Pulmonary arterial hypertension (PAH) is a rare, chronic and progressive heart and lung disease. In PAH, the pulmonary arteries thicken and constrict, making blood transfer between the heart and lungs difficult. PAH results in elevated blood pressure in the arteries in the lungs and right side of the heart.

As pressure in the pulmonary arteries increase, the right side of the heart is forced to work at unsustainable levels to move blood through the lungs. PAH leads to right sided heart enlargement and failure and may cause premature death.

The cause of PAH is unknown. It is a serious illness which presently affects over 30,000,000 people worldwide. There is no present cure for PAH. The disease does not discriminate between age, gender or race.

The World Health Organization (WHO) has classified pulmonary hypertension into five groups. PAH represents Group 1. There are four functional classes within WHO Group 1 pulmonary hypertension, each class representing the present functional stage and advancement of the disease within a PAH patient:

WHO Class I – Patients with pulmonary hypertension but without resulting limitation of physical activity. Ordinary physical activity does not cause undue dyspnea (shortness of breath) or fatigue, chest pain or near syncope (loss of consciousness).

WHO Class II – Patients with pulmonary hypertension resulting in slight limitation of physical activity. They are comfortable at rest. Ordinary physical activity causes undue dyspnea or fatigue, chest pain, or near syncope.

WHO Class III – Patients with pulmonary hypertension resulting in marked limitation of physical activity. They are comfortable at rest. Less than ordinary activity causes undue dyspnea or fatigue, chest pain, or near syncope.

WHO Class IV – Patients with pulmonary hypertension with inability to carry out any physical activity without symptoms. These patients manifest signs of right-heart failure. Dyspnea and/or fatigue may be present at rest. Discomfort is increased by any physical activity.[1]

[1] Classification cite to Rubin LJ. Diagnosis and management of pulmonary arterial hypertension: AACP Evidence Based Clinical Practice Guidelines. Introduction. Chest. 2004; 126:7S-10S.