Extremity cooling during an arctic diving training exercise.

A field study was conducted to examine the vulnerability of military divers to non-freezing cold injury (NFCI) during Arctic ice-diving operations. Participants were instrumented with temperature sensors on the back of their hands and on the bottom of their big toe for each dive to measure cooling of their extremities. While NFCI was not diagnosed in any of the participants during this field study, the data indicate that the feet were particularly vulnerable during the dives given that they were mostly in a temperature zone that could cause pain and performance decrements.

Correction factors for assessing immersion suits under harsh conditions.

Many immersion suit standards require testing of thermal protective properties in calm, circulating water while these suits are typically used in harsher environments where they often underperform. Yet it can be expensive and logistically challenging to test immersion suits in realistic conditions. The goal of this work was to develop a set of correction factors that would allow suits to be tested in calm water yet ensure they will offer sufficient protection in harsher conditions.

Reduction in predicted survival times in cold water due to wind and waves.

Recent marine accidents have called into question the level of protection provided by immersion suits in real (harsh) life situations. Two immersion suit studies, one dry and the other with 500 mL of water underneath the suit, were conducted in cold water with 10-12 males in each to test body heat loss under three environmental conditions: calm, as mandated for immersion suit certification, and two combinations of wind plus waves to simulate conditions typically found offshore. In both studies mean skin heat loss was higher in wind and waves vs.

Effect of feedback mode and task difficulty on quality of timing decisions in a zero-sum game.

Objective: The objective was to investigate the interaction between the mode of performance outcome feedback and task difficulty on timing decisions (i.e., when to act).

Thermoregulatory modeling for cold stress.

Modeling for cold stress has generated a rich history of innovation, has exerted a catalytic influence on cold physiology research, and continues to impact human activity in cold environments. This overview begins with a brief summation of cold thermoregulatory model development followed by key principles that will continue to guide current and future model development. Different representations of the human body are discussed relative to the level of detail and prediction accuracy required.

Advances, shortcomings, and recommendations for wind chill estimation.

This article discusses briefly the advances made and the remaining short-comings in the "new" wind chill charts adopted in the US and Canada in 2001. A number of indicated refinements are proposed, including the use of whole body models in the computations, verification of heat exchange coefficients by human experiments, reconsideration of "calm" wind conditions, reconsideration of frostbite threshold levels, the inclusion of cold-related pain and numbness in the charts, etc. A dynamic numerical model is applied to compare the effects of wind speeds, on the one hand, and air temperatures, on the other, on the steady-state exposed facial and bare finger temperatures.

Evaluation of two cold thermoregulatory models for prediction of core temperature during exercise in cold water.

Cold thermoregulatory models (CTM) have primarily been developed to predict core temperature (T(core)) responses during sedentary immersion. Few studies have examined their efficacy to predict T(core) during exercise cold exposure. The purpose of this study was to compare observed T(core) responses during exercise in cold water with the predicted T(core) from a three-cylinder (3-CTM) and a six-cylinder (6-CTM) model, adjusted to include heat production from exercise.

Effects of cold strain on simulated sentry duty and marksmanship.

Background: Cold exposure is not uncommon to military situations, but its effects on dismounted soldier performance are not entirely known. The present study was conducted to determine the level of cold strain that would degrade the detection, identification, and engagement of targets.

Hypothesis: Degradation in marksmanship, but not vigilance, is expected in individuals that reach significant levels of cold strain, short of uncontrollable shivering.

Prediction of facial cooling while walking in cold wind.

A dynamic model of cheek cooling has been modified to account for increased skin blood circulation of individuals walking in cold wind. This was achieved by modelling the cold-induced vasodilation response to cold as a varying blood perfusion term, which provided a source of convective heat to the skin tissues of the model. Physiologically-valid blood perfusion was fitted to replicate the cheek skin temperature responses of 12 individuals experimentally exposed to air temperatures from -10 to 10 degrees C at wind speeds from 2 to 8 ms(-1).

Association between alcohol and mortality in patients with severe traumatic head injury.

Hypothesis: Admission blood alcohol concentration (BAC) is associated with in-hospital death in patients with severe brain injury from blunt head trauma.

Design: Retrospective cohort study.

Setting: Academic level I trauma center in Toronto, Ontario.

Heat strain at high levels does not degrade target detection and rifle marksmanship.

