Cardiopulmonary exercise tests

What it tests

Integrated test of the heart, lungs, circulation, blood and muscle under load
- Answers the question resting tests cannot: which system is the limiting one?
Treadmill or cycle ergometer, incremental ramp to symptom-limited maximum, with breath-by-breath analysis of VO2, VCO2 and minute ventilation, plus continuous ECG, SpO2, BP +/- arterial line

VO2max = (SVmax x HRmax) x (CaO2max - CvO2min)
- i.e. cardiac output x arteriovenous oxygen difference - the Fick principle
VO2 rises linearly with workload; VO2max defines aerobic capacity
In health, the limit is cardiac (heart rate), not ventilatory - there is normally substantial ventilatory reserve left at peak exercise
- -> a patient who runs out of ventilation before heart rate has a respiratory problem

Normal VO2max ~35-45 mL/kg/min in untrained young adults; declines ~8-10% per decade from the 3rd decade
Falling maximal heart rate is the dominant contributor to the age-related fall in VO2max
Elite endurance athletes 70-85 mL/kg/min
<15 mL/kg/min marks significant functional impairment; <10 predicts high perioperative mortality

Limitation	Signature
Cardiac	HR reserve exhausted, low O2 pulse, early anaerobic threshold, ventilatory reserve preserved
Ventilatory (mechanical)	VE approaches MVV -> breathing reserve exhausted, dynamic hyperinflation (dec inspiratory capacity), normal HR reserve
Gas exchange / pulmonary vascular	dec SpO2 with exercise, inc VE/VCO2 slope, inc dead space fraction, low O2 pulse
Peripheral/muscular or deconditioning	Early lactate threshold, normal reserves in both systems
Obesity	High VO2 at a given workload, normal VO2/kg of lean mass
Poor effort / psychogenic	RER <1.05, erratic pattern, all reserves intact

Anaerobic (ventilatory) threshold - normally 45-65% of predicted VO2max; early AT = cardiac or circulatory disease
O2 pulse (VO2/HR) = a surrogate for stroke volume - a flat or falling O2 pulse suggests impaired stroke volume augmentation or ischaemia
VE/VCO2 slope - ventilatory efficiency; >=34-36 is a strong adverse prognostic marker in heart failure and pulmonary hypertension
Breathing reserve = 1 - (VEmax/MVV); normally >=15-20% remains
RER (VCO2/VO2) >=1.10 confirms a genuinely maximal effort

Unexplained dyspnoea or exercise intolerance when resting tests are normal or discordant
Pre-operative risk stratification, especially lung resection
Prognostication and transplant assessment in heart failure and pulmonary hypertension
Exercise-induced bronchoconstriction, exercise-induced laryngeal obstruction
Prescribing and monitoring pulmonary/cardiac rehabilitation
Impairment/disability assessment

1. FEV1 and DLCO -> calculate predicted post-operative (ppo) values by segments to be removed

2. ppoFEV1 and ppoDLCO both >60% predicted -> low risk, proceed

3. Either <60% (or either resting value reduced) -> proceed to CPET

4. CPET peak VO2:

Peak VO2	Risk
>20 mL/kg/min (or >75% predicted)	Low - any resection up to pneumonectomy
10-20 (35-75% predicted)	Intermediate - use ppo values and consider limited resection
<10 mL/kg/min (or <35% predicted)	High - avoid major resection; consider SABR or sublobar resection

Simpler surrogates: stair climbing (>22 m), shuttle walk (>400 m) - useful screens, less precise

Acute coronary syndrome or unstable angina, decompensated heart failure, uncontrolled arrhythmia, severe symptomatic aortic stenosis, acute PE/DVT, uncontrolled asthma, SpO2 <85% on room air at rest, uncontrolled hypertension

Separates cardiac from respiratory from deconditioning causes of dyspnoea -> stops the cycle of repeated normal resting tests
Heart failure: peak VO2 <14 mL/kg/min (or <12 on a beta-blocker), or <50% predicted, plus VE/VCO2 slope >=35 -> transplant/LVAD referral trigger
Pulmonary hypertension: peak VO2 and VE/VCO2 for prognosis and therapy response
Lung resection: the decision between lobectomy, sublobar resection, SABR and non-surgical management
Exercise prescription: target training intensity set from the anaerobic threshold in cardiac and pulmonary rehabilitation
Prehabilitation: 4-6 weeks of exercise training measurably improves peak VO2 before major surgery
Identifies deconditioning and obesity as the answer in a large proportion of "unexplained dyspnoea" referrals - and that answer is treatable

COPD, ILD, cystic fibrosis, bronchiectasis, pulmonary hypertension
Heart failure (both HFrEF and HFpEF - exercise haemodynamics unmask HFpEF)
Lung cancer surgical assessment; transplant assessment (heart, lung)
Mitochondrial myopathy and McArdle disease (abnormal lactate and VO2 kinetics)
Chronic fatigue syndrome/ME and long COVID (reduced peak VO2, chronotropic incompetence, post-exertional malaise - repeat testing may cause harm**)
Obesity, deconditioning, anaemia
Exercise-induced laryngeal obstruction and vocal cord dysfunction

Peak VO2 is one of the strongest independent predictors of all-cause mortality across cardiac, respiratory and surgical populations - stronger than most resting measures
Each 1 MET (3.5 mL/kg/min) increase in fitness -> ~10-25% reduction in mortality
In heart failure, peak VO2 and the VE/VCO2 slope together outperform ejection fraction for prognosis
Post-lung-resection: VO2 falls ~10-15% after lobectomy, ~20-25% after pneumonectomy, with partial recovery over 6 months
Peak VO2 is modifiable - exercise training improves it by 15-25% in most chronic disease populations, which is the basis for pulmonary and cardiac rehabilitation
A genuinely maximal test needs RER >=1.10 - otherwise the report describes effort, not capacity

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