Abstract
Maintaining the patency of the upper airway during breathing is of vital importance. The activity of various muscles is related to the patency of the upper airway. In the present study, we examined the respiratory motor activity in the efferent nerves innervating the upper airway muscles to determine the movements of the upper airway during respiration under normocapnic conditions (pH = 7.4) and in hypercapnic acidosis (pH = 7.2). Experiments were performed on arterially perfused decerebrate rats aged between postnatal days 21–35. We recorded the efferent nerve activity in a branch of the cervical spinal nerve innervating the infrahyoid muscles (CN), the hypoglossal nerve (HGN), the external branch of the superior laryngeal nerve (SLN), and the recurrent laryngeal nerve (RLN) with the phrenic nerve (PN). Inspiratory nerve discharges were observed in all these nerves under normocapnic conditions. The onset of inspiratory discharges in the CN and HGN was slightly prior to those in the SLN and RLN. When the CO2 concentration in the perfusate was increased from 5% to 8% to prepare for hypercapnic acidosis, the peak amplitudes of the inspiratory discharges in all the recorded nerves were increased. Moreover, hypercapnic acidosis induced pre-inspiratory discharges in the CN, HGN, SLN, and RLN. The onset of pre-inspiratory discharges in the CN, HGN, and SLN was prior to that of discharges in the RLN. These results suggest that the securing of the airway that occurs a certain time before dilation of the glottis may facilitate ventilation and improve hypercapnic acidosis.
Highlights
Coordination of the patency of the upper airway with contraction of the diaphragm and intercostal muscles is important during breathing
We first examined the patterns of respiratory motor activity in efferent nerves innervating the upper airway muscles under normocapnic conditions (5% CO2) to determine the activation patterns of the upper airway during respiration
Discharges in the recurrent laryngeal nerve (RLN), superior laryngeal nerve (SLN), and cervical spinal nerves (CN) emerged with the phrenic nerve (PN) discharge (Fig 1A); their onsets slightly preceded the onset of the PN discharge (Fig 1B, Table 1)
Summary
Coordination of the patency of the upper airway with contraction of the diaphragm and intercostal muscles is important during breathing. Respiratory Nerve Activity of the Upper Airway cricothyroid and inferior pharyngeal constrictor muscles innervated by the external branch of the superior laryngeal nerve (SLN) [3], and the laryngeal abductors (posterior cricoarytenoid muscle) and laryngeal adductors (lateral cricoarytenoid muscle and thyroarytenoid muscle) innervated by the recurrent laryngeal nerve (RLN) [3]. Few studies have investigated the respiratory motor activity in the other muscles of the upper airway or in the nerves innervating those muscles despite the fact that coordinated and appropriate movement of the upper airway muscles is important in regulating the airflow through the upper airway during respiration
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