Riskforrecurrenceishigh.
The pulmonary circulation normally is one of low resistance, and pulmonary blood pressures are only about one-eighth of systemic pressures. Pulmonary hypertension (defined as pressures of 25 mm Hg or more at rest) may be caused by a decrease in the cross-sectional area of the pulmonary vascular bed or, less commonly, by increased pulmonary vascular blood flow. Based on shared features, the World Health Organization has classified pulmonary hypertension into the following five groups:
Pulmonary arterial hypertension, a diverse collection of disorders that includes heritable forms of pulmonary hypertension and diseases that cause pulmonary hypertension by affecting small pulmonary muscular arterioles; these include connective tissue diseases, human immunodeficiency virus, and congenital heart disease with left to right shunts
Pulmonary hypertension due to left-sided heart disease, including systolic and diastolic dysfunction and valvular disease
Pulmonary hypertension due to lung diseases and/or hypoxia, including COPD and interstitial lung disease
Pulmonary hypertension with unclear or multifactorial mechanisms
As can be gathered from this classification, pulmonary hypertension has diverse causes. Some of the more common causes are the following:
Chronic obstructive or interstitial lung diseases (group 3). These diseases obliterate alveolar capillaries, increasing pulmonary resistance to blood flow and, secondarily, pulmonary blood pressure.
Antecedent congenital or acquired heart disease (group 2). Mitral stenosis, for example, causes an increase in left atrial pressure and pulmonary venous pressure that is eventually transmitted to the arterial side of the pulmonary vasculature, leading to hypertension.
Recurrent thromboemboli (group 4). Recurrent pulmonary emboli may cause pulmonary hypertension by reducing the functional cross-sectional area of the pulmonary vascular bed, which in turn leads to an increase in pulmonary vascular resistance.
Autoimmune diseases (group 1). Several of these diseases (most notably systemic sclerosis) involve the pulmonary vasculature and/or the interstitium, leading to increased vascular resistance and pulmonary hypertension.
Obstructive sleep apnea (also group 3) is a common disorder that is associated with obesity and hypoxemia. It is now recognized to be a significant contributor to the development of pulmonary hypertension and cor pulmonale.
http://ebooksmedicine.net
Uncommonly, pulmonary hypertension is encountered in patients in whom all known causes are excluded; this is referred to as idiopathic pulmonary arterial hypertension. This name is a misnomer, however, as up to 80% of “idiopathic” pulmonary hypertension (sometimes referred to as primary pulmonary hypertension) has a genetic basis, sometimes being inherited in families as an autosomal dominant trait. Within these families, there is incomplete penetrance, and only 10% to 20% of the family members develop overt disease. As is often the case, investigating the molecular basis of an uncommon familial form of the disease has provided new pathogenic insights, in this instance by shining a spotlight on the role of the bone morphogenetic protein (BMP)–signaling pathway. Inactivating germ line mutations in the gene encoding bone morphogenetic protein receptor 2 (BMPR2) are found in 75% of the familial cases of pulmonary hypertension and 25% of sporadic cases. More recently, mutations in other genes that are involved in the BMPR2 pathway also have been identified in affected patients. Details remain to be worked out, but it appears that defects in BMPR2 signaling leads to dysfunction of endothelium and proliferation of vascular smooth muscle cells in the pulmonary vasculature. Because only 10% to 20% of individuals with BMPR2 mutations develop disease, it is likely that modifier genes and/or environmental triggers also contribute to the pathogenesis of the disorder.