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

Association of changes of retinal vessels diameter with ocular blood flow in eyes with diabetic retinopathy

We investigated morphological changes of retinal arteries to determine their association with the blood flow and systemic variables in type 2 diabetes patients. The patients included 47 non-diabetic retinopathy eyes, 36 mild or moderate nonproliferative diabetic retinopathy (M-NPDR) eyes, 22 severe NPDR (S-NPDR) eyes, 32 PDR eyes, and 24 normal eyes as controls. The mean wall to lumen ratio (WLR) measured by adaptive optics camera was significantly higher in the PDR groups than in all of the other groups (all P < 0.001). However, the external diameter of the retinal vessels was not significantly different among the groups. The mean blur rate (MBR)-vessel determined by laser speckle flowgraphy was significantly lower in the PDR group than in the other groups (P < 0.001). The WLR was correlated with MBR-vessel (r = − 0.337, P < 0.001), duration of disease (r = 0.191, P = 0.042), stage of DM (r = 0.643, P < 0.001), systolic blood pressure (r = 0.166, P < 0.037), and presence of systemic hypertension (r = 0.443, P < 0.001). Multiple regression analysis demonstrated that MBR-vessel (β = − 0.389, P < 0.001), presence of systemic hypertension (β = 0.334, P = 0.001), and LDL (β = 0.199, P = 0.045) were independent factors significantly associated with the WLR. The increased retinal vessel wall thickness led to a narrowing of lumen diameter and a decrease in the blood flow in the PDR group.

Understanding the Dialysis access Steal Syndrome. A Review of the Etiologies, Diagnosis, Prevention and Treatment Strategies

Distal hypoperfusion ischemic syndrome (DHIS), commonly referred to as hand ischemia or “steal” after dialysis access placement, occurs in 5–10% of cases when the brachial artery is used, or 10 times that of wrist arteriovenous fistulas (AVFs) using the radial artery. It is typically seen in elderly women with diabetes, and may carry severe morbidity including tissue or limb loss if not recognized and treated. Three distinct etiologies include (1) blood flow restriction to the hand from arterial occlusive disease either proximal or distal to the AV access anastomosis, (2) excess blood flow through the AV fistula conduit (true steal), and (3) lack of vascular (arterial) adaptation or collateral flow reserve (ie atherosclerosis) to the increased flow demand from the AV conduit. These three causes of steal may occur alone or in concert. The diagnosis of steal is based on an accurate history and physical examination and confirmed with tests including an arteriogram, duplex Doppler ultrasound (DDU) evaluation with finger pressures and waveform analysis. Treatment of steal includes observation of developing symptoms in mild cases. Balloon angioplasty is the appropriate intervention for an arterial stenosis. At least three distinct surgical corrective procedures exist to counteract the pathophysiology of steal. The ultimate treatment strategy depends on severity of symptoms, the extent of patient co-morbidity, and the local dialysis access technical team support and skills available.

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.

New techniques for determining the longitudinal effects of local hemodynamics on the intima-media thickness in arteriovenous fistulae in an animal model

Remodeling in the arteriovenous fistulas (AVFs) is believed to be a hemodynamic-driven process, which results in extreme changes in the diameter and intima-media thickening (IMT) of vessels over time. This study aims to describe the successful development of techniques that enabled correlation of changes in local and longitudinal wall shear stress (WSS) with the temporal variations of the diameter and IMT in the venous segment of AVFs. An AVF was created between the femoral artery and vein of a 50-kg pig. We have previously shown the successful use of CT-scan and ultrasound techniques for anatomical and flow measurements in AVFs, respectively. In this study, we developed new techniques involving markers (both in vivo and ex vivo), casting (ex vivo), and micro-MRI (ex vivo; 7 Tesla). A radiopaque marker (ROM) was sutured to the AVF at the day of surgery, which was visible in the CT-scan images, micro-MRI, and histology sections. Therefore, ROM served as a fixed local reference for both in vivo and ex vivo states of AVFs. Immediately after sacrificing the pig, a procedure was developed to create a cast from the AVF and thus, maintaining the in vivo state of the AVF during the histology process. Then, micro-MRI and histology techniques were conducted on the AVF to measure IMT in the vein. Along the ROM, the local changes in WSS levels for two cross-sections were tracked at 2D (D: days) and 28D post surgery. WSS levels reduced from 2D to 28D for both cross-sections. Also, the recirculation zones, which formed at 2D for both sections, became smaller in size at 28D. These hemodynamic changes were then mapped onto the corresponding IMT measurements from histology and micro-MRI. It was observed that the recirculation zones at 2D and 28D corresponded to the largest IMT in the two sections. In summary, the new methodologies allowed us to define a fixed local reference at all time points in the AVF, which enabled accurate tracking of local changes in hemodynamics (WSS), configuration (diameter), and structure (IMT) of the venous segment over time. This also empowered study of the interactions between these parameters, which could improve our understanding about the hemodynamic-driven remodeling in AVFs. From a clinical point of view, this information could be translated into local and early therapeutic interventions for dialysis patients.

