Iterative assessment of a sports rehydration beverage containing a novel amino acid formula on water uptake kinetics.

PURPOSE: Rapid gastric emptying and intestinal absorption of beverages is essential for rapid rehydration, and certain amino acids (AA) may augment fluid delivery. Three sugar-free beverages, containing differing AA concentrations (AA + PZ), were assessed for fluid absorption kinetics against commercial sugar-free (PZ, GZ) and carbohydrate-containing (GTQ) beverages. METHODS: Healthy individuals (n = 15-17 per study) completed three randomised trials. Three beverages (550-600 mL) were ingested in each study (Study 1: AA + PZ [17.51 g/L AA], PZ, GZ; Study 2: AA + PZ [6.96 g/L AA], PZ, GZ; Study 3: AA + PZ [3.48 g/L AA], PZ, GTQ), containing 3.000 g deuterium oxide (D2O). Blood samples were collected pre-, 2-min, 5-min, and every 5-min until 60-min post-ingestion to quantify maximal D2O enrichment (Cmax), time Cmax occurred (Tmax) and area under the curve (AUC). RESULTS: Study 1: AUC (AA + PZ: 15,184 ± 3532 δ‰ vs. VSMOW; PZ: 17,328 ± 3153 δ‰ vs. VSMOW; GZ: 17,749 ± 4204 δ‰ vs. VSMOW; P ≤ 0.006) and Tmax (P ≤ 0.005) were lower for AA + PZ vs. PZ/GZ. Study 2: D2O enrichment characteristics were not different amongst beverages (P ≥ 0.338). Study 3: Cmax (AA + PZ: 440 ± 94 δ‰ vs. VSMOW; PZ: 429 ± 83 δ‰ vs. VSMOW; GTQ: 398 ± 81 δ‰ vs. VSMOW) was greater (P = 0.046) for AA + PZ than GTQ, with no other differences (P ≥ 0.106). CONCLUSION: The addition of small amounts of AA (3.48 g/L) to a sugar-free beverage increased fluid delivery to the circulation compared to a carbohydrate-based beverage, but greater amounts (17.51 g/L) delayed delivery.

Amino Acid-Based Beverage Interventions Ameliorate Exercise-Induced Gastrointestinal Syndrome in Response to Exertional-Heat Stress: The Heat Exertion Amino Acid Technology (HEAAT) Study.

The study aimed to determine the effects of two differing amino acid beverage interventions on biomarkers of intestinal epithelial integrity and systemic inflammation in response to an exertional-heat stress challenge. One week after the initial assessment, participants (n = 20) were randomly allocated to complete two exertional-heat stress trials, with at least 1 week washout. Trials included a water control trial (CON), and one of two possible amino acid beverage intervention trials (VS001 or VS006). On VS001 (4.5 g/L) and VS006 (6.4 g/L), participants were asked to consume two 237-ml prefabricated doses daily for 7 days before the exertional-heat stress, and one 237-ml dose immediately before, and every 20 min during 2-hr running at 60% maximal oxygen uptake in 35 °C ambient conditions. A water volume equivalent was provided on CON. Whole blood samples were collected pre-, immediately post-, 1 and 2 hr postexercise, and analyzed for plasma concentrations of cortisol, intestinal fatty acid protein, soluble CD14, and immunoglobulin M (IgM) by ELISA, and systemic inflammatory cytokines by multiplex. Preexercise resting biomarker concentrations for all variables did not significantly differ between trials (p > .05). A lower response magnitude for intestinal fatty acid protein (mean [95% CI]: 249 [60, 437] pg/ml, 900 [464, 1,336] pg/ml), soluble CD14 (-93 [-458, 272] ng/ml, 12 [-174, 197] ng/ml), and IgM (-6.5 [-23.0, 9.9] MMU/ml, -10.4 [-16.2, 4.7] MMU/ml) were observed on VS001 and V006 compared with CON (p < .05), respectively. Systemic inflammatory response profile was lower on VS001, but not VS006, versus CON (p < .05). Total gastrointestinal symptoms did not significantly differ between trials. Amino acid beverages' consumption (i.e., 4.5-6.4 g/L), twice daily for 7 days, immediately before, and during exertional-heat stress ameliorated intestinal epithelial integrity and systemic inflammatory perturbations associated with exercising in the heat, but without exacerbating gastrointestinal symptoms.

