Background: No attempt has been made to quantify the observed rib cage distortion (Hoover's sign) in terms of volume displacement. We hypothesized that Hoover's sign and hyperinflation are independent quantities.
Methods: Twenty obstructed stable patients were divided into two groups according to whether or not they exhibited Hoover's sign during clinical examination while breathing quietly. We evaluated the volumes of chest wall and its compartments: the upper rib cage, the lower rib cage and the abdomen, using optoelectronic plethysmography.
Results: The volumes of upper rib cage, lower rib cage and abdomen as a percentage of absolute volume of the chest wall were similar in patients with and without Hoover's sign. In contrast, the tidal volume of the chest wall, upper rib cage, lower rib cage, their ratio and abdomen quantified Hoover's sign, but did not correlate with level of hyperinflation.
Conclusions: Rib cage distortion and hyperinflation appear to define independently the functional condition of these patients.