title: Effects of unilateral airway occlusion on rib motion and inspiratory intercostal activity in dogs.
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.
authors.affiliation: Laboratory of Cardiorespiratory Physiology, Brussels School of Medicine and Chest Service, Erasme University Hospital, Brussels, Belgium dileduc@ulb.ac.be.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Leduc
authors.affiliation: Laboratory of Cardiorespiratory Physiology, Brussels School of Medicine and Chest Service, Erasme University Hospital, Brussels, Belgium.
authors.forename: Sarah
authors.initials: S
authors.lastname: Marechal
authors.affiliation: Laboratory of Cardiorespiratory Physiology, Brussels School of Medicine and Chest Service, Erasme University Hospital, Brussels, Belgium.
authors.forename: Olivier
authors.initials: O
authors.lastname: Taton
authors.affiliation: Laboratory of Physiology, Mons School of Medicine, Mons, Belgium.
authors.forename: Bernard
authors.initials: B
authors.lastname: Blairon
authors.affiliation: Laboratory of Physiology, Mons School of Medicine, Mons, Belgium.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Legrand
mesh_terms: D000402:Airway Obstruction / Q000503:physiopathology*; D000818:Animals; D004285:Dogs; D004576:Electromyography; D001239:Inhalation / Q000502:physiology*; D007366:Intercostal Muscles / Q000503:physiopathology*; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology; D012272:Ribs / Q000503:physiopathology*
keywords: Intercostal muscles; mechanics of breathing; pleural pressure transmission; respiratory muscles; rib cage motion