Pulmonary mechanics in patients with asthma bronchiale in symptom-free interval

Pulmonary and airway mechanics were assessed in 30 patients with asthma bronchiale during a symptom-free interval, and with normal spirometry. Static expiratory pressure-volume (PV) curves and maximum expiratory flow-volume curves were obtained, and maximum flow-static recoil (MFSR) curves were drawn-up. In 11 patients elastic pressures were significantly lower than normal at all lung volumes, but the slope of the PV curve was normal; the loss in lung elastic recoil was not associated with an increase in lung volume, suggesting that surface forces acting in the alveoli may be responsible for the elastic abnormality. In 5 patients static pressures were increased at all lung volumes, possibly due to the increase in elastic pull exerted by the thorax on the lungs. Obstruction of small airways was present in most cases: MEF50 was lower than predicted in 70% of them, and in 73.3% the upstream resistance was increased. In 17 subjects, the MFSR curves showed increased pressures at given maximal flows suggesting that the airways obstruction was generated by an intrinsic mechanism. In 4 cases, an extrinsic mechanism might be responsible since the elastic pressures at given maximal flows were lower than normal.