What is PAH?

Pulmonary arterial hypertension (PAH) is a progressive disease caused by narrowing of the pulmonary arteries, which connect the right side of the heart to the lungs.

Pulmonary hypertension (PH) refers to the elevation of blood pressure in the pulmonary arteries. PAH is a subgroup of PH caused by the narrowing of these blood vessels. PAH may occur with no identifiable cause or may be associated with one or more underlying conditions. As PAH develops, blood flow through the pulmonary arteries is restricted and the right side of the heart becomes enlarged due to the increased strain of pumping blood through the lungs. It is this strain on the heart, and decrease in blood flow to the left heart and systemic circulation that leads to the common symptoms of PAH, including breathlessness, fatigue, weakness, chest pain and syncope.1

By definition, PAH is characterised by:

  • mean pulmonary arterial pressure (PAP) ≥25 mmHg at rest
  • mean pulmonary capillary wedge pressure (PCWP) ≤15 mmHg
  • pulmonary vascular resistance (PVR) >3 Woods units

in the absence of other causes of PH.1


How common is PAH?

PAH is a rare disease, with an estimated prevalence of 10–50 cases per million in Europe,2 although the prevalence of PAH in certain at-risk groups can be substantially higher.3,4

Prevalence of PAH in Europe

Idiopathic PAH (IPAH), PAH with no identifiable risk factor, has an annual incidence of around 1 case per million people in the UK and has a female predominance of 70%.5 The demographics of patients with PAH associated with other conditions varies by type.6
Click here to read more about the different classes of PH.


Figure 1. The age and gender distribution of PAH patients in the UK PH service (2012–2013)7

PAH can occur at any age, although the mean age at diagnosis is between 50 and 65 years.1 Due to the non-specific nature of the symptoms, PAH is unfortunately most frequently diagnosed when patients have reached an advanced stage of disease.8 Early diagnosis and therapeutic intervention may offer an improved outlook for patients.9


  1. Galiè N, et al. Eur Hear J 2016;37:67–119
  2. Hoeper M and Gibbs S. Eur Respir Rev 2014;23:450–7
  3. Hachulla E, et al. Arthritis Rheum 2005;52:3792–800
  4. Mukerjee D, et al. Ann Rheum Dis 2003;62:1088–93
  5. Ling Y, et al. Am J Respir Crit Care Med 2012;186:790–6
  6. NHS Digital (2017). National Audit of Pulmonary Hypertension Great Britain, 2016-17
  7. Health and Social Care Information Centre (2013). National Audit of Pulmonary Hypertension, 2013
  8. Humbert M, et al. Am J Respir Crit Care Med 2006;173:1023–30
  9. Humbert M, et al. Circulation 2010;122:156–63

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