Aerodynamic Approach to Two-Passenger City Car Design: A Study of Square Back and Compact Shapes

Some patients with anginal chest pain and normal coronary arteries exhibit a paradoxical increase in coronary flow velocity after termination of acetylcholine infusion. The aim of this study was to investigate whether this paradoxical increase in the flow velocity is associated with the impaired microvascular dilatation to pharmacological stimuli. We infused graded doses of endothelium-dependent vasodilator acetylcholine (10, 50, and 100 microg/min for 2 min) and the endothelium-independent vasodilators, papaverine and nitroglycerin, into the left coronary artery in 15 patients with chest pain and normal coronary arteries. Coronary blood flow responses were evaluated by Doppler guidewire and quantitative angiography in the proximal left anterior descending coronary artery. Seven patients showed a paradoxical increase in coronary flow velocity after termination of acetylcholine infusion with the highest dose (100 microg/min), whereas eight showed no change or a decrease in the flow velocity. This was also observed in 50 microg/min of acetylcholine infusion. In patients with a paradoxical increase in the flow velocity, coronary flow velocity responses to acetylcholine during three graded doses were significantly blunted in comparison to those without a paradoxical increase. In contrast, coronary flow reserve to papaverine and nitroglycerin was similar in the two groups. Epicardial artery vasoreactivity to acetylcholine did not differ between the two groups. Papaverine and nitroglycerin also caused a similar degree of coronary dilatation in both groups. These results suggest that the paradoxical increase in coronary flow velocity observed immediately after termination of the intracoronary acetylcholine infusion is a marker of impaired nitric oxide-dependent dilatation of the coronary microvessels in patients with normal coronary arteries. Cathet. Cardiovasc. Intervent. 48:170-177, 1999.

921-70 Right and Left Pulmonary Artery Size and Flow Disturbances After Patent Ductus Arteriosus Coil Occlusion: A Serial Echocardiographic Study

In this paper, the supercavitation of the parallel and tandem projectiles moving underwater with high-speed under the condition with/without lateral flows is numerically simulated by the volume of fraction (VOF) model. The motion of the projectiles was handled by the overlapping grid and six degrees of freedom (DOF) techniques. The supercavitation evolution and the hydrodynamic characteristics of the projectiles were analyzed for the parallel and tandem projectiles under different conditions. The results show that the cavity shape is symmetrical under the condition without lateral flows, but is no longer symmetrical under the conditions with lateral flows. The asymmetry of the cavity contour increases with the velocity of the lateral flow. For the parallel projectiles, the change trends of the axial velocity of projectile 1 and projectile 2 are nearly the same. The offset velocity of projectile 1 and projectile 2 increases with the increase in the velocity of the lateral flow. The deflection angle of projectile 1 decreases with the increase in the lateral flow velocity but that of projectile 2 increases with the increase in the lateral flow velocity. At t = 3.0 ms, the deflection angle of projectile 2 is up to 20° under the condition of the lateral flow velocity of 11.25%, while the deflection angle of projectile 1 and 2 under other conditions is in the range of 5°. For the tandem projectiles, the axial velocity of projectile 1 gradually decreases. The change trend of the axial velocity of projectile 2 at first is the same as that of projectile 1, and then the change is dependent on the velocity of the lateral flow. Under the condition of the lateral flow velocity with 11.25%Vp, projectile 2 cannot enter the cavity of the front projectile. The change trend of the axial velocity of projectile 2 is similar as but somewhat slower than that of projectile 1. For the parallel projectiles, the ballistic stability of the projectile on the oncoming side is better than that of the projectile on the backflow side. Whether parallel or tandem projectiles, the ballistic stability of projectile 2 becomes worse with the increase in the lateral flow velocity.

