Consumer devices that can measure useful age-related cardiovascular metrics such as pulse wave velocity and heart rate variability are not that great in comparison to the much more expensive lines of medical devices. The most important difference lies in whether measuring these parameters in the periphery (arm, wrist, finger) or in the body itself (neck, torso). There is a lot more noise in the periphery, and these are already noisy metrics by their nature, prone to a lot of moment to moment and circumstantial variance. If pulse wave velocity is 6.3 m/s on day one and 8.5 m/s on day two, an entirely likely outcome, what exactly is one supposed to do with that information, other than resign oneself to a two to three week process of twice daily measurements in order to obtain a meaningful average? Still, more options are better, and researchers here suggest a metric that appears to correlate decently with cardiovascular aging, and which could in principle be added to any existing device via a suitable software update.
As age increases, the elasticity of arterial vessels decreases, and the inner diameter widens due to changes in the mechanical properties of blood vessels and the cardiovascular system. A decrease in elasticity leads to the stiffness of arterial vessels increasing and the reflected wave returning quickly, and abnormalities in proximal aortic diameter are responsible for the abnormal aortic pressure-flow relationship. This phenomenon increases arterial pressure, which elevates the risk of cardiovascular disease (CVD), including hypertension. Therefore, examining these age-related changes in arterial stiffness and appropriate indicators reflecting the stiffness caused by cardiovascular aging are important to prevent risk factors for CVD.
The pulse wave velocity (PWV), one of the representative indicators of arterial stiffness, is the speed at which a blood pressure pulse wave propagates through the arterial system. There is a distance measurement error caused by assuming a straight arterial segment, and in the most frequently used carotid-femoral PWV, the carotid and femoral pulse waves traveling in opposite directions cause overestimation of the PWV. Another measure of arterial stiffness is the augmentation index (AIx), which is the ratio of the height of the peak above the shoulder of the wave to the pulse pressure. The AIx is easier to measure and less time consuming than the PWV; additionally, the AIx enables observation of the reflective properties of the arteries. The AIx increases with age and blood pressure, which has been explained by the fact that wave reflection increases with age.
The sharpness of the pulse wave is a representative characteristic in pulse waveform analysis. Because it is well known that blunter waveforms are generally found in older people, whereas sharper pulse waveforms are found in younger people, pulse sharpness could reflect age-related characteristics, such as vascular aging or arterial stiffness, as well as the AIx. In addition, as the average pulse morphology variability near the peak point of the percussive wave was less than only 2% in a previous study, pulse sharpness could be an index with low variability. However, despite these intuitive considerations of pulse sharpness, few studies have been explored the availability of sharpness as an indicator of vascular aging or arterial stiffness, unlike the AIx. In addition, a formally accepted algorithm for detecting sharpness has not been reported.
The aim of this study was to develop a robust algorithm to quantify pulse sharpness that can complement the limitations of radial augmentation index (rAIx) and explore the role of this quantitative sharpness index in reflecting vascular aging or arterial stiffness. The pulse sharpness index (PSI) was developed by combining the end point angle and virtual height, and 528 radial pulses were analyzed.
Significant sex differences were identified in the rAIx and PSI, and significant age-dependent decreases in the PSI were observed. In addition, the PSI and age were correlated (r = - 0.550) at least as strongly as the rAIx and age (r = 0.532), and the PSI had a significant negative correlation with arterial stiffness (r = - 0.700). Furthermore, the multiple linear regression model for arterial stiffness using the PSI, age, sex and heart rate showed the excellent performance, and the PSI was found to have the greatest influence on arterial stiffness. This study confirmed that the PSI could be a quantitative index of vascular aging and has potential for use in inferring arterial stiffness with an advantage over the rAIx.