The Characteristics of Bronchial Clearance in Humans and the Effects of Cigarette Smoking

Abstract

The clearance of radioactive monodisperse ferric oxide aerosols ranging in diameter from 0.8IL to 7.9IL was studied in a total of 117 experiments on 36 subjects. In most normal subjects there were two discrete periods of bronchial clearance, with the first usually completed within one to two hours, and the second within four to ten hours after inhalation. The fraction cleared in each phase was strongly dependent on the size of the inhaled particles, with more first phase clearance for larger particles. The rates of bronchial clearance were expressed in terms of the time required for completion of 50% to 90% bronchial clearance. On the basis of the limited data thus far accumulated, bronchial clearance was impaired in eight out of fourteen cigarette smokers, three out of three former uranium miners, and two out of two emphysema cases.

Smoking Is Associated with Shortened Airway Cilia.

“…The actual depth of the airway surface fluid is reported to be 6 to 7 mm [43][44][45][46][47]. In this range, the shorter cilia in smokers would result in a reduction of effective cilia of approximately 18 to 38%, consistent with the data that smokers have a decreased mucociliary clearance compared to nonsmokers [1,7,8,[18][19][20][21][22][23][24].…”

“…Fundamental to these risks are the observations that cigarette smoking is associated with a decrease in mucociliary clearance, a process driven by ciliated airway epithelial cells functioning in a coordinated fashion to move airway surface fluid and mucus in a cephalad fashion, thus continually cleansing the respiratory surface of inhaled particulates [1,7,8]. Prior reports have attributed the smoking-related decrease in mucociliary clearance to a decrease in numbers of ciliated cells, changes in cilia structure and/or beat frequency [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]36]. While these mechanisms likely contribute to the smoking-induced dysfunction in mucociliary clearance, the present study documents a new concept to help explain decreased mucociliary clearance, that smoking is associated with an average shortening of airway epithelial cilia.…”

“…One critical component is cilia, the hair-like projections on airway epithelial cells that move in metachronal waves and work in conjunction with mucus to clear the airway of inhaled particulates [9,[14][15][16][17]. Several reports demonstrate that cigarette smoke reduces ciliary beat frequency and interrupts the intercellular coordination of the metachronal waves [18][19][20][21][22][23][24], and ultrastructural studies have documented smoking-associated increased incidence of structural defects in cilia, including missing radial spokes, nexin links, central sheath, outer and inner dynein arms, and central microtubules, as well as more peripheral doublets and fused cilia [25][26][27][28][29][30][31][32][33][34].…”

Deposition and clearance of 2 μ particles in the tracheobronchial tree of normal subjects—smokers and nonsmokers

“…We also compared the patterns of deposition and clearance observed in those subjects who were smokers with those who were nonsmokers. Previous reports in smokers had demonstrated either normal (6,9) or abnormally slow (10) Table I). The average age of smokers, although slightly higher than that of nonsmokers, was not statistically different (P > 0.1).…”

Bronchial, alveolar, and vascular-induced anaphylaxis and irritant-induced cardiovascular and pulmonary responses.

“…This retention of activity represented total deposition in the lung. The retention of radioactivity measured in the lungs 24 hr after radioaerosol inhalation (following subtraction of background and correction for radioactive decay) was taken to represent the mass of aerosol deposited in the alveoli (14). This is based on the assumption that particles deposited in the bronchi are removed by mucociliary activity within 24 hr.…”