What are the causes of chest pain that are more specific to pulmonary arterial hypertension?

One potential cause is that the increased pulmonary arterial pressures result in a "strain" on the muscle tissue of the right ventricle. To understand why this strain may cause discomfort, let's walk through the steps involved. Pulmonary arterial hypertension (PAH) leads to narrower, stiffer pulmonary arteries, similar to blocked pipes in a plumbing system. The right ventricle pumps blood through the pulmonary arteries (see the relationship between the lungs and heart), and it has to work harder to squeeze a normal level of blood flow through narrowed "pipes". This is similar to the way it takes more effort to blow air through a partially blocked straw than through an open straw.

The muscle of the right ventricle, as it works harder, needs more oxygen and nutrients (supplied via the blood) to do its work. If the blood flow through the small arteries that supply the right ventricle ("coronary arteries") isn't sufficient to meet the ventricle's demands, the muscle tissue can begin to starve for oxygen and a painful sensation may result. With exertion, such as walking, climbing stairs, running, or even daily tasks such as making a bed, there is even greater oxygen demand and this may make existing pain worse or bring on new pain (if there was none at rest). This type of pain, related to the right ventricle, is usually felt in the middle or on the right side of the chest even though the heart is on the left.

The second mechanism that may result in chest pain in patients with pulmonary hypertension involves the fact that as pulmonary pressures rise, the blood vessels themselves actually expand or stretch. This is similar to the way in which a car or bicycle tire expands as you use a pump to raise the pressure inside. Stretching the walls of the pulmonary arteries causes signals to be sent to the brain, and you end up feeling this as pain. With exertion, the heart has to pump more blood and this leads to greater stretch of the pulmonary arteries, causing increased pain (or new pain if there was none at rest). Since you have pulmonary vessels on both sides of your chest, this pain is not restricted to left or right, and may occur anywhere across the chest.