High Flow Range Research Articles

Automatic Piston-Type Flow Standard Device Calibration System

Measurement of flow is crucial for assuring product quality, increasing manufacturing effectiveness, and promoting the development of science and technology. With the advancement of calibration and automation, standard devices using the mass method, volumetric method, and master meter method have limitations, such as low calibration efficiency and automation, large size, and complex operation. Innovations in this area are desperately needed. To realize the automation of calibrating ultrasonic water meters, a piston-type flow standard device calibration system with a high degree of automation, high calibration efficiency, small size, and easy operation was designed. A piston-type flow standard device was designed, the standard device was modeled, the selection of the main hardware and the design of the automated control of the hardware parts were completed; an automation control system adapted to the flow standard device was developed; and, furthermore, a water meter flow point calibration algorithm integrating the start–stop method and the dual-time method, as well as a water meter flow correction algorithm, was devised to improve the efficiency of ultrasonic water meter calibration. An uncertainty assessment of the designed system was completed; the standard uncertainty and expanded uncertainty of the device were 0.013% and 0.026%. Meanwhile, flow calibration tests were conducted, validating the rationality of the automated calibration algorithm for ultrasonic water meters. The results show that ultrasonic water meters calibrated with flow correction have a flow error within ±3% in the “low flow range” and within ±2% in the “high flow range”, with a repeatability of less than 0.05%. This indicates that a piston-type flow standard device, coupled with an automation calibration control system, can efficiently, accurately, and conveniently perform water meter calibration, and the system has good practical value.

Whole-body vibration exercise and training increase regional CBF in mild cognitive impairment with enhanced cognitive function.

Preclinical and non-medicinal interventions are essential for preventing and treating cognitive decline in patients with mild cognitive impairment (MCI). Whole-body vibration (WBV) exercise is conducted on a platform that generates vertical sinusoidal vibrations, and WBV training may improve regional cerebral blood flow (rCBF) and cognitive function, however, the underlying mechanism remains unclear. The aim of the present study was to investigate whether WBV exercise and a 24-week WBV training protocol increased rCBF and enhanced cognitive function in patients with amnestic MCI (aMCI). [99mTc]-ECD and SPECT studies were performed on 16 aMCI patients at baseline, during WBV exercise, and on 6 of the 16 patients after 24-week WBV training. To diagnose SPECT images and select the patients, a Z-score mapping approach was used, which revealed pathological hypoperfusion in the parietal association cortex, precuneus and/or posterior cingulate gyrus for MCI at baseline. rCBF was semi-quantitatively measured and underestimation in the high flow range was corrected. Since it is difficult to quantitatively measure rCBF during WBV exercise, the rCBFratio was obtained by standardizing with the average of individual mean SPECT counts with correcting underestimation in the high flow range. The rCBFratios at baseline and after WBV training were also obtained in a similar manner. Since the changes in rCBF were regarded as corresponding to the changes in rCBFratio, the ratios were compared. Cognitive function was also evaluated and compared. We found that the rCBFratio changed with an average range of 11.5% during WBV exercise, and similar changes were observed after 24-week WBV training with a 13.0% change, resulting in improved cognitive function (MoCA-J, P = 0.028). The rCBFratio increased in the parietal association cortex and occipital lobes, including the precuneus and posterior cingulate gyrus, at which hypoperfusion was detected at baseline, but decreased in the frontal lobe and anterior cingulate gyrus. The rCBFratio increased on the right side of several motion-suppressive nuclei by WBV exercise; the bilateral red nuclei and right medial globus pallidus by WBV training. WBV exercise and training increase rCBF in aMCI patients, and WBV training enhances cognitive function and may increase the cognitive reserve. Further investigation is necessary.

Hemolysis at low blood flow rates: in-vitro and in-silico evaluation of a centrifugal blood pump

