Background: Cardiopulmonary exercise testing (CPET) is the gold standard to evaluate exertional breathlessness, a common and disabling symptom. However, interpretation of breathlessness responses to CPET is limited by a lack of normative data. We aimed to develop normative reference equations for breathlessness intensity (Borg CR10) in men and women aged ?40 years during CPET, in relation to power output (W), rate of oxygen uptake (V?O2), and minute ventilation (V?E).

Methods: Analysis of ostensibly healthy people aged ?40 years undergoing a symptom-limited incremental cycle CPET (10 W/min) in the Canadian Cohort Obstructive Lung Disease (CanCOLD) study. Participants had normal lung function and exercise capacity. The probability of each Borg CR10 breathlessness intensity rating by W, V?O2 or V?E (as absolute or relative value [% of predicted max]) was predicted using ordinal multinomial logistic regression. Model performance was evaluated by fit, calibration, discrimination (c-statistic), and externally validated in an independent sample (n=74) of healthy Canadian adults.

Results: We included 151 participants (42% women) from CanCOLD; mean age 64 (range 42?89) years, mean body mass index of 26.2 (SD 3.8) kg/m2. Reference equations were developed for females and males separately, accounting for age and/or body mass. Model performance was high across all equations, including in the validation sample (c-statistic 0.82-0.92 for males and 0.85-0.96 for females).

Conclusion: Normative reference equations are provided to compare breathlessness intensity ratings between individuals or groups, and to identify and quantify abnormal breathlessness responses during CPET.