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Interaction between left and right intercostal muscles in airway pressure generation.

The interactions between the different rib cage inspiratory muscles in the generation of pleural pressure remain largely unknown. In the present study, we have assessed in dogs the interactions between the parasternal intercostals and the interosseous intercostals situated on the right and left sides of the sternum. For each set of muscles, the changes in airway opening pressure (DeltaPao) obtained during separate right and left activation were added, and the calculated values (predicted DeltaPao) were then compared with the DeltaPao values obtained during symmetric, bilateral activation (measured DeltaPao). When the parasternal intercostals in one or two interspaces were activated, the measured DeltaPao was commonly greater than the predicted value. The difference, however, was only 10%. When the interosseous intercostals were activated, the measured DeltaPao was nearly equal to the predicted value. These observations strengthen our previous conclusion that the pressure changes produced by the rib cage inspiratory muscles are essentially additive. As a corollary, the rib cage can be considered as a linear elastic structure over a wide range of distortion.

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Patterns of gamma-motoneuron activity in the external intercostal muscles of the cat during respiration.

Recordings of gamma-motoneurons from fine filaments of external intercostal nerves were made during spontaneous breathing in the anesthetized cat. The patterns of alpha- and gamma-motoneuron activity varied within different areas of the rib cage. Areas of muscle which were recruited during inspiration received input from both tonically and phasically active gamma-motoneurons. Those areas of the rib cage which were not recruited during inspiration received activity from tonically active gamma-motoneurons. These patterns of gamma-motoneuron activity are in agreement with those suggested from previous recordings of muscle spindle activity.

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Action of the intercostal muscles on the rib cage.

Recent studies suggest that the parasternal muscles (PA) are primarily responsible for rib cage expansion during eupneic breathing with a much lesser role played by the interosseous external intercostals (EI). The purpose of the present investigation was to assess the capacity of the EI to expand the rib cage during spontaneous breathing in the absence of coincident ipsilateral PA activation. In 9 anesthetized dogs, we measured PA EMG and length in the 3rd interspace and EI EMG and length in the 3rd and 4th interspaces. During resting breathing, each muscle was electrically active and shortened to a similar degree, approximately 3% of resting length. Following ipsilateral PA denervation (1st through 6th interspaces), the level of EI shortening in the 3rd and 4th interspaces was maintained, but with an increase in neural drive to these muscles. The parasternal muscle in the 3rd interspace lengthened during inspiration. Subsequent sequential denervation of EI in the 3rd and 4th interspaces resulted in their lengthening. In 4 additional animals, axial motion of the 4th rib was measured in the mid axillary line. Ipsilateral PA denervation had no significant effect on rib motion. External intercostal denervation (3rd interspace), on the other hand, had a substantial impact on rib motion, causing the 4th rib to move in the caudal direction during inspiration. Our results indicate that: (a) the EI of the lateral rib cage are capable of elevating the ribs during inspiration independent of PA contraction; (b) PA contraction contributes to EI shortening during eupneic breathing and (c) regional loss of muscle activation results in local rib cage distortion, suggesting that the upper rib cage has multiple degrees of freedom.

Animals↗

Treatment of iatrogenic injury of membranous trachea with intercostal muscle flap.

Iatrogenic injuries of the membranous trachea are rare but potentially lethal, and most commonly require surgical treatment. Such injuries occur intraoperatively during specific thoracic surgery procedures or are associated with endotracheal anesthesia. Special technical difficulties in managing them surgically are encountered when lacerations are in proximity to the rigid rings of the trachea because of the lack of membranous tissue distal to the tear. We describe our technique used in a patient with such an iatrogenic tracheal injury during resection of invasive lung carcinoma.

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