Negligible influence of moderate to severe hyperthermia on blood-brain barrier permeability and neuronal parenchymal integrity in 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 þ2°C or absolute esophageal temperature of 39.5°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 þ2°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 þ2 °C. [ABSTRACT FROM AUTHOR]