Nonpulsatile Flow Research Articles

Investigation of the Effect of Pulsatile and Nonpulsatile Flow on Kidney in Coronary Surgery With NIRS.

Acute renal insufficiency is a significant cause of morbidity and mortality after coronary artery bypass grafting performed with cardiopulmonary bypass. Functional near-infrared spectroscopy (fNIRS) is an emerging brain-imaging technique that can be used to detect organ perfusions in adults. This study aims to determine the effects of pulsatile and nonpulsatile flow on renal circulation by using functional near-infrared spectroscopy and biochemical markers. Forty patients, who had undergone isolated CABG between March 2014 and July 2014 in the authors' clinic, were included in the study. Patients were divided in the pulsatile and nonpulsatile groups by simple randomization. Urine outputs statistically were higher in the pulsatile group, during CPB (P = .045). Renal perfusion measurements via fNIRS intra-operatively statistically were parallel between the groups. When we compared biochemical markers within the groups, in the nonpulsatile group, creatinin statistically is higher on the postoperative first day (P = .003), and BUN statistically is higher on the postoperative first (P = .015), second (P = .001), and fifth (P = .020) days, according to preoperative value. In the pulsatile group, only the postoperative second day BUN is higher (P = .007). fNIRS is being used to track cerebral functions. During operation, it also provides a correct observation for blood feeding of somatic organs, such as the kidneys, but it requires more clinical study to be accepted as routine.

Correlation Between Wall Shear Stress and Acute Degradation of the Endothelial Glycocalyx During Cardiopulmonary Bypass.

Wall shear stress (WSS) plays a key role in maintaining glycocalyx function, gene expression, and structure. Experimental studies have discussed the relationship between the shedding of the endothelial glycocalyx (EG) and WSS. However, rare literature about how WSS affects the EG during cardiopulmonary bypass (CPB) was mentioned. This study aimed to investigate the correlation between the WSS of carotid arteries and shedding of the EG during CPB in humans. The WSS level was calculated in accordance with an equation. The plasma concentrations of heparan sulfate, syndecan-1, and nitric oxide were measured to reflect shedding of the EG at six time points. A negative correlation was observed between the peak wall shear stress (PWSS) and syndecan-1 (R= - 0.5, p< 0.01) and heparan sulfate (R= - 0.461, p< 0.01) during CPB. The WSS is closely associated with the components of glycocalyx shedding during CPB. The WSS produced by non-pulsatile flow during CPB may contribute to the degradation of EG.

1322Impact of system impedance in ablation-index guided lesion formation in an in vitro model

Abstract Funding Acknowledgements Beca de la Sección de Electrofisiología y Arritmias para formación en investigación post-residencia en centros españoles INTRODUCTION Ablation Index and Lesion Size Index are novel markers of ablation lesion quality that incorporate power (W), contact force (CF), and time (T) in a weighted formula to accurately estimate lesion size. While LSI includes system impedance (I) in the formula, this parameter is not considered for AI calculation. PURPOSE The aim of our study was to analyse the impact of I in lesion formation. METHODS Radiofrequency (RF) lesions were created on porcine myocardial slabs by using an open-tip irrigated catheter with real-time monitoring of CF (a TactiCath™ Quartz Contact Force Ablation Catheter for LSI-guided lesions and a ThermoCool® SmartTouch® Catheter for AI-guided lesions). Catheters were mounted in an articulated arm and manually maneuvered over a platform placed within a tank filled with either a low impedance medium (saline solution) or a high impedance medium (running water) with a heating pump to produce non-pulsatile flow directed perpendicularly to the myocardium surface at a rate of 5 l/min and a temperature of 37ºC. For each catheter and medium, ten lesions were performed with a CF of 20 grams and a W of 25, 30, 35 and 40 watts aiming at a LSI of 5 or a AI of 400 (recommended targets for posterior wall pulmonary vein isolation for each index). After RF delivery, the myocardium was cross-sectioned at the level of each lesion and its blanched zone was measured with a dial calliper with a 0.1 mm resolution (image, panel A). Lesion volume was calculated using width and depth, according to a validated formula (image, panel B). RESULTS No difference in application time was noted in the AI-guided lesions depending on the medium (23.8 ± 1.6s, 17.2 ± 1.4s, 13.7 ± 0.8s and 12.2 ± 0.7s for 25W, 30W, 35W and 40W, respectively) while a significant reduction in application time was noted in the LSI-guided lesions performed in a low I medium (93.8 ± 6.6 ohms; 17.9 ± 1.9s, 11.3 ± 3.7s, 9.1 ± 0.9s and 7.3 ± 0.5s for 25W, 30W, 35W and 40W) compared with those performed in a high impedance medium (132.4 ± 6.6 ohms; 27.3 ± 1.4s, 17.9 ± 2.5s, 15.5 ± 1.4 and 13 ± 1.2 for the same programmed W (p &amp;lt; 0.0001 for all comparisons). Both catheters showed differences in lesion size according to the I, with lower lesion volumes in the low I medium and higher lesion volumes in the high I medium. Although globally smaller in size, higher lesion volumes were noted in the AI-guided lesions compared to LSI-guided lesions in a low I medium (image, panel C). On the contrary, a better performance of the LSI-guided lesions was observed in the high I medium (image, panel D). CONCLUSIONS System impedance affected lesion size both in LSI-guided an AI-guided ablation lesions, with smaller lesions seen in a lower I medium. Further studies are needed to assess the clinical relevance of this findings in an in-vivo scenario. Abstract Figure.

