Cardiopulmonary Exercise Testing (CPET) is an important diagnostic in determining the cause of dyspnea on exertion and determining normality of cardiac and pulmonary responses to exercise.
Cardiopulmonary stress testing is destined for tremendous growth in the coming years, according to a report from Transparency Market Research (TMR). What was a $2.08 billion market in 2016 is expected to jump to $3.08 billion by the end of 2025. The Centers for Disease Control and Prevention (CDC) predicts that by that time half of the American population will have at least one risk factor for developing heart disease. So cardiologists and pulmonologists will drive this increase as they seek early diagnosis and intervention.
Cardiopulmonary exercise testing (CPET) is used for different patient types, from healthy, normal athletes to those with advanced chronic obstructive pulmonary disease (COPD) and heart conditions. For patients with known disease, CPET becomes a prognostication tool. However, when patients present with unexplained dyspnea, the test may be used to identity the reason for the breathing limitation and help determine a differential diagnosis, according to Darren Drumsta, MA, Gas Exchange Product Manager at MGC Diagnostics. “From a heart failure standpoint, this could be a baseline test that might lead to cardiac rehab, usually if a known cardiac problem exists,” he said.
The Process
During initial preparation for CPET the clinician obtains informed consent, checks the patient’s physical activity readiness and educates him. The actual testing involves several different devices that monitor respiration, heart rate, blood pressure and oxygen saturation and help to identify normal and abnormal responses as the patient exercises on a treadmill or cycle ergometer.
The patient wears a mask or mouthpiece during the testing period and a pulse oximeter probe either on the finger, ear or forehead. Blood pressure is measured in a couple of ways; “We like the automatic blood pressure system that integrates with our software, just as the pulse oximetry does. At a higher level, you can program the cuff to fire at specific intervals,” Drumsta said, noting though that “purists” prefer taking blood pressure manually. He added that coaching is another important component to maximize performance and make a definitive diagnosis.
Drumsta explained that all the devices—spirometer, pulse oximeter, blood pressure cuff, bike and/or treadmill—are integrated so data automatically transfers to the software platform and can be reviewed during the test and reported and interpreted post-test. “We make it easier to use and test, making the site/lab more efficient,” he said. The combination of devices “…drives a myriad of data points.”
Data are collected throughout the test, from resting to recovery. Before the patient leaves the lab, the patient’s health information is captured and sent to a secure software suite, according to Drumsta. Post processing results go into a general report, which may be sent to the patient’s electronic medical record (EMR), depending on the testing process and capabilities of the facility. “The physician interpreting the test can access the results at institutions that have the capability. For those facilities that don’t have the technology to do this, the reports can be printed or scanned and converted to a PDF. “[Automating the results] is not always feasible, but this is the direction things are going. Large institutions have this approach versus smaller community hospitals,” said Drumsta.
Guidelines, Competencies and Standards
Several professional organizations, including the American Heart Association (AHA)1, the American Thoracic Society (ATS) and the American College of Chest Physicians (ACCP) have issued guidelines2 that outline the indications for use, methodology, the conceptual and physiologic basis of cardiopulmonary exercise testing measurements, reference values, normal integrative exercise response, exercise limitations in cardiopulmonary patients, and interpretation.
The AHA also created competency requirements for stress testing, although individual test sites may require operators to have certain other credentials. “The standard operating procedure is based on the institution,” Drumsta said. Higher-level professional facilities might have a standard statement, while more flexibility might be allowed at the health system level.
Most guidelines suggest eight to twelve minutes of exertion as ideal, Drumsta reported. “Selecting the protocol is critical to determine the time of the test. That goes back to the tester and physician who might change protocols to meet the patient’s needs,” he added. Several factors will impact the ultimate length of the test, including exercise history and lifestyle habits.
Protocols
Bruce is the most widely used protocol for treadmill testing. Developed in 1963 by Robert A Bruce, MD, this noninvasive protocol works the patient to exhaustion, increasing speed and incline every three minutes. The length of time on the treadmill is used as the test score and helps in determining the VO2 max value.
Another protocol, the Balke, also measures VO2 max and begins with a ten-minute warmup. Thereafter, men maintain a constant speed of 3.3 mph at an incline of zero percent. After one minute, the incline is increased 2% and then 1% every minute thereafter. Women begin walking at a speed of 3 mph at zero percent incline and increase the incline 2% after one minute. Thereafter, the elevation is increased 2.5% every three minutes for women.
