Backward-traveling Waves Research Articles

Clinical Implications

HomeHypertensionVol. 64, No. 5Clinical Implications Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBClinical Implications Originally published1 Nov 2014https://doi.org/10.1161/HYPERTENSIONAHA.114.04612Hypertension. 2014;64:905Reflection Magnitude and Death (page 958)Although the systolic and diastolic blood pressures contain important prognostic information, further knowledge can still be gained from analysis of the arterial waveform. Wave reflections, returning to the heart from the periphery in late systole, affect the central pressure waveform and increase the load on the left ventricle. In this study, we performed wave separation analysis on 5984 healthy individuals from the Multi-Ethnic Study of Atherosclerosis cohort and determined the magnitude of the forward (Pf) and backward-traveling (Pb) waves using a physiological flow approach. We found that their ratio (reflection magnitude, Pb/Pf) related to mortality, even after adjustment for traditional atherosclerotic risk factors and blood pressure. Importantly, the forward and backward waves were associated with mortality in opposite directions, with increased backward wave but decreased forward wave amplitude, associating with increased mortality. These relationships were strongest for cardiovascular death. In summary, the arterial waveform provides important incremental information beyond its peak and trough. Both the magnitudes of the forward and backward waves demonstrate significant prognostic relationships to mortality.Download figureDownload PowerPointCD8+ T cells and Hypertension (page 1108)Recent studies have implicated a role of T cells in the genesis of hypertension; however, mechanisms underlying T cell activation in this disease remain poorly defined. Naïve T cells develop in the thymus and migrate to secondary lymphoid organs, including the spleen and lymph nodes. The Vβ region of the T cell receptor gene exhibits enormous diversity, providing recognition of virtually any foreign peptide. Antigen presentation leads to expansion of T cell clones that are specific for individual antigens. In this study, we found that hypertension is associated with expansion of 3 Vβ subtypes in CD8+ T cells of the kidney. We further found that mice lacking CD8+ T cells develop blunted hypertension, as did mice with only 1 T cell receptor specific for an albumin peptide (OT1xRAG-1−/− mice, see Figure). In normal mice and mice lacking CD4+ T cells, we found that hypertension is associated with attenuation of the renal microvasculature and that CD8−/− mice are protected against this vascular perturbation. In another recent study, we identified isoketal-modified proteins as potential neoantigens in hypertension. Isoketals are oxidized products of arachidonic acid that rapidly ligate to proteins. Taken together with our present article in Hypertension, our data indicate that renal oxidative injury leads to formation of oxidatively modified proteins that are recognized as nonself and lead to an oligoclonal population of CD8+ T cells. Efforts to scavenge isoketals or reduce their formation will likely be effective in reducing inflammation, reducing renal injury, and lowering blood pressure.Download figureDownload PowerPointBlood Pressure Control in Uninsured Adults (page 997)Hypertension control in the United States is generally better in white than in black and Hispanic adults. However, all 3 race/ethnicity groups experienced significant and similar absolute percentage improvements in hypertension control between 1988 and 2008. Several reports documented lower hypertension control in uninsured and insured adults at various time points. We were concerned that uninsured individuals might be falling further behind insured adults in hypertension control. Although anticipating the gap in hypertension control between the insured and uninsured might increase, the absence of progress in the uninsured from 1988 to 2010 was unexpected (Figure). Yet during this time period, the age gap in hypertension control, with better control in younger than in older adults, was essentially eliminated.Download figureDownload PowerPointThe uninsured have lower incomes and less education than the insured, which may contribute to disparate hypertension control. Hypertension control was similar among privately and publicly insured adults from 1988 to 2010 (Figure), although education and income were similar in publicly insured and uninsured adults. Thus, insurance emerges as a major factor in hypertension control. The uninsured had fewer healthcare visits, were less aware of hypertension, and less likely to be treated when aware and controlled when treated. Despite the Affordable Care Act, 31 million Americans are likely to remain uninsured. It is important to overcome access barriers to evidence-based care and medications to translate proven benefits of hypertension control to currently uninsured adults. Previous Back to top Next FiguresReferencesRelatedDetails November 2014Vol 64, Issue 5 Advertisement Article InformationMetrics © 2014 American Heart Association, Inc.https://doi.org/10.1161/HYPERTENSIONAHA.114.04612 Originally publishedNovember 1, 2014 PDF download Advertisement

Arterial wave reflections and ventricular-vascular interaction in patients with left ventricular systolic dysfunction.

