Experimental investigation of oscillatory air flow in a bronchial tube model with HFOV mode

Mechanical ventilations for artificial respiration have been developed to improve the medical treatment of the patients showing respiratory disorder. In various types of ventilation, High Frequency Oscillatory Ventilation (HFOV) is one of the most effective techniques of medical care for pulmonary disease patients, especially, infantsor premature infants. HFOV is a ventilation technique with high breathing rate in comparison with the normal breathing rate. Some successful studies have focused on the effect of treatment using HFOV However, the mechanism of gas exchange in bronchial tube under the medical treatment by HFOV has not been clarified. In this study, the oscillatory flow in a micro-channel model of bronchial with single bifurcation in HFOV mode has been investigated experimentally with micro Particle Image Velocimetry (micro PIV) technique. The phase averaged velocity profiles changing with the driving frequency of HFOV have been inves tigated.     

Cheyne-Stokes respiration: Stability of interacting systems in heart failure

Cheyne-Stokes respiration, a breathing pattern found in patients with heart failure, is characterized by periodic changes in ventilation. This pattern of breathing is also associated with oscillations in the arousal state, blood oxygen level, carbon dioxide blood level, and the blood pressure. Although originally described as an irregular breathing pattern or an unstable breathing pattern, Cheyne-Stokes respiration may be quite stable for prolonged periods of time. This breathing pattern may represent a clinical disorder in which disease results in a low-frequency oscillation of the system. Treatment that either reduces or abolishes the oscillation results in clinical improvement because of reduced oscillation of the systems whose function is linked to the changes in ventilation.     

On the origin of respiratory artifacts in BOLD-EPI of the human brain

BOLD-based functional MRI (fMRI) can be used to explicitly measure hemodynamic aspects and functions of human neuro-physiology. As fMRI measures changes in regional cerebral blood flow and volume as well as blood oxygenation, rather than neuronal brain activity directly, other processes that may change the above parameters have to be examined closely to assess sensitivity and specificity of fMRI results. Physiological processes that can cause artifacts include cardiac action, breathing and vasomotion. Although there has been substantial research on physiological artifacts and appropriate compensation methods, controversy still remains on the mechanisms that cause the fMRI signal fluctuations. Respiratory-correlated fluctuations may either be induced by changes of the magnetic field homogeneity due to moving organs, intra-thoracic pressure differences, respiration-dependent vasodilation or oxygenation differences. The aim of this study was to characterize the impact of different breathing patterns by varying respiration frequency and/or tidal volume on EPI time courses of the resting human brain. The amount of respiration-related oscillations during three respiration patterns was quantified, and statistically significant differences were obtained in white matter only: p < 0.03 between 6 vs. 12 ml/kg body weight end tidal volume at a respiration frequency of 15/min, p < 0.03 between 12 vs. 6 ml/kg body weight and 15 vs. 10 respiration cycles/min. There was no significant difference between 15 vs. 10 respiration cycles/min at an end tidal volume of 6 ml/kg body weight (p = 0.917). In addition, the respiration-affected brain regions were very similar with EPI readout in the a-p and l-r direction. Based on our results and published literature we hypothesize that venous oxygenation oscillations due to changing intra-thoracic pressure represent a major factor for respiration-related signal fluctuations and increase significantly with increasing end tidal volume in white matter only.     

Increasing mean airway pressure reduces functional MRI (fMRI) signal in the primary visual cortex

Changes in both blood flow and blood oxygenation determine the functional MRI (fMRI) signal. In the present study factors responsible for blood oxygenation (e.g., FiO(2)) were held constant so that changes in pixel count would above all reflect changes in regional cerebral blood flow (rCBF). Continuous positive airway pressure (CPAP) breathing at 12 cm H(2)O, which was previously shown to influence rCBF, was applied in human volunteers (n = 19) to investigate the sensitivity of fMRI for changes in rCBF caused by increased mean airway pressure. Increasing the mean airway pressure decreased the pixel count in the primary visual cortex (median (range)): baseline: 219 (58-425) pixels vs. CPAP (12 cm H(2)O): 92 (0-262) pixels). These findings indicate that fMRI is sensitive to detect a reduced rCBF-response in the primary visual cortex. The underlying mechanism is likely to be a reduced basal rCBF due to constriction and/or compression of postcapillary venoles during CPAP breathing. These findings are important for interpreting fMRI results in awake and in artificially respirated patients, in whom positive airway pressure is used to improve pulmonary function during the diagnostic procedure.     

