Local Pulse Wave Velocity Measurement Research Articles

Reconstructive interpolation for pulse wave estimation to improve local PWV measurement of carotid artery.

Ultrasonic transit time (TT)-based local pulse wave velocity (PWV) measurement is defined as the distance between two beam positions on a segment of common carotid artery (CCA) divided by the TT in the pulse wave propagation. However, the arterial wall motions (AWMs) estimated from ultrasonic radio frequency (RF) signals with a limited number of frames using the motion tracking are typically discrete. In this work, we develop a method involving motion tracking combined with reconstructive interpolation (MTRI) to reduce the quantification errors in the estimated PWs, and thereby improve the accuracy of the TT-based local PWV measurement for CCA. For each beam position, normalized cross-correlation functions (NCCFs) between the reference (the first frame) and comparison (the remaining frames) RF signals are calculated. Thereafter, the reconstructive interpolation is performed in the neighborhood of the NCCFs' peak to identify the interpolation-deduced peak locations, which are more exact than the original ones. According to which, the improved AWMs are obtained to calculate their TT along a segment of the CCA. Finally, the local PWV is measured by applying a linear regression fit to the time-distance result. In ultrasound simulations based on the pulse wave propagation models of young, middle-aged, and elderly groups, the MTRI method with different numbers of interpolated samples was used to estimate AWMs and local PWVs. Normalized root mean squared errors (NRMSEs) between the estimated and preset values of the AWMs and local PWVs were calculated and compared with ones without interpolation. The means of the NRMSEs for the AWMs and local PWVs based on the MTRI method with one interpolated sample decrease from 1.14% to 0.60% and 7.48% to 4.61%, respectively. Moreover, Bland-Altman analysis and coefficient of variation were used to validate the performance of the MTRI method based on the measured local PWVs of 30 healthy subjects. In conclusion, the reconstructive interpolation for the pulse wave estimation improves the accuracy and repeatability of the carotid local PWV measurement.

Evaluation of early arterial wall lesions by elastography parameters in spontaneously hypertensive rats

BackgroundArterialsclerosis caused by hypertension can lead to many complications, such as heart attack, stroke and so on. Early diagnosis and treatment of arterialsclerosis can prevent cardiovascular and cerebrovascular diseases and improve the prognosis. The present study aimed to explore the value of ultrasonography in evaluating the early lesion of the local arterial wall in hypertensive rats and identify useful elastography parameters.MethodsA total of 24 spontaneously hypertensive rats (SHR), 10-, 20-, 30-, and 40-weeks-old, were used in this study, with 6 rats in each group. Blood pressure was recorded using the Animal Noninvasive Blood Pressure Measurement System (Kent company, model CODA, USA), and the local elasticity of the abdominal aorta of rats was measured using a ultrasound diagnostic instrument (VINNO, Suzhou city, China). According to the histopathological results, SHR were divided into two groups: the normal arterial elasticity and the early arterial wall lesions. Mann–Whitney U test was used to compare the differences in elastic parameters and influencing factors between the above two groups, and receiver operating characteristic curve (ROC) was used to analyze and judge the value of each elastic parameter in evaluating early arterial lesions.ResultsA total of 22 cases were divided into two groups: 14 in the normal arterial elasticity and 8 in the early arterial wall lesions. The differences in age, blood pressure, pulse wave velocity (PWV), compliance coefficient (CC), distensibility coefficient (DC), and elasticity parameter (EP) between the two groups were compared. The differences in PWV, CC, DC and EP were statistically significant. Subsequently, the ROC curve analysis was performed for the above four evaluation indexes of arterial elasticity; the results were as follows: the area under the curve of PWV, CC, DC, and EP was 0.946, 0.781, 0.946, and 0.911, respectively.ConclusionsEarly arterial wall lesions can be evaluated by ultrasound measurement of local PWV. PWV and DC can accurately evaluate the early arterial wall lesions in SHR, and the combined application of the two can improve the sensitivity and specificity of the approach.

Operator Variabilities in Carotid Pulse Wave Velocity Measured by an Image-free Ultrasound Device.

