The other day, one of my partners requested me to supervise a cardiopulmonary exercise test (CPET) that he ordered on a patient that he saw in our clinic. Since I would be in the hospital all day that particular day, and the exercise test would be done in a lab in the hospital anyway, so I obliged.
CPET is usually a test that we request if the cause of shortness of breath remains unclear even after initial evaluation. Most of the time when we request a CPET, we have already done lung imaging (like a chest x-ray), a pulmonary function test, and basic heart evaluation to rule out gross cardiac problems. Definitely we don’t want a patient having a heart attack and keeling over while we are performing the test.
During CPET, a patients walks/runs on a treadmill or pedals on a stationary bike, while having all these body monitors to measure the heart rate, blood pressure, and oxygen saturation level. Then they also wear a mask, like the super villain Bane in the Batman movie, that is attached to a breath analyzer where we measure not alcohol content, but the volume and gas content (oxygen and carbon dioxide) of the air they inhale and exhale. At the peak of the exercise, we also draw a blood sample to measure the level of oxygen, carbon dioxide, and lactic acid. We may not be experimenting on Captain America, but it is an intense test regardless.
cardiopulmonary exercise test (image from BMJ journal)
By the way, lactic acid is a byproduct of “overstressed” metabolism. It is produced when there’s not enough oxygen supply to the contracting muscles, so the muscle switched from aerobic to anaerobic metabolism. The build up of lactic acid in the muscles is one of the cause of having pain in your muscles few hours or few days after a viogorous exercise. I hope I am not bringing back bad memories from your high school physiology teacher.
The exercise test is usually ended in several possible ways: a patient cannot exercise anymore due to exhaustion, or we have achieved the maximum target heart rate (which is: 220 minus patient’s age), or we have reached the end of the designed exercise protocol, or the patient developed an alarming symptom, like severe chest pain.
The information we gather in this test help us delineate what is the limiting factor causing the shortness of breath, whether it is a heart problem, a lung problem, a muscle problem, or plain deconditioning. Sometimes elite athletes undergo this test to gain data on how they can improve their performance. I’m sure Gatorade lab performs lots of this.
Perhaps the most common diagnosis we reach considering the group of patients we deal with, is deconditioning, or in simple term, being out of shape. Definitely this is a scientific way, albeit expensive, to say to a patient that he is too lazy or is too fat.
The duration of the CPET is mostly less than 15 minutes, and with our patient population, it rarely last more than 10 minutes. Not a big deal for me to supervise the test, as it is short and quick.
I was busy that day so I was not able to look beforehand at the chart of the patient whose CPET I would supervise. What I just know was the time I needed to show up in the lab, the name of the patient, and his age.
I knew that the patient was in his early 50’s, a couple of years older than me. Even before meeting the patient, I already have a diagnosis in mind, as I was expecting a middle-aged man who is overweight, maybe a couch potato, and perhaps cannot accept the fact that he is way out of shape, and instead blames something is wrong with him, thus we are doing this CPET. Since I have a few half-marathons under my belt, I thought I could show him how to “exercise.”
When I came to the lab, I met our patient who was already sitting on the stationary bike. He looked fairly trim, and to be honest, he looks younger than his age. I introduced myself and explained the test that we will administer.
To get some idea of his condition, I asked him about his symptoms. He told me that he felt this “disproportionate” shortness of breath when he is running.
Sensing that he is a “runner” like me, I asked if the shortness of breath happens early, or during the latter part of his run. He answered that he experienced this shortness of breath relatively “early” in his run. I asked him then to be more specific, like how many minutes after he started his run.
Then he said, “I have this ‘unusual’ shortness of breath after running 20 to 25 miles.”
What?! Who considers 25 miles as early? Most people are not short of breath, but may not be even breathing at that point!
That’s when I learned that he was an ultra-marathoner, and runs 50 to 100 miles or more when he competes. He said that after 25 miles of running, he usually catches his “second wind” and feels good the rest of the way through.
All my preconceived notion flew out the window. Life is never short of surprises. Another lesson learned. Never assume.
I just told the lab staff to commence the exercise, and brace for a long, long test.