A direct comparison of pulsatile and non-pulsatile rough-wall turbulent pipe flow

Pulsatile rough-wall turbulent pipe flow is compared against its non-pulsatile counterpart using data obtained from direct numerical simulation. Results are presented at a mean friction Reynolds number of 540 for a set of three geometrically scaled roughness topographies at a single forcing condition, which, based on existing classifications, falls into the current-dominated very-high-frequency regime. By comparing the pulsatile data against an equivalent non-pulsatile dataset (Chan et al. , J. Fluid Mech. , vol. 854, 2018, pp. 5–33), the key differences (and similarities) between the forced and unforced configurations are identified. A major finding of this study is that the flow in the outer region retains its self-similar functional form under pulsatile rough-wall conditions, and, as a result, Townsend’s outer-layer similarity hypothesis holds for the roughness-forcing combinations considered here. On the other hand, the unsteady cases exhibit a rich array of flow physics in the region beneath the roughness crests not observed in the steady case. These differences are examined using a Moody chart, which encapsulates how the hydraulic properties of pulsatile rough-wall pipe flow differ from their non-pulsatile counterpart.

Perfusion Index Measurement in Predicting Hypovolemic Shock in Trauma Patients.

Perfusion index (PI) derived from pulse oximeter shows the ratio of the pulsatile blood flow to the nonpulsatile blood flow or static blood in peripheral tissue. The aim of this study was to investigate the relationship between PI and blood transfusion necessity in 24h and stage of hemorrhagic shock, as well as the utility of PI according to laboratory and clinical parameters, and determining the major risk of hemorrhage. PI was measured with a pulse oximeter in 338 patients (235 males, average age 41.8±17.94years). Laboratory parameters (hemoglobin, hematocrit, lactate, base deficits, pH) and clinical parameters (pulse rate, respiratory rate, SpO2, systolic blood pressure [SBP] and diastolic blood pressure [DBP]), shock index (SI) and revised trauma score (RTS) were recorded. Univariate analysis was used to determine major risk for bleeding, and the receiver operating characteristic curves were performed to compare parameters. PI was < 1 in 39 (11.5%) patients. Positive correlation between PI and hemoglobin (p<0.001; r: 0.320), hematocrit (p<0.001; r: 0.294), base deficit (p<0.001; r: 0.315), pH (p<0.05; r: 0.235), SBP (p<0.001; r: 0.146), DBP (p<0.001; r: 0.259), SpO2 (p<0.001; r: 0.197), RTS (p<0.001; r: 0.344), and negative correlation with lactate (p<0.05; r: -0.117), pulse (p<0.001; r: -0.326), respiratory rate (p<0.001; r: -0.231), and SI (p<0.001; r: -0.257) were detected. A difference was detected between class 1 and 2, and class 1 and 3 (both p<0.05) in hemorrhagic shock. Thirty-one with PI<1 had blood transfusion within 24h (p<0.001; odds ratio 111.98, sensitivity 75.6%, specificity 97.3, positive predictive value 79.5%, negative predictive value 96.7%). The main risk factors of the need for blood transfusions were PI, pulse rate, and SpO2. PI was more significant than lactate, base deficit, RTS, and SI measurements. PI might be beneficial in the detection and exclusion of critical patients and blood transfusion needs in the emergency department. PI can be used with vital signs and shock parameters in the early diagnosis of hemorrhage.