Local pulse wave velocity (PWV) has gained much attention in the last decade due to its ability to provide localized stiffness information from a target vessel and cater to several applications beyond regional PWV. Transit time-based methods are the most straightforward, but their reliability is highly dependent on the blood pulse sensing modality. Conventional ultrasound systems directly measure the blood pulse (as diameter or flow velocity); however, they offer limited frame rates resulting in poor resolution signals. Advanced systems supporting high frame rates are expensive, complex, and not amenable to field and resource-constraint settings. We have developed a high frame image-free ultrasound system to address this gap for automated and online measurement of local PWV. In an earlier in-vitro study, we have demonstrated its accuracy. In this work, we aim to investigate its in-vivo reliability. A study on 15 young, healthy subjects was conducted to assess the intra-and inter-operator repeatability of the developed system. The yielded local PWVs from the left carotid artery were within the range of 2.5 to 5.8 m/s. The device provided highly repeatable intra- and inter-operator measurements with ICC of 0.94 and 0.88, respectively. The bias for the intra- and inter-operator trials was statistically negligible (p > 0.005). The study demonstrated the potential of the high frame rate device to perform reliable measurements in-vivo. Clinical Relevance- This work aims to provide and validate an easy-to-use affordable and fully-automated high frame rate ultrasound technology for the measurement of online local PWV that is currently lacking.

Phantom Assessment of an Image-free Ultrasound Technology for Online Local Pulse Wave Velocity Measurement.

Cardiovascular community has started clinically adopting the assessment of local stiffness, contrary to the traditionally measured carotid-femoral pulse wave velocity (PWV). Though they offer higher reliability, ultrasound methods require advanced hardware and processing methods to perform real-time measurement of local PWV. This work presents a system and method to perform online PWV measurement in an automated manner. It is a fast image-free ultrasound technology that meets the methodological requirements necessary to measure small orders of local pulse transit, from which PWV is measured. The measurement accuracy and repeatability were assessed via phantom experiments, where the measured transit time-based PWV (PWVTT) was compared against the theoretically calculated PWV from Bramwell-Hill equation (PWVBH). The beat-to-beat variability in the measured PWVTT was within 3%. PWVTT values strongly correlated (r=0.98) with PWVBH, yielding a negligible bias of -0.01 m/s, mean error of 3%, and RMSE of 0.27 m/s. These pilot study results demonstrated the presented system's reliability in yielding online local PWV measurements.

First experiences of local pulse wave velocity measurements in 4D-MRI in focally stented femoropopliteal arteries

Background: In peripheral arterial disease (PAD) the femoropopliteal (FP) artery is the most frequently recanalized lower limb artery. Stent-based interventions change the biomechanical properties of FP arteries. However, no clinical tool for functional imaging is established for quantitative measurements in vivo. Four-dimensional-flow magnetic resonance imaging enables a detailed evaluation of the hemodynamics of the central and - more challenging - the peripheral arteries. The present study aimed to determine the feasibility of assessing pulse wave velocities (PWV) as a marker of vessel stiffness in PAD patients with multiple spot stents and to compare the values with age-matched subjects and young-adult healthy subjects. Patients and methods: Contrast-free 4D-flow MRI was performed in seven PAD patients with focally stented FP arteries, five age-matched subjects after exclusion of PAD, and five young, healthy adults. PWV values were calculated from flow curves by using the foot-to-foot method. Results: Four-D-flow MRI sequences offering high spatial and temporal resolution enables quantification of flow velocity measurements and estimation of PWVs. Assessment of segmental PWV as a surrogate of vascular stiffness in focally stented femoral arteries is feasible. PWV values across all groups were 15.6±5.2 m/s, 13.3±4.1 m/s, and 9.9±2.2 m/s in PAD patients, senior-aged volunteers, and young-adult volunteers respectively. PWV values in PAD patients were similar with those in the senior-aged volunteers group (15.6±5.2 vs. 13.3±4.1years, p=0.43). However, when compared to the young-adult volunteers, PAD patients had a statistically significantly higher mean local PWV (15.6±5.2 m/s vs. 9.9±2.2 m/s, p<0.05). Conclusions: Calculating segmental PWV in the femoral arteries is feasible in PAD patients with focally stented FP arteries. PWV values in PAD patients were similar to those in senior-aged volunteers, both of which were higher than in young-adult volunteers.