Central aortic pressure waveform (AoPW) is the summation of a forward-traveling wave generated by the left ventricle and a backward-traveling wave caused by the reflection of the forward wave. The aim of this study was to evaluate the effect of ventricular-vascular coupling on the morphology of AoPW in chronic heart failure patients with different degrees of left ventricular systolic dysfunction (LVSD) using pulse wave analysis (PWA). PWA of AoPW and left ventricular (LV) function were evaluated by applanation tonometry in 26 control subjects, in 12 patients with left ventricular ejection fraction (LVEF) ≤ 30%, and in 14 patients with LVEF > 30%. Augmentation pressure, augmentation index, wasted energy, and ejection duration were lower in patients with LVEF ≤ 30% than in those with LVEF > 30% and in control subjects. Furthermore, augmentation index showed an inverse correlation with Doppler mitral E-wave amplitude (r = -0.40; P = 0.04) and E/A ratio (r = -0.42; P = 0.03) and a direct correlation with deceleration time of mitral E-waves (r = 0.39; P = 0.04). In patients with severe LVSD (LVEF ≤ 30%), aortic wave reflections negatively interfere with LV function and induce a shortening of ejection duration. In contrast, AoPW is similar in patients with moderate LVSD (LVEF > 30%) and in control subjects.

Aortic pulse wave velocity and reflecting distance estimation from peripheral waveforms in humans: detection of age- and exercise training-related differences

We hypothesized that demographic/anthropometric parameters can be used to estimate effective reflecting distance (EfRD), required to derive aortic pulse wave velocity (APWV), a prognostic marker of cardiovascular risk, from peripheral waveforms and that such estimates can discriminate differences in APWV and EfRD with aging and habitual endurance exercise in healthy adults. Ascending aortic pressure waveforms were derived from peripheral waveforms (brachial artery pressure, n = 25; and finger volume pulse, n = 15) via a transfer function and then used to determine the time delay between forward- and backward-traveling waves (Δtf-b). True EfRDs were computed as directly measured carotid-femoral pulse wave velocity (CFPWV) × 1/2Δtf-b and then used in regression analysis to establish an equation for EfRD based on demographic/anthropometric data (EfRD = 0.173·age + 0.661·BMI + 34.548 cm, where BMI is body mass index). We found good agreement between true and estimated APWV (Pearson's R² = 0.43; intraclass correlation = 0.64; both P < 0.05) and EfRD (R² = 0.24; intraclass correlation = 0.40; both P < 0.05). In young sedentary (22 ± 2 years, n = 6), older sedentary (62 ± 1 years, n = 24), and older endurance-trained (61 ± 2 years, n = 14) subjects, EfRD (from demographic/anthropometric parameters), APWV, and 1/2Δtf-b (from brachial artery pressure waveforms) were 52.0 ± 0.5, 61.8 ± 0.4, and 60.6 ± 0.5 cm; 6.4 ± 0.3, 9.6 ± 0.2, and 8.1 ± 0.2 m/s; and 82 ± 3, 65 ± 1 and 76 ± 2 ms (all P < 0.05), respectively. Our results demonstrate that APWV derived from peripheral waveforms using age and BMI to estimate EfRD correlates with CFPWV in healthy adults. This method can reliably detect the distal shift of the reflecting site with age and the increase in APWV with sedentary aging that is attenuated with habitual endurance exercise.

