Imaging of Whole Body Oxygen Consumption and its Fick Determinants During Exercise: Real-Time Exercise CMR and Venous Oximetry

Motivation: There is a need for non-invasive approaches to determine the central (cardiac output, CO) and peripheral (arterio-venous oxygen difference, a-vO2diff) determinants of oxygen uptake (VO2) during exercise. Goal(s): Validate an approach (MRIFick) combining real-time cardiac magnetic resonance (CMR)-derived cardiac-output and real-time venous susceptometry-based oximetry (MROximetry, for deriving venous oxygen saturation, SvO2, in the inferior vena cava and the a-vO2diff) to calculate the VO2 during exercise. Approach: CMR and MROximetry scans were acquired with simultaneous pulmonary VO2 (reference standard) during progressive stepping exercise (50W increments to fatigue) in young adults (n=17). Results: MRIFick showed excellent agreement (R2=0.95) for measuring whole-body VO2 during stepping exercise. Impact: An MRI approach that combines real-time CMR with magnetic-susceptometry-based measures of SvO2 is feasible and allows for accurate quantification of peak VO2 and its Fick determinants (CO x a-vO2diff) without the need for invasive catheters.