Lungs airway caliber

Dolovich, M. A. (2000), Influence of inspiratory flow rate, particle size, and airway caliber on aerosolized drug delivery to the lung, Respir. Care, 45, 597-608. 

Mucociliary clearance (MCC) Ciliary dysfunction, airway caliber, mucus production >2 p,m Primary ciliary dyskinesia, bronchial disorders, lung transplantation... 

Site of deposition of tracer aerosol Particle size of aerosol Pattern of inhalation Airway caliber Lung capacity Mucus/cilia interaction Mucosal surface damage Spontaneous cough Exercise Disease Drugs... 

The flow-resistive properties of the airways are of major relevance to aerosol therapy in that they directly influence the pattern of distribution and deposition of inhaled particles within the lungs. Airway resistance increases, and hence aerosol delivery will be reduced, if the airways become partially blocked or narrowed by factors such as bronchospasm, inflammation, or secretions. Small changes in airway caliber can have dramatic effects on airway resistance. In a healthy adult, airway resistance is approximately 0.2 kPa/L/s (2 cmHp/L/s)... 

As discussed previously (Sec. II.B), bronchial smooth muscle tone is under autonomic control. Cold air and stimulation of receptors by irritants such as cigarette smoke, dust particles, and sulfur dioxide can also cause increased tone and hence bronchoconstriction (229). Bronchomotor tone is also modulated by vagal stretch reflexes and varies inversely with lung volume. Paradoxically, the rise in bronchomotor tone and/or increase in FRC during an attack of asthma may partially reverse the reduction in airway caliber that occurs in this condition, making assessment of response to therapy complex. Similarly, bronchodilators have been shown to cause paradoxical reductions in airflow and desaturation in some infants with history of wheeze, a phenomenon that has been attributed at least partially to changes in airway wall compliance (230-232). 

Figure 7 Forced expiratory flow maneuvers in normal and obstructed airways. A maximal expiratory effort from total lung capacity results in a rapid expiration of air from the lungs, the volume of which is equivalent to the forced vital capacity (FVC) and the rate of which is dependent on the caliber of the airways. The volume of air expired in the first second of a maximal expiratory effort is the FEV10. In subjects with obstructed airways, air flow is retarded as reflected in a smaller FEV10 (FEV10ob) than in subjects with normal airways (FEV10).

The caliber of airways through which the aerosol has to pass to get to the more distal parts of the lungs is of utmost importance. In functional terms, the forced expiratory volume in one second, FEVi, is usually taken as a measure of the instantaneous resistance (and, hence, the caliber) of the airways. Therefore, it is customary to attempt to relate FEVi to the deposition pattern. Using such... 

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