Backward Pulse Research Articles

Early wave reflection of carotid artery is associated with 18F-FDG PET hypometabolism in Alzheimer's brain areas of cognitively normal adults.

Arterial stiffening likely plays a role in Alzheimer disease (AD) pathogenesis. The current study investigated whether inter-individual variations in arterial stiffness and pressure wave parameters were associated with 18F-FDG positron emission tomography (PET) metabolism in AD-associated brain areas throughout adulthood, independently of age and before the onset of any neuropsychological disorders. A prospective, large age-range population of 67 patients (17 young, 16 middle-aged, and 34 older adults; 37 women) underwent a: brain 18F-FDG PET, blood pressure recording, and carotid/femoral pulse wave-based measurements, including the time-to-peak of the reflected backward carotid pulse wave (bT), on the same day. Multivariable and quantitative voxel-to-voxel analyses (P-voxel < 0.005, corrected for cluster volumes) were conducted to assess associations between vascular parameters and 18F-FDG PET metabolism in AD-associated brain areas. In the multivariable analysis, only increased age and decreased bT were independently associated with the decline of metabolic activity in AD-associated brain areas (P < 0.001). In the voxel-to-voxel analysis with age as a covariate, bT was strongly associated with the metabolic activity of 40 clusters in AD-associated brain areas (clusters cumulative volume: 63 cm3; T score max: 5.7). In a large age-range population of adult patients, who are still unaffected by neuropsychological disorders, an early reflected arterial pressure wave, as evidenced by a decreased bT value, is strongly associated with hypometabolic activity of AD-associated brain areas, independently of age.

Abstract P516: Vascular Risk Assessment in Youth With Familial Hypercholesterolemia and Combined Dyslipidemia of Obesity

Introduction: Pulse wave analysis (PWA) assesses vascular health by estimating arterial wave reflections noninvasively and is associated with cardiovascular (CV) events in adults in recent studies. However, data in youth are lacking. Individuals with CV risk factors such as familial hypercholesterolemia (FH) or combined dyslipidemia of obesity (CDO) have increased risk of adult-onset CV disease. Using PWA may help improve risk stratification of young patients with adverse CV risk factors and enhance disease management. Hypothesis: We hypothesized that youth with adverse CV risk factors would have differences in arterial wave reflections compared to controls. Methods: Demographic, anthropometric, and fasting lipid values were obtained in 124 patients aged 9-25 years in a study comparing vascular health among normolipidemic controls (N=47), FH (N=45), and CDO (N=32). PWA was obtained using the SphygmoCor XCEL device, and wave separation analyses were performed from brachial artery assessments. Group differences were assessed by chi-square, ANOVA, or Kruskal-Wallis test as appropriate by variable type and distribution normality. Results: There were significant differences between groups in adiposity (CDO with higher BMI, p&lt;0.001) and lipid levels with a more adverse lipid profile (higher TC, LDL, &amp; TG; lower HDL) for the FH and CDO groups versus controls (all p&lt;0.001). The CDO group had higher forward pulse wave amplitude (Pf) versus the control and FH groups (p=0.0002, Figure) and higher backward pulse wave amplitude (Pb) versus controls (p=0.0013). Differences in Pf or Pb between FH and controls did not reach significance. Conclusions: Adolescents and young adults with CDO have altered forward and backward wave reflections compared to normolipidemic controls. It is possible that PWA differences between the FH and control groups may become significant over time. These novel parameters suggest early vascular changes in youth with CDO and may help improve risk stratification in youth with adverse CV risk factors.

Mortality and Cardiovascular End Points In Relation to the Aortic Pulse Wave Components: An Individual-Participant Meta-Analysis.

