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Model-Based Assessment of the Reference Values of CAVI in Healthy Russian Population and Benchmarking With CAVI0

BACKGROUND

Cardio-ankle vascular index (CAVI) and its modified version (CAVI0) are promising non-invasive markers of arterial stiffness, extensively evaluated primarily in the Japanese population. In this work, we performed a model-based analysis of the association between different population characteristics and CAVI or CAVI0 values in healthy Russian subjects and propose a tool for calculating the range of reference values for both types of indices.

METHODS

The analysis was based on the data from 742 healthy volunteers (mean age 30.4 years; 73.45% men) collected from a multicenter observational study. Basic statistical analysis [analysis of variance, Pearson's correlation (r), significance tests] and multivariable linear regression were performed in R software (version 4.0.2). Tested covariates included age, sex, BMI, blood pressure, and heart rate (HR).

RESULTS

No statistically significant difference between healthy men and women were observed for CAVI and CAVI0. In contrast, both indices were positively associated with age (r = 0.49 and r = 0.43, P < 0.001), however, with no clear distinction between subjects of 20-30 and 30-40 years old. Heart rate and blood pressure were also identified as statistically significant predictors following multiple linear regression modeling, but with marginal clinical significance. Finally, the algorithm for the calculation of the expected ranges of CAVI in healthy population was proposed, for a given age category, HR and pulse pressure (PP) values.

CONCLUSIONS

We have evaluated the quantitative association between various population characteristics, CAVI, and CAVI0 values and established a method for estimating the subject-level reference CAVI and CAVI0 measurements.

The Background of Calculating CAVI: Lesson from the Discrepancy Between CAVI and CAVI0

Arterial stiffness is a good predictor of cardiovascular events. As a substitute for elastic modulus representing stiffness, pulse wave velocity (PWV) has been used for over a century as it is easy to measure; however, PWV is known to essentially depend on blood pressure at the time of measurement. The cardio-ankle vascular index (CAVI) is a relatively new index of global arterial stiffness of the origin of the aorta to the ankle arteries. The characteristic feature is its independency from blood pressure at the measuring time. Recently, a variant index CAVI₀ was proposed, which was claimed to be a more accurate arterial stiffness index than CAVI, considering independency from blood pressure. The purpose of this review is to evaluate the properties of CAVI more precisely by comparing with CAVI₀, and to confirm the true meaning of CAVI as an index of arterial stiffness. First, the properties of PWV depending on the blood pressure and the variation of PWV values in the cardiac cycle were analyzed. Then, we attempted to clarify the point at which the PWV, adopted in CAVI or in CAVI₀, was measured in cardiac cycle. A comprehensive comparison of the clinical data of CAVI and CAVI₀ showed that CAVI is more appropriate than CAVI_0. In conclusion, CAVI is reconfirmed to be a reliable and useful index of blood pressure-independent arterial stiffness composed of both organic and functional stiffness.

Evaluation of the calculation formulas of the cardio-ankle vascular index used in the Japanese apparatus

Background

Recently, coefficients in the equation of cardio-ankle vascular index (CAVI) used in VaSera^® device were disclosed. This study aimed to simulate the influence of adjusting the coefficients in the equation of CAVI and also aimed to validate the equation.

Methods

The CAVI displayed by VaSera (CAVIvs) and the CAVI estimated (CAVIes) with fixing the coefficients of the middle range of the heart-ankle stiffness parameter β (haβ) in the equation were compared. Moreover, the heart-ankle pulse wave velocity (haPWV) which corresponds to the low cutoff haβ of 7.348 was estimated in various blood pressure patterns to validate the formula.

Results

The CAVIvs was clearly lower than CAVIes in the low and the high range of CAVIvs. Moreover, it was virtually impossible to obtain the low cutoff haβ of 7.348 by using typical values of haPWV.

Conclusion

The CAVIvs in the high-range of VaSera underestimates the original property of stiffness parameter β. Moreover, there will be also a missing information in the equations introduced in the corresponding article, especially in the calculation formula of CAVIvs from haβ. Therefore, in order to make the best use of the nature of the stiffness parameter β to be used in VaSera, fixing the coefficients or termination of its use should be considered.

Comparison of Cardio-Ankle Vascular Index (CAVI) and CAVI0 in Large Healthy and Hypertensive Populations

Aim: The cardio-ankle vascular index (CAVI) represents the blood pressure-independent arterial stiffness from the origin of the aorta to the ankle. CAVI₀ has been proposed as a variant index. We aimed to clarify the difference between CAVI and CAVI₀ among large populations, and to explore reasons of the difference.

Methods: The subjects were 5,293 Japanese healthy and 3,338 hypertensive people. Simple and multiple regression analyses were performed using age, sex, body mass index, systolic, and diastolic blood pressure (Pd) as variables. Sub-group analysis was performed by sex and age. The CAVI values with and without adjustment by reference pressure were also compared.

Results: CAVI had a positive correlation with Pd, while CAVI₀ had a negative correlation with Pd in the healthy population. The CAVI values of the hypertensive group were higher than those of healthy group in both men and women, but the CAVI₀ values in women of the hypertensive group in the 30–39 age group was significantly lower than that of the corresponding healthy group. Differences of CAVI values with or without modification using the reference pressure were 1.09% ± 1.38% for the healthy group and 3.68% ± 1.66% for the hypertensive group.

Conclusion: CAVI showed the expected values, but CAVI₀ showed inexplicable results in the healthy and hypertensive populations. The differences were due to the strong dependency of CAVI₀ on Pd. Differences of CAVI values with or without reference pressure were negligible. These results indicate that CAVI obtained by the VaSera system is appropriate, but CAVI₀ is not.

Options for Dealing with Pressure Dependence of Pulse Wave Velocity as a Measure of Arterial Stiffness: An Update of Cardio-Ankle Vascular Index (CAVI) and CAVI0

Pulse wave velocity (PWV), a marker of arterial stiffness, is known to change instantaneously with changes in blood pressure. In this mini-review, we discuss two main approaches for handling the blood pressure dependence of PWV: (1) converting PWV into a pressure-independent index, and (2) correcting PWV per se for the pressure dependence. Under option 1, we focus on cardio-ankle vascular index (CAVI). CAVI is essentially a form of stiffness index β - CAVI is estimated for a (heart-to-ankle) trajectory, whereas β is estimated for a single artery from pressure and diameter measurements. Stiffness index β, and therefore also CAVI, have been shown to theoretically exhibit a slight residual blood pressure dependence due to the use of diastolic blood pressure instead of a fixed reference blood pressure. Additionally, CAVI exhibits pressure dependence due to the use of an estimated derivative of the pressure-diameter relationship. In this mini-review, we will address CAVI's blood pressure dependence theoretically, but also statistically. Furthermore, we review corrected indices (CAVI₀ and β₀) that theoretically do not show a residual blood pressure dependence. Under option 2, three ways of correcting PWV are reviewed: (1) using an exponential relationship between pressure and cross-sectional area, (2) by statistical model adjustment, and (3) through reference values or rule of thumb. Method 2 requires a population to be studied to characterise the statistical model, and method 3 requires a representative reference study. Given these limitations, method 1 seems preferable for correcting PWV per se for its blood pressure dependence. In summary, several options are available to handle the blood pressure dependence of PWV. If a blood pressure-independent index is sought, CAVI₀ is theoretically preferable over CAVI. If correcting PWV per se is required, using an exponential pressure-area relationship provides the user with a method to correct PWV on an individual basis.