MECHANISMS OF ORONASAL AIR-FLOW PARTITIONING IN DOGS

We examined the integrated (MTA) electromyographic activity (EMG) of t he hyoepiglotticus (HE) muscle and the soft palate muscles (SPM) durin g CO2 administration in 6 anaesthetised prone, mouth open dogs. As ven tilation increased nasal flow (VN) as; a percentage of total flow (VT) , i.e. VN/VT%, decreased. Breath-by-breath peak inspiratory and peak e xpiratory HE EMG activity was strongly and inversely correlated with V N/VT% (both r > 0.8, p < 0.001), whereas the correlation between SPM M TA EMG activity and VN/VT% was highly variable. Severing of the HE mus cles halved the rate at which VN/VT% was reduced with respect to incre asing ventilation while electrical stimulation of HE muscle contractio n resulted in a fall in VN/VT% to near zero levels. Active control of epiglottic position appears to be an important mechanism controlling t he patency of the epiglottic-soft palate seal and thus the oronasal pa rtitioning of airflow in dogs.