Tracheobronchial system

All stents currently available for application in the tracheobronchial system have demonstrated their... 

One of the potential advantages of metal stents over the plastic tube stents is the possibility of placement under conscious sedation by flexible endoscopy or fluoroscopy only. However, for a safe and durable access to the tracheobronchial system, the possibility for fine adjustments of the inserted stents, additional therapeutic measures, and permanent control of ventilation, most interventionists prefer to carry out stent implantations under general anesthesia and with the use of a rigid ventilating bronchoscope. Such a setting enables high frequency Venturi jet ventilation. 

The focus of this chapter is primarily on metallic stents. For a detailed overview of the results of placement of plastic tube stents for tracheobronchial obstructions due to malignant tumors, the interested reader is referred to one of the review articles on stenting of the tracheobronchial system written by experienced interventional bronchoscopists (thoracic endoscopist) (Colt and Dumon 1995 Mehta and Dasgupta 1999 Rafanan and Mehta 2000 Wood 2001). 

The first report on the oldest metal stent used in the tracheobronchial system was pubUshed by Wallace et al. in 1986 (Wallace et al. 1986). Since then, several studies on the use of this stent type have been pub-hshed and the stent became one of the most frequently applied metal stents in tracheobronchial mahgnancy. Wallace and colleagues initially reported on two cancer patients. Gianturco stents were placed in one to dilate a postoperative bronchial stenosis that caused pneumonia, and in the second to support a tracheal graft that collapsed with respiration. Stents were successfully placed and the patients symptoms improved (Wallace et al. 1986). 

Deformation and migration of Palmaz stents in three patients brought the suitability of the stent for use in the tracheobronchial system into question (Perini et al. 1999). The authors encountered stent collapse in three patients at 44 days, 78 days and 362 days after initial placement, respectively. Three stents also showed signs of complete or partial migration. The authors decided to no longer use this stent type in the tracheobronchial tree. 

The respiratory system has several mechanisms for removing deposited particles (8). The walls of the nasal and tracheobronchial regions are coated with a mucous fluid. Nose blowing, sneezing, coughing, and swallowing... 

Tracheobronchial region The middle region of the respiratory system, comprised of the trachea and the bronchi. 

Because the mucus layer or the underlying cells may serve as either final accumulation sites of toxic gases or layers through which the gases diffuse en route to the blood, we need simplified models of these layers. Altshuler et al. have developed for these layers the only available model that can be used in a comprehensive system for calculating tissue doses of inhaled irritants. It assumes that the basement membrane of the tracheobronchial region is covered with three discrete layers an inner layer of variable thickness that contains the basal, goblet, and ciliated cells a 7-Mm middle layer composed of waterlike or serous fluid and a 7-Mm outer layer of viscous mucus. Recent work by E. S. Boatman and D. Luchtel (personal communication) in rabbits supports the concept of a continuous fluid layer however, airways smaller than 1 mm in diameter do not show separate mucus and serous-fluid layers. 

New or improved methods are needed to measure local uptake experimentally. Such data can be used to verify the detailed dosage distribution predicted by the models. For example the retrograde catheter and tracheal cannula system used by Com et al. appears promising for transfer-coefficient measurements within segments of the tracheobronchial tree. A similar method was used by Battista and (3oyer to measure the absorption of acetaldehyde vapor in the dog lung. 

Particulates can either cross into the lymphatics at the spaces in the tracheobronchial wall where epithelial cells directly overlay lymphoid tissue or pass through the endothelium of thin capillary walls in the air spaces. The transfer is a portion of a clearance mechanism that assists the lung in maintaining its normal function of gas exchange. Absorbtion and transport mechanisms of a variety of materials that enter the lymphatics continue to be studied. It was shown early in this century that water, dyes, proteins, bacteria, lipids, and particulates enter the lymphatic system relatively easily. The rates of transport and quantity vary with the size and chemistry of the material. Classic studies by Kihara (1924 1950) and Nishikawa (1941) dem-... 

B[/ ]P metabolites have been shown to bind to DNA in culmred human hepatocytes and in human bladder and tracheobronchial explants. The metabolites identified were identical to those produced in other species and differed only in the relative percentages of formation. Human tissues were most active in metabolizing P>[a P and exhibited at least a threefold higher covalent binding of metabolites to DNA than hamsters, dogs, monkeys, or rats. In addition, P>[a P has been tested extensively in several bacterial and mammalian cell systems and has been chosen as a positive control for the validation of some of these systems. ... 

The rationale for basing air quality standards on smaller particles is evident from an examination of Fig. 2.12, a diagram of the human respiratory tract. Larger particles that are inhaled are removed in the head or upper respiratory tract. The respiratory system from the nose through the tracheobronchial region is covered with a layer of mucus that is continuously moved upward by the motion of small hairlike projections called cilia. Large particles deposit on the mucus, are moved up, and are ultimately swallowed. 

Figure 2.13 shows the deposition of particles in various regions of the respiratory tract as a function of particle diameter (Phalen, 1984 Phalen et al., 1991 Yeh et al., 1996). The deposition fraction of PM1() in the pulmonary and tracheobronchial regions can be quite large, so it is not surprising that health effects could be associated with these particles. Deposition in the upper portions of the respiratory system is dominated primarily by the large particles, which are readily taken out in the nose and upper airways. 

The respiratory system consists of three regions nasopharyngeal, tracheobronchial, and pulmonary. 

An understanding of common mechanisms of death due to poisoning can help prepare the care-giver to treat patients effectively. Many toxins depress the central nervous system (CNS), resulting in obtundation or coma. Comatose patients frequently lose their airway protective reflexes and their respiratory drive. Thus, they may die as a result of airway obstruction by the flaccid tongue, aspiration of gastric contents into the tracheobronchial tree, or respiratory arrest. These are the most common causes of death due to overdoses of narcotics and sedative-hypnotic drugs (eg, barbiturates and alcohol). 

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. 

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