RER Peak Index (Respiratory Exchange Ratio) Calculator

RER Peak Index (Respiratory Exchange Ratio): Explanation and Clinical Context The RER Peak Index is calculated as the ratio of carbon dioxide production (VCO₂) to oxygen consumption (VO₂) at peak exercise. It serves as an objective measure of exercise intensity and maximal effort during cardiopulmonary exercise testing (CPET). A normal RER at rest is approximately 0.8, reflecting primarily fat metabolism.

During progressive exercise, the RER increases as carbohydrate metabolism predominates. An RER value >1.1 at peak exercise is generally considered indicative of maximal exertion, confirming adequate effort during CPET. Clinically, RER Peak Index helps interpret exercise capacity, differentiate between cardiovascular and ventilatory limitations, and predict prognosis in patients with heart failure and other cardiopulmonary conditions.

It is also used to validate the maximality of exercise tests in both clinical and research settings.