MODELING THE INFLUENCE OF BODY-SIZE AND COMPOSITION ON M-MODE ECHOCARDIOGRAPHIC DIMENSIONS

The purpose of this study was to determine the optimal index for norma lizing left ventricular (LV) echocardiographic dimensions for differen ces in body size. M-mode echocardiograms defined LV internal dimension at end diastole (LVIDD) and LV wall thickness (LVWT) in 107 adults (5 9 male, 48 female). Allometric relations were assessed between cardiac dimensions (Y) and body size variables (X) of fat-free mass (FFM), he ight (H), body surface area (BSA), and fat mass (FM). Further to confi rmation of homogeneity of regression slopes, size exponents common to both genders were fitted by a log-linear model: In Y = In a + c.gender + b.lnX, where a is the proportionality coefficient, b is the size ex ponent, and c is the gender coefficient. For LVIDD, mean body size exp onents (95% confidence interval) were FFM0.35 (0.22-0.47), H-0.68 (0.3 2-1.03), and BSA(0.44) (0.26-0.62). For LVWT, the derived exponents we re FFM0.43 (0.20-0.65), H-0.65 (0-1.3), and BSA(0.56) (0.23-0.89). Bod y fatness (expressed by FM) had no influence on LV dimensions, with ex ponents not different from zero (P > 0.05). The root-mean-squares erro r from the separate regression models indicated that the FFM index was the optimal solution. Indexation of LV dimensions by H was associated with the greatest error. Because the 95% confidence interval for the FFM exponents included 0.33, we recommend that linear LV dimensions be indexed by the cube root of FFM. In the absence of FFM data, the root of BSA was found to be the best surrogate index.