BackgroundTreating severe forms of the acute respiratory distress syndrome and cardiac failure, extracorporeal membrane oxygenation (ECMO) has become an established therapeutic option. Neonatal or pediatric patients receiving ECMO, and patients undergoing extracorporeal CO2 removal (ECCO2R) represent low-flow applications of the technology, requiring lower blood flow than conventional ECMO. Centrifugal blood pumps as a core element of modern ECMO therapy present favorable operating characteristics in the high blood flow range (4 L/min–8 L/min). However, during low-flow applications in the range of 0.5 L/min–2 L/min, adverse events such as increased hemolysis, platelet activation and bleeding complications are reported frequently.MethodsIn this study, the hemolysis of the centrifugal pump DP3 is evaluated both in vitro and in silico, comparing the low-flow operation at 1 L/min to the high-flow operation at 4 L/min.ResultsIncreased hemolysis occurs at low-flow, both in vitro and in silico. The in-vitro experiments present a sixfold higher relative increased hemolysis at low-flow. Compared to high-flow operation, a more than 3.5-fold increase in blood recirculation within the pump head can be observed in the low-flow range in silico.ConclusionsThis study highlights the underappreciated hemolysis in centrifugal pumps within the low-flow range, i.e. during pediatric ECMO or ECCO2R treatment. The in-vitro results of hemolysis and the in-silico computational fluid dynamic simulations of flow paths within the pumps raise awareness about blood damage that occurs when using centrifugal pumps at low-flow operating points. These findings underline the urgent need for a specific pump optimized for low-flow treatment. Due to the inherent problems of available centrifugal pumps in the low-flow range, clinicians should use the current centrifugal pumps with caution, alternatively other pumping principles such as positive displacement pumps may be discussed in the future.

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].

Sensitivity Analysis of Multistage Compressor Characteristics Under the Spray Atomization Effect Using a CFD Model

In this paper, a CFD model is used to simulate the effect of spray atomization at the compressor inlet on a multistage axial subsonic compressor. Special attention is paid to the change of compressor characteristics with wet compression under different rotating speeds to gain the compressor characteristic lines of wet compression. The effects of pneumatic crushing and blade-wall-collision on water droplets and droplet trajectories are contrasted and analyzed under different spray conditions. Then, the whole/stage-by-stage compressor performances and the flow field are also investigated under dry and wet cases near the design operating condition. The results indicate that multistage compressor performance can be improved with wet compression under the proper water spaying rate and a small droplet size. The influence of pneumatic crushing on the water droplets below 20 μm can be ignored, and the effect of blade collision on water droplets above 5μm should be considered in the wet compression conditions. Compared to the dry compression, as measured by volume flow, wet compression with proper spaying conditions makes the front stages operate within a relatively high flow range and the back stages operate within a relatively low flow range. Additionally, the operating state with wet compression is opposite to the compressor operating near the surge boundary, which presents the phenomenon of “former surged and back blocking”.

New Regression Equation for 123I-IMP Non-invasive Cerebral Blood Flow Measurement Using the Graph Plot Method.

A graph plot (GP) method using 123I-N-isopropyl-p-iodoamphetamine (123I-IMP) has been proposed as a simple and non-invasive estimation of quantitative cerebral bloodflow (CBF). A regression equation for the GP method was estimated by the data of resting state. Therefore, the accuracy of CBF values in high flow range may be an underestimated possibility in this method.The aim of this study was to formulate a new regression equation for the GP method by the data of resting state and acetazolamide (ACZ) challenge, and to clarify the accuracy of it. The images of 26 consecutive patients who underwent both 123I-IMP chest radioisotope-angiography (RIA) and single photon emission computed tomography (SPECT) examinations were used to construct the new regression equation. Examinations of the resting state and ACZ challenge were performed in different days. All patients were analyzed by both the GP method and autoradiography (ARG) method which is the conventional examination with the one-point arterial blood sampling. A linear regression equation between the index of the input function was obtained by the GP method and CBF value of ARG. The linear regression equation based on the resting data was compared with the equation based on the resting and ACZ challenge (rest+stress) data. Goodliner correlation was obtained between the index of the input function obtained by the GP method and CBF value of the ARG method in the rest+stress state (y=2.75x+15.1, r=0.78). In contrast, correlation results between the index of the input function obtained by the GP method and CBF value of the ARG method in the resting state was expressed as y=2.28x+18.4, r=0.54 rCBF values based on the resting data was 20% underestimated in the high flow range compared with values based on the rest+stress data. The new linear regression equation for the GP method is useful for clinical study. Key words: non-invasive cerebral blood flow measurement method, graph plot (GP), autoradiography (ARG), 123I-N-isopropyl-p-iodoamphetamine (123I-IMP).

