Revisiting the peak breathing reserve < 15% criterion to indicate ventilatory limitation to treadmill incremental cardiopulmonary exercise testing in men and women aged 20 to 80 years

The respiratory system is not the limiting step to humans’ tolerance to dynamic exercise in most physiological circumstances. For instance, minute ventilation at peak exercise (VEpeak) is appreciably lower than the maximal sustained ventilatory capacity (MSVC). Using the estimated (from forced expiratory volume in one second (FEV1)) maximal voluntary ventilation (MVVest) as a surrogate of the MSVC, a peak breathing reserve (BRpeak= [1-(VEpeak /MVVest)] x 100) > 15% has been widely recommended as the decision node to rule out ventilatory limitation. Supportive evidence for this contention, however, stems from small samples tested on a cycle ergometer, an exercise modality associated with lower ventilatory demands than those elicited by treadmill - the commonest ergometer in cardiology.

To determine the prevalence of ventilatory limitation to treadmill incremental cardiopulmonary exercise testing (CPET) based on BRpeak≤15% in a large sample of apparently healthy men and women showing a large age span.

We retrospectively analyzed treadmill CPET data from 3,544 apparently healthy individuals aged 20 to 80 years living in Midwest Brazil. As recommended by current guidelines(1-2), we multiplied FEV1 by 35 or 40. We established the prevalence of BRpeak≤15% in subjects stratified by sex and age (20-39, 40-59, and 60-80 years). Anticipating a high prevalence of low BRpeak using 35 or 40, we aimed to establish which coefficient should be used to multiplying FEV1 to decrease the prevalence of ventilatory limitation to ≤5% and ≤1% in each sex.

BRpeak≤15% was found in 21.7% of women and 48.0% of men when FEV1 was multiplied by 35: corresponding values were 5.8% and 17.4% when the multiplying coefficient was 40, respectively (Figure 1). Regardless of sex, particularly high prevalence of BRpeak≤15% was found in the middle-aged group (Figure 2). Using 40.5 to multiply FEV1 in women and 45 in men resulted in ≤5% prevalence of ventilatory limitation. Further discriminative power (≤1% of BRpeak≤15%) required coefficients as high as 45 and 49 for women and men, respectively (Figure 2).

To avoid unacceptable high false positive rates for ventilatory limitation to incremental CPET on a treadmill (BRpeak≤15%), pre-exercise FEV1 should be multiplied by higher coefficients than those commonly recommended for cycle ergometer-based tests. This is particularly critical for men who reach high exercise intensities. Ever if appropriate coefficients are employed, BRpeak should be used with caution as the sole criterion to rule in or out a contribution of "the lungs" to exercise limitation in individual subjects(3).