BIOCHEMICAL CORRELATES OF AORTIC DISTENSIBILITY INVIVO IN NORMAL SUBJECTS

1. Non-invasive aortic compliance measurements have been used previous ly to assess the distensibility of the aorta in several pathological c onditions associated with increased cardiovascular risk. In adult pati ents with familial hypercholesterolaemia and those with growth hormone deficiency, aortic compliance has been found to correlate inversely w ith plasma cholesterol levels and age. We set out to establish if a re lationship existed between the biophysical measurement of aortic compl iance and biochemical variables in normal healthy adult subjects. 2. B lood pressure-corrected aortic distensibility, fasting insulin, insuli n-like growth factor-I, total cholesterol, low-density lipoprotein-cho lesterol, high-density lipoprotein-cholesterol and triacylglycerol wer e measured in 38 (18 males, 20 females) normotensive healthy adults. 3 . Blood pressure-corrected aortic distensibility was found to correlat e inversely with age (r=-0.67, P<0.001), low-density lipoprotein-chole sterol (r=-0.37, P<0.02) and the low-density lipoprotein-/high density lipoprotein-cholesterol ratio (r=-0.33, P<0.05) and positively with i nsulin-like growth factor-I (r=0.47, P<0.01). On separate analysis by sex, significant inverse correlations were observed in females between aortic distensbility and total cholesterol (r=-0.50, P<0.02), low-den sity lipoprotein-cholesterol (r=-0.55, P<0.01) and age (r=-0.74, P<0.0 01). A positive correlation was found between aortic distensibility an d insulin-like growth factor-I (r=0.48, P<0.05). On forced stepwise re gression analysis, however, only age (P<0.02) was found to be signific ant. In males, an inverse correlation was found between aortic distens ibility and age (r=-0.57, P<0.01), low-density lipoprotein-cholesterol (r=-0.51, P<0.05) and the low-density lipoprotein-/high-density lipop rotein-cholesterol ratio (r=-0.63, P<0.01). Positive correlations were observed between aortic distensibility and high-density lipoprotein-c holesterol (r=0.48, P<0.05) and insulin-like growth factor-I (r=0.48, P<0.05). On forced stepwise regression analysis the low-density lipopr otein-/high-density lipoprotein-cholesterol ratio (P<0.02) and age (P< 0.04) were found to be the only significant independent predictors of aortic distensibility in males. 4. In normal adult subjects insulin-li ke growth factor-I and high-density lipoprotein-cholesterol are associ ated with increased aortic distensibility, whereas low-density lipopro tein-cholesterol is associated with aortic stiffening. We suggest that the measurement of blood pressure-corrected aortic distensibility in normal, healthy subjects may potentially be a useful, non-invasive res earch tool for investigating the effect of biochemical factors on the biophysical properties of the aortic wall.