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Published on: May 3, 2018
Limitation of the augmentation index for evaluating arterial stiffness
Li-Tao Cheng1, Li-Jun Tang, Lei Cheng
1Division of Nephrology, Peking University First Hospital, Beijing, PR China.
Insights
The augmentation index (AIx) may not accurately reflect arterial stiffness due to its formula. Studies show AIx can be influenced by factors other than large artery function, questioning its clinical validity.
Area of Science:
- Cardiovascular Physiology
- Biomedical Engineering
- Clinical Diagnostics
Background:
- The augmentation index (AIx) is a commonly used clinical and research metric for assessing arterial stiffness.
- Conflicting data regarding the validity of AIx in reflecting true arterial stiffness have been reported.
- Previous studies have shown contradictory findings, particularly in patient populations like diabetics.
Purpose of the Study:
- To rigorously test the validity of the augmentation index (AIx) as a reliable measure of arterial stiffness.
- To investigate the mathematical and clinical factors influencing AIx values.
- To determine if AIx is a sensitive surrogate for changes in central pressure waveforms and large artery function.
Main Methods:
- Conducted three studies involving 196 peritoneal dialysis patients and mathematical ratiocination.
- Analyzed the correlation between AIx, pulse pressure (PP), augmentation pressure (AP), and central PP (C-PP).
- Utilized mathematical modeling to explore the dependency of AIx on various pressure waveform components (P1, P2, DP).
Main Results:
- AIx in diabetic patients was found to be lower than in non-diabetic patients, contradicting prior research.
- AIx showed only a weak correlation with pulse pressure, a known index of arterial stiffness.
- Mathematical analysis revealed AIx is dependent on multiple factors beyond arterial stiffness, indicating a potential flaw in its formula.
Conclusions:
- The augmentation index (AIx) may not be a sensitive or reliable indicator of changes in central pressure waveforms or large artery function.
- The formula used to calculate AIx possesses a mathematical flaw, limiting its utility as a precise measure of arterial stiffness.
- Further research and validation are needed to address the limitations of AIx in clinical and research settings.
Abstract:
Although the augmentation index (AIx) is widely used to evaluate arterial stiffness in clinics and research, some conflicting data exist in regard to its validity. We therefore performed a series of studies to test the validity of AIx. The first study in 196 peritoneal dialysis patients showed that AIx in diabetics was lower than that in non-diabetic patients (p<0.05), which was in contradiction with the previous studies. Further analysis showed that AIx was just weakly correlated with pulse pressure (PP)-a known index of arterial stiffness. We also found that the increase of augmentation pressure (AP) was usually accompanied with increased central PP (C-PP). As AP and C-PP are used as the numerator and denominator in the AIx formula, an increase in the numerator (AP) would not necessarily result in an increase of the quotient (AIx) unless the denominator (C-PP) was stable. We then conducted a second study trying to test the validity of AIx through mathematical ratiocination. The increases in the central second peak (P2) and AP were assumed to represent increased arterial stiffness. Different values of AIx were obtained by varying the central initial systolic peak (P1) and diastolic pressure (DP). Mathematical ratiocination showed that AIx was dependent on multiple factors, F=(DeltaSP-DeltaDP)x(P1-P2)+(DeltaP2-DeltaP1)x(SP-DP), which suggested that a change of AIx would not always be attributable to changes in P2 and AP. This speculation was further proved by clinical data in our third study. In conclusion, through a series of studies and ratiocination, we showed that the augmentation index (AIx or AIx@75bpm) might not be a sensitive surrogate for a change in central pressure waveforms, which is a manifestation of change in large artery function. The limitation of AIx as an index of arterial stiffness is rooted in its formula, which has a clear mathematical flaw.
