Biomedical subjects

Peter Tikuisis

Publications and source records attributed to Peter Tikuisis.

12 recordsLinked to original sources

PubMed2006

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). Resultant cheek skin temperatures met goodness-of-fit criteria and implications on wind chill predictions are discussed.

Adult↗

PubMed2006

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. PATIENTS: Using trauma registry data, between January 1, 1988, and December 31, 2003, we identified 1158 consecutive patients with severe brain injury from blunt head trauma. INTERVENTION: There was no active intervention. The primary exposure of interest was the BAC at admission, stratified into the following 3 levels: 0, no BAC; 0 to less than 230 mg/dL, low to moderate BAC; and 230 mg/dL or greater, high BAC. MAIN OUTCOME MEASURE: In-hospital death. RESULTS: In patients with severe brain injury, low to moderate BAC was associated with lower mortality than was no BAC (27.9% vs 36.3%; P = .008). High BAC was associated with higher mortality than was no BAC (44.7% vs 36.3%), although this was not statistically significant (P = .10). These associations were all statistically significant after adjusting for demographic data and injury factors using logistic regression analysis. The odds ratio for death was 0.76 (95% confidence interval, 0.52-0.98) for low to moderate BAC compared with no BAC. The odds ratio for death was 1.73 (95% confidence interval, 1.05-2.84) for high BAC compared with no BAC. CONCLUSIONS: Low to moderate BAC may be beneficial in patients with severe brain injury from blunt head trauma. In contrast, high BAC seems to have a deleterious effect on in-hospital death in these patients, which may be related to its detrimental hemodynamic and physiologic effects. Alcohol-based fluids may have a role in the management of patients with severe brain injury after they have been well resuscitated.

Adult↗

PubMed2005

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. The model was validated against three different cold conditions i.e. water immersion up to 38 h and air exposure. The predictions were found to be in good agreement with the observations.

Adult↗

PubMed2005

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.e., maximum additional load capacity). RESULTS: Out of the 24 men, 22 successfully boarded the life raft, as did 17 out of the 24 women, using all methods of entry, and their reserve capacities ranged from 2 to 23% of body mass. Men reported lower efforts of exertion and were faster than women when using the ladder or boarding OTS without weights. There were no gender differences in these measures for the ramp and weighted OTS methods of entry. Strength and tallness were positive attributes for boarding the life raft using the ladder and OTS methods of entry, but not when using the ramp, which was the easiest and fastest entry method to execute. CONCLUSIONS: Men were more successful in boarding the life raft OTS (approximately 90%) compared with women (approximately 70%), but the difference was less pronounced for the ladder and ramp entry methods. The subjects' limited reserve capacities suggest that heavy layers of wet clothing and/or loss of muscle strength can easily compromise an individual's ability to self-board a life raft.

Accidents, Aviation↗

PubMed2005

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. Physical performance was evaluated with tests of hand function and arm strength. Subjective cold sensation scale (CSS), rating of perceived exertion (RPE), and mood indicators were quantified. Core temperature (T(core0) and HR were recorded continuously throughout the courses, and fingertip temperature (T(finger)) was also recorded during testing. Hematocrit values to indicate hydration status were obtained from blood samples taken on three occasions. RESULTS: Mean air temperature (T(air)) during the testing periods ranged from -24.4 to 4.4 degrees C among the five courses. Hydration level and T(core) remained normal throughout all courses while T(finger) decreased with decreasing T(air). Finger dexterity deteriorated by 23-28% when T(finger) decreased from 18 to 10 degrees C. Muscular strength was decreased by a small (4%) but significant amount over 6 d of testing. Cognitive function was unaffected by cold air or time on the course. Mood indicators were consistent with CSS and RPE scores. CONCLUSION: Under the exposure conditions and availability of basic survival equipment, including water, described herein, and in the absence of trauma, healthy fit individuals can participate in this military training without any serious decrements in cognitive and physical performance. In an actual survival situation, similarly decreased dexterity may adversely affect survival activities.