Coronary Wave Energy

Revascularization after acute coronary syndromes provides prognostic benefit, provided that the subtended myocardium is viable. The microcirculation and contractility of the subtended myocardium affect propagation of coronary flow, which can be characterized by wave intensity analysis. The study objective was to determine in acute coronary syndromes whether early wave intensity analysis-derived microcirculatory (backward) expansion wave energy predicts late viability, defined by functional recovery. Thirty-one patients (58±11 years) were enrolled after non-ST elevation myocardial infarction. Regional left ventricular function and late-gadolinium enhancement were assessed by cardiac magnetic resonance imaging, before and 3 months after revascularization. The backward-traveling (microcirculatory) expansion wave was derived from wave intensity analysis of phasic coronary pressure and velocity in the infarct-related artery, whereas mean values were used to calculate hyperemic microvascular resistance. Twelve-hour troponin T, left ventricular ejection fraction, and percentage late-gadolinium enhancement mass were 1.35±1.21 µg/L, 56±11%, and 8.4±6.0%, respectively. The infarct-related artery backward-traveling (microcirculatory) expansion wave was inversely correlated with late-gadolinium enhancement infarct mass (r=-0.81; P<0.0001) and strongly predicted regional left ventricular recovery (r=0.68; P=0.001). By receiver operating characteristic analysis, a backward-traveling (microcirculatory) expansion wave threshold of 2.8 W m(-2) s(-2)×10(5) predicted functional recovery with sensitivity and specificity of 0.91 and 0.82 (AUC 0.88). Hyperemic microvascular resistance correlated with late-gadolinium enhancement mass (r=0.48; P=0.03) but not left ventricular recovery (r=-0.34; P=0.07). The microcirculation-derived backward expansion wave is a new index that correlates with the magnitude and location of infarction, which may allow for the prediction of functional myocardial recovery. Coronary wave intensity analysis may facilitate myocardial viability assessment during cardiac catheterization.

Electromagnetic wave scattering from a rough interface above a chiral medium: generalized field transforms

In order to derive full-wave solutions for electromagnetic wave scattering from rough interfaces between achiral media (free space for instance) and chiral media that satisfy generalized constitutive relations, it is necessary to employ complete modal expansions for the electromagnetic fields above and below the interface. To this end, the familiar Fourier transforms of the fields are expressed as generalized field transforms consisting of the radiation term, the lateral waves, and the surface waves. Maxwell's equations are converted into generalized telegraphists' equations [in the companion paper (this issue), J. Opt. Soc. Am. A 30, 335 (2013)] upon the imposition of exact boundary conditions. These telegraphists' equations are coupled first-order differential equations for the forward- and backward-traveling wave amplitudes associated with all the different species of waves (radiation, lateral, and surface waves) excited at the surface of the chiral medium. The analysis presented here includes the completeness and orthogonal relations of the basis functions associated with the modal expansions. This work is used to distinguish between depolarization due to the chiral properties of the medium and depolarization due to surface irregularities. It has applications in remote sensing and identification of biological and chemical materials based on their optical activity.

Electromagnetic wave scattering from a rough interface above a chiral medium: generalized telegraphists’ equations

Using complete modal expansions for the electromagnetic fields above and below a rough interface between free space and chiral media and on imposing exact boundary conditions at the interface, Maxwell's equations are converted into generalized telegraphists' equations for the wave amplitudes of different species of waves (radiation far fields, lateral, and surface waves). The local basis functions, used in the complete modal expansions, are functions of the fluctuating surface height and medium parameters. The generalized telegraphists' equations are coupled first-order differential equations for the forward- and backward-traveling wave amplitudes. The coupling between the different species of waves is due to the fluctuations of the rough surface height and medium parameters. A Taylor series expansion of the surface element scattering matrix in terms of the chiral parameter is used to distinguish between depolarization due to surface roughness and the chiral properties of the medium. The analysis has applications in remote sensing and identification of biological and chemical materials through their optical activity.

