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Thoracic traction on the trachea: mechanisms and magnitude
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1991
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AsthmaEngineeringCarinal DisplacementAnatomyPulmonologyAnesthesiaBiomechanicsThoracic TractionMechanobiologyVentilationLarynxRespiration (Physiology)Spontaneous BreathingPhysiologyInspiratory IncreasesPulmonary PhysiologyThoracic SurgeryLung MechanicsMechanical VentilationMedicineAnesthesiology
Inspiratory increases and tonic thoracic traction on the trachea improve upper airway patency. The study aimed to evaluate the origins and magnitude of thoracic traction on the trachea in anesthetized tracheotomized dogs. In 15 anesthetized tracheotomized dogs, a strain gauge on the thoracic tracheal stub measured Ttx(tr), esophageal pressure, and carinal displacement during spontaneous breathing, mechanical ventilation with varying PEEP, hypercapnic stimulation, and before and after vagotomy. Inspiratory Ttx(tr) averaged 81 g and rose to 174 g at 10 % end‑expiratory CO₂, and the traction was shown to result from the sum of mediastinal pull and independent intrathoracic pressure forces rather than from carinal transmission alone.
Both inspiratory increases and tonic thoracic traction (pull of the thorax) on the trachea [Ttx(tr)] have been shown to improve patency of the upper airway. To evaluate the origins and magnitude of Ttx(tr), we studied 15 anesthetized tracheotomized dogs. We divided the midcervical trachea and attached the thoracic stub to a strain gauge. Ttx(tr), esophageal pressure, and carinal displacement were observed during various conditions. These included unobstructed and obstructed spontaneous breathing, mechanical ventilation at various levels of positive end-expiratory pressure, and progressive hypercapnic stimulation. Observations during spontaneous breathing were performed before and after vagotomy. We found that inspiratory increases in Ttx(tr) were substantial, averaging 81 +/- 8 g force and increasing to 174 +/- 22 g force at an end-expiratory CO2 concentration of 10%. Ttx(tr) did not result simply from the pull of mediastinal and pulmonary structures transmitted through the carina. Changes in intrathoracic pressure acted independently to either draw the trachea into or push the trachea out of the thorax. Thus Ttx(tr) could be explained as the sum of mediastinal traction and force generated by changes in intrathoracic pressure.