Physiological Factors Important to Cardiorespiratory Fitness are Similar Between Breast Cancer Survivors and Controls

Abstract

Rationale 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. Purpose To assess differences in cardiorespiratory fitness and physiological factors (cardiac, pulmonary, and muscle oxygenation) between breast cancer survivors and age and BMI-matched control groups. Methods To examine this, 23 female breast cancer survivors (50 ± 9 yrs; 25.5 ± 2.9 kg/m2), and 23 female age and BMI-matched controls (49 ± 9 yrs; 25.7 ± 4.6 kg/m2), underwent a maximal exercise test on a cycle ergometer with cardiac function, pulmonary function, and muscle oxygenation evaluated at baseline and at peak exercise (VO2peak). Cardiac variables included stroke volume (SV), heart rate (HR), and cardiac output (Q). SV was assessed from aortic blood flow waveforms (3 cardiac cycles) obtained via Doppler echocardiography using a pedoff probe placed on the suprasternal notch. SV was calculated as = π × (LVOT2/2) × VTI, where LVOT = left ventricular outflow tract diameter and VTI = subvalvular velocity time integral. Q was calculated as SV × HR. Both SV and Q were indexed to body surface area. Pulmonary function variables included the oxygen uptake efficiency slope (OUES) and ventilation to carbon dioxide production slope (VE/VCO2 slope)) acquired from indirect calorimetry during the peak cycling exercise test. Muscle oxygenation variables (oxygenated (HbO2), deoxygenated (HHb) and total hemoglobin (Hb), and tissue saturation index (TSI)) were measured non-invasively with near-infrared spectroscopy (NIRS) from the rectus femoris. Results VO2peak was similar between groups. Both groups similarly increased all cardiac variables (HR, SV, SVindex, Q, and Qindex) at peak exercise compared to baseline (p<0.001). Breast cancer survivors, however, had higher HR and lower SVindex values (group effect, p<0.05). Breast cancer survivors also had similar OUES and VE/VCO2 slope values compared to the control group. TSI decreased and Hb and HHb increased at peak exercise compared baseline (p<0.001), with similar responses observed in both groups. Conclusion: Our data suggest breast cancer survivors do not exhibit differences in cardiac, pulmonary, and muscle function variables at peak exercise compared to controls, when both groups have similar cardiorespiratory fitness. It appears cardiorespiratory fitness may not be as consistently attenuated in breast cancer survivors as previously reported in the literature, and warrants further examination.