Shivering and digestion-related thermogenesis in pigeons during dark phase.
(9/200)
The pigeon's main source of regulated heat production, shivering, is especially likely to be used for thermoregulation during the dark phase of the day when there is little heat from locomotor activity. However, food stored in the pigeon's crop is digested during the night, and digestion-related thermogenesis (DRT) will provide heat that should decrease the need for shivering to maintain body temperature (Tb). We investigated the conditions under which DRT alters the occurrence of nocturnal shivering thermogenesis in pigeons. In fasting experiments, in which DRT was minimal, variations in pectoral shivering were closely related to the kinetics of nocturnal Tb when the ambient temperature (Ta) was moderate (21 degrees C). In that case, shivering was low while Tb fell at the beginning of the night, moderate during the nocturnal plateau in Tb, and strong during the prelight increase in Tb. Similar kinetics of nocturnal Tb occurred when Ta = 28 degrees C, but shivering was negligible throughout the dark phase. In restricted feeding experiments, nocturnal DRT was varied by providing different amounts of food late in the light phase. When Ta = 21 degrees C, 11 degrees C, and 1 degrees C, nocturnal Tb and O2 consumption were directly related to the amount of food ingested. However, nocturnal shivering tended to decrease as the food load increased and was significantly reduced at the higher loads. Because nocturnal shivering did not become more efficient in producing heat as the size of the food load increased, we conclude that nocturnal DRT decreased the need for shivering thermogenesis. (+info)
Effect of delivery temperature on endocrine stimulation of thermoregulation in lambs born by cesarean section.
(10/200)
We examined the hypothesis that exogenous stimulation with physiological doses of 3,5,3'-triiodothyronine (T(3)) and/or norepinephrine at birth can improve thermoregulation in near-term lambs delivered by cesarean section. This was achieved by investigating the effect of delivery temperature [i.e., warm (30( degrees )C) vs. cool (15( degrees )C) ambient temperatures] on hormonal stimulation on uncoupling protein-1 (UCP1) abundance in brown adipose tissue. In vivo measurements of temperature control (i. e., colonic temperature, oxygen consumption, and incidence of shivering) were made over the first 2.5 h after birth. Each lamb was injected with saline with or without T(3), norepinephrine, or T(3) plus norepinephrine. Irrespective of delivery temperature, abundance of UCP1 increased and incidence of shivering decreased by all hormonal treatments, but this only reduced the rate of decline in colonic temperature of cool-delivered lambs. Oxygen consumption was higher in cool-delivered lambs that were able to fully restore body temperature, an adaptation not observed in controls or any warm-delivered groups. Exogenous administration of endocrine stimulatory factors can enhance the abundance of UCP1 in cesarean-section-delivered lambs with the magnitude of thermoregulatory response being greater at cool than warm delivery temperatures. (+info)
Shivering in a thoroughbred mare.
(11/200)
An 11-year-old mare presented with neuromuscular deficits and what resembled shivering in the left hind limb. On necropsy, there was no evidence of denervation atrophy of the left hind gastrocnemius muscle. The spinal cord had a small, right-sided lesion at C3-C4 and C4-C5. Tests for equine herpesvirus-1 and Sarcocystis spp. were negative. (+info)
Amphotericin B colloidal dispersion (Amphocil) vs fluconazole for the prevention of fungal infections in neutropenic patients: data of a prematurely stopped clinical trial.