Non-Pulsatile Flow is Associated with Lower Levels of Circulating CD34+ Cells in LVAD-Supported Patients

The lack of pulsatility may be associated with altered angiogensis in LVAD patients. Since CD34+ cells represent an important regulator of angiogenesis in heart failure, we sought to investigate a potential correlation between flow pulsatility and circulating CD34+ cell levels in this patient population. In a single-center prospective cohort study we measured peripheral CD34+ cell numbers in patients undergoing LVAD support for at least 3 months. Patients with active infection, active hematologic disorders and history of chemotherapy were excluded. Pulsatile flow was defined as aortic valve opening in each cardiac cycle in the setting of optimized left ventricular unloading. Peripheral CD34+ cells were quantified by flow cytometry using the International Society of Hemotherapy and Graft Engineering protocol. Of 12 patients, pulsatile flow was established in 6 patients (Group A) and 6 patients failed to demonstrate flow pulsatility (Group B). The two groups did not differ in age (60±9 years in Group A vs. 59±6 years in Group B, P=0.97), gender (male; 83% vs. 83%, P=1.00), heart failure etiology (ischemic: 50% vs. 52%, P=0.84), serum creatinine (1.10±0.19 mg/dL vs. 0.97±0.17 μmol/L, P=0.35), NT-proBNP (926±587 pg/mL vs. 1562±1190 pg/mL, P=0.35), LDH levels (3.2±0.5 μmol/L vs. 3.4±3.2 μmol/L, P=0.79), length of LVAD support (932±369 days vs. 462±298 days, P=0.10), mean blood pressure (86±9 mmHg vs. 83±4 mmHg, P=0.43) or estimated pump flow (4.8±0.9 L/min vs. 4.3±0.6 L/min, P=0.32). Pulsatility index was higher in Group A than in Group B (5.6±1.2 vs. 3.6±0.6, P=0.006). Despite similar leukocyte counts (6.7±0.9x109/L in Group A vs. 7.3±0.8 x109/L in Group B, P=0.52), hemoglobin (12.6±7.3 g/dL vs. 13.5±1.6 g/dL, P=0.28) and serum iron (16±10 μmol/L vs. 14±5 μmol/L, P=0.66) we found significantly higher peripheral CD34+ cell count in Group A than in Group B (2.4±0.7x106/L vs. 1.6±0.8 x106/L, P=0.03). Overall, CD34+ cell count was inversely related to red cell distribution width (R2=0.-58 , P=0.05). Non-pulsatile flow appears to be associated with lower numbers of peripheral CD34+ cells in LVAD-supported patients. This suggests that hemodynamic changes after prolonged LVAD support may significantly alter angiogenesis and vasculogenesis pathways in chronic heart failure.

Digoxin Treatment Reverses Angiogenic Switch during HeartMate 3 Support and is Associated with Decrease Risk for Gastrointestinal Bleeding

Gastrointestinal bleeding (GIB) in LVAD patients is most commonly caused by gastrointestinal angiodysplasia (GIAD). Non-pulsatile blood flow in LVAD patients can cause splanchnic submucosal hypoperfusion and hypoxia leading to activation of a HIF1-α /Angiopoietins (Ang) signaling cascade, that can trigger pathological angiogenesis. We have recently shown that the use of digoxin, a potent inhibitor of HIF1-α, is associated with a significant reduction in GIAD related GIB in HeartMate (HM) II and HeartWare HVAD patients. However, HM3 support is associated with less GIB then previous generation pumps. We now hypothesize that dysregulation of Ang-1 and Ang-2 levels in patients with HM3 can be restored by digoxin treatment and may contribute to decreased incidence of GIB. We have collected blood samples from 7 patients supported with HM3 before and after two weeks of digoxin therapy (0.125 mg daily). Ang-1 and Ang-2 levels were measured in patients' serum by ELISA. In single-center retrospective study, charts of all patients implanted with HM3 between June 2015 and October 2019 were reviewed with emphasis on the occurrence of GIB and digoxin therapy. Pearson's chi-squared test was used to assess the frequency of overall GIB and their association with digoxin therapy. Digoxin treatment in HM3 patients increased Ang-1 (11.5 to 30.7 ng/ml, p=0.02), and decreased Ang-2 levels (14.9 to 9.4 ng/ml, p=0.04), reversing angiogenic switch. Seven of 72 patients (10%) supported by HM3 during median observation time (236, IQR76-620) days experienced a GIB. We identified 38 patients treated and 34 not treated with digoxin (age 52.38 vs. 52.65, p=0.97). The frequency of GIB was significantly lower in the patients receiving compared to the ones not receiving digoxin (3% vs. 17% p=0.03; Fig.1), respectively. Digoxin, an inhibitor of HIF1-α signaling cascade, may contribute to a lower risk of GIB in HM3 patients by restoring angiogenic equilibrium.