A Photoplethysmographic Monitor for Local Pulse Wave Velocity Measurement

A Photoplethysmographic Monitor for Local Pulse Wave Velocity Measurement

Measurement of local pulse wave velocity for carotid artery by using an ultrasound-based method

Currently, pulse wave velocity (PWV) is an important physical index for characterizing the mechanical properties of arteries. Carotid-femoral PWV (cfPWV) is a clinically-approved parameter for evaluating the cardiovascular risk and therapeutic efficacy. However, cfPWV only provides global information about vessel properties. Many recent studies have indicated that local PWV measurements provide precise evaluation of artery conditions. Here, an ultrasound (US) method based on a novel vessel displacement waveform correction, is proposed for improving the accuracy of local carotid PWV measurement. A programmable US device and a commercial array transducer were used, which allow a user to excite transducer and receive US signals arbitrarily with different beam settings. The local PWV measurement accuracy was verified using a phantom. The number of US beams used for PWV measurements was also considered, which indicates that eight elements is the acceptable setting. Subsequently, local carotid PWV and cfPWV were measured in 35 healthy human subjects (age: 21.9 ± 2.4 years) by using the US method and SphygmoCor device, respectively. The cfPWV and local carotid PWV were 6.65 ± 0.74 and 4.63 ± 0.57 m/s, respectively. A good linear correlation was observed between the two aforementioned methods (r = 0.8) for the subjects. All the results indicated that when few US beams were used, the proposed method exhibited a reliable measurement of local PWV.

Pulse Wave Analysis and Pulse Wave Velocity for Fistula Assessment

Background/Aims: Pulse wave analysis (PWA) and pulse wave velocity (PWV) provide information about arterial stiffness and elasticity, which is mainly used for cardiovascular risk stratification. In the presented prospective observational pilot study, we examined the hypothesis that radiocephalic fistula (RCF)-related changes of haemodynamics and blood vessel morphology including high as well as low flow can be seen in specific changes of pulse wave (PW) morphology. Methods: Fifty-six patients with RCF underwent local ambilateral peripheral PWA and PWV measurement with the SphygmoCor® device. Given that the output parameters of the SphygmoCor® are not relevant for the study objectives, we defined new suitable parameters for PWA in direct proximity to fistulas and established an appropriate analysing algorithm. Duplex sonography served as reference method. Results: Marked changes of peripheral PW morphology when considering interarm differences of slope and areas between the fistula and non-fistula arms were observed in the Arteria radialis, A. brachialis and arterialized Vena cephalica. The sum of the slope differences was found to correlate with an increased flow, while in patients with fistula failure no changes in PW morphology were seen. Moreover, PWV was significantly reduced in the fistula arm. Conclusion: Beside duplex sonography, ambilateral peripheral PWA and PWV measurements are potential new clinical applications to characterize and monitor RCF function, especially in terms of high and low flow.

Local Pulse Wave Velocity: Theory, Methods, Advancements, and Clinical Applications.

Local pulse wave velocity (PWV) is evolving as one of the important determinants of arterial hemodynamics, localized vessel stiffening associated with several pathologies, and a host of other cardiovascular events. Although PWV was introduced over a century ago, only in recent decades, due to various technological advancements, has emphasis been directed toward its measurement from a single arterial section or from piecewise segments of a target arterial section. This emerging worldwide trend in the exploration of instrumental solutions for local PWV measurement has produced several invasive and noninvasive methods. As of yet, however, a univocal opinion on the ideal measurement method has not emerged. Neither have there been extensive comparative studies on the accuracy of the available methods. Recognizing this reality, makes apparent the need to establish guideline-recommended standards for the measurement methods and reference values, without which clinical application cannot be pursued. This paper enumerates all major local PWV measurement methods while pinpointing their salient methodological considerations and emphasizing the necessity of global standardization. Further, a summary of the advancements in measuring modalities and clinical applications is provided. Additionally, a detailed discussion on the minimally explored concept of incremental local PWV is presented along with suggestions of future research questions.

