Pulse Wave Velocity Calculation Research Articles

An algorithm to detect dicrotic notch in arterial blood pressure and photoplethysmography waveforms using the iterative envelope mean method

Background and objectiveDetection of the dicrotic notch (DN) within a cardiac cycle is essential for assessment of cardiac output, calculation of pulse wave velocity, estimation of left ventricular ejection time, and supporting feature-based machine learning models for noninvasive blood pressure estimation, and hypotension, or hypertension prediction. In this study, we present a new algorithm based on the iterative envelope mean (IEM) method to detect automatically the DN in arterial blood pressure (ABP) and photoplethysmography (PPG) waveforms. MethodsThe algorithm was evaluated on both ABP and PPG waveforms from a large perioperative dataset (MLORD dataset) comprising 17,327 patients. The analysis involved a total of 1,171,288 cardiac cycles for ABP waveforms and 3,424,975 cardiac cycles for PPG waveforms. To evaluate the algorithm's performance, the systolic phase duration (SPD) was employed, which represents the duration from the onset of the systolic phase to the DN in the cardiac cycle. Correlation plots and regression analysis were used to compare the algorithm against marked DN detection, while box plots and Bland-Altman plots were used to compare its performance with both marked DN detection and an established DN detection technique (second derivative). The marking of the DN temporal location was carried out by an experienced researcher using the help of the 'find_peaks' function from the scipy Python package, serving as a reference for the evaluation. The marking was visually validated by both an engineer and an anesthesiologist. The robustness of the algorithm was evaluated as the DN was made less visually distinct across signal-to-noise ratios (SNRs) ranging from -30 dB to -5 dB in both ABP and PPG waveforms. ResultsThe correlation between SPD estimated by the algorithm and that marked by the researcher is strong for both ABP (R2(87,343) =0.99, p<.001) and PPG (R2(86,764) =0.98, p<.001) waveforms. The algorithm had a lower mean error of DN detection (s): 0.0047 (0.0029) for ABP waveforms and 0.0046 (0.0029) for PPG waveforms, compared to 0.0693 (0.0770) for ABP and 0.0968 (0.0909) for PPG waveforms for the established 2nd derivative method. The algorithm has high rate of detectability of DN detection for SNR of >= -9 dB for ABP waveforms and >= -12 dB for PPG waveforms indicating robust performance in detecting the DN when it is less visibly distinct. ConclusionOur proposed IEM- based algorithm can detect DN in both ABP and PPG waveforms with low computational cost, even in cases where it is not distinctly defined within a cardiac cycle of the waveform (‘DN-less signals’). The algorithm can potentially serve as a valuable, fast, and reliable tool for extracting features from ABP and PPG waveforms. It can be especially beneficial in medical applications where DN-based features, such as SPD, diastolic phase duration, and DN amplitude, play a significant role.

Use of phase-contrast MRI to measure aortic stiffness in young-onset hypertension: a pilot study.

Young-onset hypertension is defined as hypertension diagnosed before the age of 40 years. Aortic pulse wave velocity is an indication of aortic stiffness. MRI assessment has been well verified compared to invasive pressure recordings for evaluating aortic pulse wave velocity. In this study, we aimed to determine whether aortic stiffness played a role in the aetiology of young-onset hypertension by calculating pulse wave velocity using MRI. We enrolled 20 patients diagnosed with young-onset hypertension and 20 volunteers without hypertension. Aortic pulse wave velocity was measured by cardiac MRI and protocol for the pulse wave velocity measurement involved the use of a 1.5 T scanner to acquire velocity-encoded, phase-contrast transverse aortic cine images. Sagittal oblique images used to measure the distance (ΔX) between the ascending aorta and descending aorta for the calculation of pulse wave velocity. The aortic flow versus time curves of ascending aorta and descending aorta were automatically obtained from the phase-contrast MRI images. Using these curves, the temporal shift (ΔT) was measured by Segment Medviso. The mean pulse wave velocity was 8.72 (SD 2.34) m/second (range: 7-12.8 m/second) for the patient group and 5.96 (standard deviation 1.86) m/second (range: 4.8-7.1 m/second) for the control group. The pulse wave velocity values were significantly higher in the patient group compared to the control group (p < 0.001). Aortic stiffness may play a role in the aetiology of young-onset hypertension and serve as a non-invasive and reliable screening tool when measured by MRI.

