Physical determining factors of the arterial pulse waveform: theoretical analysis and calculation using the 1-D formulation

The shape of the arterial pulse waveform is intimately related to the physical properties of the cardiovascular system. It is clinically relevant to measure those properties that are related to cardiovascular function, such as the local elasticity and viscosity of the arterial wall, total compliance and net peripheral resistance of the systemic arterial tree. Most of these properties cannot be directly measured in vivo, but they can be calculated from pressure, flow and wall displacement measurements that can be obtained in vivo. We carry out a linear analysis of the one-dimensional (1-D) equations of blood flow in Voigt-type visco-elastic vessels to study the effects on pulse wave propagation of blood viscosity, flow inertia, wall visco-elasticity, total arterial compliance, net resistance, peripheral outflow pressure, and flow rate at the aortic root. Based on our analysis, we derive methods to calculate the local elastic and viscous moduli of the arterial wall, and the total arterial compliance, net resistance, time constant and peripheral outflow pressure of the systemic arterial tree from pressure, flow and wall displacement data that can be measured in vivo. Analysis of in vivo data is beyond the scope of this study, and therefore, we verify the results of our linear analysis and assess the accuracy of our estimation methods using pulse waveforms simulated in a nonlinear visco-elastic 1-D model of the larger conduit arteries of the upper body, which includes the circle of Willis in the cerebral circulation.     

Does hemodiafiltration reduce vascular stiffness measured by aortic pulse wave velocity compared with high‐flux hemodialysis?

Hemodialfiltration (HDF) has been reported to reduce the frequency of intradialytic hypotension compared with hemodialysis (HD). We wished to determine whether HDF resulted in improvement of arterial stiffness compared with HD. We reviewed peripheral blood pressure and pulse wave velocity measurements in a cross‐sectional analysis of stable HDF and HD outpatients. One hundred forty‐one HDF patients were matched to 148 HD patients in terms of age, sex, prevalence of diabetes, peripheral blood pressure, and body mass. Pulse wave velocity was not different between the HD and HDF cohorts (median 9.1 [8.0–10.7] m/s vs. 9.7 [8.5–11.6] m/s). Similarly, there were no differences in central aortic pressure (149.2 ± 30.9 mmHg vs. 151.9 ± 35.2 mmHg), or aortic (39 [25.1–51.2]% vs. 38.6 [25.8–51.4]%) and brachial (3.8 [?24.3 to 26.9]% vs. 3 [?22.4 to 27.1]%) augmentation indices, respectively. Pulse wave velocity did not differ between adult patients treated by HD and HDF, and similarly, there were no differences in central aortic pressure, aortic or brachial augmentation indices, and cardiac diastolic perfusion. Our study suggests that HDF does not appear to offer any benefit over HD in terms of vascular stiffness.     

Measurement and control of current/voltage waveforms of microwavetransistors using a harmonic load-pull system for the optimum design ofhigh efficiency power amplifiers

One of the most important requirements that RF and microwave power amplifiers designed for radiocommunication systems must meet is an optimum power added efficiency (PAE) or an optimal combination of PAE and linearity. A harmonic active load-pull system which allows the control of the first three harmonic frequencies of the signal coming out of the transistor under test is a very useful tool to aid in designing optimized power amplifiers. In this paper, we present an active load-pull system coupled to a vectorial “nonlinear network” analyzer. For the first time, optimized current/voltage waveforms for maximum PAE of microwave field effect transistors (FET's) have been measured. They confirm the theory on high efficiency microwave power amplifiers. The proposed load-pull setup is based on the use of three separated active loops to synthesize load impedances at harmonics. The measurement of absolute complex power waves is performed with a broadband data acquisition unit. A specific phase calibration of the set-up allows the determination of the phase relationships between harmonic components. Therefore, voltage and current waveforms can be extracted. The measurement results of a 600 gate periphery GaAs FET (Thomson Foundry) exhibiting a PAE of 84% at 1.8 GHz are given. Such results were obtained by optimizing the load impedances at the first three harmonic components of the signal coming out of the transistor. Optimum conditions correspond to a class F operation mode of the FET (i.e., square wave output voltage and pulse shaped output current). A comparison between measured and simulated current/voltage waveforms is also presented     

Measurement of spatial cross sections of ultrasound pressure fields by optical scanning means

