The effects of negative pressure applied to just the upper airway on nasal and laryngeal muscle activity were studied in 14 spontaneously breathing anesthetized dogs. Moving average electromyograms were recorded from the alae nasi (AN) and posterior cricoarytenoid (PCA) muscles and compared with those of the genioglossus (GG) and diaphragm. The duration of inspiration and the length of inspiratory activity of all upper airway muscles was increased in a graded manner proportional to the amount of negative pressure applied. Phasic activation of upper airway muscles preceded inspiratory activity of the diaphragm under control conditions; upper airway negative pressure increased this amount of preactivation. Peak diaphragm activity was unchanged with negative pressure, although the rate of rise of muscle activity decreased. The average increases in peak upper airway muscle activity in response to all levels of negative pressure were 18 +/- 4% for the AN, 27 +/- 7% for the PCA, and 122 +/- 31% for the GG (P less than 0.001). Rates of rise of AN and PCA electrical activity increased at higher levels of negative pressure. Nasal negative pressure affected the AN more than the PCA, while laryngeal negative pressure had the opposite effect. The effects of nasal negative pressure could be abolished by topical anesthesia of the nasal passages, while the effects of laryngeal negative pressure could be abolished by either topical anesthesia of the larynx or section of the superior laryngeal nerve. Electrical stimulation of the superior laryngeal nerve caused depression of AN and PCA activity, and hence does not reproduce the effects of negative pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of vagally mediated volume-related feedback on the activity of upper airway muscles was assessed in nine pentobarbital-anesthetized, tracheostomized, spontaneously breathing dogs. Moving average electrical activity was recorded before and during single-breath airway occlusions from the genioglossus, posterior cricoarytenoid, and alae nasi muscles and compared with simultaneously recorded tidal volume and electrical activity of the phrenic nerve (6 dogs) or diaphragm (3 dogs). The normally early peak of upper airway muscle activity during unoccluded breaths was delayed to late or end inspiration during occluded breaths. Inspiratory depression started at a lower volume above end-expiratory volume and at an earlier time after inspiratory onset for the upper airway muscles than for the phrenic nerve and the diaphragm. The amount of depression at the end of inspiratory airflow was larger for all of the upper airway muscles than for the phrenic nerve and diaphragm. Depressive effects were most prominent in the genioglossus, followed by the posterior cricoarytenoid and the alae nasi. After vagotomy, depressive effects of volume-related feedback were no longer seen. These results suggest that activity of the upper airway muscles is modulated by vagally mediated feedback, apparently to a larger extent than that of the diaphragm and phrenic nerve.

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