Noninvasive assessment of carotid-femoral pulse wave velocity: the influence of body side and body contours.

BACKGROUND: Recently, an expert group advised to measure carotid-femoral (cf) pulse wave velocity (PWV) on the right side of the body, and to use a sliding caliper when tape measure distance cannot be obtained in a straight line. The present study investigates the evidence for this advice by comparing the real travelled cf path lengths (RTPLs) at both body sides and comparing the straight distance (as can be obtained with a sliding caliper) with the tape measure distance. METHODS: RTPLs were measured with MRI in 98 individuals (49 men, age 21-76 years). Path lengths from the aortic arch to the carotid (AA-CA) and femoral (AA-FA) sites were determined. RTPL was calculated as (AA-FA) - (AA-CA) and compared between both sides. RTPLs were compared with 80% of the direct cf distance using a tape measure and the straight cf distance obtained from MRI images. RESULTS: RTPL was slightly longer [11 mm (12), P < 0.001] at the right side. The 80%-rule overestimated RTPLs with 0.5% at the right and 2.7% at the left side. Straight MRI distance tended (P = 0.09) to perform slightly better than tape measure distance. CONCLUSION: The travelled cf path is slightly longer at the right than at the left body side and the straight MRI distance tends to perform better than tape measure distance. The present study supports the advice of the expert consensus group to measure cf-PWV at the right body side using a sliding caliper when tape measure distance cannot be obtained in a straight line.

Ambulatory arterial stiffness index does not accurately assess arterial stiffness.

INTRODUCTION: The ambulatory arterial stiffness index (AASI), derived from ambulatory blood pressure monitoring (ABPM) recordings, has been proposed as a surrogate marker of arterial stiffness. However, there is controversy to what extent it reflects stiffness or is affected by other parameters. Using a previously validated one-dimensional computer model of the arterial circulation, the relative importance of the different determinants of the AASI was explored. METHODS: Arterial distensibility (inverse of stiffness), peripheral resistance, heart rate, maximal cardiac elastance and venous filling pressure were varied from 80 to 120% of their initial value in steps of 10% to generate 3125 BP values, mimicking the daily fluctuations in one theoretical patient. From this dataset, we assessed the confidence with which AASI can be derived in this patient, as well as the influence of different individual parameters on AASI. To assess the ability of AASI to detect large changes in arterial stiffness, two additional patients were simulated with a distensibility of 50 and 25% of the default distensibility, respectively. RESULTS: The distribution of AASI values, obtained from 10 000 ABPM simulations (each using 72 BP values randomly selected among 3125) was normal [AASI = 0.43 ±â€Š0.04 (SD)]. An increase in heart rate, distensibility or resistance from 80 to 120% of its default value caused the AASI to decrease by 37, 21 or 9%, respectively. Whereas there was no overlap in the distensibility ranges for the three theoretical patients, the amount of overlap between the AASI distributions was substantial. CONCLUSION: The confounding effects of vascular resistance and heart rate seriously limit the use of AASI as a marker of stiffness.

The change in arterial stiffness over the cardiac cycle rather than diastolic stiffness is independently associated with left ventricular mass index in healthy middle-aged individuals.

BACKGROUND: The current standard for arterial stiffness assessment, aortic pulse wave velocity (aPWV), is measured at diastolic pressure. Arterial stiffness, however, is pressure dependent. At the carotid artery level, the degree of this dependency can be quantified as the difference (ΔPWV) between systolic and diastolic (cPWVd) carotid pulse wave velocity. Biomechanically, a greater ΔPWV implies greater increases in left ventricular afterload with physical activity. Therefore, we hypothesized, that ΔPWV is more strongly associated with left ventricular mass index (LVMI) than aPWV and cPWVd. METHODS: In 1776 healthy individuals from the Asklepios cohort (age 35-55 years), ΔPWV was obtained from combined carotid artery ultrasound and tonometry recordings. Multiple linear regression analysis was performed to investigate the associations of ΔPWV, cPWVd and aPWV with LVMI, adjusting for age, sex, mean blood pressure (MBP), central pulse pressure, and other possible confounders. RESULTS: ΔPWV was 2.4 ±â€Š1.2 m/s (mean ±â€ŠSD), ranging from 0.8 m/s, indicating almost constant arterial stiffness over the cardiac cycle, to 4.4 m/s, reflecting substantial pressure dependency. ΔPWV was significantly associated with LVMI (ß of 2.46 g/m per m/s, P < 0.001), even after full adjustment (ß of 0.56 g/m per m/s, P = 0.03). cPWVd and aPWV had clear crude associations with LVMI (P < 0.001), but lost significance after adjustment (ß of -0.48 and -0.33 g/m per m/s, with P = 0.11 and 0.2, respectively). CONCLUSION: The change in arterial stiffness over the cardiac cycle, rather than diastolic stiffness, is independently associated with LVMI in healthy middle-aged individuals. Therefore, the pressure dependency of arterial stiffness should be considered in cardiovascular risk assessment.

