Efficiency of cough for clearing mucus from the lungs is believed to be a function of peak airflow velocities in the airways. Initial transient supramaximal flows are characteristic of cough, and these peak flow rates can be enhanced by placing a triggered shutter at the mouth, serving the role of the epiglottis. Using radiolabeled monodispersed aerosols (99mTc-iron oxide) and gamma camera analysis, we measured over a 2-h period the efficacy of 60 voluntary vs. shutter coughs for clearing mucus from the airways of patients (n = 15) with chronic airway obstruction (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 the 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 fraction of initial deposition) was significantly different for the 3 study days (control, 0.83 +/- 0.17; voluntary cough, 0.69 +/- 0.18; shutter cough, 0.75 +/- 0.19; P = 0.01), but only control vs. voluntary cough 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 different 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 buffs showed a clearance rate faster than control and similar to that associated with voluntary cough.(ABSTRACT TRUNCATED AT 250 WORDS)
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Bennett et al. (1994) studied this question.