Pendelluft is not the major contributor to respiratory insufficiency in dogs with flail chest: a mathematical analysis.

"Pendelluft", or out-of-phase movement of the airway gas between the intact and flait-chest-side lungs has long been believed to be the major contributor to respiratory dysfunction in patients with flail chest. However, conflicting findings have also been reported mainly from animal studies. The aim of this study was to provide a mathematical projection on this classical problem. We measured respiratory impedance (ZRS) of dogs with flail chest using a pseudorandom forced oscillation method. A mathematical model implementing flail chest was fitted toZRS. The fitted results were used in simulating the mechanical behavior of a respiratory system with flail chest during spontaneous breathing. Our results suggest that the paradoxical movement of breathing between the flail segment and the intact chest wall does not create substantial pendelluft and that alveolar hypoventilation is created by the wasting movement of the flail segment which interferes with effective thoracic expansion.