Cardiopulmonary exercise testing (CPET) is a dynamic and objective investigation that studies the responses of the cardiovascular, respiratory, and skeletal muscular systems to exercise stress in an integrated way.

This is achieved by the measuring gas exchange, respiratory rate and volume, heart rate and ECG parameters, BP, and oxygen saturation (Figure 1.1) whilst a patient undertakes exercise using an ergometer (a device that is used to quantify physical performance by providing a known workload).

Increasingly CPET is being used as part of the pre-operative work-up of patients for major surgery. Whilst CPET can not necessarily be used to define a specific risk for a specific patient, it can provide a broad risk stratification which can guide the need for optimisation, prehabilitation, or potential post-operative level of care. It is part of a global assessment of the patient and hard cut-off values should be avoided. A useful mental model is the ‘traffic light model’ (Figure 29.1).

VCO2 versus VO2 Plot

Energy is needed to perform the work required while exercising. This energy is supplied via cellular metabolism. In simple terms, the food that we eat supplies us with the necessary substrate for energy production. During this process, energy is ‘trapped’ in molecules of adenosine triphosphate (ATP).

There are many different potential causes of exercise limitation and there can be overlap between disease processes. We suggest applying the approach to interpretation outlined in Table 8.1 and Figure 8.7, explore what constitutes a ‘normal’ test, and how parameters may vary in different clinical scenarios.

A typical CPET for a patient with cardiovascular disease is shown in Figures 22.1 and 22.2 and Table 22.1 and described in ‘Test Review and Interpretation’.

Spirometry literally means ‘measuring of breath’, and as an investigation it reflects the lung’s bellows function and can be used to determine the extent of respiratory disease.

To understand basic spirometry, we need to describe how the total space within the lungs is divided into volumes and capacities. A volume is a specific measurement of either inspired or expired gas (or in the case of tidal volume both), whereas a capacity is combination of two or more volumes.

All 9-panel plots contain a graph of VO2 versus work rate (some also include a VCO2 plot on the same graph for a better overall appreciation of exercise capacity).

In this part, we explore the ways of presenting data as 9-panel plots and the importance, meaning, and variations of each individual plot.

The Fick principle (first described by Adolf Eugen Fick in 1870) is one of the key physiological concepts that underpins cardiopulmonary exercise testing. In his work, Fick described the use of oxygen as a ‘marker substance’ that could be used to measure the cardiac output of a dog’s heart.

Dysfunctional Breathing

A typical for a patient with pulmonary vascular limitation is shown in Figures 24.1 and 24.2 and Table 24.2.

This plot examines the end-tidal partial pressures of O2 and CO2 (the plot may also include arterial partial pressures if invasive monitoring is also used).

Cardiopulmonary exercise testing is usually performed using either a treadmill or a cycle ergometer; each has their benefits and limitations (outlined in Table 6.1). Most institutions use a cycle ergometer for CPET – although semi-recumbent ergometers can also be used and it is also possible to use a hand crank for patients with limited leg mobility. It is worth noting that CPET values reported in research papers in peri-operative medicines tend to have been derived from cycle ergometers.

This plot examines the relationship between tidal volume (Vt) and minute ventilation (VE).