EXERTIONAL BREATHLESSNESS IN PATIENTS WITH CHRONIC AIR-FLOW LIMITATION - THE ROLE OF LUNG HYPERINFLATION

There is considerable intersubject variability in the perceived intensity of breathlessness for a given level of activity among patients with chronic airflow limitation (CAL). To examine possible factors contributing to this variability we compared breathing pattern parameters, dynamic operational lung volumes, and Borg dyspnea ratings in 23 patients with severe CAL and in 10 healthy age-matched normal subjects during cycle ergometry to symptom-limitation, Patients with CAL had significantly (p < 0.01) higher levels of ventilation (%, maximal voluntary ventilation) for a given work rate (slope of VE(%MVV)/WR(% pred max) = 1.51 +/- 0.18 versus 0.63 +/- 0.10; mean +/- SEM) and greater dynamic lung hyperinflation (DH) (change [Delta] in end-expiratory lung volume [EELVdyn] = +0.31 +/- 0.11 L versus -0.16 +/- 0.22 L). Compared with normal subjects at a standardized VE (30 L/min), the CAL group was more breathless (Borg = 4 +/- 1 versus 2 +/- 1, p < 0.01) and hyperinflated (EELVdyn = 75 +/- 3 versus 46 +/- 6 %TLC, p < 0.001; end-inspiratory lung volume [EILVdyn] = 85 +/- 3 versus 67 +/- 5 %TLC, p < 0.01). Within the CAL group, change in Borg ratings correlated with Delta VE(%MVV) (r = 0.77, p < 0.001) and with slope of VE(%MVV)/WR(% pred max)(r = 0.48, p < 0.01). Regression analysis selected Delta EILVdyn (or Delta inspiratory reserve volume [Delta IRVdyn]) from various dynamic ventilatory parameters as the strongest predictor of Delta Borg (r = 0.63, p < 0.001). Components of Delta EILVdyn (i.e., Delta EELVdyn, Delta VT) each contributed significantly (p < 0.001) to breathlessness and with Delta breathing frequency accounted for 61% of the variance in Delta Borg (r = 0.78, f = 38.20, p < 0.001). Accounting for ventilation, EELVdyn continued to contribute significantly to breathlessness; at a standardized VE (30 L/min), EELVdyn predicted 31% of the variance in Borg ratings (p < 0.01). Exertional breathlessness in CAL is a function of ventilatory demand and intensifies with encroachment on the inspiratory reserve volume or ventilatory reserve. Acute DH, with its attendant intrinsic mechanical loading, contributes importantly to intersubject variability in the perception of breathlessness for a given ventilation.