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Introduction


What is pulmonary hypertension?


This chapter provides an introduction to pulmonary hypertension, its classification, pathogenesis, symptoms and signs, and highlights key background reading


Michael J Segel MD Consultant Pulmonologist Pulmonary Institute, Sheba Medical Center, Tel HaShomer, Ramat Gan; and Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel


There is a great deal of confusion regarding pulmonary hypertension (PH), not only in the lay public but in the medical profession as well. Part of this stems from a misunderstanding of the meanings of several related terms – PH, pulmonary arterial hypertension (PAH), primary PH and pulmonary vascular disease.


PH is not a disease entity. PH is, in


fact, a simple haemodynamic phenomenon – it is defined as a mean pulmonary artery pressure (mPAP) greater than 25mmHg (mPAP is <20mmHg in normal individuals, and most experts consider an mPAP of 20–24mmHg as a grey zone, borderline value). Note that this definition is based on an invasive measurement of pressure at rest. Mean PA pressure can only be accurately measured by right heart catheterisation. Although echocardiographic estimation of pulmonary artery pressure is reasonably accurate, echocardiography is still considered a screening tool in the diagnosis of PH, which must be confirmed by invasive haemodynamic measurement. It is also important to realise that echocardiography provides an estimate only of systolic PAP, and not diastolic PAP, and thus not mPAP.


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Classification PH is classified into five groups based on


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aetiology and mechanism. The clinical classification of PH will be discussed in greater detail in Chapter 3. Although PH is a feature of a wide range of clinical entities, it is generally the case that within each of these many diseases associated with PH, the presence of PH is a negative prognostic indicator. ● Group 1, is called PAH and consists of diseases that primarily affect the pulmonary arteries. The haemodynamic definition reflects the pre-capillary nature of PAH: mPAP >25mmHg with normal left ventricular filling pressure (pulmonary artery occlusion pressure (PAOP) or left ventricular end- diastolic pressure (LVEDP)


<15mmHg). Specific PAH entities share certain features of their pathology and pathogenesis. PAH may be idiopathic, heritable (for example, PAH-caused by bone morphogenic protein receptor 2 (BMP-R-2) mutations – see below) or associated with HIV, scleroderma and other connective tissue diseases, certain drugs and toxins (for example, certain anorexigens), portal hypertension, schisotosomiasis and congenital heart disease. PAH is a progressive disease which in most cases, if untreated, will lead to death from right heart failure. The rate of progression and response to therapy appears to differ significantly between


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