Real-time CMR combined with cardiopulmonary exercise testing enables integrated assessment of cardiac function during exercise

Abstract

Background Cardiopulmonary exercise testing (CPET) is the gold standard for assessing cardiopulmonary responses to physical stress. Real-time magnetic resonance imaging (RT-MRI) enables continuous cardiovascular imaging during free breathing (FB) and dynamic exercise. Objective This study aimed to develop a clinically applicable, easy-to-use MR-CPET protocol using user-friendly postprocessing software and to describe preliminary physiological observations in healthy subjects, forming the basis for future clinical applications. Material and Methods Healthy adults (n = 12) underwent conventional cine cardiac magnetic resonance imaging (CMR) and cardiac RT-MRI at rest and during submaximal exercise in a 1.5 T MR scanner. The protocol included short-axis cine imaging for volumetry and phase-contrast imaging for aortic flow quantification. CPET was performed using an MR-compatible spirometry and a supine exercise setup enabling continuous measurement of respiratory airflow and gas exchange during image acquisition and simultaneous exercise. Data processing included automated spirometry analysis, temporal synchronization with RT-MRI, and ECG- and respiratory-based binning for volumetric reconstruction. Indexed oxygen consumption (VO₂i) and cardiac index (CI) were used to calculate the arteriovenous oxygen difference (a-vO2 diff) according to the Fick equation. Participant comfort was assessed. Results The examination was well tolerated, with only minor discomfort related to the spirometry mask. RT-MRI showed strong agreement with conventional cine MRI for left ventricular volumes and ejection fraction at rest. Submaximal exercise significantly increased heart rate and ventilation, with concomitant increases in VO2i (201- 309 mL/min/m2) and CI (3.38- 4.24 L/min/m2), while ventricular volumes slightly decreased and ejection fraction remained unchanged. The calculated a-vO2 diff increased from 5.9 to 7.3 mL/dL, indicating enhanced peripheral oxygen extraction. Data conclusion Combined CPET and cardiac RT-MRI using the presented user- and participant-friendly setup enables integrated assessment of cardiopulmonary performance and cardiovascular function during submaximal exercise and provides physiologically plausible Fick-derived measures of oxygen transport and utilization.