Carotid Local Pulse Wave Velocity 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.

Advancing the Local Pulse Wave Velocity Measurement-Wave Confluence Decomposition Using a Double Gaussian Propagation Model.

Background Pulse wave velocity (PWV) is a marker of arterial stiffness and local measurements could facilitate its widescale clinical use. However, confluence of incident and early reflected waves leads to biased spatiotemporal PWV estimates. Objective We introduce the Double Gaussian Propagation Model (DGPM) to measure local PWV in consideration of wave confluence (PWV[Formula: see text]) and compare it against conventional spatiotemporal PWV (PWV[Formula: see text]), with Bramwell-Hill PWV (PWV[Formula: see text]) and blood pressure (BP) as reference measures. Methods Ten subjects ranging from normotension to hypertension were repeatedly measured at rest and with induced PWV changes. Carotid distension waveforms over a 19 mm wide segment were acquired from ultrasonography, simultaneously with noninvasive continuous BP. Per cardiac cycle, the 8-parameter DGPM (amplitude, centroid, width, and velocity, respectively of forward and backward propagating wave) was fitted to the distension waveforms' systolic foot and dicrotic notch complexes. Corresponding PWV[Formula: see text] was computed from linear fittings of respective feature timings and distances. Regression analyses were conducted with PWV[Formula: see text] and PWV[Formula: see text] as predictors, and various PWV and BP measures as response variables. Results Whereas PWV[Formula: see text] correlations were insignificant, PWV[Formula: see text] estimated the reference PWV[Formula: see text] with a significant reduction in errors (P < 0.001), explained up to 65% PWV[Formula: see text] variability at rest, demonstrated higher intra-method consistency and correlated significantly with all BP measures (P < 0.001). Conclusion The proposed DGPM measures local carotid PWV in consideration of wave confluence, showing significant correlations with Bramwell-Hill PWV and BP at two distinct waveform complexes. Thereby PWV[Formula: see text] outperforms the conventional PWV[Formula: see text] in all investigated respects, potentially enabling PWV assessment in routine clinical practice.

Subject-Specific Pressure Normalization of Local Pulse Wave Velocity: Separating Intrinsic From Acute Load-Dependent Stiffening in Hypertensive Patients.

Pulse wave velocity (PWV) is a powerful predictor of cardiovascular events. However, its intrinsic blood pressure (BP)-dependency complicates distinguishing between acute and chronic effects of increased BP on arterial stiffness. Based on the assumption that arteries exhibit a nearly exponential pressure-area (P-A) relationship, this study proposes a method to assess intersubject differences in local PWV independently from BP. The method was then used to analyze differences in local carotid PWV (cPWV) between hypertensive and healthy normotensive people before and after BP-normalization. Pressure (P) and diameter (D) waveforms were simultaneously acquired via tonometer at the left and ultrasound scanning at right common carotid artery (CCA), respectively, in 22 patients with Grade 1 or 2 hypertension and 22 age- and sex-matched controls. cPWV was determined using the D2P-loop method. Then, the exponential modeling of the P-area (A = πD2/4) relationships allowed defining a mathematical formulation to compute subject-specific changes in cPWV associated with BP changes, thus enabling the normalization of cPWV against intersubject differences in BP at the time of measurement. Carotid systolic BP (SBP) and diastolic BP (DBP) were, on average, 17.7 (p < 0.001) and 8.9 mmHg (p < 0.01) higher in hypertensives than controls, respectively. cPWV was 5.56 ± 0.86 m/s in controls and 6.24 ± 1.22 m/s in hypertensives. BP alone accounted for 68% of the cPWV difference between the two groups: 5.80 ± 0.84 vs. 6.03 ± 1.07 m/s after BP-normalization (p = 0.47). The mechanistic normalization of cPWV was in agreement with that estimated by analysis of covariance (ANCOVA). In conclusion, the proposed method, which could be easily implemented in the clinical setting, allows to assess the intersubject differences in PWV independently of BP. Our results suggested that mild hypertension in middle-aged subjects without target organ damage does not significantly alter the stiffness of the CCA wall independently of acute differences in BP. The results warrant further clinical investigations to establish the potential clinical utility of the method.