Evaluation of pulse wave velocity for predicting major advanced cardiovascular events in patients with chronic myocardial infarction

Abstract Introduction Increased aortic pulse wave velocity (PWV) as a strong predictor of major advanced cardiovascular events (MACE) has a prognostic relevance in patients after myocardial infarction (MI). Several non-invasive methods have been proposed for the assessment of arterial stiffness, but the PWV values show significant differences according to the applied techniques. Cardiac magnetic resonance imaging (CMR) provides an accurate method to measure PWV and infarct size in patients after MI. Purpose Calculated PWV values of CMR based phase-contrast (PC) and invasively validated oscillometric methods were compared in this prospective observational study. We aimed to evaluate the cut-off PWV values for each method, while MACE predicted and validated the prognostic value of high PWV in post-infarcted patients in a 6-year follow-up. Methods 3D aortic angiography and PC velocity imaging was performed using a Siemens Avanto 1,5 T CMR device. Oscillometric based Arteriograph (AG) was used to assess PWV using direct body surface distance measurements. The comparison between the two techniques was tested. Patients received follow-up for MACE comprising all-cause death, non-fatal MI, ischemic stroke, hospitalization for heart failure and coronary revascularization. Event-free survival was analysed using Kaplan-Meier plots and log-rank tests. Univariable and multivariable Cox regression analysis was performed to identify outcome predictors. Results 75 patients (56 male, 19 female, average age: 56±13 years) referred for CMR were investigated, of whom 50 had coronary artery disease (CAD) including 35 patients with previous MI developing ischaemic late gadolinium enhancement (LGE) pattern. AG and CMR derived PWV values were significantly correlated (rho: 0,343, p&amp;lt;0,05), however absolute PWV values were significantly higher for AG (median (IQR): 10,4 (9,2–11,9) vs. 6,44 (5,64–7,5); p&amp;lt;0,001). Bland Altman analysis showed an acceptable agreement with a mean difference of 3,7 m/s between the two measures. In patients with CAD significantly (p&amp;lt;0,01) higher PWV values were measured by AG and CMR, respectively. During the median follow-up of 6 years, totally 69 MACE events occurred. Optimized PWV cut-off values for MACE prediction were calculated (CMR: 6,47 m/s; AG: 9,625 m/s) by receiver operating characteristic analysis. Kaplan-Meier analysis in both methods showed a significantly lower event-free survival in case of high PWV (p&amp;lt;0,01, respectively). Cox regression analysis revealed PWV for both methods as a predictor of MACE (PWV CMR hazard ratio (HR): 2,6 (confidence interval (CI) 1,3–5,1), PWV AG HR: 3,1 (CI: 1,3–7,1), p&amp;lt;0,005, respectively). Conclusions Our study showed good agreement between the AG and CMR methods for PWV calculation. Both techniques are feasible for MACE prediction in postinfarcted patients. However, different AG and CMR PWV cut-off values were calculated to improve risk stratification. Funding Acknowledgement Type of funding sources: None. Agreement between the two methodsKaplan-Meier event curves for MACE

Accurate arterial path length estimation for pulse wave velocity calculation in growing children and adolescents

Background: Most adult cardiovascular disease begins in childhood. Given the burgeoning obesity pandemic in children worldwide, there is a need for precise and scalable surveillance methods to detect subclinical cardiovascular disease in children and adolescents. Early detection allows early intervention and intensified primary prevention strategies in affected individuals. Carotid-femoral pulse wave velocity (PWV) directly measures arterial wall stiffness, an early feature of atherosclerosis. Calculation of PWV in growing children requires an accurate estimation of the true distance travelled by the aorto-femoral pressure wave, using surface anatomy landmarks. However, a variety of methods are used to estimate this distance, and these have not previously been investigated in growing children and adolescents. We sought to investigate this by comparing true arterial path length measured on computerized tomography (CT) scans, with a variety of estimations based on surface anatomy landmarks. Methods: Arterial path lengths were measured using multi-planar reformation (MPR) imaging software. These measurements were then compared with the surface anatomy measurements obtained using the same MPR imaging software. The fidelity of a variety of arterial path length estimation methods was tested. Results: The surface anatomy distance between the suprasternal notch and the angle of the mandible (PWV recording site in the neck), should be adjusted using the formula y=4.791+(1.0534*x). This value subtracted from the unadjusted distance from the suprasternal notch to the umbilicus, through the mid-inguinal crease to the femoral PWV recording site, provides the simplest reliable approximation of true intraluminal distance travelled. Conclusions: There is high correlation between the surface anatomy distances and the arterial path lengths they represent; however, these are not equal. Most surface anatomy measurements require adjustment using the formulae that we have provided, to accurately estimate the true distance travelled by the pulse wave.

