Cellular Blood Flow

The fluid dynamics video that is presented here outlines recent advances in the simulation of multiphase cellular blood flow through the direct numerical simulations of deformable red blood cells (RBCs) demonstrated through several numerical experiments. Videos show particle deformation, shear stress on the particle surface, and the formation of particle clusters in both Hagen-Poiseuille and shear flow.Comment: 2 pages, one hyperlink to 2 video

Skin blood flow changes during apneic spells in preterm infants

Changes in skin blood flow during apneic spells were determined in 18 preterm infants using a diode laser Doppler flow meter without light conducting fibres. Heart rate, nasal air flow, impedance pneumography, skin and incubator temperature and laser Doppler skin blood flow were recorded simultaneously in each infant. During 212 apneic spells with a duration of 11.6 ± 7.5 s (mean ± S.D.) (range 6.0–48.0 s), the laser Doppler skin blood flow was measured. In all children except one, the majority of the apneic spells was associated with a decrease in skin blood flow. During 155 apneic spells (73%) skin blood flow decreased significantly P < 0.025), the maximum decrease being 16.7 ± 14.8%, 28.5 ± 23.9% and 18.9 ± 16.1% (mean ± S.D.) for central, obstructive and mixed apneic spells, respectively. The decrease in skin blood flow started immediately after the beginning of apneic spells in 71%, the rest started with a mean delay of 3.4 s (range 0.1–7.0 s). No relation was found between the decrease in skin blood flow and the duration of the apneic spells. Thirty-four percent of the apneic spells were accompanied by bradycardia. In apneic spells accompanied by bradycardia the decrease in skin blood flow was not related to the fall in heart rate

Comparison of the Effects of Ice and 3.5% Menthol Gel on Blood Flow and Muscle Strength of the Lower Arm

Context: Soft-tissue injuries are commonly treated with ice or menthol gels. Few studies have compared the effects of these treatments on blood flow and muscle strength. Objective: To compare blood flow and muscle strength in the forearm after an application of ice or menthol gel or no treatment. Design: Repeated measures design in which blood-flow and muscle-strength data were collected from subjects under 3 treatment conditions. Setting: Exercise physiology laboratory. Participants: 17 healthy adults with no impediment to the blood flow or strength in their right arm, recruited through word of mouth. Intervention: Three separate treatment conditions were randomly applied topically to the right forearm: no treatment, 0.5 kg of ice, or 3.5 mL of 3.5% menthol gel. To avoid injury ice was only applied for 20 min. Main Outcome Measures: At each data-collection session blood flow (mL/min) of the right radial artery was determined at baseline before any treatment and then at 5, 10, 15, and 20 min after treatment using Doppler ultrasound. Muscle strength was assessed as maximum isokinetic flexion and extension of the wrist at 30°/s 20, 25, and 30 min after treatment. Results: The menthol gel reduced (–42%, P \u3c .05) blood flow in the radial artery 5 min after application but not at 10, 15, or 20 min after application. Ice reduced (–48%, P \u3c .05) blood flow in the radial artery only after 20 min of application. After 15 min of the control condition blood flow increased (83%, P \u3c .05) from baseline measures. After the removal of ice, wrist-extension strength did not increase per repeated strength assessment as it did during the control condition (9–11%, P \u3c .05) and menthol-gel intervention (8%, P \u3c .05). Conclusions: Menthol has a fast-acting, short-lived effect of reducing blood flow. Ice reduces blood flow after a prolonged duration. Muscle strength appears to be inhibited after ice application

Intestinal blood flow in patients with chronic heart failure: A link with bacterial growth, gastrointestinal symptoms, and cachexia

