Cardiopulmonary exercise testing in evaluation for pulmonary hypertension
The cardiopulmonary exercise test otherwise known as a CPET or CPX is sometimes used during the screening process for pulmonary hypertension. This test helps determine if the decreased tolerance to exercise or shortness of breath with activity a patient is experiencing is caused by a cardiac disease, versus a pulmonary disease. CPET is usually used when the shortness of breath or dyspnea is not easily explained. Cardiopulmonary exercise testing aims to measure the rate that a patient’s body takes in oxygen and produces carbon dioxide while monitoring ventilatory parameters, heart rhythm, blood pressure, and oxygen saturation during maximal exercise.
How is a cardiopulmonary exercise test performed?
The cardiopulmonary exercise test is usually performed in a hospital setting as an outpatient procedure. There is minimal preparation required by the patient for the test. Each center will have their own guidelines for prep and these should be discussed with the patient. Common instructions include eating only a light meal at least two hours prior to the procedure, avoiding carbonated or caffeinated drinks as well as alcohol, and avoiding exercise the day of the test. Well fitting comfortable workout clothes and sneakers should be worn for the test.
The test is performed with the patient exercising on a stationary bicycle. Sometimes a small catheter is placed in an artery in the wrist. This arterial line is then used to draw blood samples during the test. The patient will also be breathing through a tube much like a pulmonary function test. A blood pressure cuff, pulse oximeter, and EKG leads will also be placed on the patient during the test. A physician will be present during part or all of the test.
The test begins with the patient riding on the bicycle at a comfortable rate and quickly ramping up the difficulty of the exercise. The time of exercise is patient specific but usually lasts less than 12 minutes. The test will be physically exhausting and the patient will be asked to give it their best effort. The information collected will reveal if little or no effort was put forth by the patient. Raw data such as blood gasses, blood pressure, and oxygen consumption are gathered during the test. The report will be generated and be sent to a physician, usually a pulmonologist, for interpretation.
What do the results of the CPET reveal?
The patient should set a follow up appointment for a couple of weeks post CPET to go over the results. Results are not immediately available following the test as several pieces of information have to be looked at by the physician and melded into a complete report.
The CPET is a valuable test that is useful in answering the following questions:
•Is the patient’s exercise capacity normal?
•Is the patient’s cardiovascular response to exercise normal?
•Is the patient’s ventilatory response to exercise normal?
•Is gas exchange normal?
The results of the cardiopulmonary exercise test are more useful in ruling out other causes of shortness of breath than diagnosing pulmonary arterial hypertension. If the test is not able to shed light on the cause of the exercise intolerance the physician may order additional test such as a right heart catheterization or an echocardiogram to further evaluate the patient.