What are the situations in which a person with MS becomes less symptomatic?

What are the situations in which a person with MS becomes less symptomatic?

This occurs when there is associated tricuspid stenosis, pulmonary hypertension or atrial septal defect. Tricuspid stenosis and pulmonary hypertension decreases the volume of blood reaching the pulmonary capillaries and reduces the chance for transudation. Atrial septal defect decompresses the left atrium and reduces pulmonary venous congestion.