Carotid to femoral pulse wave velocity: a comparison of real travelled aortic path lengths determined by MRI and superficial measurements.

OBJECTIVES: Carotid-femoral pulse wave velocity (PWV) is the gold standard method for determination of arterial stiffness. PWV is assessed by dividing travelled distance by travel time. Standardization and validation of the methodology for travelled distance measurement is of crucial importance. The aim of the current investigation was to standardize and validate the methodology for travelled distance measurement. METHODS: Real travelled carotid-femoral path lengths were measured with MRI in 98 healthy men/women (50% men, age 21-76 years) and are used as reference distance. This reference distance was compared with 11 estimates of aortic path length from body surface distances commonly used in PWV measurement, nine of them based on tape measures and two based on body height. Determinants of the difference between reference distance and the best body surface distance were determined. Additionally, the influence of body contours was identified. RESULTS: The tape measure distance from carotid to femoral artery (CA-FA), multiplied by 0.8, yielded the best agreement with the reference aortic path length [difference 0.26 cm (SD 3.8), not statistically significant]. Thirty percent of the variation in difference between the reference distance and tape measure distance (CA-FA × 0.8) was explained by age. Adding BMI increased this number to 34%. CONCLUSION: The tape measure distance from CA-FA, multiplied by 0.8, corresponds best with the real travelled aortic path length. This distance is moderately (yet statistically significantly) influenced by age and minimally by BMI.

Comparison of central pressure estimates obtained from SphygmoCor, Omron HEM-9000AI and carotid applanation tonometry.

BACKGROUND: The Omron HEM-9000AI is the first automated tonometer to provide an estimate of central SBP (cSBP), which is considered to be more predictive of cardiovascular events than brachial pressure. However, considerable differences between the cSBP estimate of Omron and that of SphygmoCor have been reported, but not explained. This study assesses the sources of differences between both cSBP estimates and provides a handle on which estimate is closest to reality. METHOD: For this purpose, aortic cSBP derived from calibrated carotid SBP was used as device- and algorithm-independent reference. Radial, brachial and carotid applanation tonometry were performed in 143 black South Africans, aged 39-91 years. Each individual was measured with an Omron HEM-9000AI and a SphygmoCor. RESULTS: When using both devices as advocated by their manufacturers, the corresponding cSBP estimates correlated strongly (r = 0.99, P < 0.001), but the Omron estimate was 18.8 (4.3) mmHg higher than the SphygmoCor estimate. Aortic SBP was in between both estimates: 11.7 (5.5) mmHg lower than cSBP-Omron and 7.1 (5.0) mmHg higher than cSBP-SphygmoCor. Alternative calibration of the radial SphygmoCor-curves with radial instead of brachial pressures yielded a cSBP that was 3.0 (4.2) mmHg lower than aortic SBP. The shape of the recorded pressure waves was similar in both devices: less than 5% of the observed cSBP difference was caused by differences in wave shape. CONCLUSION: The results from this study demonstrate that the considerable difference between the central pressure estimates of Omron HEM-9000AI and SphygmoCor is due to algorithm differences, and suggest that the overestimation by Omron HEM-9000AI is larger than the underestimation by SphygmoCor.

Distance measurements for the assessment of carotid to femoral pulse wave velocity.

