Black bears hibernate for 5 to 7 months a year and, during this time, do not eat, drink, urinate, or defecate. We measured metabolic rate and body temperature in hibernating black bears and found that they suppress metabolism to 25% of basal rates while regulating body temperature from 30° to 36°C, in multiday cycles. Heart rates were reduced from 55 to as few as 9 beats per minute, with profound sinus arrhythmia. After returning to normal body temperature and emerging from dens, bears maintained a reduced metabolic rate for up to 3 weeks. The pronounced reduction and delayed recovery of metabolic rate in hibernating bears suggest that the majority of metabolic suppression during hibernation is independent of lowered body temperature.

Current research on sleep using experimental animals is limited by the expense and time-consuming nature of traditional EEG/EMG recordings. We present here an alternative, noninvasive approach utilizing piezoelectric films configured as highly sensitive motion detectors. These film strips attached to the floor of the rodent cage produce an electrical output in direct proportion to the distortion of the material. During sleep, movement associated with breathing is the predominant gross body movement and, thus, output from the piezoelectric transducer provided an accurate respiratory trace during sleep. During wake, respiratory movements are masked by other motor activities. An automatic pattern recognition system was developed to identify periods of sleep and wake using the piezoelectric generated signal. Due to the complex and highly variable waveforms that result from subtle postural adjustments in the animals, traditional signal analysis techniques were not sufficient for accurate classification of sleep versus wake. Therefore, a novel pattern recognition algorithm was developed that successfully distinguished sleep from wake in approximately 95% of all epochs. This algorithm may have general utility for a variety of signals in biomedical and engineering applications. This automated system for monitoring sleep is noninvasive, inexpensive, and may be useful for large-scale sleep studies including genetic approaches towards understanding sleep and sleep disorders, and the rapid screening of the efficacy of sleep or wake promoting drugs.

In situations where the accumulation of internal heat limits physical performance, enhanced heat extraction from the body should improve performance capacity. The combined application of local subatmospheric pressure (35-45 mmHg) to an entire hand (to increase blood volume) and a heat sink (18-22 degrees C) to the palmar surface were used to draw heat out of the circulating blood. Subjects walked uphill (5.63 km/h) on a treadmill in a 40 degree C environment. Slopes of the treadmill were held constant during paired experimental trials (with and without the device). Heat extraction attenuated the rate of esophageal temperature rise during exercise (2.1 +/- 0.4 degrees and 2.9 +/- 0.5 degrees C/h, mean +/- SE, with and without the device, respectively; n = 8) and increased exercise duration (46.1 +/- 3.4 and 32.3 +/- 1.7 min with and without the device, respectively; n = 18). Hand cooling alone had little effect on exercise duration (34.1 +/- 3.0, 38.0 +/- 3.5, and 57.0 +/- 6.4 min, for control, cooling only, and cooling, and subatmospheric pressure, respectively; n = 6). In a longer term study, nine subjects participated in two or four trials per week for 8 wk. The individual workloads (treadmill slope) were varied weekly. Use of the device had a beneficial effect on exercise endurance at all workloads, but the benefit proportionally decreased at higher workloads. It is concluded that heat can be efficiently removed from the body by using the described technology and that such treatment can provide a substantial performance benefit in thermally stressful conditions.

The body temperatures (Tb) of golden-mantled ground squirrels maintained under constant dim light (< 20 1x red light) at an ambient temperature of 10 degrees C were monitored via telemetry throughout the hibernation season. During euthermia, when Tb ranged from 34 to 39 degrees C, these animals exhibited robust circadian Tb rhythms. During bouts of hibernation, when Tb rhythms persisted, although the amplitudes of the rhythms were considerably dampened compared with euthermia. The periods of the intrabout Tb rhythms were within the ranges observed during euthermia and were stable within an individual bout but varied between hibernation bouts. Arousals from hibernation occurred at a fixed phase angle of the Tb cycle. Once the period of an intrabout Tb rhythm was determined, it was possible to predict the timing of arousal from the hibernation bout to within 1 h of any 24-h period. This study confirms previous speculation about the persistence of circadian rhythms in golden-mantled ground squirrels during deep hibernation and demonstrates that the circadian system is involved in the timing of periodic arousals from hibernation.

Background: Many individuals afflicted with multiple sclerosis (MS) experience a transient worsening of symptoms when body temperature increases due to ambient conditions or physical activity. Resulting symptom exacerbations can limit performance. We hypothesized that extraction of heat from the body through the subcutaneous retia venosa that underlie the palmar surfaces of the hands would reduce exercise-related heat stress and thereby increase the physical performance capacity of heat-sensitive individuals with MS.