Characteristics of a micro-mechanical thermal flow sensor based on a two hot wires principle with constant temperature operation in a small channel

A thermal mass flow sensor with high dynamic flow range in silicon bulk micromachining membrane technology is presented. The response behavior of this sensor based on a two hot wire principle is described. This sensor configuration uses two hot wires mounted closely spaced one behind the other within a thin membrane, kept at the same temperature. The power to compensate cooling of and the interaction between the two hot wires are used to calculate mass flows and directionality of flows of gaseous and liquid fluids in a small channel. The response shows both anemometric and calorimetric behavior, depending on fluid, channel height and flow range. The hot wires are heated relative to temperature sensors located also on an isolated membrane on the same chip. Choosing an appropriate evaluation procedure an independence of the signal from the ambient temperature is achieved. This configuration will be discussed in view of the published results of single heater flow sensors, being of calorimetric or anemometric type. A calculation method for the determination of linear and power law range of the response is given.

Noise at the mid to high flow range of a turbocharger compressor

The acoustic and performance characteristics of an automotive centrifugal compressor are studied on a steady-flow turbocharger test bench, with the intention of identifying operating regions associated with flow noise within the compressor and connected ducting. Near choke, discrete tones including rotor-order frequency and its harmonics (bladepass) are observed. As the flow rate is reduced, the current compressor exhibited a broadband elevation of noise in the 4-12 kHz band, which was evident both in the upstream compressor duct and external sound pressure level (SPL) measurement locations. At all rotational speeds studied here, the total SPL in this frequency range demonstrates a strong dependence on the incidence angle of the incoming flow with the blades at the inducer of the impeller. When the incidence angle is further increased (mass flow rate is decreased) beyond a critical value, the temperature near the inducer tips increases sharply, suggesting local flow reversal, and the total SPL in the 4-12 kHz range suddenly reduces.

Effect of inlet vanes on centrifugal compressor acoustics and performance

The effect of inlet guide vanes (IGVs) on the acoustic and performance characteristics of an automotive centrifugal compressor is studied on a steady-flow turbocharger experimental facility. Broadband noise accompanying flow separation occurs as the flow rate of the compressor is reduced and the incidence angle of the flow relative to the leading edge of the inducer blades increases. The addition of IGVs upstream of the inducer imparts a tangential (swirl) velocity component in the same direction of impeller rotation, which improves the incidence angle particularly at low to mid-flow rates. In the present study, experimental data is compared for three compressor inlet geometries, including a no-swirl baseline along with two different IGV configurations. IGVs were shown to slightly improve the surge line at the highest rotational speed considered in this study, while compromising the maximum flow rate at all rotational speeds. In the high-flow range, IGVs are observed to increase compressor inlet noise levels over a wide frequency range. At the more common low to mid-flow range, however, broadband whoosh noise is reduced with the addition of IGVs in the 5-12 kHz band.

원뿔형 벤츄리수로의 수리특성

This study analyzed the hydraulic characteristics of a venturi flume with a circular cone using a 3-D numerical model which uses RANS(Reynolds-Averaged Navier-Stokes Equation) as the governing equation. The venturi flume with the circular cone efficiently measures the discharge in the low-flow to high-flow range and offers the advantage of accurate discharge measurements in the case of a low flow. With no influence of the tail-water depth, the stage-discharge relationship and the flow behaviors were analyzed to verify the numerical simulation results. Additionally, this study reviewed the effect of the tail-water depth on the flow. The stage-discharge relationship resulting from a numerical simulation in the absence of an effect by the tail-water depth showed a maximum margin of error of 4 % in comparison to the result of a hydraulic experiment. The simulation results reproduced the overall flow behaviors observed in the hydraulic experiment well. The flow starts to become influenced by the tail-water depth when the ratio of the tail-water depth to the total head exceeds approximately 0.7. As the ratio increases, the effect on the flow tends to grow dramatically. As shown in this study, a numerical simulation is effective for identifying the stage-discharge relationship of a venturi flume with various types of venturi bodies, including a venturi flume with a circular cone.

Three dimensional CFD analysis and experimental test of flow force acting on the spool of solenoid operated directional control valve

Solenoid direct operated spool type directional control valves are often used in various machines and equipment. A subject of the analysis presented in the paper is the directional control valve WE10H produced by several manufacturers. The continual development of this type of valves has allowed for significant reduction of the flow resistance through the channels and consequently for relatively high flow range. The increase of flow range causes a growth of flow forces which may change the balance of forces acting on the spool and prevent the correct operation of the valve. That is why the undertaken task is important.The paper proposes calculation of the forces associated with the flow (pressure force and viscous force) using 3D CFD modeling. In the proposed method, first the surface affected by the forces associated with the flow through each path was defined and then, using CFD method, values of the flow forces were determined.To confirm the obtained results of CFD calculations a device for measuring forces acting along the axis of the spool was prepared. The force values obtained in the CFD calculations were compared with those obtained on the test bench. The resulting accuracy was satisfactory. In order to reduce flow forces additional internal channels in the valve body were introduced. The innovative solution of the valve allowed for a higher flow range of about 45% without any change of spring or solenoid.

