Breathing Reserve (%) Calculator

About breathing reserve

Breathing reserve (BR) estimates how much ventilatory capacity remains unused at peak exercise. It is calculated by comparing peak exercise ventilation (VEpeak) with maximal voluntary ventilation (MVV).

Formula: BR (%) = [(MVV − VEpeak) / MVV] × 100.

Clinical interpretation

A reduced breathing reserve may support ventilatory limitation during CPET, but the threshold depends on the protocol and clinical context. A value below 15% is a commonly used indicator; some references and laboratories use a threshold around 15–20%. A value of 20–40% is often described as a typical reserve range, but it should not be treated as a universal normal range.

• Below 15%: reduced reserve; may support ventilatory limitation.
• 15–19.9%: borderline or reduced reserve; interpret with other CPET findings.
• 20% or higher: reserve is not reduced by these commonly used percentage thresholds alone.
• Negative result: VEpeak exceeds the entered MVV; verify measurements and the MVV estimate.

Important limitations

Breathing reserve is only one component of CPET interpretation. Review symptoms, test effort, spirometry, oxygen saturation, ventilatory pattern, dynamic operating lung volumes when available, and the overall clinical picture. A preserved BR does not exclude all respiratory or cardiac causes of exercise intolerance.

References