Mehmet Kaya1, Vignesh Balasubramanian2, John K-J Li3. 1. Department of Biomedical and Chemical Engineering and Sciences, Florida Institute of Technology, 150 W University Blvd, Melbourne, FL, 32901, USA. Electronic address: mkaya@fit.edu. 2. Department of Biomedical and Chemical Engineering and Sciences, Florida Institute of Technology, 150 W University Blvd, Melbourne, FL, 32901, USA. Electronic address: vbalasubrama2016@my.fit.edu. 3. Department of Biomedical Engineering, and Robert Wood Johnson Medical School, Rutgers University, The State University of New Jersey, 599 Taylor Road, Piscataway, NJ, 08854, USA. Electronic address: johnkjli@soe.rutgers.edu.
Abstract
BACKGROUND: Augmentation index (AIx) is used to quantify the augmented systolic aortic pressure that impedes ventricular ejection. Its use as an index of wave reflections is questionable. We hypothesize that AIx is quantitatively different from the reflection coefficient under varied physiological conditions. METHODS: 42 datasets of aortic pressure and flow waveforms were obtained during induced hypertension (methoxamine infusion) and vasodilation (nitroprusside infusion) in our mongrel dog experiments (n = 5) and from Mendeley data during various interventions (vasoconstrictors, vasodilators, pacing, stimulation, hemorrhage and hemodilution). Wave reflections and principal components of reflection coefficients were computed for comparison to AIx and heart rate normalized AIx. RESULTS: Principal reflection coefficient, Γ1, increased in hypertension and decreased in vasodilation, hemorrhage and hemodilution. AIx followed the trend in many cases but was consistently lower than Γ1 in almost all the subjects. The Bland-Altman analysis also showed that both AIx and normalized AIx underestimated Γ1. The relationship between augmentation index and reflection coefficient was explained by a linear regression model (r2 = 0.23, p < 0.01) in which AIx followed directional changes in Γ1 and the normalization of AIx resulted in a linear model that explained less variation in the relationship between AIx and Γ1. CONCLUSION: AIx is a reasonable clinical trend indicator, albeit not an accurate surrogate measure of the amount of wave reflections.
BACKGROUND: Augmentation index (AIx) is used to quantify the augmented systolic aortic pressure that impedes ventricular ejection. Its use as an index of wave reflections is questionable. We hypothesize that AIx is quantitatively different from the reflection coefficient under varied physiological conditions. METHODS: 42 datasets of aortic pressure and flow waveforms were obtained during induced hypertension (methoxamine infusion) and vasodilation (nitroprusside infusion) in our mongrel dog experiments (n = 5) and from Mendeley data during various interventions (vasoconstrictors, vasodilators, pacing, stimulation, hemorrhage and hemodilution). Wave reflections and principal components of reflection coefficients were computed for comparison to AIx and heart rate normalized AIx. RESULTS: Principal reflection coefficient, Γ1, increased in hypertension and decreased in vasodilation, hemorrhage and hemodilution. AIx followed the trend in many cases but was consistently lower than Γ1 in almost all the subjects. The Bland-Altman analysis also showed that both AIx and normalized AIx underestimated Γ1. The relationship between augmentation index and reflection coefficient was explained by a linear regression model (r2 = 0.23, p < 0.01) in which AIx followed directional changes in Γ1 and the normalization of AIx resulted in a linear model that explained less variation in the relationship between AIx and Γ1. CONCLUSION: AIx is a reasonable clinical trend indicator, albeit not an accurate surrogate measure of the amount of wave reflections.
Authors: Ronald J Headid; Elizabeth J Pekas; TeSean K Wooden; Won-Mok Son; Gwenael Layec; John Shin; Song-Young Park Journal: Am J Physiol Heart Circ Physiol Date: 2020-07-10 Impact factor: 4.733
Authors: Elizabeth J Pekas; TeSean K Wooden; Santosh K Yadav; Song-Young Park Journal: Am J Physiol Regul Integr Comp Physiol Date: 2021-06-23 Impact factor: 3.210