Cardiopulmonary exercise test

Cardiopulmonary exercise test

An illustration of Treadmill cardio exercise test

Cardiopulmonary exercise testing (CPET) is a non-invasive diagnostic assessment that evaluates the integrated function of the cardiovascular, respiratory, and musculoskeletal systems during physical exertion. It was developed in the early 20th century. It has become a gold standard in the assessment of cardiorespiratory function. It is useful in evaluating individuals' tolerance towards exercise, diagonsing cardiopulmonary diseases and guiding personalised treatment plans. This test involves continuously monitoring key physiological parameters, like heart rate, blood pressure, and ventilation when the patient performs progressively intense exercise, typically on a treadmill or cycle ergometer.

Advanced data analysis techniques are also incorporated as a part of CPET, providing insights into how the patient’s body adapts to stress and also used in evaluating exercise intolerance in athletes. However, this test is generally not for patients after myocardial infarction, or respiratory failure and should be taken under medical supervision for patients with cardiovascular diseases.

History

The development of cardiopulmonary exercise testing (CPET) began in the early 20th century with investigations into physiological responses to physical exertion. In the 1920s, researchers established the measurement of oxygen consumption during exercise as a diagnostic approach for assessing cardiopulmonary function, marking the foundation of modern CPET. Another major milestone came in the 1950s with the introduction of the ‘Douglas bag method’, which enabled more accurate measurement of gas exchange (oxygen intake and carbon dioxide output) during exercise and improved the precision of its diagnosis. With the advancement of computerized systems in the 1980s, these technological improvements enhanced the test’s diagnostic accuracy. Today, it is used to diagnose and manage conditions such as heart failure, pulmonary diseases, and metabolic disorders. It provides critical insights into functional capacity and helps identify the causes of exercise intolerance.

Procedure

Cardiopulmonary exercise testing (CPET) evaluates the body’s integrated physiological responses during exercise through advanced monitoring of gas exchange, cardiovascular function, and respiratory dynamics. The test employs breath-by-breath analysis to measure oxygen and carbon dioxide uptake and output, alongside respiratory volumes, synchronized with real-time workload data. In the test, patients perform graded exercise, typically on a stationary cycle ergometer or treadmill, progressing from rest to maximal exertion. The progressive increase in workload challenges the cardiovascular and respiratory systems, exposing limitations in oxygen delivery, metabolic efficiency, or ventilatory capacity not apparent at rest. The protocol of this test is structured into four distinct phases to systemically assess adaptation to stress.

1. Resting phase (2-3 minutes):  Establishes pre-exercise values for heart rate, blood pressure and gas exchange. This phase allows a direct comparison of physiological changes during exercise.
2. Unloaded phase (2-3 minutes): By low-intensity exercise (e.g., cycling without resistance on an ergometer or walking at a slow pace on a treadmill), this phase acclimates patients to the equipment and stabilizes physiological variables, reducing abrupt transition. It also allows the respondents to warm up to precisely measure the maximum workload the respondents can tolerate in this test.
3. Incremental exercise phase (8-12 minutes): Tests the maximal stress the individuals can tolerate. During this phase, the workload increases progressively based on fitness level. I.e. severely impaired individuals will have a slower increment rate than fitter subjects. The test terminates at maximal exertion, indicated by the respiratory exchange ratio (RER). RER is calculated as the ratio of VCO2 to VO2 (RER = VCO2/VO2); when this ratio exceeds 1.15, it indicates maximal exertion in the test.
4. Recovery phase (3-5 minutes): Monitors post-exercise stabilization of heart rate, blood pressure, and ventilation. CPET is invaluable for diagnosing in a clinical setting. CPET’s holistic analysis distinguishes cardiovascular, respiratory, or metabolic dysfunction, guiding targeted therapeutic strategies.

Analysis

Parameter analysed

• Pulmonary metrics: O2 consumption (VO2), CO2 production (VCO2), oxygen saturation in blood (SpO2), minute ventilation (VE)
• Cardiovascular metrics: Heart rate, blood pressure, ECG-derived contractility
• Functional capacity: Peak workload (watts/speed) and maximal oxygen uptake

9-panel analysis

In Cardiopulmonary Exercise Testing (CPET), a variety of physiological parameters are measured during incremental exercise to evaluate the integrated function of the heart, lungs, and muscles. The analysis of CPET data is commonly facilitated by a standardized 9-panel display, which organizes key variables into a graphical format to aid interpretation. This display consists of nine specific plots that collectively provide a comprehensive overview of a patient’s cardiopulmonary performance during exercise, making it a critical tool for clinicians and researchers.

9-panel analysis of cardiopulmonary exercise test.