Change of Seasons: Boston Marathon Wet Bulb Globe Temperature Index in October.

INTRODUCTION: The importance of providing wet bulb globe temperature (WBGT) heat stress flag category measurements in real time is well recognized by road race directors, and it is bound to become even more important with the rise of extreme weather and pandemic outbreaks. The purpose of this paper is to describe the WBGT index and its components measured during the 125th running of the Boston Marathon on October 11, 2021, for qualitative comparison to measurements made similarly on its traditional April date, 2014 to 2019. METHODS: Monitoring occurred at the 7 km, 18 km, and 32 km marks of the race in the towns of Ashland, Natick-Wellesley, and Newton. The outdoor WBGT index was calculated from direct hourly measurements of the dry bulb, black globe, and natural wet bulb temperatures from 0900 to 1500 h. RESULTS: The WBGT index was not different among towns; thus, the average hourly values for the 3 towns were compared to historical data averaged identically. Although the black globe temperature fluctuated considerably in response to changing cloud cover, on average, partly cloudy skies kept the solar load comparable to what has been observed in April. Dry bulb and wet bulb temperatures were higher than those on most April dates shown, which resulted in a yellow (or amber) flag day for most of the race. CONCLUSIONS: The historic October Boston Marathon was among the warmest in recent history. Like the impact of COVID-19 on the 2021 Boston Marathon, future climate challenges around outdoor activities could necessitate rescheduling; they underscore the importance of real-time WBGT index measures.

Personalized Hydration Requirements of Runners.

This study sought to (a) estimate how the duration of running influences sweat losses and contributes to the daily fluid requirement, and (b) empirically estimate the drinking rates required to prevent significant dehydration (≥2% body weight as body water). Individual sweating data and running duration were obtained from male (n = 83) and female (n = 36) runners (n = 146 total observations) performing under highly heterogeneous conditions and over a range of exercise durations (33-280 min). Running <60 min/day increased daily fluid needs by a factor of 1.3, whereas running >60 min/day increased the daily fluid need by a factor of 1.9-2.3. Running <60 min/day generally required no fluid intake to prevent significant dehydration before run completion (31/35 runners). In contrast, running >60 min/day required more than 50% replacement of sweating rates to prevent the same (65/111 runners). Overall sweat losses ranged from ∼0.2 to ∼5.0 L/day, whereas the drinking rates required to prevent significant dehydration ranged from 0 to 1.4 L/hr. The characterization of sweat losses, sweat rate, and required drinking among runners in this study indicate wide individual variability that warrants personalized hydration practices, particularly when running is prolonged (>60 min) and performance is important. This study may serve as a useful guidepost for sports dietitians when planning and communicating fluid needs to athletes, as well as complement guidance related to both personalized programmed and thirst-driven drinking strategies.

Can an amino acid mixture alleviate gastrointestinal symptoms in neuroendocrine tumor patients?

BACKGROUND: Neuroendocrine tumors, although relatively rare in incidence, are now the second most prevalent gastrointestinal neoplasm owing to indolent disease biology. A small but significant sub-group of neuroendocrine tumor patients suffer from diarrhea. This is usually secondary to carcinoid syndrome but can also be a result of short gut syndrome, bile acid excess or iatrogenic etiologies. Recently, an amino acid based oral rehydration solution (enterade® Advanced Oncology Formula) was found to have anti-diarrheal properties in preclinical models. METHODS: A retrospective chart review of all NET patients treated with enterade® AO was performed after IRB approval. RESULTS: Ninety-eight NET patients who had received enterade® AO at our clinic from May 2017 through June 2019 were included. Patients (N = 49 of 98) with follow up data on bowel movements (BMs) were included for final analysis. Eighty-four percent of patients (41/49) had fewer BMs after taking enterade® AO and 66% (27/41) reported more than 50% reduction in BM frequency. The mean number of daily BMs was 6.6 (range, 3-20) at baseline before initiation of therapy, while the mean number of BMs at 1 week time point post enterade® AO was 2.9 (range, 0-11). CONCLUSIONS: Our retrospective observations are encouraging and support prospective validation with appropriate controls in NET patients. This is first published report of the potential anti-diarrheal activity of enterade® AO in NET patients.

