What is Pulmonary Hypertension?

1. Normal Blood Flow Through the Heart and Lungs

• The blood drains back to the heart via the veins and then into the superior and inferior vena cavae. This blood is low in oxygen as it has been used by muscles and organs around the body.
• The low oxygen blood enters the right atrium of the heart and then flows through the tricuspid valve to the right ventricle.
• The right ventricle pumps the blood through the pulmonary valve into the lungs via the pulmonary arteries. This is normally a very low pressure circuit and the right ventricle is a weak muscle.
• Once the blood has obtained oxygen in the lungs it drains back to the heart via the pulmonary veins.
• High oxygen blood passes from the left atrium of the heart through the mitral valve into the left ventricle.
• The left ventricle is a powerful muscle and pumps this high oxygen blood to the muscles and organs of the body through the aortic valve and into the aorta then the various arteries of the body. This is a much higher pressure system.

2. Definition of Pulmonary Hypertension.Pulmonary hypertension is defined as an abnormal increase in the blood pressure in the pulmonary arteries. As outlined above this is usually a very low pressure system. With normal pressures around a mean of 14mmHg. Pulmonary hypertension is defined as a mean pulmonary artery pressure of >25mmHg at rest or >30mmHg on exercise. These pressures are normally much lower than the systemic blood pressure from the left side of the heart (this is the pressure measured in your arm) and is normally around 120/80 with a mean of 75 to 80 mmHg.3. What Causes Pulmonary Hypertension?Pulmonary hypertension occurs when the blood vessels in the lungs receiving the low oxygen blood from the heart become narrowed. This is narrowing in the pulmonary arteries. Like a kink in a hose as the arteries narrow, the pressure required to keep the same amount of blood flowing needs to go up. Eventually the heart is not able to keep up the same flow rate and symptoms of breathlessness, fatigue and dizziness result.4. Types of Pulmonary HypertensionPulmonary hypertension can occur alone or in association with other diseases.

• Idiopathic Pulmonary Hypertension
  • Previously called primary pulmonary hypertension
  • Occurs in 3-10 per million population
  • More common in women
  • Peak onset at age 20-40yrs, but can occur at any age
  • Cause unknown
  • Family history in 10-12% of cases
• Pulmonary Hypertension related to Connective Tissue Diseases:
  • Scleroderma most common associated disease
  • May also occur in systemic lupus erythematosis and rarely rheumatoid arthritis
• Thrombo-embolic Pulmonary Hypertension:
  • Occurs when blood clots usually from the veins in the legs are dislodged to the lungs and fail to dissolve.
  • Then blocked arteries reduce the area of blood vessels and as a result increase the pressure
• Congenital Heart Disease:
  • Most commonly occurs when there is an abnormal connection between the right and left sides of the heart (hole in the heart).
  • The abnormal flow through the right side of the heart with the higher pressures of the left side results in damage to the pulmonary arteries and eventually pulmonary hypertension.
• Other:
  • Rarer associations with pulmonary hypertension are:
    • HIV - 1 in every 200 people with HIV will develop pulmonary hypertension
    • Portal hypertension (high blood pressure in the liver circulation)
    • Drugs – Diet pills (dexfenfluramine), Cocaine, Hallucinogens

DR HELEN WHITFORDRespiratory Physician Department of Allergy, Immunology & Respiratory Medicine Lung Transplantation Service, The Alfred