Presence Of Flow Reversal Research Articles

Abstract 17323: Avoiding Procedural Closure of the Patent Ductus Arteriosus Following Late Acetaminophen Therapy in Preterm Infants

Introduction: Management of a hemodynamically significant patent ductus arteriosus (hsPDA) in preterm infants beyond 3 weeks of age continues to be a debate. Clinical equipoise exists between pharmacologic agents versus procedural closure techniques (surgical ligation or transcatheter occlusion). The efficacy of acetaminophen for early closure of hsPDA has been demonstrated, but there remains a paucity of data for late closure. Hypothesis: To test the hypothesis that late administration of acetaminophen for a hsPDA is associated with reduced rates of procedural closure in preterm infants. Methods: We performed a post-hoc analysis of preterm infants (<37 weeks) referred to Boston Children’s Hospital for ongoing management of a hsPDA from January 2019 to January 2023. We compared neonates with a hsPDA exposed and not exposed to acetaminophen at > 3 weeks of age. The primary outcome was avoidance of procedural closure. We assessed for predictors of closure following acetaminophen therapy. Results: We identified 110 preterm infants (median gestational age of 25 weeks at birth) referred for closure of a hsPDA beyond 3 weeks of age (Fig). Late acetaminophen was used in 26 patients (median postnatal age of 31 days). Late acetaminophen was associated with higher rates of non-procedural PDA closure 10/26 (38%), compared to 6/84 (7%) of infants who did not receive late acetaminophen (OR 0.12, CI 0.04 - 0.39, p < 0.01). Presence of flow reversal in the descending aorta was associated with lower likelihood of PDA closure with late acetaminophen (OR 0.09, CI 0.01 - 0.85, p=0.017). Conclusions: This study found that preterm infants with a hsPDA treated with late acetaminophen had a decreased need for procedural closure. Infants who responded were less likely to have flow reversal in the descending aorta, suggesting that consideration of a course of late acetaminophen prior to procedural closure of a hsPDA in preterm neonates should be selective and based on patient-specific risk factors.

Interaction between the Stress Phase Angle (SPA) and the Oscillatory Shear Index (OSI) Affects Endothelial Cell Gene Expression.

Hemodynamic forces play an important role in the non-uniform distribution of atherosclerotic lesions. Endothelial cells are exposed simultaneously to fluid wall shear stress (WSS) and solid circumferential stress (CS). Due to variations in impedance (global factors) and geometric complexities (local factors) in the arterial circulation a time lag arises between these two forces that can be characterized by the temporal phase angle between CS and WSS (stress phase angle–SPA). Asynchronous flows (SPA close to -180°) that are most prominent in coronary arteries have been associated with localization of atherosclerosis. Reversing oscillatory flows characterized by an oscillatory shear index (OSI) that is great than zero are also associated with atherosclerosis localization. In this study we examined the relationship between asynchronous flows and reversing flows in altering the expression of 37 genes relevant to atherosclerosis development. In the case of reversing oscillatory flow, we observed that the asynchronous condition upregulated 8 genes compared to synchronous hemodynamics, most of them proatherogenic. Upregulation of the pro-inflammatory transcription factor NFκB p65 was confirmed by western blot, and nuclear translocation of NFκB p65 was confirmed by immunofluorescence staining. A comparative study between non-reversing flow and reversing flow found that in the case of synchronous hemodynamics, reversing flow altered the expression of 11 genes, while in the case of asynchronous hemodynamics, reversing flow altered the expression of 17 genes. Reversing flow significantly upregulated protein expression of NFκB p65 for both synchronous and asynchronous conditions. Nuclear translocation of NFκB p65 was confirmed for synchronous and asynchronous conditions in the presence of flow reversal. These data suggest that asynchronous hemodynamics and reversing flow can elicit proatherogenic responses in endothelial cells compared to synchronous hemodynamics without shear stress reversal, indicating that SPA as well as reversal flow (OSI) are important parameters characterizing arterial susceptibility to disease.

Cross-Sectional Associations of Flow Reversal, Vascular Function, and Arterial Stiffness in the Framingham Heart Study.

Experimental studies link oscillatory flow accompanied by flow reversal to impaired endothelial cell function. The relation of flow reversal with vascular function and arterial stiffness remains incompletely defined. We measured brachial diastolic flow patterns along with vasodilator function in addition to tonometry-based central and peripheral arterial stiffness in 5708 participants (age 47±13 years, 53% women) in the Framingham Heart Study Offspring and Third Generation cohorts. Brachial artery diastolic flow reversal was present in 35% of the participants. In multivariable regression models, the presence of flow reversal was associated with lower flow-mediated dilation (3.9±0.2 versus 5.0±0.2%; P<0.0001) and reactive hyperemic flow velocity (50±0.99 versus 57±0.93 cm/s; P<0.0001). The presence of flow reversal (compared with absence) was associated with higher central aortic stiffness (carotid-femoral pulse wave velocity 9.3±0.1 versus 8.9±0.1 m/s), lower muscular artery stiffness (carotid-radial pulse wave velocity 9.6±0.1 versus 9.8±0.1 m/s), and higher forearm vascular resistance (5.32±0.03 versus 4.66±0.02 log dyne/s/cm5; P<0.0001). The relations of diastolic flow velocity with flow-mediated dilation, aortic stiffness, and forearm vascular resistance were nonlinear, with a steeper decline in vascular function associated with increasing magnitude of flow reversal. In our large, community-based sample, brachial artery flow reversal was common and associated with impaired vasodilator function and higher aortic stiffness. Our findings are consistent with the concept that flow reversal may contribute to vascular dysfunction.

