Lung function and ventilation inhomogeneity in rat lungs after allergen challenge

We studied the early response to ovalbumin challenge in sensitized Brown-No rway rats through its effect on Nz, He, and SF6 phase III slopes of the sin gle-breath washout and on indexes of lung function. Sensitized rats showed varying degrees of response in terms of pulmonary pressure (PL), with incre ases ranging between 125 and 225% of baseline. The sensitized rats presente d decreased quasistatic compliance, forced vital capacity, and end-expirato ry flow, with all three lung function indexes showing a significant negativ e correlation with corresponding PL values. They also showed significant po sitive correlations of PL with the N-2, He, and SF6 phase III slopes, refle cting diffusion-convection-dependent inhomogeneities generated by conformat ion changes throughout the entire rat lung. In addition, the rats showing t he most marked PL increases (>150% baseline PL) also revealed a reversal of the SF6-He slope difference because of a more marked SF6 than He slope inc rease. This latter finding suggests that the degree of structural heterogen eity during early response is even more marked in the most peripheral rat l ung generations.