What are the details of cardiopulmonary exercise testing?

Cardiopulmonary Exercise Testing (CPET): Comprehensive Overview

What CPET Measures and Why It Matters

CPET is the gold standard for evaluating exercise intolerance because it provides an integrated, dynamic assessment of the pulmonary, cardiovascular, hematopoietic, neuropsychologic, and skeletal muscle systems during stress—information that cannot be obtained from resting measurements of individual organ function. 1

The test measures respiratory gas exchange (oxygen uptake [V̇O₂], carbon dioxide output [V̇CO₂], and minute ventilation [V̇E]) alongside continuous 12-lead ECG, blood pressure, pulse oximetry, and perceptual responses during symptom-limited progressive exercise. 1, 2

Primary Clinical Indications

CPET should be performed when basic evaluation (history, physical examination, chest radiography, pulmonary function tests, resting ECG) leaves clinical questions unanswered. 2

Key indications include:

• Unexplained exercise intolerance or dyspnea when symptoms are disproportionate to resting cardiopulmonary tests 1, 2
• Functional capacity determination for disability assessment, with peak V̇O₂ providing objective quantification 1, 2
• Heart failure evaluation and prognosis, particularly for heart transplantation selection—peak V̇O₂ outperforms all other clinical, exercise, and hemodynamic data in determining mortality risk 1
• Preoperative risk stratification, especially for lung resection surgery where peak V̇O₂ <50-60% predicted indicates increased perioperative morbidity and mortality 2
• Pulmonary rehabilitation planning and outcome assessment in COPD, interstitial lung disease, and cystic fibrosis 1, 3

Test Protocols and Standardization

The symptom-limited incremental protocol with progressive work-rate increases is the gold-standard initial CPET method. 1, 2

The protocol should increase workload in small, fixed steps each minute (or as a smooth continuous ramp) to allow comprehensive assessment across the entire tolerable range. 1 Cycle ergometry is most commonly used, though treadmill testing is also appropriate. 1

High-intensity constant-load tests are increasingly employed to sensitively detect functional improvements after therapeutic interventions, typically performed at 50-70% of maximal work rate achieved during incremental testing for 5-10 minutes. 1, 2

Pre-Test Requirements and Patient Preparation

Patients must:

• Abstain from smoking for at least 8 hours before testing 1
• Refrain from exercise on the day of testing 1
• Have a light breakfast no less than 2 hours before the test 1
• Continue their optimal medication regimen (for functional evaluation and disability assessment) 1
• Wear appropriate exercise clothing and tennis shoes 1

Required preliminary testing includes:

• Spirometry and maximal voluntary ventilation (MVV); lung volumes and DLCO if clinically warranted 1
• Resting arterial blood gases if hypoxemia is suspected 1
• Recent hemogram and electrolytes when appropriate 1
• Cardiology consultation for patients with known coronary artery disease 1

A screening visit with exercise familiarization (pedaling at low work rate with mouthpiece, noseclip, and monitoring devices) helps patients understand communication techniques, hand signs, and symptom scoring. 1

Core Physiologic Measurements

Peak V̇O₂ (V̇O₂peak) is the gold-standard metric of aerobic capacity, providing objective global assessment of functional status. 1, 2

Anaerobic (lactate) threshold identifies the exercise intensity at which anaerobic metabolism begins supplementing aerobic energy production. 1, 2

V̇E/V̇CO₂ slope reflects ventilatory efficiency and pulmonary gas-exchange performance—an elevated slope is an independent prognostic marker in severe heart failure. 1, 2

Oxygen pulse (V̇O₂/HR) serves as a surrogate for stroke volume and cardiac output. 1, 2

Heart rate response and cardiac frequency reserve, along with breathing reserve, are essential for identifying cardiovascular versus ventilatory limitations. 1, 2

Interpretation Framework: The Five Critical Questions

Interpretation must address five core questions systematically: 1, 2

1. Is aerobic capacity (peak V̇O₂) normal? Compare measured values to appropriate reference values for age, sex, and body size 1, 2

