What causes pulmonary hypertension?
The normal person has a vast unused pulmonary circulation at rest. When a healthy person is sitting or resting, cardiac output is low and the pressures in the pulmonary circulation are quite low – in the order of 25/10 compared with 120/80 in the systemic circulation, which is measured on the arm with a blood pressure cuff. When a healthy person exercises, cardiac output can increase five to 10 times. Normally, the pulmonary artery pressures do not change at all, which allows the right ventricle to increase its workload normally by increasing the frequency of contraction and the volume of blood squeezed per contraction. This can only happen when unused pulmonary blood vessels are “recruited” and opened up.
