The effects of sleep deprivation and extreme exertion on cognitive performance at the world-record breaking Suffolk Back Yard Ultra-marathon.

Using a prospective observational design, this study investigated the hypothesis that competing in the Suffolk Back Yard Ultra-marathon, would result in impaired cognitive performance and examined whether pre-race sleep patterns could mitigate this. Fifteen runners (1 female) volunteered to undertake this study and eleven males were included in the final analysis. Before the race and after withdrawal participants completed the following cognitive performance tasks: 2 Choice Reaction Time (2CRT), Stroop, and the Tower Puzzle. Pre-race sleep strategies were subjectively recorded with a 7-day sleep diary. Following race withdrawal, reaction time increased (Δ 77±68 ms; p = 0.004) in the 2CRT and executive function was impaired in the Stroop task (Interference score Δ -4.3±5.6 a.u.; p = 0.028). Decision making was not affected in the Tower Puzzle task. There was a significant correlation between the pre-race 7-day average sleep scores and both 2CRT Δ throughput (r = 0.61; p = 0.045) and 2CRT Δ RT (r = -0.64; p = 0.034). This study supports the hypothesis that running an ultra-marathon, which includes at least one night of sleep deprivation, impairs cognitive performance and provides novel evidence suggesting good sleep quality, in the week prior to an ultra-marathon, could minimise these effects.

The effects of sleep deprivation, acute hypoxia, and exercise on cognitive performance: A multi-experiment combined stressors study.

INTRODUCTION: Both sleep deprivation and hypoxia have been shown to impair executive function. Conversely, moderate intensity exercise is known to improve executive function. In a multi-experiment study, we tested the hypotheses that moderate intensity exercise would ameliorate any decline in executive function after i) three consecutive nights of partial sleep deprivation (PSD) (Experiment 1) and ii) the isolated and combined effects of a single night of total sleep deprivation (TSD) and acute hypoxia (Experiment 2). METHODS: Using a rigorous randomised controlled crossover design, 12 healthy participants volunteered in each experiment (24 total, 5 females). In both experiments seven executive function tasks (2-choice reaction time, logical relations, manikin, mathematical processing, 1-back, 2-back, 3-back) were completed at rest and during 20 min semi-recumbent, moderate intensity cycling. Tasks were completed in the following conditions: before and after three consecutive nights of PSD and habitual sleep (Experiment 1) and in normoxia and acute hypoxia (FIO2 = 0.12) following one night of habitual sleep and one night of TSD (Experiment 2). RESULTS: Although the effects of three nights of PSD on executive functions were inconsistent, one night of TSD (regardless of hypoxic status) reduced executive functions. Significantly, regardless of sleep or hypoxic status, executive functions are improved during an acute bout of moderate intensity exercise. CONCLUSION: These novel data indicate that moderate intensity exercise improves executive function performance after both PSD and TSD, regardless of hypoxic status. The key determinants and/or mechanism(s) responsible for this improvement still need to be elucidated. Future work should seek to identify these mechanisms and translate these significant findings into occupational and skilled performance settings.

The effect of repeated hot water immersion on insulin sensitivity, heat shock protein 70, and inflammation in individuals with type 2 diabetes mellitus.

Repeated hot water immersion (HWI) can improve glycemic control in healthy individuals but data are limited for individuals with type 2 diabetes mellitus (T2DM). The present study investigated whether repeated HWI improves insulin sensitivity and inflammatory status and reduces plasma ([extracellular heat shock protein 70]) [eHSP70] and resting metabolic rate (RMR). Fourteen individuals with T2DM participated in this pre- versus postintervention study, with outcome measures assessed in fasted (≥12 h) and postprandial (2-h post-75 g glucose ingestion) states. HWI consisted of 1 h in 40°C water (target rectal temperature 38.5°C-39°C) repeated 8-10 times within a 14-day period. Outcome measures included insulin sensitivity, plasma [glucose], [insulin], [eHSP70], inflammatory markers, RMR, and substrate utilization. The HWI intervention increased fasted insulin sensitivity (QUICKI; P = 0.03) and lowered fasted plasma [insulin] (P = 0.04), but fasting plasma [glucose] (P = 0.83), [eHSP70] (P = 0.08), [IL-6] (P = 0.55), [IL-10] (P = 0.59), postprandial insulin sensitivity (P = 0.19), plasma [glucose] (P = 0.40), and [insulin] (P = 0.47) were not different. RMR was reduced by 6.63% (P < 0.05), although carbohydrate (P = 0.43) and fat oxidation (P = 0.99) rates were unchanged. This study shows that 8-10 HWIs within a 14-day period improved fasting insulin sensitivity and plasma [insulin] in individuals with T2DM, but not when glucose tolerance is challenged. HWI also improves metabolic efficiency (i.e., reduced RMR). Together these results could be clinically important and have implications for metabolic health outcomes and well-being in individuals with T2DM.NEW & NOTEWORTHY This is the first study to investigate repeated HWI to raise deep body temperature on insulin sensitivity, inflammation, eHSP70, and substrate utilization in individuals with T2DM. The principal novel findings were improvements in fasting insulin sensitivity and fasting plasma [insulin] but no change in fasting plasma [glucose], postprandial insulin sensitivity, plasma [insulin], or [glucose]. There was also no change in eHSP70, inflammatory status, or substrate utilization but there were reductions in RMR and oxygen consumption.

