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

View Article: PubMed Central - PubMed

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.

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Parasternal intercostal and external intercostal EMG activity, and inspiratory cranial rib displacement on both sides of the thorax during unilateral bronchial occlusion sustained during 10 respiratory cycles. EMG activities are expressed as percentages of control activity. Note the progressive increase in EMG activity in the parasternal and external intercostal muscles on both sides of the thorax. Inspiratory rib motion decreased in the first occluded breath but remained unchanged during the subsequent occluded cycles. Values are means ± SE from eight animals.
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phy213242-fig-0004: Parasternal intercostal and external intercostal EMG activity, and inspiratory cranial rib displacement on both sides of the thorax during unilateral bronchial occlusion sustained during 10 respiratory cycles. EMG activities are expressed as percentages of control activity. Note the progressive increase in EMG activity in the parasternal and external intercostal muscles on both sides of the thorax. Inspiratory rib motion decreased in the first occluded breath but remained unchanged during the subsequent occluded cycles. Values are means ± SE from eight animals.

Mentions: The effects of sustained unilateral bronchial obstruction on parasternal intercostal and external intercostal EMG activity and rib displacement are shown in Figure 4 for the eight animals. During occlusion, the EMG activity of the parasternal intercostals gradually increased after the second respiratory cycle (P < 0.001). This increase in EMG activity was similar on the ipsilateral and contralateral side (P = 0.822), EMG/Ti reaching, respectively, 130.6 ± 3.5% of control and 132.8 ± 6.4% of control at the 10th occluded inspiratory cycle.


Effects of unilateral airway occlusion on rib motion and inspiratory intercostal activity in dogs
Parasternal intercostal and external intercostal EMG activity, and inspiratory cranial rib displacement on both sides of the thorax during unilateral bronchial occlusion sustained during 10 respiratory cycles. EMG activities are expressed as percentages of control activity. Note the progressive increase in EMG activity in the parasternal and external intercostal muscles on both sides of the thorax. Inspiratory rib motion decreased in the first occluded breath but remained unchanged during the subsequent occluded cycles. Values are means ± SE from eight animals.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5392528&req=5

phy213242-fig-0004: Parasternal intercostal and external intercostal EMG activity, and inspiratory cranial rib displacement on both sides of the thorax during unilateral bronchial occlusion sustained during 10 respiratory cycles. EMG activities are expressed as percentages of control activity. Note the progressive increase in EMG activity in the parasternal and external intercostal muscles on both sides of the thorax. Inspiratory rib motion decreased in the first occluded breath but remained unchanged during the subsequent occluded cycles. Values are means ± SE from eight animals.
Mentions: The effects of sustained unilateral bronchial obstruction on parasternal intercostal and external intercostal EMG activity and rib displacement are shown in Figure 4 for the eight animals. During occlusion, the EMG activity of the parasternal intercostals gradually increased after the second respiratory cycle (P < 0.001). This increase in EMG activity was similar on the ipsilateral and contralateral side (P = 0.822), EMG/Ti reaching, respectively, 130.6 ± 3.5% of control and 132.8 ± 6.4% of control at the 10th occluded inspiratory cycle.

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Related in: MedlinePlus