ARTERIAL STIFFNESS AND ITS CORRELATION WITH LABORATORY PARAMETERS AND INDICATORS OF OBESITY IN DIABETIC HYPERTENSIVE PATIENTS

Objective: Arterial stiffness can be assessed by a variety of non-invasive methods. One of the measures of arterial stiffness that has been used in clinic for some time now is pulse wave velocity (PWV). PWV can be measured with “Agedio B900” device which, in addition to measuring arterial pressure, gives information about arterial stiffness and cardiovascular age. The aim of this study was to evaluate correlations of PWV with age, laboratory parameters and indicators of obesity in Dalmatian diabetic hypertensive patients. Design and method: 106 hypertensive diabetic patients, 66 (62.3 %) men and 40 (37.7%) women, aged 69.5 (range 36-94) years were included. For each patient data about age, gender, body weight and height were collected and BMI (body mass index), WC (waist circumference) and MUAC (mid-upper circumference) were calculated. Also, values of laboratory parameters such as haemoglobin (Hg), urea, creatinine, urate, albuminuria, cholesterol and triglycerides were taken for each patient. The Agedio B900 device was used for the measurement of arterial pressure and PWV calculation. Each study subject was measured with Tanita MC780 Multi Frequency segmental body composition analyser to record whole body and segmental measurements of body composition. Results: PWV was significantly higher in patients over 65 years old than those younger than 65. Among the laboratory parameters statistically significant correlation was found only between PWV and Hg (Rho= -0.365, p = 0.02). Among the indicators of obesity, only MUAC showed significant correlation (Rho = -0.316, p = 0.01). However, statistical significance was reached after making adjustments for age, eGFR, urea, creatinine and albuminuria. All of the variables of body composition affected PWV (p &lt; 0.001, R2 = 0.28) but BMI (p &lt; 0.001), fat mass (p &lt; 0.001) and muscle mass (MM) of the trunk (p &lt; 0.001) and skeletal MM to body fat ratio (p &lt; 0.001) stood out. Conclusions: PWV was correlated to all the variables of body composition after making adjustments for age and markers of kidney function. Future studies with larger number of participants should evaluate correlation of PWV with the observed parameters in this population of patients.

Acute salt loading and cardiotonic steroids in resistant hypertension.

The study addresses the association of marinobufagenin (MBG), a natriuretic and vasoconstrictor steroid, and Na/K-ATPase (NKA) activity with pressor response to salt-loading and arterial stiffness in resistant hypertension (RH). Thirty-four patients (18 males and 16 females; 56±8 years) with RH on a combined (lisnopril/amlodipine/hydrochlorothiazide) therapy and 11 healthy age-matched normotensive subjects (7 males and 4 females; 54±2 years) were enrolled in this study. Salt-loading was performed via intravenous infusion of 1000mL saline (0.9% NaCl) for 1h. Arterial stiffness was measured by Sphygmocor Px device with a calculation of pulse-wave velocity (PWV). Activity of NKA was measured in erythrocytes. We demonstrated that plasma levels of MBG and magnitude of NaCl-induced MBG-dependent NKA inhibition are associated with PWV, and that this association has gender- and age-specific fashion in RH patients.

