Dietary Intakes From Ad Libitum Consumption of Canadian Armed Forces Field Rations Compared With Usual Home Dietary Intakes and Military Dietary Reference Intakes.

INTRODUCTION: Diet has an impact on weight status, health, and physical performance. Assessing the usual at-home dietary intakes of military personnel can help ascertain their nutritional status before field training or operations. Preference for foods consumed on a routine basis can also impact the military's preference for and consumption of field rations. Military personnel are limited by the inherent nature of the field rations and availability of calories and food types; and despite previous studies indicating a high acceptability of the field rations, it is unknown whether military personnel self-select the same number of calories when faced with a restricted list of field ration options as they would from their usual foods. Although field rations are intended to be nutritionally sufficient for standard military operations, there are limited data on the ad libitum intake of nutrients of Canadian Armed Forces (CAF) personnel from field rations in comparison to the military dietary reference intake (MDRI) recommendations, which establishes standards intended to meet the nutritional requirements of military personnel on duty. Thus, assessing the adequacy of their usual diets at home and longer-term sustenance on field rations in relation to MDRIs can provide insight on CAF personnel's operational readiness. The objectives of this study were to describe and compare, in a convenience sample of CAF, their ad libitum nutrient intakes from the consumption of self-selected field rations at home with their usual home intakes and to compare both with MDRI recommendations. MATERIALS AND METHODS: Eighteen CAF participants weighed and recorded their dietary intake from the ad libitum consumption of field rations at home and their usual at-home diets. Both MDRIs and the Institute of Medicine's dietary reference intake recommendations were used to assess the adequacy of intakes for each individual. Paired Student's t-test or Wilcoxon-matched paired tests were used to compare nutrient intake levels between usual at-home diets and field rations consumed at home. RESULTS: Mean daily energy intakes were similar between ad libitum intakes from field rations (2,688 ± 619 kcal) and usual home diets (2,657 ± 580 kcal), although participants had significantly higher intakes of protein and fat from their home diets and higher intakes of carbohydrates from the field rations (P ≤ 0.05). Participants had less than the recommended intakes of some micronutrients (vitamins A and D, folate, calcium, magnesium, and potassium), from both their home diets and field rations, but adequate intakes of vitamin C and iron. CONCLUSIONS: The results of this study showed no difference in energy intake between the consumption of field rations and home diets, with levels consistent with recommendations for individuals with average physical activity levels. The results also demonstrated less than the recommended intakes (in comparison with MDRIs) of some nutrients from both home diets and self-selected consumption of field rations, warranting further research into nutritional adequacy for operational readiness.

Establishing Healthcare Worker Performance and Safety in Providing Critical Care for Patients in a Simulated Ebola Treatment Unit: Non-Randomized Pilot Study.

Improving the provision of supportive care for patients with Ebola is an important quality improvement initiative. We designed a simulated Ebola Treatment Unit (ETU) to assess performance and safety of healthcare workers (HCWs) performing tasks wearing personal protective equipment (PPE) in hot (35 °C, 60% relative humidity) or thermo-neutral (20 °C, 20% relative humidity) conditions. In this pilot phase to determine the feasibility of study procedures, HCWs in PPE were non-randomly allocated to hot or thermo-neutral conditions to perform peripheral intravenous (PIV) and midline catheter (MLC) insertion and endotracheal intubation (ETI) on mannequins. Eighteen HCWs (13 physicians, 4 nurses, 1 nurse practitioner; 2 with prior ETU experience; 10 in hot conditions) spent 69 (10) (mean (SD)) minutes in the simulated ETU. Mean (SD) task completion times were 16 (6) min for PIV insertion; 33 (5) min for MLC insertion; and 16 (8) min for ETI. Satisfactory task completion was numerically higher for physicians vs. nurses. Participants' blood pressure was similar, but heart rate was higher (p = 0.0005) post-simulation vs. baseline. Participants had a median (range) of 2.0 (0.0-10.0) minor PPE breaches, 2.0 (0.0-6.0) near-miss incidents, and 2.0 (0.0-6.0) health symptoms and concerns. There were eight health-assessment triggers in five participants, of whom four were in hot conditions. We terminated the simulation of two participants in hot conditions due to thermal discomfort. In summary, study tasks were suitable for physician participants, but they require redesign to match nurses' expertise for the subsequent randomized phase of the study. One-quarter of participants had a health-assessment trigger. This research model may be useful in future training and research regarding clinical care for patients with highly infectious pathogens in austere settings.

