Tracheal afferent nerves

Localization of Adductor and Abductor Motor Nerve Fibers to the Larynx

Knowledge of the location of motor nerve fibers to the adductor and abductor muscles of the larynx may be useful in the diagnosis and treatment of innervation disorders in this organ. Anterograde degeneration and retrograde tracer anatomical techniques have demonstrated the central and peripheral positions of these two groups of motor nerve fibers in the cat. Traditional nerve fiber degeneration methods applied following intracranial transection of the vagus nerve rootlets indicated that: 1) Most of the fibers in the recurrent laryngeal nerve (RLN) are motor; 2) Almost all of these motor fibers leave the brain stem in the most rostral rootlet(s) of the vagus nerve; and 3) Motor fibers to the larynx form a discrete bundle within the trunk of the vagus nerve before forming the RLN. A tracer (horseradish peroxidase) of retrograde axoplasmic flow in motor neurons has been employed to demonstrate: 1) Dorsoventral division of the adductor and abductor neurons in the nucleus ambiguus; and 2) Diffuse arrangement of both adductor and abductor nerve fibers in the vagus nerve but collection of these fibers into abductor and adductor halves of the RLN prior to entering the larynx. These findings dispel theories of differential cord paralysis (Semon's law) based on a vulnerable position of abductor fibers at the periphery of the RLN. Furthermore, the diffuse arrangement of these fiber groups explains the usually mixed functional results obtained following reimplantation of the RLN into a laryngeal muscle.

A new method to produce obstructive sleep apnoea in conscious unrestrained rats

We developed a new method to produce obstructive apnoea in conscious rats. An inflatable balloon contained in a rigid Teflon tube was implanted in the trachea to allow the induction of apnoea without inducing pain. We also developed a balloon-tipped catheter that was advanced along the trachea into the mediastinum for the measurement of intrathoracic pressure. Rats recovered well from implantation of these balloons. The tracheal implant, while deflated, did not significantly impair normal breathing (thoracic pressure swing during rest was 4.5 ± 0.4 mmHg before implantation and 5.8 ± 0.5 mmHg 4 weeks after implantation; P > 0.2; n = 7). Apnoeas of up to 16 s could be made during rapid eye movement sleep without awakening the rat. During 15 s of balloon inflation, arterial O(2) saturation fell from 98 ± 0 to 80 ± 2% and partial pressure of CO(2) increased from 35 ± 1 to 44 ± 1 mmHg (n = 9; P < 0.001). Intrathoracic pressure changes during the respiratory cycle increased from 6.3 ± 0.2 to 38.5 ± 6.0 mmHg (P < 0.001; n = 4), indicating increased breathing effort. Heart rate fell from 373 ± 23 to 141 ± 18 beats min(-1) (P < 0.001; n = 4), and the heart beat became irregular, with few beats during expiratory effort. These responses remained intact after 60 apnoea episodes. Responses developed slightly more slowly when apnoea started at the end than at the beginning of the respiratory cycle. As these balloons last for a long time, cause few complications, allow induction of apnoea during sleep, allow induction of apnoeas that start at a fixed point in the respiratory cycle and elicit cardiorespiratory responses similar to those observed in humans, these balloons may aid investigation of both acute apnoea and chronic intermittent sleep apnoea.

The use of a silicone T-tube to treat tracheal stenosis in a llama

A female llama was presented at 4 days of age with severe dyspnea resulting from bilateral choanal atresia. A tracheostomy was performed before surgical treatment of the airway obstruction. Although the choanal atresia was successfully corrected, tracheal stenosis secondary to mucosal necrosis, malacia of the cartilage rings, and proliferation of intraluminal granulation tissue at and distal to the tracheal stoma developed. The affected segment of the trachea was resected and an end-to-end anastomosis was performed, but the lumen again became obstructed by granulation tissue. A silicone "T-tube" was placed in the trachea to provide a patent airway and intraluminal support. The llama has done well for 12 months with this prosthesis, and the complications that are often seen with long-term use of traditional tracheostomy tubes have not developed.

Extravagal innervation of canine tracheal stretch receptors

In dogs an extravagal pathway consisting of the pararecurrent nerve, the ramus anastomoticus, the internal branch of the superior laryngeal nerve, and the superior laryngeal nerve carries nerve fibres from the upper trachea. A segment of the upper trachea innervated by fibres in this pathway was isolated in situ and ventilated separately from the rest of the respiratory tract. Single unit and whole nerve neurograms recorded from the pararecurrent nerve, the ramus anastomoticus, and the interior branch of the superior laryngeal nerve demonstrated discharge patterns characteristic of airway stretch receptors. The discharge was strongly modulated by ventilatory manoeuvres of the isolated tracheal segment but not the rest of the respiratory tract. The number of tracheal stretch receptors with fibres in this non-vagal pathway was found to be similar to the number innervated by vagal pathways. A search for the presence of extravagal fibres innervating rapidly adapting receptors, however, was unsuccessful. A non-vagal pathway exists between tracheal stretch receptors and the nodose ganglion. The functional significance of this pathway was not determined.