A=8.2%);
HR (Alow= 0.21±0.09, Ahigh = 0.15±0.07, p=0.031,
A=43%);
CC (Alow = 0.23±0.08, Ahigh = 0.14±0.07, p<0.001,
A=68%).
(Authors 1, 2): Graduate School of Biomedical Engineering, University of New South Wales
Images of the aortic elastin network display a textural pattern. The degree of organisation of this elastin structure can be characterised by its fractal dimensions which are used to produce a Directional Fractal Curve (DFC). The DFC parameters take structural orientation into account and are used to quantify the degree of organisation of the elastin network. Previous scanning electron microscopy studies indicate that structural disorganisation increases with age. We used light microscopy sections of paraffin-embedded aortic tissue, stained for elastin, to compare images from a range of animals (n=35) with different heart rates (40-203 beats/min) and lifespans (3-45 years). Fractal texture analysis of light microscopy sections has not been reported to our knowledge. Animals were ranked according to age, heart rate (HR) and total number of cardiac cycles (CC), a function of both age and HR. Each ranked set was divided into two groups for comparison of the DFC amplitude
(A): Age [young (8.8±3.6, n=17) versus old (25.6±11.5, n=18)];
HR [low (68±20, n=19) versus high (151±37, n=16)];
CC [low (3.7 x 108±1.5 x 108, n=17) versus high (1.6 x 109±1.0 x 109, n=18)].
Results were:
Age (Ayoung = 0.19±0.07, Aold = 0.18±0.11, p=NS, A=8.2%);
HR (Alow= 0.21±0.09, Ahigh = 0.15±0.07, p=0.031, A=43%);
CC (Alow = 0.23±0.08, Ahigh = 0.14±0.07, p<0.001, A=68%).
Conclusions: (a) fractal texture analysis in combination with light microscopy is a valuable tool for quantifying the degree of structural disorganisation of aortic elastic tissue; (b) this structural disorganisation is not merely age-dependent, but is due to the combined effects of heart rate and age.