Discrepancy between in-vivo measure and ex-vivo calculation of pulse wave velocity in retinal arteries

BackgroundPulse wave velocity (PWV) in large arteries is a pressure-dependent marker of arterial stiffness. The retinal vasculature provides unique access to the microcirculation. There is inconsistency between reported values of retinal PWV (rPWV). The pressure dependency of rPWV was measured in-vivo and calculated ex-vivo using retinal artery material properties to investigate the inconsistencies.MethodsHigh-speed fundus videos (125 fps) from three Sprague Dawley rats were recorded simultaneously with electrocardiogram and blood pressure. rPWV was measured using the cardiac component of retinal artery diameter waveforms at two retinal sites across a physiological range (70–130 mmHg) of mean arterial pressure (MAP). Ex-vivo tensile testing was performed on bovine retinal arteries, rat retinal arteries being too small for myography. Diameter and wall thickness of the retinal artery adjacent to the optic disc were measured using optical coherence tomography. Tensile testing was performed using a wire myograph in 9 bovine retinal artery specimens.ResultsIn-vivo results showed a significant positive correlation between rPWV (4.9 ±1.8 mm/s) and MAP (R2 = 0.58, p < 0.001) as expected. Ex-vivo, calculated rPWV using material stiffness and geometry measurement ranged between 4.6 and 7.0 m/s at effective distending pressures between 70 and 100 mmHg.ConclusionsEx-vivo and in-vivo results differed by three orders of magnitude but should be the same. Ex-vivo results are in the same order as measured in-vivo in large arteries. In-vivo rPWV was lower than expected yet was responsive to changes in MAP. Further studies are required to uncover what rPWV is a measurement of, if not arterial stiffness.

3D aortic morphology and stiffness in MRI using semi-automated cylindrical active surface provides optimized description of the vascular effects of aging and hypertension

BackgroundClinically, aortic geometry assessment is mainly based on the measurement of maximal diameters at different anatomic locations, which are subsequently used to indicate prophylactic aortic surgery. However, 3D evaluation of aortic morphology could provide volumetric quantification, which integrates both aortic dilatation and elongation and might thus be more sensitive to early geometric changes than diameters. Precise aortic morphology is also required for the calculation of pulse wave velocity (PWVMRI), an established marker of aortic stiffness. Accordingly, we proposed a 3D semi-automated analysis of thoracic aorta MRI data optimizing morphological and subsequent stiffness assessment. MethodsWe studied 74 individuals (40 males, 50 ± 12years): 21 healthy volunteers and 53 patients with hypertension in whom aortic 3D MRI angiography and 2D + t phase-contrast and cine imaging were performed. A semi-automated method was proposed for volumetric aortic segmentation and was evaluated by studying resulting measurements (length, diameters, volumes and PWVMRI) in terms of: 1) reproducibility, 2) correlations with well-established 2D aortic length and diameters, 3) associations with age, carotid-femoral PWV (cf-PWV) and presence of hypertension. ResultsThe measurements obtained with the proposed method were reproducible (coefficients of variation ≤ 5.1%) and were highly correlated with 2D measurements (arch length: r = 0.80, Bland-Altman mean bias [limits]: 2.7 mm [-25; 30]; PWVMRI: r = 0.95, 0.22 m/s [-1.9; 2.4]). Higher or similar correlations with age were found for the proposed 3D method compared to the 2D approach (arch length: r = 0.47 (2D), r = 0.60 (3D); PWVMRI: r = 0.63 (2D), r = 0.64 (3D)). Moreover, a significant association was found between PWVMRI and cf-PWV (r = 0.49, p < 0.001). All aortic measurements increased with hypertension (p < 0.05) and with age: arch length (+9mm/decade); diameters: ascending (+1.2mm/decade) and descending aorta (+1.0mm/decade); volumes: ascending (+2.6mL/decade) and descending aorta (+4.0mL/decade); PWVMRI (+1.7 m s−1/decade). ConclusionsA semi-automated method based on cylindrical active surfaces was proposed for the 3D segmentation of the aorta using a single MRI dataset, providing aortic diameters at anatomical landmarks, aortic volumes and the aortic centerline length used for PWV estimation. Such measurements were reproducible and comparable to expert measurements, which required time-consuming centerline delineation. Furthermore, expected relationships with age and hypertension were found indicating the consistency of our measurements.

