A comparison of 2 methods of measuring rectal temperatures with digital thermometers.

BACKGROUND: Digital rectal thermometers typically have 2 distinct modes of operation: dwell or monitor, in which body temperature is displayed continuously, and predictive, in which body temperature is mathematically estimated on the basis of the curve of temperature rise that occurs after the thermometer is inserted. Although the dwell mode is generally considered more accurate, the predictive mode allows more rapid measurement. Direct comparisons of these 2 methods are lacking. OBJECTIVE: To determine if measurements of rectal temperatures obtained with the predictive mode differ significantly from those obtained with the dwell mode. METHODS: For each of 10 subjects, both dwell and predictive modes were used to measure early morning rectal temperature. For comparison of the 2 modes during states of temperature flux, 8 subjects had rectal temperatures measured after swimming in cold water. Initial predictive values were measured directly after each subject exited from the water. Initial dwell values were estimated by linear extrapolation of measured 3- and 6-minute dwell values. Paired-sample statistical methods were used to compare data. RESULTS: Measurements of early-morning temperatures obtained with the predictive mode did not differ significantly from those obtained with the dwell mode (P = .64). Predictive values also did not differ significantly from extrapolated dwell values for measurements obtained during mild temperature flux after immersion in cold water (P = .33). CONCLUSION: The predictive and dwell modes of digital rectal thermometers yield similar measurements of temperature during steady-state conditions and during states of mild temperature flux.

Hypothermia and afterdrop following open water swimming: the Alcatraz/San Francisco Swim Study.

To determine whether or not participants in open water swim events experience hypothermia and afterdrop, rectal temperature was measured for up to 45 minutes in 11 subjects following the New Year's Day Alcatraz Swim. This event was held in open water (11.7 degrees C [53.0 degrees F]) in the San Francisco Bay, and participants did not wear wetsuits or other protective clothing. Biophysical parameters, including surfacelvolume ratio, body mass index, and percent body fat were measured before the swim, and statistical analysis was done to determine predictors of temperature decrease and afterdrop duration. Applying the American Heart Association definition of hypothermia (less than 36.0 C [96.8 degrees F]), hypothermia was seen in 5 of the 11 subjects. Using a more rigorous and traditional definition (less than 35.0 degrees C [95.0 degrees F]), hypothermia was seen in only one subject. Afterdrop, defined as continued cooling following removal from cold stress, was seen in 10 of the 11 subjects. Surface/volume ratio (S/V) and body mass index (BMI) predicted the lowest recorded temperatures (P < .05; r(S/V) = -.71, r(BMI) = .72) and afterdrop duration (P < .05; r(SN) = -.75, r(BMI) = .69). These results suggest that hypothermia and afterdrop can occur commonly after recreational open water swimming, and that participants should be observed for signs of temperature decrease following removal from cold stress.

Functional independence of layer IV barrels in rodent somatosensory cortex.

Layer IV of rodent primary somatosensory cortex is characterized by an array of whisker-related groups of neurons, known as "barrels." Neurons within each barrel respond best to a particular whisker on the contralateral face, and, on deflection of adjacent whiskers, display relatively weak excitation followed by strong inhibition. A prominent hypothesis for the processing of vibrissal information within layer IV is that the multiwhisker receptive fields of barrel neurons reflect interconnections among neighboring barrels. An alternative view is that the receptive field properties of barrel neurons are derived from operations performed on multiwhisker, thalamic inputs by local circuitry within each barrel, independently of neighboring barrels. Here we report that adjacent whisker-evoked excitation and inhibition within a barrel are unaffected by ablation of the corresponding adjacent barrel. In supragranular neurons, on the other hand, excitatory responses to the ablated barrel's associated whisker are substantially reduced. We conclude that the layer IV barrels function as an array of independent parallel processors, each of which individually transforms thalamic afferent input for subsequent processing by horizontally interconnected circuits in other layers.

Optical imaging and electrophysiology of rat barrel cortex. I. Responses to small single-vibrissa deflections.

A study was undertaken to investigate the response of the rodent somatosensory barrel cortex to single-whisker, near-threshold vibrissal stimuli. Cortical responses to controlled whisker deflections were recorded by (i) conventional multi-unit extracellular recording within the cytochrome oxidase rich barrels centers and the interbarrel septa, and (ii) intrinsic signal optical imaging, a technique that provides a spatial view of cortical activation thought to be related to the deoxygenation of hemoglobin in activated areas. Barrel cortex neurons responded weakly to whisker deflections of 0.04 degrees. Their response to a series of small stimuli of increasing amplitude was well-fitted by a logarithmic function. Responses to larger stimuli declined monotonically with distance from the center of the barrel column, and were characterized by greater onset and offset firing rates, by greater post-excitatory reduction of firing to below spontaneous levels, and by shorter response latency. In comparison to measurements taken previously from primary vibrissal afferent fibers, we conclude that cortical cells can respond to activity in a very small fraction of first-order sensory neurons.

Optical imaging and electrophysiology of rat barrel cortex. II. Responses to paired-vibrissa deflections.

