Methods for studying the effectiveness of bronchial cleansing

Studies in viscous liquids and their behavior in motion through capillaries in physics by I. Newton led the clinicians to the idea that sputum, being viscous in nature, when subject to movement along a bronchial tree, obeys the same laws. And its speed is greatly hampered in the case of a sharp increase in viscosity, which is observed in the exacerbation of the disease. And this, in turn, leads to the stagnation of bronchial contents and obstruction of the respiratory tract.
The first attempts to measure the viscosity of sputum, assess the speed of mucus transport in the bronchi and its connection with the activity of the ciliated epithelium, in fact, allowed to form the concept of the structure of the mucociliary system, which was mentioned above. Under normal conditions, the rate of removal of bronchial secretions is determined, firstly, by ciliary activity, and secondly, by the rheological properties of mucus.
Studies of sputum transport disorders in asthma patients began with attempts to link this with the deterioration of rheological properties — viscosity, elasticity, and later — adhesion values. However, when measuring the viscoelastic characteristics, the results were sometimes obtained directly opposite to the expected ones. Although, in fairness, it should be said that the axiom stating that viscous and thick sputum is excreted more slowly and coughs with difficulty has been confirmed. But no more than that.
Researchers’ failures in measuring the viscosity of sputum are explained by the fact that it belongs to the so-called “non-Newtonian” fluids, heterogeneous systems, the exact determination of the viscous properties of which is impossible, since their behavior does not obey the Newton equation describing the movement of viscous media. The study of the molecular structure of the sputum gel revealed that it is a structured system formed by glycoprotein molecules. Under the electron microscope, the sputum structure is represented by long fibers interconnected. Such a structure of sputum gel and determines its “non-Newtonian” character and gives it not only viscous, but also elastic properties. The study of sputum transport in the experiment revealed that its rate of excretion from the respiratory tract is more closely related to its elasticity than to its viscosity. However, further studies have shown that sputum is intermediate between liquid (viscous) and solid (elastic) bodies. Therefore, when measuring the viscosity and elasticity as a result of mechanical action, the structure of its gel can be deformed, which significantly distorts the results obtained.
As for the adhesive properties, they, causing an increased “stickiness” of the secret to the wall of the bronchus, also affect the efficiency of its evacuation from the respiratory tract. Adhesion is closely related to the surface-active characteristics that determine the magnitude of the surface tension and affect the strength of the contact formed with the wall of the bronchus. Literary and our own data (Solopov V.N., Lunichkina I.V., 1988, 1989) confirmed that the rate of sputum transport from the respiratory tract is closely related to adhesive and surface active properties.
But nevertheless, the conducted studies of the rheological properties of sputum in different phases of the disease and in different cohort of patients could not explain the patterns of obstruction of the respiratory tract of asthmatics. Therefore, the main efforts were aimed at determining the speed of movement of mucus in the mucociliary system.
The methods used for assessing the speed of mucociliary transport are most often based on determining the time of removal of inhaled radioisotope particles, in particular technetium-99, from the respiratory tract. Measuring the speed of mucociliary transport in healthy subjects revealed that the time for complete elimination of particles with the inhaled radioactive isotope technetium-99 takes from 1 to 20 hours, and the speed of movement of mucus is on average 4-10 mm / min. As for patients with asthma, it was revealed that even in the remission phase, the speed of mucociliary transport was reduced by 10-55%. At the same time, comparative studies have revealed a reduction in the rate of mucociliary transport in smokers and elderly subjects not suffering from asthma. Without dwelling further on this topic, it should only be noted that most of the research in this area, according to the figurative expression of one of the scientists, leads to “results that are embarrassing and contradictory.”
Thus, no one was able to find answers to the following questions: 1) to what extent does the violation of mucus formation affect the degree of bronchial obstruction? 2) why, with similar at first glance, disorders in the mucociliary system, congestion, accumulation of mucus and obturation of the bronchial tree in some patients develop quickly, and in others – rather slowly? and 3) how are disorders of mucus formation in asthma associated with fatal outcomes?

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