Accelerometric patch probe for cuffless blood pressure evaluation from carotid local pulse wave velocity: design, development, and in vivo experimental study

Objective: In this work, we demonstrate an accelerometric patch probe and associated measurement system for local pulse wave velocity (PWV) measurement and its application in cuffless blood pressure (BP) measurement. Approach: The proposed system consists of dual accelerometric patch probe to capture acceleration plethysmography (APG) signals from the carotid artery. The probe was integrated to an application-specific analog front-end circuitry with negligible inter-channel delay and a data acquisition module. Real-time signal processing and local PWV evaluation were performed using custom software. The functionality of the developed system and the relationship between local PWV and reference BP parameters were experimentally validated by multiple in vivo studies on a cohort of 26 subjects. Inter- and intra-subject BP-local pulse transit time (PTT) models were developed and used for cuffless BP measurement. Further, the reliability of the proposed method in long-term BP monitoring was validated by performing a study over a week. Main results: Reliability of the proposed novel approach for local PWV measurement using APG signals has been demonstrated. Measured baseline carotid local PWV values were in the range of 3–4.2 m s−1, with high reproducibility (R = 0.94) and with an inter-beat variation range of 2.61%–15.5%. Mean local PTT versus brachial systolic, diastolic, and mean arterial BP obtained from both sitting and standing posture correlated well with an R-value > 0.8. Beat-by-beat BP parameters and local PWV during the post-exercise recovery of each individual yielded statistically significant intra-subject trends. Cuffless BP estimation with intra-subject BP-local PTT models results in more reliable assessments of BP parameters than inter-subject models. The developed BP prediction models found to be reliable over a period of one week with a root-mean-square error ≤1.7 mmHg. Significance: A non-invasive cost-effective system for continuous monitoring central aortic BP parameters and local arterial stiffness indices.

In Vitro Validation of 4D Flow MRI for Local Pulse Wave Velocity Estimation.

Arterial stiffness has predictive value for cardiovascular disease (CVD). Local artery stiffness can provide insight on CVD pathology and may be useful for diagnosis and prognosis. However, current methods are invasive, require real-time expertise for measurement, or are limited by arterial region. 4D Flow MRI can non-invasively measure local stiffness by estimating local pulse wave velocity (PWV). This technique can be applied to vascular regions, previously accessible only by invasive stiffness measurement methods. MRI PWV data can also be analyzed post-exam. However, 4D Flow MRI requires validation before it is used in vivo to measure local PWV. PWV, calculated from 4D Flow MRI and a benchtop experiment, was compared with petersons elastic modulus (PEM) of in vitro models. PEM was calculated using high-speed camera images and pressure transducers. Three transit-time algorithms were analyzed for PWV measurement accuracy and precision. PWV from 4D Flow MRI and reference benchtop experiments show strong correlation with PEM (R2 = 0.99). The cross correlation transit-time algorithm showed the lowest percent difference between 4D Flow MRI and benchtop experiments (4-7%), and the point to point of 50% upstroke algorithm had the highest transit-time vs. distance data average R2 (0.845). 4D Flow MRI is a feasible method for estimating local PWV in simple in vitro models and is a viable tool for clinical analysis. In addition, choice in transit-time algorithm depends on flow waveform shape and arterial region. This study strengthens the validity of 4D Flow MRI local PWV measurement in simple models. However, this technique requires validation in more complex models before it is used in vivo.

Can pulse wave velocity be measured in the fetal ascending aorta?

BackgroundRoutine ultrasound exams are conducted to assess fetus development. Heart defects and cardiac function are the main areas investigated in an ultrasound assessment. However, prenatal assessment of the fetal arterial stiffness is yet to be established in the ascending aorta.AimTo investigate whether pulse wave velocity (PWV) can be determined in the fetus ascending aorta using ultrasound examination.Methods35 fetuses (19 normal, 16 growth restricted) were included in the study. High quality recordings were achieved in 6 normal and 8 fetuses diagnosed with fetal growth restriction (FGR). Images of the diameter and blood velocity in the ascending aorta were recorded (Voluson, GE and Samsung) with a curvilinear probe 2–8MHz/1–7MHz. The diameter and velocity waveforms were extracted from DICOM images, offline, using in-house developed codes in Matlab. The extraction was based on thresholding of the grey-scale images. Local PWV was determined using the ln(D) U-loop method [1].ResultsPWV in the fetal ascending aorta increased with gestational age in both normal (r2 = 0.77) and FGR (r2 = 0.55) fetuses. Mean PWV in the fetal ascending aorta per gestational week was 0.045m/s in normal and 0.066m/s in FGR fetuses, with a percentage difference of 32%.Figure 1PWV vs gestational age in weeks for normal (blue diamond ♦) and FGR (red squares ■) fetuses and the trendlines with equations describing them and their r2 values. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)ConclusionsDespite the challenging ultrasound images of the fetal ascending aorta, local PWV measurement has proven to be possible through recordings of diameter and blood velocity. PWV increases with gestational age and it is higher in FGR than normal fetuses. Further studies are needed to determine the potential clinical predictive value of fetus PWV.

