Relationship between leg lean mass Z-score and cardiac output at exercise as measured by exercise cardiac magnetic resonance imaging

Abstract

Background We previously showed that leg lean mass Z-score (LLMZ) correlates with metabolic exercise performance in Fontan patients. However, the mechanism by which leg lean mass influences exercise is not clear since LLMZ does not correlate with ventricular function or cardiac output at rest. We hypothesized that LLMZ would correlate with cardiac output at exercise and the change in cardiac output from rest to exercise. Methods Thirteen patients had leg lean mass measured by dual energy x-ray absorptiometry within mean of 40 (range 0-258) days of completing an exercise cardiac magnetic resonance (CMR) protocol. LLMZs were generated from healthy reference data. Ventricular volumes and phase contrast flow measurements (all indexed to body surface area) of the ascending (Ao) and descending (DAo) aorta, and superior vena cava (SVC) were obtained by CMR at rest and just after supine ergometer exercise to a heart rate associated with anaerobic threshold (determined by previous metabolic exercise test). Change in systemic flow (Qs = SVC + DAo) and indexed ventricular output (CI) during exercise, as well as baseline and peak exercise measures of Qs and CI were compared to LLMZ by linear regression.