The measurement of spatial cross sections of ultrasound pressure fields is an essential element of exposimetry of ultrasonic medical equipment. An optical technique is presented that allows the two-dimensional (2-D) determination of ultrasound pressure using an optical multilayer hydrophone in which a laser beam with suitable wavelength is partially reflected from a dielectric optical multilayer system. By detecting the change in reflectivity of the multilayer coating induced by the incident ultrasound, the pressure time waveform can be determined. A 2-D data acquisition covering an area of at least 15 mm x 5 mm was realized by two complementary approaches. A serial detection scheme was set up by scanning the sensing point across the area of interest by a micromechanically engineered scanning mirror and acquiring pressure time waveforms sequentially and pointwise. This allows the measurement of repeating ultrasonic waveforms with a spatial resolution of better than 70 microm and a minimal detectable pressure of 50 kPa (bandwidth: 50 MHz) in a few seconds. In an alternative approach exploiting the parallel processing capabilities of a charge-coupled devices (CCD) camera chip, the probe was strobe-illuminated by a large-diameter collimated beam of a pulsed laser diode. The 2-D pressure distribution at a particular moment was derived from captured reflectivity distributions with a spatial resolution of 75 microm. By successive delaying of the laser pulse with respect to the ultrasound pulse, the complete 2-D pulse waveform was acquired with high spatial resolution. Measurement results on ultrasound fields from plane and focusing transducers are presented and compared to simulation results. Individual advantages and drawbacks of both approaches are discussed. A combined setup merging both detection schemes into a single device was developed and represents a milestone on the way toward constructing an optical ultrasound measuring camera.     

复外周阻力弹性腔模型—活体动脉顺应性测量的重新讨论

因为与细小动脉和毛细血管内血液总和流动近似为定常流的已知基本实验观察事实矛盾,动脉系统的弹性腔模型理论的传统的描述方程,和在此基础上推导的动脉顺应性C的传统活体检测的计算方法都是错误的。因此,本研究引入复数型外周阻力R_μ jwL_μ取代传统的实数型外周阻力R,用于描述入口为脉动压力波、流量波,出口为近似定常流的血管床复数型外周阻力弹性腔模型,导出了新的弹性腔模型的微分方程。本研究对新方程略作简化,建立一种基于最小二乘法的动脉顺应性C(p)的新的活体测量计算方法,并推导了简化的顺应性的近似计算公式,讨论了在相应的特定条件下与传统模型动脉顺应性的计算公式的差别。     

Use of a Compaction Simulator System in Tabletting Research

The components and principal operating features of a compaction simulator system are described. Initial experiments with 8 model materials, using single-ended and double-ended compression waveforms are reported. Data obtained at two tablet machine speeds (30 and 150rpm) and at two compressional pressure levels (80 and 400MPa) demonstrate a correlation between total work or average power consumed during the process and the tensile strength of the tablets. Non-linearity of Heckel plots and limited compliance with the Walker equation are also shown.     

Sliding electric arc discharge as a means of aircraft trajectory control

The dynamics of sliding electric arc discharge and the formation of shock waves in the stages of leader motion and the electric arc development in a supersonic air flow behind the shock wave have been studied for an initial pressure of 0.09–0.5 atm (bar). The air flow in the discharge was imaged using an optical system comprising a shadow device (IAB-458), an optical interference attachment (RP-452), and a modified ruby laser (OGM-20) producing 10–15 output pulses per pumping pulse. Stable initiation of sliding electric arc discharge takes place in a supersonic air flow behind the shock waves with 1.7<M<3.4. This discharge produces shock waves leading to separation of the boundary layer and to an increase in the pressure at the surface. These shock waves can be used for modifying gasdynamics in the air flow streamlining the surface and for controlling the motion of an aircraft.     

Cracking of AFNOR 7020 aluminium alloy component: A metallurgical investigation

Aluminium alloy of Al–4.5Zn–1.5Mg system, belonging to age hardenable, high strength category is being used for the fabrication of various components. The Al alloy component was part of a conduit line for filling the liquid chemical to its storage tank. The component consisted of an extruded tube, TIG welded to a bulb, which was fabricated from Al alloy forgings. A crack was observed on the conduit tube at the region where tube was welded to the bulb. Detailed investigations were carried out on the cracked component, which revealed insufficient working of the ingot during forging, resulting in remnant cast structure along with a heavy network of low melting point compound throughout the material. The cracks, which were initiated under the stresses induced during thermal treatment, machining and assembly, were found propagating through the eutectic network.

This paper highlights the investigations carried out on the failed components.     