Ultrafast Ultrasound-Derived Muscle Strain Measure Correlates with Carotid Local Pulse Wave Velocity in Habitual Resistance-Trained Individuals

Purpose: this study investigated the effects of the intensity of machine-based bicep curl resistance exercise on ultrafast ultrasound-derived muscle strain rate and carotid ultrafast pulse wave velocity (ufPWV), and examined the association between muscle strain rate, ufPWV, and established carotid function measures in habitual resistance-trained individuals. Methods: twenty-three young habitual resistance-trained males (age: 24 ± 1 year, body mass index = 24 ± 1 kg/m2) were recruited to participate in two bouts of acute bicep curl exercise. After one-repetition maximum determination (1RM), the participants were randomly assigned to engage in bicep curls at 40 or 80%1RM intensity (10 reps × five sets) by a crossover study design. The muscle strain rate of bicep muscle, carotid ufPWV during systole(ufPWV-sys), and diastole (ufPWV-dia) were obtained pre- and post-exercise. In addition, carotid function measures were calculated by obtained carotid diameter and central blood pressure changes. Results: compared with pre-exercise, the reduction in post-exercise muscle strain rate and its area under the curve of 80%1RM was greater than those of 40%1RM. Both ufPWV-sys and ufPWV-dia increased regardless of exercise intensity. Baseline bicep muscle strain rate correlated not only with ufPWV-sys (r = −0.71, p = 0.001), ufPWV-dia (r = −0.74, p = 0.001), but also carotid compliance (r = 0.49, p = 0.02), distensibility (r = 0.54, p = 0.01) and ß stiffness (r= −0.84, p &lt; 0.0001). The ufPWVs also correlated with ß stiffness (r = 0.64–0.76, p = 0.01). Conclusion: muscle stiffness measured by ultrafast ultrasound elastography increases positively with resistance exercise intensity, and it appears to correlate with carotid ufPWV and established carotid function measures in habitual resistance-trained individuals.

Noninvasive carotid pressure-diameter loops to identify viscoelastic properties in ageing, hypertension and type 2 diabetes.

Arterial stiffness as pulse wave velocity (PWV) predicts cardiovascular events independently of blood pressure (BP). PWV does not distinguish between stiffness in systole and diastole. This cross-sectional study aimed to test the hypothesis that viscous and elastic carotid wall properties differ between systole and diastole, distinguishing effects of ageing, hypertension and T2 diabetes (T2DM). We examined carotid visco-elasticity in 307 people (180 men), with hypertension alone (n = 69), combined hypertension/T2DM (H-T2DM, n = 99), normotensive (N-T2DM, n = 25) and healthy controls (n = 114). Diameter (D)/pressure (P) waveforms were measured at right /left common carotid arteries, respectively. Local carotid PWV and distensibility in systole and diastole were evaluated by the D2P-loop method, and wall viscosity from hysteresis, the area (HA) within the P--D loop, as a dynamic measure of systolic loading and diastolic unloading. Controls' hysteresis fell quadratically with age (R2 = 0.23, P < 0.001). Yet mean HA in hypertensive patients (0.95, 95% CI 0.65-1.23) was six-fold higher than in age-matched controls (0.14, -0.20 to 0.49, P < 0.001) with a 2.5× difference between diastolic (dDs) to systolic (sDs) distensibility (P < 0.05) in hypertensive patients. HA was higher in hypertensive patients and H-T2DMs (0.80, 0.58-1.04) than N-T2DMs (0.20, -0.17 to 0.54, P < 0.05), but similar between controls and N-T2DMs. BP-adjusted carotid diameters in all T2DM were significantly greater compared with controls and hypertensive patients. Higher BP increased wall viscosity, hysteresis and relative difference between systolic and diastolic distensibility across groups. Carotid diameters were increased in all T2DMs, more in H-T2DM, probably altering BP-flow dynamics in T2DM.

Weight Loss After Bariatric Surgery Significantly Improves Carotid and Cardiac Function in Apparently Healthy People with Morbid Obesity