To Estimate Pulmonary Arterial Compliance and Pulse Wave Velocity in Cerebral-Cardiovascular Patients Using CT Cardiac Images

Arterial stiffness has been proven to be one of the most promising diagnostic and prognostic features of many cardiovascular diseases (CVD). Arterial compliance (AC) and pulse wave velocity (PWV) allows a good quantitative assessment of arterial stiffness. To estimate pulmonary Arterial Compliance and Pulse Wave Velocity in Cerebral-Cardiovascular Patients using 64-Row Multi-Detector Computed Tomography Cardiac Images. Here in this work, we have used an in house developed three-dimensional reconstruction algorithm that extracts high-resolution cardiac Computer Tomography images in Digital Imaging and Communications in Medicine (DICOM) format from nine subjects. The subjects consist four patients with stroke (SR) turned to atrial fibrillation (AF) and five patients with both SR and AF. The calculation showed strok volume of Left and Right Ventricles, which are near equal to 62.56±12.61 ml and 65.95±13.13 ml, respectively, with a good positive correlation (R = 0.717, p < 0.0001) while pulse wave velocity and arterial compliance are calculated to be 0.21±0.0665 m/s and 0.09 ± 0.0547 ml/mmHg for patients with SR turned AF, 0.15±0.0502 m/s and 0.10 ± 0.0438 for the SR and AF patients. We concluded that the derived methodology for calculation of PWV and AC from 3D cardiac CT images could be used as an index in the evaluation of arterial stiffness.

Aortic length measurements for pulse wave velocity calculation: manual 2D vs automated 3D centreline extraction

BackgroundPulse wave velocity (PWV) is a biomarker for the intrinsic stiffness of the aortic wall, and has been shown to be predictive for cardiovascular events. It can be assessed using cardiovascular magnetic resonance (CMR) from the delay between phase-contrast flow waveforms at two or more locations in the aorta, and the distance on CMR images between those locations. This study aimed to investigate the impact of different distance measurement methods on PWV. We present and evaluate an algorithm for automated centreline tracking in 3D images, and compare PWV calculations using distances derived from 3D images to those obtained from a conventional 2D oblique-sagittal image of the aorta.MethodsWe included 35 patients from a twin cohort, and 20 post-coarctation repair patients. Phase-contrast flow was acquired in the ascending, descending and diaphragmatic aorta. A 3D centreline tracking algorithm is presented and evaluated on a subset of 30 subjects, on three CMR sequences: balanced steady-state free precession (SSFP), black-blood double inversion recovery turbo spin echo, and contrast-enhanced CMR angiography. Aortic lengths are subsequently compared between measurements from a 2D oblique-sagittal plane, and a 3D geometry.ResultsThe error in length of automated 3D centreline tracking compared with manual annotations ranged from 2.4 [1.8-4.3] mm (mean [IQR], black-blood) to 6.4 [4.7-8.9] mm (SSFP). The impact on PWV was below 0.5m/s (<5%). Differences between 2D and 3D centreline length were significant for the majority of our experiments (p < 0.05). Individual differences in PWV were larger than 0.5m/s in 15% of all cases (thoracic aorta) and 37% when studying the aortic arch only. Finally, the difference between end-diastolic and end-systolic 2D centreline lengths was statistically significant (p < 0.01), but resulted in small differences in PWV (0.08 [0.04 - 0.10]m/s).ConclusionsAutomatic aortic centreline tracking in three commonly used CMR sequences is possible with good accuracy. The 3D length obtained from such sequences can differ considerably from lengths obtained from a 2D oblique-sagittal plane, depending on aortic curvature, adequate planning of the oblique-sagittal plane, and patient motion between acquisitions. For accurate PWV measurements we recommend using 3D centrelines.

Review of MRI-based measurements of pulse wave velocity: a biomarker of arterial stiffness.

Atherosclerosis is the leading cause of cardiovascular disease (CVD) in the Western world. In the early development of atherosclerosis, vessel walls remodel outwardly such that the vessel luminal diameter is minimally affected by early plaque development. Only in the late stages of the disease does the vessel lumen begin to narrow-leading to stenoses. As a result, angiographic techniques are not useful for diagnosing early atherosclerosis. Given the absence of stenoses in the early stages of atherosclerosis, CVD remains subclinical for decades. Thus, methods of diagnosing atherosclerosis early in the disease process are needed so that affected patients can receive the necessary interventions to prevent further disease progression. Pulse wave velocity (PWV) is a biomarker directly related to vessel stiffness that has the potential to provide information on early atherosclerotic disease burden. A number of clinical methods are available for evaluating global PWV, including applanation tonometry and ultrasound. However, these methods only provide a gross global measurement of PWV-from the carotid to femoral arteries-and may mitigate regional stiffness within the vasculature. Additionally, the distance measurements used in the PWV calculation with these methods can be highly inaccurate. Faster and more robust magnetic resonance imaging (MRI) sequences have facilitated increased interest in MRI-based PWV measurements. This review provides an overview of the state-of-the-art in MRI-based PWV measurements. In addition, both gold standard and clinical standard methods of computing PWV are discussed.

