Pulmonary mechanics in methacholine induced asthma.

We submitted eight asthmatics (age range 24-51 years) to progressively increasing doses of inhaled methacholine. Mechanical studies were done before and after each dose of methacholine and also after an inhalation of 240 micrograms of Ipratropium Bromide (IB). Recordings included: Thoracic gas volume at FRC (TGV), airways resistance (Raw), flow volume loops and static pressure/volume relationship (Pst/V). Exponential fitting of Pst/V curve was done according to previous studies, and maximal flow/static recoil curves were drawn with the data previously obtained. Considering the variation of SGaw as an index of airway reaction we found a good correlation between this parameter and MEF. Cdyn and the slope between MEF. The increase of TGV was in good correlation with SGaw as a percentage of control value. We could not find any significant variation in Specific Distensibility (Dsp) or Pst max. Our results support previous studies that have shown a insignificant modification of the elastic properties of the lung. The volume increases observed by plethysmography must be cautiously interpreted. We suggest that this modification may be the result of various factors, i.e. technical, mechanical (airways collapse, air trapping) and biological factors (surface forces, alveolar relaxation). Our data confirms the predominant central action of Ipratropium Bromide.