Wave separation analysis enables individualized evaluation of the aortic pulse wave components. Previous studies focused on the pressure height with overall positive but differing results. In the present analysis, we assessed the associations of the pressure of forward and backward (Pfor and Pref) pulse waves with prospective cardiovascular end points, with extended analysis for time to pressure peak (Tfor and Tref). Participants in 3 IDCARS (International Database of Central Arterial Properties for Risk Stratification) cohorts (Argentina, Belgium, and Finland) aged ≥20 years with valid pulse wave analysis and follow-up data were included. Pulse wave analysis was done using the SphygmoCor device, and pulse wave separation was done using the triangular method. The primary end points consisted of cardiovascular mortality and nonfatal cardiovascular and cerebrovascular events. Multivariable-adjusted Cox regression was used to calculate hazard ratios. A total of 2206 participants (mean age, 57.0 years; 55.0% women) were analyzed. Mean±SDs for Pfor, Pref, Tfor, and Tfor/Tref were 31.0±9.1 mm Hg, 20.8±8.4 mm Hg, 130.8±35.5, and 0.51±0.11, respectively. Over a median follow-up of 4.4 years, 146 (6.6%) participants experienced a primary end point. Every 1 SD increment in Pfor, Tfor, and Tfor/Tref was associated with 27% (95% CI, 1.07-1.49), 25% (95% CI, 1.07-1.45), and 32% (95% CI, 1.12-1.56) higher risk, respectively. Adding Tfor and Tfor/Tref to existing risk models improved model prediction (∆Uno's C, 0.020; P<0.01). Pulse wave components were predictive of composite cardiovascular end points, with Tfor/Tref showing significant improvement in risk prediction. Pending further confirmation, the ratio of time to forward and backward pressure peak may be useful to evaluate increased afterload and signify increased cardiovascular risk.

A directional coupler for partial discharge measurements in gas-insulated substations

This paper introduces a directional coupler for partial discharge (PD) measurements in gas-insulated substations (GIS). The sensor comprises a combination of magnetic and electric couplers, effectively segregating forward and backward pulses to enhance PD charge estimation and defect location. The sensor's design was supported with finite element method simulations and measurements conducted in a transverse electromagnetic test bench. Comparative analyses were performed against independent magnetic and electric couplers. The charge estimation and the directional coupler's directivity were evaluated in both the test bench and a full-scale GIS with different PD defects. Initially, the combined magnetic and the electric couplers exhibited undesired interactions, prompting corrective measures. Subsequent adjustments included changes to the electric coupler material and modifications to the magnetic coupler construction. The resulting high-voltage directional coupler performed better than the separated couplers in a GIS with discontinuities. This partial discharge sensor emerges as a candidate for future SF6-free alternative GIS.

Insulin-induced vasoconstriction is prevalent in muscle microvasculature of otherwise healthy persons with type 1 diabetes.

Insulin's microvascular actions and their relationship to insulin's metabolic actions have not been well studied in adults with type 1 diabetes mellitus (T1DM). We compared the metabolic and selected micro- and macrovascular responses to insulin by healthy adult control (n = 16) and subjects with T1DM (n = 15) without clinical microvascular disease. We measured insulin's effect on 1) skeletal muscle microvascular perfusion using contrast-enhanced ultrasound (CEU), 2) arterial stiffness using carotid-femoral pulse-wave velocity (cfPWV) and radial artery pulse wave analysis (PWA), and 3) metabolic insulin sensitivity by the glucose infusion rate (GIR) during a 2-h, 1 mU/min/kg euglycemic-insulin clamp. Subjects with T1DM were metabolically insulin resistant (GIR = 5.2 ± 0.7 vs. 6.6 ± 0.6 mg/min/kg, P < 0.001). Insulin increased muscle microvascular blood volume and flow in control (P < 0.001, for each) but not in subjects with T1DM. Metabolic insulin sensitivity correlated with increases of muscle microvascular perfused volume (P < 0.05). Baseline measures of vascular stiffness did not differ between groups. However, during hyperinsulinemia, cfPWV was greater (P < 0.02) in the T1DM group and the backward pulse wave pressure declined with insulin only in controls (P < 0.03), both indices indicating that insulin-induced vascular relaxation in controls only. Subjects with T1DM have muscle microvascular insulin resistance that may precede clinical microvascular disease.NEW & NOTEWORTHY Using contrast ultrasound and measures of vascular stiffness, we compared vascular and metabolic responses to insulin in patients with type 1 diabetes with age-matched controls. The patients with type 1 diabetes demonstrated both vascular and metabolic insulin resistance with more than half of the patients with diabetes having a paradoxical vasoconstrictive vascular response to insulin.

Control of SBS pulse compression by interaction geometrical parameters

In this paper, the effect of the interaction geometry parameters on the stimulated Brillouin scattering process in a generator cell to achieve maximum compression is studied experimentally. For this purpose, variations of the input energy flux to the cell and the interaction length on the backward stokes pulse width and energy reflectivity were studied by changing the cell length and the distance of the lens to the cell. Our results show that the distance of the lens to the cell window can be considered as a determinative parameter to explore the position of the generated stokes pulse in the generator cell for obtaining the Maximum interaction length. Therefore, by adjusting the distance of the lens and input energy to the cell, the pulse compression ratio is controlled and maximum pulse compression can be obtained.