Pulsatile Versus Nonpulsatile Flow During Cardiopulmonary Bypass: Extent of Hemolysis and Clinical Significance.

Pulsatile flow has been used during cardiopulmonary bypass (CPB) for decades and its use is increasing with advancing extracorporeal technology. Pulsatile flow generates higher circuit pressures and shear forces than nonpulsatile flow at comparable pump flow and patient mean arterial pressure. Very little is known about the effect this has on erythrocytes. We included 62 adult patients (32 in the pulsatile group and 30 in the nonpulsatile group) undergoing elective coronary artery bypass grafting in this prospective observational study. Blood samples were collected at routine sampling times throughout surgery and were analyzed for the presence of free heme and globin using mass spectroscopy. Patient characteristics, CPB, and aortic cross-clamp times, pump flow as well as patient mean arterial pressure were similar in both groups. Maximum circuit pressure in the pulsatile flow group was statistically significantly higher than that in the nonpulsatile flow group (257.12 vs. 190.64 mmHg, p < 0.0001). Both heme and globin levels were higher in the pulsatile flow group. This reached statistical significance with globin at 30 minutes of CPB and with heme after aortic unclamping. We conclude that pulsatile CPB using roller pumps results in a greater extent of hemolysis. The clinical significance, however, is not yet known.

Flow profile characteristics in Fontan circulation are associated with the single ventricle dilation and function: principal component analysis study.

The Fontan circulation is characterized as a nonpulsatile flow propagation without a pressure-generating ventricle. However, flow through the Fontan circulation still exhibits oscillatory waves as a result of pressure changes generated by the systemic single ventricle. Identification of discrete flow patterns through the Fontan circuit may be important to understand single ventricle performance. Ninety-seven patients with Fontan circulation underwent phase-contrast MRI of the right pulmonary artery, yielding subject-specific flow waveforms. Principal component (PC) analysis was performed on preprocessed flow waveforms. Principal components were then correlated with standard MRI indices of function, volume, and aortopulmonary collateral flow. The first principal component (PC) described systolic versus diastolic-dominant flow through the Fontan circulation, accounting for 31.3% of the variance in all waveforms. The first PC correlated with end-diastolic volume (R = 0.34, P = 0.001), and end-systolic volume (R = 0.30, P = 0.003), cardiac index (R = 0.51, P < 0.001), and the amount of aortopulmonary collateral flow (R = 0.25, P = 0.027)-lower ventricular volumes and a smaller volume of collateral flow-were associated with diastolic-dominant cavopulmonary flow. The second PC accounted for 19.5% of variance and described late diastolic acceleration versus deceleration and correlated with ejection fraction-diastolic deceleration was associated with higher ejection fraction. Principal components describing the diastolic flow variations in pulmonary arteries are related to the single ventricle function and volumes. Particularly, diastolic-dominant flow without late acceleration appears to be related to preserved ventricular volume and function, respectively.NEW & NOTEWORTHY The exact physiological significance of flow oscillations of phasic and temporal flow variations in Fontan circulation is unknown. With the use of principal component analysis, we discovered that flow variations in the right pulmonary artery of Fontan patients are related to the single ventricle function and volumes. Particularly, diastolic-dominant flow without late acceleration appears to be related to more ideal ventricular volume and systolic function, respectively.

Pathophysiology and Complications during Extracorporeal Circulation.