Adaptation, Physiological↗

PubMed2005

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. METHODS: There were 11 subjects (mean +/- SD of 28.9 +/- 6.0 yr, 177 +/- 10 cm, and 81.2 +/- 18.8 kg) who participated in 3 counterbalanced trials: control (CN); heat with hydration (HH); and heat without hydration (HD). Core temperature was increased through a combination of exercise and passive heating over 4 h. Measures of shooting performance every half hour included target detection and engagement times, friend-foe discrimination, and shooting accuracy using a small arms trainer. RESULTS: All physiological measures and indices indicated that a significantly elevated heat strain was attained during HH and HD compared with CN. Mean heart rates and core temperatures approached 150 bpm and 39 degrees C, respectively, at the end of the heated trials. Aside from minor differences in target detection and identification owing to target type, no detrimental impact on TD&M due to heat strain, whether hydrated or dehydrated, was observed. CONCLUSIONS: High levels of heat strain do not adversely affect target detection and rifle marksmanship performance, at least for a period of time not exceeding 4 h in a non-threatening environment.

Adult↗

PubMed2004

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. remaining inactive. METHODS: In a water-filled hyperbaric chamber, 39 healthy male subjects were compressed to a pressure of 450 kPa (45 msw) for 30 min followed by 55 min of staged decompression. Subjects were either active or inactive at the bottom phase (450 kPa) and/or during the decompression. Activity comprised three 5-min intervals of moderate arm or leg exercise at the bottom and five such intervals during decompression. After decompression, VGE were monitored at the precordium and subclavian vein sites using Doppler detection. Bubble activity scores were converted to various indices and analyzed using non-parametric statistics. RESULTS: VGE activity was invariant as to whether subjects were active or sedentary during the bottom phase of the dive. However, it was significantly lower for all indices examined (p < 0.05) after dives in which exercise was performed during decompression vs. inactive decompression. CONCLUSION: Moderate, intermittent physical activity during decompression decreases VGE activity after diving.

Adult↗

PubMed2004

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. METHODS: There were 20 subjects (mean +/- SD of 26.7 +/- 7.2 yr of age, 179 +/- 6 cm in height, and 84.5 +/- 10.8 kg in weight) who participated in double-blind caffeine and placebo trials where each trial involved a 24-h control period (with sleep) followed by 22 h of mixed mental and physical activity with no sleep. At the end of this period, subjects engaged in a 1-h rifle-shooting task. Subjects ingested 400, 100, and 100 mg of caffeine or placebo at 7.5, 3, and 0 h, respectively, prior to shooting. Measures of shooting performance included target engagement time (between target appearance and firing), friend-foe discrimination, accuracy, and precision. RESULTS: Most measures of performance were degraded in the placebo sleep-deprived condition, but only the target engagement time and the number of shots fired were restored by caffeine ingestion. CONCLUSIONS: These findings concur with other research involving different periods of sleep deprivation, and indicate that the cognitive component of the shooting task (i.e., target detection) can benefit from caffeine whereas the psychomotor component (marksmanship) does not. It appears that once the target is detected, the subject is sufficiently aroused to engage the target regardless of the subject's level of alertness prior to detection.

Adult↗

PubMed2004

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. METHODS: There were 12 reservists who ingested 5 mg x kg(-1) body mass of caffeine (C) or placebo (P) 1 h before beginning a 2.5-h loaded march and 1.0-h sandbag wall construction task. Following exercise, participants were given a re-dose of 2.5 mg x kg(-1) body mass of C or P. An hour after ingestion, participants commenced a 2.5-h shooting session on a small arms simulator, which included friend-foe discrimination (FF) and vigilance (VIG) tasks. Marksmanship performance measures included engagement time (ET), the number of shots fired (NS), accuracy, and precision. RESULTS: C ingestion (initial and/or redose) did not affect shooting performance during the FF task. ET and NS improved during the VIG task with C ingestion (mean +/- SD of 2.82 +/- 0.27 s and 29.2 +/- 1.9 shots out of 30 targets, respectively) compared with the P trial (3.00 +/- 0.26 s and 28.0 +/- 3.0 shots; p < 0.05). CONCLUSION: Caffeine ingestion improves target detection and engagement speed during vigilance situations, but is not effective during more complex operations requiring higher levels of cognitive processing and fine motor control and coordination.