Background: Blood flow in the intestinal arteries is reduced in patients with stable heart failure (HF) and relates to gastrointestinal (GI) symptoms and cardiac cachexia. Objectives: The aims of this study were to measure arterial intestinal blood flow and assess its role in juxtamucosal bacterial growth, GI symptoms, and cachexia in patients with HF. Methods: A total of 65 patients and 25 controls were investigated. Twelve patients were cachectic. Intestinal blood flow and bowel wall thickness were measured using ultrasound. GI symptoms were documented. Bacteria in stool and juxtamucosal bacteria on biopsies taken during sigmoidoscopy were studied in a subgroup by fluorescence in situ hybridization. Serum lipopolysaccharide antibodies were measured. Results: Patients showed 30% to 43% reduced mean systolic blood flow in the superior and inferior mesenteric arteries and celiac trunk (CT) compared with controls (p < 0.007 for all). Cachectic patients had the lowest blood flow (p < 0.002). Lower blood flow in the superior mesenteric artery and CT was correlated with HF severity (p < 0.04 for all). Patients had more feelings of repletion, flatulence, intestinal murmurs, and burping (p < 0.04). Burping and nausea or vomiting were most severe in patients with cachexia (p < 0.05). Patients with lower CT blood flow had more abdominal discomfort and immunoglobulin A–antilipopolysaccharide (r = 0.76, p < 0.02). Antilipopolysaccharide response was correlated with increased growth of juxtamucosal but not stool bacteria. Patients with intestinal murmurs had greater bowel wall thickness of the sigmoid and descending colon, suggestive of edema contributing to GI symptoms (p < 0.05). In multivariate regression analysis, lower blood flow in the superior mesenteric artery, CT (p < 0.04), and inferior mesenteric artery (p = 0.056) was correlated with the presence of cardiac cachexia. Conclusions: Intestinal blood flow is reduced in patients with HF. This may contribute to juxtamucosal bacterial growth and GI symptoms in patients with advanced HF complicated by cachexia

Topical Menthol, Ice, Peripheral Blood Flow, and Perceived Discomfort

Context : Injury management commonly includes decreasing arterial blood flow to the affected site in an attempt to reduce microvascular blood flow and edema and limit the induction of inflammation. Applied separately, ice and menthol gel decrease arterial blood flow, but the combined effects of ice and menthol gel on arterial blood flow are unknown. Objectives : To compare radial artery blood flow, arterial diameter, and perceived discomfort before and after the application of 1 of 4 treatment conditions. Design : Experimental crossover design. Setting : Clinical laboratory. Participants or Other Participants : Ten healthy men, 9 healthy women (mean age = 25.68 years, mean height = 1.73 m, mean weight = 76.73 kg). Intervention(s) : Four treatment conditions were randomly applied for 20 minutes to the right forearm of participants on 4 different days separated by at least 24 hours: (1) 3.5 mL menthol gel, (2) 0.5 kg of crushed ice, (3) 3.5 mL of menthol gel and 0.5 kg of crushed ice, or (4) no treatment (control). Main Outcome Measure(s) : Using high-resolution ultrasound, we measured right radial artery diameter (cm) and blood flow (mL/min) every 5 minutes for 20 minutes after the treatment was applied. Discomfort with the treatment was documented using a 1-to-10 intensity scale. Results : Radial artery blood flow decreased (P \u3c .05) from baseline in the ice (−20% to −24%), menthol (−17% to −24%), and ice and menthol (−36% to −39%) treatments but not in the control (3% to 9%) at 5, 10, and 15 minutes. At 20 minutes after baseline, only the ice (−27%) and combined ice and menthol (−38%) treatments exhibited reductions in blood flow (P \u3c .05). Discomfort was less with menthol than with the ice treatment at 5, 10, and 20 minutes after application (P \u3c .05). Arterial diameter and heart rate did not change. Conclusions : The application of 3.5 mL of menthol was similar to the application of 0.5 kg of crushed ice in reducing peripheral blood flood. Combining crushed ice with menthol appeared to have an additive effect on reducing blood flow

Cerebral blood flow predicts differential neurotransmitter activity

Application of metabolic magnetic resonance imaging measures such as cerebral blood flow in translational medicine is limited by the unknown link of observed alterations to specific neurophysiological processes. In particular, the sensitivity of cerebral blood flow to activity changes in specific neurotransmitter systems remains unclear. We address this question by probing cerebral blood flow in healthy volunteers using seven established drugs with known dopaminergic, serotonergic, glutamatergic and GABAergic mechanisms of action. We use a novel framework aimed at disentangling the observed effects to contribution from underlying neurotransmitter systems. We find for all evaluated compounds a reliable spatial link of respective cerebral blood flow changes with underlying neurotransmitter receptor densities corresponding to their primary mechanisms of action. The strength of these associations with receptor density is mediated by respective drug affinities. These findings suggest that cerebral blood flow is a sensitive brain-wide in-vivo assay of metabolic demands across a variety of neurotransmitter systems in humans

