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

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.

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.

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.

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.

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.