Impaired Thermoregulatory Function during Dynamic Exercise in Multiple Sclerosis

Abstract

Introduction: Impairments in sudomotor function during passive whole-body heating have been reported in multiple sclerosis (MS), a demyelinating disease of the CNS that disrupts autonomic function. However, the capability of the thermoregulatory system to control body temperature during exercise has never been assessed in MS. Thus, the aim of the present study was to test the hypothesis that thermoregulatory function is impaired in MS patients compared with healthy controls (CON) exercising at similar rates of metabolic heat production.

Methods: Sweating and skin blood flow responses were compared between 12 individuals diagnosed with relapsing-remitting MS (9 females, 3 males) and 12 sex-, age-, mass-, and BSA-matched CON during a single bout of cycling exercise (rate of metabolic heat production: ∼4.5 W·kg) for 60 min in a climate-controlled room (25°C, 30% RH).

Results: Individuals with MS exhibited an attenuated increase in cumulative whole-body sweat loss after 30 min (MS, 72 ± 51 g; CON, 104 ± 37 g; P = 0.04) and 60 min (MS, 209 ± 94 g; CON, 285 ± 62 g; P = 0.02), as well as lower sweating thermosensitivity (MS, 0.49 ± 0.26 mg·cm·min·°C; CON, 0.86 ± 0.30 mg·cm·min·°C; P = 0.049). Despite evidence for thermoregulatory dysfunction, there were no differences between MS and CON in esophageal or rectal temperatures at 30- or 60-min time points (P > 0.05). Cutaneous vasculature responses were also not different in MS compared with CON (P > 0.05).

Conclusion: Taken together, MS blunts sweating responses during exercise while cutaneous vasculature responses are preserved. Altered mechanisms of body temperature regulation in persons with MS may lead to temporary worsening of disease symptoms and limit exercise tolerance under more thermally challenging conditions.

Figure 1.

Mean changes in esophageal temperature (∆T_eso) from resting baseline (±SD) at 30 min and 60 min of exercise at a fixed rate of heat production in persons with multiple sclerosis (MS) and healthy controls (CON; panel A); individual changes in esophageal temperature (∆T_eso) from resting baseline for each healthy control during exercise (panel B); individual changes in esophageal temperature (∆T_eso) from resting baseline for each individual with MS during exercise (panel C).

Figure 2.

Mean changes in rectal temperature (∆T_rec) from resting baseline (±SD) at 30 min and 60 min of exercise at a fixed rate of heat production in persons with multiple sclerosis (MS) and healthy controls (CON; panel A); individual changes in rectal temperature (∆T_rec) from resting baseline for each healthy control during exercise (panel B); individual changes in rectal temperature (∆T_rec) from resting baseline for each individual with MS during exercise (panel C).

Figure 3.

Mean changes in local sweat rate (∆LSR) from resting baseline (±SD) at 30 min and 60 min of exercise at a fixed rate of heat production in persons with multiple sclerosis (MS) and healthy controls (CON, panel A); individual changes in mean local sweat rate (∆LSR) from resting baseline for each healthy control during exercise (panel B), individual changes in mean local sweat rate (∆LSR) for each individual with MS during exercise (panel C).

Figure 4.

Mean changes in whole-body sweat loss (WBSL) from resting baseline (±SD) at 30 min and 60 min of exercise at a fixed rate of heat production in persons with multiple sclerosis (MS) and healthy controls (CON). *Significantly different from CON.

Figure 5.

Mean changes in cutaneous vascular conductance (∆CVC_max) from resting baseline (±SD) at 30 min and 60 min of exercise at a fixed rate of heat production in persons with multiple (MS) and healthy controls (CON); individual changes in mean cutaneous vascular conductance (∆CVC_max) for each healthy control during exercise (panel B); individual changes in mean cutaneous vascular conductance (∆CVC_max) for each individual with MS during exercise (panel C).

Figure 6.

Mean slope (±SD) of the relationship between local sweat rate (∆LSR) relative to changes in T_eso (i.e., thermosensitivity) during exercise at a fixed rate of heat production in persons with multiple sclerosis (MS) and healthy controls (CON; panel A); representative individual tracings of changes in local sweat rate (∆LSR) expressed relative to the change in esophageal temperature (T_eso) from one individual with MS and a matched healthy control (panel B); mean slope (±SD) of the relationship between cutaneous vascular conductance (∆CVC_max) relative to changes in T_eso (i.e., thermosensitivity) during exercise in persons with multiple sclerosis (MS) and healthy controls (CON, panel C); representative individual tracings of changes in cutaneous vascular conductance (∆CVC_max) expressed relative to the change in mean esophageal temperature (T_eso) from one individual with MS and a matched healthy control (panel D). *Significantly different than CON.