title: Effect of passive whole body heating on central conduction and cortical excitability in multiple sclerosis patients and healthy controls.
abstract: Heat stress is associated with increased fatigue perception and decrements in function for individuals with multiple sclerosis (MS). Similarly, healthy individuals experience decrements in exercise performance during hyperthermia. Alterations in central nervous system (CNS) function during hyperthermia include reduced voluntary activation of muscle and increased effort perception. The purpose of this investigation was to test the hypothesis that passive heat exposure in MS patients will produce increased subjective fatigue and impairments in physiological measures of central conduction and cortical excitability compared with healthy individuals. Eleven healthy individuals and 11 MS patients completed a series of transcranial magnetic stimulation studies to examine central conduction and cortical excitability under thermoneutral and heat-stressed (HS) conditions at rest and after a fatiguing thumb abduction task. Passive heat stress resulted in significantly greater fatigue perception and impairments in force production in MS patients. Central motor conduction time was significantly shorter during HS in controls; however, in MS patients normal increases in conduction velocity with increased temperature were not observed centrally. MS patients also exhibited decreased cortical excitability during HS, evidenced by significant increases in resting motor threshold, decreased MEP amplitude, and decreased recruitment curve slope. Both groups exhibited postexercise depression of MEP amplitude, but the magnitude of these decrements was amplified in MS patients during HS. Taken together, these results suggest that CNS pathology in MS patients played a substantial role in reducing cortical excitability during HS.
authors.affiliation: Department of Exercise & Sport Science, University of Utah, Salt Lake City, Utah 84112, USA. andrea.white@hsc.utah.edu
authors.forename: Andrea T
authors.initials: AT
authors.lastname: White
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Vanhaitsma
authors.forename: Jamie
authors.initials: J
authors.lastname: Vener
authors.forename: Scott L
authors.initials: SL
authors.lastname: Davis
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D002490:Central Nervous System / Q000502:physiology*; D055724:Electrophysiological Phenomena / Q000502:physiology; D019054:Evoked Potentials, Motor / Q000502:physiology; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D006979:Hyperthermia, Induced; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009103:Multiple Sclerosis / Q000503:physiopathology*; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D013696:Temperature; D050781:Transcranial Magnetic Stimulation / Q000379:methods
keywords: passive hyperthermia; recruitment curve; transcranial magnetic stimulation