Continuous forearm cooling attenuates gastrointestinal temperature increase during cycling.

Hot environmental conditions can challenge thermoregulation resulting in exacerbated heat strain. This study evaluated the influence of continuous inner forearm cooling on gastrointestinal temperature (TGI) and physiological responses to exercise in hot (30°C) and humid (relative humidity: 70%) conditions. Eleven trained cyclists (seven male age: 37±12 years; four female age: 41±15 years; mean±standard deviation) performed two experimental trials, cycling at 66% of their self-reported functional threshold power (average work rate over an hour of maximum effort cycling; 175±34W) for 45 minutes in an environmental chamber. One trial employed continuous inner forearm cooling (COOL) with 5°C water passing through aluminum heat exchangers, while the other had no cooling (CONTROL). Heat was removed from the body at an average rate of 30.3±6.6W during the COOL trial resulting in an attenuation of TGI rise (CONTROL: 2.46±0.70, COOL: 2.03±0.63°C·h-1; p=0.002). The change in heart rate from the 10th minute to the end of exercise, as an indicator of cardiovascular drift, was reduced (CONTROL: 20±7, COOL: 17±6beats·min-1; p=0.050) and end-exercise thermal comfort was improved in the COOL trial with a trend for reduced rating of perceived exertion (p=0.055). Findings suggest that continuous cooling of the inner forearms can attenuate the rise of TGI and help mitigate the risk of heat injury during exercise in hot and humid conditions.

Energy Balance of Canadian Armed Forces Personnel during an Arctic-Like Field Training Exercise.

Operating in temperature extremes frequently leads to a discrepancy in energy balance. Investigating the effects of operating in extreme cold temperatures on metabolic requirements has not been well described in Canadian Armed Forces (CAF) personnel. The objective was to accurately assess energy deficits using the "gold standard" methodology for measuring energy intake (EI) and energy expenditure (EE). Nutritional intake of a convenience sample of 10 CAF Class A Reservists, completing a basic military qualification (land) course under winter weather conditions, was assessed using the daily measured food intake/food waste collections. EE was measured by the doubly-labelled water method. Average EI was 2377 ± 1144 kcal/day, which was below the EE (4917 ± 693 kcal/day), despite having ~5685 kcal available in the field rations. A significant body weight loss of 2.7% was associated with the average daily energy deficit of 2539 ± 1396 kcal. As a result, participants demonstrated voluntary anorexia. Such results may have important implications for the impairment of performance and health under longer duration operations.

Comparison of dietary intakes of Canadian Armed Forces personnel consuming field rations in acute hot, cold, and temperate conditions with standardized infantry activities.

BACKGROUND: Dietary Reference Intakes are used to guide the energy intake of the Canadian Armed Forces (CAF) field rations provided to military personnel deployed for training or operations. However, the high energy expenditures likely to occur under harsh environmental/metabolically challenging deployment conditions may not be adequately considered. This study examined the Ad libitum energy and nutrient intakes of CAF personnel (n = 18) consuming field rations in a resting thermoneutral environment and during a day of standardized strenuous infantry activities at varying environmental temperatures. METHODS: Dietary intake was assessed using a measured food intake/food waste method during the experimental treatment and for 6 h after treatment. Four treatments were administered in a randomized counterbalanced design: exercise (as standardized infantry activities) in the heat (30 °C), exercise in the cold (- 10 °C), exercise in temperate thermoneutral (21 °C) air temperatures and a resting (sedentary) trial (21 °C). RESULTS: The average Ad libitum consumption of field rations was 70% of the provided total energy (2776 ± 99 kcal/8 h) during all treatments. Even with an acute challenge of increased energy expenditure and temperature stress in the simulated field conditions, participants' energy intakes (1985 ± 747 kcal/8 h) under hot, cold and temperate treatments did not differ from energy intake during the sedentary condition (1920 ± 640 kcal/8 h). Participants' energy intakes (1009 ± 527 kcal/6 h) did not increase during the 6 h posttreatment period when the stresses of the strenuous physical activities and the harsh environmental temperatures had subsided. CONCLUSION: These results should be considered when planning the provision of field rations for CAF personnel expected to be engaged in strenuous physical activities with prolonged exposure to temperature extremes.

