Effects of heart rate on arterial stiffness

Both elevated heart rate (HR) and increased arterial wall stiffness are independent predictors for cardiovascular disease and mortality. Whilst it is well established that arteries stiffen with age and increased blood pressure (BP), research findings to date have failed to converge on the relationship between HR and arterial stiffness. This thesis explores the HR-arterial stiffness relationship through the study of pulse wave velocity (PWV) changes, a surrogate measure of arterial stiffness, with changes in HR induced by artificial cardiac pacing in both rodents and humans. In both the rodent study and human study, HR was shown to exert an independent effect on PWV, with PWV increasing as HR increased, and the intrinsic HR dependency of PWV was quantified in the human study as 0.17 m/s per 10 bpm increase in HR. As external cardiac pacing is often used as a means to induce HR changes, as it was in the studies in this thesis,the effect of different pacing modalities on indices of pulse wave analysis and arterial stiffness was also explored. Practical applications of the associations between HR, BP and PWV were also demonstrated through the estimation of systolic times that utilised pulse wave analysis and PWV. To investigate a possible mechanism by which HR exerts an influence on arterial stiffness,a computerised transmission line model of the human arterial tree was utilised to simulate effects of HR on PWV at different scenarios where arterial wall elasticity was modelled with varying frequency dependence. Model simulations showed that frequency dependency of arterial wall elasticity, beyond a critical point, could partly explain the observed increases in PWV with increasing HR. The findings in this thesis not only lend further evidence to an independent HR effect on arterial stiffness, but also provide an insight into the mechanisms behind this relationship. Quantification of the intrinsic HR dependency on PWV will allow for practical application of this established relationship in future cardiovascular studies.