Age-related alterations of cardiac tissue microstructure and material properties in Fischer 344 rats

The cardiac aging process is accompanied by global mechanical dysfunction t hat reflects increased myocardial stiffness. Accordingly, age-related chang es in microscopic material properties of myocardium were delineated with hi gh-frequency ultrasound (US) (30 to 14 MHz) tissue characterization methods for aging Fischer 344 rats at 6 (adult), 18 (aged), and 24 (senescent) mon ths of age. The excised lateral wall of the left ventricle of rats (n = 10 per group) was insonified with a 50-MHz acoustic microscope for determinati on of integrated backscatter, backscatter coefficient and attenuation coeff icient. Histological and biochemical analyses for collagen content and card iac myocyte diameter were performed. Collagen concentration increased progr essively with age, with the greatest increments occurring from 6 to 18 mont hs (38.0 +/- 6.3 to 53.0 +/- 7.1 mg/g dry wt), and leveling off at 24 month s (60.0 +/- 7.4 mg/g dry wt). Tissue microscopic material properties also c hanged progressively from 6 to 24 months of age, as determined by US method s: integrated backscatter increased (-44.7 +/- 1.8 vs. -40.8 +/- 1.9 dB,p < 0.05), attenuation increased (47.1 +/- 5.9 to 65.3 +/- 7.8 dB/cm, p < 0.05 ), and the backscatter coefficient increased (0.73 +/- 0.16 x 10(-5) to 3.7 6 +/- 1.6 x 10(-5) cm(-1), p < 0.05), from 6 to 24 months of age in each ca se. Age-related alterations in indices of cardiac microscopic material prop erties were closely correlated with the changes in cardiac microstructure. Ultrasonic tissue characterization may prove to be a sensitive tool to moni tor changes in the cardiac microstructure, such as increased collagen depos ition, that occur within age-related diastolic dysfunction, (E-mail: saw@ h owdy.wustl.edu) (C) 2001 World Federation for Ultrasound in Medicine & Biol ogy.