Effect of different levels of acute hypoxia on subsequent oral glucose tolerance in males with overweight: A balanced cross-over pilot feasibility study.

Previous research has shown that ≤60 min hypoxic exposure improves subsequent glycaemic control, but the optimal level of hypoxia is unknown and data are lacking from individuals with overweight. We undertook a cross-over pilot feasibility study investigating the effect of 60-min prior resting exposure to different inspired oxygen fractions (CON FI O2  = 0.209; HIGH FI O2  = 0.155; VHIGH FI O2  = 0.125) on glycaemic control, insulin sensitivity, and oxidative stress during a subsequent oral glucose tolerance test (OGTT) in males with overweight (mean (SD) BMI = 27.6 (1.3) kg/m2 ; n = 12). Feasibility was defined by exceeding predefined withdrawal criteria for peripheral blood oxygen saturation (SpO2 ), partial pressure of end-tidal oxygen or carbon dioxide and acute mountain sickness (AMS), and dyspnoea symptomology. Hypoxia reduced SpO2 in a stepwise manner (CON = 97(1)%; HIGH = 91(1)%; VHIGH = 81(3)%, p < 0.001), but did not affect peak plasma glucose concentration (CON = 7.5(1.8) mmol∙L-1 ; HIGH = 7.7(1.1) mmol∙L-1 ; VHIGH = 7.7(1.1) mmol∙L-1 ; p = 0.777; η2  = 0.013), plasma glucose area under the curve, insulin sensitivity, or metabolic clearance rate of glucose (p > 0.05). We observed no between-conditions differences in oxidative stress (p > 0.05), but dyspnoea and AMS symptoms increased in VHIGH (p < 0.05), with one participant meeting the withdrawal criteria. Acute HIGH or VHIGH exposure prior to an OGTT does not influence glucose homeostasis in males with overweight, but VHIGH is associated with adverse symptomology and reduced feasibility.

Exploring patients' experiences of the impact of dialysis therapies on quality of life and wellbeing.

BACKGROUND: When people with chronic kidney disease reach kidney failure, renal replacement therapy is usually required to improve symptoms and maintain life. Although in-centre haemodialysis is most commonly used for this purpose, other forms of dialysis are available, including home haemodialysis and peritoneal dialysis. OBJECTIVES: We aimed to explore the experiences of adults living with chronic kidney disease who were either approaching the need for dialysis or had reached kidney failure and were receiving a form of dialysis. In particular, we explored how different forms of dialysis affect their quality of life, wellbeing, and physical activity. METHODS: Individual semistructured interviews were conducted with 40 adults with kidney failure, comprising four groups (n = 10 each): those receiving in-centre haemodialysis, home haemodialysis or peritoneal dialysis, or predialysis. Interviews were transcribed verbatim, thematically analysed, and then composite vignettes were subsequently developed to present a rich narrative of the collective experiences of each group. FINDINGS: Compared with adults who were predialysis, quality of life and wellbeing improved upon initiation of their home haemodialysis or peritoneal dialysis. Conversely, minimal improvement was perceived by those receiving in-centre haemodialysis. Low physical activity was reported across all four groups, although those receiving home haemodialysis and peritoneal dialysis reported a greater desire and ability to be physically active than those in-centre. CONCLUSION: These findings highlight that dialysis modalities not requiring regular hospital attendance (i.e., home haemodialysis and peritoneal dialysis) improve independence, quality of life, wellbeing, and can facilitate a more physically active lifestyle.

Sex differences in response to exercise heat stress in the context of the military environment.