The objective of this study was to assess the collateral circulation and blood flow velocity in arteries forming collateral circulation in patients with cerebral aneurysms and the occlusion of the brachiocephalic vessels. Between 1989 and 2004 we examined a group of seven consecutive patients with diagnosed cerebral aneurysm and occlusion of the extracranial artery by means of cerebral angiography, transcranial color-coded sonography (TCCS) and color Doppler sonography of extracranial arteries. The Doppler examination results achieved in this group were compared with the Doppler results of 40 healthy subjects from a control group. Three patients were diagnosed with an occluded innominate artery. In four other cases an occlusion of the extracranial segment of the internal carotid artery was found. The aneurysms were located on intracranial arteries of collateral flow. The innominate artery occlusion resulted in a hemodynamic effect which was a complete vertebral steal and systolic deceleration (in one case) or alternating flow (in two cases) in the right common carotid artery. An additional route of collateral circulation in all these cases led from extracranial carotid branches through the right external carotid artery to the ipsilateral internal carotid artery. In all seven patients, 13 intracranial collateral pathways were examined. In eight of them, including four cases with cerebral aneurysms, an increase in blood flow velocity was observed. In the remaining five cases, including three cases with cerebral aneurysms, the mean blood velocity was within the normal range. The anterior communicating artery (AComA) formed the main intracranial collateral pathway which was found in seven patients, including three patients with diagnosed AComA aneurysm. Blood flow velocity in ipsilateral (on the obstructed side) and contralateral (on the unobstructed side) anterior cerebral artery, as well as pulsatility and resistance indexes in contralateral anterior cerebral and middle cerebral arteries were higher compared with healthy control subjects. In the ipsilateral middle cerebral artery a relative, insignificant decrease of pulsatility and resistance indexes was detected. Ipsilateral and contralateral middle cerebral artery blood flow velocities were lower compared with the control group. Occlusion of the brachiocephalic vessels leads to formation of collateral circulation through the circle of Willis and the extracranial collaterals connecting the external and internal carotid arteries. An increase in blood flow velocity is commonly observed in intracranial arteries forming a collateral pathways. In some cases, not excluding arteries with a cerebral aneurysm, the increase in blood flow velocity is insignificant or none at all. This study shows that formation of a cerebral aneurysm is not always related to an increase in the flow velocity of collateral arteries.

Improved doppler detection of proximal left anterior descending coronary artery stenosis after intravenous injection of a lung-crossing contrast agent: A transesophageal doppler echocardiographic study

Effect of hemisphere-selective repetitive magnetic brain stimulation on middle cerebral artery blood flow velocity

This study was conducted to elucidate the changes in hepatic arterial blood flow after portal vein embolization. We prospectively measured the flow velocity and resistive index of the common, right, and left hepatic arteries, using Doppler sonography, in 21 patients who underwent embolization of the right portal vein. The measurements were performed before and 1, 3, 5, 7, and 14 days after embolization. We assessed the changes in liver volume with a volumetric study using CT. After embolization, flow velocity in the common hepatic artery increased significantly (p < 0.0001). Flow velocity in the right hepatic artery also increased significantly (p < 0.0001), with a significant decrease in resistive index (p < 0.0001). The flow velocity and resistive index of the left hepatic artery were unchanged. The increase in flow velocity in the right hepatic artery significantly correlated with that in the common hepatic artery (r = 0.514, p < 0.05). The calculated volume of the embolized right hepatic lobe significantly (p < 0.0001) decreased, from 685 +/- 32 cm(3) before embolization to 568 +/- 28 cm(3) after embolization. The atrophy rate of the right hepatic lobe significantly correlated with the increase in flow velocity in the right hepatic artery (r = 0.700, p < 0.0005). Portal vein embolization induces an increase in hepatic arterial blood flow velocity in the embolized hepatic segments, resulting from an increase in common hepatic arterial flow, but not from a steal phenomenon due to decreased hepatic arterial blood flow in the nonembolized hepatic segments. This observation may be explained by the simple mechanical effect of interposing a slower flowing stream (portal flow) in the path of a faster flowing stream (arterial flow).

Hemodynamic effect of intermittent pneumatic compression and the position of the body.

