Towards a more comprehensive assessment of cardiovascular fitness - magnetic resonance augmented cardiopulmonary exercise testing (MR-CPEX)
© Pandya et al; licensee BioMed Central Ltd. 2013
Published: 30 January 2013
Assessment of exercise intolerance is important in patients with cardiovascular disease. Traditionally, this is achieved by measuring maximum VO2 during cardio-pulmonary exercise testing (CPEX). However, this cannot discriminate between cardiac output and tissue extraction problems. A better approach may be to assess VO2 and cardiac output simultaneously (which also allows calculation of tissue extraction). Thus, we developed MR augmented CPEX in which real- time PCMR is performed at the same time as respiratory gas analysis. The purpose of this study was to validate this novel technology.
Ten volunteers underwent MR-CPEX in a 1.5T scanner using a ramped protocol on an MR compatible Ergometer. All volunteers exercised till exhaustion and the total test period was 9 minutes. Expired gases and respiratory flow data were collected with a calibrated MR compatible respiratory analysis system. Using this data continuous VO2, VCO2 and Ve were calculated for the whole test period. Aortic flow was measured continuously during the test period using real-time UNFOLD-SENSE spiral PCMR (spatial resolution: 2.5x2.5 mm, temporal resolution: 30 ms, 16000 frames). Flow data was segmented using a semi-automated technique to calculate cardiac output during exercise. Cardiac output and VO2 were used to calculate arterio-venous oxygen content gradient (tissue oxygen extraction). All volunteers also underwent traditional bicycle CPEX for comparison.
This study shows that MR-CPEX is a viable technique that can provide a comprehensive assessment of all the components of exercise physiology. During MR-CPEX only submaximal exercise is possible, both due to movement limitation and lack of stroke volume augmentation in the supine position. Nevertheless, there was as strong correlation between traditional CPEX and MR-CPEX. This implies that MR-CPEX does measure useful parameters that are linked to maximal exercise. We believe that the ability to fully measure the cardio-pulmonary and peripheral response to exercise will allow better assessment of exercise intolerance in many cardiac diseases.
British Heart Foundation Project Grant. Dr Vivek Muthurangu and Dr Bejal Pandya.
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