Finger cold-induced vasodilation test does not predict subsequent cold injuries: A lesson from the 2018 Canadian Forces Exercise.

A cold-induced vasodilation (CIVD) test was administered to 113 Canadian Armed Forces (CAF) soldiers (age 25.6 ± 6 yrs) during pre-deployment to a Canadian Arctic training exercise. The incidence and rates/types of subsequent peripheral cold injuries, as well as the relationship of CIVD responses against other hypothesized/reported risk factors (smoking, gender, age, ethnicity and prior cold injury), were analyzed. Although there was a wide range of CIVD RIF (resistance index to frostbite) scores (mean = 5.0 ± 1.5), there were no systematic relationships between RIF and injury type/location and rate, and the other risk factors analyzed. The absence of physiological links to cold injury occurrence suggests that in a military cold deployment setting, other factors are in play, which might include clothing, training, leadership and doctrine. These factors should be examined in future work.

The effects of exercise and ambient temperature on dietary intake, appetite sensation, and appetite regulating hormone concentrations.

BACKGROUND: It is not clear whether the frequently reported phenomenon of exercise-induced anorexia is exacerbated or blunted in warm or cold environments. Therefore, this study investigated the effects of exercise in three different environmental temperatures vs. rest, on perceptions of appetite, appetite regulating hormones, and food intake. METHODS: In a randomized repeated-measures design, 18 Canadian Armed Forces members (14 male, 4 female) completed four 8-h trials in a thermally-controlled chamber: one 8-h resting trial at 21 °C (Sedentary); and three trials where participants completed two 2-h circuits of standardized military tasks interspersed with two 2-h rest periods, once at 30 °C (Hot), once at 21 °C (Temperate), and once at - 10 °C (Cold). Participants consumed military field rations ad libitum and had their appetite assessed with visual analogue scales. Plasma concentrations of GLP-1, PYY, acylated ghrelin, and leptin were also determined. RESULTS: Appetite was perceived as being suppressed in the heat compared to the cold (p < 0.05). While neither exercise nor environmental temperature altered circulating GLP-1 levels, exercise in all environments increased blood concentrations of PYY (p < 0.05). Leptin concentrations were elevated in the heat and diminished in the cold (p < 0.05), and acylated ghrelin concentrations were affected by both exercise and ambient temperature resulting in Sedentary = Cold>Temperate = Hot (p < 0.05). Contrary to the changes in appetite perceptions and hormonal concentrations, dietary intake was not different between conditions (p > 0.05). Relative energy intake (total 24 h energy intake minus 24 h energy expenditure) on the other hand, was significantly higher during the Sedentary condition than it was during any of the active conditions (p < 0.05). Most (83%) of the participants were in a positive energy balance during the Sedentary condition, whereas during most (80%) of the active conditions (Hot, Temperate, Cold) participants were in a negative energy balance. CONCLUSIONS: In this study where food was freely available, variations in ambient temperature, exercise vs. rest, appetite-regulating hormone concentrations, and subjective appetite sensation were not associated with any changes in dietary intake within 24-h of acute, prolonged exercise.

Medical Encounters During a Joint Canadian/U.S. Exercise in the High Arctic (Exercise Arctic Ram).

The Arctic Ram Exercise was conducted in February 2016, near Resolute Bay on Cornwallis Island in Nunavut, Canada, to demonstrate the ability of the Canadian Armed Forces (CAF) to rapidly deploy to the arctic as an immediate response team. This report describes medical problems experienced by the 187 CAF and 28 U.S. forces involved in the exercise. Sixty-six airborne soldiers performed tactical static line jumps and linked up with soldiers on the ground for the exercise. Medical events were recorded by medics on the drop zone and by medical personnel at the Unit Medical Station in Resolute Bay. Average temperature during the exercise was -21°C and wind chill was -44°C. Two U.S. soldiers were injured in association with the jump and an additional 62 patients presented at the clinic during the exercise for an overall medical event incidence of 30%. The incidence of frostbite was 17%. At the end of the exercise, a physician actively examined CAF soldiers in one unit (n = 126) and found that 21% had experienced frostbite. The incidence of frostbite was high in this exercise compared to past cold-weather military operations, likely related to the very low temperatures and wind chills.