In cremaster muscle of pentobarbital-anesthetized rats, temporary occlusion of an arteriole increased red blood cell velocity (mean increase, 8.2 +/- 1.0 mm/sec from a control velocity of 7.9 +/- 0.7 mm/sec) in proximal parallel arteriolar branches (mean control diameter, 19.4 +/- 0.6 microns). Increases in flow velocity were consistently followed by proportional delayed (6-15 seconds) increases in arteriolar diameter (5.8 +/- 0.7 microns). Administration of NG-monomethyl-L-arginine (200 microM), an inhibitor of the synthesis of endothelium-derived relaxing factor that blocked the arteriolar responses to acetylcholine (1 microM) but not to arachidonic acid (10 microM), did not affect the dilation (mean increase, 8.9 +/- 1.1 microns) due to increases in red blood cell velocity (13.4 +/- 1.5 mm/sec). However, the cyclooxygenase inhibitor indomethacin (or meclofenamate), which completely blocked the dilator response to arachidonic acid but did not change the response to acetylcholine, inhibited the arteriolar dilation (mean increase, 0.3 +/- 0.2 micron) due to increases in red blood cell velocity (9.3 +/- 1.0 mm/sec). Inhibition of prostaglandin synthesis also reduced the increase in calculated blood flow by 57% during occlusion. These results suggest that the arterioles are sensitive to increases in blood flow velocity (wall shear stress), in response to which they release prostaglandins, eliciting vasodilation. The existence of this phenomenon in the skeletal muscle microcirculation suggests a new regulatory mechanism that, by modulation of vascular resistance in the microvascular network, has the role of normalizing wall shear stress and providing for substantial increases in tissue blood flow.

The increase in carotid artery blood flow velocity is a measure of the severity of the carotid artery stenosis caused by atherosclerosis. Carotid artery stenosis is progressive and is of great importance due to the risk of stroke it creates. As an alternative to radiological examinations in these patients, patient follow-up can be facilitated by associating novel laboratory parameters with the severity of stenosis. In this study, we aimed to investigate the effect of the calculated plasma osmolality and atherogenic index of plasma on carotid artery blood flow velocities in patients with carotid artery stenosis. A total of 161 patients diagnosed with carotid artery stenosis who admitted to our clinic between May 2018 and May 2020 were retrospectively analyzed. According to the carotid artery blood flow velocities measured with the Doppler ultrasonography, the patients were divided into two groups as "Normal flow velocity group" (n = 62) and "Increased flow velocity group" (n = 99). The calculated plasma osmolality, atherogenic index of plasma, and mean platelet volume were significantly associated with increased carotid artery blood flow velocity (p < 0.001, p < 0.001, p = 0.006; respectively). Calculated plasma osmolality and atherogenic index of plasma were identified as independent predictors of increase in carotid artery blood flow velocity (p < 0.001, p < 0.001; respectively). In the Receiver Operating Characteristic curve analysis, the plasma osmolality cut-off value, which predicts the increase in carotid artery blood flow velocity was found to be 291.45 mOsm/kg (Area Under the Curve: 0.746, p < 0.001, 65.7% sensitivity, and 67.7% specificity), and atherogenic index of plasma cut-off value was 0.20 (Area Under the Curve: 0.735, p < 0.001, 65.7% sensitivity, and 66.1% specificity). There was a significant relationship between the increase in carotid artery blood flow velocity and the increase in plasma osmolality and atherogenic index of plasma values. As a result, we can predict the increase in carotid artery blood flow velocity, that is, the increase in the severity of the carotid artery stenosis, with plasma osmolality and atherogenic index of plasma values that can be calculated simply from routine biochemical tests.

Most floating offshore platforms are cylindrical with low aspect ratios, whereas most existing research focuses on structures with high aspect ratios. Research on the influence of the free-end effect on the flow around a cylinder at low aspect ratios is still insufficient. Therefore, in this study, the computational fluid dynamics (CFD) method was used to numerically simulate the flow characteristics of finite and infinite cylinders at different flow rates, and the influence of the free-end effect on the flow characteristics of the cylinders was discussed. The results show that the free-end effect significantly interferes with the flow characteristics of finite cylinders. In particular, for a shorter cylinder (L/D = 2), the free-end effect caused obvious vortex separation and flow instability, resulting in a higher vortex intensity. With an increase in flow velocity, the influence of the free-end effect weakened; however, the flow remained unstable. In contrast, the flow of an infinite cylinder is not affected by the free-end effect and always maintains a stable flow. The vortex region was small, and with the increase in flow velocity, the flow gradually tended to be inertia-dominant, showing more stable flow characteristics.

