- In normal individuals the right ventricle plays little role in augmenting
circulatory flow with most of the driving pressure for flow coming from the left ventricle
and the venous return. In fact, children with tricuspid atresia can be successfully
treated by joining the right atrium to the pulmonary artery (Fontan procedure).
- When the right ventricle is exposed chronically to increased afterload it
hypertrophies and assumes a more important role in maintaining flow through the pulmonary
- If the afterload elevation is severe enough, the right ventricle limits the
overall cardiac output. RV afterload can increase due to (1) obstruction or destruction of
the pulmonary circulation, (2) hypoxic pulmonary vasoconstriction, (3) cardiac disease, or
(4) idiopathic causes.
- Obstruction or destruction of any part of the pulmonary circulation from the
pulmonic valve to the left atrium results in increased RV afterload. Examples include (1)
pulmonary arterial obstruction (acute or chronic pulmonary emboli), (2) destruction of the
pulmonary microvasculature (emphysema, fibrotic lung diseases), or (3) obstruction of the
pulmonary veins (pulmonary veno-occlusive disease, sickle cell disease, some
- Hypoxic pulmonary vasoconstriction is the vasoconstriction of small pulmonary
arteries and arterioles at oxygen tensions less than 60 torr. This response results in
improved ventilation to perfusion matching at the expense of increased pulmonary vascular
resistance. Chronic obstructive pulmonary disease, chest wall diseases, obstructive sleep
apnea, and interstitial fibrosis all cause pulmonary hypertension via this mechanism.
- Idiopathic causes of pulmonary hypertension include
- Finally, cardiac disease can result in pulmonary hypertension either through
increased left atrial pressures (mitral stenosis) or through chronic L to R shunting.
Idiopathic proliferation of pulmonary arterioles and dropout of pulmonary capillaries
eventually leads to irreversible increases in the pulmonary vascular resistance so repair
of the underlying defect may not alleviate the right heart failure. In patients with
chronic L to R shunts, R sided pressures may eventually exceed left sided pressures
leading the R to L shunting (Eisenmenger physiology).