventilation while electrical stimulation of HE muscle contraction resulted in a fall in Vn/Vt% to near zero levels. Active control of epiglottic position appears to be an important mechanism controlling the patency of the epiglottic-soft palate seal and thus the oronasal partitioning of airflow in dogs.