Cardiovascular Hemodynamic Response to Peak Exercise in Individuals with Multiple Sclerosis

Abstract

Multiple sclerosis (MS) is a chronic, progressive neurological condition that results in physical disability brought about, in part, by decreased aerobic capacity. Physical disability and aerobic deconditioning may increase risks of cardiovascular morbidity and mortality. The reduction in aerobic capacity may be associated with low maximal heart rate and/or low cardiac output. Yet it is unclear if the cardiovascular hemodynamic response to peak exercise differs between individuals with and without MS who have similar aerobic capacities. Purpose: To compare the cardiovascular hemodynamic response to peak exercise between individuals with and without MS, with similar aerobic capacities. We hypothesized individuals with similar aerobic capacities would also exhibit similar hemodynamic responses, regardless of disease condition. Methods: Individuals with MS (n=14 (2 males), 38 ± 8 yrs, 24.6 ± 4.5 kg/m 2 ) and without MS (n=14 (1 male), 33 ± 9 yrs, 28.8 ± 13.8 kg/m 2 ) underwent maximal incremental cycle exercise test to assess maximal aerobic capacity (VO 2 peak). Heart rate (HR) was measured continuously via Polar Heart Rate Monitor. Ascending aortic blood flow velocity images (VTI) via continuous wave Doppler echocardiography, and brachial blood pressure (BP) via brachial sphygmomanometry were obtained every other minute of the exercise test. Stroke volume (SV) was calculated from VTI and the area of the aorta, cardiac output (Q) was calculated as SV × HR, and Mean arterial pressure (MAP) was calculated from BP. Maximal arteriovenous oxygen difference (avO2diff) was calculated as VO 2 peak ⁄ Q. Results: There was no significant difference in VO 2 peak between groups (MS: 30.8 ml/kg·min -1 vs CON: 28.2 ml/kg·min -1 , p=0.65). Both groups (MS and CON) had significant time (rest to peak) differences in SV (rest: MS = 74.6 ± 32.5 mL, CON = 65.7 ± 23.1 mL, peak: MS = 114.4 ± 42.4 mL, CON = 84.2 ± 33.3 mL; p<0.001), HR (rest: MS = 65 ± 15 bpm, CON = 61 ± 10 bpm, peak: MS = 167 ± 13 bpm, CON = 175 ± 11 bpm; p<0.001), Q (rest: MS = 4.7 ± 2.2 L/m, CON = 4.0 ± 1.3 L/m, peak: MS = 12.3 ± 5.0 L/min, CON = 12.3 ± 5.1 L/min; p<0.001), and MAP (rest: MS = 84 ± 10 mmHg, CON = 83 ± 13 mmHg, peak: MS = 102 ± 7 mmHg, CON = 104 ± 17 mmHg, p <0.001). There was also a significant group by time interaction in HR (p = 0.04), but no group by time interactions in SV, Q, or MAP. Finally, there was not significant difference in avO 2 diff between groups (MS: 2.3 ± 1.2 mL/100 mL vs CON: 2.7 ± 1.5 mL/100 mL). Conclusion: Our findings suggest that individuals with MS exhibit different cardiac hemodynamics to achieve maximal aerobic capacity than those without MS. Individuals with MS reached maximal Q via a slightly higher, although statistically non-significant, stroke volume but a lower HR. This suggests that people with MS may rely on different mechanisms for achieving VO2peak compared to controls, but future research is needed to elucidate this hemodynamic pattern. Department of Defense office of the Congressionally Directed Medical Research Program on Multiple Sclerosis This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.