Cardiovagal Tone: A Predictor of Heart Rate Adjusted Augmentation Index in Men but Not in Women

Abstract

Purpose: Aortic augmentation index (AIx) and cardiovagal tone (CVT) are indicators of cardiovascular health. Associations between these variables provide information about their roles in cardiovascular disease. However, evaluating these associations from a gender perspective and gaining an understanding of the relationship between cardiorespiratory fitness and AIx based on gender can provide additional information. Therefore, we examined the relationships between CVT, measured as the log transformed high-frequency power of R-R intervals from electrocardiogram measurements (lnHFR-R); cardiorespiratory fitness, measured as maximum oxygen consumption (VO2max); and AIx at a heart rate of 75 beats·min-1(AIx@75). We hypothesized that the relationships between CVT, cardiorespiratory fitness, and AIx@75 would differ based on gender. Methods: We examined the associations between lnHFR-R, VO2max, and AIx@75 in 41 women and 39 men. Power spectral density analysis of heart rate variability determined lnHFR-R, radial tonometry determined AIx@75 and the Bruce Treadmill Protocol determined VO2max. Results: In men, lnHFR-R positively correlated with and significantly predicted AIx@75 (P = 0.005) but not in women (P = 0.49). For every unit increase in lnHFR-R, there was a 4.6 unit increase in AIx@75 in men versus a 1.0 unit increase in women. There was a significant inverse relationship between VO2max and AIx@75, with VO2max being a significant predictor of AIx@75 in men (P = 0.01). For every unit increase in VO2max, there was a 0.60 unit decrease in AIx@75 in men versus a 0.2 unit decrease in women. Conclusions: The associations between CVT and AIx@75 and between cardiorespiratory fitness and AIx@75 differ by gender. CVT and cardiorespiratory fitness are significant predictors of AIx@75 in men but not in women.