Risk associated with forward and backward arterial pulse waves.

Risk associated with forward and backward arterial pulse waves.

Altered Aortic Waveform Responses To Insulin In Late Chronotype With Metabolic Syndrome

PURPOSE: Late chronotype (LC) is linked to insulin resistance & cardiovascular disease. However, it is unclear if insulin reduces aortic waveforms & inflammation in LC versus early chronotype (EC). METHODS: Using the Morning-Eveningness Questionnaire (MEQ), adults with metabolic syndrome (MetS; 54.9 ± 1.1y; VO2MAX 22.2 ± 0.7 ml/kg/min, 3.5 ± 0.1 ATP-III score) were classified as either LC (n = 19 (16F); MEQ = 45.5 ± 1.3) or EC (n = 20 (16F); MEQ = 63.5 ± 1.2). A 120 min euglycemic clamp (40 mU/m2/min, 90 mg/dl) with indirect calorimetry was used to determine metabolic insulin sensitivity (glucose infusion rate (GIR)) & non-oxidized glucose disposal (NOGD; GIR-total carbohydrate oxidation). Aortic waveforms via applanation tonometry were taken at 0 & 120-min of the clamp & included augmentation index (AIx75), augmentation pressure (AP), pulse pressure amplification (PPA), mean arterial pressure (MAP), as well as forward (Pf) & backward (Pb) pulse wave. Inflammation (ICAM, VCAM, hs-CRP, TNF-α, & MMP-7) was also assessed before and after the clamp. RESULTS: While age, fat mass, & ATP III score were similar between groups, LC had higher FFM (P = 0.04) and lower VO2MAX (P = 0.05), GIR (P < 0.01) and NOGD (P < 0.01) than EC. No difference in 0 min waveforms were noted. Nonetheless, LC had increases in Pf versus EC (∆:1.9 ± 1.1 vs. -2.3 ± 1.0 mmHg; P = 0.007) during insulin infusion, though reflection magnitude decreased similarly (∆: -6.0 ± 2.2 vs. -5.9 ± 2.3%; P = 0.02). Further, both LC and EC had elevated PPA (∆: 0.04 ± 0.02 vs. 0.05 ± 0.02 mmHg; P = 0.02) & reduced AP (∆: -2.0 ± 1.0 vs. -2.8 ± 1.1 mmHg; P = 0.02) in response to insulin, while only EC had lower AIx75 (P = 0.02). LC had increased TNF-α (P = 0.04) and decreased MMP-7 (P = 0.04) in response to insulin, and EC decreased in hs-CRP (P = 0.009), ICAM (P = 0.009), and VCAM (P = 0.09). VO2MAX correlated with insulin-mediated reductions in AIx75 (r = -0.56, P < 0.01) and AP (r = -0.49, P < 0.01), while NOGD related to decreased AP during insulin (r = -0.44, P = 0.03) and Pf (r = -0.43, P = 0.04). Insulin-mediated reductions in VCAM also correlated with lower MAP during the clamp (r = 0.41, P = 0.03). CONCLUSIONS: LC was depicted by altered aortic waveform and inflammatory responses to insulin in MetS. More work is needed to assess peripheral endothelial function in chronotype. Funding: NIH RO1-HL130296

Magnetic and electric antennas synergy for partial discharge measurements in gas-insulated substations: Power flow and reflection suppression

One of the main difficulties in measuring partial discharges (PD) in gas-insulated substations (GIS) is the overlapping of pulses at the sensor’s location, which distorts the pulse resolution and the charge estimation. This research presents a new method called “synergy,” which identifies and suppresses reflections using magnetic and electric antennas in the very-high frequency range. By scaling the antennas’ outputs and adding them, it is possible to segregate forward and backward pulses. Additionally, by multiplying the electric and magnetic signals, the power flow of the pulses is obtained, which identifies the propagation direction and the location of discontinuities in the transmission path. The synergy method is evaluated in three scenarios: a fully matched test bench using a calibrated pulse, a full-scale GIS using a calibrated pulse, and a full-scale GIS using a PD defect. The results showed that the pulse reflections can be eliminated from the incident pulse, improving the charge calculation when the pulses overlap. The output of this research represents an improvement for PD monitoring in GIS, exhibiting a tool for better defect localization, pulse wave shape construction, charge estimation, and possible interference rejection.© 2017 Elsevier Inc. All rights reserved.