Investigation of Millimeter-Wavelength 20-Vane Spatial-Harmonic Magnetron Using Three-Dimensional Particle-in-Cell Simulation

We investigate, using the 3-D particle-in-cell simulation code MAGIC, the millimeter-wavelength 20-vane magnetron operating at one of the spatial nonfundamental harmonics of the backward-traveling wave. This spatial harmonic is characterized by 16 (p = 16) RF electric field variations along the circumference of the magnetron interaction space (oscillation region). We call this magnetron as the “spatial-harmonic” magnetron operating in the “spatial-harmonic mode.” Calculated electron distribution reveals 16 electron spokes in the interaction space, which confirms the spatial-harmonic mode of the magnetron operation at p = 16. We observe a saturated output power of 3.2 kW, which corresponds to a power conversion efficiency of 12.3% when the applied voltage is 6.5 kV and the external magnetic field is 0.4 T. The operating frequency is 35.2 GHz. The collected anode current is 4 A when the current emitted from the cathode is 6.3 A. The dissipated power at each anode vane, depending on the anode vane position, is varied by the factor 1.8. The energy of back-bombarding electrons on the cathode increases from 305 to 503 eV while the spatial-harmonic magnetron operation is stabilized.

Direction of wave propagation in the cochlea for internally excited basilar membrane

Otoacoustic emissions are an indicator of a normally functioning cochlea and as such are a useful tool for non-invasive diagnosis as well as for understanding cochlear function. While these emitted waves are hypothesized to arise from active processes and exit through the cochlear fluids, neither the precise mechanism by which these emissions are generated nor the transmission pathway is completely known. With regard to the acoustic pathway, two competing hypotheses exist to explain the dominant mode of emission. One hypothesis, the backward-traveling wave hypothesis, posits that the emitted wave propagates as a coupled fluid-structure wave while the alternate hypothesis implicates a fast, compressional wave in the fluid as the main mechanism of energy transfer. In this paper, we study the acoustic pathway for transmission of energy from the inside of the cochlea to the outside through a physiologically-based theoretical model. Using a well-defined, compact source of internal excitation, we predict that the emission is dominated by a backward traveling fluid-structure wave. However, in an active model of the cochlea, a forward traveling wave basal to the location of the force is possible in a limited region around the best place. Finally, the model does predict the dominance of compressional waves under a different excitation, such as an apical excitation.

Wave intensity analysis of para-aortic counterpulsation

Wave intensity analysis (WIA) was used to delineate and maximize the efficacy of a newly developed para-aortic blood pump (PABP). The intra-aortic balloon pump (IABP) was employed as the comparison benchmark. Acute porcine experiments using eight pigs, randomly divided into IABP (n = 4) and PABP (n = 4) groups, were conducted to compare the characteristics of intra- and para-aortic counterpulsation. We measured pressure and velocity with probes installed in the left anterior descending coronary artery and aorta, during and without PABP assistance. Wave intensity for aortic and left coronary waves were derived from pressure and flow measurements with synchronization correction applied. To achieve maximized support efficacy, deflation timings ranging from 25 ms ahead of to 35 ms after the R-wave were tested. Similar to those associated with IABP counterpulsation, the PABP-generated backward-traveling waves predominantly drove aortic and coronary blood flows. However, in contrast with IABP counterpulsation, the nonocclusive nature of the PABP allowed systolic unloading to be delayed into early systole, which resulted in near elimination of coronary blood steal without diminution of systolic left ventricular ejection wave intensities. WIA can elucidate subtleties among different counterpulsatile support means with high sensitivity. Total accelerating wave intensity (TAWI), which was defined as the sum of the time integration of accelerated parts of the positive and negative wave intensities, was used to quantify counterpulsation efficacy. In general, the larger the TAWI gain, the better the counter-pulsatile support efficacy. However, when PABP deflation timings were delayed to after the R-wave, the TAWI was found to be inversely correlated with coronary perfusion. In this delayed deflation timing setting, greater wave cancellation occurred, which led to decreased TAWI but increased coronary perfusion attributed to blood regurgitation reduction.

