Common tests for patients with pulmonary hypertension

What is Pulmonary hypertension?

The heart has 2 sides. The right side of the heart gets blood from the body and it sends this blood to the lungs to be 'cleaned'. The lungs give oxygen to this blood and get rid of toxic gases such as carbon di-oxide (abbreviated as CO2). This 'clean' blood now makes its way to the left side of the heart which then gets pumped to the rest of the body. Then the blood makes its way back to the right side of the heart, and so on and so forth. This is a continuous cycle that happens minute after minute throughout our life.

Most people have heard the term "hypertension" which is increased pressure. But this typically refers to increased pressure that the left side of the heart is exposed to, and is measured usually with a cuff that is wrapped around a person's arm. This is very different from, and is usually not associated with, "Pulmonary Hypertension".

Pulmonary hypertension reflects increased pressures in the blood vessels in the lungs, which makes it difficult for the right side of the heart to send blood to the lungs to be 'cleaned'. This is not easily directly measured (that is, there is not "blood pressure cuff" for the lungs) and requires both non-invasive clues as well as invasive means to accurately measure.

Pulmonary hypertension has many possible causes that are too numerous to be listed here. Depending on the specific cause of someone's pulmonary hypertension, the treatment may be different. That's why a patient suspected of having pulmonary hypertension usually goes through many tests to make sure we identify the specific cause of her/his pulmonary hypertension.

Pulmonary arterial hypertension, or PAH, is a specific kind of pulmonary hypertension. It is caused by destruction of small blood vessels in the lungs. PAH is a kind of pulmonary hypertension that is not caused by lung disease, heart disease that is primarily affecting the left side of the heart, or large blood clots in the lungs. For the sake of simplicity, we will use the term pulmonary hypertension broadly in the rest of this section, although most of the time we will be referring to pulmonary arterial hypertension.

Common tests for patients with pulmonary hypertension may include:

Blood tests

Pulmonary hypertension could be caused or worsened by many medical conditions. So a long list of blood tests are required during the initial evaluation of patients suspected of having pulmonary hypertension, and subsequently and on a regular basis after the diagnosis is made. Listed here are some of the more common tests:

• CBC (Complete Blood Count) is a simple count of the different kinds of blood cells. This test is important to check, for example, for anemia (low red blood cell counts) which is a possible cause of trouble breathing and fatigue. Some of the pulmonary hypertension medications may cause abnormalities in the cell counts as well.
• BMP (Basic Metabolic Panel) is a list of blood tests that measure the function of the kidney and a variety of electrolytes including sodium and potassium for example.
• LFTs (Liver Function Tests) are a list of blood tests that reflect the function of the liver. They include among other tests: ALT (Alanine aminotransferase), AST (Aspartate aminotransferase), alkaline phosphatase, bilirubin, albumin, and other proteins.
• CMP (Comprehensive Metabolic Panel) is the blood test that includes both the BMP (basic metabolic panel) and the LFTs (liver function tests).
• TSH (Thyroid Stimulating Hormone) is a measure of the thyroid function. If the thyroid gland is not functioning well, then this may cause or worsen pulmonary hypertension. Abnormalities in the thyroid gland function could also cause trouble breathing and fatigue irrespective of pulmonary hypertension.
• BNP (B-type Natriuretic Peptide, or brain-type natriuretic peptide) or pro-BNP (which is a related protein to BNP) are small proteins that are found in our blood and are released from the heart. They get released from the heart when the heart is exposed to increased strain, such as in pulmonary hypertension.

Chest X-Ray

A Chest X-Ray, sometimes referred to as CXR, is usually one of the first tests done on patients who have some trouble with their breathing. The Chest X-ray takes a picture or two of the chest, which would show any gross abnormalities in the lungs.

Sometimes, a Chest X-ray is not sensitive enough to find subtle or small abnormalities in the chest, so a CT (computed tomography scan, sometimes referred to as "CAT scan" or "CT scan") is needed. A CT scan is a much more detailed and refined X-Ray but with higher exposure to radiation. If the CT scan is not done too often, the extent of radiation exposure from a CT scan is not dangerous.

Pulmonary function tests

Pulmonary function tests, also called PFTs, are a set of non-invasive tests that measure different aspects of a patient's breathing. This is a very important test for patients who have trouble with their breathing. The information from this test may show different causes of someone's trouble breathing, including for example asthma, COPD, emphysema, or "pulmonary fibrosis" / lung scarring. Pulmonary hypertension has a specific abnormal pattern on PFTs. PFTs include multiple different tests:

• Spirometry measures how fast a patient can breathe out. Patients with asthma or COPD for example can't breathe out too fast because of limitations in their airways. Patients with pulmonary hypertension should not have a problem with their airways, so their spirometry test is usually normal or close to normal.
• Lung volumes measure the lung ability in total to breathe in and out, and may reflect how "restricted" a patient's breathing is.
• Diffusion capacity (also called DLCO) reflects the extent of the damage to the blood vessels in the lungs. It may also reflect any scarring that is going on in the lungs. It is a measure of how well oxygen can get across the lung to the blood vessels.

Sleep study and/or overnight oximetry study

One of the causes of pulmonary hypertension is poor quality breathing during sleep. If someone's oxygen levels are low during sleep, this condition puts a lot of strain on the lungs and heart and may lead to pulmonary hypertension. Since a patient would be asleep when these abnormalities of breathing are occurring, she/he may not feel that their breathing is limited during sleep and may not be aware of this.