The Nine Panels:

The nine panels are arranged in order from left to right, from top to bottom. In nine panels, Panel 2,3,5 indicates the cardiovascular system ; Panel 1,4,7 shows ventilation; Panel 6,8,9 represents ventilation-perfusion relationships.

1. VO₂, VCO₂, VE vs. time: Tracks oxygen uptake, CO₂ output, and ventilation, showing exercise response. VE is supposed to increase with workload smoothly. EOV (exercise oscillaotry ventilation) is noted.
2. Heart rate & O₂ pulse vs. time: Monitors heart rate and oxygen delivery efficiency. It shows the maximum cardiac ability to pump blood for oxygen delivery.
3. VE vs. VCO₂: Measures ventilatory efficiency via the slope of ventilation to CO₂ output.
4. VE vs. VO₂: Assesses breathing efficiency relative to oxygen use.
5. VO₂ vs. work rate: Links oxygen uptake to workload, spotting abnormal responses.
6. VCO₂ vs. VO₂: Marks the anaerobic threshold where CO₂ exceeds O₂ due to lactic acid.
7. PetO₂ & PetCO₂ vs. time: Reflects lung gas exchange through end-tidal O₂ and CO₂.
8. VE/VCO₂ & VE/VO₂ vs. time: Indicates gas exchange efficiency. It represents the ventilatory limitations during exercise.
9. RER vs. time: Shows respiratory exchange ratio (VCO₂/VO₂), highlighting fuel use and anaerobic shift.

Key interpretation

Cardiopulmonary exercise testing provides a multidimensional assessment of cardiovascular, respiratory, and metabolic function during physical exertion. It can provide several key interpretations (integrated information). Below are the critical parameters, according to alphabetical order.

• Anaerobic threshold (AT)

The anaerobic threshold marks the exercise intensity at which energy production of an individual shifts from aerobic respiration (oxygen-dependent) to anaerobic respiration. This transition occurs when oxygen delivery to muscles becomes insufficient to meet demand, leading to lactate accumulation. This threshold can be identified by VCO2 (volume of carbon dioxide exhaled) and VO2 (volume of oxygen exhaled). A sudden increase in VCO2 relative to VO2 signifies the anaerobic threshold.  The anaerobic threshold usually occurs between 47% and 64% of VO2 max, meaning 47-64% of maximum oxygen uptake in the test.

• Electrocardiographic findings

Through this test, we can check the heart contractility during exercise stress, with the heart's recovery after exercise. The ECG should show minimal waveform changes and no significant deviation from normal sinus rhythm. . It gives insight into the stability of cardiac rhythm under stress.

• Gas exchange efficiency

The ability to oxygenate blood and remove CO2 can also be measured during the test. By increasing the exercise intensity, we expose the maximum efficiency of individuals’ gas exchange efficiency. Especially the appearance of exercise-induced desaturation, which signifies a ventilatory error during exercise with a SpO2 drop of more than 4%. It may indicate potential interstitial lung disease.

• Peak oxygen uptake

The highest rate of oxygen consumption is achieved during maximal exercise, which reveals the maximal pulmonary capacity during stress. Indicated by a plateau in the VO2 curve. During the plateau, VO2 no longer increases even with progressive increments in exercise workload. The VO2 max will be compared to a predicted value based on age, sex, and height. Decreased VO2 max is defined as a measured value smaller than 85% of the predicted value.

• EOV (exercise oscillatory ventilation)

It is described as the oscillating frequency of ventilation during exercise. In normal individuals, continuous linear rise instead of oscillating, an oscillatory pattern that persists ≥60% time of the exercise test at an amplitude of ≥15% of the average resting value represents potential respiratory conditions.

These act as further proof to evaluate if the key indicators match the preliminary diagnosis of the clinicians.

Equipment

Cardiopulmonary exercise testing relies on specialized equipment to collect precise physiological data during exercise.

• Cycle ergometer or Treadmill

This equipment determines the exercise modality. While running is more convenient in clinical settings, cycling is preferred for patients with balance issues, severe obesity, or orthopaedic limitations.

A cycle ergometer is a stationary exercise bike which allows the respondents to pedal the bike under medical supervision. It can measure the amount of work done (in units of watts) by the respondent when he is performing the test. To increase the exercise intensity, the resistance will be increased over time.

The treadmill simulates walking/ running, the speed of which is adjusted incrementally to increase metabolic load in the test.

• Spirometer

Spirometers assess lung function by measuring tidal volume (VT), respiratory rate (RR),  forced expiratory volumes (FEV), and airflow rates. It aids in diagnosing restrictive lung diseases or obstructive lung diseases.