Are oral rehydration solutions optimized for treating diarrhea?

BACKGROUND: A historical turning point occurred in the treatment of diarrhea when it was discovered that glucose could enhance intestinal sodium and water absorption. Adding glucose to salt water (oral rehydration solution, ORS) more efficiently replaced intestinal water and salt losses. AIM: Provide a novel hypothesis to explain why mainstream use of ORS has been strongly recommended, but weakly adopted. METHODS: Traditional (absorptive) and novel (secretory) physiological functions of glucose in an ORS were reviewed. RESULTS: Small amounts of glucose can stimulate both intestinal absorption and secretion. Glucose can exacerbate a net secretory state and may aggravate pathogen-induced diarrhea, particularly for pathogens that affect glucose transport. CONCLUSION: A hypothesis is made to explain why glucose-based ORS does not appreciably reduce diarrheal stool volume and why modern food science initiatives should focus on ORS formulations that replace water and electrolytes while also reducing stool volume and duration of diarrhea.

Predicted sweat rates for group water planning in sport: accuracy and application.

This study tested the accuracy of a novel, limited-availability web application (H2Q™) for predicting sweat rates in a variety of sports using estimates of energy expenditure and air temperature only. The application of predictions for group water planning was investigated for soccer match play. Fourteen open literature studies were identified where group sweat rates were reported (n = 20 group means comprising 230 individual observations from 179 athletes) with fidelity. Sports represented included: walking, cycling, swimming, and soccer match play. The accuracy of H2Q™ sweat rates was tested by comparing to measured group sweat rates using the concordance correlation coefficient (CCC) with 95% confidence interval [CI]. The relative absolute error (RAE) with 95% [CI] was also assessed, whereby the mean absolute error was expressed relative to an acceptance limit of 0.250 L/h. The CCC was 0.98 [0.95, 0.99] and the RAE was 0.449 [0.279, 0.620], indicating that the prediction error was on average 0.112 L/h. The RAE was < 1.0 for 19/20 observations (95%). Drink volumes modeled as a proxy for sweat losses during soccer match play prevented dehydration (< 1% loss of body mass). The H2Q™ web application demonstrated high group sweat prediction accuracy for the variety of sports activities tested. Water planning for soccer match play suggests the feasibility of easily and accurately predicting sweat rates to plan group water needs and promote optimal hydration in training and/or competition.

Biological variation of arginine vasopressin.

PURPOSE: There is growing interest in the measurement of plasma levels of arginine vasopressin (AVP) for the assessment of mild dehydration. However, the principles of biological variation have not been applied to the study of AVP and understanding biological variation of AVP may provide insights regarding measurement thresholds. The purpose of this investigation was to determine the biological variation of AVP in healthy euhydrated individuals to understand the potential for establishing both static and/or change thresholds of importance. METHODS: We studied 29 healthy volunteers (24 men and 5 women) while controlling for hydration and pre-analytical factors. All subjects completed between 2-8 trials where biological variation was determined using widely published methods. We determined the intraindividual, interindividual, and analytical coefficients of variation (CVI, CVG, and CVA, respectively) and subsequently the index of individuality and heterogeneity (II and IH, respectively). RESULTS: AVP did not reach the IH threshold required to be considered useful in the dynamic assessment of physiological deviations from normal. AVP levels approached the II threshold required to be considered useful in the static assessment of physiological deviations from normal. CONCLUSIONS: This analysis demonstrates that AVP assessment is unlikely to yield useful information about hydration status.

Biological variation of resting measures of ventilation and gas exchange in a large healthy cohort.