Identification of human myocardial infarction in vitro based on the frequency dependence of ultrasonic backscatter.

It has been reported previously that acute and mature myocardial infarction in dogs can be differentiated in vitro and in vivo by ultrasonic tissue characterization based on measurement of the frequency dependence of ultrasonic backscatter. To characterize human infarction with an index of the frequency dependence of backscatter that could be obtained in patients, cylindrical biopsy specimens from 7 normal regions and 12 regions of infarction of 6 fixed, explanted human hearts in 2-deg steps around their entire circumference with a 5-MHz broadband transducer were insonified. One to six consecutive transmural levels were studied for each specimen. The dependence of apparent (uncompensated for attenuation or beam width) backscatter, /B(f)/2, on frequency (f) was computed from spectral analyses of radio-frequency data as /B(f)/2 = afn, where from theoretical considerations the magnitude of n decreases as scatterer size increases. Apparent integrated backscatter was computed as the average of /B(f)/2 from 3 to 7 MHz. The average value for n for normal tissue (0.9 +/- 0.1) exceeded that for tissue from regions of infarction (0.6 +/- 0.1; p less than 0.05). Infarct manifested a significant decrease of n from epicardial to endocardial levels (epi----mid----endo: 0.9----0.7----0.2; p less than 0.05) whereas normal tissue manifested similar values for n at each transmural level (0.8----1.1----0.9; p = NS). Average integrated backscatter across all transmural levels for infarct was significantly greater than for normal tissue (-48.3 +/- 0.5 vs -53.4 +/- 0.4 dB, infarct versus normal; p less than 0.05). The presence of fibrosis was associated with smaller values of n and greater integrated backscatter.(ABSTRACT TRUNCATED AT 250 WORDS)     

A laser Doppler velocimeter for pulsatile water flow measurements in resonant hydraulic circuits

Described is a laser Doppler velocimeter designed to measure a small oscillatory velocity component superposed to the steady water flow of a resonant hydraulic circuit in fully developed turbulent conditions. A frequency tracker with lock-in analysis of the velocity output is used. The rms amplitude of the oscillatory velocity component is measured with an accuracy of 1.5 mm s^-1, and the mean velocity is about 3 ms^-1. The resonance behaviour of the velocity amplitude measured at a fixed point of the circuit is reported for the exciting frequency range 2–5 Hz.     

脉动流在分叉管中通栓效果的晶格玻尔兹曼方法研究

血栓引发的各种心血管疾病一直威胁着人们的健康. 在已经产生血栓的血管中, 脉动对于疏通血管有良好的作用. 由于血液的黏滞作用以及红细胞的惯性, 脉动流的频率会影响血管通栓的效果. 在分叉管模型中, 低压差的条件下, 由于另一畅通管子的导通作用减少了回流, 导致通栓效果不理想. 通过增大压差和提高脉动流的振幅, 降低畅通管子导通作用的影响, 研究脉动流在分叉管中的通栓效果. 研究发现, 脉动低频通栓效果好, 但是通栓需要的时间较长; 高频通栓时间短, 但是当频率高于一定值, 则通栓效果不明显. 细胞和管壁的摩察系数对通栓效果也有影响.     

