Simulated upright exercise cardiac magnetic resonance imaging with a novel lower body negative pressure pant suit: A pilot and feasibility study (RF_SA_475)

Exercise cardiac magnetic resonance imaging (cMRI) offers several major advantages over contemporary stress imaging approaches, including improved spatial resolution and the absence of ionizing radiation. A major limitation of exercise cMRI however, is the physical constraints of the scanner itself, forcing subjects to exercise while laying supine.  Not only is this body position incongruent with typical activity patterns of daily living, but being supine causes a major hemodynamic shift toward the central circulation, minimizing the overall cardiac response to exercise, and potentially masking clinically relevant changes in cardiac systolic and diastolic function.

Methods: To overcome this limitation, we constructed lower body negative pressure (LBNP) pants (Figure 1A) based on the mobile LBNP suit for spaceflight. This design simulates normal orthostatic stress caused by gravity during upright exercise while allowing for dynamic leg motion during exercise within the MRI bore. Imaging was performed using a 3T Phillips MRI scanner. Exercise was performed using an MR compatible ergometer (Cardio Step, Ergospect GmbH, Innsbruck, Austria) with and without a LBNP target of -35 mmHg to compare the hemodynamic response. Volumetric data were measured from a stack of short axis cine images spanning the length of the left ventricle from base to apex.

Results: Six male participants ranging in age from 18 to 31 years were included in this investigation. As illustrated in Figure 1, in the absence of LBNP, only modest changes in left ventricular end-diastolic volume (LVEDV) and end-systolic volume (LVESV) were observed, contributing to a 9+15mL/m² increase in stroke volume (LVSV) with exercise.  With LBNP, LVEDV and LVESV decreased by 18+24 mL/m² and 8+9 mL/m², at rest, respectively. Exercise-LBNP returned LVEDV within 98+23% of baseline values, while LVESV continued to decrease with exercise, resulting in a 17+15 mL/m² increase in LVSV.

Conclusion: To our knowledge, these are the first data to report the exercise cMRI hemodynamic response during lower body negative pressure. That the dynamic range for stroke volume was almost doubled under orthostatic stress highlights the importance of performing exercise cMRI under conditions that best simulate normal activities of daily living. More work is needed to confirm these early results and extend this work to clinical populations.