AIRWAY COMPLIANCE DURING ARTIFICIAL VENTILATION

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Abstract
The relationship of anatomical deadspace to transpulmonary pressure was studied in eight subjects awake, breathing spontaneously without endotracheal intubation, and anaesthetized intubated and ventilated artificially. Anatomical deadspace was determined according to the equal area method (Fowler) using carbon dioxide as a tracer gas. Volume measurements were performed using a pneumotachograph. Transpulmonary pressure was measured using an oesophageal balloon and a catheter which was connected to the mouthpiece during spontaneous breathing and inserted into the endotracheal tube during artificial ventilation. Anatomical deadspace was approximately the same during artificial ventilation and spontaneous breathing, despite bypass of the upper airway during anaesthesia. Anatomical deadspace was related linearly to transpulmonary pressure. The regression lines indicated an airway compliance of 3.6 ml/cm H2O during spontaneous breathing and 7.4 ml/cm H2O during artificial ventilation. The alteration in airway compliance caused by artificial ventilation is ascribed to a reduction in bronchial muscle tone

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