A Novel Transient Directional Unit Based on Adaptive Median Filtering

A new transient directional unit for extra high voltage(EHV) power transmission lines is proposed, which identifies fault direction by means of comparing the time-domain transient energy of the forward traveling-wave with that of the backward one in the very short period of time after fault occurs. The unit algorithm is designed with the technology of adaptive median filtering, which is first employed to process the forward and backward traveling-waves, and then calculates the time-domain transient energy ratio of the forward traveling-wave to the back one, by which the fault direction is discriminated. Numerous ATP-EMTP simulation tests show that this proposed directional unit not only operates reliably, sensitively and ultra-high-speed, but also endure the influences of various factors, including different fault types, fault locations, transition resistances or fault inception angles. It will be worthy of application greatly.

Live Electrooptic Imaging Camera for Real-Time Visual Accesses to Electric Waves in GHz Range

Recent progresses in the live electrooptic imaging (LEI) technique are reviewed with emphasis on its functionality of real-time visual accesses to traveling electric waves in the GHz range. Together with the principles, configurations, and procedures for the visual observation experiments by an LEI camera system, the following results are described as examples indicating the wide application ranges of the technique; Ku-band waves on arrayed planar antennas, waves on a Gb/s-class digital circuit, W-band waves traveling both in slab-waveguide modes and aerially, backward-traveling wave along composite right/left-handed transmission line, and, waves in monolithic microwave integrated circuit module case.

Variable open-end wave reflection in the pulmonary arteries of anesthetized sheep

The aim of this study was to re-evaluate wave reflection in the healthy pulmonary arteries of sheep utilizing the time-domain-based method of wave intensity analysis. A thorough understanding of patterns of wave reflection during health and disease may provide future sensitive markers of early pulmonary vascular disease. Wave intensity was calculated from the simultaneous acquisition of proximal pulmonary arterial pressure and velocity in 12 anesthetized open-chest sheep. Normal pulmonary arterial wave speed was 2.1±0.3ms(-1). The incident forward compression wave generated by right ventricular systole was reflected in an open-end manner as a backward expansion wave from a site 3cm downstream, corresponding to the main pulmonary bifurcation, and in a closed-end manner as a backward compression wave from a site 21cm downstream, corresponding to the pulmonary microcirculation. The proximal open-end reflection site was not present throughout the entire cardiac cycle. Wave reflection was minimal with only 1% of the incident forward compression wave energy reflected as a backward expansion wave and 2% as a backward compression wave. The normal pulmonary artery in open-chest sheep is characterized by variable proximal open-end reflection from the main pulmonary bifurcation and fixed closed-end reflection from the microcirculation, generating backward-travelling waves of minimal intensity.

Generation of unipolar pulses from nonunipolar optical pulses in a nonlinear medium

A unipolar electromagnetic pulse is a pulse with nonzero value of the static component of the Fourier spectrum of its real electric field (and not its envelope). We show how to efficiently generate unipolar pulses through propagation of an initially nonunipolar pulse in a nonlinear optical medium. One of the major results is the demonstration that the static component can only be generated in equal portions between the forward- and backward-traveling waves in the presence of nonlinear backscattering in a nonlinear medium.

41 Reduced arterial wave reflection and enhanced LV relaxation contribute to warm-up angina

BackgroundThe mechanisms of the clinically observed phenomenon of reduced angina on second exertion, or warm-up angina, are poorly understood. This study compared changes in central haemodynamics, peripheral wave reflection and...