PurposeObesity clearly increases cardiovascular risk, often inducing high blood pressure (BP), impaired left ventricular (LV) function, and increased arterial stiffness. Intensive weight loss and bariatric surgery induce improvement in hypertension and diabetes for morbid obesity. Carotid artery haemodynamics is a powerful prognostic indicator for stroke and cognitive decline independent of BP. The aim of this study was to evaluate the impact of a 3-stage bariatric strategy of diet, bariatric surgery, and consequent weight loss on carotid haemodynamics and cardiac diastolic function.Material and MethodsThis prospective study included 26 patients (45 ± 10 years, 4 men) with severe obesity undergoing bariatric surgery without comorbidities (hypertension, diabetes, etc.). Anthropometry, BP, Doppler echocardiography, and common carotid haemodynamics by ultrasound were measured at three times: (1) baseline, (2) after 1-month diet (post-diet), and (3) 8 months after surgery (post-surgery). The lnDU-loop method was used to estimate local carotid pulse wave velocity (ncPWV).ResultsBaseline BMI was 47.9 ± 7.1 kg/m2 and reduced by 5% and 30% post-diet and post-surgery, respectively. BP decreased only post-diet, without pulse pressure change. However, ncPWV, 6.27 ± 1.35 m/s at baseline, was significantly reduced by 10% and 23% post-diet and post-surgery, respectively, also adjusted for BP changes. The E/A ratio rose from 0.95 ± 0.20 to 1.27 ± 0.31 (p < 0.005), without change in LV geometry or mass, while heart rate and cardiac output fell substantially.ConclusionWeight loss following diet and bariatric surgery is associated with reduced carotid arterial stiffness and improved LV diastolic function. Diet and bariatric surgery are effective treatments for morbid obesity with its concomitant adverse cardiovascular effects.

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.

P24 Restored Physiological Local Carotid Pulse Wave Velocity After Bariatric Surgery in Obese Subjects

Obesity is a risk factor for cardiovascular events and is associated with increased arterial stiffness [1,2]. However, the effect of drastic changes in Body Mass Index (BMI) on arterial mechanics has not been fully investigated. Our study aimed at evaluating changes in local carotid PWV (cPWV) in obese patients before and 6 months after bariatric surgery. N = 20 obese subjects free of cardiovascular events and diabetes (44 ± 9 years, 5 men, BMI = 48.8 ± 7.5 kg/m2) undergoing bariatric surgery were recruited in the Pisa University Hospital (Italy). Flow and diameter waveforms were acquired by ultrasound scanner (Aloka Alpha10, Hitachi Group, Japan) (1 kHz) at the right common carotid artery at baseline, after a 32.4 ± 7.6 days diet period, and 6.5 ± 2.7 months post-intervention. The lnDU-loop method was used for the estimation of cPWV [3]. Basal cPWV was 6.05 ± 1.21 m/s. The 1-month diet period produced a 2 kg/m2 reduction in BMI, while cPWV decreased by approx. 0.6 m/s. 6–7 months after bariatric surgery, BMI dropped to 35.3 ± 6.5 kg/m2 and cPWV furtherly decreased of approx. 0.9 m/s reaching a mean value of 4.57 ± 1.02 m/s (76% of the basal value) (Figure 1). Bariatric surgery and the consequent intensive weight loss produced a significant decrease of arterial stiffness and restored cPWV to physiological values of age-matched healthy subjects [4]. The fast reversal of increased arterial stiffness suggests a functional mechanism possibly related to a reduced haemodynamic load. Moreover, while having a small effect on the BMI, 1-month diet regulation effectively decreased cPWV by 10%, possibly indicating the short-term positive effects of a healthy lifestyle on haemodynamics.Figure 1

Regional Upstroke Tracking for Transit Time Detection to Improve the Ultrasound-Based Local PWV Estimation in Carotid Arteries.

Pulse wave velocity (PWV) is the most important index for quantifying the elasticity of an artery. The accurate estimation of the local PWV is of great relevance to the early diagnosis and effective prevention of arterial stiffness. In ultrasonic transit time-based local PWV estimation, the locations of time fiduciary point (TFP) in the upstrokes of the propagating pulse waves (PWs) are inconsistent because of the reflected waves and ultrasonic noise. In this study, a regional upstroke tracking (RUT) approach that involved identifying the most similar TFP-centered region in the upstrokes is proposed to detect the time delay for improving the local PWV estimation. Five RUT algorithms with different tracking points are assessed via simulation and clinical experiments. To quantitatively evaluate the RUT algorithms, the normalized root-mean-squared errors and standard deviations of the estimated PWVs are calculated using an ultrasound simulation model. The reproducibility of the five RUT algorithms based on 30 human subjects is also evaluated using the Bland-Altman analysis and coefficient of variation (CV). The obtained results show that the RUT algorithms with only three tracking points provide greater accuracy, precision, and reproducibility for the local PWV estimation than the TFP methods. Compared with the TFP methods, the RUT algorithms reduce the mean errors from 12.23% ± 3.10% to 7.13% ± 2.31%, as well as the CVs from 21.76% to 13.39%. In conclusion, the proposed RUT algorithms are superior to the TFP methods for local carotid PWV estimation.