Changes in Whole Blood Viscosity at Low Shear Rates Correlate with Intravascular Volume Changes during Hemodialysis

Background:

Elevated blood viscosity has been shown to be independently correlated with cardiovascular risk factors and associated with increased risk of major cardiovascular events, including death and acute myocardial infarction. The aim of the present study was to investigate changes in whole blood viscosity (WBV) at shear rates of 1, 5, and 300 s-1 before and after hemodialysis in patients with end-stage renal disease (ESRD). We also examined the relationship between the changes of WBV and intravascular blood volume.

Methods:

43 patients with ESRD receiving maintenance hemodialysis were enrolled. WBV was measured using a scanning capillary tube viscometer pre- and post-dialysis to quantify dialytic viscosity surges. Body weight, blood pressure, and hematocrit were also measured before and after hemodialysis, as was the fluid removed during the session.

Results:

Hemodialysis had a 3 times greater impact on the low-shear WBV at a shear rate of 1 s-1 (i.e., 44.1% change) than on the high-shear WBV at a shear rate of 300 s-1 (i.e., 15.9% change). Changes in the low-shear WBV obtained at shear rates of 1 and 5 s-1 during hemodialysis were significantly correlated with changes in hematocrit. The intravascular blood volume reduction during hemodialysis was positively correlated with the changes in both high-shear and low-shear WBVs.

Conclusions:

These results suggest that the WBV parameter may hold additional information beyond hemoconcentration. Further research is needed to evaluate the relationship between low-shear WBV surges and increased morbidity in the patient population with ESRD.

Flow-induced arterial remodeling relates to endothelial function in the human forearm

BACKGROUND

Chronic changes in blood flow stimulate arterial remodeling, which contributes to the maintenance of vascular homeostasis. Experimental studies suggest that remodeling represents a response to local changes in endothelial shear stress and is nitric oxide-dependent.

METHODS AND RESULTS

To investigate determinants of outward arterial remodeling in humans, we measured ulnar artery flow, diameter, and flow-mediated dilation before and after removal of the adjacent radial artery in 53 patients who were undergoing coronary bypass surgery (age 60+/-11 years; 13% female). Removal of the radial artery increased ulnar artery blood flow by 35% (P=0.009) and increased ulnar artery diameter by 9% (P<0.001) 4 to 8 weeks after surgery. At 1 week, ulnar artery shear stress was increased by 58% (P<0.001), but it was no longer different from baseline at longer-term follow-up. The contralateral ulnar artery was unaffected, which suggests that these findings were not attributable to the systemic effects of medications or the postoperative state. Extent of outward remodeling correlated with the increase in blood flow (r=0.50, P=0.001) and with flow-mediated dilation at baseline (r=0.50, P=0.001). Remodeling correlated inversely with baseline endothelial expression of P-selectin in the radial artery (r=-0.76, P=0.004, n=14).

CONCLUSIONS

A sustained increase in blood flow in the ulnar artery induced outward arterial remodeling despite the presence of risk factors and coronary artery disease. The remodeling response was related to endothelial phenotype, as reflected by flow-mediated dilation and expression of P-selectin. These findings provide evidence that the endothelium plays an important role in the regulation of vascular structure in humans.