INHALED PLATELET-ACTIVATING-FACTOR WORSENS GAS-EXCHANGE IN MILD ASTHMA

To investigate the potential effects of inhaled platelet-activating-fa ctor (PAF) (12 mu g) to perturb pulmonary gas exchange in bronchial as thma, six patients (mean +/- SE, 23 +/- 2 yr) with intermittent asthma (FEV(1), 90% predicted) were studied before and 5, 15, and 45 min aft er challenge. Circulating white blood cells, respiratory system resist ance (Rrs), systemic and pulmonary hemodynamics, and respiratory and i nert pulmonary gas exchange were measured. Five minutes after PAF leuk ocytes fell, Rrs increased (by 27%). PaO2 decreased (by 15 mm Hg), and AaPO(2) increased (twofold) (p < 0.05 each). Ventilation-perfusion (V A/Q) distributions worsened in a pattern similar to that commonly obse rved in patients with moderate to severe asthma. Dispersions of pulmon ary blood flow (log SD Q) and of alveolar ventilation (log SD V), and an overall index of VA/Q heterogeneity (DISP R-E) increased significa ntly (123% for DISP R-E; p < 0.05, each). Gas exchange indices and Rr s were still minimally abnormal at 15 min but returned towards baselin e at 45 min. Ventilatory and hemodynamic variables remained unaltered throughout the study. These results suggest that endogenous PAF may be implicated in the arterial blood gas abnormalities shown during exace rbations of bronchial asthma.