Mechanics and composition of human subcutaneous resistance arteries in essential hypertension

Mechanical properties of arteries are altered in some pat models of hyperte nsion, and this may influence peripheral resistance and blood pressure as w ell as some of the complications of hypertension, It has usually been assum ed that arterial wall stiffness is increased in hypertension, although rece nt studies suggest that this may not necessarily be the case in large arter ies. We determined whether the mechanics of human resistance arteries are a ltered in hypertension. Subcutaneous resistance arteries (lumen diameter<30 0 mu m) were isolated from hypertensive and normotensive subjects of simila r ages (46+/-3 and 43+/-4 years, respectively). Vessels were mounted in a p ressurized myograph, deactivated, and exposed to intraluminal pressures ran ging from 3 to 140 mm Hg. At each pressure, lumen and media dimensions were measured. Media-to-lumen ratio and media width were greater in hypertensiv e vessels, reducing wall stress (P<0.01), whereas media cross section was s imilar in vessels from both groups. Isobaric elastic modulus (which is infl uenced by vessel geometry and by wall component stiffness) was lower in hyp ertensive vessels (P<0.01). Stiffness of wall components (slope of incremen tal elastic modulus versus stress, which is geometry-independent) was signi ficantly lower in hypertensive vessels (8.2+/-0.7) versus normotensive vess els (11.0+/-1.0, P<0.05), whereas distensibility was unchanged. Electron mi croscopic analysis of the media of the small arteries showed a greater coll agen to elastin ratio (P<0.05) in the media of vessels from hypertensive pa tients. In conclusion, the stiffness of wall components (slope of elastic m odulus versus stress) is not increased but is in fact decreased in subcutan eous resistance arteries from patients with mild essential hypertension. Re duced stiffness of resistance arteries from hypertensive patients does not appear to relate to changes in volume density of extracellular matrix compo nents but may be the result of changes in extracellular matrix architecture or cell-matrix attachment, which remains to be established.