The negative effect of high temperature (fever) on the central nervous system
It is known that at very high body temperature, brain damage can develop, leading to death. With heat stroke, the CNS suffers. However, it is not clear at what exactly temperature this occurs. In addition to temperature, many other factors undoubtedly influence the outcome of the disease, such as blood oxygenation, hemodynamics, etc.
Resistance to hyperthermia is more dependent on the type of animal. Thus, in some species of gazelles during running, the body temperature rises to 45.6 ° C, but it does not lead to any harmful consequences. In dogs and a number of other non-primate mammals, at the base of the brain there is an arterial vascular plexus, which is a network of small vessels inside the carotid arterial system.
The cooled venous blood flowing from the nasal concha washes the arterial network from inside and outside and cools the arterial blood flowing through the brain with the help of a countercurrent heat exchange mechanism. According to Baker, the temperature of arterial blood passing through the plexus is significantly lower than the temperature of blood in the aorta. A person does not have such a plexus.
It is not entirely clear at what temperature brain damage occurs in humans, but, in general, this is observed at a temperature of 42.2 ° C in the oral cavity or 42.8 ° C in the rectum. Such an extremely high temperature in febrile conditions usually does not happen, but it is noted in thermal diseases. But is it always harmless to have a lower temperature rise? In one study, mice were overheated, reaching a “core” temperature of 41 ° C and higher.
Electron micrography of their brain tissue showed slight damage to the mitochondria at a temperature of 41 ° C and significant destruction at 42 ° C. On the other hand, Bynum in human volunteers, which were overheated until the temperature in the esophagus reached 42 ° C for 1 hour, did not reveal any effects, except for a moderate increase in serum enzyme levels in 2 out of 5 subjects. Naturally, in this experiment, no microscopic examination of the brain tissue was performed.
Clasen showed that fever has an adverse effect on physically damaged brain tissue in monkeys. After standardized damage to the brain and the temperature of the “core” to 40 ° C for 2 hours, the edema in the injured hemisphere of the brain was 40% higher than that of animals that maintained normal body temperature. The clinical significance of these observations for diseases such as head trauma, meningitis, Reye syndrome is quite obvious.