RESPIRATORY-FUNCTION OF VELOPHARYNGEAL CONSTRICTOR MUSCLES DURING WAKEFULNESS IN NORMAL ADULTS

The levator veli palatini (LVP) and the superior pharyngeal constricto r (SPC) influence velopharyngeal patency and soft palate position, but their behavior during respiration is incompletely characterized. To f urther clarify their respiratory function, we recorded electromyograph ic activity (EMG) in the LVP and the SPC in awake normal subjects brea thing orally. EMG data were obtained in six subjects for the LVP and i n nine subjects for the SPC. EMG activity and timing and ventilation w ere measured during isocapnic hypoxia and hyperoxic hypercapnia. Phasi c EMG activity was inconsistently present during unstimulated oral bre athing. Timing of EMG phasic activity was variable for both muscles. P eak LVP activity was mainly or exclusively expiratory in three of six subjects. Peak SPC activity was mainly or exclusively expiratory in fi ve of nine subjects. With chemostimulation, recruitment of phasic acti vity was observed in the LVP in four of six subjects and in the SPC in five of nine subjects. Tonic activity increased in four of six subjec ts for the LVP and in three of nine subjects for the SPC. However, the response was alinear, and intersubject as well as breath-to-breath va riability was substantial. In conclusion, LVP and SPC are characterize d by the high inter- and intrasubject variability of EMG activity timi ng of activation, and response to chemostimulation.