A second-order biomechanical model of flow-mediated dilation response in obese post-menopausal women

Abstract

Endothelial function (EF) can be assessed via flow-mediated dilation (FMD) and act as a surrogate indicator of general cardiovascular health. A recently completed project studied how 1 session of exercise can affect EF. This study consisted of eleven, obese post-menopausal women aged 54 to 70, and they were subjected to two one-hour sessions (on separate visits) of exercise at 50% and 70% of their maximum heart rate, as well as a resting control trial. Their EF was evaluated before and immediately after exercise and at two, 24, 48, and 72 hours post-exercise via FMD measurements using ultrasound images of the brachial artery. Images were made at each of these time-points before 5 minutes of occlusion by a pressure cuff and for 5 minutes after (at 30 second intervals) the occlusion was removed. The usual metrics derived from these measurements, e.g., maximum dilation, led to the conclusion that this study did not show there was a statistically significant difference in EF resulting from either of these exercise sessions. Alternatively, we propose to model the time response of the endothelial diameter's deviation from its baseline value by a linear mass-spring-damper system in order to determine (in subsequent work) if that model's parameters may be useful for assessing EF. Our results indicate that these FMD time responses, at rest and after exercise, are modeled reasonably well by such a system, although there is not insignificant variability of the goodness-of-fit, with R2 varying between 0.00279 and 0.957 (mean 0.534, SD 0.261). From the estimated model parameters, the endothelium's natural frequency was calculated to be between 2.51 x10-6 and 0.101 (mean 0.00887, SD 0.0102) radians/s; although it should be noted that the better fitting results mostly yield a natural frequency higher than this mean, while the worse fitting results mostly yield a natural frequency lower than this mean. © 2010 International Federation for Medical and Biological Engineering.