Extracorporeal circulation, unlike pulsatile flow based on the beating heart, is the non-pulsatile flow through a blood pump, and the systemic circulation falls into non-physiological conditions. The living body shows various reactions to extracorporeal circulation. The pathophysiology of extracorporeal circulation includes changes in hemodynamics, coagulation, fibrinolysis, acid-base equilibrium, electrolytes, incretion, metabolism, and immune system. With advances in extracorporeal circulation technology, operability has been dramatically improved and safety has rapidly advanced as well. However, there are specific complications with extracorporeal circulation. We need to have a good knowledge of the pathophysiology and complications during extracorporeal circulation, as well as each component of the extracorporeal circulation system.

The perfusion index could early predict a nerve block success: A preliminary report.

Introduction:In literature, there is plenty of material regarding regional anesthesia techniques and block safety, but lacks about block success prevision. The perfusion index (PI) is an oximetry reliability indicator, available on many monitors as non-invasive parameter, indicating the ratio of arterial blood flow (pulsatile flow) to venous, capillary, and tissue blood flow (non-pulsatile blood flow). We hypothesized that that analysis of PI variations after performing regional anesthesia could have a role in predicting a successful nerve block.Methods:Twenty-four consecutive patients regularly scheduled for limb surgery in regional anesthesia were included in our observation. PI measurements were recorded before regional anesthesia, and 1, 2, 3, 5, and 10 min after needle withdrawal. Along with PI, also sensation to cold (ice test), tactile sensation, and motor function were recorded before regional anesthesia, and 1, 2, 3, 5, and 10 min after needle withdrawal on the limb where the block were performed.Results:Ten sciatic nerve blocks, 6 spinal anesthesia, 8 brachial plexus block were performed and resulted successful. In all cases, PI values tripled at 5 min after the block execution and increased linearly, reaching at 10 min an average PI value 3.8 times higher for the interscalene group, 4 times for the spinal group, and 8 for the sciatic group.Conclusions:A tripled PI within 5 min from performing regional anesthesia showed to be a reliable indicator of nerve block success, but a bigger trial involving more patients and different anesthetic concentrations may be necessary to confirm this assumption.

EFFECT OF PULSATILE FLOW ON RENAL FUNCTION IN ELDERLY PATIENTS UNDERGOING CORONARY ARTERY BYPASS SURGERY

The incidence of acute kidney injury (AKI) after on-pump coronary artery bypass graft (CABG) varies among studies but can be reduced if pulsatile flow is used. The aim of this study is to evaluate pulsatile flow impact on renal function of elderly patients undergoing CABG. Over one year (April 2014 to April 2015) 48 patients above the age of 65 underwent on-pump CABG in our institute. Patients were divided into two groups; pulsatile flow (PFG) and non-pulsatile flow (NPFG) groups. Serum creatinine (S.Cr), creatinine clearance (Cr.Cl) and per-perfusion urine output (UO) were measured. AKI Network criteria were adopted for diagnosis. Mean age was 68 in PFG and 69 in NPFG. Males constituted 83.3% of PFG and 79.2% of NPFG. Although 37.5% of PFG and 41.7% of NPFG were hypertensive, all patients had normal ejection fraction (EF). Both groups had nearly 3 coronary anastomoses, cardiopulmonary bypass (CPB) time of 90 min, cross clamp time of 71 min and mean perfusion pressure of 70 mmHg. Mean S.Cr was the same (0.8 mg/dl) in both groups on 1st postoperative day (POD) but UO was significantly larger (708 ml in PFG vs. 648 ml in NPFG). On 3rd POD, S. Cr didn’t change in PFG but it has significantly increased in NPFG (from 0.76 to 1.0 mg/dl). Moreover, Cr.Cl has significantly improved in PFG (81 vs. 72 ml/min in NPFG). Seven of 48 patients (14.6 %) developed AKI (6; 25% in NPFG). In conclusion; Pulsatile perfusion technique is a simple and safe measure to minimize AKI in the elderly. Keywords: Coronary artery bypass graft, elderly, cardiopulmonary bypass, pulsatile flow, non-pulsatile flow, acute kidney injury, serum creatinine, creatinine clearance

Non-pulsatile blood flow is associated with enhanced cerebrovascular carbon dioxide reactivity and an attenuated relationship between cerebral blood flow and regional brain oxygenation

