What is CardioPulmonary Exercise Testing (CPET)?
Cardiopulmonary exercise testing, often abbreviated as CPX, CPEX or CPET, is now the 'gold standard' objective tool for the evaluation of VO2 Max, Cardiopulmonary function and fitness. It is an entirely non-invasive and objective method of assessing the exercise response of the pulmonary, cardiovascular and skeletal muscle systems. These are not adequately measured individually, hence CPET evaluates the way in which your heart, lungs and circulation simultaneously respond to exercise.
Cardiopulmonary exercise testing adds important additional information to that provided by a standard exercise test. Due to the ability of a CPET to objectively assess breath by breath gas analysis (via a facemask), a multitude of objective exercise indicators can be collected that simply cannot be ascertained using a normal treadmill or alternative forms of exercise testing.
What information will be analysed?
· 12 lead ECG (Resting and exertion)
· Lung function: Spirometry and lung volume flow loops
· Oxygen Consumption during exercise · VO2 max
· Anaerobic Threshold (Lactate threshold)
· Metabolism during exercise (Fat vs. carbohydrate burning)
· Cardiac and respiratory function during exercise
Why Test Scientifically?
Having your fitness levels measured scientifically and accurately can provide a tangible definition of exactly how fit you are as well as a baseline for any future improvements to be measured against. By using your test results you will be able to exercise more effectively with a greater understanding of how to design your training in the future.
Heart rate response to exercise is multifactorial and very individual. Normally your heart rate will increase in response to exercise as well how strongly it beats. It does this to increase the oxygen and nutrient delivery to the muscles and also to remove the waste products of energy production.
Changes in fitness levels can affect a person’s heart rate response to exercise, making monitoring it during exercise testing vital. Heart rate is an excellent surrogate marker of exercise intensity when used correctly, especially when used with Heart rate zone training.
VO2 Max Testing
At rest the body utilises enough oxygen to enable it to produce enough necessary to cope with all basic functions, such as breathing, digestion etc.
During exercise the working muscles demand more oxygen because more energy is needed to do the work of exercise. As this exercise gets harder, more energy is required. The maximal amount of oxygen someone can use is a measure of how cardiovascular fit or gifted they are. This figure can be improved with training and does differ due to genetics, body size, age etc.
This point achieved during the test, indicates the exercise intensity above which you start to utilise less sustainable forms of energy production. Because of this less sustainable energy source fatigue starts to become a factor above this level of exercise. Through correct training you may be able to raise your anaerobic threshold and therefore enable you to work harder at higher levels of intensity before fatigue sets in.
Physiological Basis of CPEX (CPET)
Cardiopulmonary exercise testing is arguably now the 'gold standard' for evaluation of cardiopulmonary function. It supersedes ECG treadmill studies which are focused on detection of ischaemia. It is one of the best ways of evaluating fitness of athletes and CPEX is commonplace in Sports Institutes. CPEX is also used to evaluate patients for cardiac transplantation in many centres.
The following description of the physiological basis of CPEX is taken from P. Older and colleagues and provides a useful conceptual approach to the subject.
Exercise requires immediate breakdown of intracellular adenosine triphosphate (ATP) as a source of high energy phosphate. The source of this ATP is aerobic oxidation of mainly glycogen (via carbohydrate) and fatty acids; and in addition by anaerobic hydrolysis of phosphocreatine. If aerobic metabolism is unable to support the requirement of ATP, anaerobic metabolism of glucose via pyruvate and lactic acid will provide some ATP but in much smaller amounts. Aerobic metabolism supplies the majority of ATP up to the anaerobic threshold and after that there is an increasing need for anaerobic supplementation. When anaerobic production of ATP commences (at the anaerobic threshold), aerobic production does not cease; anaerobic metabolism merely supplements aerobic production of ATP as the work rate increases. Because different metabolic pathways have different signatures on gas exchange it is possible for a CPEX study to identify aerobic metabolism, anaerobic metabolism and indeed the intracellular response to exercise; it looks therefore at the 'total metabolic picture'.
This entire system is finally limited by, and must be supported by, substrate and oxygen availability which is a direct function of the cardiopulmonary system. The change from predominant aerobic to partial anaerobic metabolism is not only detectable by CPEX it is actually the basis for determination of the anaerobic threshold and therefore of cardiopulmonary function.
Cellular respiration is coupled to external respiration via the cardiovascular and pulmonary systems. This may be best understood by using the schematic devised by Professor Karlman Wasserman and his group, and described in detail in their book 'Principles of Exercise Testing and Interpretation". A simplified version is used here.
From this schematic one can see that any increase in QO2 will result in an increase in QCO2; the carbon dioxide will be transported to the lungs via the systemic circulation and the pulmonary circulation. At the same time the increase in oxygen requirement will be met by the same pathway. Similarly substrate will need to be transported. The limiting factors in this chain become the cardiac function (i.e. is cardiac output adequate?), the effectiveness of ventilation ( i.e. are Ve and V/Q matching adequate?), the state of the vascular system (i.e. is there widespread vascular disease?), the pulmonary vascular system (i.e. is there significant pulmonary artery hypertension?) and finally the actual intracellular metabolic pathways (i.e. is the oxygen and substrate being utilized?).