The 24-hour pulse wave velocity, aortic augmentation index, and central blood pressure in normotensive volunteers.

The purpose of this study was to examine the pulse wave velocity, aortic augmentation index corrected for heart rate 75 (AIx@75), and central systolic and diastolic blood pressure during 24-hour monitoring in normotensive volunteers. Overall, 467 subjects (206 men and 261 women) were recruited in this study. Participants were excluded from the study if they were less than 19 years of age, had blood test abnormalities, had a body mass index greater than 2 7.5 kg/m2, had impaired glucose tolerance, or had hypotension or hypertension. Ambulatory blood pressure monitoring (ABPM) with the BPLab® device was performed in each subject. ABPM waveforms were analyzed using the special automatic Vasotens® algorithm, which allows the calculation of pulse wave velocity, AIx@75, central systolic and diastolic blood pressure for “24-hour”, “awake”, and “asleep” periods. Circadian rhythms and sex differences in these indexes were identified. Pending further validation in prospective outcome-based studies, our data may be used as preliminary diagnostic values for the BPLab ABPM additional index in adult subjects.

Robust segmentation methods with an application to aortic pulse wave velocity calculation

Aortic stiffness has proven to be an important diagnostic and prognostic factor of many cardiovascular diseases, as well as an estimate of overall cardiovascular health. Pulse wave velocity (PWV) represents a good measure of the aortic stiffness, while the aortic distensibility is used as an aortic elasticity index. Obtaining the PWV and the aortic distensibility from magnetic resonance imaging (MRI) data requires diverse segmentation tasks, namely the extraction of the aortic center line and the segmentation of aortic regions, combined with signal processing methods for the analysis of the pulse wave. In our study non-contrasted MRI images of abdomen were used in healthy volunteers (22 data sets) for the sake of non-invasive analysis and contrasted magnetic resonance (MR) images were used for the aortic examination of Marfan syndrome patients (8 data sets). In this research we present a novel robust segmentation technique for the PWV and aortic distensibility calculation as a complete image processing toolbox. We introduce a novel graph-based method for the centerline extraction of a thoraco-abdominal aorta for the length calculation from 3-D MRI data, robust to artifacts and noise. Moreover, we design a new projection-based segmentation method for transverse aortic region delineation in cardiac magnetic resonance (CMR) images which is robust to high presence of artifacts. Finally, we propose a novel method for analysis of velocity curves in order to obtain pulse wave propagation times. In order to validate the proposed method we compare the obtained results with manually determined aortic centerlines and a region segmentation by an expert, while the results of the PWV measurement were compared to a validated software (LUMC, Leiden, the Netherlands). The obtained results show high correctness and effectiveness of our method for the aortic PWV and distensibility calculation.

A Technical Assessment of Pulse Wave Velocity Algorithms Applied to Non-invasive Arterial Waveforms

Non-invasive assessment of arterial stiffness through pulse wave velocity (PWV) analysis is becoming common clinical practice. However, the effects of measurement noise, temporal resolution and similarity of the two waveforms used for PWV calculation upon accuracy and variability are unknown. We studied these effects upon PWV estimates given by foot-to-foot, least squared difference, and cross-correlation algorithms. We assessed accuracy using numerically generated blood pressure and flow waveforms for which the theoretical PWV was known to compare with the algorithm estimates. We assessed variability using clinical measurements in 28 human subjects. Wave shape similarity was quantified using a cross correlation-coefficient (CCCoefficient), which decreases with increasing distance between waveform measurements sites. Based on our results, we propose the following criteria to identify the most accurate and least variable algorithm given the noise, resolution and CCCoefficient of the measured waveforms. (1) Use foot-to-foot when the noise-to-signal ratio ≤10%, and/or temporal resolution ≥100 Hz. Otherwise (2) use a least squares differencing method applied to the systolic upstroke.