BACKGROUND: Carotid-femoral pulse wave velocity can be determined using different distances - either direct carotid-femoral distance or subtracted [(sternal-femoral) - (carotid-sternal)] distance - resulting in pulse wave velocity differences of up to 30%. The present study aims to present and validate a population-based model for the conversion between distances. METHOD: Three thousand one hundred and sixteen participants from the Asklepios study (n = 2510) and Hôpital Européen Georges Pompidou (n = 606) databases, in which all distance measurements were available, were randomly distributed in a model (n = 311) and validation (n = 2805) population. Model parameters for the conversion equations were selected and evaluated using multiple linear regression with stepwise selection of covariates (age, sex, weight, height, BMI and waist circumference). The proposed model was evaluated on the validation population. RESULTS: The difference between direct and subtracted distances was found to be partially dependent on body height, and its inclusion in the multivariate model improved model performance by over 20%. Other combinations of adjustments did not improve model prediction. Conversion equations derived in the model population were: Estimated Direct_distance = 0.45*Subtracted_distance + 0.21*height + 0.08 and Estimated Subtracted_distance = 1.04*Direct_distance - 0.11*height - 0.02, respectively. Applying these equations for estimation of direct and subtracted distances in the validation population yielded good correspondence to measured results (r = 0.73 and 0.57, respectively), with nonsignificant mean differences between estimated and measured values. Increasing the size of the model population did not significantly change the model validity. CONCLUSION: In cases in which not all distance measurements are available for exact conversion, the presented equations can be used to convert between distance definitions.

Age and gender related patterns in carotid-femoral PWV and carotid and femoral stiffness in a large healthy, middle-aged population.

BACKGROUND: The relationship between aortic (carotid-femoral) pulse wave velocity and stiffness measures based on local diameter and pressure readings is not yet fully understood. METHODS: We compared the relationship with age and gender of aortic pulse wave velocity to stiffness indices (compliance and distensibility coefficient) evaluated at the common carotid and femoral arteries in 2195 (1131 women) apparently healthy subjects, aged 35-55 years participating in the Asklepios study. Aortic pulse wave velocity was further compared with previously reported central arterial stiffness parameters on the same population. Subjects were divided into four age groups for analysis. RESULTS: Femoral arterial stiffness was higher in men than in women (P < 0.001) but did not change with age and no age-gender interaction was evident. Carotid arterial stiffness increased with age (P < 0.001) and showed a significant (P < 0.001) age-gender interaction, with carotid stiffness increasing more rapidly in women than in men, crossing over around the age of 45. Aortic pulse wave velocity did not differ between men and women, but did increase with age (P < 0.001). No age-gender interaction was evident. CONCLUSION: The relation with age and gender of local and central stiffness measures is not the same over the age range 35-55 in apparently healthy men and women. Depending on the central stiffness parameter used, age-gender effects evident at the carotid artery are or are not found centrally. Though the relevance of these differences requires further evaluation in a longitudinal study with outcome data, they need to be kept in mind when designing or interpreting results from arterial stiffness evaluation studies.

Noninvasive (input) impedance, pulse wave velocity, and wave reflection in healthy middle-aged men and women.

The relation between arterial function indices, such as pulse wave velocity and augmentation index with parameters derived from input impedance analysis, is still incompletely understood. Carotid pressure, central flow waveforms, and pulse wave velocity were noninvasively acquired in 2026 apparently healthy, middle-aged subjects (1052 women and 974 men) 35 to 55 years old at inclusion. Input and characteristic impedance, reflection coefficient, the ratio of backward-to-forward pressure amplitude (reflection magnitude), and augmentation index were derived. Pulse wave velocity increased by 15% (from 6.1 to 7.0 m/s) both in men and women. In qualitative terms, input impedance evolved from a pattern indicative of wave transmission and reflection to a pattern more compatible with a windkessel-like system. In women, a decrease in total arterial compliance led to an increased input impedance in the low frequency range, whereas few changes were observed in men. Characteristic impedance did not change with age in women and even decreased in men (P<0.001) and could not be identified as the primary determinant of central pulse pressure. Augmentation index increased with age, as was expected, and was systematically higher in women (P<0.001). Reflection coefficient and reflection magnitude increased with age (P<0.001) without gender differences. We conclude that, in healthy middle-aged subjects, the age-related increase in arterial stiffness (pulse wave velocity) is not fully paralleled by an increase in arterial impedance, suggesting a role for age-dependent modulation of aortic cross-sectional area. Wave reflection increases with age and is not higher in women than in men.