Noninvasive measurement of shear rate in autologous and prosthetic bypass grafts

Low Carotid Artery Wall Shear Stress is Associated with Significant Coronary Artery Disease in Patients with Chest Pain

AIM

To investigate the relationships among carotid wall shear stress (WSS), carotid intima-media thickness (IMT), and total plaque area (TPA) using ultrasound (US) in the common carotid artery (CCA) in patients with suspected coronary artery disease (CAD).

METHODS

Carotid artery US was performed in 950 patients with suspected CAD, and mean IMT, TPA, and hemodynamic parameters of CCA, including peak and mean WSS, were measured. We analyzed the carotid parameters according to the presence of CAD and the predictive values of WSS and TPA for the presence of significant CAD.

RESULTS

Compared with patients without CAD (n=667), patients with CAD (n=283) demonstrated significantly higher mean IMT (0.66 vs. 0.74 mm, p ＜ 0.001), TPA (0.13 vs. 0.20 cm(2), p=0.002), and beta stiffness index (5.12 vs. 5.60, p=0.045) and lower mean WSS (2.59 vs. 2.23 dyne/cm(2), p ＜ 0.001). Mean WSS revealed significant negative correlations with the beta stiffness index (r=-0.116, p ＜ 0.001), mean IMT (r=-0.193, p=0.007), and TPA (r =-0.296, p ＜ 0.001). Mean WSS, mean IMT and TPA revealed significant difference with respect to CAD severity (for all p ＜ 0.001). Age [OR, 1.038 (95% CI, 1.010-1.066), p=0.007], diabetes mellitus [1.606 (1.194-1.807), p= 0.011], smoking [1.758 (1.564-1.866), p ＜ 0.001], carotid TPA [2.615 (1.320-5.183), p=0.006], and mean WSS [0.554 (0.371-0.838), p=0.005] were significant CAD predictors.

CONCLUSIONS

In patients with chest pain, low local shear stress and high plaque burden in the carotid arteries were significant CAD predictors. These findings indicate that carotid WSS has a role as an index of atherosclerosis and serves as a predictor of significant coronary atherosclerosis.

Wall shear stress in hypertensive patients is associated with carotid vascular deformation assessed by speckle tracking strain imaging

Introduction

Wall shear stress (WSS) is critically important in both vascular remodeling and atherosclerosis. Carotid intima-media thickness (IMT) and deformation parameters have been used as relevant indicators of carotid atherosclerosis. This study aimed to investigate the relationships between hemodynamic parameters in the common carotid artery (CCA) and the severity of carotid atherosclerosis in untreated hypertensive patients.

Methods

Carotid artery ultrasound was performed in 100 untreated hypertensive patients. Morphologic and hemodynamic parameters of the CCA, including peak and mean WSS, global circumferential strain, peak posterior radial strain assessed by two-dimensional speckle tracking method, and IMT, were measured.

Results

In patients with hypertension, there were significant correlations between carotid strain parameters and peak/mean WSS. Stepwise multiple regression analysis for carotid strain parameters after adjustment for age, carotid IMT, and brachial pulse wave velocity showed that peak WSS was an independent determinant of peak posterior radial strain (p = 0.009) and global circumferential strain (p = 0.002).

Conclusions

These findings indicate that local shear stress is associated with carotid vascular deformation, which could be an underlying mechanism for the progression of atherosclerosis.

Electronic supplementary material

The online version of this article (doi:10.1186/2056-5909-20-10) contains supplementary material, which is available to authorized users.

Fontan Procedure: old lessons and new frontiers

The Fontan procedure is an operation created for patients with single ventricular physiology. These patients have the potential to survive well into adulthood, however new problems can arise. Various topics, including physiological constraints, patient care, morbidity and clinical outcomes are discussed. The aim of this review is to identify current topics within the care of the Fontan patient population for the physician not comfortable with their unique physiology and complications.

Numerical Model Study of Flow Dynamics through an End-to-Side Anastomosis: Choice of Anastomosis Angle and Prosthesis Diameter

The purpose of this numerical model study was to determine the angle of anastomosis and prosthesis-to-artery diameter ratio that theoretically limits development of myointimal hyperplasia (MIH). Blood flow patterns were investigated in a model simulating a distal end-to-side anastomosis on a 2-mm-diameter artery. Tests were carried out under steady and pulsatile flow conditions with and without taking into account the non-Newtonian behavior of blood and compliance. The wall shear stress gradient (WSSG), a potential factor for development of MIH, was analyzed as a function of the angle of anastomosis (18 degrees , 25 degrees , 35 degrees , and 45 degrees ) and prosthesis diameter (4, 5, and 6 mm). The angle of anastomosis that minimized WSSG was 18 degrees . Prosthesis diameter had no effect on WSSG, with similar results for all three diameters. These findings suggest that surgeons should choose as acute an angle of anastomosis as possible. Prosthesis diameter played no role in reducing WSSG values.

Diabetes and distal access location are associated with higher wall shear rate in feeding artery of PTFE grafts

BACKGROUND

Surgical creation of permanent vascular access for haemodialysis leads to considerable haemodynamic changes. They could be implicated in the pathogenesis of access complications, which limit access survival, especially in diabetics. Physiologically, the relation between arterial diameter and blood velocity is maintained by wall shear stress (WSS), which is directly related to both blood viscosity and wall shear rate (WSR = blood velocity/internal diameter). Because of methodological difficulties, WSR is used as a measure of WSS. Extremely high values of WSS might induce hypercoagulable states, which might contribute to access thrombosis. We performed a study, which was aimed to (i) describe WSR values in feeding arteries of various polytetrafluoroethylene access types and (ii) prove that diabetic patients have higher WSR than non-diabetics.

METHODS

A linear-array 11 MHz probe of SONOS 5500 (Phillips, USA) was used to obtain blood velocity and internal diameter in the feeding arteries of radial or brachial polytetrafluoroethylene grafts. WSR was calculated as 4 x blood velocity/internal diameter. We compared observed values of WSR according to feeding artery (radial vs brachial artery) and according to diabetic status using unpaired t-test.

RESULTS

We included 106 patients (58 non-diabetic and 48 diabetic) in the study. WSR was significantly higher in radial arteries compared with brachial arteries independent of diabetes status. Diabetic subjects had significantly higher WSR in both radial and brachial arteries.

CONCLUSIONS

Diabetes mellitus and distal vascular access creation are associated with higher WSR in the feeding artery. This could be of relevance in the pathogenesis of access complications, e.g. thrombosis, and thus lower patency rates in diabetic patients.