Role of BMI and Venous Resistance in Modulation of Cardiac Filling.

Objective: Through our experiment studying the effect of supine exercise on conduit veins, we attempt to investigate the physiology of venous return, cardiac filling, and its relationship to BMI. Design: Uncontrolled longitudinal study. Setting: Single urban academic medical center. Subjects: Adult subjects free of cardiovascular disease, and without a history of abdominal surgery that might interfere with CT scan measurements of IVC size and no contraindications to performing near-maximal levels of exercise. Interventions: we studied 14 healthy subjects at supine rest, legs elevated and incremental levels of supine exercise. We calculated an index of venous resistance (VR), and measured aortic and IVC cross-sectional areas (CSA), transmitral filling parameters, and IVC ellipticity. The participants were dichotomized based on BMI: normal BMI ≤ 25 (n=6) and elevated BMI >25 (n=8). Measurements and main results: Measurements included: Hemodynamics, Transthoracic mitral inflow, Computed Tomography and BMI data. There was decreased IVC CSA in the elevated BMI group at each intervention (p=0.007). VR of the elevated BMI group was consistently higher at all interventions with a group effect noted 1.15 ± 0.14 cm H2O.min/L vs. 0.55 ± 0.15 cm H2O. min/L (p=0.011). Ellipticity was lower in the normal BMI group (p=0.032). EVTI during exercise was lower in the elevated BMI group 11.0 ± 0.90 vs. 15.8 ± 1.04 (p=0.004) and also correlated negatively with VR (r=-0.848 p=0.007). Conclusion: VR and ellipticity are higher; and IVC CSA is lower in the elevated BMI group. This study points to a negative effect of increasing BMI on cardiac filling due to diminutive IVC remodeling and extramural compression