Why am I getting lightheaded?
Like shortness of breath and chest pain, lightheadedness is a non-specific symptom that can be caused by a number of different problems. What is common to almost all kinds of lightheadedness is that there is insufficient blood flow to the brain. The brain, like all other organs, requires a constant supply of blood bringing oxygen to its cells.
Why does pulmonary hypertension result in decreased blood flow to the brain? We have to go back to how blood is being pumped through the lungs from the right ventricle and eventually back into the left ventricle because it is from the left ventricle that blood gets pumped up to the brain. Because there is a higher resistance to blood flow through the narrowed pulmonary arteries of people with pulmonary hypertension, blood flow through the lungs will be lower than it should be. The left ventricle, which is downstream of the pulmonary arteries, will in turn receive less blood, and it will therefore have less blood to pump out to the brain and other parts of the body.
A reduction in the amount of blood being pumped by the heart is known in medical terms as decreased cardiac output. One of the main consequences of a decreased cardiac output is reduced blood flow to the brain; this causes the sensation of lightheadedness.
Why do I get faint or lightheaded when I go up the stairs or bend over to pick something up?
As mentioned above, cardiac output may be decreased in pulmonary hypertension. Normally, with exertion, cardiac output increases to deliver more blood and oxygen to the body, particularly the muscles involved in walking, such as the big muscles in your legs. In pulmonary hypertension, the cardiac output may not be able to increase appropriately during exercise due to the increased resistance to blood flow through the lungs. This increased resistance results in a decrease in blood flow returning to the left side of the heart, and consequently less blood pumped by the heart to the brain, causing the symptom of lightheadedness.
When you have been sitting for a long time, blood accumulates in your legs and feet due to gravity. If you suddenly stand up, it takes a few moments for your body to get this blood back to your heart, and as a result there is a brief period of reduced blood flow into the right side of the heart. Less flow to the right side means reduced flow through the lungs and to the left side of the heart, and therefore less blood being pumped to the brain. A similar thing happens when you bend over to pick something up and then stand up quickly. As you stand up, blood moves toward the legs due to gravity, and this reduces the amount of blood flow being returned through the venous system to the heart. Less blood flow back to the heart means less blood to the brain, and you get lightheaded.
Lightheadedness can occur in these cases even in people who don't have pulmonary hypertension. In those who do, however, the problem is made worse by the fact that the right ventricle has difficulty pumping blood through the narrowed, stiffened pulmonary arteries to the left ventricle and from there on to the brain.