Phenotyping Exertional Breathlessness Using Cardiopulmonary Cycle Exercise Testing in People With Chronic Airflow Limitation.

Abstract

Background: Exertional breathlessness is a cardinal symptom of people with chronic airflow limitation (CAL) and can be evaluated using cardiopulmonary exercise testing (CPET).

Research question: Does abnormally high exertional breathlessness in relationship to the rate of oxygen uptake (V'O₂) and minute ventilation (V'_E) indicate different underlying pathophysiologic mechanisms and clinical characteristics in people with CAL?

Study design and methods: Analysis of people aged ≥ 40 years with CAL (FEV₁ to FVC ratio after bronchodilation less than lower limit of normal) undergoing symptom-limited incremental cycle CPET in the Canadian Cohort Obstructive Lung Disease study. Using published normative references, breathlessness phenotypes at peak exercise were categorized as abnormal (Borg 0-10 scale intensity rating more than upper limit of normal) by V'O₂ alone, abnormal by both V'O₂ and V'_E, or normal by both V'O₂ and V'_E. Exercise physiologic responses and clinical characteristics were compared between groups.

Results: We included 325 people (44% female) with CAL (mean [SD]) FEV₁, 75.4 [17.5] % predicted). Compared with the normal by both V'O₂ and V'_E group (n = 237 [73%]), the abnormal by V'O₂ only group (n = 29 [9%]) showed lower pulmonary diffusing capacity and greater exercise ventilatory inefficiency, whereas the abnormal by both V'O₂ and V'_E group (n = 50 [15%]) showed even worse lung function, dynamic critical inspiratory constraints, and exertional breathlessness along with greater symptom burden in daily life, lower physical activity, and worse health status.

Interpretation: Our results show that exertional breathlessness phenotyped in relationship to V'O₂ and V'_E using normative reference equations enables multivariable analyses of underlying symptom mechanisms and associated clinical characteristics.