Validation of a Tablet Application for Assessing Dietary Intakes Compared with the Measured Food Intake/Food Waste Method in Military Personnel Consuming Field Rations.

The collection of accurate dietary intakes using traditional dietary assessment methods (e.g., food records) from military personnel is challenging due to the demanding physiological and psychological conditions of training or operations. In addition, these methods are burdensome, time consuming, and prone to measurement errors. Adopting smart-phone/tablet technology could overcome some of these barriers. The objective was to assess the validity of a tablet app, modified to contain detailed nutritional composition data, in comparison to a measured food intake/waste method. A sample of Canadian Armed Forces personnel, randomized to either a tablet app (n = 9) or a weighed food record (wFR) (n = 9), recorded the consumption of standard military rations for a total of 8 days. Compared to the gold standard measured food intake/waste method, the difference in mean energy intake was small (-73 kcal/day for tablet app and -108 kcal/day for wFR) (p > 0.05). Repeated Measures Bland-Altman plots indicated good agreement for both methods (tablet app and wFR) with the measured food intake/waste method. These findings demonstrate that the tablet app, with added nutritional composition data, is comparable to the traditional dietary assessment method (wFR) and performs satisfactorily in relation to the measured food intake/waste method to assess energy, macronutrient, and selected micronutrient intakes in a sample of military personnel.

Cardiovascular consequences of high-performance aircraft maneuvers: implications for effective countermeasures and laboratory-based simulations.

The gravitational stress encountered by pilots of high-performance aircraft can cause dramatic shifts in blood volume and circulatory pressure, thus placing the cardiovascular system under significant stress, sometimes resulting in loss of consciousness due to cerebral under-perfusion. Since pilots experience both increased and decreased gravitational stress in high-risk environments, it is important not only to examine the cardiovascular effects of altered gravitational exposure, but also to create effective countermeasures that will increase pilot safety. In this review, we discuss the cardiovascular consequences of rapid changes in gravitational forces. We also examine the effectiveness of the countermeasures that have been developed to combat gravity-induced loss of consciousness. Finally, we examine those current laboratory-based techniques that simulate hyper-gravity and the "push-pull effect"; making it possible to investigate the cardiovascular mechanisms responsible for maintaining cerebral perfusion and consciousness.

Carotid sinus pressure changes during push-pull maneuvers.

INTRODUCTION: The push-pull maneuver (PPM) is defined as a reduction in G-tolerance when positive acceleration (+Gz) immediately follows negative acceleration (-Gz) exposure, with the carotid baroreceptors presumably playing a dominant role in the ensuing BP (SBP) responses. The objective of this study was to determine whether application of neck pressure (NP) during the preceding -Gz phase maintains +Gz tolerance during subsequent +Gz. METHODS: There were 10 experienced men who were exposed to 3 centrifuge run types using a multi-axis centrifuge: a relaxed control run from +1.4 baseline to visual tolerance; a relaxed control PPM run (PPM-C) consisting of 5 s of -1 Gz followed by 15 s of +Gz to visual tolerance; and an experimental PPM run performed with pressurized neck (PPM-NP) consisting of -1 Gz for 5 s followed by 15 s of +Gz at the previous PPM-C G-tolerance level. RESULTS: Relaxed control G tolerance (3.6 _ 0.26 Gz) was greater vs. the PPM-C (3.0 +/- 0.21 Gz) and PPM-NP (3.1 +/- 0.20 Gz) conditions, but the two PPM conditions did not differ significantly. During -Gz, mean R-R interval for PPM-NP was significantly shorter than in the PPM-C from second 1 to second 3. During the +Gz phase, however, R-R interval responses between PPM-C and PPM-NP differed only at seconds 8 and 9. There were no differences in carotid sinus SBP between PPM-C and PPM-NP during -Gr. During +Gz, carotid sinus SBP was significantly depressed in PPM-NP and PPM-C conditions vs. Control. DISCUSSION: Application of NP during the -Gz phase, despite altering R-R interval, did not ameliorate SBP responses or reductions in G tolerance during subsequent +Gz exposure. Despite neck compression counteracting increased carotid hydrostatic pressure during -Gz, the carotid baroreceptor response is likely opposed by the aortic or other baroreceptors.

