Influence of Lung Stretch Receptors on the Cough Reflex in Rabbits

Abstract

The cough reflex in anaesthetized rabbits was elicited by irritation of the larynx with ammonia, inhalation of ammonia into the lungs, and mechanical stimulation of the tracheobronchial tree with a catheter. After block of lung stretch receptors with sulphur dioxide and virtual abolition of the Breuer-Hering inflation reflex, the cough response to all three stimuli was far less frequent and, when it occurred, was weaker especially with respect to the expiratory efforts. It is concluded that the Breuer-Hering reflex enhances the cough reflex, although modification of the sensitivity of tracheobronchial cough and irritant receptors by sulphur dioxide may also influence the cough.

Neurogenesis of cough, other airway defensive behaviors and breathing: A holarchical system?

“…Suppression of pump cell activity by antitussive drugs is unlikely to be responsible for our observations because in our study these drugs had no effect on eupneic respiratory phase durations or diaphragm EMG amplitude (Bolser et al, 1999). SAR afferent input does have an integral role in the production of tracheobronchial cough, and it is a permissive one (Hanacek et al, 1984;Sant'Ambrogio et al, 1984). Indeed, in a recent study, we found no evidence for a direct role of SAR afferent input on phase durations during tracheobronchial cough (Bolser and Davenport, 2000a).…”

“…Decreased excitability of this group of neurons would be expected to result in prolongation of cough phase durations. Indeed, unilateral vagotomy elicits exactly this effect on the cough reflex induced by ammonia in rabbits (Hanacek et al, 1984). This intervention decreased the frequency of coughing without altering the number of coughs per trial, indicating that cough phase durations were prolonged.…”

“…These gating elements also integrate afferent feedback from SARs through their interneurons (pump cells). Unlike their integral role in the production of tracheobronchial cough, SARs only have a facilitatory effect on laryngeal cough (Hanacek et al, 1984;Sant'Ambrogio et al, 1984). Each holon utilizes the reconfigured core respiratory network to regulate the spatiotemporal features of the cough motor pattern.…”

“…Indeed, pulmonary slowly adapting receptor (SAR) feedback is not inspiratory-inhibitory during cough as it is during breathing. Instead, SAR afferent input is permissive for the production of cough induced from the trachea and facilitatory for laryngeal cough (Hanacek et al, 1984;Sant'Ambrogio et al, 1984). The effects of chemoreceptive feedback also are different for cough and breathing.…”

Experimental models and mechanisms of enhanced coughing

“…The model is modified from Bolser and Davenport [29] and depicts: (a) augmented tracheal cough receptor [30] activity, (b) laryngeal cough receptors, (c) tracheal and laryngeal relay neurones (interneurones), (d) convergent relay neurones in the NTS and medial reticular formation that receive synaptic input from both tracheal and laryngeal interneurons, (e) a tracheobronchial gating mechanism, (f) a laryngeal gating mechanism that is functionally subdivided into elements controlling excitability of the cough/respiratory pattern generator [31] and the magnitude of expiratory motor drive, and (g) inspiratory and expiratory premotor neurons. Pulmonary slowly adapting stretch receptors facilitate laryngeal cough and have a permissive effect on tracheobronchial cough [32,33]. These elements have been omitted from the model for clarity.…”