Numerical Analysis on Laser-Generated Guided Elastic Waves in a Hollow Cylinder

Numerical analyses are presented for laser-generated guided elastic waves in a hollow cylinder. Time-dependent displacement at the outer surface of a hollow cylinder is expressed by summation of longitudinal and flexural type modes by employing the normal mode expansion (NME) method, then the transient waveforms excited by a single beam of laser pulse and four beams of laser pulse with an axisymmetric spatial distribution are calculated numerically. The influence of the spatial distribution of laser pulses on the waveforms are discussed in detail, and the features of major modes are explained based on dispersion curves. Finally, the total waveform of longitudinal modes obtained by the NME method is compared to that predicted by the finite element method (FEM), and a good agreement is obtained.     

Myocardial contractile function and intradialytic hypotension

Dialysis‐induced hypotension remains a significant problem in hemodialysis (HD) patients. Numerous factors result in dysregulation of blood pressure control and impaired myocardial reserve in response to HD‐induced cardiovascular stress. Episodic intradialytic hypotension may be involved in the pathogenesis of evolving myocardial injury. We performed an initial pilot investigation of cardiovascular functional response to pharmacological cardiovascular stress in hypotension‐resistant (HR) and hypotension‐prone (HP) HD patients. We studied 10 matched chronic HD patients (5 HP, 5 HR). Dobutamine‐atropine stress (DAS) was performed on a nondialysis short interval day, with noninvasive pulse‐wave analysis using the Finometer^® to continuously measure hemodynamic variables. Baroreflex sensitivity was assessed at rest and during DAS. Baseline hemodynamic variables were not significantly different. The groups had differing hemodynamic responses to DAS. The Mean arterial pressure was unchanged in the HR group but decreased in HP patients (?13.6 ± 3.5 mmHg; P<0.001). This was associated with failure to significantly increase cardiac output in the HP group (cf. increase in cardiac output in the HR group of +33.4 ± 6%; P<0.05), and a reduced response in total peripheral resistance (HP ?10.3 ± 6.8%, HR ?22.7 ± 2.9%, P=NS). Baroreflex sensitivity was not significantly different between groups at baseline or within groups with increasing levels of DAS; however, the mean baroreflex sensitivity was higher in HR cf. HP subjects throughout pharmacological stress (P<0.05). Hypotension‐prone patients appear to have an impaired cardiovascular response to DAS. The most significant abnormality is an impaired myocardial contractile reserve. Early identification of these patients would allow utilization of therapeutic strategies to improve intradialytic tolerability, potentially abrogating aggravation of myocardial injury.     

Calculation of ultrasonic surface waves from an extended thermoelastic laser source

A method is developed to calculate ultrasonic surface waveforms generated by an extended laser source, operating in the thermoelastic regime of laser-pulse energy density. This approach integrates over a suitably weighted distribution of point surface centers of expansion, for observation to within 1 mm of the edge of the source. Power spectra as well as both horizontal and vertical displacements are presented and discussed for ultrasonic waveforms on an aluminium surface, for incident laser pulses having Gaussian lateral profiles of various sizes. Far from the source, the waveform is dominated by a dipolar Rayleigh (R) wave, whose amplitude and spectral content depend on laser spot size. Weak, monopolar pulses also occur at the intersection of bulk pressure and shear wavefronts with the surface (denoted assP andsS, respectively). Close to the source, thesP wave amplitude approaches that for theR wave, and overlaps theR wave for large source sizes. The fall-off with distance for bothsP andR waves is given. Finally, the changes in pulse shape and amplitude are calculated when anR wave from an extended thermoelastic source is reflected or transmitted by a right-angled corner of an aluminium block.     

Spatial noise phenomena of longitudinal magnetic recording media

The authors have studied the spatial noise characteristics of uniformly magnetized media and implemented a synchronous magnetic pulse detection technique to measure waveforms from precise radial and azimuthal locations on a magnetically recorded disk. They introduce a correlation analysis which includes measuring noise waveforms from the same position on the disk under different remanent magnetic states. Results from this analysis demonstrate that at remanence only minor changes occur in the output waveform and its (presumed) corresponding magnetic structure from write to write, while at DC demagnetization large variations are seen for successive writes. This sensitive correlation technique is used to analyze the random and deterministic components of media and head noise     

Arterial pulse wave propagation across stenoses and aneurysms: assessment of one-dimensional simulations against three-dimensional simulations and in vitro measurements