(12/200)
We conducted an open label, randomised clinical trial to compare amphotericin B colloidal dispersion (ABCD, Amphocil) 2 mg/kg/day intravenously with fluconazole 200 mg/day orally, for the prevention of fungal disease in neutropenic patients with haematological malignancies. In the event of unresolved fever after 4 days of empirical antibacterial therapy, patients in both treatment groups were to receive ABCD, 4 mg/kg/day. However, the study had to be stopped in an early phase, due to severe side-effects of ABCD. A total of 24 patients were enrolled, 12 patients were randomly assigned to receive prophylactic ABCD, which was administered for a mean of 13.9 days. Fluconazole prophylaxis was given to 12 patients for a mean of 21.2 days. Therapeutic ABCD, 4 mg/kg, was initiated in four patients because of suspected fungal infection, all of whom had initially received fluconazole. A high rate of infusion-related toxicity of ABCD was observed. Chills occurred in 15/16 ABCD recipients (94%), accompanied by a temperature rise of >/=2 degrees C in 4/16 patients and of >/=1 degrees C but <2 degrees C in 10/16 patients. Other ABCD-related adverse events were hypotension (4/16), nausea with vomiting (5/16), tachycardia (7/16), headache (3/16) and dyspnoea (3/16). For premedication patients received: antihistamines (12/16), hydrocortisone (9/16) and/or morphine (6/16). ABCD was discontinued in 8/16 patients (50%) due to side-effects, which ultimately dictated early termination of the study. We conclude that ABCD is not suitable for antifungal prophylaxis in neutropenic patients due to severe infusion-related side-effects. Subject numbers were too low for conclusions on variables of antifungal efficacy. (+info)
Elevated thermostatic setpoint in postoperative patients.
(13/200)
BACKGROUND: The mechanism and clinical relevance of increased core temperature (Tc) after surgery are poorly understood. Because fever is used as a diagnostic sign of infection, it is important to recognize what constitutes the normal postoperative thermoregulatory response. In the current study the authors tested the hypothesis that a regulated increase in Tc setpoint occurs after surgery. METHODS: The authors prospectively studied 271 patients in the first 24 h after a variety of vascular, abdominal, and thoracic surgical procedures. Tc measured in the urinary bladder, skin-surface temperatures, thermoregulatory responses (vasoconstriction and shivering), and total leukocyte counts were assessed. In a subset of 34 patients, plasma concentrations of tumor necrosis factor, interleukin (IL)-6, and IL-8 were measured before and after surgery. RESULTS: In the early postoperative period, the maximum increase in Tc above the preoperative baseline averaged 1.4 +/- 0.8 degrees C (2.5 +/- 1.4 degrees F), with the Tc peak occurring 11.1 /- 5.8 h after surgery. Fifty percent of patients had a maximum Tc greater than or equal to 38.0 degrees C (100.4 degrees F) and 25% had a maximum Tc greater than or equal to 38.5 degrees C (101.3 degrees F). The progressive postoperative increase in Tc was clearly associated with cutaneous vasoconstriction and shivering, indicating a regulated elevation in Tc setpoint. The elevated Tc was associated with an increased IL-6 response but not with leukocytosis. Maximum postoperative Tc was positively correlated with duration and extent of the surgical procedure. CONCLUSIONS: A regulated elevation in Tc setpoint (fever) occurs normally after surgery. The association between Tc elevation, extent and duration of surgery, and the cytokine response suggests that early postoperative fever is a manifestation of perioperative stress. (+info)
Thermoregulatory changes induced by cholinomimetic substances introduced into the cerebral ventricles of sheep.
(14/200)
1 Thermoregulatory responses have been recorded from Welsh Mountain sheep exposed to warm, neutral or cold environments while injections of cholinomimetic drugs and/or their antagonists have been given into a lateral cerebral ventricle. 2. Carbachol and physostigmine inhibited panting of animals at high ambient temperature (ta), caused vasoconstriction and initiated shivering at neutral ta, and accentuated shivering at low ta. Rectal temperature (tre) invariably increased. Oxotremorine had apparently identical effects. 3. Nicotine and another ganglionic stimulant, the quaternary methyl derivative of dopamine, had no effects on thermoregulation. 4. Atropine given 10 min before injections of carbachol, physostigmine or oxotremorine completely inhibited their hyperthermic effects, but pretreatment with the ganglion-blocking drug, pempidine, caused no inhibition. The cholinergic synapses that respond to cholinomimetic drugs injected into the lateral cerebral ventricles of sheep are therefore muscarinic and not nicotinic. 5. When atropine was given to sheep exposed to cold, no detectable reduction of shivering occurred and tre decreased only slightly, even with doses of atropine far greater than needed to inhibit shivering induced by physostigmine. This may be because shivering is controlled by neural pathways unaffected by drugs administered intracerebroventricularly or because the cholinergic synapses activated by physostigmine do not carry the input from cold sensors. (+info)
Only UCP1 can mediate adaptive nonshivering thermogenesis in the cold.