Body Composition and Physical Fitness Affect Central Hemodynamics in Young Children.

Objective: Central hemodynamics are related to cardiovascular (CV) outcomes in adults, but associations with childhood CV risk remain unclear. The study aimed to investigate the association of obesity, physical activity, and fitness with parameters of central pulse wave reflection in young prepubertal children.Methods: In this cross-sectional study, 1,324 primary school children (aged 7.2 ± 0.4 years) were screened for parameters of pulse wave reflection such as augmentation index (AIx), central pulse pressure (CPP), body mass index (BMI), and cardiorespiratory fitness (CRF) by standardized procedures for children.Results: The mean AIx and AIx@75 were 22.2 ± 7.7 and 29.2 ± 9.2%, respectively. With each unit increase in BMI, AIx [−0.226 (−0.328; −0.125)%] and AIx@75 [−0.444(−0.660; −0.229)%] decreased, whereas peak forward pulse wave increased (p < 0.001). Increasing BMI was associated with higher CPP, but did not remain significant after adjustment for CRF and heart rate. One unit increase in CRF was associated with lower AIx@75 [−0.509(−0.844; −0.173)%, p = 0.003] and lower reflection magnitude [RM: −0.559 (−0.890; −0.227), p = 0.001], independent of body weight and height. Girls had significantly higher AIx, AIx@75, peak backward pulse wave, and RM compared with boys.Conclusion: Childhood obesity was associated with higher CPP but lower augmentation of the reflected pulse wave in children. Assessment of central blood pressures appears to be a valuable asset to childhood CV risk screening. The validity of augmentation indices during childhood development and the association with early vascular aging in children need to be verified in long-term follow-up studies. Physical activity and fitness have the potential to improve vascular hemodynamics in susceptible children and, thus, counteract vascular aging.Trial registry: ClinicalTrials.gov: Exercise and Arterial Modulation in Youth. Identifier: NCT02853747; URL: https://clinicaltrials.gov/ct2/show/NCT02853747.

Impact of moderate altitude exposure on cardiovascular risk

Acute exposure to extreme altitude increases arterial stiffness by activation of the sympathetic and endothelin system as well as hypoxia-induced reactive oxygen species production. Beyond a certain individual threshold, these physiological adaptations represent a relevant cardiovascular risk factor. In this pilot study we investigated to what extent temporary exposure to moderate altitude, as present during hiking, skiing or in aeroplanes, leads to changes in vascular tone. Pulse wave parameters of 8 healthy individuals were assessed with a BR-102 plus pulse wave analyser (Schiller, Germany) at baseline (521 m) and after 24 h exposure to moderate altitude (2650 m). We identified a significant increase in heart rate (61 vs. 68/min, p = 0.021) as well as changes in central (35.6 vs. 41.4 mmHg, p = 0.024) and peripheral pulse pressure (44.7 vs. 52.6 mmHg, p = 0.006). Amplitudes of forward (21.6 vs. 25.4 mmHg, p = 0.012) and backward pulse waves (15.3 vs. 17.6 mmHg, p = 0.043) were significantly elevated. Pulse wave velocity showed no significant change from 5.8 m/s at baseline to 6.1 m/s at moderate altitude (p = 0.056). We show that temporary exposure to moderate altitude leads to mild changes in vascular tone reflected by pulse pressure and pulse wave amplitude in healthy adults. Although the observed effects were mild in our study, it indicates that adaptation capacity is of crucial importance and any restrictions by disease or simply with the process of ageing demand increased awareness, even in moderate altitude.

Pulsatile load and wasted pressure effort are reduced following an acute bout of aerobic exercise.