Blood flow in microvascular networks

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Simulation of blood presents a very complex haemodynamics problem especially in relation to the understanding of atherogenesis. In many simulations, blood has been treated as a single-phase homogeneous fluid, a classical approach that does not account for the presence of red blood cells (RBCs). Although this approach provides satisfactory tools to describe certain aspects of blood flow in large arteries, it fails to give an adequate representation of the flow field in the vessels of smaller diameter where the size of the RBC becomes significant relative to vessel diameter. So, this article is concerned with the study of non-Newtonian blood flow in microvascular networks with the intention of developing a new cell depletion layer model to represent the behaviour of RBCs through bifurcating networks. The model is tested in a microvascular network constructed possessing realistic bifurcation features, with controlled dimensions and angles. The RBC depletion model treats blood as two continuum layers, with a central, non-Newtonian core region of concentrated red cell suspension that is surrounded by a layer of plasma (Newtonian fluid) adjacent to the vessel wall. In the central core region, blood is described by Quemada's non-Newtonian rheological model. Geometry differences are shown to significantly affect flow rates, haematocrit distributions and the corresponding cell depletion layers

Mechanics of blood flow in capillaries

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Blood is a concentrated suspension of red blood cells (RBCs). Motion and deformation of RBCs can be analyzed based on knowledge of their mechanical characteristics. Models for single-file motion of RBCs in capillaries yield predictions of apparent viscosity in good agreement with experimental results for diameters up to about 8 μm. In living microvessels, flow resistance is also strongly influenced by the presence of a ~ 1-micron layer of macromolecules bound to the inner lining of vessel walls, the endothelial surface layer. Two-dimensional simulations, in which each RBC is represented as a set of interconnected viscoelastic elements, predict that off-center RBCs take asymmetric shapes and drift toward the center-line. Predicted trajectories agree closely with observations in microvessels of the rat mesentery. Realistic simulation of multiple interacting RBCs in microvessels remains as a major challenge for future work.This work was supported by NIH Grant HL034555

Abnormal Myocardial Blood Flow Reserve Observed in Cardiac Amyloidosis

We performed real-time myocardial contrast echocardiography on a patient with cardiac amyloidosis and previous normal coronary angiography presenting with atypical chest pain to assess myocardial blood flow reserve (MBFR). Myocardial contrast echocardiography was performed and flash microbubble destruction and replenishment analysis was used to calculate myocardial blood flow. Dipyridamole was used to achieve hyperemia. MBFR was derived from the ratio of peak myocardial blood flow at hyperemia and rest. The results show a marked reduction in MBFR in our patient. Previous reports of luminal obstruction of intramyocardial rather than epicardial vessels by amyloid deposition may be causing microvascular dysfunction

Large-Eddy simulation of pulsatile blood flow

Large-Eddy simulation (LES) is performed to study pulsatile blood flow through a 3D model of arterial stenosis. The model is chosen as a simple channel with a biological type stenosis formed on the top wall. A sinusoidal non-additive type pulsation is assumed at the inlet of the model to generate time dependent oscillating flow in the channel and the Reynolds number of 1200, based on the channel height and the bulk velocity, is chosen in the simulations. We investigate in detail the transition-to-turbulent phenomena of the non-additive pulsatile blood flow downstream of the stenosis. Results show that the high level of flow recirculation associated with complex patterns of transient blood flow have a significant contribution to the generation of the turbulent fluctuations found in the post-stenosis region. The importance of using LES in modelling pulsatile blood flow is also assessed in the paper through the prediction of its sub-grid scale contributions. In addition, some important results of the flow physics are achieved from the simulations, these are presented in the paper in terms of blood flow velocity, pressure distribution, vortices, shear stress, turbulent fluctuations and energy spectra, along with their importance to the relevant medical pathophysiology