1.2 Augmentation Index is Not a Valid Measure of Wave Reflection when it is Negative and this Distorts the Presumed Relationship Between Aging and Wave Reflection

• Published in: Artery research Vol. 4; no. 4; p. 144
• Main Authors: Hughes, A. D., Park, C. M., Davies, J. E., Curtis, S., Thom, S. A. M., Mayet, J., Parker, K. H.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-12-2010; Springer Nature B.V; BMC
• Subjects: Aging; Carotid arteries; Flow velocity; Oral Presentation Abstracts
• ISSN: 1872-9312; 1876-4401; 1876-4401
• DOI: 10.1016/j.artres.2010.10.028

Background
The relationship between aging and wave reflection has been disputed [1, 2]. Augmentation index (AI
x
) increases with increasing age, however the validity of AI
x
as a measure of wave reflection, particularly when AI
x
is negative is unknown.
Methods
Measurements of carotid pressure and flow velocity were made in the carotid artery of 65 healthy normotensive individuals (age 21–78yr; 43 male). AI
x
, wave reflection index (WRI) and P
b
/P
f
were calculated.
Results
AI
x
was positively correlated with age (beta (95% CI) = 0.46 (0.19, 0.73); p = 0.001). In contrast log WRI and P
b
/P
f
showed negative associations with age (beta (95% CI) = −0.009 (−0.016, −0.002) p = 0.01 and −0.001 (−0.001, −0.000); p = 0.001 respectively). AI
x
did not correlate with WRI or P
b
/P
f
, although AI
x
and WRI correlated weakly when AI
x
was restricted to positive values (rho = 0.35; p = 0.03). In contrast log WRI and P
b
/P
f
were closely correlated (r = 0.66; p < 0.001). Wave intensity analysis showed that negative augmentation was due to a forward decompression wave in mid systole and was consequently an unreliable indicator of reflected compression waves.
Conclusions
Augmentation index is not a valid measure of wave reflection when it is negative; this is common in younger individuals and distorts the relationship between aging and wave reflection. In healthy normotensive individuals wave reflection in the common carotid artery decreases with increasing age