Alveolar clearance

One of the studies at the Fraunhofer Institute clearly indicated that the toxicity resulting from chronic inhalation of diesel engine exhaust was due to the particulate component of the exhaust and not the gases (21). Rats were exposed by inhalation over most of their life span to filtered or unfiltered diesel exhaust. Exposures were 19 h/day, 5 days/wk with soot concentrations of 4 mg/m3. All of the measures of toxicity determined, including decreases in body weight, alveolar clearance, and various measures of lung function, as well as the induction of lung tumors, were observed only In animals exposed to the unfiltered exhaust. 

Stober W, Morrow PE, Koch W et al. 1994. Alveolar clearance and retention of inhaled insoluble particles in rats simulated by a model inferring macrophage particle load distributions. J Aerosol Sci 25 975-1002. 

With distal progression, the protective liquid lining diminishes and clearance rates slow down. Soluble compounds as well as some poorly soluble ultrafine particles may cross the air-liquid interface to enter the tissues and the blood especially in the alveolar region. Depending on the solubility of the particle retention may take years. Alveolar clearance is not a linear process and half live increases with the elimination time. 

Perez A 4th, Rogers RM. Enhanced alveolar clearance with chest percussion therapy and positional changes during whole-lung lavage for alveolar proteinosis. Chest 2004 125(6) 2351-2356. 

Landrigan PJ, Cherniack MG, Lewis FA et al (1986) Silicosis in a grey iron foundry. The persistence of an ancient disease. Scand J Work Environ Health 12 32-39 Lauweryns JM, Baert JH (1977) Alveolar clearance and the role of pulmonary lymphatics. Am Rev Respir Dis 115 625-683... 

After inhalation exposure, the absorption of Cd compotmds varies greatly depending on the physico-chemical properties of the Cd compounds involved, site of deposition in the lungs and particle size [22]. In the Itmgs, deposition, mucociliary clearance, and alveolar clearance determine the absorption of inhaled particles. Large particles, dusts (>10 pm in diameter) tend to be deposited in the upper airways, while small particles, fumes, cigarette smoke (approximately 0.1 pm in diameter) penetrate into the alveoli, which are the major site of absorption. Between 50-100% of Cd in the alveoli are transferred to the blood. In the average... 

Clearance of foreign materials (particles) from the lung and airways depends on the function of macrophages, ciliated cells and secretory cells, and on the physical and chemical properties of the alveolar cells. All these are affected by ozone exposure. Single acute exposure of animals and humans to ozone concentrations less than 0.6 ppm have been shown to accelerate clearance of particles from the tracheobronchial tree whereas acute exposures to ozone levels greater than 0.6 ppm caused a delay in particles clearance [79, 261]. Repeated exposures (2 h daily for 14 days) to 0.1 ppm ozone gave rise to acceleration in alveolar clearance of latex particles but had no effect on tracheobronchial clearance. These results, related to morphological studies, are consistent with certain adaptation [278-283]. 

Recent studies in healthy subjects have suggested that a sizeable If action of particles deposited in the bronchiolar region is retained for more than 72-96 hr, and that these particles clear more similarly to alveolarly deposited particles. An increased deposition with retentions in the smallest ciliated airways is supported by the similarity in the clearance patterns from these airways, by healthy subjects, for particles inhaled by bolus and particles inhaled expemely slowly (0.05 L/sec), with an intermediate phase of continued clearance between 24 and 96 hr (17,54). From these studies, clearance in the smallest ciliated airways seems to be incomplete, with retentions of about 40% of the particles assumed to have been deposited in the tracheobronchial region, probably because of ineffective mucociliary transport and cough clearance in small airways. Clearance from the bronchiolar region may have features in common with alveolar clearance (65). This region may thus eonstitute a vulnerable zone in which small airway diseases eventually may arise after repeated exposures to noxious agents. 

Freedman AP, Robinson SE, Street MR. Magnetopneumographic study of human alveolar clearance in health and disease. Aim Occup Hyg 1988 32 809-820. 

Foster WM. Is 24 hour lung retention an index of alveolar clearance J Aerosol Med 1988 1 1-10. 

Lehnert BE, Morrow PE. Association of 59-iron oxide with alveolar macrophages during alveolar clearance. Exp Lung Res 1985 9 1-16. 

Lehnert BE, Ortiz JB, London JE, Valdez YE, Cline AJ, Sebring RJ, Tietjen GL. Migratory behaviors of alveolar macrophages during alveolar clearance of light and heavy burdens of particles. Exp Lung Res 1990 16 451-479. 

Lauweryns JM, Baert JH. Alveolar clearance and the role of the pulmonary lymphatics. Am Rev Respir Dis 1977 115 625-683. 

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