Southeast Texas Medical Associates, LLP James L. Holly, M.D. Southeast Texas Medical Associates, LLP


About SETMA - Special Services - Cardiopulmonary Exercise Testing (CPET)
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Special Services

Do you have shortness of breath? Is it caused by:
  • your heart,
  • your lungs or
  • being "out of shape"?
For the first time, that distinction can be made accurately and a treatment plan devised without painful, invasive and potentially dangerous testing. SETMA's CPET evaluation program is overseen by board certified pulmonologist (Lung Specialists) and critical care specialists.

Science and Clinical Medicine

Perhaps, in no other area of medicine is the knowledge of the basic sciences of biochemistry and physiology more intimately related to clinical medicine than with the CPET. Oxygen is required for exercise because ultimately oxygen is required to produce the energy necessary to move muscles and bone. That energy is "packaged" in units called ATPs (adenosine triphosphate, high energy phosphate bonds), which provide the power for muscles to do their work. Limitations on work in the body, as evidenced by limitations on walking, running, jogging, lifting, etc., are dictated by oxygen utilization (symbolized as "QO2", with a dot over the Q)

Oxygen utilization is determined by:

Maximal cardiac output - the amount of blood your heart pumps with each beat multiplied by the number of times it beats in a minute.

Arterial oxygen content - how much oxygen there is in the blood in your arteries.

Distribution of cardiac output to the exercising muscle - how effectively blood is "sent to" the muscles by the arteries to and in your muscles.

Ability of the muscle to extract oxygen from the blood - how much of the oxygen delivered to the muscle can be accepted by the muscles.

CPET Definitions

The three most important data points in the CPET are "VO2max" or "peak VO2" if the maximum is not achieved, the "anaerobic threshold" and the "breathing reserve."

VO2max (oxygen uptake) -- This is the volume of oxygen extracted from inspired air in a given period of time expressed in milliliters per minute or liters per minute. This can differ from oxygen consumption. Oxygen consumption is the amount of oxygen utilized by the body's metabolic processes in a given time and is expressed in units of liters per minute. In the steady state, oxygen uptake and oxygen consumption are equal. Traditionally, the VO2max is the highest attainable oxygen uptake for a given subject. If the maximum is not achieved, then the highest level is termed the peak VO2.

"O2 consumption" (designated as "QO2") is the amount of oxygen utilized by the body's metabolic processes in a given time and is expressed in units of liters per minute. As the "VO2" (oxygen uptake) increases with increasing external work, some of the determinants of oxygen uptake -- stroke volume, heart rate or tissue extraction -- may begin to level off. The main determinants of VO2max or peak VO2 are genetic factors and the quantity of exercising muscle. These values are also determined by age, sex, body size, obesity, and training.

Anaerobic Threshold is considered as an estimator of the onset of metabolic acidosis caused predominantly by the increased rate of rise in arterial lactate during exercise. The anaerobic threshold is referenced to the "VO2" (oxygen uptake) and is expressed as a percentage of the "VO2max" predicted value. Ultimately, the limitation on the work load of a muscle is determined by oxygen uptake and the anaerobic threshold. As both the "VO2" and AT go up, the person is able to go farther, faster and longer.

Breathing Reserve is the amount of breathing capacity expressed as a percent of the Maximum Voluntary Ventilation (MVV) which remains when a person stops their CPET evaluation due to fatigue, dypsnea or pain. The MVV is conventionally measured at rest from maximal volitional effort for short periods of time, e.g., twelve seconds, and expressed in units of liters per minute. If the breathing reserve is normal, then any abnormality of the CPET is probably related to the heart and/or muscles as opposed to the lungs.

Assessment

If the "VO2max" is 85% or above of predicted; if the anaerobic threshold is 40-60% of the "VO2max" and if the breathing reserve is 10-40% of the MVV, then the patient for all intents and purposes is normal. If one of these is abnormal, the CPET can lead to the making of an accurate and specific diagnoses ranging from COPD to ischemic heart disease to Congestive Heart Failure, to primary pulmonary hypertension, to deconditioning due, to a sedentary life style. There are unique patterns which can tell you if the patient has a right to left cardiac shunt due to a patent foramen ovale or a number of other cardiac, pulmonary, and muscle diseases.

Getting a CPET

Currently, SETMA is the only clinic in Southeast Texas which performs CPET. This gives us the ability to provide our patients with superior care and diagnostic capabilities. It also provides us the opportunity to encourage other clinicians to begin performing this very excellent test.

If you are a patient of SETMA and have shortness of breath or other cardiovascular symptoms, ask your healthcare provider to order a CPET. If you want to know what your aerobic power or critical power is (see The Examiner, April 8, 2004) so that you can be given an effective exercise prescription, ask your health care provider for a referral for a CPET. If your insurance company will not pay for the test either because you are not a patient of SETMA, or because you are not ill, the cost of the test is not great and the information is incredibly valuable to you. It will be worth paying for the test yourself in order to benefit from the knowledge.