The pressure-dependency of local measures of arterial stiffness

Estimated Pulse-Wave Velocity and Magnetic Resonance Imaging Markers of Cerebral Small-Vessel Disease in the NOMAS

BACKGROUND

Pulse-wave velocity is a measure of arterial stiffness and a risk factor for cardiovascular disease. Recently, an estimated pulse-wave velocity (ePWV) was introduced that was predictive of increased risk of cardiovascular disease. Our objective was to determine whether ePWV was associated with cerebral small-vessel disease on magnetic resonance imaging.

METHODS AND RESULTS

We included 1257 participants from the NOMAS (Northern Manhattan Study). The ePWV values were calculated using a nonlinear function of age and mean arterial blood pressure. The association between ePWV and white matter hyperintensity volume was assessed. Modification by race and ethnicity was evaluated. Associations between ePWV and other cerebral small-vessel disease markers, covert brain infarcts, cerebral microbleeds, and enlarged perivascular spaces, were explored as secondary outcomes. Mean±SD age of the cohort was 64±8 years; 61% were women; 18% self-identified as non-Hispanic Black, 67% as Hispanic, and 15% as non-Hispanic White individuals. Mean±SD ePWV was 11±2 m/s in the total NOMAS population and was similar across race and ethnic groups. The ePWV was significantly associated with white matter hyperintensity volume (β=0.23 [95% CI, 0.20-0.26]) after adjustment. Race and ethnicity modified the association between ePWV and white matter hyperintensity volume, with stronger associations in Hispanic and non-Hispanic Black individuals. Significant associations were found between ePWV and covert brain infarcts, cerebral microbleeds, and perivascular spaces after adjustment.

CONCLUSIONS

The ePWV function may provide a vascular mechanism for deleterious cerebrovascular outcomes in individuals with cerebral small-vessel disease and is particularly apparent in the racial and ethnic minorities represented in the NOMAS cohort.

Pulse-wave velocity assessments derived from a simple photoplethysmography device: Agreement with a referent device

Objective

Pulse-wave velocity (PWV), a common measure of arterial stiffness, can be measured continuously and across multiple body sites using photoplethysmography (PPG). The objective was to determine whether a simple photoplethysmography PPG PWV method agrees with a referent device.

Approach

Photoplethysmography heart-finger PWV (hfPWV) and heart-toe PWV (htPWV) were compared to oscillometric carotid-wrist PWV (cwPWV) and carotid-ankle PWV (caPWV) referent measurements, respectively. In 30 adults (24.6 ± 4.8 years, body mass index 25.2 ± 5.9 kg/m², 18 female), three measurements were made: two supine baseline measurements (Base 1, Base 2) and one measurement (Tilt) 5 min after a modified head-up tilt test (mHUTT). Overall agreement and repeated measures agreement (change in PPG PWV from Base to Tilt vs. change in referent PWV from Base to Tilt) were calculated using linear mixed models. Agreement estimates were expressed as intra-class correlation coefficients (ICC).

Main results

For hfPWV there was strong overall agreement (ICC: 0.77, 95%CI: 0.67-0.85), but negligible and non-significant repeated measures agreement (ICC: 0.10, 95%CI: -0.18 to 0.36). For htPWV, there was moderate overall agreement (ICC:0.50, 95%CI: 0.31-0.65) and strong repeated measures agreement (ICC: 0.81, 95%CI: 0.69-0.89).

Significance

Photoplethysmography can continuously measure PWV at multiple arterial segments with moderate-strong overall agreement. While further work with upper-limb PPG PWV is needed, PPG can adequately capture acute changes in lower-limb PWV.

Converting and Standardizing Various Measures of Arterial Stiffness to Pulse Wave Velocity

Background

A variety of arterial stiffness measures have been used to assess the impacts of disease states and various interventions without clear consensus among them. One of the primary problems faced by investigators conducting systematic reviews and meta-analyses is the lack of standardized methodology with a same unit to evaluate and compare investigations using different arterial stiffness measures. Therefore, the purpose of this study was to derive and summarize standardized equations to convert commonly used image-based measures of arterial stiffness to local pulse wave velocity (PWV).

Methods

We first conducted a literature search to obtain and summarize conversion equations in the published literature such that these equations can be found in one convenient location. Then, we generated regression equations using the data collected in a well-controlled laboratory-based study, in which all measures of arterial stiffness were obtained in 49 apparently healthy participants.

Results

All literature-based conversion equations produced similar local PWV values and were moderately and significantly correlated with directly measured carotid-femoral PWV (cfPWV) with a Pearson's r ranging from 0.41 to 0.50. The local PWV using laboratory-based equations were modestly associated with cfPWV (r = 0.39-0.49) with an exception of incremental elastic modulus (r = 0.15, p > 0.05).

Conclusion

Commonly used measures of ultrasound-based arterial stiffness can be converted to local PWV and compared with a reference standard measure of arterial stiffness.

In vivo parameter identification in arteries considering multiple levels of smooth muscle activity

In this paper an existing in vivo parameter identification method for arteries is extended to account for smooth muscle activity. Within this method a continuum-mechanical model, whose parameters relate to the mechanical properties of the artery, is fit to clinical data by solving a minimization problem. Including smooth muscle activity in the model increases the number of parameters. This may lead to overparameterization, implying that several parameter combinations solve the minimization problem equally well and it is therefore not possible to determine which set of parameters represents the mechanical properties of the artery best. To prevent overparameterization the model is fit to clinical data measured at different levels of smooth muscle activity. Three conditions are considered for the human abdominal aorta: basal during rest; constricted, induced by lower-body negative pressure; and dilated, induced by physical exercise. By fitting the model to these three arterial conditions simultaneously a unique set of model parameters is identified and the model prediction agrees well with the clinical data.

Effect of Menopause on Arterial Stiffness and Central Hemodynamics: A Pulse Wave Analysis-Based Cross-sectional Study from Gujarat, India

Background:

Menopause, a cardiovascular risk in mid-life women, is studied in terms of blood pressure mostly. Arterial stiffness (AS) and central hemodynamics (CH) are direct surrogates measured by pulse wave analysis (PWA) with no study from our region.

Objective:

We studied AS, CH in relation to menopause using PWA.

Materials and Methods:

A cross-sectional study was performed in 134 middle-aged females divided into groups with or without menopause. Oscillometric PWA done by Mobil-o-Graph (IEM, Germany) gave – AS like augmentation pressure, augmentation index at heart rate (HR) 75, aortic pulse wave velocity (aPWV), and total AS pulse pressure amplification; CH like aortic blood pressure, cardiac output and related parameters, peripheral resistance, stroke work, prevalent brachial/central hypertension, and raised central pulse pressure. They were further compared between groups, in relation to body mass index (BMI) and by multiple regressions with P < 0.05 as statistical significance.

Results:

Postmenopausal women were significantly elder, physically inactive with comparable BMI and showed higher AS (only aPWV was significantly different) and CH. BMI was unrelated to AS or CH in postmenopausal group. Age (except for aPWV), BMI, and HR (except for AIx@75) were insignificant predictors, while systolic blood pressure (SBP) in premenopausal and diastolic blood pressure (DBP) in postmenopausal group was major AS predictors. Age, HR, and BMI were insignificant predictors, while SBP more than DBP was significant predictors of CH.

Conclusions:

In obese, predominantly sedentary midlife Gujarati women, menopause negatively affects AS and hemodynamics, central more than peripheral. Menopause accelerates cardiovascular aging, independent of BMI, and age that calls for further studies.