PURPOSE: Resting measures of ventilation and gas exchange are impacted by a variety of physiological stressors, such as those resulting from a research intervention or an extreme environment. However, the biological variation of these parameters, an important statistical consideration for identifying a meaningful physiological change, has not been quantified. METHODS: We performed a retrospective analysis of 21 studies completed by the U.S. Army Research Institute of Environmental Medicine (USARIEM) from 1985 to present, totaling 411 healthy volunteers. First, we determined the intraindividual, interindividual, and analytic coefficients of variation (CVI, CVG, and CVA, respectively) and subsequently the index of individuality and heterogeneity (II and IH, respectively). Second, when deemed appropriate via these outcomes, we defined the accompanying static and dynamic thresholds, beyond which a significant deviation from normal is indicated. RESULTS: End-tidal partial pressure of oxygen (PETO2) and the respiratory exchange ratio (RER) approached the II threshold required to be considered useful in the static assessment of physiological deviations from normal. PETO2 and peripheral oxygen saturation (SpO2) approached the IH threshold required to be considered useful in the dynamic assessment of physiological deviations from normal. CONCLUSIONS: This analysis identifies RER and PETO2 as parameters that might be most useful when aiming to identify a meaningful ventilatory change following a research intervention or stressor. Alternatively, other parameters of ventilation and gas exchange, such as PETCO2 and VE, may be less useful for observing an anticipated physiological change.

Importance of sample volume to the measurement and interpretation of plasma osmolality.

BACKGROUND: Small sample volumes may artificially elevate plasma osmolality (Posm) measured by freezing point depression. The purpose of this study was to compare two widely different sample volumes of measured Posm (mmol/kg) to each other, and to calculated osmolarity (mmol/L), across a physiological Posm range (~50 mmol/kg). METHODS: Posm was measured using freezing point depression and osmolarity calculated from measures of sodium, glucose, and blood urea nitrogen. The influence of sample volume was investigated by comparing 20 and 250 µL Posm samples (n = 126 pairs). Thirty-two volunteers were tested multiple times while EUH (n = 115) or DEH (n = 11) by -4.0% body mass. Protinol™ (240, 280, and 320 mmol/kg) and Clinitrol™ (290 mmol/kg) reference solutions were compared similarly (n = 282 pairs). RESULTS: The 20 µL samples of plasma showed a 7 mmol/kg positive bias compared to 250 µL samples and displayed a nearly constant proportional error across the range tested (slope = 0.929). Calculated osmolarity was lower than 20 µL Posm by the same negative bias (-6.9 mmol/kg) but not different from 250 µL Posm (0.1 mmol/kg). The differences between 20 and 250 µL samples of Protinol™ were significantly higher than Clinitrol™. CONCLUSIONS: These results demonstrate that Posm measured by freezing point depression will be ~7 mmol/kg higher when using 20 µL vs 250 µL sample volumes. Approximately half of this effect may be due to plasma proteins. Posm sample volume should be carefully considered when calculating the osmole gap or assessing hydration status.

Fluid Needs for Training, Competition, and Recovery in Track-and-Field Athletes.

The 2019 International Amateur Athletics Federation Track-and-Field World Championships will take place in Qatar in the Middle East. The 2020 Summer Olympics will take place in Tokyo, Japan. It is quite likely that these events may set the record for hottest competitions in the recorded history of both the Track-and-Field World Championships and Olympic Games. Given the extreme heat in which track-and-field athletes will need to train and compete for these games, the importance of hydration is amplified more than in previous years. The diverse nature of track-and-field events, training programs, and individuality of athletes taking part inevitably means that fluid needs will be highly variable. Track-and-field events can be classified as low, moderate, or high risk for dehydration based on typical training and competition scenarios, fluid availability, and anticipated sweat losses. This paper reviews the risks of dehydration and potential consequences to performance in track-and-field events. The authors also discuss strategies for mitigating the risk of dehydration.

Sympathetic neural and hemodynamic responses to head-up tilt during isoosmotic and hyperosmotic hypovolemia.