BackgroundSystemic blood flow in patients on extracorporeal assist devices is frequently not or only minimally pulsatile. Loss of pulsatile brain perfusion, however, has been implicated in neurological complications. Furthermore, the adverse effects of absent pulsatility on the cerebral microcirculation are modulated similarly as CO2 vasoreactivity in resistance vessels. During support with an extracorporeal assist device swings in arterial carbon dioxide partial pressures (PaCO2) that determine cerebral oxygen delivery are not uncommon—especially when CO2 is eliminated by the respirator as well as via the gas exchanger of an extracorporeal membrane oxygenation machine. We, therefore, investigated whether non-pulsatile flow affects cerebrovascular CO2 reactivity (CVR) and regional brain oxygenation (rSO2).MethodsIn this prospective, single-centre case-control trial, we studied 32 patients undergoing elective cardiac surgery. Blood flow velocity in the middle cerebral artery (MCAv) as well as rSO2 was determined during step changes of PaCO2 between 30, 40, and 50 mmHg. Measurements were conducted on cardiopulmonary bypass during non-pulsatile and postoperatively under pulsatile blood flow at comparable test conditions. Corresponding changes of CVR and concomitant rSO2 alterations were determined for each flow mode. Each patient served as her own control.ResultsMCAv was generally lower during hypocapnia than during normocapnia and hypercapnia (p < 0.0001). However, the MCAv/PaCO2 slope during non-pulsatile flow was 14.4 cm/s/mmHg [CI 11.8–16.9] and 10.4 cm/s/mmHg [CI 7.9–13.0] after return of pulsatility (p = 0.03). During hypocapnia, non-pulsatile CVR (4.3 ± 1.7%/mmHg) was higher than pulsatile CVR (3.1 ± 1.3%/mmHg, p = 0.01). Independent of the flow mode, we observed a decline in rSO2 during hypocapnia and a corresponding rise during hypercapnia (p < 0.0001). However, the relationship between ΔrSO2 and ΔMCAv was less pronounced during non-pulsatile flow.ConclusionsNon-pulsatile perfusion is associated with enhanced cerebrovascular CVR resulting in greater relative decreases of cerebral blood flow during hypocapnia. Heterogenic microvascular perfusion may account for the attenuated ΔrSO2/ΔMCAv slope. Potential hazards related to this altered regulation of cerebral perfusion still need to be assessed.Trial registrationThe study was retrospectively registered on October 30, 2018, with Clinical Trial.gov (NCT03732651).

Perfusion Index Analysis in Patients Presenting to the Emergency Department Due to Synthetic Cannabinoid Use

Background and Objectives: The perfusion index (PI) indicates the ratio of pulsatile blood flow in peripheral tissue to non-pulsatile blood flow. This study was performed to examine the blood perfusion status of tissues and organs of patients using synthetic cannabinoids (SCs). Materials and Methods: The records of patients aged 17 or over presenting to the adult emergency department due to SC use between 1 January 2016 and 31 December 2017 were examined in this single-center, retrospective, cross-sectional study. Examined factors included time from consumption of SC to presentation to the emergency department, as well as simultaneously determined systolic and diastolic blood pressures, heart rate (beats per min), Glasgow Coma Score (GCS), and PI values. Patients were divided into two groups, A and B, depending on the amount of time that had elapsed between SC consumption and presentation to the emergency department, and statistical data were compared. Results: The mean PI value in Group A was lower than that in Group B. Therefore, we concluded that peripheral tissue and organ blood perfusion is lower in the first 2 h following SC consumption than after 2 h. Systolic, diastolic, and mean arterial blood pressure and mean GCS values were also statistically significantly lower in Group A than in Group B. Conclusions: A decreased PI value may be an early sign of reduced-perfusion organ damage. PI is a practical and useful parameter in the early diagnosis of impaired organ perfusion and in monitoring tissue hypoxia leading to organ failure.

Numerical investigation of wall pressure fluctuations downstream of concentric and eccentric blunt stenosis models.

Pressure fluctuations that cause acoustic radiation from vessel models with concentric and eccentric blunt stenoses are investigated. Large eddy simulations of non-pulsatile flow condition are performed using OpenFOAM. Calculated amplitude and spatial-spectral distribution of acoustic pressures at the post-stenotic region are compared with previous experimental and theoretical results. It is found that increasing the Reynolds number does not change the location of the maximum root mean square wall pressure, but causes a general increase in the spectrum level, although the change in the shape of the spectrum is not significant. On the contrary, compared to the concentric model at the same Reynolds number, eccentricity leads to an increase both at the distance of the location of the maximum root mean square wall pressure from the stenosis exit and the spectrum level. This effect becomes more distinct when radial eccentricity of the stenosis increases. Both the flow rate and the eccentricity of the stenosis shape are evaluated to be clinically important parameters in diagnosing stenosis.

