Respiratory Mechanics and Gas Exchange

In order to understand diseases of the respiratory system and how they can be treated, it is necessary to have an overview of the normal function of the respiratory system that is the structures involved, the mechanism of breathing and gas exchange and the control and variation of breathing rate. Air must be able to get in and out of the lungs efficiently and gas exchange must be adequate. Any condition that interferes with these processes will cause disease. 

Markers of physiological effects can be useful in identifying early changes in respiratory functions of the lung due to inhaled material. Biomarkers are available to measure lung mechanical properties, ventilation, expiratory flow, intrapulmonary gas distribution, alveolar-capillary gas exchange, and perfusion. Such measurements have been used to test the effects of exposure to an array of inhaled toxicants. These assays can reveal functional manifestation of structural changes in the respiratory system, whether... 

Most of the symptoms produced by phosgene poisoning occur as a consequence of damage to the lung and its associated structures. Man s respiratory system is highly specialized for gas exchange in air. The internal surfaces of the system are brought into contact with the air via the respiratory tract and the operation of a tidal ventilation mechanism (see Fig. 2.1). 

Chapter 11 presents models used to study the continual interaction of the respiratory mechanical system and pulmonary gas exchange. Traditionally, the respiratory system is described as a chemo-stat — ventilation increases with increased chemical stimulation. Alternatively, the author proposes that quantitative description of the respiratory central pattern generator, a network of neuronal clusters in the brain, is a much more sophisticated and realistic approach. Study of this dynamic, optimized controller of a nonlinear plant is interesting from both physiological and engineering perspectives, the latter due to applications of these techniques for new, intelligent control system design. 

Like any closed-loop system, the behavior of the respiratory control system is defined by the continual interaction of the controller and the peripheral processes being controlled. The latter include the respiratory mechanical system and the pulmonary gas exchange process. These peripheral processes have been extensively studied, and their quantitative relationships have been described in detail in previous reviews. Less well understood is the behavior of the respiratory controller and the way in which it processes afferent inputs. A confounding factor is that the controller may manifest itself in many different ways, depending on the modeling and experimental approaches being taken. Traditionally, the respiratory control system has been modeled as a closed-loop feedback/feedforward regulator whereby homeostasis of arterial blood gas and pH is maintained. Alternatively, the respiratory controller may be viewed as a... 

Exercise limitation and functional disability in COPD have a complex, multifactorial basis. Ventilatory limitation is caused by increased airways resistance, static and dynamic hyperinflation, increased elastic load to breathing, gas exchange disturbances, and mechanical disadvantage and/or weakness of the respiratory muscles (4-6). Car-diocirculatory disturbances (7,8), nutritional factors (9), and psychological factors, such as anxiety and fear, also contribute commonly to exercise intolerance. Skeletal muscle dysfunction is characterized by reductions in muscle mass (10,11), atrophy of type I (slow twitch, oxidative, endurance) (12,13) and type Ila (fast twitch) muscle fibers (14), altered myosin heavy chain expression (15), as well as reductions in fiber capillarization (16) and oxidative enzyme capacity (17,18). Such a dysfunction is another key factor that contributes... 

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