We hypothesized that muscle sympathetic nerve activity (MSNA) during head-up tilt (HUT) would be augmented during exercise-induced (hyperosmotic) dehydration but not isoosmotic dehydration via an oral diuretic. We studied 26 young healthy subjects (7 female, 19 male) divided into three groups: euhydrated (EUH, n = 7), previously exercised in 40°C while maintaining hydration; dehydrated (DEH, n = 10), previously exercised in 40°C during which ~3% of body weight was lost via sweat loss; and diuretic (DIUR, n = 9), a group that did not exercise but lost ~3% of body weight via diuresis (furosemide, 80 mg by mouth). We measured MSNA, heart rate (HR), and blood pressure (BP) during supine rest and 30° and 45° HUT. Plasma volume (PV) decreased similarly in DEH (-8.5 ± 3.3%) and DIUR (-11.4 ± 5.7%) (P > 0.05). Plasma osmolality was similar between DIUR and EUH (288 ± 4 vs. 284 ± 5 mmol/kg, respectively) but was significantly higher in DEH (299 ± 5 mmol/kg) (P < 0.05). Mixed-model ANOVA was used with repeated measures on position (HUT) and between-group analysis on condition. HR and MSNA increased in all subjects during HUT (main effect of position; P < 0.05). There was also a significant main effect of group, such that MSNA and HR were higher in DEH compared with DIUR (P < 0.05). Changes in HR with HUT were larger in both hypovolemic groups compared with EUH (P < 0.05). The differential HUT response "strategies" in each group suggest a greater role for hypovolemia per se in controlling HR responses during dehydration, and a stronger role for osmolality in control of SNA.NEW & NOTEWORTHY Interactions of volume regulation with control of vascular sympathetic nerve activity (SNA) have important implications for blood pressure regulation. Here, we demonstrate that SNA and heart rate (HR) during hyperosmotic hypovolemia (exercise-induced) were augmented during supine and tilt compared with isoosmotic hypovolemia (diuretic), which primarily augmented the HR response. Our data suggest that hypovolemia per se had a larger role in controlling HR responses, whereas osmolality had a stronger role in control of SNA.

Myths and methodologies: Making sense of exercise mass and water balance.

NEW FINDINGS: What is the topic of this review? There is a need to revisit the basic principles of exercise mass and water balance, the use of common equations and the practice of interpreting outcomes. What advances does it highlight? We propose use of the following equation as a way of simplifying exercise mass and water balance calculations in conditions where food is not consumed and waste is not excreted: ∆body mass - 0.20 g/kcal-1  = ∆body water. The relative efficacy of exercise drinking behaviours can be judged using the following equation: percentage dehydration = [(∆body mass - 0.20 g kcal-1 )/starting body mass] × 100. Changes in body mass occur because of flux in liquids, solids and gases. This knowledge is crucial for understanding metabolism, health and human water needs. In exercise science, corrections to observed changes in body mass to estimate water balance are inconsistently applied and often misinterpreted, particularly after prolonged exercise. Although acute body mass losses in response to exercise can represent a close surrogate for body water losses, the discordance between mass and water balance equivalence becomes increasingly inaccurate as more and more energy is expended. The purpose of this paper is briefly to clarify the roles that respiratory water loss, gas exchange and metabolic water production play in the correction of body mass changes for fluid balance determinations during prolonged exercise. Computations do not include waters of association with glycogen because any movement of water among body water compartments contributes nothing to water or mass flux from the body. Estimates of sweat loss from changes in body mass should adjust for non-sweat losses when possible. We propose use of the following equation as a way of simplifying the study of exercise mass and water balance: ∆body mass - 0.20 g kcal-1  = ∆body water. This equation directly controls for the influence of energy expenditure on body mass balance and the approximate offsetting equivalence of respiratory water loss and metabolic water production on body water balance. The relative efficacy of exercise drinking behaviours can be judged using the following equation: percentage dehydration = [(∆body mass - 0.20 g kcal-1 )/starting body mass] × 100.

Am I Drinking Enough? Yes, No, and Maybe.

Adequate fluid intake can be dually defined as a volume of fluid (from water, beverages, and food) sufficient to replace water losses and provide for solute excretion. A wide range of fluid intakes are compatible with euhydration, whereby total body water varies narrowly from day to day by 600 to 900 mL (<1% body mass). One measure of fluid intake adequacy involves enough fluid to prevent meaningful body water deficits outside this euhydration range (i.e., dehydration). Another measure of fluid intake adequacy involves enough fluid to balance the renal solute load, which can vary widely inside the euhydration range. The subtle but important distinction between the 2 types of adequacy may explain some of the ambiguity surrounding the efficacy of hydration status markers. Both perspectives of fluid intake adequacy are discussed in detail and a simple tool is reviewed that may help healthy, active, low-risk populations answer the question, "Am I drinking enough?" Key Teaching Points • Adequate fluid intake can be dually defined as a volume of fluid (from water, beverages, and food) sufficient to replace water losses and provide for solute excretion. • Fluid needs can differ greatly among individuals due to variation in the factors that influence both water loss and solute balance; thus, adequacy is consistent with a wide range of fluid intakes and is better gauged using hydration assessment methods. • Adequacy of fluid intake for replacing meaningful water losses (dehydration) can be assessed simply, inexpensively, and with reasonable fidelity among healthy, active, low-risk individuals. • Adequacy of fluid intake for solute excretion per se can also be assessed among individuals but is more difficult to define and less practical to measure.