Effects of concurrent inspiratory and expiratory muscle training on respiratory and exercise performance in competitive swimmers.

The efficiency of the respiratory system presents significant limitations on the body's ability to perform exercise due to the effects of the increased work of breathing, respiratory muscle fatigue, and dyspnoea. Respiratory muscle training is an intervention that may be able to address these limitations, but the impact of respiratory muscle training on exercise performance remains controversial. Therefore, in this study we evaluated the effects of a 12-week (10 sessions week(-1)) concurrent inspiratory and expiratory muscle training (CRMT) program in 34 adolescent competitive swimmers. The CRMT program consisted of 6 weeks during which the experimental group (E, n = 17) performed CRMT and the sham group (S, n = 17) performed sham CRMT, followed by 6 weeks when the E and S groups performed CRMT of differing intensities. CRMT training resulted in a significant improvement in forced inspiratory volume in 1 s (FIV1.0) (P = 0.050) and forced expiratory volume in 1 s (FEV1.0) (P = 0.045) in the E group, which exceeded the S group's results. Significant improvements in pulmonary function, breathing power, and chemoreflex ventilation threshold were observed in both groups, and there was a trend toward an improvement in swimming critical speed after 12 weeks of training (P = 0.08). We concluded that although swim training results in attenuation of the ventilatory response to hypercapnia and in improvements in pulmonary function and sustainable breathing power, supplemental respiratory muscle training has no additional effect except on dynamic pulmonary function variables.

Impairment of cardiovascular and vasomotor responses during tilt table simulation of "push-pull' maneuvers.

BACKGROUND: Numerous studies have shown that tolerance to positive acceleration (+Gz) is impaired subsequent to an exposure of less than +1 Gz. HYPOTHESIS: Vasodilation induced by antecedent negative Gz (-Gz) exposure delays sympathetic vasoconstriction during subsequent +Gz, further reducing G-tolerance. METHODS: There were 20 subjects tested on an electronic tilt table, and exposed to the following randomized head-up tilt (HUT) and head-down tilt (HDT) conditions: +75 degrees HUT for 60 s, followed by transition to either 0 degrees (supine) HDT, or -25 degrees HDT, or -45 degrees HDT for 7 or 15 s at tilt rate of 45 degrees x s(-1). This was followed by HUT, divided into three periods: HUT1 (approximately 3-10 s), HUT2 (approximately 15-22 s), and HUT3 (approximately 27-35 s). Systolic blood pressure (SBP) was normalized to heart and head-levels. Stroke volume (SV) was estimated using impedance cardiography; forearm blood flow (FBF) estimated by venous occlusion plethysmography and forearm vascular resistance (FVR) was calculated from FBF and SBP. Total peripheral resistance (TPR) was estimated by MAP/(SV*HR). RESULTS: Heart-level SBP decreased significantly during HDT for both HDT durations (p < 0.01). SBP increased significantly at head-level during HDT (p < 0.001). During HUT1 heart and head-level SBP decreased for all conditions (p < 0.001), recovering to baseline levels by HUT2. TPR decreased significantly for all HDT conditions (p < 0.001), with this decrease related to the degree of HDT angle (p < 0.05). During HUT1, TPR remained depressed below baseline. At HUT2, TPR remained decreased for the -45 degrees/7-s condition only (p < 0.01). FBF decreased significantly during HDT (p < 0.02), with the magnitude related to the HDT angle. FBF remained elevated during HUT1 (p < 0.01). FVR decreased as a function of HDT angle during HDT (p < 0.001), with the decrease persisting into the HUT1 phase (p < 0.01). By the HUT2 and HUT3 periods, FVR were above baseline levels for the -45 degrees HDT condition (p < 0.01). CONCLUSION: These results confirm in humans the delayed recovery of peripheral vascular resistance observed in animal studies when -Gz precedes +Gz. Since SV recovered to baseline levels during the "pull" phase (HUT1-3), with TPR and forearm vascular resistance remaining depressed, baroreflex-mediated peripheral vascular control is delayed. This delay at higher subsequent +Gz levels is dangerous for the military pilot, since symptoms of G-intolerance due to delay in head-level BP recovery will ensue at lower absolute +Gz levels during push-pull type maneuvers.