Respiratory Factors Contributing to Exercise Intolerance in Breast Cancer Survivors: A Case-Control Study.

Context: Breast cancer survivors often experience activity-related dyspnea and exercise intolerance, but the underlying mechanisms remain unknown.

Objectives: We evaluated physiological contributors to reduced peak oxygen uptake (VO2), with particular attention to the role of respiratory impairment.

Methods: We compared symptom assessments, respiratory and peripheral muscle strength, pulmonary function, and ventilatory responses to symptom-limited incremental treadmill exercise in 29 women who had survived breast cancer and 29 age-matched healthy controls.

Results: Peak VO2 was reduced more than 20%, on average, in the cancer group compared with controls (P < 0.001). Slopes of dyspnea intensity ratings over ventilation or VO2 were >50% greater in the cancer group compared to controls (P < 0.05). Women with breast cancer had lower lung diffusing capacity for carbon monoxide (DLCO), respiratory and limb muscle strength, and ventilatory thresholds during exercise compared with controls (all P < 0.05). During exercise, indices of ventilatory efficiency were similar to controls, but inspiratory capacity (IC) was lower and breathing pattern was more rapid and shallow in the cancer group (P < 0.05). The lower peak VO2 in the cancer group was associated with greater dyspnea intensity, and lower DLCO, IC and ventilatory threshold (all P < 0.05).

Conclusion: Breast cancer survivors had greater peripheral and respiratory muscle weakness, greater reduction of IC, impaired lung diffusion, and evidence of deconditioning compared with controls. Exercise intolerance was multifactorial and correlated well with the combination of these factors as well as with exertional dyspnea. Individualized physiological testing in breast cancer survivors can identify important contributors to exercise intolerance which can be targeted for treatment.