Heart Health
Unmasking the varied causes of breathlessness and fatigue
Cardiopulmonary exercise testing can help reveal unusual reasons for these common symptoms — and also shed light on long COVID.
One of the vexing things about certain common health complaints is the range of possible underlying causes. For example, feeling short of breath is perfectly normal after a burst of vigorous exercise. But for some people, even mild exertion can trigger a sensation of breathlessness, or what doctors call dyspnea. It's often accompanied by symptoms such as fatigue and lightheadedness.
Most of the time, heart or lung issues are to blame. In many cases, routine tests — including a chest x-ray, echocardiogram (heart ultrasound), lung function tests, and blood tests — can uncover the underlying reason for a person's breathlessness.
"But sometimes, all the results are perfectly normal, or the findings don't fully explain the nature or severity of the person's symptoms," says Dr. David Systrom, who directs the Dyspnea Clinic at Harvard-affiliated Brigham and Women's Hospital. That's where cardiopulmonary exercise testing (CPET) can play a role (see "What is cardiopulmonary exercise testing?").
What is cardiopulmonary exercise testing?A standard exercise stress test (also called a cardiac stress test) monitors your heart rate, heart rhythm, and blood pressure while you walk on a treadmill or pedal a stationary bike. A cardiopulmonary exercise test (CPET) is more involved, as it collects additional information about both your heart and lung function to assess how your body responds to exercise. During a CPET, you also wear a small sensor called a pulse oximeter on your finger that measures your blood oxygen level. You're also fitted with a mouthpiece or mask attached to a device that monitors your breathing to see how efficiently you take in oxygen and exhale carbon dioxide. In an advanced version of the test, doctors use thin, flexible tubes (catheters) to insert two temporary pressure-monitoring devices, one into a neck vein to access the pulmonary artery (which brings blood from the heart to the lungs to pick up oxygen and off-load carbon dioxide) and another in the radial artery in the arm. Together, these devices show how well blood and oxygen is delivered to and used by your muscles as you exercise. The exercise portion includes a short warm-up followed by just five to eight minutes pedaling on an exercise bike with gradual increases in intensity. Although the test is invasive, topical painkillers keep the discomfort from the catheters to a minimum. "In fact, more than 90% of people who've undergone invasive CPET testing say that the test is not as bad as having a cavity drilled and repaired by a dentist," says pulmonologist Dr. David Systrom, assistant professor of medicine at Harvard Medical School. |
Unusual causes
At one time, about half of the people referred to the Dyspnea Clinic who underwent CPET were found to have pulmonary hypertension (an uncommon condition in which the arteries to the lungs become thick and stiff) or heart failure with preserved ejection fraction (a form of heart failure resulting from stiffness in the heart's lower left chamber). "But about five years ago, we also started seeing more patients with chronic fatigue syndrome," says Dr. Systrom. Officially known as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), this complex disease involves abnormalities in many organ systems, most notably the nervous and vascular systems.
The COVID connection
Many people with ME/CFS have unusual circulation problems that happen because the peripheral nervous system fails to signal the large veins in the legs, pelvis, and abdomen to constrict and deliver blood back up to the heart. This leads to what doctors call pre-load insufficiency, which means the heart's upper right chamber (atrium) doesn't fill up and reach a normal pressure before each beat. This problem is not only ubiquitous in people with ME/CFS but also extremely common in people with a condition known as long COVID, says Dr. Systrom.
Most people who get COVID-19 recover within weeks or a few months. But some experience lingering fatigue, lightheadedness, palpitations, brain fog, and breathlessness, which is often described as long COVID. Experts now refer to this long-lasting illness as PASC, which stands for post-acute sequelae SARS-CoV-2 infection (SARS CoV-2 is the virus that causes COVID-19). PASC, which is most common in young women, typically affects those with only mild infections.
Infectious disease expert and White House medical adviser Dr. Anthony Fauci has speculated that PASC is the same as or very similar to ME/CSF, which can be triggered by infections, including mononucleosis and Lyme disease. Dr. Systrom and colleagues (along with other research teams across the country) are using CPET to better understand PASC, in hopes of paving the way for effective treatments.
Image: © Tashi-Delek/Getty Images
About the Author
Julie Corliss, Executive Editor, Harvard Heart Letter
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