Contraction-related variation in frequency dependence of acoustic properties of canine myocardium

Results of experiments performed in several laboratories indicate that contracting myocardium exhibits a cyclic variation of the magnitude of ultrasonic backscatter, with maxima occurring at end-diastole and minima at end-systole. The mechanisms responsible for this variation are not well understood. The purpose of the present study was to determine whether the frequency dependence of backscatter exhibits systematic variation throughout the cardiac cycle, analysis of which may facilitate improved understanding of biologic factors responsible for the cyclic variation of the magnitude of backscatter. In this study, the myocardial backscatter coefficient, as a function of frequency, was measured throughout the cardiac cycle in nine open-chest dogs. The frequency dependence of the backscatter coefficient was computed from a least-squares linear fit to log backscatter coefficient versus log frequency data. A cyclic variation of frequency dependence of backscatter was found with maximum near end-diastole (f2.6 +/- 0.1) and minimum near end-systole (f2.2 +/- 0.1), a significant variation (p less than 0.01). These results suggest that mechanisms responsible for the cyclic variation of backscatter may include changes in the effective size of the dominant scatterers throughout the cardiac cycle. An alternative explanation for the observed variation is an increase in the myocardial attenuation coefficient during systole followed by a decrease in diastole.     

Oscillatory Flow Phenomena in Simple and Complex Fluids

Pulsatile and oscillatory flows are prevalent in many biological, industrial, and natural systems. Nuclear magnetic resonance (NMR) is a noninvasive method for evaluating fluid mechanics and can be used to obtain spatially resolved velocity maps in simple and complex fluids. A system has been constructed to provide a controllable and predictable oscillatory flow in order to gain a better understanding of the impact of oscillatory flow on Newtonian and non-Newtonian fluids, specifically water, xanthan gum, polyacrylamide and a colloidal suspension. A core shell particle colloidal suspension is used as a model system since measurements can be obtained separately from the suspending fluid (water) and the liquid particle core (hexadecane oil) using NMR. The oscillatory flow system coupled with NMR measures the velocity distributions and dynamics of the fluid undergoing oscillatory flow at specific points in the oscillation cycle.     

Experimental analysis of oscillatory airflow in a bronchiole model with stenosis

As the mechanism of gas transport and exchange in human respiratory ventilation, the complicated processes of mixing and diffusion in airways of human lungs are considered. However the mechanism has not been clarified enough. On the other hand, the analysis of detailed mechanism in the case of artificial ventilation like HFOV (High Frequency Oscillatory Ventilation) is strongly required for the development of clinical treatments on patients with respiration disorder. In HFOV, it is considered that pendelluft becomes one of the important factors of gas transport and exchange because of high frequency ventilation in comparison with natural breathing. As increase of the frequency, the different time constants of lung units generate phase lag of ventilation in airways of lungs. The phase lag of ventilation causes to generate pendelluft. The time constant is determined by compliance and flow resistance of lung unit. In order to investigate the effect of the different time constants induced by the difference of flow resistance in a part of respiratory bronchiole of human lungs, the experimental study has been carried out by using multi-bifurcated micro channels as a model of bronchiole. The flow resistance in the model channels was produced by a stenosis. The velocity distributions of ventilation flows in the channels with and without the stenosis have been measured by using μ-PIV technique. The results obtained show the frequency effects on the flow pattern in the bronchiole model channels and the appearance of pendelluft.     

