Indications of CPET (Cardiopulmonary exercise test)

Cardiopulmonary exercise testing is used to evaluate a patient’s functional capacity, identifying cardiac or pulmonary disease in patients with abnormal diagnostics (echocardiograms, lung functions tests, diagnostic sleep studies, etc)¹. Whilst on a stationary cycle ergometer or a motorized treadmill, the patient exercises until failure, whilst under constant supervision from a scientist or physician. During the testing period, physiological data such as ECG, blood pressure, heart rate, oxygen uptake, carbon dioxide output is collected. From this data, overall cardiopulmonary function can be calculated as well as determining exercise capacity, cause of cardiopulmonary limitation, abnormal cardiopulmonary responses to exercise, evaluation of therapeutic intervention, or unexplained dyspnoea (shortness of breath) when other tests have failed to determine a cause.

There are several major variables assessed during a CPET:

1. VO₂: Is the volume of oxygen inhaled during pulmonary ventilation in a period of time. VO₂ max is the maximum amount of oxygen that an individual can utilise, despite progressive increase of the load applied during intense exercise. A VO₂ max of below 85% of predicted values is considered abnormal, which can be indicative of heart failure, pulmonary hypertension, COPD, etc.
2. Pulmonary ventilation (VE): Is the volume of air (in litres) moved in and out of the lungs per minute and can be used to determine the severity of disease in patients with heart failure.
3. Respiratory coefficient (R): Expresses the ratio between CO₂ production and O₂ consumption (VCO₂/VO₂). A value of 1 or above indicates intense exercise, showing that CO₂ production is higher than O₂.
4. Anaerobic threshold: The VO₂ at which anaerobic metabolism sets in during intense exercise. Direct measurement of anaerobic threshold requires continuous sampling of arterial lactate, however it can be determined from physiological data, such as the abrupt increase in VCO₂ indicates an increase in the rate of CO₂ production from lactate buffering.³

If clinically relevant, a CPET can be a non-invasive resource to assess both exercise capacity and determine cardiopulmonary function.

Reference list:

1. Razvi Y, Ladie DE. Cardiopulmonary Exercise Testing [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2022. https://www.ncbi.nlm.nih.gov/books/NBK557886/
2. Datta, Debapriya, et al. “Cardiopulmonary Exercise Testing in the Assessment of Exertional Dyspnea.” Annals of Thoracic Medicine, vol. 10, no. 2, 2015, p. 77, www.ncbi.nlm.nih.gov/pmc/articles/PMC4375746/, https://doi.org/10.4103/1817-1737.151438. Accessed 1 Mar. 2019
3. Laveneziana P, Di Paolo M, Palange P. The clinical value of cardiopulmonary exercise testing in the modern era. European Respiratory Review. 2021 Jan 6;30(159):200187.