Am. J. Respir. Crit. Care Med., Vol 151, No. 5, May 1995, 1481-1485.
Rib cage distortion in a canine model of flail chest
M Cappello, C Yuehua and A De Troyer
Laboratory of Cardiorespiratory Physiology, Brussels School of Medicine, Belgium.
Although blunt chest injuries frequently lead to respiratory failure, the
effects of flail chest on the mechanics of breathing have not been
evaluated. In the present studies, we have measured the respiratory
displacements of the ribs and sternum and the electromyograms (EMG) of the
parasternal and external intercostal muscles in eight supine, anesthetized,
spontaneously breathing dogs before and after the third to sixth ribs on
the right side of the chest were fractured both dorsally and ventrally.
After flail, the fractured ribs moved inward, rather than outward, during
inspiration, but their inspiratory cranial displacement remained unchanged.
The inspiratory outward and caudal displacement of the sternum, the
inspiratory EMG activity of the parasternal intercostals, the pattern of
breathing, and the arterial blood gases were also unaltered. However, the
inspiratory EMG activity recorded from the external intercostals increased
consistently to 327 +/- 101% of control (p < 0.05). These observations
indicate that with flail chest, the disconnected segment of the rib cage
shows paradoxical motion exclusively along the lateral axis; the increased
external intercostal activation may account, at least in part, for the
persistent inspiratory cranial motion of the ribs. These observations also
suggest that the harmful effects of blunt chest injuries are related to
pulmonary contusion and pain, rather than to flail chest per se.