• A sleep study is a study done in a sleep center (which is typically not a hospital). The patients come to the sleep center in the evening, get hooked up to different monitors including an oxygen monitor and are asked to sleep (most patients' first reaction is that they won't be able to sleep in a "strange environment" other than their own bed, & hooked up to different monitors. But most patients end up sleeping enough to give us the data needed). When they wake up in the morning, they go back home. If a patient indeed has trouble with her/his breathing when asleep, they may need to be on oxygen or use certain masks, such as a CPAP (continuous positive airway pressure), at night to help with their breathing and to improve their pulmonary hypertension.
• An overnight oximetry study is a test in which a recording "pulse oximeter monitor" (a small non-invasive machine with a probe that is taped to the finger) continuously measures a patient's oxygen level and heart rate overnight. This test could be done in someone's home. This is more convenient than the sleep study but does not give us all the information needed.

Electrocardiogram, or EKG or ECG

An EKG is a non-invasive test that measures the electricity of the heart. It involves placing what is called 'leads' on the chest, arms, and legs. The patient does not feel any electricity or discomfort during this test. The EKG provides information about how fast and regular the heart is beating and gives us a general sense about the global function of the different parts of the heart, which in turn need to be confirmed by an echocardiogram.

Echocardiogram

The echocardiogram (sometimes referred to as the "echo") is a non-invasive ultrasound test of the heart that does not involve any radiation. It is very safe to have echocardiograms. The ultrasound technician would be using gel (which may sometimes feel cold) on an ultrasound probe that is connected to the ultrasound machine. That machine has a screen similar to a desktop computer screen. Multiple images are recorded during this test.

The echo test is extremely important because it gives us a general idea about the size and function and interaction of the different heart chambers. It can also assess the function of the different heart valves. An echocardiogram is done on every patient who is suspected to have pulmonary hypertension, and then on a regular basis after the diagnosis is made.

Six-minute walk test

A six-minute walk (sometimes referred to as 6MW) test is as its name suggests: a walk for exactly six minutes. During these 6 minutes, the patient's heart rate and oxygen level (measured by a non-invasive monitor typically placed on one's finger, called "pulse oximeter") are recorded at the beginning of the 6MW test and then again at the end of the 6 minutes. The distance walked is also recorded. This is an extremely important test to check the functional ability of patients with pulmonary hypertension, and to assess the need for oxygen therapy. This non-invasive test is typically done on every single clinic visit for patients with pulmonary hypertension.

Heart catheterization

Heart catheterization is the gold standard for confirming the diagnosis of pulmonary hypertension and quantifying its severity. It is an invasive procedure whereby a physician introduces a catheter (which a narrow plastic tube) into a vein under full sterile measures. This catheter is then advanced towards the heart. There are 2 major kinds of heart catheterizations, a "left heart catheterization" and a "right heart catheterization":

• Left heart catheterizations are often done looking for "blockages" in the heart vessels. Patients who are at risk of heart attacks would typically get a left heart catheterization. Heart stents for example are done during left heart catheterizations. Contrast is a "colored" material or 'tracer' that shows up on X-rays and is commonly used for left heart catheterization. Right heart catheterizations do not typically require injection of contrast.
  
• Right heart catheterizations are an invasive procedure typically done in the outpatient setting, and it is the only way to diagnose pulmonary arterial hypertension at this time. Every patient with suspected pulmonary hypertension must have a right heart catheterization before deciding on pulmonary hypertension therapy.

Most patients with pulmonary hypertension do not really need a left heart catheterization. Patients with suspected pulmonary hypertension need what's called a right heart catheterization which is the kind of heart catheterization during which the catheter is advanced through the right side of the heart to measure pressures on the right side of the heart and in a large blood vessel called the "Pulmonary Artery". The pulmonary artery is the vessel that connects the right side of the heart to the lungs.

Ventilation/Perfusion scan

The Ventilation/Perfusion scan (also called a V/Q scan) looks for blood clots in the lungs. A V/Q scan is 2 tests combined into one. The 'V' stands for ventilation part of the test, and the 'Q' stands for the perfusion part of the test. This test involves exposure to a very small amount of radiation that is believed to be in the safe range as long as this test is not done too often. Typically this test is done once during the evaluation of a patient with pulmonary hypertension, and only rarely needs to be repeated. Almost all patients with pulmonary hypertension should have a V/Q scan test done to make sure that their pulmonary hypertension is not caused by blood clots. The treatment of pulmonary hypertension that is caused by chronic blood clots in the lungs is different from pulmonary hypertension caused by other reasons. A CT scan is not adequate to exclude this cause of pulmonary hypertension.

• During the ventilation part of the test (the 'V' part), a patient is asked to breath a safe gas that has in it a "tracer" that shows up on Xray. This test shows which parts of the lung are getting air into them.
• The perfusion part of the test (the 'Q' part) is very similar but the tracer is given through an intravenous catheter (an "IV"), and it also shows up on an X-ray to show where the blood is going to in the lungs.
• Blood clots would be suspected if certain areas of the lungs are getting air (as shown on the ventilation part of the test) but that same lung area is not getting blood (as shown on the perfusion part of the test).

For inquiries about the PVD program at Yale, please contact Dr. Inderjit Singh at inderjit.singh@yale.edu