Cellular Senescence, Vascular Disease, and Aging

> You must remember this, > > A kiss is just a kiss, > > A sigh is just a sigh, > > The fundamental things apply, > > As time goes by. “As Time Goes By,” by Herman Hupfeld, Casablanca (1942)1 The increasing prevalence of older-age people in our society represents the culmination of centuries of medical, scientific, and social endeavors. At least in Western society, now relatively freed from pestilence, abject poverty, gross malnutrition, and polluted water and food sources, an increasing proportion of the population can expect to make it to old age. However, although US age-adjusted death rates from cardiovascular disease, coronary heart disease, and stroke continue to fall, a disproportionate number of people who reach old age (≈80% of people aged ≥80 years) suffer from these diseases.1a In this 2-part review, we consider important pathobiological changes that occur with aging in the cardiovascular system, exploring promising areas of recent scientific progress and novel insights that may be translatable into targeted clinical strategies to help to alleviate the excess morbidity and mortality imposed by cardiovascular disease in the elderly. In this second installment, we focus specifically on vascular disease states of the elderly, including systolic hypertension, vascular calcification, and dementia, and we review relevant basic and clinical discoveries that further elucidate these conditions. ### The Elderly Vascular Phenotype Aging is associated with various changes in the vascular system at differing structural and functional levels. At the macroscopic level, an increase in arterial lumen size and arterial wall thickening, mainly of the intima, are observed.2 In addition, increased vascular calcification and a generalized stiffening of the arterial tree lead to increased arterial wave reflectance, increased systolic blood pressure, decreased diastolic blood pressure, and a widened pulse pressure. An interesting aspect of vascular biology in which significant inroads have been made is our understanding of pulse wave velocity, which …

Distortion products and backward-traveling waves in nonlinear active models of the cochlea

This study explores the phenomenology of distortion products in nonlinear cochlear models, predicting their amplitude and phase along the basilar membrane. The existence of a backward-traveling wave at the distortion-product frequency, which has been recently questioned by experiments measuring the phase of basilar-membrane vibration, is discussed. The effect of different modeling choices is analyzed, including feed-forward asymmetry, micromechanical roughness, and breaking of scaling symmetry. The experimentally observed negative slope of basilar-membrane phase is predicted by numerical simulations of nonlinear cochlear models under a wide range of parameters and modeling choices. In active models, positive phase slopes are predicted by the quasi-linear analytical computations and by the fully nonlinear numerical simulations only if the distortion-product sources are localized apical to the observation point and if the stapes reflectivity is unrealistically small. The results of this study predict a negative phase slope whenever the source is distributed over a reasonably wide cochlear region and/or a reasonably high stapes reflectivity is assumed. Therefore, the above-mentioned experiments do not contradict "classical" models of cochlear mechanics and of distortion-product generation.

Wave Propagation and Reflection in the Canine Aorta: Analysis Using a Reservoir-Wave Approach

Background Our objective was to demonstrate wave propagation and reflection in the canine aorta. Recently we proposed that aortic pressure is the instantaneous sum of wave-related or “excess” pressure and reservoir or windkessel pressure. Accordingly, in this research we calculated reservoir pressure and subtracted it from measured pressure to identify the change in pressure due to forward- or backward-travelling waves. Methods In 8 anesthetized dogs, excess pressures were calculated from pressure and flow measurements at 4 locations along the aorta; wave intensity analysis was employed to identify wavefronts and the type of waves. Results We found that forward compression and decompression waves generated by the left ventricle are reflected, first, from a negative or “open-end” reflection site near the renal arteries (32.0 ± 0.8 cm [SEM] from the aortic root) and, second, from a positive site in the femoral arteries (65.3 ± 2.8 cm or 54.9 ± 2.1 cm, based on 2 alternative extrapolation techniques). Conclusions Aortic wave propagation and reflection can be demonstrated clearly and directly by wave intensity analysis after volume-related changes–changes in reservoir or windkessel pressure–in aortic pressure are accounted for.

