18th IAA Humans in Space Symposium (2011)
2147.pdf
Smith W, Gilbrech R, Liao J, Weed B, Sourav P, Summers RL. Influence of
Microgravity on Left Ventricular Sphericity in a Finite Element Model of the Heart.
Background: There is concern regarding the long-term effects of microgravity exposure
on cardiac function with some evidence of a loss of ventricular mass. According to
Laplace’s law, the geometry of the ventricle is an important factor determining
segmental wall stress and inducing alterations in the structure of the myocardium. If
microgravity exposure results in a variation in the geometry of the ventricle, then we
might also expect some cardiac remodeling during extended spaceflights. In this study
we analyze the theoretical impact of microgravity on changes in the geometric
conformation of a finite element model (FEM) of the left ventricle (LV) attributed with
material properties consistent with myocardial tissue.
Methods: Mimics and 3-matic software were used to create a finite element mesh
model of the heart using the 3-dimensional geometry acquired from CT scans, MRI
scans, and cryosection images in the NIH Visible Human Project ® of the National
Library of Medicine. The myocardial mesh was exported to ABAQUS for comparison
analyses and the myocardial material properties were incorporated into the elements.
The Geometric Aspect Ratios (GAR) of the left ventricle were calculated and compared
as the LV length to width quotient during simulations of the upright anatomic diastolic
position in Earth’s gravity and in microgravity.
Results: The theoretical application of microgravity to the FEM model of the heart
resulted in a 3.6% lower GAR of the LV as compared to that calculated for Earth’s
gravity while the overall volume remained stable.
Conclusions: The geometry of the heart and its impact on the segmental wall stress
are a known driving force for cardiac remodeling. This study examined the theoretical
impact of microgravity exposure on the shape of the LV. Changes in ventricular
sphericity associated with local changes in the radius of curvature of the myocardial wall
were observed in simulated microgravity.