Chaos suppression in gas-solid fluidization

Fluidization in granular materials occurs primarily as a result of a dynamic balance between gravitational forces and forces resulting from the flow of a fluid through a bed of discrete particles. For systems where the fluidizing medium and the particles have significantly different densities, density wave instabilities create local pockets of very high void fraction termed bubbles. The fluidization regime is termed the bubbling regime. Such a system is appropriately termed a self-excited nonlinear system. The present study examines chaos suppression resulting from an opposing oscillatory flow in gas-solid fluidization. Time series data representing local, instantaneous pressure were acquired at the surface of a horizontal cylinder submerged in a bubbling fluidized bed. The particles had a weight mean diameter of 345 &mgr;m and a narrow size distribution. The state of fluidization corresponded to the bubbling regime and total air flow rates employed in the present study ranged from 10% to 40% greater than that required for minimum fluidization. The behavior of time-varying local pressure in fluidized beds in the absence of a secondary flow is consistent with deterministic chaos. Kolmogorov entropy estimates from local, instantaneous pressure suggest that the degree of chaotic behavior can be substantially suppressed by the presence of an opposing, oscillatory secondary flow. Pressure signals clearly show a "phase-locking" phenomenon coincident with the imposed frequency. In the present study, the greatest degree of suppression occurred for operating conditions with low primary and secondary flow rates, and a secondary flow oscillation frequency of 15 Hz. (c) 1998 American Institute of Physics.     

The effects of ultrasound on the mechanical properties of rat cardiac muscle

The mechanical properties of cardiac muscle during ultrasonic irradiation have been studied in vitro. Left anterior papillary muscle from normal rats was suspended in buffered lactated Ringers solution equilibrated with 95% O2, and 5% CO2 and maintained at 20 degrees C. The muscles were stimulated to contract isometrically three times per minute at the length which produced maximum tension. Each muscle was irradiated with a MHz ultrasound at an average power of 2.4 Wcm-2 for a period of 10 min with a 10 min recovery period. Irradiation caused an average increase in temperature of the muscle of 1.7 +/- 0.2 degrees C (mean +/- SEM). Irradiation caused the resting tension (1.46 +/- 0.13g) to decrease by 17.8 +/- 4.7% and the developed tension (3.33 +/- 0.61g) to decrease by 4.1 +/- 0.9%. Since changes in contractile properties have been reported with temperature the bath temperature was raised and changes in contraction observed. When compensated for effects of temperature, the changes in resting tension became - 13.3 +/- 4.1% while the change in developed tension became + 1.6 +/- 2.3%. The change in resting tension is highly significant (p less than 0.05 paired t-test) while the change in developed tension is not. Thus 1 MHz ultrasound at an intensity of 2.4 Wcm-2 appears to affect resting tension of cardiac muscle without affecting the active tension. Since changes in cardiac mechanics of this type have not been described previously the effects of ultrasound appears to be unique.     

互耦相对论返波管等同锁相和功率放大的粒子模拟

推导了两个互耦高功率微波振荡系统等同锁相后的锁定频率公式,并利用粒子模拟软件对两个互耦相对论返波管进行了数值仿真实验。模拟时将相同结构的两个相对论返波管并排放置在一起,在它们的慢波结构的第１个波谷处,用一条饼状狭缝将它们并联起来,分别输入不同的加速电压,让它们工作于不同的状态。粒子模拟的结果表明：这两个并联的互耦相对论返波管之间进行了等同锁相,它们的频率都被锁定在同一个特定的频率点上,且其注波能量转换效率都提高了,总输出功率比单独工作时的总功率增加了约10%,同时耦合之后功率输出更平稳。     

互耦相对论返波管等同锁相和功率放大的粒子模拟

推导了两个互耦高功率微波振荡系统等同锁相后的锁定频率公式,并利用粒子模拟软件对两个互耦相对论返波管进行了数值仿真实验。模拟时将相同结构的两个相对论返波管并排放置在一起,在它们的慢波结构的第１个波谷处,用一条饼状狭缝将它们并联起来,分别输入不同的加速电压,让它们工作于不同的状态。粒子模拟的结果表明:这两个并联的互耦相对论返波管之间进行了等同锁相,它们的频率都被锁定在同一个特定的频率点上,且其注波能量转换效率都提高了,总输出功率比单独工作时的总功率增加了约10%,同时耦合之后功率输出更平稳。     

Discrete coherent amplification of oscillations by nonresonant forcing

A new mechanism of generation of oscillations in a linear forced oscillatory system is found. Natural oscillations may be generated at a "sharp" pulse (rapid variation) of the natural frequency. In this process oscillations are generated by nonresonant forcing, e.g., by the action of a constant, nonperiodic or periodic force (with driving frequency much less than the natural one). Repetitive pulses of the natural frequency result in emergence of oscillations that interfere and may give a powerful resultant output. These phenomena relate to a basis of the theory of open linear oscillatory systems.     

