3 The Febrile Response

Abstract

I. FEVER VERSUS HYPERTHERMIA
Although fever has often been defined as any elevation in body temperature, this definition would result in considerable confusion between true fever and hyperthermia. In fever, as a result of the elevated thermoregulatory “set-point,” a person’s heat production increases, while at the same time heat loss decreases. Snell and Atkins (1968) defined four categories of body temperature based on the set-point theory of temperature regulation:Normothermia—where set-point and actual body temperature coincide. This condition exists most of the time.

Hypothermia—where set-point may or may not be normal, but actual body temperature is below this set-point. Hypothermia can occur as a response to a drug, disease, or exposure to the cold.

Hyperthermia—where set-point may or may not be normal, but actual body temperature is higher than this set-point. Hyperthermia can occur as a response to a drug, disease, or exposure to a warm environment.

Fever—where set-point is raised and deep body temperature may or may not be raised to the same level.

Studies with human subjects (e.g., Cooper et al. 1964; Cabanac and Massonnet 1974) and with experimental animals (e.g., Cabanac et al. 1970; Sharp and Hammel 1972; Vaughn et al. 1974; Satinoff et al. 1976) have shown that the thermoregulatory set-point is indeed raised during fever.

II. MEDIATORS OF FEVER
For many years, fever in response to endotoxin or purified lipopolysaccharide (LPS) or other “exogenous pyrogen,” was assumed to be caused by the release into the blood of...