title: Cardiovascular and respiratory consequences of tension pneumothorax.
abstract: The physiologic responses to acute pneumothorax were investigated in awake, standing sheep. Pleural pressure (Ppl) was raised in graded increments by injecting air from a 500 ml syringe into the pleural cavity of eight sheep to produce pneumothorax volumes of 0, 17, 35 and 45 ml.kg-1. At the maximum value of 45 ml.kg-1 (approximately equal to 1,400 ml), Ppl at end-expiration was raised to 10 +/- 2 mmHg (mean +/- SD) whereas end-inspiratory Ppl remained negative in half the sheep as the result of increased thoracic pressure swings. The most striking haemodynamic impairment was a 22% fall in stroke volume. Cardiac output, however, remained fixed at baseline values as a result of a 28% rise in heart rate. Although hypotension has been commonly held as a consequence of severe pneumothorax, mean systemic arterial pressure increased, rising by 19% in the entire group at the maximal pneumothorax tolerated. Pulmonary gas exchange was significantly disrupted by pneumothorax, as indicated by both a 40% fall in Pao2 and a 19% reduction in arterial oxygen content. Despite a reduction in tidal volume, the sheep initially remained eucapnic by generating an increased respiratory rate and slightly increasing minute-ventilation. However, at pneumothorax volumes of 45 ml X kg-1, the sheep were no longer able to sustain minute-ventilation and a small rise in PaCO2 followed. The reduced arterial oxygen content and the fixed cardiac output led to a progressive reduction in systemic oxygen transport.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000208:Acute Disease; D000818:Animals; D001794:Blood Pressure; D005260:Female; D006439:Hemodynamics; D010100:Oxygen / Q000097:blood; D011030:Pneumothorax / Q000503:physiopathology*; D011652:Pulmonary Circulation; D011659:Pulmonary Gas Exchange; D012119:Respiration; D012756:Sheep
chemical_list: D010100:Oxygen