Is 24-hour augmentation index a better indicator of arterial stiffness compared to clinic augmentation index?

Abstract

Arterial Stiffness is a major independent risk factor that is strongly associated with an increased risk of developing cardiovascular diseases (CVDs), making it an important marker in the assessment of CVD risk. Therefore, in an effort to reduce the rising incidence of cardiovascular diseases in South Africa, it is crucial to determine the best indicator for arterial stiffness. Currently two indices are used to measure arterial stiffness, pulse wave velocity (PWV) and augmentation index (AI). Since arterial stiffness measurement techniques were developed much later than blood pressure (BP) measurement techniques, important lessons can be learned from BP measurement. Studies have indicated that 24-hour BP measurement is a much better tool of measurement compared to a once off conventional BP measurement. This creates a possibility that 24-hour arterial stiffness assessment is a better tool for measuring arterial stiffness compared to a once off clinic arterial stiffness measurement. Therefore, in this study we compared 24-hour AI to in-clinic AI and also assessed gender differences. Previous studies conducted on 24-hour AI were focused on establishing normal 24-hour AI reference values. To date, no studies have been conducted to compare 24-hour AI to in-clinic AI. Moreover, gender differences in the 24-hour arterial stiffness profile have never been studied. We recruited 125 individuals of black African descent and took anthropometric measurements. We measured both conventional BP and 24-hour BP. Pulse wave analysis was performed to obtain both in-clinic and 24-hour AI. In the total population, 24-hour augmentation index (AI24) was significantly higher than in-clinic augmentation index (AIC) (p<0.0001). When participants were stratified according to gender, AI24 was significantly higher than AIC in both men (p<0.0001) and women (p<0.0001). Night-time augmentation index (AIN) in the total population was significantly higher than daytime augmentation index (AID) (p=0.0143). When participants were stratified according to gender, our results show that AIN was only significantly higher in women (p=0.0291) and not in men. Our results show that AIC may grossly be underestimating the prevalence of arterial stiffness and its adverse effects on cardiovascular target organs. Secondly, our results also show that there are gender differences in arterial stiffness fluctuations over the 24-hour period. In men, daytime arterial stiffness does not differ from night-time arterial stiffness. However, in women arteries become stiffer during the night-time compared to the daytime. These findings indicate that special attention must be given to night-time arterial stiffness because it may be more closely related to target organ damage than daytime arterial stiffness.