Background: A recent investigation found no degradation in rifle marksmanship due to mild heat strain (up to a 1 degrees C increase in core temperature) even though the subjective sensation of discomfort was significant. The present study was conducted to determine if, and at what level of heat strain would degradation in both target detection and marksmanship (TD&M) occur.

Hypothesis: Degradation in TD&M performance is expected in individuals who reach a level of high heat strain.

Physical and cognitive performance during long-term cold weather operations.

Background: Physiological responses, physical performance, and cognitive performance were measured during military cold weather survival courses to determine the effects of long-term cold exposure on training safety and potential survival ability.

Methods: There were 28 males, from 5 9-d winter survival courses, who participated. Cognitive performance was evaluated through logical reasoning, planning, and vigilance.

Thermoregulatory model for prediction of long-term cold exposure.

A multi-segmental mathematical model has been developed for predicting shivering and thermoregulatory responses during long-term cold exposure. The present model incorporates new knowledge on shivering thermogenesis, including the control and maximal limits of its intensity, inhibition due to a low core temperature, and prediction of endurance time. The model also takes into account individual characteristics of age, height, weight, % body fat, and maximum aerobic capacity.

Life raft entry from water: effect of strength, tallness, and weight burden in men and women.

Background: The recurring failure of survivors of accidental water immersion to self-board a life raft prompted us to quantify the requisite physical attributes for successful self-boarding for predictive purposes.

Methods: There were 24 men and 24 women (18 to 52 yr) who attempted to self-board an inflated double-tube life raft using ladder, ramp, and over-the-side (OTS) entry methods while wearing a lifejacket in warm, calm water. The OTS method was also tested under weight-bearing conditions to determine the subject's 'reserve' capacity (i.

Acute caffeine intake before and after fatiguing exercise improves target shooting engagement time.

Introduction: Previous research has identified acute caffeine ingestion as an effective aid in counteracting the decline in vigilance experienced during sentry duty and sustained operations. However, further research is needed to clarify caffeine's effects under various stressors and additional operational conditions. The purpose of the present study was to examine the effect of caffeine on target detection and rifle marksmanship during simulated combat operations.

Caffeine restores engagement speed but not shooting precision following 22 h of active wakefulness.

Background: Current military missions occasionally require combat readiness of soldiers who might be experiencing a sustained period of activity without sleep. Strategies to overcome the debilitating effects of sleep deprivation include the ingestion of caffeine. Unknown is the efficacy of caffeine use on specific elements of target detection and marksmanship following a modest period of sustained wakefulness.

Exercise effects during diving and decompression on postdive venous gas emboli.

Background: Exercise and diving have generally been associated with an increased risk of decompression sickness (DCS), thus accounting for the lack of studies involving exercise during decompression. However, theoretical and observational evidence contrary to this association motivated the present investigation on the effects of moderate, intermittent exercise during diving and/or during decompression on venous gas emboli (VGE) activity following a dive.

Hypothesis: VGE observed at both the precordium and subclavian vein sites after diving should be reduced if moderate exercise is performed during decompression vs.

Heat balance precedes stabilization of body temperatures during cold water immersion.

Certain previous studies suggest, as hypothesized herein, that heat balance (i.e., when heat loss is matched by heat production) is attained before stabilization of body temperatures during cold exposure.

Investigation of rifle marksmanship on simulated targets during thermal discomfort.

Background: Marksmanship has been reported to deteriorate during exposure to heat or cold, yet the effect of the resultant thermal strain in isolation of the inflicting thermal stress is not entirely clear. In most studies, the debilitating effects on marksmanship are confounded by an evolving thermal strain (in terms of body heat storage/debt).

Hypothesis: Thermal strain (hot and cold) should degrade marksmanship, more with moving targets than with conventional pop-up targets that are deemed less challenging.

Perceptual versus physiological heat strain during exercise-heat stress.

Purpose: The physiological strain index (PSI) has been proposed as a universally applicable measure of exercise-heat strain. Unknown is whether this index, based on normalized increases in core temperature and heart rate, is matched by its perceptual analog.

Methods: By using a similar mathematical construct to the PSI, the perceptions of thermal sensation and perceived exertion were combined, and the resultant index, PeSI, was compared with its physiological counterpart, denoted as PhSI, for the exercise-heat stress specific to this study.