The contribution of FEV1 and airflow limitation on the intensity of dyspnea and leg effort during exercise. Insights from a real‐world cohort

RATIONALE: The effort required to cycle and breathe intensify as power increases during incremental exercise. It is currently unclear how changes in FEV₁ in the presence or absence of airflow limitation) impacts the intensity of dyspnea and leg effort. This is clinically important as the improvement in FEV₁ is often the target for improving dyspnea. OBJECTIVES: To investigate the relationship between dyspnea (D), leg effort, power (P), and FEV₁ with and without airflow limitation using direct psychophysical scaling performed during incremental exercise testing to symptom limited capacity. METHODS: Retrospective analysis of consecutive patients over the age of 35 referred for cardio-pulmonary exercise testing at McMaster University Medical Centre from 1988-2012.The modified Borg scale was used to measure dyspnea throughout incremental exercise testing. MEASUREMENTS AND RESULTS: 38,788 patients were included in the analysis [Mean Age 58.6 years (SD ±11.8), Males 61%, BMI 28.1 kg/m² (SD ±5.1), FEV₁ was 2.7 L (SD ±0.85), 95% predicted (SD ±20.4), FVC 3.4 L (SD ± 1.0), 94% predicted (SD ±17.0)], and 10.9% had airflow limitation (AL, FEV₁ /FVC < 70%). In a nonlinear regression analysis, the intensity of dyspnea increased in a positively accelerating manner with power and as the FEV₁ % predicted decreased: Dyspnea = 0.06 * Power^1.03  * FEV₁ %Pred^-0.66 (r = .63). The intensity of leg effort increased with power and declining quadricep strength and FEV1% predicted: Leg Effort = 0.06 * Power^1.22  * Quad^-0.56 *FEV₁ %Pred^-0.39 (r = .73). There was no independent effect of AL on dyspnea of leg effort. CONCLUSION: Power, quadriceps strength and FEV1 are the dominant factors contributing to dyspnea and leg effort, irrespective of the degree of airflow limitation.