Mucus transport

FIGURE 5.24 Components of ciliary movement, (a) Power and recovery phases of ciliary movement. Arrows indicate the direction of ciliary travel, (b) Net mucociliary transport. Dotted arrows show the direction of cilia while the solid arrows show mucus transport. Note that net gel movement is forward in I and III while no gel movement occurs in II during the cilia recovery phase. Modified from Ful-ford and Blake. ... 

Inhalation route adults subjected to 50,000 or 200,000 pg acrolein/L (113 or 454 mg/m3) air via an endotracheal cannula for up to 27 days Air sac injection route embryos 2-3 days old examined at day 13 Decreases in trachea complement of ciliated and goblet cells inhibited mucus transport activity in trachea lymphocytic inflammatory lesions in the tracheal mucosa changes were more pronounced at the higher dose and with increasing exposures 2... 

Clearance in the upper, or ciliated, region is governed by the rate of mucus transport along the airways. These rates have been measured in the human nose and in dogs, rats, and other species. Asmundsson and Kilbum, Hilding, and Iravani established that mucociliary clearance rates increase from the distal bronchi toward the trachea. Because bronchial openings retard mucus flow, bifurcations receive an accumulation of mucus and associated particles. The rate of mucus production and mucus thickness and velocity vary from one person to another. Thickness increases and velocity decreases greatly when some toxic elements are present in the airway. 

If the periciliary fluid were too shallow, the cilia would become entangled in the mucus gel and mucus transport would again be compromised. 

The cilium unrolls within the periciliary fluid ready for the next effective stroke. Undergoing the recovery stroke beneath the mucus layer prevents retrograde mucus transport (Figure 9.5). 

Zahm JM, Galabert C, Chaffin A, Chazalette JP, Grosskopf C, Puchelle E. Improvement of cystic fibrosis airway mucus transportability by recombinant human DNase is related to changes in phospholipid profile. AM J Respir Crit Care Med 1998, 157, 1779-1784. 

Bemfeld, R, C.W. Nixon, and F. Homburger Studies on the effect of irritant vapors on cUiary mucus transport. I. Phenol and cigarette smoke Toxicol. Appl. Pharmacol. 6... 

Mucus transport of Tc labelled human albumin minimicrospheres (mean aerodynamic diameter 0.75 (Jon) in chronic bronchitis patients treated with cistinexine dihydrochloride for two weeks was significantly promoted in those patients who showed a greater impairment of transport rate before treatment (Santolicandro et al. 1995). 

The relation between the viscosity and elasticity of the secretions is one of the determining factors in transport velocity. If the gel phase is in practice the only one really transported, the sol phase creates a low-resistance milieu where the cilia can beat, an environment that is essential for transport in the direction of the upper airways. One of the most important rheological properties of mucus is viscosity. Viscosity is resistance to flow and represents the capacity of a material to absorb energy while it moves. Elasticity is the capacity to store the energy used to move or deform material. The ratio between viscosity and elasticity appears to be an important determinant of the transport rate (6,10). Mucus transport by ciliary beating is influenced by the viscoelastic and surface properties of the mucus. Theoretical models suggest that a decrease in the ratio of viscosity to elasticity can result in an increase in mucociliary transport (13). 

At any point on the bronchial tree, the transport surface is determined by the inside diameter and the number of airways at this level. Moving from the center toward the periphery, diameters decrease, but the number of airways increases exponentially so that the transport surface decreases proportionally. As a result, the transporting surface of the airways decreases from the peripheral to the central airways. Accumulation of mucus in the central airways is normally countered by the higher mucus transport rate centrally than peripherally, and possibly by a greater reabsorption of watery constituents centrally. 

In asthmatic patients, the most common symptoms are dyspnea and bronchospasm than can usually be reversed with bronchodilatation therapy that probably has no effect on mucus clearance transport (20). Hypersecretion is usually present in the acute episodes of asthma and normally mucus transport is impaired due to reduction of ciliary activity (21). Mucus hypersecretion and changes in the rheological or surface properties of mucus may also cause reduction of ciliary activity (6). In these patients, mucus transport can be recovered or remain reduced, despite favorable changes in mucus viscoelasticity after an exacerbation. 

Respiratory physiotherapy interventions can be evaluated using different outcome variables, such as bronchial mucus transport measurement, measurement of the amount of expectorated mucus, pulmonary function, medication use, frequency of acute exacerbations and quality of life (2,5,33). 

Approaches to preventing airway secretion retention include pharmacotherapy to reduce mucus hypersecretion or to liquefy secretions, and the application of chest physiotherapy (CPT) techniques. (CPT) can be defined as the external application of a combination of forces to increase mucus transport that include PD, special breathing exercises, manual chest vibration and percussion, autonomous instmmental techniques, and manually assisted coughing. 

High or low pressure PEP may be prescribed. The prescription for high pressure PEP requires the patient to perform forced VC maneuvers through the range of expiratory resistances with the mask connected to a spirometer. The possible benefit of PEP and high pressure PEP on mucus transport remains to be proven. However, PEP is useful when there are indications to at least temporarily increase lung volume. 

H) ersecretion, reduced mucus transport, and airflow obstruction are impairments, while chronic coughing and expectoration of mucus or dyspnea can limit the patient in daily or recreational activities and can therefore be classified as disabilities. The impact of secretion clearance appears to be a strong one in the improvement of the patient s quality of life, since it has direct influence on the improvement of symptoms related to secretion encumbrance. 

Hansen LG, Warwick WJ, Hansen KL. Mucus transport mechanisms in relation to the effect of high frequency chest compression (HFCC) on mucus clearance. Pediatr Pulmonol 1994 17(2) 113-118. 

Hence, mucocihary transport is a complex interaction of ciliary beat and elastoviscous properties of the overlaying mucus and its (dis)continuity in the various airway generations. Mucociliary action is an important function of the airway walls, and the determination of this function is essential to assess the functional and structural integrity of the conducting airways. To study this function, suitably labeled particles are deposited in the airways and mucus transport is determined by external measurement of the label. 

Foster et al. (32) also measured mucociliary clearance in the main bronchi after inhalation of radiolabeled particles, using a gamma-camera. For healthy nonsmokers, a linear velocity of 2.4 0.5 mm/min was measured in the bronchi, compared with 5.5 0.4 mm/min in the trachea. Furthermore, they (32) found a correlation between tracheal and bronchial mucous velocities. There is no direct information available about mucous velocities in more distal airways. From the foregoing observation, it can be assumed that linear mucous velocity will decrease in more peripheral airways. By making assumptions about the properties of mucus during its transport from distal airways towards the trachea, mucous velocity has been modeled by several authors (33-36). From these calculations the mucus-transport velocity in terminal bronchioli could be more than three orders of magnitude lower than in the U achea. 

Iravani J, van As A. Mucus transport in the tracheobronchial tree of normal and bronchitis rats. J Pathol 1972 106 81-93. 

Foster WM, Langenback EG, Bergofsky EH. Lung mucociliary function in man interdependence of bronchial and tracheal mucus transport velocities with lung clearance in bronchial asthma and healthy subjects. Ann Occup Hyg (Inhaled Particles V) 1982 26 227-244. 

Puchelle E, Zahm JM, Duvivier C. Spinnability of bronchial mucus relationship with viscoelasticity and mucus transport properties. Biorheology 1993 20 239-249. 

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