Pulmonary Pathophysiology

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3.8.1 Bronchitis

Bronchitis is an inflammation of the airways resulting in excessive mucus production in the bronchial tree. Bronchitis occurs when the inner walls of the bronchi become inflamed. It often follows a cold or other respiratory infection and happens in virtually all people, just as the common cold. When the bronchitis does not go away quickly but persists, then it is termed chronic bronchitis.

3.8.2 Emphysema

Emphysema is a chronic disease in which air spaces beyond bronchioles are increased. The stiffness of the alveoli is decreased, (static compliance is increased), and airways collapse more easily. Because of the decreased stiffness of the lung, exhalation requires active work and the work of breathing is significantly increased. The surface area of the alveoli become smaller, and the air sacs become less elastic. As carbon dioxide accumulates in the lungs, there becomes less and less room available for oxygen to be inhaled, thereby decreasing the partial pressure of oxygen in the lungs. See Fig. 3.11 which shows a picture of an emphysematous lung.

Emphysema is most often caused by cigarette smoking, although some genetic diseases can cause similar damage to the alveoli. Once this damage has occurred, it is not reversible.

3.8.3 Asthma

Asthma is a chronic disease which affects 5 million children in the United States. In asthma, the airways become overreactive with increased mucus production, swelling, and muscle contraction. Because of the decreased size of the bronchi and bronchioles, flow of air is restricted and both inspiration and expiration become more difficult.

3.8.4 Pulmonary fibrosis

Pulmonary fibrosis affects 5 million people worldwide and 200,000 in the United States. Pulmonary fibrosis is caused by a thickening or scarring of pulmonary membrane. The result is that the alveoli are gradually replaced by fibrotic tissue becoming thicker, with a decreased compliance (increased stiffness) and a decrease in diffusing capacity. Symptoms of pulmonary fibrosis include a shortness of breath, chronic dry, hacking cough, fatigue and weakness, chest discomfort, loss of appetite, and rapid weight loss. Traditionally, it was thought that pulmonary fibrosis might be an autoimmune disorder or the result of a viral infection. There is growing evidence that there is a genetic link to pulmonary fibrosis.

Figure 3.11 Normal lung versus an emphysematous lung. (a) Normal lung; (b) emphysematous lung. (With permission from West, 1992, Figure 4.3, p. 61.)

Figure 3.11 Normal lung versus an emphysematous lung. (a) Normal lung; (b) emphysematous lung. (With permission from West, 1992, Figure 4.3, p. 61.)

3.8.5 Chronic obstructive pulmonary disease (COPD)

Chronic obstructive pulmonary disease (COPD) is a slowly progressive disease of the lung and airways. COPD can include asthma, chronic bronchitis, chronic emphysema, or some combination of these conditions. The disease is characterized by a gradual loss of lung function. The most significant risk factor for COPD is cigarette smoking. Other documented causes of COPD include occupational dusts and chemicals. Genetic factors can also play a significant role in some forms of this disease.

3.8.6 Heart disease

Heart disease should be mentioned in any discussion of pulmonary pathologies. While cardiac disease is not strictly speaking, a pulmonary pathology, some forms of cardiac disease can certainly lead to respiratory pathologies. For example, a stenotic regurgitant mitral valve can cause back pressure in pulmonary capillaries leading to fluid in the lungs.

3.8.7 Comparison of pulmonary pathologies

Figure 3.12 shows the volume versus time curve for a normal lung compared to that for a patient with fibrosis, asthma, and emphysema. In the patients with fibrosis, asthma, and emphysema, note the shallow slope

Asthma And Fibrosis
Figure 3.12 Spirometer comparisons between a normal lung, fibrosis, asthma, and emphysema. (From Selkurt, 1982, Figure 9.20, p. 342.)

of the curve during forced inspiration and expiration. In other words, the change in volume over time, dV/dt, is much smaller in patients with lung disease compared to the dV/dt in the normal lung. The airflow rate is much smaller in all three cases.

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