The stimulus of acute smoking also reduced the STT,
but with less intensity compared with moderate aerobic
exercise, although no significant difference was found be-
tween these 2 stimuli. This acute change in mucociliary
clearance was also reported by Proenca et al,5 who found¸
that the STT in smokers immediately after smoking equaled
that in nonsmokers at baseline. Such behavior may be
explained by the acceleration in ciliary beat frequency due
to the stimulus of inflammatory mediators generated by an
acute response of the respiratory epithelium to the offend-
ing agent (cigarette smoke)44 and the stimulation of sym-
pathetic activity caused by nicotine, which activates gen-
eral metabolism.45 However, the acute effect of smoking
remains only until the nicotine is metabolized, after which
mucociliary clearance slows again, reflecting the chronic
effect of smoking.5