EFFECT OF ELECTRICAL-STIMULATION OF THE HYPOGLOSSAL NERVE ON AIR-FLOWMECHANICS IN THE ISOLATED UPPER AIRWAY

To determine the influence of electrical hypoglossal (HG) nerve stimul ation on upper airway airflow mechanics, we analyzed pressure-flow rel ationships obtained during bilateral supramaximal HG nerve stimulation over a range of frequencies from 0 to 100 Hz in the isolated feline u pper airway. Inspiratory airflow (VI), hypopharyngeal pressure (Php), and pharyngeal pressure (Pph) immediately upstream from the flow-limit ing site (FLS) were recorded while Php was rapidly lowered to achieve inspiratory flow limitation in the isolated upper airway. Pressure-flo w relationships were analyzed to determine the maximum in VI (VImax) a nd the mechanical determinants of VImax, the upper airway critical pre ssure (Pcrit) and the nasal resistance (RN) upstream to the FLS. In gr oups of decerebrate spinally anesthetized (n = 6) and unanesthetized ( n = 6) cats, graded increases in VImax (p < 0.05) and decreases in Pcr it (p < 0.001) were observed as the stimulation frequency of the intac t HG nerves was increased. In the cats with and without spinal anesthe sia, VImax increased by 139 and 201%, and Pcrit decreased by 159 and 2 80%, respectively. RN was also correlated with stimulation frequency i n the cats without spinal anesthesia (p = 0.01) and increased in four of six cats with spinal anesthesia. In an additional six decerebrate c ats, significant increases in VImax (p < 0.001) and decreases in Pcrit (p = 0.01) were elicited by stimulating the distal cut HG nerve ends (50 Hz), whereas no changes were noted in these parameters when the pr oximal ends were stimulated. The findings suggest that HG stimulation increases VImax by decreasing Pcrit, which indicates a decrease in upp er airway collapsibility at the FLS. We speculate that this fall in co llapsibility was due to tongue protrusion, which decreased the tissue pressure surrounding the FLS in the velopharyngeal region. Increases i n VImax, however, were partially offset by concomitant increases in RN , which may have been due to narrowing of the upstream segment.