Spot Urine Concentrations Should Not be Used for Hydration Assessment: A Methodology Review.

A common practice in sports science is to assess hydration status using the concentration of a single spot urine collection taken at any time of day for comparison against concentration (specific gravity, osmolality, color) thresholds established from first morning voids. There is strong evidence that this practice can be confounded by fluid intake, diet, and exercise, among other factors, leading to false positive/negative assessments. Thus, the purpose of this paper is to provide a simple explanation as to why this practice leads to erroneous conclusions and should be curtailed in favor of consensus hydration assessment recommendations.

Novel Cooling Strategies for Military Training and Operations.

The deleterious effects of environmental heat stress, combined with high metabolic loads and protective clothing and equipment of the modern Warfighter, impose severe heat strain, impair task performance, and increase risk of heat illness, thereby reducing the chance for mission success. Despite the implementation of heat-risk mitigation procedures over the past decades, task performance still suffers and exertional heat illness remains a major military problem. We review 3 novel heat mitigation strategies that may be implemented in the training or operational environment to reduce heat strain and the risk of exertional heat illness. These strategies include ingestion of ice slurry, arm immersion cooling, and microclimate cooling. Each of these strategies is suitable for use in different scenarios and the choice of cooling strategy is contingent on the requirements, circumstances, and constraints of the training and operational scenario. Ingestion of ice slurry and arm immersion cooling are practical strategies that may be implemented during training scenarios; ice slurry can be ingested before and during exercise, whereas arm immersion cooling can be administered after exercise-heat exposure. In the operational environment, existing microclimate cooling can be implemented with retrofitted vehicles and as an unmounted system, and it has the potential for use in many military occupational scenarios. This review will discuss the efficacy, limitations, and practical considerations for field implementation of each strategy.

Human Performance Optimization Metrics: Consensus Findings, Gaps, and Recommendations for Future Research.

Human performance optimization (HPO) is defined as "the process of applying knowledge, skills and emerging technologies to improve and preserve the capabilities of military members, and organizations to execute essential tasks." The lack of consensus for operationally relevant and standardized metrics that meet joint military requirements has been identified as the single most important gap for research and application of HPO. In 2013, the Consortium for Health and Military Performance hosted a meeting to develop a toolkit of standardized HPO metrics for use in military and civilian research, and potentially for field applications by commanders, units, and organizations. Performance was considered from a holistic perspective as being influenced by various behaviors and barriers. To accomplish the goal of developing a standardized toolkit, key metrics were identified and evaluated across a spectrum of domains that contribute to HPO: physical performance, nutritional status, psychological status, cognitive performance, environmental challenges, sleep, and pain. These domains were chosen based on relevant data with regard to performance enhancers and degraders. The specific objectives at this meeting were to (a) identify and evaluate current metrics for assessing human performance within selected domains; (b) prioritize metrics within each domain to establish a human performance assessment toolkit; and (c) identify scientific gaps and the needed research to more effectively assess human performance across domains. This article provides of a summary of 150 total HPO metrics across multiple domains that can be used as a starting point-the beginning of an HPO toolkit: physical fitness (29 metrics), nutrition (24 metrics), psychological status (36 metrics), cognitive performance (35 metrics), environment (12 metrics), sleep (9 metrics), and pain (5 metrics). These metrics can be particularly valuable as the military emphasizes a renewed interest in Human Dimension efforts, and leverages science, resources, programs, and policies to optimize the performance capacities of all Service members.

Assessment of extracellular dehydration using saliva osmolality.

