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Cardiopulmonary Exercise Test, what is that?

By StadiaSportsMedicine | Published January 29, 2015
Who might benefit from Cardiopulmonary Exercise Testing?
Though this list is not exhaustive, CPET can be useful in such instances as

  • Evaluation of patients who have experienced an unexplained drop-off in their exercise capacity.
  • Screening patients with certain risk factors prior to the initiation of a regular exercise program.
  • Risk-stratification of patients — The fitness level, or “VO2 MAX” is a well-established predictor of cardiovascular mortality risk.
  • Establishment of optimal training zones in endurance athletes to minimize the risk of overtraining syndrome and optimize training gains.
  • Evaluation of work capacity in individuals being considered for hire or in existing employees who have experienced a drop-off in work capacity.  This is well-suited towards employees in service occupations such as firefighting, law enforcement or the military.
  • Exercise challenge testing for patients with known or suspected asthma
  • Periodic monitoring of individuals with known progressive disease states (such as Cystic Fibrosis) to monitor changes in peak exercise capacity over time.
What happens during a Cardiopulmonary Exercise Test?
When you come in for your test, we’ll ask you some general questions about your overall state of health as well as any symptoms you might currently be experiencing.  Your blood pressure, resting heart rate and a resting electrocardiogram will be taken.  Following this, you’ll be fitted with a mask that contains an analyzer that measures airflow into and out of your lungs, as well as the amount of oxygen inhaled and carbon dioxide exhaled.  Baseline measurements of lung function will be obtained by having you breath in and out several times, and a resting metabolic rate will be recorded as well.  Following this, you will be exercised on a treadmill, with ongoing measurements of your heart response, respiratory gas exchange, pulmonary function and blood pressure.  The test is progressive in the sense that it becomes more difficult over time, and we will continue to monitor you either until you tell us to stop or there is a reason to stop the test that is noted from the testing data.  After the test is over, we will continue to monitor your blood pressure, heart rate recovery, electrocardiogram and any symptoms that may be present.  Once the test is complete, we’ll arrange a follow-up visit to review the test results and what they mean to you.
    What is being monitored during the test?
    The utility of CPET comes from the ability to accurately measure both oxygen consumption and carbon dioxide exhalation.  While oxygen is used to power cellular metabolism during exercise, end-expiratory carbon dioxide levels are an indirect measure of the by-products of cellular energy utilization.  If exercise requirements continue to increase beyond the ability of the heart, lungs or vascular system to provide adequate oxygen to the mitochondrial engines of the muscle cells, these cells will shift to non-oxygen utilizing (anaerobic) energy sources so that exercise can continue.  We call this the anaerobic threshold.

    The by-product of anaerobic metabolism is lactic acid, which quickly accumulates in the muscle and begins to cause muscle fatigue and a sense of growing exhaustion.  To combat this, the body buffers out the lactic acid by converting it to carbon dioxide, which is eliminated in the lungs.  The increase in carbon dioxide output is measured during CPET, and is used, with other data, to determine level of fitness, the extent and source of exercise limitations, or the target exercise training zone for the tested individual.

    Since airflow measurements during exercise are also being recorded, it is possible to tell if a person’s exercise limitations are coming from inadequate lung function (versus cardiac limitations or simple deconditioning).

    In certain instances, 12-lead electrocardiography is also recorded, which allows us to more closely monitor the heart’s response to exercise and to exercise recovery.  In conjunction with the gas exchange data referenced to above, a more detailed overall picture of an individual’s exercise capacity can be obtained.

     

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