Abnormal exertional breathlessness on cardiopulmonary cycle exercise testing in relation to self-reported and physiological responses in chronic airflow limitation

Background: Exertional breathlessness is a cardinal symptom of cardiorespiratory disease. Research Question: How does breathlessness abnormality graded using normative reference equations during cardiopulmonary exercise testing (CPET) relate to self-reported and physiological responses in people with chronic airflow limitation (CAL). Study Design and Methods: Analysis of people aged ≥40 years with CAL undergoing CPET in the Canadian Cohort Obstructive Lung Disease study. Breathlessness intensity ratings (Borg 0-10 category ratio scale [CR10]) were evaluated in relation to power output (W), rate of oxygen uptake (V'O2), and minute ventilation (V'E) at peak exercise using normative reference equations as: 1) probability of breathlessness normality (probability of having an equal or greater Borg CR10 rating among healthy; lower probability reflecting more severe breathlessness); and 2) presence of abnormal breathlessness (rating above the upper limit of normal [ULN]). Associations with relevant participant-reported and physiologic outcomes were evaluated. Results: We included 330 participants (44% women): mean±SD age 64±10 years (range 40-89), FEV1/FVC 57.3±8.2%, FEV1 75.6±17.9%predicted. Abnormally low exercise capacity (peak V'O2< lower limit of normal) was present in 26%. Relative to peak W, V'O2 and V'E, abnormally high breathlessness was present in 26%, 25% and 18% of participants. For all equations, abnormally high exertional breathlessness was associated with worse lung function, exercise capacity, self-reported symptom burden, physical activity, health-related quality of life; and greater physiological abnormalities during CPET. Interpretation: Abnormal breathlessness graded using CPET normative reference equations was associated with worse clinical, physiological, and functional outcomes in people with CAL supporting construct validity of abnormal exertional breathlessness.