A study was undertaken to investigate the response of the rodent somatosensory barrel cortex to paired-whisker stimuli. Cortical responses to controlled whisker deflections were recorded by (i) conventional multi-unit extracellular recording within the cytochrome oxidase rich barrels centers, and (ii) intrinsic signal optical imaging, a technique that measures an optical correlate of neuronal activity thought to be related to the deoxygenation of hemoglobin in activated regions. Stimuli were applied to two whiskers in sequence, at temporal separations ranging from 0 to 60 ms. Over intervals of 10-40 ms, the primary effect of paired-whisker stimulation was suppressive. We suggest that paired-whisker inhibition results from the activation of layer IV fast-spike units within the principle whisker's barrel, by excitatory input arriving from a surround-whisker. Paired-whisker stimulation produces inhibition in intrinsic images, because it results in a net reduction in layer II/III and/or layer IV metabolism. Intra-cortical inhibition may serve to convert the sequence of inputs from the whisker array into a barrel cortex magnitude code that can be read by higher cortical areas.

The effect of retinol and retinoic acids on lipoxygenase activity.

Lipoxygenase catalyzes the dioxygenation of polyenoic fatty acids such as linoleate and arachidonate. The aim of the present study was to examine the effect of retinol, all-trans-retinoic acid and 13-cis-retinoic acid on the activity of lipoxygenase-1 and lipoxygenase-2 towards linoleic acid. Lipoxygenase activity toward linoleic acid was followed by determining changes in absorption at 234 nm. All retinoids inhibited lipoxygenase-1 and lipoxygenase-2 activity. Lipoxygenase-2 activity towards linoleic acid was rapid at pH 6.5; all-trans-retinol (10 microM) caused a 50% inhibition in reaction rate. All-trans-retinol was oxidized in parallel with diene production by lipoxygenase-2. Lipoxygenase-2 activity on linoleic acid was competitively inhibited by all-trans-retinol and all-trans-retinoic acid; 13-cis-retinoic acid exhibited mixed type inhibition. Activity of lipoxygenase-1 towards linoleic acid at pH 9.0 was also inhibited by retinoic acids by 32-73%. All-trans-retinoic acid and 13-cis-retinoic acid inhibited lipoxygenase-1 activity competitively, whereas all-trans-retinol inhibited lipoxygenase-1 activity in a mixed manner. These findings suggest that retinoids may bind to the active site of the enzyme or simultaneously act as an antioxidant.

A new approach to optical imaging applied to rat barrel cortex.

Several groups have described using intrinsic optical imaging to form images of activity patterns in the cortex. Because the signal is small, the general approach has been to use expensive camera equipment with a high dynamic range to make these measurements. However, by using signal averaging to compensate for lower dynamic range, images can be obtained using equipment already available in many laboratories. This modified technique has been used for imaging activity in 'barrel' cortex of the rat. A map of the representation of a single whisker as determined by the imaging technique corresponded well with a similar map made using standard electrophysiology. A map of several whiskers was made by overlaying images of single-whisker representations. The details of the images differ from those previously described. Possible mechanisms for the signal are discussed.

Effect of changing feedback delay on spontaneous oscillations in smooth pursuit eye movements of monkeys.

1. Our goal was to discriminate between two classes of models for pursuit eye movements. The monkey's pursuit system and both classes of model exhibit oscillations around target velocity during tracking of ramp target motion. However, the mechanisms that determine the frequency of oscillations differ in the two classes of model. In "internal feedback" models, oscillations are controlled by internal feedback loops, and the frequency of oscillation does not depend strongly on the delay in visual feedback. In "image motion" models, oscillations are controlled by visual feedback, and the frequency of oscillation does depend on the delay in visual feedback. 2. We measured the frequency of oscillation during pursuit of ramp target motion as a function of the total delay for visual feedback. For the shortest feedback delays of approximately 70 ms, the frequency of oscillation was between 6 and 7 Hz. Increases in feedback delay caused decreases in the frequency of oscillation. The effect of increasing feedback delay was similar, whether the increases were produced naturally by dimming and decreasing the size of the tracking target or artificially with the computer. We conclude that the oscillations in eye velocity during pursuit of ramp target motion are controlled by visual inputs, as suggested by the image motion class of models. 3. Previous experiments had suggested that the visuomotor pathways for pursuit are unable to respond well to frequencies as high as the 6-7 Hz at which eye velocity oscillates in monkeys. We therefore tested the response to target vibration at an amplitude of +/- 8 degrees/s and frequencies as high as 15 Hz. For target vibration at 6 Hz, the gain of pursuit, defined as the amplitude of eye velocity divided by the amplitude of target velocity, was as high as 0.65. We conclude that the visuomotor pathways for pursuit are capable of processing image motion at high temporal frequencies. 4. The gain of pursuit was much larger when the target vibrated around a constant speed of 15 degrees/s than when it vibrated around a stationary position. This suggests that the pursuit pathways contain a switch that must be closed to allow the visuomotor pathways for pursuit to operate at their full gain. The switch apparently remains open for target vibration around a stationary position. 5. The responses to target vibration revealed a frequency at which eye velocity lagged target velocity by 180 degrees and at which one monkey showed a local peak in the gain of pursuit.(ABSTRACT TRUNCATED AT 400 WORDS)