Estimation of flushing time in a monsoonal estuary using observational and numerical approaches

Estimation of flushing time (T F) in an estuary is important for water quality analysis, and it is one of the major transport time scales used in estuaries to quantify the hydrodynamic processes and for water resources management strategies. Thus, the main objective of the present study was to estimate the T F in the Mandovi estuary (a monsoonal estuary) on the west coast of India. In the study, field observations of salinity (FOS) and a numerical model are used to describe the T F during the south-west monsoon (heavy river discharge), post-monsoon (moderate river discharge) and pre-monsoon (negligible river discharge). T F was calculated for 12 (months) river discharge scenarios (the calculation was done under monthly mean flow conditions). Among the 12 scenarios, four scenarios were within an extremely low flow range: 0.8–2.2 m3s−1; four were in a moderate flow range: 4.3–67 m3s−1; and the remaining four were in a high flow range: 119.0–506.6 m3s−1. The T F calculated from FOS and numerical model showed good matches during the periods of heavy river discharge and moderate river discharge. The results from FOS (numerical model) showed that the T F was 1.12 (1.11) days for a river flow of 506.6 m3s−1 (during the south-west monsoon), and the T F reached 251.28 (592.38) days under extreme low flow of 0.8 m3s−1 (during the pre-monsoon). Regression equations fitted by power and exponential functions were derived from FOS and numerical model simulations to correlate T F with monthly mean river discharges. The power regression equation derived from FOS (numerical model) showed good statistical fit with data (r = −0.997 (−1.0)) for any given river discharge compared to the exponential regression equation (r = −0.81 (−0.80)). Hence, the power regression equation can be used for the rapid evaluation of the impact of drought (during the pre-monsoon) and flood (during the SW monsoon) scenarios in the estuary.

Nasal Cannula, CPAP, and High-Flow Nasal Cannula: Effect of Flow on Temperature, Humidity, Pressure, and Resistance

Delivery of warm, humidified, supplemental oxygen via high-flow nasal cannula has several potential benefits; however, the high-flow range may not maintain humidification and temperature and in some cases may cause excessive expiratory pressure loading. To compare the effect of flow on temperature, humidity, pressure, and resistance in nasal cannula (NC), continuous positive airway pressure (CPAP), and high-flow nasal cannula (HFNC) in a clinical setting. The three delivery systems were tested in the nursery using each instrument's recommended specifications and flow ranges (0-3 L/min and 0-8 L/min). Flow, pressure, temperature, and humidity were measured, and resistance was calculated. For all devices at 0-3 L/min, there was a difference (p<0.01) in temperature (NC 35.9°C > CPAP 34.5°C > HFNC 34.0°C), humidity (HFNC 82% > CPAP 77% > NC 57%), pressure (HFNC 22 cmH(2)O > NC 4 cmH(2)O > CPAP 3 cmH(2)O), and resistance (HFNC 636 cmH(2)O/L/sec > NC 270 cmH(2)O/L/sec > CPAP 93 cmH(2)O/L/sec) as a function of flow. For HFNC and CPAP at 0-8 L/min, there was a difference (p<0.01) in temperature (CPAP 34.5°C > HFNC 34.0°C) in humidity (HFNC 83 % > CPAP 76 %), pressure (HFNC 56 cmH(2)O > CPAP 14 cmH(2)O) and resistance (HFNC 783 cmH(2)O/L/sec > CPAP 280 cmH(2)O/L/sec) as a function of flow. Gas delivered by HFNC was more humid than NC and CPAP. However, the higher pressure and resistance delivered by the HFNC system may have clinical relevance, such as increased work of breathing, and warrants further in vivo studies.

Thermal flow sensors for MEMS spirometric devices

Sleep-specific respiration disturbances and their coprevalences with basic cardiovascular diseases constitute a supplementary risk for the cardiovascular system and require both urgent diagnostic assessment as well as consistent therapeutic measures. Thus, the need for controlling the breathing of these patients over a long period has become a new focus of interest. Due to its small thermal mass, the micro-machined thermal flow sensor fits the specific requirements in the patient respiration control of high dynamic flow range combined with a fast response time. We present the development of our flow sensor with a special adaptation for spirometric applications. The sensor exhibits a high accuracy, a short response time (<1 ms) and a low power consumption (10 mW). Furthermore, heating structures are added onto the chip to prevent condensation. Hence, it represents an attractive solution for the use of portable equipment for preventive exploration of breathing in home-care applications.