A third treadmill protocol is the Naughton, which places electrocardiography (ECG) sensors on the patient’s chest during the test. This test is less intense than Bruce and keeps the heart rate in a zone lower than the maximum as it progresses through several stages, each one slightly more intense than the previous one. The heart rate gradually increases until it reaches 80 to 90% of maximum. Given its lower intensity, the Naughton is typically used for diseased populations and those at higher risk of coronary disease. In spite of the difference in intensity, a study3 published in the European Heart Journal found that the Bruce and Naughton protocols were both equally effective in detecting ischemic abnormalities in patients six weeks after a heart attack.
Customized Protocol
The pulmonary function lab at the Cleveland Clinic uses CPET for several different diagnoses and conditions on the 240 patients it tests annually and adheres to a strict protocol, using a cycle ergometer, according to lab manager Jose Ramos, RT. “We exercise to exhaustion. The bike is a safe haven. Patients could fall off a treadmill,” he said. RTs administering the test ramp up the incline to a level that challenges the patient and try to find the “sweet spot” regarding elevation and resistance.
For patients with emphysema and chronic bronchitis, CPET assesses lung volume and evaluates the need for surgical intervention. CPET might detect blood clots in patients with pulmonary hypertension, which necessitates surgical removal.
“Patients who have had other tests that came back normal, but still have unexplained dyspnea need to know why,” Ramos said. “A physician might order CPET to uncover the reason.” Respiratory therapists also conduct CPET on patients with cancer, pulmonary hypertension or pectus excavatum to check functioning at their lab. Mainly, the test is used to determine if a condition is truly cardiac or pulmonary in nature, he added.
Ramos explained that CPET at the Cleveland Clinic is minimally invasive; RTs take an arterial blood gas (ABG) using “…a free hand stick at rest and at maximum exercise.” Additionally, the RTs use two pulse oximeters, one on the forehead and one on the finger. “We record both numbers and have to find the best spot to get the saturation. We’ve seen discrepancies. It doesn’t always match up,” he said. “We rely on the forehead probe more than the finger. The patient is holding the handlebars and might have white knuckles.”
Ramos said, “Some physicians are doing research in non-invasive cardiac output to identify more things without doing an invasive process. It’s necessary to what the future holds and [will assure] high quality care for the patient.”
Different Techniques
Some sites follow Cleveland Clinic’s lead and use a minimally invasive technique, while others engage in a more invasive process that requires right heart catheterization. In this case, a tube is inserted in the brachial or jugular artery, but not in the legs, depending on the mode of exercise. With invasive CPET, the operator can look at the patient’s hemodynamic responses, although noninvasive is viewed as a safer option. One of the more recent trends is to pair imaging with the traditional method, although this technique is most probably found at specialty institutions.
A 2017 study4 explored the use of CPET in combination with echocardiography or imaging, “…which provides basic information regarding cardiac and valve morphology and function.” The authors asserted that CPET “…has a definitive place in the armamentarium of the practicing clinician for the evaluation of cardiopulmonary disorders, primarily HF.” They added that invasive CPET and CPET imaging allows for better insight into pulmonary hemodynamics and offers enhanced clinical cardiac information. RT
Phyllis Hanlon is a contributing writer to RT. For more information, contact [email protected].
References
- Fletcher GF, Ades PA, Kligfield P, Arena R, Balady GJ, Bittner VA, Coke LA, Fleg JL, Forman DE, Gerber TC, Gulati M, Madan K, Rhodes J, Thompson PD, Williams MA; on behalf of the American Heart Association Exercise, Cardiac Rehabilitation, and Prevention Committee of the Council on Clinical Cardiology, Council on Nutrition, Physical Activity and Metabolism, Council on Cardiovascular and Stroke Nursing, and Council on Epidemiology and Prevention. “Exercise standards for testing and training: a scientific statement from the American Heart Association.” Circulation. 2013.128:873–934.
- “ATS/ACCP Statement on cardiopulmonary exercise testing.” American Journal of Respiratory and Critical Care Medicine. 2003 Jan 15;167(2):211-77.
- Handler CE, Sowton E. “A comparison of the Naughton and modified Bruce treadmill exercise protocols in their ability to detect ischaemic abnormalities six weeks after myocardial infarction.” European Heart Journal. 1984. Sep;5(9):752-5.
- Guazzi M, Bandera F, Ozemek C, et al. “Cardiopulmonary Exercise Testing: What Is Its Value?” Journal of the American College of Cardiology. 2017. 70(13):1618-1636.