One-dimensional (1-D) arterial blood flow modelling was tested in a series of idealized vascular geometries representing the abdominal aorta, common carotid and iliac arteries with different sizes of stenoses and/or aneurysms. Three-dimensional (3-D) modelling and in vitro measurements were used as ground truth to assess the accuracy of 1-D model pressure and flow waves. The 1-D and 3-D formulations shared identical boundary conditions and had equivalent vascular geometries and material properties. The parameters of an experimental set-up of the abdominal aorta for different aneurysm sizes were matched in corresponding 1-D models. Results show the ability of 1-D modelling to capture the main features of pressure and flow waves, pressure drop across the stenoses and energy dissipation across aneurysms observed in the 3-D and experimental models. Under physiological Reynolds numbers (Re), root mean square errors were smaller than 5.4% for pressure and 7.3% for the flow, for stenosis and aneurysm sizes of up to 85% and 400%, respectively. Relative errors increased with the increasing stenosis and aneurysm size, aneurysm length and Re, and decreasing stenosis length. All data generated in this study are freely available and provide a valuable resource for future research.     

Numerical sampling rules for paraxial regime pulse diffraction calculations

Sampling rules for numerically calculating ultrashort pulse fields are discussed. Such pulses are not monochromatic but rather have a finite spectral distribution about some central (temporal) frequency. Accordingly, the diffraction pattern for many spectral components must be considered. From a numerical implementation viewpoint, one may ask how many of these spectral components are needed to accurately calculate the pulse field. Using an analytical expression for the Fresnel diffraction from a 1-D slit, we examine this question by varying the number of contributing spectral components. We show how undersampling the spectral profile produces erroneous numerical artifacts (aliasing) in the spatial-temporal domain. A guideline, based on graphical considerations, is proposed that determines appropriate sampling conditions. We show that there is a relationship between this sampling rule and a diffraction wave that emerges from the aperture edge; comparisons are drawn with boundary diffraction waves. Numerical results for 2-D square and circular apertures are presented and discussed, and a potentially time-saving calculation technique that relates pulse distributions in different z planes is described.     

Shift and shape of grating diffracted beams

Abstract

The grating diffraction of beams is theoretically investigated by applying an electromagnetic method (the Integral Equation System Method with Parametrization of the grating profile = IESMP) to their plane wave components. For the first time, explicit values for the displacement of grating diffracted Gaussian beams are calculated with this method. For total reflection this displacement of beams is known as the Goos-Hänchen shift. A maximum shift of 36 μm has been found for the investigated sinusoidal grating near an anomaly which is much greater than the known Goos–Hänchen shift of about 1 μm for the total reflection case. The replacement of the angular spectrum of plane waves with constant wavelength by a wavelength spectrum of plane waves of constant direction allows an analogous treatment of short-time pulses. Surprisingly, the above anomaly causes a maximum temporal shift of 80 fs for the pulse diffraction. These temporal shifts and additional effects like pulse deformations can influence ultra short-time pulse experiments. Furthermore, the behaviour of temporally and spatially Gaussian shaped light pulses (TSG pulses) by grating diffraction are studied considering the diffraction of an angular and wavelength dependent spectrum of plane waves. The diffraction of a short TSG pulse at the above grating deforms the pulse and creates an additional smaller satellite pulse. All described effects occur only at positions of the space–time complex filtering function in the angular-wavelength frequency space with high gradient of the phase.     

Residual renal function and arterial stiffness mediated the blood pressure change during interdialytic weight gain in hemodialysis patients

Volume overload is thought to be the main cause of hypertension in dialysis patients. However, the effect of interdialytic weight gain (IDWG) in hemodialysis (HD) patients, which was considered as an increase in extracellular water (ECW), on blood pressure (BP) change, was controversial. Our aim was to examine the changes in hemodynamics and arterial stiffness during IDWG in HD patients and attempt to explore the possible mechanism of diverse BP change. Thirty prevalent patients on HD were enrolled. The height, weight, BP, blood chemistry, volume status assessed by bioelectrical impedance analysis, hemodynamic parameters obtained by echocardiography, and pulse wave velocity (PWV) were collected within 1 hour postdialysis and again just before the next dialysis session. Meanwhile, blood samples were drawn to analyze vasoactive hormones, including renin, angiotensin II, catecholamine, and endothelin. The patients' weights and ECWs during the next predialysis were significantly higher than those during the postdialysis. The BP showed no difference between postdialysis and the next predialysis. There was an obvious increase in cardiac output and decrease in total peripheral resistance as a whole during the next predialysis than that during postdialysis. When patients were divided into the BP increase group (BPI group, 13 patients) and BP decrease group (BPD group, 11 patients) according to the change in systolic BP higher than 10 mmHg, both groups displayed a significant increase in weight, ECW, cardiac output, and a decrease in total peripheral resistance. As compared with the BPI group, patients in the BPD group had significantly lower IDWG, shorter time on dialysis treatment, and higher residual renal function. A decrease in catecholamine and endothelin in the next predialysis was obvious in the BPD group. There was a significant decrease in PWV at the next predialysis in the BPD group while the PWV did not change significantly in the BPI group. Our results showed that the diverse BP change during IDWG was significantly affected by residual renal function, PWV, and vasoactive substances.     

