Studies on laryngeal calibre during stimulation of peripheral and central chemoreceptors, pneumothorax and increased respiratory loads

Abstract

SUMMARY1. The effects of asphyxia, hypoxia, hypercapnia, stimulation of peripheral chemoreceptors, pneumothorax and breathing through resistances have been investigated on laryngeal resistance to airflow in anaesthetized cats, with and without bilateral vagotomy below the origin of the recurrent laryngeal nerves.2. Resistance to airflow of the innervated larynx was usually measured with the larynx isolated in situ with constant flow from the trachea to a pharyngeal opening, and expressed by the relationship between translaryngeal pressure and airflow.3. Asphyxia, hypoxia and hypercapnia each stimulated breathing and decreased laryngeal resistance to airflow, in both the inspiratory and expiratory phases. After vagotomy the effect was reduced, abolished or (usually) reversed to a laryngeal constriction, especially in expiration.4. Intra-arterial injections of potassium cyanide (to stimulate carotid body chemoreceptors) caused a short apnoea or an augmented breath followed by hyperpnoea, concurrently with expiratory constrictions of the larynx. The responses were usually stronger after bilateral vagotomy.5. Pneumothorax caused tachypnoea, inspiratory dilatations and expiratory constrictions of the larynx. The responses were abolished by vagotomy.6. Imposition of respiratory resistances dilated the larynx, in inspiration and expiration, while complete closure of trachea caused expiratory

Laryngeal Effects on Respiratory Pressures and Timing in Rabbits: Role of the Vagi

“…Chronic rabbits after variably long survival times present normocapnic hypoxia [16, and this work], which was shown to cause tracheal con striction [13], to narrow laryngeal slit in lung-denervated animals [4]. The latter was effectively abolished by peripheral chemodenervation [1], We cannot rule out this possibility in our chronic rabbits.…”

“…4 As expected, inclusion of the larynx to the breathing circuit induced significant, prominent increases in the intratracheal pressures in both experimental groups. In the control rabbits, the rises in inspiratory and expiratory pressures were proportion ally similar, but after cervical vagotomy there was a far larger increase in the nega tive inspiratory pressure ( fig.…”

“…To isolate the laryngeal con tribution to these respiratory variables, we have used rabbits with chronic bilateral intrathoracic vagotomy, deprived of vagal lung influence but with preserved innerva- tion of the larynx. Since these animals be come hypoxic [16], we have to eliminate a constrictor effect of hypoxia on the larynx [1,4] by cutting the carotid sinus/body nerves. The last experimental step (midcervical vagotomy) was to test whether motor denervation of the larynx acted solely by changing the resistive load to re spiration.…”

Endotracheal Measurement of Thyroarytenoid Activity in Newborn Lambs

“…Both posture and local air temperature were held constant. Potent, independent effects of local laryngeal stimulation on SLN discharges and laryngeal motor function have been demonstrated [15,16]. However, placement of the ET tube does not appear to stimulate the larynx chronically.…”

“…These include: behavioral state [8,[11][12][13], posture [12], anesthesia [14], local air temperature [12], superior laryngeal nerve (SLN) afferent input [15,16], rib cage afferent input [17], and blood gas changes mediated via central and peripheral chemorecep- A time tracing is shown with airflow, tidal volume, ET-TA EMG activity and intrinsic TA EMG activity under baseline conditions and when an end-expiratory volume withdrawal was performed. In this quiet awake lamb at this stage of the study, baseline TA activity was not present.…”