Radiographic visualization of airway wall movement during oscillatory flow in dogs

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Abstract
It has been suggested that radial movement of the central airway walls during oscillatory flow might contribute to the increased frequency dependence of compliance seen in chronic obstructive pulmonary disease (COPD) (J. Appl. Physiol. 26: 670–677, 1969). Radial airway wall motion has also been invoked to explain the frequency-dependent decreases in the efficiency of gas exchange during low-volume high-frequency ventilation (HFV) in histamine-bronchoconstricted dogs and in patients with respiratory insufficiency. To test the possibility that airway wall motion increases with bronchoconstriction, we measured central airway diameters using cinebronchoradiography in anesthetized tracheostomized dogs during oscillatory HFV [50 and 100 ml tidal volume (VT) at frequencies (f) of 2, 6, and 12 Hz], under control conditions, during electrical stimulation of the vagi, and after exposure to histamine aerosol. Cineradiobronchograms from two dogs were evaluated quantitatively for tracheal diameter and for lengths and diameters of a number of major airways. Under control conditions, the diameter of the airways fluctuated 7–9% of the mean with VT of 50 ml and 9–18% with VT of 100 ml in the range of frequencies studied. Bronchoconstriction produced by aerosolized histamine increased radial airway wall movement to 10–47% with VT of 50 ml, and during vagal stimulation diameters changed 7–20% at VT of 50 ml. After histamine, the central airways displayed large diameter changes during HFV, whereas more peripheral airways were markedly constricted and did not change in diameter.