Effect of stratification on hydrodynamic pressures on dams

Summary The effect of stratification of the fluid in the reservoir on hydrodynamic pressures on dams due to horizontal, harmonic ground accelerations has been analyzed. It has been found that both the zeroth-order solution, which corresponds to the constant-density solution, and the first-order solution have two components in the hydrodynamic pressure distribution, an in-phase component and an out-of-phase component which is 90° lagging. The out-of-phase components vanish in the absence of surface waves, and they become dominant when the wave-effect parameter C becomes large. The wave-effect parameter C is defined as 49-1, where g is the gravitational constant, the oscillation frequency and h the height of the fluid in the reservoir. The total horizontal force on a dam due to harmonic ground excitations has also been presented.     

Time-frequency analyses of fluid–solid interaction under sinusoidal translational shear deformation of the viscoelastic rat cerebrum

During normal extracellular fluid (ECF) flow in the brain glymphatic system or during pathological flow induced by trauma resulting from impacts and blast waves, ECF–solid matter interactions result from sinusoidal shear waves in the brain and cranial arterial tissue, both heterogeneous biological tissues with high fluid content. The flow in the glymphatic system is known to be forced by pulsations of the cranial arteries at about 1 Hz. The experimental shear stress response to sinusoidal translational shear deformation at 1 Hz and 25% strain amplitude and either 0% or 33% compression is compared for rat cerebrum and bovine aortic tissue. Time-frequency analyses aim to correlate the shear stress signal frequency components over time with the behavior of brain tissue constituents to identify the physical source of the shear nonlinear viscoelastic response. Discrete fast Fourier transformation analysis and the novel application to the shear stress signal of harmonic wavelet decomposition both show significant 1 Hz and 3 Hz components. The 3 Hz component in brain tissue, whose magnitude is much larger than in aortic tissue, may result from interstitial fluid induced drag forces. The harmonic wavelet decomposition locates 3 Hz harmonics whose magnitudes decrease on subsequent cycles perhaps because of bond breaking that results in easier fluid movement. Both tissues exhibit transient shear stress softening similar to the Mullins effect in rubber. The form of a new mathematical model for the drag force produced by ECF–solid matter interactions captures the third harmonic seen experimentally.     

The reservoir pressure concept: the 3-element windkessel model revisited? Application to the Asklepios population study

Traditionally the arterial system is either modeled as a lumped-parameter windkessel or a wave system. Recently, a hybrid model has been proposed in which the arterial system is considered to be a reservoir allowing for superimposed wave phenomena. This approach was applied to non-invasively obtained carotid pressure waveforms from 2019 subjects from the Asklepios population to investigate the contribution of reservoir pressure (PP _res,WS) to carotid pulse pressure (PP _car) with age and gender. Additionally, reservoir pressures were compared to the reservoir pressure (PP _res,WK) obtained from a 3-element windkessel model. PP _res,WK and PP _res,WS were determined by applying a 3-element windkessel model and the wave separation model to scaled carotid artery tonometry readings. The evolution of PP _car, PP _res,WK and PP _res,WS was examined for men and women after stratification into age quartiles. PP _car increased with age regardless of sex, but was more pronounced in women, with significant (P < 0.001) age–gender interaction. PP _res increases with age (P < 0.001), regardless of the model used for its determination, but more significantly for women. In men it only increases markedly in the oldest age group. Overall, the reservoir pressure concept showed large similarities to the classical 3-element windkessel model, especially in subjects characterized by a high reflection magnitude and high “windkesselness” of their arterial system. When applied to the Asklepios population, both models show the increase of pulse pressure with age to be largely due to increasing reservoir pressures.