Effects of unilateral airway occlusion on rib motion and inspiratory intercostal activity in dogs.

Dimitri Leduc,Alexandre Legrand,Sarah Marechal,Olivier Taton,Bernard Blairon

doi:10.14814/phy2.13242

Abstract

Unilateral bronchial occlusion, a complication of many lung diseases, causes dyspnea but the mechanism of this symptom is uncertain. In this study, electromyographic (EMG) activity in the parasternal and external intercostal muscles in the third intercostal space and inspiratory motion of the third rib on both sides of the thorax were assessed during occlusion of a main bronchus for a single breath in anesthetized dogs. Occlusion produced a 65% increase in external intercostal EMG activity in both hemithoraces without altering parasternal EMG activity. Concomitantly, the inspiratory cranial rib motion showed a 50% decrease on both sides of the thorax. These changes were unaffected by bilateral vagotomy. However, when an external, caudally oriented force was applied to the third rib on the right or left side so that its inspiratory cranial displacement was abolished, activity in the adjacent external intercostals showed a twofold increase, but rib motion and external activity in the contralateral hemithorax remained unchanged. It is concluded that during occlusion of a main bronchus, the increase in external intercostal activity is induced by the decrease in inspiratory cranial rib displacement in both hemithoraces, and that this decrease is determined by the increase in pleural pressure swings on both sides of the mediastinum. This mechanism, combined with the decrease in PaO2, induces similar alterations when unilateral bronchial occlusion is maintained for a series of consecutive breaths.

Highlights

Occlusion of a main bronchus is a common complication of bronchial cancer but can occur in nonneoplastic pathologies, such as after inhalation of a foreign body or after accumulation of bronchial secretions
The parasternal intercostal electrodes were implanted in the third interspace in the muscle bundles near the sternum (De Troyer et al 2005), while the external intercostal electrodes were positioned in the dorsal portion of the third interspace, immediately ventral to the rib angle (Kirkwood et al 1982; Greer and Martin 1990; De Troyer et al 2005)
The inspiratory EMG activity recorded from the third parasternal intercostal muscle remained unchanged, both when occlusion was performed on the ipsilateral side and on the contralateral side

Summary

Introduction

Occlusion of a main bronchus is a common complication of bronchial cancer but can occur in nonneoplastic pathologies, such as after inhalation of a foreign body or after accumulation of bronchial secretions. This setting is frequently associated with dyspnea (Scoggin 1988), but the mechanism of this symptom remains unclear. Based on the previous observations of tracheal occlusion in dogs (De Troyer 1991b), it would be expected that occlusion of a main bronchus would impede the cranial motion of the ribs, the caudal motion of the diaphragm, and the shortening of the inspiratory muscles, including the diaphragm and the parasternal intercostal muscles, in the ipsilateral hemithorax (De Troyer 1991b).

Methods

Results

Conclusion