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CHAPTER SUMMARY AND CENTRAL ILLUSTRATION
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Chapter Summary
This chapter addresses the pathogenesis, pathophysiology, and management of pulmonary hypertension (PH) in the setting of structural lung disease, commonly referred to as cor pulmonale. Airway obstruction, lung fibrosis with restriction, or a combination of both factors causes a loss of pulmonary vascular surface area and impairment in intrapulmonary gas exchange, leading to hypoxemia with or without hypercarbia, which are potent stimuli for pulmonary vasoconstriction and vascular remodeling. Polycythemia with increased blood viscosity, resulting from hypoxia-induced increased red blood cell production, may further increase pulmonary vascular resistance. The subsequent elevations in pulmonary artery pressure result in right ventricular pressure and volume overload that may ultimately lead to right heart failure and death (see Fuster and Hurst’s Central Figure). The presence of cor pulmonale may be inferred from echocardiographic signs of right ventricular enlargement and hypertrophy, along with measurement of an increased tricuspid regurgitant jet velocity, but the definitive diagnosis requires the direct measurement of pulmonary hemodynamics. Management of cor pulmonale is primarily directed at optimizing lung function and gas exchange with conventional medical therapies (ie, bronchodilators, corticosteroids, and other anti-inflammatory agents), minimizing hypoxemia with supplemental oxygen, and identifying and treating comorbid conditions. The role of pulmonary arterial hypertension–targeted therapies in cor pulmonale is controversial and can result in worsening V/Q mismatching and clinical deterioration.
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INTRODUCTION AND DEFINITIONS
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The term cor pulmonale was coined by Paul Dudley White nearly a century ago and has long been used as a surrogate for right ventricular failure.1 The development of sophisticated invasive and noninvasive techniques has facilitated the study of right heart and pulmonary circulatory structure and function, yielding a greater understanding of the unique properties of the cardiopulmonary circuit in normal and disease states.
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The normal mean pulmonary artery pressure is less than 20 mm Hg at rest.2 The pulmonary circulation is a high-flow, low-resistance system capable of accepting the entire cardiac output at a pressure one-fifth that of the systemic circulation. Even with maximal exercise, when pulmonary blood flow may increase 5-fold, pulmonary artery pressure changes little, owing to pulmonary vasodilation and recruitment of unused vasculature. This remarkable capacity of the pulmonary circulation to adapt is further demonstrated by the fact that the loss of 50% of the vascular surface area, for example due to pneumonectomy or widespread parenchymal destruction in the setting of advanced lung disease, results in little change in resting pulmonary artery pressures. Pulmonary hypertension (PH), defined as a mean pulmonary artery pressure greater than 25 mm Hg at rest measured by right heart catheterization,2 may be due to a variety of conditions, as summarized in Table 59–1.
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