Interaction of macro- and microvascular function underlies brachial artery flow-mediated dilation in humans.

Brachial artery flow-mediated dilation (BAFMD) is induced by hyperemic wall shear rate (WSR) following forearm ischemia. In older adults, there appears to be a reduced brachial hyperemic WSR and altered stimulus-response relationship compared with young adults. However, it is unclear if an altered forearm microvascular response to ischemia influences brachial hyperemic WSR in older adults.

Microstructural Characterization of Resistance Artery Remodelling in Diabetes Mellitus.

Introduction: Microvascular remodelling is a symptom of cardiovascular disease. Despite the mechanical environment being recognized as a major contributor to the remodelling process, it is currently only understood in a rudimentary way.

Objective: A morphological and mechanical evaluation of the resistance vasculature in health and diabetes mellitus.

Intermittent compression induces transitory hypoxic stimuli, upstream vasodilation and enhanced perfusion of skin capillaries, independent of age and diabetes.

The benefit of enhanced shear stress to the vascular endothelium has been well-documented in conduit arteries but is less understood in skin microcirculation. The aim of this study was to provide physiological evidence of the vascular changes in skin microcirculation induced by intermittent pneumatic compression (IPC) of 1 s cuff inflation (130 mmHg) every 20 s to the palm of the hand for 30 min. The oxygenation and hemodynamics of dorsal mid-phalangeal finger skin microcirculation were assessed by laser Doppler fluximetry and reflectance spectroscopy before, during, and after IPC in 15 young (18-39 years old) and 39 older (40-80 years old) controls and 32 older subjects with type 2 diabetes mellitus.

Arterial wall shear rate response to reactive hyperaemia is markedly different between young and older humans.

Key Points: The vasodilatory response to reactive hyperaemia is impaired with advancing age, but it is unclear whether this is because of an altered wall shear rate (WSR) stimulus or an altered flow-mediated dilatation (FMD) response. Using new technology that allows detailed WSR measurement, we assessed the WSR-FMD response in healthy older people. Our data show that older people have a markedly altered and diminished WSR response to reactive hyperaemia compared to young people, but reduced WSR alone does not fully explain reduced FMD.

Brachial artery vasodilatory response and wall shear rate determined by multigate Doppler in a healthy young cohort.

Wall shear rate (WSR) is an important stimulus for the brachial artery flow-mediated dilation (FMD) response. However, WSR estimation near the arterial wall by conventional Doppler is inherently difficult. To overcome this limitation, we utilized multigate Doppler to accurately determine the WSR stimulus near the vessel wall simultaneously with the FMD response using an integrated FMD system [Ultrasound Advanced Open Platform (ULA-OP)].

The role of perfusion in the oxygen extraction capability of skin and skeletal muscle.

Oxygen extraction (OE) by all cells is dependent on an adequate supply of oxygen in proximal blood vessels and the cell's need and ability to uptake that oxygen. Here the role of blood flow in regulating OE in skin and skeletal muscle was investigated in lean and obese men. OE was derived by two optical reflectance spectroscopy techniques: 1) from the rate of fall in mean blood saturation during a 4 min below knee arterial occlusion, and thus no blood flow, in calf skin and skeletal muscle and 2) in perfused, unperturbed skin, using the spontaneous falls in mean blood saturation induced by vasomotion in calf and forearm skin of 24 subjects, 12 lean and 12 obese.

Blood Oxygen Saturation After Ischemia is Altered With Abnormal Microvascular Reperfusion.

Objective: We have previously described a distinct abnormality in the cutaneous microcirculation that is characterized by an abnormal reperfusion response following an ischemic stimulus. We investigated the physiological significance of this abnormality; by measuring microvascular perfusion and blood oxygen saturation in groups stratified by three distinct reperfusion responses.

Methods: Cutaneous microvascular reperfusion after four minutes of arterial occlusion above the ankle was measured on the foot using laser Doppler fluximetry and optical reflectance spectroscopy in almost 400 adults.

An association between vasomotion and oxygen extraction.

Vasomotion is defined as a spontaneous local oscillation in vascular tone whose function is unclear but may have a beneficial effect on tissue oxygenation. Optical reflectance spectroscopy and laser Doppler fluximetry provide unique insights into the possible mechanisms of vasomotion in the cutaneous microcirculation through the simultaneous measurement of changes in concentration of oxyhemoglobin ([HbO(2)]), deoxyhemoglobin ([Hb]), and mean blood saturation (S(mb)O(2)) along with blood volume and flux. The effect of vasomotion at frequencies <0.

Is mean blood saturation a useful marker of tissue oxygenation?

Increasingly we are monitoring the distribution of oxygen through the microcirculation using optical techniques such as optical reflectance spectroscopy (ORS) and near-infrared spectroscopy. Mean blood oxygen saturation (S(mb)O(2)) and tissue oxygenation index measured by these two techniques, respectively, evoke a concept of the measurement of oxygen delivery to tissue. This study aims to establish whether S(mb)O(2) is an appropriate indicator of tissue oxygenation.