CSF flow artifact reduction using cardiac cycle ordered phase-encoding method

The flow effects appear as a change of phase as well as signal intensity in NMR imaging. Since the flow of blood and CSF (cerebrospinal fluid) is pulsatile due to the heart pumping, their velocities are not constant during NMR imaging. This type of velocity fluctuation such as the blood or CSF flow induces irregular flow-dependent phase shifts, which have been one of the main causes of flow artifacts in NMR imaging. In order to reduce the flow artifacts, especially the CSF flow artifacts, a new cardiac cycle ordered phase encoding method is proposed and has been studied. This proposed technique utilizes the cardiac cycle as a precursor for the phase encoding gradients similar to the ROPE (respiratory ordered phase encoding) technique which has been used for respiratory motion artifact reduction. The basic concept and its applications are discussed together with the experimental results obtained with human volunteers using the KAIS 2.0 2.0 T whole-body NMR imaging system.     

Lattice Boltzmann method simulating hemodynamics in the three-dimensional stenosed and recanalized human carotid bifurcations

By using the lattice Boltzmann method(LBM)pulsatile blood flows were simulated in three-dimensional moderate stenosed and recanalized carotid bifurcations to understand local hemodynamics and its relevance in arterial atherosclerosis formation and progression.The helical flow patterns,secondary flow and wall dynamical pressure spatiotemporal distributions were investigated,which leads to the disturbed shear forces in the carotid artery bifurcations.The wall shear stress distributions indicated by time-averaged wall shear stress(TAWSS),oscillatory shear index(OSI),and the relative residence time(RRT)in a cardiac cycle revealed the regions where atherosclerotic plaques are prone to form,extend or rupture.This study also illustrates the point that locally disturbed flow may be considered as an indicator for early atherosclerosis diagnosis.Additionally the present work demonstrates the robust and highly efficient advantages of the LBM for the hemodynamics study of the human blood vessel system.     

Flow and oxygenation dependent (FLOOD) contrast MR imaging to monitor the response of rat tumors to carbogen breathing

Gradient recalled echo (GRE) images are sensitive to both paramagnetic deoxyhaemoglobin concentration (via T2*) and flow (via T1*). Large GRE signal intensity increases have been observed in subcutaneous tumors during carbogen (5% carbon dioxide, 95% oxygen) breathing. We term this combined effect flow and oxygenation-dependent (FLOOD) contrast. We have now used both spin echo (SE) and GRE images to evaluate how changes in relaxation times and flow contribute to image intensity contrast changes. T1-weighted images, with and without outer slice suppression, and calculated T2, T2* and "flow" maps, were obtained for subcutaneous GH3 prolactinomas in rats during air and carbogen breathing. T1-weighted images showed bright features that increased in size, intensity and number with carbogen breathing. H&E stained histological sections confirmed them to be large blood vessels. Apparent T1 and T2 images were fairly homogeneous with average relaxation times of 850 ms and 37 ms, respectively, during air breathing, with increases of 2% for T1 and 11% for T2 during carbogen breathing. The apparent T2* over all tumors was very heterogeneous, with values between 9 and 23 ms and localized increases of up to 75% during carbogen breathing. Synthesised "flow" maps also showed heterogeneity, and regions of maximum increase in flow did not always coincide with maximum increases in T2*. Carbogen breathing caused a threefold increase in arterial rat blood PaO2, and typically a 50% increase in tumor blood volume as measured by 51Cr-labelled RBC uptake. The T2* increase is therefore due to a decrease in blood deoxyhaemoglobin concentration with the magnitude of the FLOOD response being determined by the vascular density and responsiveness to blood flow modifiers. FLOOD contrast may therefore be of value in assessing the magnitude and heterogeneity of response of individual tumors to blood flow modifiers for both chemotherapy, antiangiogenesis therapy in particular, and radiotherapy.     

