Evaluation of alterations on mitral annulus velocities, strain, and strain rates due to abrupt changes in preload elicited by parabolic flight

Abstract

We tested the hypothesis that in normal subjects, cardiac tissue velocities, strain, and strain rates (SR), measured by Doppler tissue echocardiography (DTE), are preload dependent. To accomplish it, immediately preceding image acquisition, reversible, repeatable, acute nonpharmacological changes in preload were induced by parabolic flight. DTE has been proposed as a new approach to assess left ventricular regional myocardial function by computing tissue velocities, strain, and SR. However, preload dependence of these parameters in normal subjects still remains controversial. DTE images (Philips) were obtained in 10 normal subjects in standing upright position at normogravity (1 Gz), hypergravity (1.8 Gz), and microgravity (0 Gz) with and without -50 mmHg lower body negative pressure (LBNP). Myocardial velocity curves in the basal interventricular septum were reconstituted offline from DTE images, from which peak systolic (S'), early (E') and late (A') diastolic velocities, SR, and peak systolic strain (PSepsilon) were measured and averaged over four beats. At 1.8 Gz (reduced venous return), S', E', and A' decreased by 21%, 21%, and 26%, respectively, compared with 1-Gz values, while at 0 Gz (augmented venous return), E', A', and PSepsilon increased by 57%, 53%, and 49%, respectively. LBNP reduced E' and PSepsilon. In conclusion, our results were in agreement with those obtained in animal models, in which preload was changed in a controlled, acute, and reversible manner, and image acquisition was performed immediately following preload modifications. The hypothesis of preload dependence was confirmed for S', E', A', and PSepsilon, while SR appeared to be preload independent, probably reflecting intrinsic myocardial properties.