Following aerobic exercise, sustained vasodilation and concomitant reductions in total peripheral resistance (TPR) result in a reduction in blood pressure that is maintained for two or more hours. However, the time course for postexercise changes in reflected wave amplitude and other indices of pulsatile load on the left ventricle have not been thoroughly described. Therefore, we tested the hypothesis that reflected wave amplitude is reduced beyond an hour after cycling at 60% V̇o2peak for 60 min. Aortic pressure waveforms were derived in 14 healthy adults (7 men, 7 women; 26 ± 3 yr) from radial pulse waves acquired via high-fidelity applanation tonometry at baseline and every 20 min for 120 min postexercise. Concurrently, left ventricle outflow velocities were acquired via Doppler echocardiography and pressure-flow analyses were performed. Aortic characteristic impedance (Zc), forward (Pf) and backward (Pb) pulse wave amplitude, reflected wave travel time (RWTT), and wasted pressure effort (WPE) were derived. Reductions in aortic blood pressure, Zc, Pf, and Pb were all sustained postexercise whereas increases in RWTT emerged from 60 to 100 min post exercise (all P < 0.05). WPE was reduced by ∼40% from 40 to 100 min post exercise (all P < 0.02). Stepwise multiple regression analysis revealed that the peak ΔWPE was associated with ΔRWTT (β = -0.57, P = 0.003) and ΔPb (β = 0.52, P = 0.006), but not Δcardiac output, ΔTPR, ΔZc, or ΔPf. These results suggest that changes in pulsatile hemodynamics are sustained for ≥100 min following moderate intensity aerobic exercise. Moreover, decreased and delayed reflected pressure waves are associated with decreased left ventricular wasted effort after exercise.NEW & NOTEWORTHY We demonstrate that pulsatile load on the left ventricle is diminished following 60 min of moderate intensity aerobic exercise. During recovery from exercise, the amplitude of the forward and backward traveling pressure waves are attenuated and the arrival of reflected waves is delayed. Thus, the work imposed upon the left ventricle by reflected pressure waves, wasted pressure effort, is decreased after exercise.

Extraordinary Fast Forward and Backward Light in Transparent Non‐Hermitian Systems

AbstractThe phenomenon of fast forward and backward light pulse propagation in effectively transparent non‐Hermitian photonic systems is reported. Specifically, the propagation eigenmodes are analyzed in several parity‐time‐symmetric coupled waveguides. In contrast to a previous finding that showed slow light due to an exceptional point in such systems, a critical point in its close proximity that displays a diverging dispersion is identified. Superluminal light pulse propagation in the forward and backward directions is then found and observed numerically on the two sides of the critical point, respectively. This abnormal phenomenon can be understood by a conservation relation of group velocities, which can be extended to other transparent non‐Hermitian photonic systems with different symmetries. More importantly, the abrupt transition across the critical point between the fast forward and backward light can be tuned, indicating the possibility of detecting atom‐scale movement of the waveguides with little time delay. In addition, bandwidth broadening and a passive superluminal propagation configuration are discussed.

D'Alembert digitized: A wave pulse method for visualizing electromagnetic waves in matter and for deriving the finite difference time domain method for numerically solving Maxwell's equations

An alternative way of visualizing electromagnetic waves in matter and of deriving the Finite Difference Time Domain (FDTD) method for simulating Maxwell's equations for one-dimensional systems is presented. The method uses d'Alembert's splitting of waves into forward and backward pulses of arbitrary shape and allows for grid spacing and material properties that vary with the position. Constant velocity of waves in dispersionless dielectric materials, partial reflection and transmission at boundaries between materials with different indices of refraction, and partial reflection, transmission, and attenuation through conducting materials are derived without recourse to exponential functions, trigonometric functions, or complex numbers. Placing d'Alembert's method on a grid is shown to be equivalent to the FDTD method and allows for simple and visual proof that the FDTD method is exact for dielectrics when the ratio of the spatial and temporal grid spacing is the wave speed, a straightforward way to incorporate reflectionless boundary conditions and a derivation that the FDTD method retains second-order accuracy when the grid spacing varies with the position and the material parameters make sudden jumps across layer boundaries.

The supercontinuum generation with Pearcey-Gaussian pulses in an optical fiber

In this paper, the supercontinuum generation in an optical fiber with forward and backward Pearcey-Gaussian pulses near the zero-dispersion wavelength is investigated. By using the split-step Fourier transform to solve the generalized nonlinear Schrödinger equation (GNLSE), we have shown an interesting phenomenon that the spectrum bandwidth of the forward Pearcey-Gaussian pulse is broader than that from hyperbolic secant pulse with the same parameters. By investigating the time–frequency dynamics of the pulse propagation, the underlying mechanism is analyzed.