Single-source PPG-based local pulse wave velocity measurement: a potential cuffless blood pressure estimation technique

Objective: A novel photoplethysmograph probe employing dual photodiodes excited using a single infrared light source was developed for local pulse wave velocity (PWV) measurement. The potential use of the proposed system in cuffless blood pressure (BP) techniques was demonstrated. Approach: Initial validation measurements were performed on a phantom using a reference method. Further, an in vivo study was carried out in 35 volunteers (age  =  28  ±  4.5 years). The carotid local PWV, carotid to finger pulse transit time (PTTR) and pulse arrival time at the carotid artery (PATC) were simultaneously measured. Beat-by-beat variation of the local PWV due to BP changes was studied during post-exercise relaxation. The cuffless BP estimation accuracy of local PWV, PATC, and PTTR was investigated based on inter- and intra-subject models with best-case calibration. Main results: The accuracy of the proposed system, hardware inter-channel delay (<0.1 ms), repeatability (beat-to-beat variation  =  4.15%–11.38%) and reproducibility of measurement (r  =  0.96) were examined. For the phantom experiment, the measured PWV values did not differ by more than 0.74 m s−1 compared to the reference PWV. Better correlation was observed between brachial BP parameters versus local PWV (r  =  0.74–0.78) compared to PTTR (|r|  =  0.62–0.67) and PATC (|r|  =  0.52–0.68). Cuffless BP estimation using local PWV was better than PTTR and PATC with population-specific models. More accurate estimates of arterial BP levels were achieved using local PWV via subject-specific models (root-mean-square error  ⩽2.61 mmHg). Significance: A reliable system for cuffless BP measurement and local estimation of arterial wall properties.

Design and Functional Testing of a Novel Blood Pulse Wave Velocity Sensor

The multiphotodiode array (MPA) is a novel transmission photoplethysmography (PPG) sensor to measure pulse wave velocity (PWV) in the finger. To validate the MPA, a setup was built to generate a red laser dot traveling over the MPA with known and constant scanning velocities. These scanning velocities were chosen to include speeds at least twice as high as those found in the normal range of PWV in healthy populations and were set at 12.9, 25.8, 36, or 46.7 m/s. The aim of this study was to verify the functionality of the MPA: performing local noninvasive PWV measurements. To illustrate the applicability of the MPA in clinical practice, an in vivo pilot study was conducted using the flow-mediated dilation (FMD) technique. The in vitro accuracy of the MPA was ±0.2%, 0.3%, 0.5%, and 0.6% at the applied scanning velocities. The MPA can measure PWVs with a maximum deviation of 3.0%. The in vivo pilot study showed a PWV before the FMD of 1.1±0.2 m/s. These results suggest that this novel MPA can reliably and accurately measure PWV within clinically relevant ranges and even well beyond.

A Magnetic Plethysmograph Probe for Local Pulse Wave Velocity Measurement.

We present the design and experimental validation of an arterial compliance probe with dual magnetic plethysmograph (MPG) transducers for local pulse wave velocity (PWV) measurement. The MPG transducers (positioned at 23 mm distance apart) utilizes Hall-effect sensors and permanent magnets for arterial blood pulse detection. The MPG probe was initially validated on an arterial flow phantom using a reference method. Further, 20 normotensive subjects (14 males, age = 24 ± 3.5 years) were studied under two different physical conditions: 1) Physically relaxed condition, 2) Postexercise condition. Local PWV was measured from the left carotid artery using the MPG probe. Brachial blood pressure (BP) was measured to investigate the correlation of BP with local PWV. The proposed MPG arterial compliance probe was capable of detecting high-fidelity blood pulse waveforms. Reliable local pulse transit time estimates were assessed by the developed measurement system. Beat-by-beat local PWV was measured from multiple subjects under different physical conditions. A profound increment was observed in the carotid local PWV for all subjects after exercise (average increment = 0.42 ± 0.22 m/s). Local PWV values and brachial BP parameters were significantly correlated (r ≥ 0.72), except for pulse pressure (r = 0.42). MPG arterial compliance probe for local PWV measurement was validated. Carotid local PWV measurement, its variations due to physical exercise and correlation with BP levels were examined during the in vivo study. A novel dual MPG probe for local PWV measurement and potential use in cuffless BP measurement.