Evaluation of Carotid Wave Intensity in Firefighters Following Firefighting

Sudden cardiac events are the number one cause of line-of-duty firefighter deaths, but little information exists elucidating the physiologic response to firefighting. Wave intensity (WI) is a new hemodynamic index that provides information about the dynamic behavior of the heart and the vascular system and their interaction. The larger first peak wave (W1) occurs during early systole and is associated with cardiac contractility. The second smaller peak (W2) follows a period of relatively little net wave production during mid-systole and is associated with end systole/early diastole. A small backward-traveling compression wave occurs after the first peak of wave intensity referred as negative area (NA), caused by reflected waves from the peripheral vascular tone and resistance. PURPOSE: To examine changes in arterial ventricular coupling associated with firefighting. METHODS: We examined 39 firefighters (2 females) with a mean age of 28 ± 1 yrs and BMI of 26.6 ± 0.7 kg/m2 at rest and immediately after 4 hours of live firefighting drills. WI was assessed on the right common carotid artery using an Aloka alpha 10 high-resolution ultrasound scanner with color Doppler system for blood flow velocity measurement combined with an echo-tracking method for detecting vessel diameter changes. The vessel changes were automatically converted to pressure waveforms by calibrating its peak and minimum values by systolic and diastolic carotid blood pressure. Carotid blood pressure was measured by applanation tonometery. RESULTS: The magnitude of the W1 decreased significantly from 15925 ± 1341 to 11540 ± 886 mmHg m s-2, p<.05. The magnitude of W2 remained unchanged (W2: from 2080± 200 to 2144 ± 358 mmHg m s-2). Net NA decreased from 53 ± 5 to 40 ± 4 mmHg m s-2. Carotid blood pressures did not change significantly (carotid SBP: from 126 ± 2 to 122 ± 2mmHg; carotid DBP: from 79 ± 1 to 78 ± 1 mmHg). CONCLUSIONS: Cardiac contractility deteriorated after live firefighting drills reflected by reduced W1. This was partly offset by a reduction in wave reflection but without changes in early diastole or carotid pressure. The decrease in cardiac contractility (or altered ventricular-arterial coupling) may be associated with clinical events during firefighting, but this needs further investigation. Supported by Dept of Homeland Security EMW2006FP02459

Wave energy patterns of counterpulsation: A novel approach with wave intensity analysis

In counterpulsation, diastolic augmentation increases coronary blood flow and systolic unloading reduces left ventricular afterload. We present a new approach with wave intensity analysis to revisit and explain counterpulsation principles. In an acute porcine model, a standard intra-aortic balloon pump was placed in descending aorta in 4 pigs. We measured pressure and velocity with probes in left anterior descending artery and aorta during and without intra-aortic balloon pump assistance. Wave intensities of aortic and left coronary waves were derived from pressure and flow measurements with synchronization correction. We identified predominating waves in counterpulsation. In the aorta, during diastolic augmentation, intra-aortic balloon inflation generated a backward compression wave, with a "pushing" effect toward the aortic root that translated to a forward compression wave into coronary circulation. During systolic unloading, intra-aortic balloon pump deflation generated a backward expansion wave that "sucked" blood from left coronary bed into the aorta. While this backward expansion wave translated to reduced left ventricular afterload, the "sucking" effect resulted in left coronary blood steal, as demonstrated by a forward expansion wave in left anterior descending coronary flow. The waves were sensitive to inflation and deflation timing, with just 25 ms delay from standard deflation timing leading to weaker forward expansion wave and less coronary regurgitation. Intra-aortic balloon pumps generate backward-traveling waves that predominantly drive aortic and coronary blood flow during counterpulsation. Wave intensity analysis of arterial circulations may provide a mechanism to explain diastolic augmentation and systolic unloading of intra-aortic balloon pump counterpulsation.

Dynamic characteristics of traveling waves for a rotating laminated circular plate with viscoelastic core layer

The dynamic governing equations and the corresponding boundary conditions for a rotating thin laminated circular plate with a viscoelastic core layer are derived in this paper based on the Hamilton principle. The analysis on dynamic features of the forward and Backward Traveling Waves for the rotating laminated plate is performed by means of Galerkin's method. The frequency-dependent complex modulus model for describing the constitutive behavior of the viscoelastic core layer is employed. The dynamic characteristics of frequencies and dampings of traveling waves for the rotating plate are obtained numerically. The effects of geometrical and material parameters on the critical speed of the rotating laminated plate with viscoelastic core are discussed in detail.