Rheology of mucus

VI. Contributions of Living Particles to the Rheology of Mucus and Its Clearance... 

Tomkiewicz RP, Boyd WA, Feng W, App EM, Rubin BK, King M. Tracheal clearance and rheology of mucus after aerosol ization of 3 and 7% hypertonic saline in healthy dogs. Am J Respir Crit Care Med 1997 155 A780. 

GP Martin, C Marriott, I Kellaway. (1976). The effect of natural surfactants on the rheological properties of mucus. J Pharm Pharmacol 28 76P. 

Eylers, J. P. (2008). Mucus and slime Structure and rheology of natural polysaccharides. 

The coordination of cilia motility is controlled by neural innervation, chemical pacemaking, and hormonal stimulation, and the effects of ions such as calcium and potassium. Cilia beat in a coordinated fashion to achieve the unidirectional propulsion of mucus with the frequency of the ciliary beat, which is dependent upon the environment. Human nasal cilia have been reported to beat, in vitro, with an average frequency of 10 Hz. Any rheological abnormalities in the mucus gel, particularly those that alter the elastic properties of mucus, can greatly affect clearance and undermine ciliary activity in the nasal cavity. In such circumstances, the adhesiveness of the mucus layer may allow it to remain in contact with the underlying cell layers and retain any substances introduced into the nasal cavity. 

Chronic diseases include cystic fibrosis in which nasal mucus is thick and viscous as a result of abnormal chloride transport across the membrane of the epithelial cells, leading to reduced water secretion. Similarly, chronic sinusitis also reduces nasal mucociliary clearance due to an increase in the rheological properties of mucus. 

As noted in Section HE, both layers decrease the absorption rate, especially of large water-soluble molecules, since the diffusion coefficient is directly proportional to the reciprocal values of both the hydrodynamic radius and the viscosity of the layers. About the influence of absorption enhancers on mucus rheology very little is known. Bib salts and phospholipids are known to reduce the viscoelasticity of bronchial mucus aid probably also of mucus layers in the gastxointestinal tract [40. Hie results should be interpreted with caution since it is not the observed macro )viscosity that determines the diffusion rate in polymer... 

It is widely held that mucus should possess specific rheological properties for clearance from the airway to occur. Any alteration in mucus rheology that compromises clearance can predispose the individual to airway disease and infection. Some agents capable of altering mucus rheology are listed in Table 9.2. In addition, the state of mucus hydration (or mucin concentration) will affect the properties of the gel. In... 

Table 9.2 Agents capable of altering the rheological properties of mucus...

Quraishi MS, Jones NS, Mason J. The rheology of nasal mucus a review. Clin Otolaryngol 1998, 23, 403-413. 

Baneijee R, Bellare J, Puniyani R. Effect of phospholipid mixtures and surfactant formulations on rheology of polymeric gels, simulating mucus, at shear rates experienced in the tracheobronchial tree. Biochem Eng J 2001, 7, 195-200. 

M. King, J. M. Zahm, D. Pierrot, S. Vaquez-Girod, and E. Puchelle. The role of mucus gel viscosity, spinnability and adhesive properties in clearance by simulated cough. Bio rheology 26 737-745 (1989). 

See, for example, Silberberg A. Basic rheological concepts Litt M, Wolf DP, Kahn MA. Functional aspects of mucus rheology Pringle R. Gastric mucus viscosity and peptic ulcer, all in Elstein M, Parke DV (eds) Mucus in Health and Disease. New York, Plenum Press, 1977, pp 181-190, 191-201,202-216. 

Mucins are the major structural components of mucus, a thick gelatinous fluid secreted by specialized epithelial cells such as goblet cells that covers and protects many human organs. Mucins are responsible for the rheological properties of mucus and are very high molecular weight... 

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). 

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. 

However, neutrophils also release large quantities of proteases, such as elastase and cathepsin G. These proteases are the most potent secretagogues known (39). Not only do they stimulate the output of mucus from secretory cells, but they are also capable of degrading mucous glycoproteins, particularly when the DNA and actin that accompany the mucins in purulent secretions become degraded (40). Thus the net effect of the by-products of infection on mucus s rheology is rather unpredictable. 

King M, Rubin BK. Rheology of airway mucus relationship with clearance function. In Takashima T, Shimura S, eds. Airway Secretion Physiological Bases for the Control of Mucous Hypersecretion. New York Marcel Dekker, 1994 283-314. 

Lutz RJ, Lift M, Chakrin LW. Physical-chemical factors in mucus rheology. In Gabelnick HL, Lift M, eds. Rheology of Biological Systems. Springfield, IL Charles C Thomas, 1973 158-194. 

Holma, B. (1985). Influence of buffer capacity and pH-dependent rheological properties of respiratory mucus on health effects due to acidic pollution. Set. Total Environ. 41, 101-123. 

Madsen, F., Eberth, K., and Smart, J.D., A rheological assessment of the nature of interactions between mucoadhesive polymers and a homogenised mucus gel. Biomaterials, 19 1083-1092 (1998). 

Ewoldt, R. H., Clasen, C., Hosoi, A. E., and McKinley, G. H. (2007). Rheological fingerprinting of gastropod pedal mucus and synthetic complex fluids for biomimicking adhesive locomotion. Soft Matter 3, 634-643. 

---