10th March 2024

Pathophysiology

Each group has its separate pathophysiology, clinical presentation, and management. Generally speaking, the pathophysiology of pulmonary hypertension can be easily understood by considering Ohm’s law that when adapted reads:

Pressure = Flow x Resistance

An increase in pulmonary vascular resistance is the most common cause of detectable pulmonary hypertension. In most situations, increased flow (i.e. right ventricle output) and increased pulmonary venous pressure alone are not sufficient to cause pulmonary hypertension due to available compensatory mechanisms, but they can prove to be significant in chronic conditions.

When applied to the pulmonary circulation, all the variables in Ohm’s law can be affected by different medical conditions:

• In Group 1, occlusive vasculopathy of the small pulmonary arteries and arterioles increases pulmonary vascular resistance
• In Group 2, congenital heart disease with left-to-right shunt may increase flow. Mitral valve disease, left ventricular systolic or diastolic dysfunction, or restrictive cardiomyopathy can increase pulmonary venous pressure.
• In Group 3, conditions that decrease the cross-sectional area of the pulmonary vascular bed (ILD) or induce hypoxic vasoconstriction (hypoventilation, parenchymal lung disease) cause an increase in pulmonary vascular resistance.
• In Group 4, multiple thrombotic events reduce the cross-sectional area of the pulmonary vascular bed, resulting in an increase in PVR.

As management and therapy vary depending on the specific type of pulmonary hypertension, these will be dealt with separately in this section.