Mucociliary clearance in adult asthma

Severe impairment of mucociliary clearance (MC) in hospitalized asthmatics has recently been demonstrated in peripheral and central airways. MC was also shown to improve with clinical recovery and hospital discharge (2). In the present study, we measure MC in chronic, stable asthma in subjects with a wide range of obstruction to see if MC was related to the severity of chronic disease. We separated the subjects into those with severe obstruction with expiratory flow limitation during tidal breathing (FL subjects) and those without tidal flow limitation (NFL subjects) to see if the presence of chronic flow limitation was associated with regional MC abnormalities. Seventeen asthmatic patients were studied. Mucociliary clearance was assessed using inhaled radioaerosol and serial measurements of the retention of radioactivity over 2 h. By controlling breathing pattern, the initial pattern of deposition in the lungs was matched, with all subjects having a predominance of particles in the central airways. This pattern was normalized for regional lung volume using a xenon equilibrium scan and expressed as a specific central to peripheral (sC/P) ratio. The percentage retention of deposited radioactivity at 120 min ranged from 19 to 83% (mean, 52%). FL subjects had a mean retention at 120 min of 66% (range, 55 to 83%). The NFL subjects had a mean retention at 120 min of 33% (range, 19 to 51%). Throughout the 2-h study period, retention by the FL group was significantly greater than that of the NFL group with separation of 95% confidence intervals. At the beginning of the study, the sC/P of both the NFL and the FL groups were similar (FL mean ± SEM = 1.97 ± 0.14; NFL = 1.72 ± 0.10, p = NS, Mann-Whitney tent). Analysis of regional MC, using serial sC/P ratios, revealed that after 2 h the mean sC/P (± SEM) of the FL subjects was unchanged (2.33 ± 0.33, p = NS, Wilcoxon's signed rank test), indicating persistent retention of particles in central airways. In contrast, mean (± SEM) sC/P ratio for the NFL patients decreased significantly (1.10 ± 0.07, p = 0.014, Wilcoxon's signed rank test), indicating that these patients emptied central airways. We conclude that measurement of MC in chronic asthma reveals a broad range of abnormality. Categorizing patients into those with and those without tidal flow limitation effectively separated the patients on the basis of their rate of MC. Relative to previously published studies of MC in normal volunteers at this center using identical techniques and similar deposition patterns, the NFL patients had faster than normal rates of MC. In the FL patients, MC was slower than normal with prolonged retention of particles in central airways.