Local adaptation at the range peripheries of Sitka spruce

High-dispersal rates in heterogeneous environments and historical rapid range expansion can hamper local adaptation; however, we often see clinal variation in high-dispersal tree species. To understand the mechanisms of the species' distribution, we investigated local adaptation and adaptive plasticity in a range-wide context in Sitka spruce, a wind-pollinated tree species that has recently expanded its range after glaciations. Phenotypic traits were observed using growth chamber experiments that mimicked temperature and photoperiodic regimes from the limits of the species realized niche. Bud phenology exhibited parallel reaction norms among populations; however, putatively adaptive plasticity and strong divergent selection were seen in bud burst and bud set timing respectively. Natural selection appears to have favoured genotypes that maximize growth rate during available frost-free periods in each environment. We conclude that Sitka spruce has developed local adaptation and adaptive plasticity throughout its range in response to current climatic conditions despite generally high pollen flow and recent range expansion.

Properties of ITO films prepared by reactive magnetron sputtering

Indium tin oxide (ITO) thin films were deposited by mid frequency pulsed dual magnetron sputtering using a metallic alloy target with 10 wt.% tin in an atmosphere of argon and oxygen. The aim of the work was to study the interdependence of structural, electrical and optical properties of ITO films deposited in the reactive and transition target mode, respectively. The deposition rate in the transition mode exceeds the deposition rate in the reactive mode by a factor of six, a maximum value of 100 nm·m min−1 could be achieved. This corresponds to a static deposition rate of 200 nm min−1. The lowest electrical resistivity of 1.1·10−3 Ω cm was measured at samples deposited in the high oxygen flow range in the transition mode. The samples show a good transparency in the visible range corresponding to extinction coefficients being below 10−2. X-ray diffraction was used to characterise crystalline structure as well as film stress. ITO films prepared in the transition mode show a slightly preferred orientation in (211) direction, whereas films deposited in the reactive mode are strongly (222) oriented. Compared to undoped In2O3 all samples have an enlarged lattice. The lattice strain perpendicular to the surface is about 0.8% and 2.0% for films grown in the transition and the reactive mode, respectively. Deposition in the transition mode introduces a biaxial film stress in the range of −300 MPa, while stress in reactive mode samples is −1500 MPa.

Cylinder head covers with integrated, switched cyclone-type oil mist separator

Polytec Automotive has developed a new engine ventilation system for integration into cylinder head covers with operating features which distinguish it from all other systems presently on the market. The performance curve for this new switched, patented cyclone separator has been optimized at low flow rates and tuned to reduce the pressure in the high flow range. The wide operating range allows the separating performance of this switched cyclonetype separator to be adjusted to all engines, ensuring universal application.

Effective discharge for sediment transport in a mountain river: Computational approaches and geomorphic effectiveness

Dominant, effective, bankfull and channel-forming discharges are different concept-based flows, often applied as design parameters in river management and restoration. In order to achieve a better understanding of channel-forming conditions in high-gradient, boulder-bed streams, the long-term sediment loads data obtained from the Rio Cordon (Italian Alps) measuring station have been analysed. The effective discharge ( Q e, calculated using both Wolman and Miller's method and the so-called ‘mean’ approach) for bedload transport proves to be more appropriate than that determined for the suspended sediment load in describing the channel formation and maintenance for this type of channels. The analysis demonstrates that Q e is strongly influenced by the number of flow classes, the fraction of transported sediments and the methodology used in its computation. The result questions the appropriateness in considering Q e as an unique value, and also suggests the possible definition of two dominant discharge ranges for steep mountain rivers: (a) a relatively frequent flow range responsible for maintaining channel form; and (b) a more infrequent high flow range responsible for macro-scale channel shaping.