(15/200)
Adaptive nonshivering thermogenesis may have profound effects on energy balance and is therefore therefore is a potential mechanism for counteracting the development of obesity. The molecular basis for adaptive nonshivering thermogenesis has remained a challenge that sparked acute interest with the identification of proteins (UCP2, UCP3, etc.) with high-sequence similarity to the original uncoupling protein-1 (UCP1), which is localized only in brown adipose tissue. Using UCP1-ablated mice, we examined whether any adaptive nonshivering thermogenesis could be recruited by acclimation to cold. Remarkably, by successive acclimation, the UCP1-ablated mice could be made to subsist for several weeks at 4C during which they had to constantly produce heat at four times their resting levels. Despite these extreme requirements for adaptive nonshivering thermogenesis, however, no substitution of shivering by any adaptive nonshivering thermogenic process occurred. Thus, although the existence of, for example, muscular mechanisms for adaptive nonshivering thermogenesis has recurrently been implied, we did not find any indication of such thermogenesis. Not even during prolonged and enhanced demand for extra heat production was any endogenous hormone or neurotransmitter able to recruit any UCP1-independent adaptive nonshivering thermogenic process in muscle or in any other organ, and no proteins other than UCP1-not even UCP2 or UCP3-therefore have the ability to mediate adaptive nonshivering thermogenesis in the cold. (+info)
Comparison of two different temperature maintenance strategies during open abdominal surgery: upper body forced-air warming versus whole body water garment.
(16/200)
BACKGROUND: A new system has been developed that circulates warm water through a whole body garment worn by the patient during surgery. In this study the authors compared two different strategies for the maintenance of intraoperative normothermia. One strategy used a new water garment warming system that permitted active warming of both the upper and lower extremities and the back. The other strategy used a single (upper body) forced-air warming system. METHODS: In this prospective, randomized study, 53 adult patients were enrolled in one of two intraoperative temperature management groups during open abdominal surgery with general anesthesia. The water-garment group (n = 25) received warming with a body temperature (rectal) set point of 36.8 degrees C. The forced-air-warmer group (n = 28) received routine warming therapy using upper body forced-air warming system (set on high). The ambient temperature in the operating room was maintained constant at approximately 20 degrees C. Rectal, distal esophageal, tympanic, forearm, and fingertip temperatures were recorded perioperatively and during 2 h after surgery. Extubated patients in both groups were assessed postoperatively for shivering, use of additional warming devices, and subjective thermal comfort. RESULTS: The mean rectal and esophageal temperatures at incision, 1 h after incision, at skin closure, and immediately postoperatively were significantly higher (0.4-0.6 degrees C) in the group that received water-garment warming when compared with the group that received upper body forced-air warming. The calculated 95% confidence intervals for the above differences in core temperatures were 0.7-0.1, 0.8-0.2, 0.8-0.2, and 0.9-0.1, retrospectively. In addition, 14 and 7% of patients in the control upper body forced-air group remained hypothermic (< 35.5 degrees C) 1 and 2 h after surgery, respectively. No core temperature less than 35.5 degrees C was observed perioperatively in any of the patients from the water-garment group. A similar frequency of the thermal stress events (shivering, use of additional warming devices, subjective thermal discomfort) was observed after extubation in both groups during the 2 h after surgery. CONCLUSIONS: The investigated water warming system, by virtue of its ability to deliver heat to a greater percentage of the body, results in better maintenance of intraoperative normothermia that does forced-air warming applied only to the upper extremities, as is common practice. (+info)