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Cerebrovascular and corticomotor function during progressive passive hyperthermia in humans
Emma Z Ross1, James D Cotter, Luke Wilson
1Univ. of Brighton, Chelsea School, Denton Road, Eastbourne BN20 7SR, UK. e.z.ross@brighton.ac.uk
Journal of Applied Physiology (Bethesda, Md. : 1985)
|December 3, 2011
Summary
Passive heating impairs central motor drive and maximal voluntary contraction by reducing cerebral blood flow and causing hypocapnia. Restoring eucapnia with CO2 partially reverses these effects, suggesting a link between brain perfusion, CO2 levels, and motor control during heat stress.
Area of Science:
- Physiology
- Neuroscience
- Environmental Health
Background:
- Passive heating is a common environmental stressor.
- Understanding its effects on the central nervous system is crucial for performance and safety.
- Previous research has explored hyperthermia's impact on physiological systems, but its specific effects on central motor control require further elucidation.
Purpose of the Study:
- To investigate the integrative effects of passive heating on cerebral perfusion and central motor drive.
- To determine how increasing core body temperature affects neuromuscular and cortical function.
- To examine the role of cerebral blood flow and CO2 levels in mediating these changes.
Main Methods:
- Eight participants underwent passive hyperthermia with incremental increases in core temperature.
- Cerebral blood flow velocity (CBFv) and respiratory responses were continuously monitored.
- Femoral nerve stimulation and transcranial magnetic stimulation (TMS) assessed neuromuscular and cortical voluntary activation (VA).
Main Results:
- Cerebral blood flow velocity (CBFv) decreased by approximately 20% from baseline.
- Maximal voluntary contraction (MVC) and cortical voluntary activation (VA) were significantly reduced at higher core temperatures.
- Reductions in cortical VA correlated with changes in ventilation, end-tidal CO2, and CBFv.
Conclusions:
- Passive heating progressively impairs descending voluntary motor drive as core temperature increases.
- Reduced cerebral blood flow and hyperthermia-induced hypocapnia contribute to this impairment.
- Restoring eucapnia with CO2 partially reversed deficits in MVC and cortical VA, highlighting the importance of CO2 homeostasis and brain perfusion.
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