Role Of Arterial Smooth Muscle Tone And Geometry In The Regulation Of Peripheral Conduit Artery Mechanics By Shear Stress

Abstract

1. Although arterial blood flow is recognized as an important modulator of vascular tone and geometry, the effect of acute changes in shear-stress on conduit artery mechanics has not been fully investigated in humans because of technical limitations. 2. To assess, respectively, the effects of decreases and increases in flow and shear stress on radial artery tone and mechanics, arterial pressure (photoplethysmography), total blood viscosity, radial artery internal diameter, wall thickness (echotracking) and blood flow (Doppler) were measured in healthy volunteers (mean (+/-SEM) age 25 +/- 1 years) during a distal flow arrest (n=12) and hand skin heating (n=18). 3. Radial artery flow decreased from 31 +/- 4 to 7 +/- 1 10(-3) L/min during distal flow arrest (P< 0.001) and increased from 10 +/- 2 to 22 +/- 4 and 69 +/- 6 10(-3) L/min during heating (P < 0.001). At mean arterial pressure, these changes in flow were respectively associated with a parallel flow-dependent reduction and increase in diameter and midwall stress. There was no significant modification in mean elastic modulus. Compliance did not change when flow decreased and only increased at the highest level of flow. Finally, the cross-sectional compliance and incremental modulus were fitted as functions of midwall stress. The decrease in flow was associated with an upward shift of the modulus-midwall stress curve and a downward shift of the compliance-midwall stress curve. The increase in flow was associated with a downward shift of the modulus-midwall stress curve and an upward shift of the compliance-midwall stress curve at each level of wall shear stress. 4. By using two different procedures, we obtained similar results concerning the direct effects of increases and decreases in flow on stiffness of the arterial wall and on arterial compliance and demonstrated the presence of a flow-dependent regulation of arterial smooth muscle tone of peripheral conduit arteries in humans.

Early stage detection of conduit artery endothelial dysfunction in patients with type 1 diabetes

“…36 This hypothesis is consistent with the inappropriate adaptation of radial artery mechanics in response to the increase in flow in uncomplicated patients, which is also dependent on EDHF release. 16 Since cytochrome-related EDHF displays numerous vascular protective biological properties, 14,37 additional experiments are warranted to characterise in vivo during type 1 diabetes the evolution of the balance between NO and this EDHF using invasive pharmacological testing. This could lead to the development of a new pharmacological approaches to reverse endothelial dysfunction and enhance vascular protection in type 1 diabetes.…”

“…The diameter-shear stress relationships were constructed in type 1 diabetic patients and control subjects with similar increase in shear stress to compare these two groups at the same level of stimulus. 13,14,16,17 In addition, the adaptation of arterial mechanics to flow increase was evaluated in these subjects by the calculation of arterial compliance at 34°C and 44°C. In this respect, from the values of arterial pressure (p), internal diameter (d), and wall thickness (h), the cross-section (S)-pressure curve was adjusted as S=a[p/2+tang…”

“…r e /r)²/(r e ²-r i ²) where r e and r i were the external and internal radii, respectively, and i the radius at midwall (r=(r e +r i )/2). 16,17 Then, the compliancemidwall stress curves were constructed at 34°C and 44°C to assess the effect of flow increase in uncomplicated diabetic patients and controls at identical levels of wall-loading conditions, i.e. suppressing the confounding effects of changes in arterial geometry or pressure.…”

“…16,17 This is particularly important since this adaptation mainly contributes to maintaining an appropriate arterial conductance and ventricular vascular coupling, in particular during exercise. 16,17 Therefore, in present study we were prompted to evaluate whether hand skin heating may facilitate the early detection of conduit artery endothelial dysfunction in type 1 diabetic patients, as compared with post-ischaemic hyperaemia.…”

Physiological Society Symposium – the Athlete's Heart

“…In normal healthy individuals, acute decreases and increases in shear stress increased and decreased vascular tone in the radial artery, respectively (Joannides et al 2001) , increased the cross-sectional area of the ascending and abdominal aortas by 16 % and 24 %, respectively (Miyachi et al 1998). Twelve weeks of more moderate walking exercise (60-80 % of maximum heart rate) for 40-50 min a day, 5-7 days per week, increased diameter and intima-media thickness of the femoral artery by 9 % and 14 %, respectively (Dinenno et al 2001).…”