Impaired inactive limb blood flow regulation in adults with multiple sclerosis during sympathoexcitatory stimuli

Individuals with multiple sclerosis (MS) exhibit reduced physical capacity, partly due to autonomic dysfunction. Autonomic impairments are well documented, but peripheral blood flow regulation during exercise remains unclear. We compared peripheral vascular responses to dynamic handgrip exercise, with and without a mild sympathoexcitatory stimulation, in individuals with and without MS. Twenty-one individuals with MS (M/F: 4/17; 43 ± 10 yrs) and 27 individuals without MS (M/F: 10/17; 28 ± 6 yrs) completed a 5-min supine dynamic handgrip exercise at 15% and 30% maximal voluntary contraction, which were repeated during -20 mmHg lower body negative pressure (LBNP). BP was assessed using finger photoplethysmography, and brachial artery blood flow via ultrasound. Individuals with MS had increased forearm vascular conductance to the inactive limb at baseline and in response to exercise compared to controls (Baseline to 30% MVC with LBNP: MS: +32% vs. Non-MS: -12%; p for interaction <0.05). These changes occurred despite no differences between groups for forearm vascular conductance of the inactive limb (p for interaction = 0.523), and an attenuated increase in MAP in the group with MS during LBNP (p for interaction = 0.024). These findings suggest impaired vasomotor regulation in individuals with MS, particularly in response to combined mild sympathoexcitatory stimuli, compared to individuals without MS.