SOFT PALATE MUSCLE-ACTIVITY IN RESPONSE TO HYPOXIC HYPERCAPNIA

We studied the effects of increasing respiratory drive on electromyogr aphic (EMG) soft palate muscle (SPM) activity in nine anesthetized tra cheostomy-breathing dogs during hypoxic hypercapnia (HH) with a 14% O- 2-8% CO2-78% N-2 inspired gas mixture. Moving time average EMG activit y was recorded from palatinus (PAL), levator veli palatini (LP), and t enser veli palatini (TP) muscles (with bipolar fine-wire electrodes) a nd diaphragm (DIA; with bipolar hook electrodes). During HH, peak insp iratory DIA activity increased from 18.8 +/- 1.3 to 30.1 +/- 2.0 arbit rary units and minute ventilation increased from 6.2 +/- 0.3 to 18.3 /- 1.8 l/min (both P < 0.001). Phasic inspiratory, expiratory, and/or tonic EMG activity was present in each SPM during room air breathing ( control) and increased during HH (P < 0.05), except for phasic inspira tory PAL and phasic expiratory TP activities. Peak inspiratory LP and TP activities increased during HH to 250 and 179% of control, respecti vely, and peak expiratory activity increased to 187, 235, and 181% of control in PAL, LP, and TP, respectively. These findings demonstrate r espiratory-related regulation of SPM activity independent of local ref lex control from the upper airway. However, the combined inspiratory a nd expiratory phasic recruitment of these muscles differs from the ins piratory recruitment of known upper airway dilator muscles.