2. Does cardiovascular function contribute to exercise limitation? Look for reduced peak V̇O₂ with near-normal peak heart rate, flat or decreasing oxygen pulse trajectory, low anaerobic threshold, steeper HR-V̇O₂ relationship with reduced cardiac frequency reserve, and elevated V̇E/V̇CO₂ slope 1, 2, 4

3. Does ventilatory function contribute to exercise limitation? Assess breathing reserve (normal is >15-20% of MVV remaining at peak exercise) and flow-volume loop patterns during exercise 1, 2

4. Does pulmonary gas exchange contribute to exercise limitation? Evaluate for arterial oxygen desaturation and abnormal alveolar-arterial oxygen gradient 1, 2

5. Is there premature metabolic acidosis? Assess lactate threshold relative to predicted values 1, 2

Cardiac Limitation Patterns

In heart failure, the characteristic CPET constellation includes: 1, 2, 4

• Reduced V̇O₂peak with near-normal peak heart rate
• Flat or decreasing oxygen pulse trajectory indicating limited stroke volume augmentation
• Low anaerobic threshold
• Steeper HR-V̇O₂ relationship with reduced cardiac frequency reserve
• Elevated V̇E/V̇CO₂ slope in the moderate-intensity domain

A fall or plateau in systolic blood pressure during exercise signifies inability of the heart to increase output sufficiently, reflecting cardiac pump limitation—in healthy individuals, systolic blood pressure rises progressively (~10 mmHg per MET) as cardiac output increases. 4

Importantly, leg discomfort is the most frequent limiting symptom in chronic heart failure, underscoring the contribution of peripheral muscle dysfunction and deconditioning. 4

Pulmonary Disease Applications

In COPD, CPET identifies exercise-induced hypoxemia requiring supplemental oxygen titration and demonstrates reductions in ventilatory demand after pulmonary rehabilitation. 2, 3

For interstitial lung disease, CPET detects early gas-exchange abnormalities not evident at rest, aiding early intervention. 2, 3

In cystic fibrosis, CPET provides prognostic information and guides therapeutic decision-making. 2, 3

Critical Interpretation Principles

Submaximal data and trend analysis throughout the test are emphasized over sole reliance on peak values, providing insight into dynamic physiologic responses. 1, 2

Comparison of the patient's CPET response pattern with established disease-specific patterns is essential for accurate diagnosis, though significant overlap exists in exercise responses between different respiratory and cardiac diseases. 1

Algorithms based on single key measurements are inadequate—an integrative approach emphasizing interrelationships, trending phenomena, and patterns of key variable responses in clinical context is required. 1

Very fit individuals and athletes may experience significant reductions in peak V̇O₂ due to illness yet still fall within normal confidence intervals for sedentary subjects, highlighting the importance of considering baseline fitness level. 1

Safety and Personnel Requirements

Testing must be performed by personnel trained in exercise testing and emergency response, with immediate availability of resuscitation equipment. 2

A brief medical history and physical examination are recommended before testing, with particular attention to medications that alter heart rate (β-blockers) and skeletal abnormalities of the lower limbs. 1

Integration into Pulmonary Rehabilitation

CPET should be performed before initiating pulmonary rehabilitation to establish baseline safety parameters (identifying arrhythmias, occult cardiac ischemia, arterial desaturation requiring supplemental oxygen) and repeated after training to document physiologic improvement and refine ongoing exercise prescription. 3

CPET is preferable to 6-minute walk testing for exercise prescription because it provides precise metabolic and ventilatory data unavailable from field tests. 3

Common Pitfalls to Avoid

Do not rely exclusively on peak exercise values—submaximal responses and trending phenomena provide critical diagnostic information. 1, 2

Do not use a single algorithm or key measurement—multiple coexisting conditions are common, requiring integrative pattern recognition. 1

Do not compare results to inappropriate reference values—very fit individuals require different normative standards than sedentary populations. 1

Do not ignore the clinical context—CPET results are most valuable when interpreted alongside resting studies and the specific clinical question being addressed. 3