Post‐Exercise Central Hypotension is Associated with Changes in Forward Pulse Wave Amplitude and Reflected Pulse Wave Timing in Young, Healthy Individuals

In the hours following moderate intensity aerobic exercise (AE), persistent dilation of the arterial circulation supplying previously exercised muscle decreases total peripheral resistance (TPR) and contributes to post‐exercise hypotension. In addition to the effect of vasodilation on TPR, the diameter and tone of arterial vessels also influences central blood pressures via changes in the amplitude of forward (Pf) and backward (Pb) pulse waves, as well as the apparent wave reflection return timing (i.e. reflected wave transit time, RWTT). Prior research has assessed these parameters over a limited timeframe (e.g. 15 min) and relied on synthesized aortic flow waves rather than measured left ventricular outflow. As such, the prolonged post exercise effects of AE on pulse wave characteristics and central blood pressure are unclear.PurposeThis study aimed to characterize changes in pulsatile hemodynamics in the two hours following AE. We hypothesized that Pf and Pb would be reduced, and RWTT would be increased post‐AE relative to baseline (BL).MethodsTwelve young, recreationally active participants (8M/4F, 26±3 years, VO2max: 50.8±14.3 ml·kg−1·min−1) were studied at BL and then every 20 min after completing 60 min of upright cycling at 60% VO2max. At each timepoint, central pressure waveforms were derived from radial artery applanation tonometry and aortic inflow waves were acquired via echocardiographic pulsed‐Doppler assessment of blood velocity in the left ventricular outflow tract. Pressure and flow waves were averaged over 10 cardiac cycles and pressure‐flow relations were determined offline via wave separation analysis.ResultsAs expected, brachial systolic blood pressure (SBP) was decreased across the 120 min period post‐AE relative to BL (time effect P&lt;0.001) while TPR was only reduced at 20 min (Δ−15±5%, P&lt;0.05 vs BL) and cardiac output (CO) was maintained at all timepoints (time effect P=0.12). The nadir in central SBP occurred at 60 min post‐AE (Δ−11±2%, P&lt;0.001 vs BL). At 60 min post‐AE, Pf and Pb were reduced by Δ−14.3±2.5% and Δ−24.2±3.3%, respectively (each P&lt;0.001 vs BL) and RWTT was increased (Δ19.5±5.3% P&lt;0.02 vs BL). The percent change in central SBP from BL to 60 min was related to changes in RWTT (r=−0.79, P=0.02) and Pf (r=0.65, P=0.02) but not Pb (r=0.38, P=0.22), CO (r=0.27, P=0.40) or TPR (r=0.14, P=0.66).ConclusionsThese data highlight the contribution of changes in pulsatile hemodynamic parameters, in contrast to changes in non‐pulsatile parameters (CO and TPR), to reductions in central BP following moderate intensity AE.Support or Funding InformationSupported by NIH grants R01‐HL104106 and P20‐GM113125

Central hemodynamics in relation to low-level environmental lead exposure

Purpose: Arterial stiffness predicts cardiovascular complications. The association between arterial stiffness and blood lead (BL) remains poorly documented. We aimed to assess the association of central hemodynamic measurements, including pulse wave velocity (aPWV), with blood lead in a Flemish population.Materials and Methods: In this Flemish population study (mean age, 37.0 years; 48.3% women), 267 participants had their whole BL and 24-h urinary cadmium (UCd) measured by electrothermal atomic absorption spectrometry in 1985–2005. After 9.4 years (median), they underwent applanation tonometry to estimate central pulse pressure (cPP), the augmentation index (AI), pressure amplification (PA), and aPWV. The amplitudes of the forward (Pf) and backward (Pb) pulse waves and reflection index (RI) were derived by a pressure-based wave separation algorithm.Results: BL averaged 2.93 μg/dL (interquartile range, 1.80–4.70) and UCd 4.79 µg (2.91–7.85). Mean values were 45.0 ± 15.2 mm Hg for cPP, 24.4 ± 12.4% for AI, 1.34 ± 0.21 for PA, 7.65 ± 1.74 m/s for aPWV, 32.7 ± 9.9 mm Hg for Pf, 21.8 ± 8.4 mm Hg for Pb, and 66.9 ± 18.4% for RI. The multivariable-adjusted association sizes for a 2-fold higher BL were: +3.03% (95% confidence interval, 1.56, 4.50) for AI; −0.06 (−0.08, −0.04) for PA; 1.02 mm Hg (0.02, 2.02) for Pb; and 3.98% (1.71, 6.24) for RI (p ≤ .045). In 206 participants never on antihypertensive drug treatment, association sizes were +2.59 mm Hg (0.39, 4.79) for cPP and +0.26 m/s (0.03, 0.50) for aPWV. Analyses adjusted for co-exposure to cadmium were consistent.Conclusion: In conclusion, low-level environmental lead exposure possibly contributes to arterial stiffening and wave reflection from peripheral sites.

