Physiological Factors Impacting Fitness in Breast Cancer Survivors

Breast cancer is the most common type of cancer in the United States, and breast cancer survivors have a high prevalence of cardiovascular disease (CVD) and reduced cardiorespiratory fitness. Cardiorespiratory fitness is a major predictor of CVD and all-cause mortality in the general population, and an important predictor of survival in breast cancer survivors. However, the physiological factors that contribute to reduced cardiorespiratory fitness in breast cancer survivors have not been completely elucidated yet. The purpose of this study was to evaluate what primary physiological factors (cardiac, pulmonary, and muscle function) contribute to reduced cardiorespiratory fitness in breast cancer survivors. To examine this, 23 breast cancer survivors (50 ± 9 yrs; 25.5 ± 2.9 kg/m2), and 23 age-BMI matched controls (49 ± 9 yrs; 25.7 ± 4.6 kg/m2), underwent a cycling exercise test and variables of cardiac, pulmonary and muscle function were evaluated at baseline and at peak exercise. Cardiac hemodynamics (stroke volume (SV), heart rate (HR), cardiac output (CO) were evaluated and calculated using ultrasonography. Pulmonary function was evaluated using the oxygen uptake efficiency slope (OUES) and ventilation to carbon dioxide production slope (VE/VCO2 slope)) during the peak cycling exercise test. Muscle oxygenation variables (oxygenated (HbO2), deoxygenated (HHb) and total hemoglobin (Hb), and tissue oxygenation index (TOI)) were measured non-invasively with near-infrared spectroscopy (NIRS). Breast cancer survivors had similar VO2peak, OUES, VE/VCO2 slope values compared to the control group. All the hemodynamic variables (HR, SV, SVindex, CO, COindex) increased at peak exercise compared to baseline (p<0.001). Group effects were detected for HR and SVindex, with breast cancer survivors having higher HR and lower SVindex (p<0.05) values, but both groups had the same cardiac hemodynamic responses from baseline to peak exercise. TOI decreased at peak exercise compared to baseline (Table 7 p<0.001), and Hb and HHb increased at peak exercise compared baseline (Table 7, p<0.001), and both groups responded the same from baseline to peak exercise. The results of our study suggest that breast cancer survivors do not exhibit differences in cardiac, pulmonary, and muscle function at peak exercise compared to controls, at least when they have similar cardiorespiratory fitness.