Porth's Essentials of Pathophysiology, 4e

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Respiratory Function

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pathogenesis of primary pulmonary arterial hyperten- sion. Oral endothelin antagonists (e.g., ambristan, bosentran) have proved to be effective in treating mod- erate to severe primary pulmonary hypertension and may become the treatment of choice for all stages of the disease. 66 Sildenafil (e.g., Revatio), a highly selective phosphodiesterase-5 inhibitor that acts in a manner sim- ilar to nitric oxide to produce vasodilation, is approved for use in pulmonary hypertension. Lung transplan- tation may be an alternative for persons who do not respond to other forms of treatment. Cor Pulmonale The term cor pulmonale refers to right heart failure resulting from primary lung disease or pulmonary hypertension. The increased pressures and work result in hypertrophy and eventual failure of the right ven- tricle. The manifestations of cor pulmonale include the signs and symptoms of the primary lung disease and the signs of right-sided heart failure (see Chapter 20). Signs of right-sided heart failure include venous congestion, peripheral edema, shortness of breath, and a productive cough, which becomes worse during periods of heart failure. Plethora (i.e., redness), cyanosis, and warm, moist skin may result from the compensatory polycythe- mia and desaturation of arterial blood that accompany chronic lung disease. Drowsiness and altered conscious- ness may occur as the result of carbon dioxide retention. Management of cor pulmonale focuses on the treatment of the lung disease and heart failure. Low-flow oxygen therapy may be used to reduce the pulmonary hyper- tension and polycythemia associated with severe hypox- emia caused by chronic lung disease. ■■ The pulmonary circulation is a low-pressure system that links the right heart and systemic venous system with the left heart and the systemic arterial system and functions as a conduit for exchange of the dissolved gases in the blood with the ventilated air in the alveoli. ■■ Pulmonary embolism develops when a blood- borne substance lodges in a branch of the pulmonary artery and obstructs blood flow. The embolus can consist of a thrombus, air, fat, or amniotic fluid.The most common form is thromboemboli arising from the deep venous channels of the lower extremities. ■■ Pulmonary hypertension represents an elevation in the pulmonary arterial pressure. It may arise as a secondary disorder associated with other disease conditions, usually cardiac or pulmonary, or as a primary disorder, characterized by SUMMARY CONCEPTS

Acute Respiratory Disorders The function of the respiratory system is to add oxygen to the blood and remove carbon dioxide. Disruptions in gas exchange occur with acute lung injury respiratory distress syndrome, and respiratory failure. Although the mechanisms prompting these conditions may vary, both are life-threatening situations with a high risk of mor- bidity and mortality. abnormal proliferation and contraction of vascular smooth muscle, coagulation abnormalities, and marked intimal fibrosis leading to obliteration or obstruction of the pulmonary arteries and arterioles. ■■ Cor pulmonale describes right heart failure caused by pulmonary disease and long-standing pulmonary hypertension. Acute Lung Injury/Acute Respiratory Distress Syndrome Acute respiratory distress syndrome (ARDS) is a clini- cal syndrome that is characterized by severe dyspnea of rapid onset, hypoxemia, and pulmonary infiltrates. Acute lung injury (ALI) is a less-severe form of the dis- order, but has the potential for evolving into ARDS. The two conditions are differentiated by the extent of hypox- emia as determined by the ratio of the partial pressure of oxygen in the arterial blood (PO 2 ) to fraction of inspired oxygen (FIO 2 ). 67–70 The incidence of ALI/ARDS is not consistently reported, although it is estimated to occur in approximately 150,000 to 200,000 persons each year in North America. Despite the most sophisticated inter- ventions, the mortality rate varies from 35% to 60% and morbidity is extensive, including physical, cogni- tive, and emotional sequelae. 15,71 Both ARDS and ALI can result from a number of con- ditions, including aspiration of gastric contents, major trauma (with or without fat emboli), sepsis secondary to pulmonary or nonpulmonary infections, acute pan- creatitis, hematologic disorders, metabolic events, and reactions to drugs and toxins (Chart 23-2). Etiology and Pathogenesis Although a number of conditions may lead to ALI/ARDS, they all produce similar pathologic lung changes that include diffuse epithelial cell injury with increased perme- ability of the alveolar–capillary membrane (Fig. 23-15). The increased permeability permits fluid, plasma pro- teins, and blood cells to move out of the vascular com- partment into the interstitium and alveoli of the lung. 15,69 Diffuse alveolar cell damage leads to accumulation of fluid, surfactant inactivation, and formation of a hyaline membrane that is fibrous and impervious to gas exchange.