Detection of atomic oxygen in a plasma-assisted flame via a backward lasing technique.

In this Letter, we have investigated 845nm lasing generation in atomic oxygen, present in a lean methane-air flame, using two-photon pumping with femtosecond 226nm laser pulses, particularly focusing on the impact of nanosecond repetitively pulsed glow discharges forcing on the backward lasing signal. Characterizations of the backward lasing pulse, in terms of its spectrum, beam profile, pump pulse energy dependence, and divergence, were conducted to establish the presence of lasing. With plasma forcing of the flame, the backward lasing signal was observed to be enhanced significantly, ∼50%. The vertical concentration profile of atomic oxygen was revealed by measuring the backward lasing signal strength as a function of height in the flame. The results are qualitatively consistent with results obtained with two-dimensional femtosecond two-photon-absorption laser-induced fluorescence, suggesting that the backward lasing technique can be a useful tool for studies of plasma-assisted combustion processes, particularly in geometries requiring single-ended standoff detection.

Dynamic properties of ultrashort two-photon pumped transient cavityless lasing in a Coumarin-dye solution

The dynamic spectral and temporal properties of femtosecond two-photon pumped frequency upconversion lasing in a Coumarin-500 dye solution are presented. Forward and backward lasing in a 1 cm pathlength dye solution with a concentration of 0.1 M occurs at wavelengths of 491 nm and 493.5 nm, respectively, whereas the peak wavelength of the ordinary steady-state fluorescence emission is at 513 nm. There is a real time delay of ∼2 ps between the forward pump pulse peak and the first burst of the two-photon pumped forward lasing pulse, which corresponds to the build-up time of the effective population inversion sufficient for transient lasing. In contrast, the backward output lasing pulse can involve two temporally separate components, i.e. the original backward lasing pulse as well as an additional component, due to the reflection of the forward lasing pulse from the output window. At much higher pump levels than the threshold, the output/input characteristic curve deviates from the quadratic law. The physical explanations for these experimental results are proposed.

Retinal Microvasculature in Relation to Central Hemodynamics in a Flemish Population.

Arterial stiffness and wave reflection predict cardiovascular mortality and morbidity and are associated with renal microvascular disease. We hypothesized that the retinal microvascular traits might be associated with central hemodynamic properties. In 735 randomly recruited Flemish (mean age, 50.3 years; 47.1% women), we derived central pulse pressure and carotid-femoral pulse wave velocity by applanation tonometry and calculated forward (Pf) and backward (Pb) pulse waves, using an automated pressure-based wave separation algorithm. We measured central retinal arteriolar (CRAE) and venular equivalent and their ratio, using IVAN software (Vasculomatic ala Nicola, version 1.1). Mean values for pulse wave velocity (n=554), Pf and Pb were 7.50 m/s, 32.0 mm Hg, and 21.5 mm Hg, respectively. In multivariable-adjusted analyses, CRAE was 4.62 µm and 1.26 µm smaller (P≤0.034) for a 1-SD increment in central mean arterial pressure (+11.3 mm Hg) and central pulse pressure (+15.2 mm Hg); a 1-SD increment in the augmentation ratio (+7.0%), aortic pulse wave velocity (+1.66 m/s), Pf (+10.0 mm Hg), and Pb (+8.5 mm Hg), was associated with smaller CRAE; the association sizes were -1.91 µm, -1.59 µm, -1.45 µm, and -2.38 µm (P≤0.014), respectively. Associations of arteriole-to-venule diameter ratio with the central hemodynamic traits mirrored those of CRAE. None of the multivariable-adjusted associations of central retinal venular diameter with the central hemodynamic traits reached significance with the exception of central diastolic blood pressure (-1.62 µm; P=0.030). In conclusion, in the general population, higher central pulse pressure, pulse wave velocity, Pf, and Pb were associated with smaller CRAE.