• Metabolic cart or gas analyser

This kind of tool is used to measure the composition of exhaled gas, mostly to detect the oxygen concentrations (VO) and carbon dioxide concentrations (VCO2) in exhaled air. This system makes use of infrared CO2 analyzers and zirconium oxide O2 sensors to detect the concentrations. This data will synchronize gas exchange data with workload and spirometer data to obtain comprehensive data in evaluating the pulmonary function of an individual.

• 12-lead electrocardiography system (ECG)

Continuously monitors cardiac electrical activity to detect arrhythmias, ischemia, ST-segment changes (a key landmark for contractility error in the heart), or conduction abnormalities during exercise. This is the major tool to assess heart function during exercise, which is applied similarly in cardiac stress tests.

• Ancillary tools

This kind of equipment is not compulsory but is often added to this test to ensure precise measurement and safety. Blood pressure cuffs track systolic and diastolic pressures at 2-3 minute intervals to monitor the blood pressure of the individual in the test. Pulse oximeters measure peripheral oxygen saturation to detect exercise-induced hypoxemia. Safety gear, some bronchodilators, or defibrillators are prepared to address rare complications like asthma in the test.

Before testing, all devices should undergo rigorous calibration by technicians to ensure accurate measurement, with medical supervision mandated throughout.

Contraindications

Although cardiopulmonary exercise testing (CPET) is a well-established diagnostic tool, it carries certain risks depending on the patient's health condition. These risks can be categorised as absolute contraindications (conditions where CPET should not be performed) and relative contraindications(conditions requiring careful risk-benefit assessment before testing).

Absolute Contraindications

Absolute contraindications involve acute cardiopulmonary conditions that significantly increase the risk of adverse events during exercise. These include:

• Active/Post Myocardial ischemia – Reduced blood flow to the heart muscle, which may worsen under exercise, potentially leading to myocardial infarction (heart attack) if oxygen demand exceeds supply.
• Pulmonary edema – Fluid accumulation in the lungs' alveoli, impairing gas exchange and reducing oxygen uptake.
• Respiratory failure – Inadequate oxygenation or ventilation due to airway obstruction or impaired gas diffusion, leading to ventilation-perfusion mismatch and hypoxemia (low blood oxygen).
• Decompensated heart failure
• uncontrolled arrhythmias
• untreated pulmonary embolism or deep venous thrombosis
• Other severe cardiopulmonary-related conditions

These conditions compromise cardiopulmonary function, limiting oxygen delivery during exercise and increasing the risk of hypoxemic hypoxia (oxygen deficiency in tissues).

Relative Contraindications

Relative contraindications include chronic conditions that may elevate risk but do not outright prohibit testing. Key examples are:

• Hypertension – Persistently elevated blood pressure, often linked to endothelial dysfunction(impaired blood vessel dilation due to reduced nitric oxide bioavailability). Chronic hypertension can damage arterial walls, promoting atherosclerosis.
• Coronary heart disease (CHD) – Atherosclerotic plaque buildup in coronary arteries, which may rupture during exercise, triggering thrombosis (blood clot formation) and vessel occlusion. This can lead to acute myocardial ischemia or infarction.
• Pregnancy
• symptomatic tachycardia or bradycardia

Both conditions impair cardiovascular efficiency, increasing the strain on the heart and lungs during CPET. And may lead to severe consequences if CPET is in progress.

If the below are observed in the patients during the test, this test needs to be terminated immediately.

• Hypotension
• Arrhythmias
• Leg claudication
• ST-segment depression
• Cardiac chest pain

Clinical significance

The cardiopulmonary exercise test is widely used in clinical treatment, from pre-operative risk stratification to determining a specific disease process. CPET is used for many things, such as checking whether your body condition is suitable for having surgery, evaluating how well heart failure treatments are working, or assisting athletes in designing their treatment plans.

• Prognosis in heart failure, assessing severity and guiding decisions on therapy, device implantation, or transplantation. Monitoring disease progression and treatment efficacy, tracking changes in functional capacity over time.

• Used in preoperative assessment to evaluate surgical risk, especially in patients with known or suspected cardiopulmonary disease. It could also be used to assess fitness for transplantation, especially determining cardiopulmonary reserve for procedures like heart or lung transplants.
• Identify the intolerance to exercise of an individual, especially athletes. It could be used to show the cardiopulmonary vascular limitation and to show the improvement in individuals who are in rehabilitation programs.

Future directions

More applications of the CPET may appear by combining the results with other medical tests, as well as introducing wearable technology, which makes it more accessible to the public. Future developments include integrating CPET with imaging like echocardiography for detailed cardiac function analysis, introducing wearable technology and telemedicine, which could enable remote assessments, enhancing accessibility of CPET, or research into advanced algorithms aims to improve diagnostic accuracy and outcome prediction, promising to expand CPET’s role in patient care.