Sex differences in thoracic adaptation to pulmonary hyperinflation in cystic fibrosis.

Sex differences in thoracic adaptation have been reported in patients with cystic fibrosis (CF). The interplay between the pattern of thoracic adaptation and the function of the respiratory muscles in male and female CF patients with pulmonary hyperinflation was investigated. Thoracic dimensions and diaphragm length were measured at residual volume, functional residual capacity and total lung capacity using chest radiography in 23 CF (12 males) and 18 normal (11 males) subjects. Respiratory muscle recruitment during resting breathing was assessed by recording intrathoracic and intra-abdominal pressures. In female CF patients, ribcage expansion was predominant, tending to preserve diaphragm length. In male CF patients, thoracic configuration was normal and diaphragm shortening consequently greater. Ribcage cross-sectional area for a given rib inclination was greater in CF patients, indicating a structural expansion of the ribcage 2.5 times greater in females than males. The contribution of inspiratory ribcage muscles to inspiratory pressure was also greater relative to the diaphragm in the CF group. In conclusion, a structural expansion of the ribcage occurs in cystic fibrosis patients with lung hyperinflation that is greater in females than males. This is associated with an apparent greater contribution of inspiratory ribcage muscles to inspiratory pressure.