Journal
JOURNAL OF APPLIED PHYSIOLOGY
Volume 130, Issue 3, Pages 792-800Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/japplphysiol.00645.2020
Keywords
heat stress; brain; neurovascular unit
Categories
Funding
- National Science and Engineering Research Council Grant [DG RGPIN-2020-05760]
- Swedish Research Council [2018-02532, 2017-00915]
- European Research Council [681712]
- Swedish State Support for Clinical Research [ALFGBG-720931]
- Alzheimer Drug Discovery Foundation (ADDF) USA Grant [201809-2016862]
- UK Dementia Research Institute at UCL
- Alzheimer Drug Discovery Foundation USA [RDAPB-201809-2016615]
- Swedish Alzheimer Foundation [AF-742881]
- Hj_arnfonden, Sweden [FO2017-0243]
- Swedish government [ALFGBG-715986]
- Swedish County Councils, the ALF-agreement [ALFGBG-715986]
- European Union Joint Program for Neurodegenerative Disorders [JPND2019-466-236]
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The study demonstrates that passive heating for approximately 1 hour until an increase of +2 degrees Celsius in esophageal temperature in healthy men does not lead to increased release of neuronal parenchymal stress biomarkers in the brain, suggesting the integrity of the neurovascular unit is maintained. This preliminary study suggests that passive heating is safe for the brain, at least in young healthy men.
With growing use for hyperthermia as a cardiovascular therapeutic, there is surprisingly little information regarding the acute effects it may have on the integrity of the neurovascular unit (NVU). Indeed, relying on animal data would suggest hyperthermia comparable to levels attained in thermal therapy will disrupt the blood-brain barrier (BBB) and damage the cerebral parenchymal cells. We sought to address the hypothesis that controlled passive hyperthermia is not sufficient to damage the NVU in healthy humans. Young men (n = 11) underwent acute passive heating until +2 degrees C or absolute esophageal temperature of 39.5 degrees C. The presence of BBB opening was determined by trans-cerebral exchange kinetics (radial-arterial and jugular venous cannulation) of S100B. Neuronal parenchymal damage was determined by the trans-cerebral exchange of tau protein, neuron-specific enolase (NSE), and neurofilament-light protein (NF-L). Cerebral blood flow to calculate exchange kinetics was measured by duplex ultrasound of the right internal carotid and left vertebral artery. Passive heating was performed via a warm-water perfused suit. In hyperthermia, there was no increase in the cerebral exchange of S100B (P = 0.327), tau protein (P = 0.626), NF-L (P = 0.447), or NSE (P = 0.908) suggesting the +2 degrees C core temperature is not sufficient to acutely stress the NVU in healthy men. However, there was a significant condition effect (P = 0.028) of NSE, corresponding to a significant increase in arterial (P = 0.023) but not venous (P = 0.173) concentrations in hyperthermia, potentially indicating extra-cerebral release of NSE. Collectively, results from the present study support the notion that in young men there is little concern for NVU damage with acute hyperthermia of +2 degrees C. NEW & NOTEWORTHY The acute effects of passive whole-body hyperthermia on the integrity of the neurovascular unit (NVU) in humans have remained unclear. We demonstrate that passive heating for similar to 1 h until an increase of +2 degrees C esophageal temperature in healthy men does not increase the cerebral release of neuronal parenchymal stress biomarkers, suggesting the NVU integrity is maintained. This preliminary study indicates passive heating is safe for the brain, at least in young healthy men.
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