Cardiopulmonary Exercise Testing (CPET) is a diagnostic test which looks at the heart and lungs of an individual during exercise. The human body is designed with vast reserves, and many illnesses or problems cannot be detected at the rest state. By putting the body under stress during exercise, we can recognise some of these conditions.
The CPET test is one of the most powerful non-invasive diagnostic tests available in modern medicine. CPET has been utilised for many years within respiratory medicine as a differential diagnosis for shortness of breath, allowing the physician to determine if it is of Cardiac or respiratory cause. Recently the importance of the test as a Cardiac screening tool has become more prevalent and is used in Heart Failure patients as well as diagnosis of coronary heart disease (CHD).
The biggest growth in CPET testing has been seen in the Peri-operative sector where diagnostic CPET is used to assess the fitness level of prospective surgical patients, in an effort to better manage their post-operative care and thus improve surgical outcomes.
The test is known by various other names, including the Exercise Test and the Stress Test. However, they are, in essence, the same thing, measuring four main components. Including Heart Rate, which is done via a full 12 lead ECG, Oxygen Uptake, Carbon Dioxide output and Breathing rate, usually measured using a combined gas and flow analyser. Finally, the body will require some form of an exercise device. This may be any device, but in a hospital situation, it is usually a cycle ergometer, or possibly a treadmill.
Who might need a CPET test?
For many years, Cardiopulmonary Exercise Testing (CPET) has been used in two main areas. In hospitals it is predominantly used as a differential diagnosis tool, enabling the physician to determine the underlying cause of shortness of breath. Shortness of breath or Dyspnea can have many causes, some being respiratory such as COPD or Lung Cancer whilst other causes may be Cardiac such as Congestive Heart Failure, it is also possible for shortness of breath to be caused by a circulatory problem.
CPET also found favour in the sports and fitness arena, in particular as a tool to determine fitness by assessing the volume of Oxygen Output of a person under exercise (VO2).
More recently, obtaining a diagnosis from a body under exercise has been adopted by more and more specialists within the hospital environment. In areas such as cardiology, the CPET test has been shown to be a more useful diagnostic tool than the standard ECG stress test.
The use of CPET in the perioperative setting utilises the measurement to assess an individual’s fitness prior to surgery. This assessment is better allowing the surgical and anaesthetics teams to determine the person’s post-operative level of care. Dependant on the results of the test, an individual may not need to be referred directly to an ICU bed, but instead downgraded to an HDU bed or even directly back to the ward.
High-quality evidence shows that the fitter a person is prior to surgery, the shorter their stay, and the fewer complications are incurred throughout and postsurgery.
What does CPET involve?
Modern Cardiopulmonary Exercise Testing (CPET) is performed on a cycle ergometer, it is usually designed around a work protocol that ramps a subject to their maximum exercise tolerance, and the protocol will increase the effort required to pedal at a continuous rate, at a 5, 10, 15 watts per minute increase, or more for fitter individuals. The optimum workload ramp is between 8 and 12 minutes, so most protocols are designed to reach an individual’s max workload in 10 minutes.
The maximum workload for an individual can be calculated from their age, height and weight, but there’s also need to consider their current level of physical activity to determine their level of fitness. Creating a ramp that is too short may give too little data for interpretation, and a ramp that is too long can alter the result. A test should start with a 3-minute rest phase, followed by a 3-minute freewheel phase, and finally finish with 5 minutes of recovery, to ensure heart rate and breathing values normalise to the rest state.
Data for the test is recorded through a number of sensors. Usually, respiratory data is collected through a flow sensor connected to a facemask. It is also possible to use a mouthpiece, although this can be a little messier with saliva build-up at the end of the test. As mentioned before, Heart Rate is usually recorded via a 12 lead ECG, requiring 12 ECG electrodes placed around the subject’s chest. Other measurements that may be taken include Blood pressure, via an arm cuff and Pulse Oximetry via an ear sensor.
A good education for the subject is vital before a test, as patients can often misunderstand the results, thinking that a poor test proves that surgery is required. This is quite the opposite; the better the test results from a CPET test, the more likely the team will be happy to move a patient forward to surgery. This is because there is much less risk associated with carrying out surgery on fitter individuals.
Are there any risks?
Risks from Cardiopulmonary Exercise Testing (CPET) is minimal. The level of risk is comparable to carrying out mild to moderate exercise. However, the CPET test is performed in a controlled and managed environment, with trained staff on hand in the event of any problems. Less than one in a thousand patients experience some adverse reaction similar to that of a cardiology exercise test. During a CPET test, additional observations can be made including breathing patterns, Blood Pressure and Pulse Oximetry, alongside the full 12 lead ECG. If a patient exhibits any adverse symptoms, the test will be stopped immediately, and in the event of a problem, the Cycle Ergometer offers the safest option for the patient.
What information will be analysed?
All of the test data will be analysed by the clinical team to build a complete picture of the subjects overall health and fitness level. The analysis does not focus solely on the maximum level of exercise, although this is considered. It is also essential for the team to calculate the Anaerobic or Lactate Threshold, sometimes called the AT, at the point at which aerobic energy production is supplemented by anaerobic mechanisms, causing a sustained increase in lactate and metabolic acidosis. The AT is an excellent determinant of an individual’s fitness level, which can be improved with training.
It could be the case that someone with poor results is required to complete a safe exercise regime before surgery to reduce the risk and shorten the recovery time. Although more research is needed, many teams have been led to look at the advantages of ‘Prehabilitation’ or training prior to any surgical intervention, of which the current evidence suggests is largely beneficial to the patient’s wellbeing, during and after surgery. For more information about exercising prior to surgery, particularly heart surgery, click here. Around 8 million surgical procedures are performed in the UK each year with a low 2% complication rate. However, it’s possible that exercise regimes prior to surgical intervention performed more widely could lower the complication rate even further.
What to wear for the test
Simply consider Cardiopulmonary Exercise Testing (CPET) to be exercise, wear comfortable, loose-fitting clothes, training clothes if they are available and suitable footwear such as trainers, allowing the subject to perform the test to the best of their ability.
Before the test
Before visiting the hospital for a CPET test, some simple rules that should be followed, to avoid a poor result:
- Don’t Eat – Subjects should be advised to avoid eating a minimum of 2 hours before the test.
- No Alcohol – Subjects should be advised to avoid alcohol for a minimum of 4 hours before the test.
- Avoid Exercise – Subjects should be advised not to perform any intense exercise before the test.
- No Smoking – Subjects should be advised to avoid smoking a minimum of 1 hour before the test
Any and all medications should be discussed with the physician beforehand to determine if it can be used normally before the CPET test.
If the patient has experienced any of the following, they should contact the team performing the test.
- Chest Pain on or just before the day of the test
- Chest Infection on or up to 3 weeks before the test
- Heart Attack or Stroke within 4 weeks
- Recent surgery in particular Eye, stomach or chest
- Attendance at A&E for any other reason within last week
Want to learn more?
We run a number of Cardiopulmonary Exercise Testing (CPET) Interpretation training courses each year which suit all levels and areas of speciality. So if you are keen to learn more about performing and interpreting CPET, why not drop us an email to firstname.lastname@example.org to find out when our next course is.