Pulmonary hypertension (PH) is a spectrum of diseases involving the pulmonary vasculature, and is defined as an elevation in pulmonary arterial pressures (mean pulmonary artery pressure >22 mmHg). Pulmonary arterial hypertension (PAH) is a relatively rare form of PH and is characterized by symptoms of dyspnea, chest pain, and syncope. If left untreated, the disease carries a high mortality rate, with the most common cause of death being decompensated right heart failure. There have been significant advances in this field in regard to understanding the pathogenesis, diagnosis, and classification of PAH. Despite these significant advances, there is still a substantial delay in diagnosis of up to 2 years. In many cases, patients whose primary complaint is dyspnea on exertion are frequently misdiagnosed with more common diseases such as asthma or chronic obstructive pulmonary disease. The availability of newer drugs has resulted in a radical change in the management of this disease with significant improvement in both quality of life and mortality. A delay in diagnosis results in an obvious delay in the initiation of appropriate treatment. Clinicians should be able to recognize the signs and symptoms of PH and to complete a systematic workup in patients suspected of having it. In this way, early diagnosis, prompt treatment, and improved outcomes for patients become achievable.
Vasoconstriction, vascular proliferation, thrombosis, and inflammation appear to underlie the development of PAH (Fig. 49-1). In long-standing PH, intimal proliferation and fibrosis, medial hypertrophy, and in situ thrombosis characterize the pathologic findings in the pulmonary vasculature. Vascular remodeling at earlier stages may be confined to the small pulmonary arteries. As the disease advances, intimal proliferation and pathologic remodeling progress, resulting in decreased compliance and increased elastance of the pulmonary vasculature. The outcome is a progressive increase in the right ventricular afterload or total pulmonary vascular resistance (PVR) and, thus, right ventricular work. In subjects with moderate to severe pulmonary vascular disease with significantly increased PVR, as the resting PVR increases, there will be a corresponding increase in mean pulmonary artery pressure (PAP) until the cardiac output (CO) is compromised and starts to fall. With a decline in CO, the PAP will fall. As CO declines as a result of increased afterload and decreased contractility, tachycardia is a compensatory response. Tachycardia decreases filling time and, thus, preload, and results in a reduced fraction of stroke volume available to distend the pulmonary vascular tree.
The left panels show examples of plexogenic pulmonary arteriopathy. These are obstructive and proliferative lesions of the small muscular pulmonary arteries, composed primarily of endothelial cells with intermixed inflammatory cells, myofibroblasts, and connective tissue components. The lower left panel demonstrates proliferating cells (red PCNA stained cells). Panels on the right demonstrate medial hypertrophy of muscular pulmonary arteries. (Photographs on the left are courtesy of Dr. Stephen Archer, Queen’s University School of Medicine, Kingston, Ontario, Canada.)