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Diagnostic Tests

I get tests fairly often. What are the common tests and what do these tests measure?

One of the tests we have already discussed is the TTE. This is essentially a video ultrasound of the heart and it is very useful to look at the heart and pulmonary arteries. From a PAH standpoint, its most important use is to measure and monitor your pulmonary artery (PA) pressures in a non-invasive manner. However, it can also visualize abnormalities in the heart valves and how well the ventricles are pumping (in PAH, the right ventricle may become enlarged or dilated and it may not pump normally).

Another frequently used test is the 6-minute walk test. By seeing how far you can walk in this period, the doctor can get an idea of your overall functioning and exercise capacity in a simple, non-invasive manner. A healthy individual should be able to walk nearly 2000 feet (or about 6 football fields) in 6 minutes. For people who have symptoms caused by PAH, the distance will be reduced. This test is also useful for monitoring the response to medical therapies. In addition to the distance covered, a person's heart rate, blood pressure, respiratory rate, oxygen saturation and sense of breathing discomfort (dyspnea rating) are also measured as part of the walk test.

Pulmonary function tests (PFTs) are used to measure overall lung function and are often used to help diagnose various lung diseases that can be associated with pulmonary hypertension. There are several components to PFTs, and most of them involve you breathing in and out through a tube into a machine that measures how fast you can expel the air in your lungs (spirometry), how much air you have in your lungs (lung volumes) and how well your lungs can exchange gases including oxygen and carbon dioxide (measured by a number called the diffusion limitation for carbon monoxide, or DLCO – also sometimes referred to as diffusing capacity).

Typically in PAH patients, pulmonary function tests will show a mild restrictive defect. This means that the lungs are slightly stiffer than normal and have more trouble expanding to their full volume during inhalation – their movement is "restricted." Additionally in PAH, the DLCO will be reduced, because as discussed earlier, in PAH gas exchange from the alveoli to the capillaries (and vice versa) is compromised (see discussion in Why is my oxygen level low at rest and with exercise?). Pulmonary function tests are also very useful for patients who have other lung diseases, such as emphysema. Emphysema and other smoking-related diseases cause an obstructive defect (difficulty blowing the air out of your lungs) rather than a restrictive defect.

Finally, your doctor may order blood tests. There are many different blood tests you may have, but two that you will see used frequently are the INR (international normalized ratio) and BNP (b-type or brain natriuretic peptide). The INR is used when you are on a blood thinner (anticoagulant) called warfarin (brand name Coumadin) to prevent blood clots in the pulmonary vessels. The INR is used to make sure you are taking the right dose of warfarin, and the dose is adjusted until the INR is in the goal range (typically 1.5-2.0). However, the INR is very sensitive to changes in many factors, including other medications and certain foods, so it needs to monitored frequently (about once a month) for your safety, even after you have been on a steady dose of warfarin for a while.

BNP is a protein that is released by the muscle tissue of the heart, particularly the ventricles. The amount that is released increases as the heart is stretched or strained, as is the case in PAH where increased resistance in the pulmonary arteries causes the right ventricle to work harder. The amount of strain can be monitored by checking the BNP. It is not yet known how helpful it is to follow the BNP in an individual patient , and this is an area that is under active investigation.