An insufficient perfusion of the brain tissue can cause a decrease in cognitive functions, and long-term ischemia also leads to emotional and motor disorders. At the same time, check-up of the state of the cerebral blood flow is an important aspect of monitoring the progression of many pathological conditions. The amino acid glycine has been widely used in neurological practice for over 30 years, which helps improve hemodynamic characteristics and metabolic processes in the brain tissue.The aim of the work was to analyze the effect of a sublingual administration of glycine on the cerebral blood flow velocity in practically healthy subjects using transcranial Doppler (TCD) sonography.Material and methods. The pilot randomized controlled study included 20 healthy subjects aged 25 to 65 years, equally divided into 2 groups, one of which took glycine sublingually at a dose of 300 mg/day for 30 days, and the second group was a control group and did not receive the drug. In the first group, a load testing was carried out with 1000 mg of glycine, and in the control group – with 1000 mg of placebo. All the subjects underwent an assessment of the blood flow in the extracranial and intracranial vessels using standard protocols of TCD.Results. In Group I, after a month of glycine intake, the peak systolic (by 11.9 cm/s) and average maximum (by 6.3 cm/s) velocities in the left middle cerebral artery (MCA) increased significantly (p &lt;0.01), while in the right MCA there was an increase in the peak systolic (by 9.3 cm/s), and diastolic (by 2.8 cm/s) and average maximum (by 5.8 cm/s) velocities. In turn, in the control group, there was no significant increase in velocity. During the load testing with glycine / placebo, the relative increase in the peak systolic velocity in the MCA in the main group was 7.6% [1.2; 10.9], in control group was 1.5% [-3.6; 5.5] (p=0.03).Conclusion. Glycine intake for 30 days contributes to a reliable improvement in cerebral hemodynamics in healthy individuals, such as an increase in the linear blood flow velocity in the MCA. At the same time, a single dose of 1000 mg of glycine leads to an increase in the peak systolic and average maximum intracranial blood flow velocities up to 10%.

Background. Orthostatic hypotension (OH) is an important nonmotor manifestation of Parkinson's disease (PD). Changes in cerebrovascular reactivity may contribute to this manifestation and can be monitored using transcranial Doppler. Objective. To identify possible changes in cerebrovascular reactivity in patients with OH. Methods. Twenty-two individuals were selected and divided into three groups: with and without OH and controls. Transcranial Doppler was used to assess basal mean blood flow velocity, postapnea mean blood flow velocity, percentage increase in mean blood flow velocity, and cerebrovascular reactivity as measured by the breath-holding index. Results. PD patients had lower values of basal velocity (p = 0.019), postapnea velocity (p = 0.0015), percentage increase in velocity (p = 0.039), and breath-holding index (p = 0.04) than the controls. Patients with OH had higher values of basal velocity (p = 0.09) and postapnea velocity (p = 0.19) but lower values of percentage increase in velocity (p = 0.22) and breath-holding index (p = 0.32) than patients without OH. Conclusions. PD patients present with abnormalities in a compensatory mechanism that regulates cerebral blood flow. OH could be an indicator of these abnormalities.

Antarctic sea ice extent reached a record minimum in 2023. Whilst the buttressing resistance provided by ice shelves has been quantified through past numerical studies, the degree to which sea ice can buttress and regulate upstream ice flow is not known. If significant, a future decline in sea ice extent would lead to increased ice discharge rates and a higher global mean sea level.The January 2022 disintegration of landfast sea ice in the Larsen B embayment was closely followed by a significant increase in ice flow velocities and retreat rates of numerous outlet glaciers in the region. Notably, Crane glacier saw an initial ~8km retreat over six weeks, during which time a 5% increase in velocity was observed. Afterwards, the full evacuation of ambient sea ice between October and November was accompanied by the most significant monthly increase in velocities.We use the numerical ice flow model, Ua, to investigate the buttressing effect of sea ice to Crane glacier. The ice-sheet model was initialised with sea ice included and constrained with observational velocity and geometry data sets. We conducted perturbation experiments on sea ice properties to explore its impact on the glacier. The results suggest that sea ice provided significant buttressing to the glacier before its collapse.

Detachment of coal fines deposited in proppant packs induced by single-phase water flow: Theoretical and experimental analyses