Overall and regional lung function in dogs exposed acutely to ozone

Regional distribution of ventilation and overall function of the lungs were compared in anesthetized, paralyzed, mechanically ventilated dogs exposed to ozone. Three animals were exposed at each concentration (0,0.13,0.22, and 0.45 ppm ozone) for 3 hr. There were no significant changes in pulmonary flow resistance, dynamic compliance, or flow rates derived from maximum forced expiratory maneuvers. The distribution of inspired gas was determined using air containing 13N and a positron camera to follow wash-in in each of 80 or more regions of the lung. The mean wash-in time (T) and its standard deviation did not change in sham-treated dogs, but T increased by 40 to 100% in exposed animals. Dogs showing increases in T also had increased frequency dependence of compliance (correlation significant at P less than 0.05). The changes in 13N wash-in reflected less uniform distribution of ventilation, with the greatest disparity occurring between central and marginal regions. Altered regional mechanical function, in the absence of overall changes, suggested that the initial effect of ozone was on the small airways. The measurement may be a sensitive indicator of acute irritation in the lung periphery.