Extrathoracic airways changes during plethysmographic measurements of lung volume

In six healthy subjects cineradiographic studies during panting against a closed shutter showed widening and narrowing of the whole extrathoracic airways. At the epiglottic level, the mean lateral maximum diameter was 121% of the minimum diameter for an applied pressure of 11.4 cm H2O and 152% for 28.4 cm H2O, while posteroanterior diameter changes were 148% for 12.3 cm H2O and 182% for 28.2 cm H2O, respectively. There was a significant correlation between anteroposterior diameter changes and mouth pressure (Pm) swings (P less than 0.05). In 6 cadavers, the compliance of extrathoracic airways (isolated from the lower respiratory tract by an inflated balloon in the upper trachea) was 1.5 ml X cm H2O-1 after adding 30 ml of air, and 1 ml X cm H2O-1 after removing 30 ml of air. Flow rate in and out the extrathoracic airways averaged 0.089 and 0.163 L X sec-1 for swings in Pm of 9.5 and 18.5 cm H2O, respectively. There was a significant correlation (P less than 0.05) between flow rate and delta Pm. For a given delta Pm, flow was higher in those cadavers with more compliant extrathoracic airways. We conclude that extrathoracic airways change their volume during panting, and that these volume changes, as well as the internal flow rate thus created, depend on the Pm swings.