A 4D flow MRI evaluation of the impact of shear-dependent fluid viscosity on in vitro Fontan circulation flow.

The Fontan procedure for univentricular heart defects creates a nonphysiologic circulation where systemic venous blood drains directly into the pulmonary arteries, leading to multiorgan dysfunction secondary to chronic low-shear nonpulsatile pulmonary blood flow and central venous hypertension. Although blood viscosity increases exponentially in this low-shear environment, the role of shear-dependent ("non-Newtonian") blood viscosity in this pathophysiology is unclear. We studied three-dimensional (3D)-printed Fontan models in an in vitro flow loop with a Philips 3-T magnetic resonance imaging (MRI) scanner. A 4D flow phase-contrast sequence was used to acquire a time-varying 3D velocity field for each experimental condition. On the basis of blood viscosity of a cohort of patients who had undergone the Fontan procedure, it was decided to use 0.04% xanthan gum as a non-Newtonian blood analog; 45% glycerol was used as a Newtonian control fluid. MRI data were analyzed using GTFlow and MATLAB software. The primary outcome, power loss, was significantly higher with the Newtonian fluid [14.8 (13.3, 16.4) vs. 8.1 (6.4, 9.8)%, medians with 95% confidence interval, P < 0.0001]. The Newtonian fluid also demonstrated marginally higher right pulmonary artery flow, marginally lower shear stress, and a trend toward higher caval flow mixing. Outcomes were modulated by Fontan model complexity, cardiac output, and caval flow ratio. Vortexes, helical flow, and stagnant flow were more prevalent with the non-Newtonian fluid. Our data demonstrate that shear-dependent viscosity significantly alters qualitative flow patterns, power loss, pulmonary flow distribution, shear stress, and caval flow mixing in synthetic models of the Fontan circulation. Potential clinical implications include effects on exercise capacity, ventilation-perfusion matching, risk of pulmonary arteriovenous malformations, and risk of thromboembolism.NEW & NOTEWORTHY Although blood viscosity increases exponentially in low-shear environments, the role of shear-dependent ("non-Newtonian") blood viscosity in the pathophysiology of the low-shear Fontan circulation is unclear. We demonstrate that shear-dependent viscosity significantly alters qualitative flow patterns, power loss, pulmonary flow distribution, shear stress, and caval flow mixing in synthetic models of the Fontan circulation. Potential clinical implications include effects on exercise capacity, ventilation-perfusion matching, risk of pulmonary arteriovenous malformations, and risk of thromboembolism.

Vascular ultrasonographic findings in canine patients with clinically diagnosed phlebitis.

Peripheral vein phlebitis (inflammation) is a relatively frequent complication in dogs, however, published information on the ultrasonographic characteristics is currently lacking. This prospective, observational study describes the ultrasound (US) characteristics of normal canine cephalic veins, and veins with clinical phlebitis. Correlations among US findings and between US findings versus time that the intravenous catheter was in place were investigated. Safety of the US procedure was evaluated. Fifty patients were prospectively recruited for the study and 18 met the final inclusion criteria. Each patient underwent daily US examinations and was assessed for multiple criteria (vascular wall appearance, compressibility, spontaneity of flow, color fill, and presence/absence of filling defects, flow contour, direction, non‐pulsatility). Characteristics of normal canine cephalic veins were as follows: smooth and thin wall, complete compressibility, no flow disturbances, no filling defects, smooth flow contours, and unidirectional, non‐pulsatile flow with no turbulence. Characteristics of cephalic veins with clinical phlebitis were as follows: wall thickening (83%), decreased compressibility (55%), filling defects consistent with intraluminal thrombus (55%), vessel wall hyperechogenicity (44%), and abnormal color Doppler flow (39%). Significant correlations were found between Doppler filling defects and compressibility, Doppler filling defects and presumed thrombosis, and compressibility and presumed thrombosis (P = .001, P = .001, P = .000, respectively). No correlation was found between the US findings and time the intravenous catheter was in place. Findings indicated that duplex and compressibility US are feasible and safe methods for characterizing and monitoring cephalic veins in dogs with clinical phlebitis.

