Estimating Breathing Reserve at Peak Treadmill Exercise: Influence of Sex and Fitness

A low breathing reserve (peak ventilation [Epeak]/estimated maximum ventilation [Emax] ≤ 15%) is recommended as the decision node to indicate abnormal ventilatory limitation during incremental cycle ergometry. Given higher Epeak during weight-bearing exercise, we aim to establish which coefficients should multiply the forced expiratory volume in 1 second (FEV1) to reduce the prevalence of a low breathing reserve in healthy subjects undergoing treadmill exercise.

We determined the coefficients for FEV1 multiplication associated with <5% prevalence of a low breathing reserve in 3544 healthy individuals aged 20 to 80 years. We then contrasted their performance in differentiating healthy subjects (N = 148) from patients with chronic obstructive pulmonary disease (COPD) (N = 133) in an external validation sample.

A low breathing reserve was found in 22% and 6% of women versus 48% and 17% of men when FEV1 was multiplied by 35 and 40, respectively. Sex-adjusted coefficients required to decrease the prevalence of a low breathing reserve ranged from 33 and 48 in women versus 36.5 and 50 in men in those showing peak oxygen uptake <80% and >120% predicted, respectively. Breathing reserve using the new sex- and fitness-adjusted coefficients were superior to previous values in differentiating health from disease, regardless of COPD severity.

Higher coefficients for FEV1 multiplication are required to estimate Emax at peak treadmill exercise in men than in women, increasing as a function of cardiorespiratory fitness in both sexes. These data are poised to improve the yield of cardiopulmonary exercise tests in accurately indicating pathological ventilatory limitation in patients with respiratory diseases.