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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 * Power1.03  * 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 * Power1.22  * 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.

Original publication




Journal article


Physiological reports

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Division of Respirology, Department of Medicine, McMaster University, Hamilton, ON, Canada.