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.

In Vivo Dynamic Deformation of the Mitral Valve Annulus

“…A number of previous studies have attempted to, in part, characterize some degree of annular motion. Stoylen et al ,43 Caiani et al ,9 and George et al 15 all utilized a form of Doppler tissue imaging to determine annular velocity, strain, and strain rate. These studies, however, were limited to a 2D analysis of annular deformation and relied on image tracking to calculate the kinematic descriptors.…”

“…In particular, the annulus, a dense connective tissue ring surrounding the MV orifice, is known to deform considerably during the cardiac cycle 46. Yet, despite extensive studies2,9,15,19,23,28,29,46 a complete description of MV annular kinematics over a cardiac cycle remains lacking. In the present work, we utilized high fidelity 3D positions of ultrasound transducers implanted in the ovine MV annulus to quantify the complete 3D kinematics of the MV annulus under normal cardiac conditions.…”

Gravity, the hydrostatic indifference concept and the cardiovascular system

“…With acceleration forces other than 9.81 m/s 2 , the pattern of hydrostatic pressure gradients, and conceivably also hydrostatic indifference locations, would be altered. Such effects may come into play for short time periods, such as in parabolic flight (Caiani et al 2007), and for micro-, hypo-, or hypergravity conditions of longer duration. Moreover, experimental data on pertinent hydrostatic indifference point changes have not been gathered.…”

Effect of Position Changes on Myocardial Velocity in Healthy Subjects Evaluated by Tissue Doppler Echocardiography*

“…1 It allows recording of myocardial peak systolic velocity (Sm), peak early diastolic velocity (Em), and peak late diastolic velocity (Am). 3 A large number of studies have investigated the load dependency of tissue velocity using a variety of maneuvers to alter preload (i.e., saline loading, lower body negative pressure, pharmacological maneuvers, blood volume reduction). 3 A large number of studies have investigated the load dependency of tissue velocity using a variety of maneuvers to alter preload (i.e., saline loading, lower body negative pressure, pharmacological maneuvers, blood volume reduction).…”

“…2 The data on the influence of preload on tissue Doppler velocities are conflicting. [2][3][4][5][6] The effects of postural changes on myocardial tissue Doppler velocities in healthy subjects have previously been studied. [2][3][4][5][6] The effects of postural changes on myocardial tissue Doppler velocities in healthy subjects have previously been studied.…”