Airway anatomy

Chediak AD, Wanner A (1990) The circulation of the airways anatomy, physiology and potential role in drug delivery to the respiratory tract. Adv Drug Deliv Rev 5 11-18. 

Harkema JR (1991) Comparative aspects of nasal airway anatomy Relevance to inhalation toxicology. Toxicol Pathol 19(4 Pt l) 321-336. 

The pattern of deposition of inhaled particles in a normal lung is dependent on particle size, flow rate, and airway anatomy (branching). There are also patient specific variables that influence aerosol deposition. These include respiratory rate, tidal volume, and other anatomical features. The presence of airflow obstruction characteristic of some lung diseases will affect deposition. 

Part 2 Prior to anesthesia induction, the patient is identified again by name and birth date, which are compared with ID bracelet and records. The scheduled surgical procedure is confirmed by the patient, and the surgical site marking by the OR staff. A brief review of patient s written informed consent, allergies, fasting interval, airway anatomy, ordered antibiotic prophylaxis, availability of blood products and readiness of anesthesia equipment is completed. Specifically in these patients, preoperative information is verified on correct medication intake, on fluid restriction orders, the interval since last hemodialysis and residual urinary output. 

Airway cross-sections have the nominal anatomy shown in Fig. 5.16. Airway surface liquid (AST), primarily composed of mucus gel and water, surrounds the airway lumen with a thickness thought to vary from 5 to 10 mm. AST lies on the apical surface of airway epithelial cells (mostly columnar ciliated epithelium). This layer of cells, roughly two to three cells thick in proximal airways and eventually thinning to a single cell thickness in distal airways, rests along a basement membrane on its basal surface. Connective tissue (collagen fibers, basement membranes, elastin, and water) lies between the basement membrane and airway smooth muscle. Edema occurs when the volume of water within the connective tissue increases considerably. Interspersed within the smooth muscle are respiratory supply vessels (capillaries, arteriovenous anastomoses), nerves, and lymphatic vessels. 

Local host defenses of both the upper and lower respiratory tract, along with the anatomy of the airways, are important in preventing infection. Upper respiratory defenses include the mucodliary apparatus of the nasopharynx, nasal hair, normal bacterial flora, IgA antibodies, and complement. Local host defenses of the lower respiratory tract include cough, mucodliary apparatus of the trachea and bronchi, antibodies (IgA, IgM, and IgG), complement, and alveolar macrophages. Mucus lines the cells of the respiratory tract, forming a protective barrier for the cells. This minimizes the ability of organisms to attach to the cells and initiate the infectious process. The squamous epithelial cells of the upper respiratory tract are not ciliated, but those of the columnar epithelium of the lower tract are. The cilia beat in a uniform fashion upward, moving particles up and out of the lower respiratory tract. 

Fig. 1 The anatomy of the lungs showing the major airway subdivisions.

The underpressure created in the respiratory tract is the driving force for the airflow through an inhalation device. The attainable underpressure and the rate of the airflow both depend on the total resistance in the airways and inhaler. The pressure drop achieved during inhalation is furthermore a function of the anatomy of the lungs, the effort made by the patient, pathological factors and the presence of exacerbations (e.g. in case of asthma). 

Fig. 3.1 Schematic diagram of the human respiratory system. The gross anatomy of the lung, the covering membranes (pleura), airways and air sacs (alveoli) are shown. The average diameter of portions of the air flow system are indicated trachea, 20 mm bronchus, 8 mm terminal and respiratory bronchioles, 0.5 mnn alveolar duct, 0.2 mm alveolar sacs, 0.3 mm.

The size of the fibrous particles that appear to induce disease in the animal models is compatible with the measured respiratory range in humans (Lipp-man, 1977). Most particulate deposition takes place not in the upper or conducting portion of the airways but in the alveolar region of the pulmonary tree (the respiratory unit). Some surface deposition may occur at bifurcations in the bronchial tree, but the actual amount at each location is influenced by anatomy, specific to the species—probably to an individual—as well as the variety of fiber. A large proportion of airborne particulates are rejected as part of the normal clearance mechanisms in animals, but in humans clearance mechanisms may be compromised by smoking, for example. We are unaware of any experiments on fiber toxicity using smoking rats ... 

Figure 27.4. Anatomy of the distal airways and functional units (alveoli) in the lower respiratory tract. (Adapted from LifeART illustration series, Lippincott Williams Wilkins, Hagerstown, MD, 1994. This figure was completely redrawn by the author from materials cited.)...

While chemical composition is important in determining the toxicity of particles and fibers, it is equally or more important to determine where a particle or fiber will deposit in the respiratory tract and how long it will stay there. The quantity and location of particle deposition in the respiratory tract depends on factors related to both the exposed individual and the inhaled particles. The mechanism of deposition is determined by the physical (size, shape, and density) and chemical (hygroscopicity and charge) characteristics of the inhaled particles. Particle deposition is also affected by biological factors inherent to the exposed individual such as breathing pattern (volume and rate), route of breathing (mouth versus nose), and the anatomy of the airways. 

In the context of aerosol design and delivery, such a static overview represents a satisfactorily simple model. However, many factors beyond the anatomy of the airways are relevant to the therapeutic use of aerosols. 

Previously, the anatomy and physiology of the airways were considered. In clinical practice, the assessment of pulmonary function is important in diagnosis of the airway disease, in determination of appropriate therapy, and in evaluation of the success of therapy. 

Factors that also govern the therapeutic effect are the anatomy and physiology of the individual and diseases of the lung. These are uncontrollable variables that are important to be aware of. The lung divides dichotomously over 23 generations until it reaches the alveolar sacs. There are 300 million of these covering more than 140 m2. The conducting airways are covered with smooth muscle and are... 

Tyler WS, Julian MD. Gross and subgross anatomy of the lungs, pleura, connective tissue septa, distal airways, and structural units. In Comparative Biology of the Normal Lung, Parent RA, ed. CRC Press Boca Raton, FL, 1991, pp. 37-48. 

Merigo F, Benati D, Di Chio M, Osculati F, Sbarbati A (2007) Secretory cells of the airway express molecules of the chemoreceptive cascade. Cell Tissue Res 327 231-247 Miller IJ Jr (ed) (1995) Anatomy of the peripheral taste system. Dekker, New York Miller IJ Jr, Reedy FE Jr (1990) Variations in human taste bud density and taste intensity perception. Physiol Behav 47 1213-1219... 

Gaseous pesticides are evenly dispersed in the air. In the case of inhalation, the anatomy and physiology of the respiratory system diminishes the pesticide concentration in inspired air. As pesticides are mostly lipid-soluble, they are usually not removed in the upper airways but tend to deposit in the distal portion of the lung, the alveoli [83] and may then be absorbed into the blood stream. 

Basic Facts about Asthma. Patient s knowledge is improved. The anatomy of the lungs and bronchi and the manner in which inflammation can lead to airway hyperreactivity and bronchoconstriction should be explained in easy-to-understand terms. The link between allergic inflammation and bronchoconstriction should be clarified. Patients may be instructed to use two basic types of medications bronchodilatory (relievers) and anti-inflammatory (controllers) medications. Charts and airway models can clarify the programme. 

FIGURE 11.2 Anatomy of the human respiratory tract. Deposition of nerve agent vapor or aerosols in the different regions of the lung can lead to different symptomology. Upper airway deposition can lead to immediate respiratory distress. Alveolar deposition leads to systemic distribution of the nerve agent. 

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