Individual variability in the peripheral and core interthreshold zones.
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The purpose of the study was to investigate the degree of subject variability in the peripheral and core temperature thresholds of the onset of shivering and sweating. Nine healthy young male subjects participated in three trials. In the first two trials, wearing only shorts, they were exposed to air temperatures of 5 degrees C and 40 degrees C until the onset of shivering and sweating, respectively. In the second experiment, subjects wore a water perfused suit that was perfused with 25 degrees C water at a rate of 600 cc/min. They exercised on an ergometer at 50% of their maximum work rate for 10-15 min. At the onset of sweating, the exercise was terminated, and they remained seated until the onset of shivering, as reflected in oxygen uptake. In the first two trials, rectal temperature (Tre) was stable, despite displacements in skin temperature (Tsk), whereas in the third trial, Tsk (measured at four sites) was almost constant (30-32 degrees C), and the thermoregulatory responses were initiated due to changes in Tre alone. The results of the first two trials established the peripheral interthreshold zone, whereas the results of the third trial established the core interthreshold zone. The results demonstrated individual variability in the peripheral and core interthreshold zones, a proportional correlation between both zones (r=0.87), and a relatively higher contribution of adiposity in both zones as compared with those of other non-thermal factors such as height, weight, body surface area, surface area-to mass ratio, and the maximum work load. (+info)
Marsupial uncoupling protein 1 sheds light on the evolution of mammalian nonshivering thermogenesis.
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Brown adipose tissue expressing uncoupling protein 1 (UCP1) is responsible for adaptive nonshivering thermogenesis giving eutherian mammals crucial advantage to survive the cold. The emergence of this thermogenic organ during mammalian evolution remained unknown as the identification of UCP1 in marsupials failed so far. Here, we unequivocally identify the marsupial UCP1 ortholog in a genomic library of Monodelphis domestica. In South American and Australian marsupials, UCP1 is exclusively expressed in distinct adipose tissue sites and appears to be recruited by cold exposure in the smallest species under investigation (Sminthopsis crassicaudata). Our data suggest that an archetypal brown adipose tissue was present at least 150 million yr ago allowing early mammals to produce endogenous heat in the cold, without dependence on shivering and locomotor activity. (+info)
Forced convective head cooling device reduces human cross-sectional brain temperature measured by magnetic resonance: a non-randomized healthy volunteer pilot study.
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Intrathecal meperidine for prevention of shivering during transurethral resection of prostate.
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INTRODUCTION: The aim of this study was to investigate low-dose intrathecal meperidine for prevention or alleviation of shivering after induction of spinal anesthesia for transurethral resection of the prostate (TURP). MATERIALS AND METHODS: In a randomized controlled trial, 80 patients scheduled for TURP under spinal anesthesia were assigned into two groups of case and control. Spinal anesthesia was performed using 75 mg of hyperbaric lidocaine 5% plus meperidine, 15 mg, in the patients of the case group and the same dose of lidocaine plus normal saline in the patients of the control group. Shivering episodes were recorded during the operation and in the recovery room. Data on systolic blood pressure, heart rate, arterial oxygen saturation, and body temperature were collected before the induction of anesthesia; 5, 15, and 30 minutes after the induction; and in the recovery room. RESULTS: Maximum level of sensory block was similar in the patients of the case and control groups. Shivering was not seen in the patients who received meperidine, while in the control group, 11 (27.5%) experienced some degrees of shivering (P = .001). Blood pressure, body temperature, and arterial oxygen saturation did not have a clinically significant change and they were not different between the two groups. Side effects of opioids were unremarkable. CONCLUSION: Low-dose intrathecal meperidine is effective and safe in reducing the incidence of shivering associated with spinal anesthesia for TURP. (+info)
Central control of thermogenesis in mammals.
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Dissociation of thermoregulation in cats with cytotoxic pontine lesions.
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Neurons of the pontine tegmentum of the cat were lesioned by microinjection of ibotenic acid into the brainstem. The threshold ambient temperatures for heat-gain (shivering) and for heat-loss (panting) responses, together with brain and skin temperatures, were measured in intact animals and after the neurotoxic lesioning. After the lesioning the shivering threshold was altered but the panting threshold did not change. The results indicate that certain neurons involved in the shivering response reside in the pontine tegmentum. Neurons involved in the panting response, however, may lie outside the lesioned areas. (+info)
Comparison of prophylactic use of midazolam, ketamine, and ketamine plus midazolam for prevention of shivering during regional anaesthesia: a randomized double-blind placebo controlled trial.
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