Assessment of Vascular Function: Pulse Wave Velocity
Article Outline
Abbreviations: baPWV, Brachial-ankle pulse wave velocity, CVD, Cardiovascular disease, PWV, Pulse wave velocity
In recent years, several non-invasive techniques have been developed and tested to measure vascular properties that may predict later-onset cardiovascular morbidity and mortality. Among these properties are arterial compliance, distensibility, and stiffness. These measures represent different facets of arterial structure and function. Three different approaches of investigation have been developed in adults: analysis of pressure waveforms; vessel diameter changes in response to pressure changes; and measuring pulse wave velocity.
See related article, p 247
Arterial pulse waveform analysis is performed by application tonometry, which requires a transfer function to derive central aortic waveforms. The derivation and validation procedures require intra-arterial catheter measurements, excluding this technology for children, who cannot be enrolled in such studies.
Arterial distensibility is the change in vessel size (diameter as a proxy for cross-sectional area) in response to pressure change. It is a reciprocal of arterial stiffness, estimating vessel elastic properties. The vessel diameters are measured with ultrasound scanning. Studies in adults have shown impairments in patients with hypertension, diabetes mellitus, and dyslipidemia. The measures also predict future adverse cardiovascular outcomes. Few studies have been performed in children, but the results have shown data that parallel adult study results. The limitations to this technique include the precision with which vessel measurements must be done and the extrapolation of the vascular pressures obtained at a site distant from the ultrasound scanning measures. In addition, the process of pressure application at the skin over the artery will alter the vessel shape and pressure waveform.
In this issue of The Journal of Pediatrics, Im et al report their findings of brachial-ankle pulse wave velocity (baPWV) and its correlations with known risk factors for cardiovascular disease (CVD) in a population of healthy Korean adolescents.1 Pulse wave velocity (PWV) measurement as a surrogate for arterial stiffness was first reported in 1922, but only recently were automated devices produced to measure it. It is now recognized as being a highly sensitive measurement of arterial tree stiffness and a strong predictor of CVD mortality in adults. It is non-invasive and has been validated repeatedly in adults. PWV increases as arteries become more damaged and stiffer. Therefore PWV is highly associated with atherosclerotic and hypertensive vessel pathologies. Blancher et al have stated that PWV is the strongest independent predictor of clinical cardiovascular morbidity.2
There are several methodologies to measure PWV, but each detects the onset of the pressure wave form in relation to an electrocardiogram time point. The distance along the arterial tree is measured/estimated and the velocity calculated.
Studies in adults are now plentiful and have been performed in patients with many chronic diseases known to increase cardiovascular pathology. Studies in children are limited, but have been performed in healthy volunteers and patients with diabetes mellitus, neurofibromatosis, snoring, Kawasaki’s disease, polyarteritis nodosa, and coarctation of the aorta after surgical repair.
The automated system used by Im et al uses oscillometric pressure cuffs to obtain measurements at the brachia and ankles. The results from this technique give higher PWV values compared with carotid-femoral measurements, because baPWV reflects wavefront transmissions in both central (elastic) and peripheral (muscular) arteries. Our laboratory recently reported baPWV measures in 205 normotensive, healthy adolescents.3 We found that baPWV was greater in male patients than in female patients, and, probably more importantly, higher in African-American than Caucasian volunteers between the ages of 12 and 21 years. Our results were similar to those found in another biracial community in the Southern United States.4
The results reported by Im et al confirm our earlier findings and those of Niboshi et al,5 who compared male and female adolescents. Their group was able to measure the associations of baPWV to many recognized cardiovascular risk factors, including body mass index, waist circumference, waist-hip ratio, systolic and diastolic blood pressure, insulin measures, triglyceride levels, C-reactive protein levels, and homocysteine levels. In separate analyses by sex, other risk factors were also significantly related to baPWV.
Im et al used the exclusion criterion of a resting blood pressure >140/90 mm Hg to define hypertension. This threshold is an adult criterion for hypertension and would indicate significantly elevated blood pressure (clinical hypertension) in some of the age groups represented. Because percentile blood pressure measurements based on sex, age, and height6 are typically used in the United States to define hypertension in pediatric populations, the use of such an adult threshold is likely to have allowed subjects to participate who had elevated blood pressure on the basis of appropriate percentile standards. This does not invalidate the findings presented in this paper. However, it likely would, to some extent, change the statistical significance of the sex differences reported for baPWV because the presence of blood pressure elevation is known to increase PWV significantly.
The value of a totally non-invasive marker for later-onset CVD is, as the current media commercial says, “priceless.” If primary care physicians could screen youth for early signs of atherosclerosis and implement early, effective interventions, morbidity and mortality from CVD, the leading cause of death in Westernized societies, could be substantially reduced. More data are needed from populations worldwide for a “normal control” database. Longitudinal studies from childhood would establish the true value of baPWV in preventive cardiology. The data extant suggest that PWV is a useful research method and perhaps should become a more routine screening test in high-risk populations of youth.
References
- . Association between brachial-ankle pulse wave velocity and cardiovascular risk factors in healthy adolescents. J Pediatr. 2007;150:247–251
- . Aortic pulse wave as a marker of cardiovascular risk in hypertensive patients. Hypertension. 1999;33:1111–1117
- . Differences in arterial compliance among normotensive adolescent groups [abstract]. Am J Hypertens. 2006;8:A11
- . Childhood blood pressure as a predictor of arterial stiffness in young adults: the Bogalusa Heart Study. Hypertension. 2004;43:541–546
- . Characteristics of brachial-ankle pulse wave velocity in Japanese children. Eur J Pediatr. 2006;165:625–629
- . The fourth report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents. Pediatrics. 2004;114(Suppl 2):1–22
PII: S0022-3476(06)01215-7
doi:10.1016/j.jpeds.2006.12.042
© 2007 Mosby, Inc. All rights reserved.
Refers to article:
- Association between Brachial-Ankle Pulse Wave Velocity and Cardiovascular Risk Factors in Healthy Adolescents
