The use of shear rate-diameter dose-response curves as an alternative to the flow-mediated dilation test

Assessment of power spectral density of microvascular hemodynamics in skeletal muscles at very low and low-frequency via near-infrared diffuse optical spectroscopies

In this work, we used a hybrid time domain near-infrared spectroscopy (TD-NIRS) and diffuse correlation spectroscopy (DCS) device to retrieve hemoglobin and blood flow oscillations of skeletal muscle microvasculature. We focused on very low (VLF) and low-frequency (LF) oscillations (i.e., frequency lower than 0.145 Hz), that are related to myogenic, neurogenic and endothelial activities. We measured power spectral density (PSD) of blood flow and hemoglobin concentration in four muscles (thenar eminence, plantar fascia, sternocleidomastoid and forearm) of 14 healthy volunteers to highlight possible differences in microvascular hemodynamic oscillations. We observed larger PSDs for blood flow compared to hemoglobin concentration, in particular in case of distal muscles (i.e., thenar eminence and plantar fascia). Finally, we compared the PSDs measured on the thenar eminence of healthy subjects with the ones measured on a septic patient in the intensive care unit: lower power in the endothelial-dependent frequency band, and larger power in the myogenic ones were observed in the septic patient, in accordance with previous works based on laser doppler flowmetry.

Endothelial Function Assessment by Flow-Mediated Dilation Method: A Valuable Tool in the Evaluation of the Cardiovascular System

Cardiovascular diseases (CVDs) in the course of atherosclerosis are one of the most critical public health problems in the world. Endothelial cells synthesize numerous biologically active substances involved in regulating the functions of the cardiovascular system. Endothelial dysfunction is an essential element in the pathogenesis of atherosclerosis. Thus, the assessment of endothelial function in people without overt CVD allows for a more accurate estimate of the risk of developing CVD and cardiovascular events. The assessment of endothelial function is primarily used in scientific research, and to a lesser extent in clinical practice. Among the tools for assessing endothelial function, we can distinguish biochemical and physical methods, while physical methods can be divided into invasive and non-invasive methods. Flow-mediated dilation (FMD) is based on the ultrasound assessment of changes in the diameter of the brachial artery as a result of increased blood flow. FMD is a non-invasive, safe, and repeatable test, but it must be performed by qualified and experienced medical staff. The purpose of this paper is to present the literature review results on the assessment of endothelial function using the FMD method, including its methodology, applications in clinical practice and research, limitations, and future perspectives.

Effects of Intermittent Pneumatic Compression on Leg Vascular Function in People with Spinal Cord Injury: A Pilot Study

Objective: The purpose of this pilot study was to determine whether 60 mins of intermittent pneumatic compression therapy (IPC) could acutely increase leg blood flow-induced shear stress and enhance vascular endothelial function in persons with spinal cord injury (SCI). Design: Pretest with multiple posttests, within subject randomized control design. Setting: University of Southern Mississippi, Spinal Cord Injury Research Program within the School of Kinesiology, recruiting from the local community in Hattiesburg, Jackson, and Gulfport, MS. Participants: Eight adults with SCI (injury level: T3 and below; ASIA class A-C; age: 41±17 yrs). Interventions: A 60-min IPC session was performed in one leg (experimental leg; EXP), with the other leg serving as a control (CON). Outcomes Measures: Posterior-tibial artery shear rate (Doppler-ultrasound) was examined at rest, and at 15 and 45 mins during IPC. Endothelial function was assessed using the flow-mediated dilation (FMD) technique, before and after IPC. Results: Resting FMD (mm) was similar between legs at rest. A two-way repeated measures ANOVA (leg x time) revealed that during IPC, peak shear rate increased in the EXP leg (215±137 to 285±164 s^-1 at 15 mins; +39±29%, P = 0.03), with no change occurring in the CON. In addition, FMD significantly increased in the EXP leg (Pre IPC: 0.36±0.14 vs. Post IPC: 0.47±0.17 mm; P = 0.011, d = 0.66), with no change occurring in the CON leg. Conclusion: These preliminary findings suggests that IPC therapy may acutely increase leg shear stress within 15 mins, with a resultant moderate-large improvement in vascular endothelial function after 60 mins in people with SCI.

Exposure-response modeling of flow-mediated dilation provides an unbiased and informative measure of endothelial function

The brachial artery flow-mediated dilation (FMD) test is the most widely utilized method to evaluate endothelial function noninvasively in humans by calculating the percent change in diameter (FMD%). However, the underutilized velocity and diameter time course data, coupled with confounding influences in shear exposure, noise, and upward bias, make the FMD test less desirable. In this study, we developed an exposure-response, model-based approach that not only quantifies FMD based on the rich velocity and diameter data, it overcomes previously acknowledged challenges. FMD data were obtained from 15 apparently healthy participants, each exposed to four different cuff occlusion durations. The velocity response following cuff release was described by an exponential model with two parameters defining peak velocity and rate of decay. Shear exposure derived from velocity was used to drive the diameter response model, which consists of additive constriction and dilation terms. Three parameters describing distinct aspects of the vascular response to shear (magnitude of the initial constriction response, and magnitude and time constant of the dilation response) were estimated for both the individuals and population. These parameters are independent of shear exposure. Thus this approach produces identifiable and physiologically meaningful parameters that may provide additional information for comparing differences between experimental groups or over time, and provides a means to completely account for shear exposure.NEW & NOTEWORTHY While flow-mediated dilation (FMD) is a valuable tool for evaluating endothelial function, analytical challenges include confounding influences of shear exposure, upward bias, and underutilization of rich time course data collected during FMD testing. We have developed an exposure-response, model-based approach that quantifies endothelial function based on the velocity and diameter data and fully accounts for shear exposure. It produces physiologically meaningful parameters that may provide useful information for comparing differences between experimental groups or over time.