Pulmonary hypertension

Pulmonary hypertension is defined as a chronic increase in pulmonary artery systolic pressure above 30 mm Hg or a mean pressure greater than 20-25 mm Hg. From a consideration of Poiseuille's equation (page 187) it is apparent that pulmonary hypertension may be expected to occur in the following circumstances:

1 When there is a reduction in the number of vessels perfused.

2 When there is a narrowing of the vessels as a result of intimai thickening, muscle hypertrophy, vascular spasm, or a decrease in the transmural pressure holding them open.

3 When there is an increase in the pulmonary venous pressure.

4 When there is an increase in blood viscosity (for example, as a result of polycythaemia).

The clinical conditions that may cause pulmonary hypertension are listed in the box. For convenience these are grouped under five main headings:

• those predominantly associated with a reduction in the size of the vascular bed

• those associated with a narrowing of the vessels

• those associated with an increase in pulmonary venous pressure

• primary or idiopathic (cause unknown)70

• diverse aetiology.

It will, however, become apparent that such a categorisation is somewhat artificial for there are often a number of factors contributing to the hypertension in each patient.

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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