Bed form genesis from bed defects under unidirectional, oscillatory, and combined flows

New experimental data on bed form initiation under unidirectional, oscillatory, and combined flows are presented to gain quantitative insight into bed form genesis from artificially generated defects on a flat sediment-laden bed. Planform changes revealed in time-lapse photography allowed study of the evolution of the downstream and upstream edges of defects from their initial geometric center. Based on this temporal data set and flow velocity profiles, it was observed that combined flow bed forms share the same bed form initiation processes as unidirectional and oscillatory flows, which are reflected directly in the generation of similar geometric patterns regardless of the hydrodynamic conditions. The development of these bed defects is strongly coupled to the direction and magnitude of the shear stress applied to the bed throughout the wave cycle. Under current-dominated combined flow conditions, no defect propagation occurred in the upstream direction, despite the presence of flow reversal. In addition, spectral analysis of the evolution of the downstream and upstream edges of the defects demonstrated that (i) periodicity in the defect growth pattern scales with the wave period for pure oscillatory flows; (ii) wave-dominated combined flows possess a period-driven peak with respect to defect growth in experiments with relatively short wave periods, but this peak is absent in experiments possessing relatively long wave periods (T >15 s); and (iii) current-dominated combined flows and pure unidirectional flows do not display a period-driven peak in defect growth. These results suggest that the occurrence of long-period combined flow bed forms may be underrepresented in the sedimentary record.

Heat Transfer and Flow Pattern Characteristics for HFE-7100 Within Microchannel Heat Sinks

This study investigates the heat transfer characteristics and flow pattern for the dielectric fluid HFE-7100 within multiport microchannel heat sinks with hydraulic diameters of 480 μm and 790 μm. The test results indicate that the heat transfer coefficient for the smaller channel is generally higher than that of the larger channel. It is found that the heat transfer coefficients are roughly independent of heat flux and vapor quality for a modest mass flux ranging from 200 to 400 kg m−2 s−1 at a channel size of 480 μm and there is a noticeable increase of heat transfer coefficient with heat flux for hydraulic diameters of 790 μm. The difference arises from flow pattern. However, for a smaller mass flux of 100 kg m−2 s−1, the presence of flow reversal at an elevated heat flux for hydraulic diameters of 480 μm led to an appreciable drop of heat transfer coefficient. For a larger channel size of 790 μm, though the flow reversal is not observed at a larger heat flux, some local early partial dryout still occurs to offset the heat flux contribution and results in an unconceivable influence of heat flux. The measured heat transfer coefficients for hydraulic diameters of 790 μm are well predicted by the Cooper correlation. However, the Cooper correlation considerably underpredicts the test data by 35–85% for hydraulic diameters of 480 μm. The influence of mass flux on the heat transfer coefficient is quite small for both channels.

Echocardiographic predictors of failure in patients undergoing coil occlusion of patent ductus arteriosus

In this study, we sought to determine whether the risk of failure of coil occlusion of patent ductus arteriosus (PDA) could be predicted on the basis of echocardiographic variables. The echocardiographic characteristics of patients in whom PDA coil occlusion failed were compared with those in whom the procedure was successful. A total of 5 variables were evaluated: PDA diameter (PDAd); indexed PDAd; PDA shape; left ventricular end-diastolic diameter; and the presence of flow reversal in the descending aorta. We found that 2 variables related to the size of the duct (PDAd and PDAd/body surface area), and 2 related to the magnitude of the shunt (left ventricular end-diastolic diameter and flow reversal) were positively associated with failure ( P < .05). PDAd and flow reversal had the greater effect in each group and remained significant when they were put into a logistic regression model to predict failure ( P = .004 and .053, respectively). In conclusion, echocardiographic variables can predict risk of failure in patients undergoing PDA coil occlusion.

On the Reynolds-number independence of mixed convection in a vertical channel subjected to asymmetric wall temperatures with and without flow reversal

The problem of mixed convection in a vertical channel with asymmetric wall temperatures including situations of flow reversal is studied numerically. The SIMPLER algorithm with a staggered grid system is employed to solve the corresponding numerical equations formulated by the finite-volume method. A second-order upwind scheme is used to model the convective term, and a suitable grid distribution is introduced. The ranges of the parameters studied are 0 ⩽ r t ⩽ 1, 1 ⩽ Re ⩽ 1000, and 0 ⩽ Gr/Re ⩽ 500. The numerical results, with the streamwise coordinate scaled by the Reynolds number (Re), show that solutions for the velocity and temperature fields are independent of the Reynolds number when Re ⩾ 50, even in the presence of flow reversal. These solutions, however, are dependent on r t and Gr/Re. Subsequently, correlations are proposed for the bulk temperature distribution and the local Nusselt numbers along the hot wall and the cold wall.