Ventricular-Vascular Coupling in Individuals with Multiple Sclerosis

Multiple Sclerosis (MS) is a chronic neuroinflammatory disease of the central nervous system that is a leading cause of morbidity and disability in young adults. Ultimately, individuals with MS have an increased risk of all-cause mortality, partly due to higher cardiovascular mortality. Aerobic capacity, a marker of total health and a strong independent predictor of cardiovascular disease and mortality among the general population, is typically reduced in individuals with MS. Aerobic capacity depends on the ability of the cardiac and vascular system to meet increased demand, achieved via complex alterations of both the cardiac and vascular systems as well as the interaction of the systems. Understanding the mechanisms of reduced aerobic capacity in individuals with MS may present opportunities for targeted disease treatment to lower cardiovascular disease risk in this population. Therefore, the overall objective of this project was to understand the cardiovascular response to exercise in individuals with MS. To determine potential physiologic limitations to exercise we investigated the hemodynamic response to maximal exercise in twenty-one individuals with and twenty-one without MS. Additionally, we examined the interaction between the cardiac and vascular systems, termed ventricular vascular coupling, before, after, and in a subset of individuals during exercise to determine if coupling was different between individuals with and without MS. Our cohort was relatively fit, as those with MS achieved about ninety-five percent of the general populations age-predicted aerobic capacity. Aerobic capacity was not different between those with and without MS. We found similar hemodynamic responses to maximal exercise in individuals with MS and without MS, likely due to similar aerobic capacities. However, unfit individuals with MS exhibited higher blood pressure than fit individuals with MS. In contrast, higher fit and unfit controls exhibited similar blood pressures. Ventricular vascular coupling was also similar between individuals with and without MS. However, even with similar aerobic capacity, individuals with MS exhibited higher arterial and ventricular elastance than those without MS, primarily as a function of higher pressure needed to facilitate the same blood volume. The implications of this study are two-fold. First, fitness is important in individuals with MS. Even with moderate disability, individuals with MS can be seemingly free from physiologic exercise limitations, suggesting exercise may partially serve as protection from disease-related impairments. Second, although ventricular vascular coupling was similar between groups, greater arterial and ventricular elastance suggest individuals with MS may experience increased cardiovascular load and reduced efficiency. Taken together, while fitness is important and likely offers some protection against cardiovascular impairments in this population, disease mediated impairments may contribute to the increased cardiovascular risk and mortality of individuals with MS.