Brain temperature and limits on transcranial cooling in humans: quantitative modeling results

Area of Science:

• Physiology
• Thermoregulation
• Mathematical Modeling

Background:

• Selective brain cooling (SBC) is observed in mammals for thermoregulation.
• The potential for SBC in humans remains debated due to a lack of obvious specializations.

Purpose of the Study:

• To investigate the efficacy of surface cooling in regulating human cerebrum temperature using mathematical modeling.

Main Methods:

• A hemispheric model of the human brain (1.33 L) was developed, incorporating cerebrospinal fluid, skull, and scalp layers.
• The bio-heat equation was used to model thermal conduction and blood flow under varying core temperatures, air temperatures, and sweat evaporation rates.
• Model parameters were derived from existing literature for physical properties and physiological characteristics.

Main Results:

• Cerebral temperatures remained largely insensitive to external conditions, with only superficial layers (<1.5 mm) affected.
• Parenchymal temperatures stayed 0.2-0.3°C above arterial temperatures, irrespective of surface conditions, even under extreme heat and hyperthermia.
• Low surface-to-volume ratio, low tissue conductivity, and high cerebral perfusion limit the effectiveness of surface cooling methods.

Conclusions:

• Human cerebral temperature is primarily regulated by systemic mechanisms, closely following arterial temperature.
• The dense capillary network and physiological properties of the brain minimize the impact of head surface temperature on brain temperature.
• Evidence suggests a lack of significant transcranial venous flow, and surface cooling may not protect but could increase vulnerability to thermal injury.