Abstract P112: Sex Differences and the Role of G Protein-Coupled Estrogen Receptor in Arterial Stiffening

Pulse wave velocity (PWV) independently predicts cardiovascular events and is exacerbated in women following menopause. Since our previous work shows that G protein-coupled estrogen receptor (GPER) plays a protective role in the vasculature, the current study evaluated sex differences and the impact of GPER on arterial stiffening. We hypothesized that genetic deletion of GPER attenuates sex differences in arterial stiffness. Male and female wildtype (wt) and global GPER knockout (ko) mice (n=46) were used between 16-21 weeks of age. Ang II infusion (700 ng/kg/day for two weeks) was used to induce hypertension, and SBP was measured using tail cuff plethysmography. Local PWV within the carotid artery was obtained via high frequency ultrasound in both color Doppler and M-mode. The excised carotid was subjected to passive biaxial mechanical testing followed by four fiber family constitutive modeling. Statistical analysis was performed using two-way ANOVA with Sidak’s multiple comparisons test. Baseline SBP was significantly lower in females (P=0.035) but was not impacted by genotype. Baseline PWV was significantly higher in male versus female wt mice (P&lt;0.01) but was not different in ko mice. Baseline axial (P&lt;0.01) and circumferential (P=0.027) stiffness was higher in female wt mice but was not impacted by genotype. Ang II infusion significantly increased SBP (P&lt;0.001) and PWV (P&lt;0.001) in all groups, removing any impact of sex or genotype. Ang II increased axial stiffness and decreased diagonal collagen in male and female GPER ko mice. In conclusion, we found that GPER deletion did not impact blood pressure but removed sex differences in PWV. While female wt mice had the lowest PWV at baseline, genetic deletion of GPER or Ang II infusion removed this protection independent of BP. Therefore, local carotid PWV may provide information on vascular status independent of BP, and GPER plays an important role in vascular compliance and arterial stiffening.

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.

Abstract 113: Female Protection From Arterial Stiffness Diminishes With G Protein-Coupled Estrogen Receptor Deletion or Angiotensin II Hypertension

Arterial stiffness independently predicts cardiovascular mortality, coronary events, and stroke in hypertensive subjects and is exacerbated in women following menopause. Previously, our laboratory indicated that G protein-coupled estrogen receptor (GPER) plays a protective role in the vasculature. Therefore, the current study assessed the impact of sex and GPER on arterial stiffening in control and hypertensive conditions. We hypothesized that genetic deletion of GPER attenuates sex differences in arterial stiffness. Male and female wildtype (wt) and global GPER knockout (ko) mice (n=46) were used between 16-21 weeks of age. Angiotensin II (Ang II) infusion (700 ng/kg/day for two weeks) was used to induce hypertension, and systolic blood pressure (SBP) was measured using tail cuff plethysmography. Local pulse wave velocity (PWV) within the carotid artery was obtained via high frequency ultrasound in both color Doppler and M-mode. Statistical analysis was performed using two-way ANOVA with Sidak’s multiple comparisons test. Baseline SBP was significantly lower in females (P=0.035) but was not impacted by genotype (P=0.78). Baseline PWV was significantly higher in male versus female wt mice (1.29 vs. 0.804 m/s, P=0.003) but was not different in ko mice (1.25 vs. 1.04 m/s, P=0.22). Ang II infusion significantly increased SBP (P&lt;0.001) and PWV (P&lt;0.001) in all groups, removing any impact of sex or genotype. In addition, significant correlations were found between Doppler and M-mode methods for obtaining carotid PWV (r=0.67, P&lt;0.001) and between PWV and ex vivo carotid wall thickness (r=0.70, P=0.004). In contrast, SBP did not correlate with PWV (P=0.77) or carotid wall thickness (P=0.68). In conclusion, we found that GPER deletion did not impact blood pressure either in normotensive or hypertensive conditions. While arteries from female wt mice were less stiff at baseline, genetic deletion of GPER or Ang II infusion removed this protection independent of blood pressure. Moreover, we found that local carotid PWV provides information on vascular status that could not be obtained via blood pressure. This data indicates that GPER plays an important role in female vascular physiology that is absent in pathological conditions.

Carotid Local Pulse Wave Velocity Measurement using Dual- Element Accelerometric Patch Probe.