A LABVIEW-BASED MULTI-PARAMETER MEASURING SYSTEM OF ARTERY STIFFNESS AND CLINICAL STUDY

An artery stiffness measuring system was developed based on LabVIEW for the multiparameter measurement of cardiovascular hemodynamics. The overall hardware and software design of the system were introduced. The basic theory and methods were described for the calculation of pulse wave velocity (PWV), artery stiffness index (ASI), aorta compliance (C1) and arteriole compliance (C2). In order to illustrate the effectiveness of the system, the comparative clinical trial was performed on 218 participators by measuring carotid intima-media thickness (CIMT) using ultrasonography instrument and measuring the multiparameters by the developed system. In addition, age and blood pressure were divided respectively into five and three groups to analyze their correlation with the multi-parameters of the system. The results showed that the age and blood pressure groups are positively correlated with PWV and ASI, and negatively with C1 and C2; PP, ASI and PWV are positively correlated with CIMT; C2 is negatively correlated with CIMT. The results demonstrated that the system could be used to detect and diagnose artery stiffness from different aspects by measuring the multi-parameters.

맥파 전달 속도(PWV) 측정을 위한 특징점 검출 알고리즘 개발

The compliance and stiffness of artery are closely related with disease of arteries. Pulse wave velocity(PWV) in the blood vessel is a basic and common parameter in the hemodynamics of blood pressure and blood flow wave traveling in arteries because the PWV is affected directly by the conditions of blood vessels. However, there is no standardized method to measure the PWV and it is difficult to measure. The conventional PWV measurement has being done by manual calculation of the pulse wave transmission time between coronary arterial proximal and distal points on a strip chart on which the pulse wave and ECG signal are recorded. In this study, a pressure sensor consisting of strain gauges is used to measure the blood pressure of arteries in invasive method and regular ECG electrodes are used to record the ECG signal. The R-peak point of ECG is extracted by using a reference level and time windowing technique and the ascending starting point of blood pressure is determined by using differentiation of the blood pressure signal and time windowing technique. The algorithm proposed in this study, which can measure PWV automatically, shows robust and good results in the extraction of feature points and calculation of PWV.

The Method of Distance Measurement and Torso Length Influences the Relationship of Pulse Wave Velocity to Cardiovascular Mortality

The method of estimating distance traveled by the pulse wave, used in the calculation of pulse wave velocity (PWV), is not standardized. Our objective was to assess whether different methods of distance measurement influenced the association of PWV to cardiovascular mortality in hemodialysis (HD) patients. Ninety-eight chronic HD patients had their PWV measured using three methods for distance estimation; PWV1: suprasternal notch-to-femoral site minus suprasternal notch-to-carotid site, PWV2: carotid-to-femoral site, PWV3: carotid-to-femoral site minus suprasternal notch-to-carotid site. Carotid-to-femoral distance was used to approximate torso length. Patients were followed for a median of 30 months and the association of PWV and cardiovascular mortality was assessed using survival analysis before and after stratification for torso length. The three methods resulted in significantly different PWV values. During follow-up 50 patients died, 32 of cardiovascular causes. In log-rank tests, only tertiles of PWV1 was significantly related to outcome (P values 0.017, 0.257, 0.137, for PWV1, PWV2, and PWV3, respectively). In adjusted Cox, proportional hazards regression only PWV1 was related to cardiovascular mortality. In stratified analysis, however, among patients with below median torso length all PWV values were related to outcome, whereas in patients with above median torso length none of the PWV methods resulted in significant relationship to outcome. PWV calculated using suprasternal notch-to-femoral distance minus suprasternal notch-to-carotid distance provides the strongest relationship to cardiovascular mortality. Longer torso weakens the predictive value of PWV, possibly due to more tortuosity of the aorta hence, more error introduced when using surface tape measurements.