Local versus global aortic pulse wave velocity in early atherosclerosis: An animal study in ApoE-/--mice using ultrahigh field MRI.

Increased aortic stiffness is known to be associated with atherosclerosis and has a predictive value for cardiovascular events. This study aims to investigate the local distribution of early arterial stiffening due to initial atherosclerotic lesions. Therefore, global and local pulse wave velocity (PWV) were measured in ApoE-/- and wild type (WT) mice using ultrahigh field MRI. For quantification of global aortic stiffness, a new multi-point transit-time (TT) method was implemented and validated to determine the global PWV in the murine aorta. Local aortic stiffness was measured by assessing the local PWV in the upper abdominal aorta, using the flow/area (QA) method. Significant differences between age matched ApoE-/- and WT mice were determined for global and local PWV measurements (global PWV: ApoE-/-: 2.7±0.2m/s vs WT: 2.1±0.2m/s, P<0.03; local PWV: ApoE-/-: 2.9±0.2m/s vs WT: 2.2±0.2m/s, P<0.03). Within the WT mouse group, the global PWV correlated well with the local PWV in the upper abdominal aorta (R2 = 0.75, P<0.01), implying a widely uniform arterial elasticity. In ApoE-/- animals, however, no significant correlation between individual local and global PWV was present (R2 = 0.07, P = 0.53), implying a heterogeneous distribution of vascular stiffening in early atherosclerosis. The assessment of global PWV using the new multi-point TT measurement technique was validated against a pressure wire measurement in a vessel phantom and showed excellent agreement. The experimental results demonstrate that vascular stiffening caused by early atherosclerosis is unequally distributed over the length of large vessels. This finding implies that assessing heterogeneity of arterial stiffness by multiple local measurements of PWV might be more sensitive than global PWV to identify early atherosclerotic lesions.

Single source photoplethysmograph transducer for local pulse wave velocity measurement.

Cuffless evaluation of arterial blood pressure (BP) using pulse wave velocity (PWV) has received attraction over the years. Local PWV based techniques for cuffless BP measurement has more potential in accurate estimation of BP parameters. In this work, we present the design and experimental validation of a novel single-source Photoplethysmograph (PPG) transducer for arterial blood pulse detection and cycle-to-cycle local PWV measurement. The ability of the transducer to continuously measure local PWV was verified using arterial flow phantom as well as by conducting an in-vivo study on 17 volunteers. The single-source PPG transducer could reliably acquire dual blood pulse waveforms, along small artery sections of length less than 28 mm. The transducer was able to perform repeatable measurements of carotid local PWV on multiple subjects with maximum beat-to-beat variation less than 12%. The correlation between measured carotid local PWV and brachial BP parameters were also investigated during the in-vivo study. Study results prove the potential use of newly proposed single-source PPG transducers in continuous cuffless BP measurement systems.

Comparison of Different Pulse Waveforms for Local Pulse Wave Velocity Measurement in Healthy and Hypertensive Common Carotid Arteries in Vivo

Pulse wave velocity (PWV), a measurement of arterial stiffness, can be estimated locally by determining the time delay of the pulse waveforms for a known distance as measured in an ultrasound image. Our aim was to compare three ultrasound-based methods for estimation of local PWV based on the measurement of diameter distension waveforms, displacement waveforms of the anterior wall and displacement waveforms of the posterior wall, respectively, in human common carotid arteries in vivo. The local PWVs at both systolic foot (PWVsf) and dicrotic notch (PWVdn) were estimated from ultrasound radiofrequency data of 25 healthy and 24 hypertensive patients for each method. PWV estimation using the distension waveform method was found to have the highest precision in both groups. Both PWVsf and PWVdn were significantly higher in the hypertensive group compared with the healthy group using the distension waveform method (PWVsf: 6.08 ± 1.70 m/s vs. 4.75 ± 0.92 m/s, p = 0.000014; PWVdn: 7.83 ± 2.26 m/s vs. 5.21 ± 0.95 m/s, p < 0.000001), whereas there was no significant difference at a significance level of 0.01 between the two groups when the anterior or posterior wall waveform method was used. Thus, the difference in arterial stiffness between the two groups could be discriminated well by the distension waveform method. The local PWV estimated using distension waveforms might be a promising index for arterial stiffness characterization and hypertension management.