In this work, we demonstrate an accelerometric patch probe with two microelectromechanical accelerometer sensors for local pulse wave velocity (PWV) measurement from the carotid artery. Dual acceleration plethysmogram (APG) signals were acquired from a small section of the artery by keeping the sensors at 32 mm apart. A custom analog front-end circuit (inter-channel delay $< 0.15$ ms) was used for reliable signal acquisition. Simultaneously acquired dual APG signals were processed in real-time and local PWV was evaluated in a beat-by-beat manner. A transversal study on a cohort of 15 volunteers (4 males, 11 females, mean age = $25.6 \pm 1.92$ years) was conducted to validate the developed prototype system. During the study, carotid local PWV and brachial blood pressure (BP) parameters were recorded from both sitting and standing posture. The absolute values of measured carotid local PWV were in the range of 3 m/s - 4.2 m/s (beat-to-beat variation $=$ 2.61% - 13.07%). Measured local PWV values significantly correlated with brachial systolic BP ($\textbf{R}^{\mathbf {2}} =$ 0.87) and diastolic BP ($\textbf{R}_{\mathbf {\, }}^{\mathbf {2}} \quad =$ 0.79). Logarithmic functions provided the best monotonic model for carotid local PWV versus brachial BP parameters for the recorded data points. The developed population-specific mathematical models were then used for cuffless evaluation of BP parameters from carotid local PWV. The root-mean-square error in the estimated systolic and diastolic pressure was 7.53 mmHg and 6.0 mmHg respectively. Study results illustrate the potential application of the developed dual-accelerometric system in non-invasive, continuous cuffless BP measurement techniques.

Local Evaluation of Variation in Pulse Wave Velocity over the Cardiac Cycle using Single-Element Ultrasound Transducer.

A method and system for single-site measurement of local pulse wave velocity (PWV) and its variation over the cardiac cycle are presented. The proposed system employs a single-element ultrasound transducer and associated custom technology to record arterial diameter and wall thickness waveforms in real-time. Simultaneously acquired blood pressure, diameter and wall thickness parameters were used to evaluate diastolic local PWV (CD) and systolic local PWV (Cs) from an arterial site of interest. The developed prototype system was validated on a cohort of 15 subjects (age $=43\pm 12$ years) that includes normotensives and hypertensives. Cs and CD measurements were obtained from the left carotid artery. A significant difference between carotid Cs and CD $(\Delta \mathrm{C})$ was observed in all recruited subjects (group average $\Delta \mathrm{C} = 0.92\pm 0.76\mathrm{m}/\mathrm{s})$, illustrating the arterial pressure dependency of local PWV. The absolute values of Cs and CD were within a range of 3.39 m/s to 7.5 m/s and 3.12 m/s to 5.82 m/s respectively. Normotensive versus hypertensive group-wise analysis was performed to investigate the degree of variation in the carotid local PWV over a cardiac cycle among different BP categories. Study results demonstrated that the proposed approach has a potential to provide valuable surrogate markers for cardiovascular risk assessment.

Arterial Blood Pressure Estimation From Local Pulse Wave Velocity Using Dual-Element Photoplethysmograph Probe

An arterial compliance, dual-element photoplethysmograph probe for local pulse wave velocity (PWV) measurement was developed. Initially, the experimental validation study was performed on 25 young volunteers (age =24.5 ± 4 years). Local PWV was assessed from a small section (23 mm) of the carotid artery. The prototype device demonstrated its capability of measuring reliable, repeatable, and reproducible carotid local PWV. Further, in 15 healthy male volunteers (age = 22.25 ± 3.5 years), carotid local PWV and brachial blood pressure (BP) were continuously recorded during their postexercise recovery period. Local PWV followed the changes in arterial BP parameters. The group average correlation coefficients (r) of local PWV versus BP parameters were between 0.772 ± 0.033 and 0.934 ± 0.028. In a population of 50 patients (normotensive and hypertensive) aged 24–80 years, local PWV–BP correlations were investigated. Local PWV tended to follow the diastolic BP (DBP; $r = 0.82$ ) and mean arterial pressure ( $r = 0.83$ ) better than systolic BP (SBP; $r = 0.69$ ). It was significantly inferior in tracking pulse pressure values ( $r = 0.35$ ). Cuffless estimation of arterial pressure was also performed on the same patients using measured carotid local PWV with best-case calibrations. Local PWV yielded good DBP prediction than SBP prediction. Statistically, significant correlation ( $r = 0.79$ ) and a root-mean-square error of 5.26 mmHg versus reference brachial DBP were achieved. The introduced technique has a potential for short- or long-term noninvasive, cuffless monitoring of BP parameters from superficial arteries.

