Tracheobronchial deposition

Tracheobronchial deposition of such carriers may not be desirable as clearance on the mucociliary escalator will occur in a relatively short time providing insufficient time for release from these controlled-release systems. Alveolar deposition will, in contrast, result in extended clearance times which are dependent on the nature of the carrier particle and may therefore be a better option for the effective use of such carrier systems for pulmonary drag delivery. 

Anderson M, Svartengren M, Canmer P. Human tracheobronchial deposition and effect of a cholinergic aerosol inhaled by extremely slow inhalations. Exp Lung Res 1999 25 335-352. 

Anderson et al. examined the effect of altering inspiratory flow rate on the regional lung deposition of inert particles and on the pulmonary response to histamine aerosol. In one experiment, six healthy nonsmokers inhaled 6-pm Teflon particles that were labeled with the radioisotope indium 111 (" In) at 0.04 and 0.5 L/s. Tracheobronchial deposition averaged 50% after inhaling at 0.04 L/s, compared to 30% after inhaling at 0.5 L/s. Alveolar deposition increased from 1 to 28% with the lower inspiratory rate (69). 

For the small child compared to the adult, models predict that tracheobronchial deposition will be higher for all particle sizes, with the largest differences predicted to be between 7-month-old babies and adults. These differences need to be confirmed in vivo. 

Aerosol delivered with a droplet size distribution suitable for pulmonary or tracheobronchial deposition... 

Figure 3 Relation between the parameter ADT and tracheobronchial deposition in percentage of particles entering the trachea. Each point represents a mean from six to ten healthy adults (median age 27, range 19-54 years and 15% women). On the lower. r-axis the AD F values are shown, and on the upper, the corresponding particle sizes at an inhalation flow of 30 L/min. The formula of the regression line isy = -99.3 + 21.8 Inx), r = 0.96.

Measurements of whole-lung clearance in healthy subjects using inhaled radiolabeled test aerosols show a rapid clearance phase, which is completed within 24 hr (44,45,52). The rapidly cleared fraction has generally been equated with tracheobronchial deposition, and the retained fraction with alveolar deposition. Recently, results from studies using a shallow bolus technique indicate that particles... 

Therapeutic aerosols play a prominent role in the treatment of diseases of the lower airways, such as bronchial asthma and chronic bronchitis. It has been proposed that an increased deposition in the peripheral airways would be of value, in particular for treatment with inhaled corticosteroids. In patients with asthma, tracheobronchial deposition could be increased, practically independent of airway dimensions, by inhaling large aerosol particles extremely slowly (17,114). This could be a potentially useful approach of therapeutic importance, particularly in the treatment of patients with airways obstruction. Still, another possibility to enhance deposition of therapeutic aerosols in asthmatics could be the use of carrier gases such as helium-oxygen mixture (113). 

Everard et al. (202) discuss different technical factors, such as driving gas force and the effect of aerosol output. They also conclude that at high tidal volume, drug delivery is dependent on the aerosol concentration and volume of available aerosol, but essentially independent of tidal volume. This is consistent with the relations between the AD F and oropharyngeal and tracheobronchial deposition (see Figs. 2 and 3). At low tidal volume, the influence of tidal volume is important. Equipment dead space, consequently, is especially important in treatment of small children. 

Svartengren K, Philipson K, Svartengren M, Anderson M, Camner P. Tracheobronchial deposition and clearance in small airways in asthmatic subjects. Eur Respir J 1996 9 1123-1129. 

Phalen RF, Oldham MJ, Kleinman MT, Crocker TT. Tracheobronchial deposition predictions for infants, children, and adolescents. Ann Occup Hyg 1988 32 11-21. 

Yeates DB, Gerrity TR, Garrard CS. Characteristics of tracheobronchial deposition and clearance in man. Ann Occup Hyg (Inhaled Particles V) 1982 26 245-257. 

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