Adult↗

PubMed2003

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. This phenomenon is explained through a theoretical analysis of heat distribution in the body applied to an experiment involving cold water immersion. Six healthy and fit men (mean +/- SD of age = 37.5 +/- 6.5 yr, height = 1.79 +/- 0.07 m, mass = 81.8 +/- 9.5 kg, body fat = 17.3 +/- 4.2%, maximal O2 uptake = 46.9 +/- 5.5 l/min) were immersed in water ranging from 16.4 to 24.1 degrees C for up to 10 h. Core temperature (Tco) underwent an insignificant transient rise during the first hour of immersion, then declined steadily for several hours, although no subject's Tco reached 35 degrees C. Despite the continued decrease in Tco, shivering had reached a steady state of approximately 2 x resting metabolism. Heat debt peaked at 932 +/- 334 kJ after 2 h of immersion, indicating the attainment of heat balance, but unexpectedly proceeded to decline at approximately 48 kJ/h, indicating a recovery of mean body temperature. These observations were rationalized by introducing a third compartment of the body, comprising fat, connective tissue, muscle, and bone, between the core (viscera and vessels) and skin. Temperature change in this "mid region" can account for the incongruity between the body's heat debt and the changes in only the core and skin temperatures. The mid region temperature decreased by 3.7 +/- 1.1 degrees C at maximal heat debt and increased slowly thereafter. The reversal in heat debt might help explain why shivering drive failed to respond to a continued decrease in Tco, as shivering drive might be modulated by changes in body heat content.

Adipose Tissue↗

PubMed2002

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. Twenty-six young and healthy subjects wore semi-impermeable clothing and walked (3.5 km.h(-1)) under hot conditions (40 degrees C and 30% RH) until exhaustion or when their core temperature reached 39.5 degrees C. Subjects were divided into two fitness groups [endurance trained (T) and untrained (U)] comprised of 10 men and 3 women each. U subjects had a higher level of body fatness (mean +/- SD 18.1 +/- 5.3 vs 12.6 +/- 4.5%; P=0.010) and a lower level of aerobic fitness ((.)VO(2max)= 43.6 +/- 3.8 +/- vs 59.0 +/- 6.2 mL.min(-1).kg(-1); P<0.001). RESULTS: During the first hour of exposure, there was no group difference in PhSI, yet T perceived their physiological strain (PeSI) lower than U (P=0.002). Further, the indices were not different for U whereas PhSI was higher than PeSI for T (P=0.008). At the end of the exposure, T had a higher value of PhSI than U (8.23 +/- 0.72 vs 6.74 +/- 1.47; = 0.002), but there was no group difference in PeSI. Although the indices were again not different for U, PhSI at the end was higher than PeSI for T (6.14 +/- 1.68; P<0.001). CONCLUSION: T underestimated and U consistently perceived their physiological strain, as defined by PhSI, in accordance with the measured increases in core temperature and heart rate throughout an exposure to uncompensable exercise-heat stress.

Adult↗

PubMed2002

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. METHODS: The 12 rifle-trained military reservists (7 men and 5 women) were tested on their marksmanship skills using a small arms simulator. Subjects conducted three trials in an environmentally controlled chamber, 1 wk apart in a counter-balanced order. Trial conditions were neutral (N; 22 degrees C), hot (H; 35 degrees C), and cold (C; 5 degrees C), and all were preceded with an immersion in water to chest level to establish thermal strain (for H and C) or to maintain thermal neutrality prior to shooting. Subjects fired a C7 rifle at various targets during sixteen 5-min engagements over 2 h. Targets were presented either as moving in an urban setting or as pop-ups in a lane setting. Body temperatures, heart rate, saliva cortisol concentration, subjective ratings, and measures of marksmanship accuracy and precision were recorded and analyzed using a repeated measures design. RESULTS: Mean +/- SD of the rectal temperature during the shooting were 36.9 +/- 0.2 degrees C, 37.7 +/- 0.3 degrees C, and 36.8 +/- 0.6 degrees C for N, H, and C, respectively (H > N, C). Corresponding hand temperatures were 31.5 +/- 1.2 degrees C, 35.2 +/- 0.7 degrees C, and 19.4 +/- 3.0 degrees C (H > N > C). These body temperatures were consistent with the subjective indices of heat illness, cold discomfort, and muscle discomfort. Cortisol concentration and perceived exertion were higher during H. Surprisingly, thermal strain did not degrade marksmanship. Instead, some aspects of precision (horizontal displacement) and accuracy (shooting error) were poorer during N compared with H and C. CONCLUSIONS: Deep body temperatures not higher than approximately 37.9 degrees C and not less than 36.4 degrees C (accompanied by hand temperatures of not less than 19 degrees C) do not negatively affect rifle marksmanship performance, even if significant respective sensations of heat and cold are present.

Adult↗