Pulmonary artery size is associated with functional clinical status in the Fontan circulation

ObjectiveIn the Fontan circulation, non-pulsatile pulmonary blood flow is suggested to negatively affect pulmonary artery growth. The pulmonary vasculature is regarded a key determinant of outcome after Fontan completion. We...

Uncoupling of cerebral blood flow and brain oxygen saturation under non-pulsatile flow conditions

Introduction Non-pulsatile blood flow has been associated with altered microcirculatory perfusion. Soon after loss of pulsatility a marked heterogenous flow profile in the very small vessels ensues that is coupled with impaired oxygen extraction [1]. We investigated if changes in cerebral blood flow during non-pulsatile perfusion would affect brain tissue oxygenation assessed by near-infrared spectroscopy. Methods After approval by the local ethics committee thirty-two patients were included in this trial. They were studied during general anaesthesia, and stable hemodynamic conditions. Cerebral blood flow velocity in the middle cerebral artery was measured during non-pulsatile flow in the course of cardiac surgery on total extracorporeal bypass and again postoperatively on the intensive care unit during pulsatile flow. We modified cerebral blood flow by changing arterial partial pressures of carbon dioxide between 30, 40 and 50 mmHg. This was conducted either by a change of sweep gas flow at the heart lung machine or by changing respiratory rate at the respirator. In addition to flow measurements patients' regional brain oxygenation was determined. Relative changes in blood flow velocity were plotted against relative changes in regional brain saturation for both flow conditions and compared using Pearson's correlation. A p-value Results Absolute cerebral blood flow velocity was slightly higher during non-pulsatile flow when serum hemoglobin was diluted. Relative changes in cerebral blood flow velocity and regional brain oxygenation were tightly coupled independent of the flow condition. R-values for non-pulsatile and pulsatile blood flow were 0.724 and 0.796, respectively. However, during non-pulsatile flow the slope of the regression line was less steep as compared with pulsatile flow (P Discussion Despite greater cerebral perfusion during hypercapnia and non-pulsatile flow there was no equivalent rise in cerebral oxygenation. Assuming similar cerebral oxygen delivery this finding could be explained by impaired brain oxygen extraction in the high flow range while partial pressure of carbon dioxide was elevated. In contrast, during hypocapnia, when cerebral blood flow was decreased to a greater extent as during pulsatile flow, the concomitant desaturation was less pronounced. Both findings are in line with shunting on the microcirculatory level, whereby hyperperfused vessels coexist with vessels lacking adequate flow. These findings substantiate that loss of pulsatility seems to negatively affect nutritive tissue perfusion. Raised neurological morbidity in patients supported with non-pulsatile extracorporeal cardiac assist devices could potentially be attributable to the observed perfusion deficit [2].

A Propensity Score Analysis of Renal Dysfunction in Patients after On-Pump and Off-Pump Coronary Artery Bypass Surgery

INTRODUCTION- Cardiovascular disease has emerged as a major health burden worldwide with coronary artery disease [CAD] causing highest mortality and morbidity. Coronary revascularization is the preferred treatment for patients with multivessel CAD. Based on the application of cardiopulmonary bypass [CPB], Coronary revascularization can be on-pump [OPCAB] or off-pump [CABG].The CPB is known to have multifactorial effects on all end-organ functions due to nonpulsatile flow and inflammation response. Renal function alteration is one of the multiple deleterious effects. There have been reports on superior renal function using off-pump CABG . The present study aimed to investigate and compare the prevalence of renal dysfunction in the two techniques [OPCAB versus CABG].METHODS- This was a single-center retrospective study conducted with the data from 199 patients categorized into two groups of off-pump [n=106] and on-pump [n=93]. Renal parameters were monitored on the days 0, 1, 3, 5 after the operation using Glomerular Filtration Rate [GFR]. Creatinine clearance [CrCl] of patients with diabetes, hypertension, both diabetes and hypertension, and normal patients was also correlated.RESULTS- Two groups of on-pump and off-pump were combined and classified according to Propensity Score. Renal functions were compared between the two groups no significant difference in renal function between the off-pump and on-pump groups.CONCLUSION-In the present study, there were no significant differences between the two techniques in renal outcomes. Both groups shared an almost similar change of trends in renal functions.