The impact of age and risk factors on carotid and carotid-femoral pulse wave velocity.

Segmental carotid-femoral pulse-wave velocity (PWV) is a gold standard method for arterial stiffness assessment; recently, a local carotid PWV measurement by ultrasound has been developed. The present study compared the impact of age and established risk factors on carotid and carotid-femoral PWV. Three hundred and seven volunteers (167 men; age from 15 to 78 years) free of cardiovascular disease, diabetes, antihypertensive and lipid-lowering treatment underwent sequential measurement of carotid and carotid-femoral PWV. In the entire study population, both carotid and carotid-femoral PWV were independently associated mainly with age and blood pressure. In individuals more than 50 years old (N = 132, 80 men), carotid-femoral PWV, but not carotid PWV, was also associated with high-density lipoprotein (HDL)-cholesterol and fasting glucose. The annual increase in carotid and carotid-femoral PWV was similar (0.087 ± 0.004 and 0.090 ± 0.005  m/s, respectively; P = 0.69). Carotid PWV increased with age more rapidly in women than in men (0.099 ± 0.005 vs. 0.076 ± 0.005  m/s per year, P < 0.005), whereas carotid-femoral PWV showed a steeper increase in individuals more than 50 years old than individuals aged 50 years or less (0.150 ± 0.019 vs. 0.088 ± 0.007  m/s per year, P = 0.001). In apparently healthy population, both carotid and carotid-femoral PWV were influenced above all by age and blood pressure. Other established cardiovascular risk factors had a limited impact only on carotid-femoral PWV of older individuals. The age-related increase in carotid and carotid-femoral PWV seemed to follow different patterns; increase in carotid PWV showed age-sex interaction, being steeper in women, whereas increase in carotid-femoral PWV was more prominent in older individuals.

Effects of parameters on the accuracy and precision of ultrasound-based local pulse wave velocity measurement: a simulation study.

Quantification of arterial stiffness, such as pulse wave velocity (PWV), is increasingly used in the risk assessment of cardiovascular disease. Pulse wave imaging (PWI) is an emerging ultrasound-based technique to noninvasively measure the local PWV instead of the global PWV, as in conventional methods. In PWI, several key parameters, including the frame rate of ultrasound imaging, motion estimation rate (MER), number of scan lines, image width, PWV value, and sonographic signal-to-noise ratio (SNRs), play an important but still unclear role in the accuracy and precision of PWV measurement. In this study, computer simulations were performed to investigate the fundamental effects of these parameters on the PWV measurement. The pulse waveform was estimated by speckle tracking on ultrasound RF signals acquired at a frame rate of 2083 Hz from a location on the common carotid artery of a healthy subject. By applying different time delays on the estimated waveform based on specific PWI parameters, the pulse waveforms at others locations were simulated. Ultrasound RF signals of the artery during the pulse wave propagation were generated from a 2-D convolutional image formation model. The PWI technique was applied to estimate the PWV at different values of frame rate, MER, number of scan lines, image width, PWV, and SNRs. The performance of the PWV estimation was evaluated by measuring the relative error, coefficient of variation (CV) and coefficient of determination (R(2)). The results showed that PWVs could be correctly measured when the frame rate was higher than a certain value (i.e., minimum frame rate), below which the estimated error increased rapidly. The minimum frame rate required for PWV estimation was found to increase with the value of PWV. An optimal MER was found (i.e., about 200 Hz) and allowed better performance of PWV measurement. The CV of PWV estimation decreased and R(2) increased with number of scan lines and image width, indicating that the performance of the PWV estimation could be improved with a larger number of scan lines and image width. For a given sufficiently high frame rate, a higher PWV value was found to deteriorate the PWV estimation, as indicated by an increasing CV and decreasing R(2). The simulation results were in good agreement with the theoretical analysis. Finally, high-quality PWV estimation could be obtained as long as the SNRs was higher than about 30 dB. The quantitative effects of the key parameters obtained from this study might provide important guidelines for parameter optimization in ultrasound-based local PWV measurement in vivo.