Apparent diffusion coefficient (ADC) measurements may be more reliable and reproducible than lesion volume on diffusion-weighted images from patients with acute ischaemic stroke-implications for study design

Early ischemic change after stroke can be demonstrated with diffusion-weighted imaging (DWI) and quantified by measuring the apparent diffusion coefficient (ADC) and/or lesion volume. We examined the reliability and reproducibility of lesion volume and ADC measurement on DWI images, and discuss the implications for clinical studies. Using 38 DWI scans from 15 stroke patients, two observers (a physicist and a neuroscience graduate) blind to each other, recorded the lesion volume on DWI sequences, measured the ADC values in this volume and calculated the ratio of ischemic: control ADC (ADCr). One observer repeated his measurements blind to his first, and also examined the effect on lesion volume and ADC of deliberately varying by only one pixel, the outline of the visible boundary of the lesion. The inter and intra-rater reliability were worse for lesion volume than ADC or ADCr measurements: lesion volume, inter-rater coefficient of variation (CoV) 85 +/- 130%, intra-rater CoV 20+/-SD80% (p < 0.05); ADC inter-rater CoV 7.7 +/- SD 19%, intra-rater CoV 0.2 +/- SD 12% (p = NS); and ADCr inter-rater CoV 8 +/- SD27%, intra-rater CoV 0.8 +/- SD73% (p = NS). Altering the position of the outline tracing of the lesion boundary by one pixel altered the measured volumes by 22 +/- SD25% (p < 0.05), but ADC values were altered by only 2.9 +/- SD4.9% and ADCr by 2.7 +/- SD4.8% (p = NS). ADC and ADCr values are more reliable and reproducible than DWI lesion size in acute ischemic stroke because altering where the lesion boundary is measured has a much greater impact on lesion volume than on the ADC or ADCr. This effect is greatest in large lesions.     

Reliability of mean transit time obtained using perfusion-weighted MR imaging; comparison with positron emission tomography

The purpose of this project was to assess the reliability of the cerebral mean transit time (MTT) obtained using perfusion-weighted MR imaging by comparing it with the MTT obtained when performing positron emission tomography (PET). Ten patients with chronic occlusive cerebrovascular disease were investigated. They had either unilateral internal carotid artery occlusion or middle cerebral artery occlusion. The regions-of-interest were placed in non-infarcted areas within the territory of the middle cerebral artery on the affected side. Control regions-of-interest were placed in mirrored regions of the contralateral side. Linear regression analyses were performed using the parameters of the MTT obtained with perfusion-weighted MR imaging and the MTT, cerebral blood flow, vascular reactivity, and oxygen extraction fraction obtained with PET. The respective MTTs of the affected and non-affected sides obtained with perfusion-weighted MR imaging versus those with PET were 7.3 +/- 2.2 s and 6.0 +/- 1.2 s versus 8.2 +/- 3.0 s and 6.4 +/- 1.7 s. The MTT obtained using perfusion-weighted MR imaging and PET demonstrated statistically significant correlation (r = 0.87, p < 0.0001). The MTT obtained with perfusion-weighted MR imaging correlated statistically with cerebral blood flow (r = -0.74, p < 0.001), vascular reactivity (r = -0.73, p < 0.001) and oxygen extraction fraction (r = 0.61, p < 0.01). Similarly, the MTT obtained using PET statistically correlated with cerebral blood flow (r = -0.78, p < 0.0001), vascular reactivity (r = -0.51, p < 0.05) and oxygen extraction fraction (r = 0.68, p < 0.01). The reliability of the MTT obtained using perfusion-weighted MR imaging appears to be approximately equal to that obtained with positron emission tomography.