Design of Industrial Axial Compressor Blade Sections for Optimal Range and Performance

Background: The blade sections of industrial axial flow compressors require a wider range from surge to choke than typical gas turbine compressors in order to meet the high volume flow range requirements of the plant in which they operate. While in the past conventional blade profiles (NACA65 or C4 profiles) at moderate Mach number have mostly been used, recent well-documented experience in axial compressor design for gas turbines suggests that peak efficiency improvements and considerable enlargement of volume flow range can be achieved by the use of so-called prescribed velocity distribution (PVD) or controlled diffusion (CD) airfoils. Method of approach: The method combines a parametric geometry definition method, a powerful blade-to-blade flow solver and an optimization technique (breeder genetic algorithm) with an appropriate fitness function. Particular effort has been devoted to the design of the fitness function for this application which includes non-dimensional terms related to the required performance at design and off-design operating points. It has been found that essential aspects of the design (such as the required flow turning, or mechanical constraints) should not be part of the fitness function, but need to be treated as so-called “killer” criteria in the genetic algorithm. Finally, it has been found worthwhile to examine the effect of the weighting factors of the fitness function to identify how these affect the performance of the sections. Results: The system has been tested on the design of a repeating stage for the middle stages of an industrial axial compressor. The resulting profiles show an increased operating range compared to an earlier design using NACA65 profiles. Conclusions: A design system for the blade sections of industrial axial compressors has been developed. Three-dimensional CFD simulations and experimental measurements demonstrate the effectiveness of the new profiles with respect to the operating range.

脳血行再建術における血行力学的脳虚血の定量的重症度評価

Hemodynamic cerebral ischemia can be stratified into Stage I and Stage II (Misery perfusion). According to vasodilatory and metabolic compensation toward reduction of CPP, Stage I ischemia is defined as both preservation of resting CBF and reduction of vascular reserve. Stage II ischemia is defined as reduction of resting CBF, loss of vascular reserve and elevation of oxygen extraction fraction (OEF). The vasodilatory response to acetazolamide, a carbonic anhydrase inhibitor, provides an effective parameter of cerebrovascular reserve. Recently, quantitative measurement of CBF and cerebrovascular reserve (VR): (acetazolamide-activated CBF / resting CBF — 1)× 100% was introduced in clinical practice and hemodynamic cerebral ischemia can be quantitatively stratified into Stage I and Stage II. Both 123I-IMP-microsphere method and 123I-IMP-ARG method indicate acceptable accuracy, and can be commonly used as quantitative brain perfusion SPECT imaging. In 123I-IMP-ARG methods, Stage I ischemia is defined as follows: resting CBF more than 34 ml/100 g/min (this value corresponds to 80% of mean CBF of normal subjects) or VR from 10% to 30%, Stage II ischemia is defined as follows: rCBF less than 34 ml/100 g/min and VR less than 10%. Hemodynamically normal subjects are involved in VR more than 30% (Stage 0).Twenty-four patients with hemodynamic stroke were selected for a recent EC-IC bypass study. In this study, EC-IC Bypass surgery was performed in patients with Stage II and I (nearly II) ischemia using 123I-IMP-ARG methods. In the affected areas, the mean values of resting CBF and VR after surgery (35.0+/−7.2 ml/100 g/min, 32.9+/−15.2%) were significantly improved compared with the values before surgery (29.6+/−5.3 ml, −4.5+/−12.4%). In the unaffected areas, the mean values of resting CBF and VR after surgery (38.8+/−7.9 ml/100 g/min, 40.8+/−15.8%) were not significantly different than those values before surgery. The stage after surgery (Stage 0 in 16, Stage I in 8, Stage II in 0) was statistically improved in comparison with the stage before surgery (Stage 0 in 0, Stage I in 7, Stage II in 17). Stage II hemodynamic cerebral ischemia defined by quantitative brain perfusion SPECT imaging was successfully reversed to Stage I or 0 by EC-IC Bypass surgery. A Japanese EC-IC Bypass trial (JET Study) is being carried out to clarify the surgical benefits for Stage II ischemia, and quantitative measurement of CBF and VR has been recognized to be essential for the inclusion criteria for this trial.99mTc-HMPAO or 99mTc-ECD-Patlak plot method could be another option for quantitative brain perfusion SPECT imaging. However, these methods can indicate acceptable values of resting CBF but could not demonstrate accurate values of VR activated by acetazolamide challenge. First-pass extraction of these radiotracers is generally lower in the relative high-flow range. Therefore the quantitative CBF value tends to be underestimated in the area with normally vasodilatory response under acetazolamide-activated condition. Linearization corrections should be modified in these methods, especially using acetazolamide activation.Hemodynamic cerebral ischemia can be stratified into Stage I and Stage II (Misery perfusion) and the stratification may be important to determine future risk of stroke. The characteristics and kinetics of brain perfusion radiotracers should be considered in quantitative stratification of hemodynamic cerebral ischemia using brain perfusion SPECT.