INTRODUCTION: When substantial solute losses accompany body water an isotonic hypovolemia (extracellular dehydration) results. The potential for using blood or urine to assess extracellular dehydration is generally poor, but saliva is not a simple ultra-filtrate of plasma and the autonomic regulation of salivary gland function suggests the possibility that saliva osmolality (Sosm) may afford detection of extracellular dehydration via the influence of volume-mediated factors. PURPOSE: This study aimed to evaluate the assessment of extracellular dehydration using Sosm. In addition, two common saliva collection methods and their effects on Sosm were compared. METHODS: Blood, urine, and saliva samples were collected in 24 healthy volunteers during paired euhydration and dehydration trials. Furosemide administration and 12 h fluid restriction were used to produce extracellular dehydration. Expectoration and salivette collection methods were compared in a separate group of eight euhydrated volunteers. All comparisons were made using paired t-tests. The diagnostic potential of body fluids was additionally evaluated. RESULTS: Dehydration (3.1 ± 0.5% loss of body mass) decreased PV (-0.49 ± 0.12 L; -15.12 ± 3.94% change), but Sosm changes were marginal (<10 mmol/kg) and weakly correlated with changes in absolute or relative PV losses. Overall diagnostic accuracy was poor (AUC = 0.77-0.78) for all body fluids evaluated. Strong agreement was observed between Sosm methods (Expectoration: 61 ± 10 mmol/kg, Salivette: 61 ± 8 mmol/kg, p > 0.05). CONCLUSIONS: Extracelluar dehydration was not detectable using plasma, urine, or saliva measures. Salivette and expectoration sampling methods produced similar, consistent results for Sosm, suggesting no methodological influence on Sosm.

A comparison of whole blood and plasma osmolality and osmolarity.

BACKGROUND: Substituting whole blood osmolality for plasma osmolality could expedite treatments otherwise delayed by the time required to separate erythrocytes from plasma. The purpose of this study was to compare the measured osmolality (mmol/kg) and calculated osmolarity (mmol/l) of whole blood and plasma. METHODS: The osmolality of whole blood and plasma was measured using freezing point depression by micro-osmometer and osmolarity calculated from biosensor measures of sodium, glucose, and blood urea nitrogen. The influence of sample volume was also investigated post hoc by comparing measured osmolality at 20 and 250 µl. RESULTS: Sixty-two volunteers provided 168 paired whole blood and plasma samples for analysis. The mean difference (whole blood - plasma; ±standard deviation) in osmolality was 10 ± 3 mmol/kg. Whole blood was greater than plasma in 168 of 168 cases (100%) and data distributions overlapped by 27%. The mean difference in osmolarity was 0 ± 2 mmol/l. Whole blood was greater than plasma in 90 of 168 cases (56%) and data distributions overlapped by 90%. The osmol gap (osmolality - osmolarity) was 16 ± 6 mmol for whole blood and 7 ± 5 mmol for plasma. Ten volunteers were tested on one occasion post hoc to investigate the potential effects of sample volume. The difference between whole blood and plasma was reduced to 3 ± 2 mmol/kg with a larger (250 µl vs. 20 µl) sample volume. CONCLUSIONS: This investigation provides strong evidence that whole blood and plasma osmolality are not interchangeable measurements when a 20 µl sample is used.

Heat removal using microclimate foot cooling: a thermal foot manikin study.

BACKGROUND: It has been proposed that microclimate cooling systems exploit the peripheral extremities because of more efficient heat transfer. The purpose of this study was to quantify, using a patented microclimate cooling technique, the heat transfer from the plantar surface of the foot for comparison to other commonly cooled body regions. METHODS: A military boot was fitted with an insole embedded with a coiled, 1.27 m length of hollow tubing terminating in inlet and outlet valves. A thermal foot manikin with a surface temperature of 34 degrees C was placed in the boot and the valves were connected to a system that circulated water through the insole at a temperature of 20 degrees C and flow rate of 120 ml x min(-1). The manikin foot served as a constant heat source to determine heat transfer provided by the insole. Testing was done with the foot model dry and sweating at a rate of 500 ml x h(- 1) x m(-2). Climatic chamber conditions were 30 degrees C with 30% RH. RESULTS: Heat loss was approximately 4.1 +/- 0.1 and approximately 7.7 +/- 0.3 W from the dry and sweating foot models, respectively. On a relative scale, the heat loss was 3.0 W and 5.5 W per 1% (unit) body surface area, respectively, for the dry and sweating conditions. DISCUSSION: The relative heat loss afforded by plantar foot cooling was similar compared to other body regions, but the absolute amount of heat removal is unlikely to make an impact on whole body heat balance.