EFFECT OF ENHANCED SUPRAMAXIMAL FLOWS ON COUGH CLEARANCE

Efficiency of cough for clearing mucus from the lungs is believed to b e a function of peak airflow velocities in the airways. Initial transi ent supramaximal flows are characteristic of cough, and these peak flo w rates can be enhanced by placing a triggered shutter at the mouth, s erving the role of the epiglottis. Using radiolabeled monodispersed ae rosols (Tc-99m-iron oxide) and gamma camera analysis, we measured over a 2-h period the efficacy of 60 voluntary vs. shutter coughs for clea ring mucus from the airways of patients (n = 15) with chronic airway o bstruction (mean ratio of forced expired volume in 1 s to forced vital capacity = 0.55). In a subset of patients (n = 9), we also measured t he efficacy of forced expirations, or huffs, without glottis closure. Peak flow rate was greater for shutter than voluntary coughs [9.4 +/- 2.0 (SD) vs. 4.1 +/- 1.9 l/s; P < 0.001]. Retention at 60 min (as a fr action of initial deposition) was significantly different for the 3 st udy days (control, 0.83 +/- 0.17; voluntary cough, 0.69 +/- 0.18; shut ter cough, 0.75 +/- 0.19; P = 0.01), but only control vs. voluntary co ugh values were significantly different from each other (P = 0.01). In contrast, retention at 120 min was significantly different for the 3 days, but both voluntary and shutter coughs were significantly differe nt from control (P = 0.01 and P = 0.02, respectively) (control, 0.73 /- 0.16; voluntary cough, 0.61 +/- 0.20; shutter cough, 0.65 +/- 0.20) . Patients studied with huffs showed a clearance rate faster than cont rol and similar to that associated with voluntary cough. These results indicate that increased supramaximal flows do not cause further impro vement in mucus clearance from the lung.