Reply
SIR—We thank Dr Soiza, Williams and Crilly for their interest in our paper regarding the relationships between applanation tonometry, pulse wave analyses and age.Their experience, although in a smaller population than ours, substantially confirms our findings of a linear regression of Augmentation Pressure (AG) on age and a quadratic regression of Augmentation Index (AI) on age [1]. In fact they found an initial linear regression for AI before levelling off at 55 years whilst a plateau only after 75 years for AG. They conclude that this final dip reflects a possible ‘healthy survivor effect’ rather than a true physiological reversal of arterial ageing. We agree that cross-sectional data are difficult to interpret in this type of study. However, our findings of a linear regression of AG on age clearly show that there is an increased stiffness in old age also in our study populations, confirming previous studies [2–4]. Taking into consideration this finding, it is difficult to consider that the quadratic regression of AI on age reflects a ‘healthy survivor effect’. If this was so we would have found a quadratic regression for both the indices and not only for AI. AI does not increase with age in old age because of the method used to calculate AI, which includes a denominator Pulse Pressure (PP) [1]. PP increases disproportionately with age compared with AG and AI should not be considered a surrogate of biological age in the elderly.
For this reason we still suggest that AI should not be employed in an older population as there is physiological increase of PP [5] which negatively influences the measure of AI.
AG, which is the real measure of contribution that the wave reflection makes to the systolic arterial pressure, measured in mmHg, does not take into consideration PP and, especially in the elderly, is a better index of arterial function and overall cardiovascular health than AI.
We agree with Soiza et al. that AI varied with heart rate (HR) [6] and for this reason we compared the two groups of the study population (under and over 55 years) in terms of HR and we did not find any significant differences.
Of course we agree that some further and possibly longitudinal studies are required before using pulse wave analytic analysis in clinical practice.
1 Brighton and Sussex Medical School, Brighton, UK
2 Section of Geriatric Medicine, Imperial College School of Medicine, London, UK
* To whom correspondence should be addressed Email: francescofantin{at}hotmail.com
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[Abstract/Free Full Text]
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