Shivering

Abstract: In recent years, it has been shown that humans have active brown adipose tissue (BAT) depots, raising the question of whether activation and recruitment of BAT can be a target to counterbalance the current obesity pandemic. Here, we show that a 10-day cold acclimation protocol in humans increases BAT activity in parallel with an increase in nonshivering thermogenesis (NST). No sex differences in BAT presence and activity were found either before or after cold acclimation. Respiration measurements in permeabilized fibers and isolated mitochondria revealed no significant contribution of skeletal muscle mitochondrial uncoupling to the increased NST. Based on cell-specific markers and on uncoupling protein-1 (characteristic of both BAT and beige/brite cells), this study did not show “browning” of abdominal subcutaneous white adipose tissue upon cold acclimation. The observed physiological acclimation is in line with the subjective changes in temperature sensation; upon cold acclimation, the subjects judged the environment warmer, felt more comfortable in the cold, and reported less shivering. The combined results suggest that a variable indoor environment with frequent cold exposures might be an acceptable and economic manner to increase energy expenditure and may contribute to counteracting the current obesity epidemic.

Abstract: Most clinically available thermometers accurately report the temperature of whatever tissue is being measured. The difficulty is that no reliably core-temperature measuring sites are completely non-invasive and easy to use — especially in patients not having general anesthesia. Nonetheless, temperature can be reliably measured in most patients. Body temperature should be measured in patients having general anesthesia exceeding 30 minutes in duration, and in patients having major operations under neuraxial anesthesia. Core body temperature is normally tightly regulated. All general anesthetics produce a profound dose-dependent reduction in the core temperature triggering cold defenses including arterio-venous shunt vasoconstriction and shivering. Anesthetic-induced impairment of normal thermoregulatory control, and the resulting core-to-peripheral redistribution of body heat, is the primary cause of hypothermia in most patients. Neuraxial anesthesia also impairs thermoregulatory control, although to a lesser extant than general anesthesia. Prolonged epidural analgesia is associated with hyperthermia whose cause remains unknown.

Abstract: Summary 1. Non-shivering thermogenesis (NST) is a heat-production mechanism participating in the chemical thermoregulation of mammals. 2. NST is additional to shivering and takes place at temperatures close to the thermoneutral zone. 3. NST occurs in newborn mammals and in those that hibernate. In some adult mammals it can be induced by adaptation to cold. 4. In small mammals NST produces approximately the same amount of heat as shivering. It becomes less important with increasing body weight of the animals. 5. NST is regulated by the hypothalamus and it is based predominantly on the calorigenic action of noradrenaline released from sympathetic nerve-endings. Participation of other calorigenic substances and of the specific dynamic action of food cannot be excluded. 6. NST is localized mainly in skeletal muscles and in brown adipose tissue. Small amounts of NST may come from liver, intestine, heart and brain. 7. The biochemical basis of the calorigenic action of noradrenaline has not yet been fully elucidated.

Abstract: IN homeothermic species, a thermoregulatory system coordinates defenses against cold and heat to maintain internal body temperature within a narrow range, thus optimizing normal physiologic and metabolic function. The combination of anesthetic-induced thermoregulatory impairment and exposure to a cool environment makes most unwarmed surgical patients hypothermic. Although shivering is but one consequence of perioperative hypothermia, and rarely the most serious, it occurs frequently (i.e., 40–60% after volatile anesthetics), and it remains poorly understood. While coldinduced thermoregulatory shivering remains an obvious etiology, the phenomenon has also been attributed to numerous other causes. Our first goal is to review the organization of the thermoregulatory system, and particularly the physiology of postanesthetic shivering. We then discuss the pharmacology of thermoregulation and review the putative mechanisms and sites of action of various antishivering drugs.