Carotid stiffness is significantly correlated with wall-to-lumen ratio of retinal arterioles.

Wall-to-lumen ratio of retinal arterioles (W/L ratio) might serve as an in-vivo parameter of microvascular damage. No study has investigated the relationship between carotid stiffness and W/L ratio of retinal arteries. Therefore, the aim of the current study was to assess the correlation between local carotid stiffness, as assessed by echotracking technique, and W/L ratio of retinal arterioles, as assessed by noninvasive flowmetry in normotensive patients and in patients with primary hypertension. Two hundred and twenty-seven patients underwent renal arteries W/L ratio and local carotid-pulse wave velocity (carotid PWV) measurement. One hundred and fifteen patients had a diagnosis of primary hypertension, whereas 112 were normotensive patients. W/L ratio and carotid PWV were both related with clinic SBP (r = 0.17, P < 0.05; r = 0.50, P < 0.001), clinic pulse pressure (r = 0.22, P < 0.001; r = 0.55, P < 0.001), carotid SBP (r = 0.18, P < 0.05; r = 0.51, P < 0.001) and carotid pulse pressure (r = 0.24, P < 0.001; r = 0.56, P < 0.001). W/L ratio was correlated with carotid PWV (r = 0.18, P < 0.005). At multivariate analysis, carotid PWV remained independently associated with W/L ratio. In hypertensive and normotensive patients, carotid stiffness is significantly correlated with W/L ratio of retinal arteries, independently of possible confounders.

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.

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.

Measurement of carotid blood pressure and local pulse wave velocity changes during cuff induced hyperemia.

We present a prototype design of dual element photoplethysmograph (PPG) probe along with associated measurement system for carotid local pulse wave velocity (PWV) evaluation in a non-invasive and continuous manner. The PPG probe consists of two identical sensing modules placed 23 mm apart. Simultaneously measured blood pulse waveforms from these arterial sites were processed and the pulse transit time delay was resolved using the developed application-specific software. The ability of developed PPG probe and associated measurement system to detect acute changes in carotid local PWV due to blood pressure (BP) variations was experimentally validated by an in-vivo study. Intra-subject carotid BP elevation was achieved by an upper arm cuff based occlusion, which offered a controlled way of local PWV escalation. The elevated carotid BP values were also recorded by a calibrated pressure tonometer prior to the study, and was used as a reference. A significant increment (1.0 - 2.6 m/s) in local PWV was observed and was proportional to the BP increment induced by the occlusive reactive hyperemia. Study results demonstrated the feasibility of real-time signal acquisition and reliable local PWV evaluation under normal and elevated BP conditions using the developed measurement system.

Assessment of local carotid stiffness in seronegative and seropositive rheumatoid arthritis

Objectives: Rheumatoid arthritis (RA) is a chronic, inflammatory disease associated with increased risk of cardiovascular (CV) disease. Arterial stiffness (AS) is an independent predictor of CV events. This study aimed to analyse local carotid AS parameters in seronegative and seropositive RA patients. Design: Of 347 consecutive RA patients, we selected specifically those who were free of established CV diseases and risk factors. As a result, 140 patients (126 women, 52.2 ± 10 years) and 140 healthy controls (122 women, 52.7 ± 8.0 years) were enrolled into this study. The common carotid AS was evaluated using radio frequency echo-tracking system to determine the local carotid pulse wave velocity (cPWV) and carotid intima-media thickness (cIMT). Based on rheumatoid factor (RF) and/or anti-citrullinated protein antibody (ACPA) positivity, RA patients were categorized into seronegative and seropositive subgroups. Results: Carotid PWV was determined to be significantly higher in all patients and subgroups than controls (p < .001 for all). Although cIMT was similar between the patients, controls and seropositive subgroup, seronegative patients had significantly higher cIMT compared to controls (p = .035) and seropositive group (p = .010). Moreover, a significant positive correlation was found between cPWV and age (r: 0.603, p < .001), ESR (r: 0.297, p = .004), ACPA (r: 0.346, p = .001) and cIMT (r: 0.290, p = .005) in seropositive patients. Conclusions: RA per se is sufficient to cause arteriosclerosis in the absence of classical CV risk factors. However, arterial hypertrophy is only increased in seronegative patients but not in seropositive group.