THE METHOD OF DISTANCE MEASUREMENT AND TORSO LENGTH INFLUENCES THE RELATIONSHIP OF PULSE WAVE VELOCITY TO CARDIOVASCULAR MORTALITY: PP.31.235

Objective: The method of estimating the distance traveled by the pulse wave, used in the calculation of pulse wave velocity (PWV), is not standardized. Our objective was to assess whether different methods of distance measurement influenced the association of PWV to cardiovascular mortality in hemodialysis patients. Design and Methods: 98 chronic hemodialysis patients had their PWV measured using three methods for distance estimation; PWV1: sternal notch–femoral site minus sternal notch–carotid site, PWV2: carotid–femoral site, PWV3: carotid–femoral site minus sternal notch–carotid site. Carotid–femoral distance was used to approximate torso length. Patients were followed for a median of 30 (range 1–51) months and the association of PWV and cardiovascular mortality was assessed using survival analysis before and after stratification for torso length. Results: The three methods resulted in significantly different PWV values (11.2 (3.3), 14.8 (4.2), 12.6 (3.7) m/s, respectively). During follow up 50 patients died (mortality rate 20.3/100 patient years), 32 of cardiovascular causes. In log-rank tests only PWV1 tertiles but not those of PWV2 or PWV3 were significantly related to outcome (p-values 0.017, 0.257, 0.138, respectively). In adjusted Cox proportional hazards regression only PWV1 was related to cardiovascular mortality (HR for 1m/s higher PWV 1.18[1.03–1.35], 1.10[0.99–1.21], 1,13[1.00–1.27], for the three PWVs respectively). In stratified analysis, however, among patients with below median torso length all three PWV values were related to outcome, while in patients with above median torso length neither PWV methods resulted in significant relationship to outcome. Conclusion: PWV calculated using the sternal notch–femoral distance minus sternal notch–carotid distance provides the strongest relationship to cardiovascular mortality. Longer torso weakens the predictive value of PWV, possibly due to more tortuosity of the aorta hence more error introduced when using surface tape measurements.

Response to Modeled Decomposition of Aortic Pressure Waveforms Does Not Provide Estimates for Pulse Wave Velocity

We thank Hermeling et al1 for their interest in our recent study on the use of a single pressure pulse wave for the estimation of aortic pulse wave velocity (PWV).2 The main aim of the study was to propose a noninvasive and also a nonintrusive means of measuring aortic PWV. Aortic PWV is conventionally estimated from transit time (TT) between the carotid and femoral arteries, and this requires exposure of the groin. In addition, in many subjects with excessive adiposity in the groin area, it is difficult to obtain reliable femoral pulses. We agree that any noninvasive method has a certain number of assumptions and compromises, but we believe that we have obtained acceptable agreement between aortic PWV estimated from the single pulse method and aortic PWV measured directly using noninvasive external tonometric …

Relationship between albumin excretion rate and aortic stiffness in untreated essential hypertensive patients.

To evaluate, in a group of nondiabetic essential hypertensive patients with normal renal function, the relationship between albumin excretion rate (AER) and carotid-femoral pulse wave velocity (PWV), as an index of aortic stiffness. Cross-sectional study. Outpatient hypertension clinic. Seventy patients with mild-to-moderate essential hypertension, aged 42 +/- 8 years, never pharmacologically treated. All subjects underwent routine laboratory tests, 24-h ambulatory blood pressure (BP) monitoring, measurement of carotid-femoral PWV, by means of a computerized method, and AER. Microalbuminuric patients (AER > or = 20 microg min(-1); n = 19), when compared with normoalbuminuric subjects, showed more elevated 24-h BP (136/88 +/- 10/10 vs. 128/83 +/- 7/6 mmHg; P < 0.001 and P = 0.013, for systolic and diastolic BP respectively) and higher values of carotid-femoral PWV (10.4 +/- 2 m s(-1) vs. 9.2 +/- 1.3; P = 0.006). This latter difference remained statistically significant, even after correction by ancova for 24-h systolic and diastolic BP, and body mass index (BMI, P = 0.016). Univariate regression analysis disclosed a tight correlation between AER and carotid-femoral PWV (r = 0.42; P = 0.0003). This association was confirmed in a multiple regression model (beta = 0.35; P = 0.009) in which, as independent variables, besides PWV, 24-h BP, age, serum glucose values, smoking status, gender and BMI, were added. Our results seem to confirm that microalbuminuria may represent the early renal manifestation of a widespread vascular dysfunction, and therefore it is an integrated marker of cardiovascular risk.