Women can now serve in ground close combat (GCC) roles, where they may be required to operate alongside men in hot environments. However, relative to the average male soldier, female soldiers are less aerobically fit, with a smaller surface area (A D), lower mass (m) with higher body fat and a larger A D/m ratio. This increases cardiovascular strain, reduces heat exchange with the environment and causes a greater body temperature increase for a given heat storage, although a large A D/m ratio can be advantageous. Physical employment standards for GCC roles might lessen the magnitude of fitness and anthropometric differences, yet even when studies control for these factors, women sweat less than men at high work rates. Therefore, the average female soldier in a GCC role is likely to be at a degree of disadvantage in many hot environments and particularly during intense physical activity in hot-arid conditions, although heat acclimation may mitigate some of this effect. Any thermoregulatory disadvantage may be exacerbated during the mid-luteal phase of the menstrual cycle, although the data are equivocal. Likewise, sex differences in behavioural thermoregulation and cognition in the heat are not well understood. Interestingly, there is often lower reported heat illness incidence in women, although the extent to which this is influenced by behavioural factors or historic differences in role allocation is unclear. Indeed, much of the extant literature lacks ecological validity and more work is required to fully understand sex differences to exercise heat stress in a GCC context.

Experiences of adults living with a kidney transplant-Effects on physical activity, physical function, and quality of life: A descriptive phenomenological study.

BACKGROUND: Although kidney transplantation is the best treatment for kidney failure, scarce research has examined its effects on physical activity, physical function and quality of life. OBJECTIVES: To investigate the experiences of a group of adults living with advanced kidney disease focusing on quality of life, physical activity and function and to see how findings differ in a group of kidney transplant recipients. APPROACH: Individual semi-structured interviews were conducted with adults with advanced kidney disease (n = 10; 70.5 ± 8.9 years) and adults who had received a kidney transplant (n = 10; 50.7 ± 11.5 years; transplant age: 42.7 ± 20.9 months). Interviews were transcribed verbatim, thematically analysed and composite vignettes developed. FINDINGS: Individuals with advanced kidney disease described a sense of loss and alteration to their life plans. Kidney transplant recipients reported increased freedom, independence and a return to near normality, with improved quality of life, physical activity and function compared with their pre-transplant lives. However, transplant recipients also described living with anxiety about the health of their transplant and fear it may fail. CONCLUSION: Whilst adults living with advanced kidney disease often experience a reduced quality of life, physical activity and function, kidney transplantation can help facilitate a return to pre-disease levels of physical activity, physical function and quality of life. However, transplant recipients also reported living with anxiety around their new kidney failing. This study demonstrates the variability in the lived experiences of adults living with advanced kidney disease or a kidney transplant and highlights the need for patient-centred care.

Marathon Performance and Pacing in the Doha 2019 Women's IAAF World Championships: Extreme Heat, Suboptimal Pacing, and High Failure Rates.

PURPOSE: The Doha 2019 women's World Championship marathon took place in extreme hot (32 °C), humid conditions (74% relative humidity) culminating in unprecedented (41%) failure rates. We explored whether extreme heat or suboptimal pacing was responsible for diminished performance against a temperate "control" (London 2017: 19 °C, 59% relative humidity) and whether physical characteristics (eg, body surface area, estimated maximal oxygen uptake, habitual heat exposure) explained performance. METHOD: Five-kilometer-pace (km·h-1) data underwent repeated-measures analyses of hot (Doha, n = 40) versus temperate pacing and performance (London, n = 78) within and between marathon pacing (finisher quartiles normalized against personal best; n = 10 per group) and within hot marathon finishers versus nonfinishers (up to 10 km; normalized data). Possible predictors (multiple regression) of hot marathon pacing were explored. Tests to .05 alpha level, partial eta squared (ηp2) indicates effect size. RESULTS: Mean (SD) of Doha (14.82 [0.96] km·h-1) pace was slower (London: 15.74 [0.96] km·h-1; P = .00; ηp2=.500). In hot conditions, athletes finishing in positions 1 to 10 (group 1) started more conservatively (93.7% [2.1%] of personal best) than slower runners (groups 3 and 4; 96.6% [2.8%] of personal best; P < .05, ηp2=.303). Groups were not different at 15 km and then slowed immediately (groups 3 and 4) or after 20 km (group 2). Finishers and nonfinishers adopted similar pace up to 10 km (P > .05, ηp2 =.003). World ranking predicted (P = .00; r2 = .248) average pace in Doha. CONCLUSION: Extreme hot conditions reduced performance. Top 10 athletes adopted a conservative initial pace, whereas lower-placing athletes adopted a faster, aggressive start. Pacing alone does not explain high failure rates in nonfinishers. Athletes competing in the heat should initially pace conservatively to optimize performance.

The effect of medium-term heat acclimation on endurance performance in a temperate environment.

We investigated whether an 11-day heat acclimation programme (HA) enhanced endurance performance in a temperate environment, and the mechanisms underpinning any ergogenic effect. Twenty-four males (V̇O2max: 56.7 ± 7.5 mL·kg-1·min-1) completed either: (i) HA consisting of 11 consecutive daily exercise sessions (60-90 min·day-1; n = 16) in a hot environment (40°C, 50% RH) or; (ii) duration and exertion matched exercise in cool conditions (CON; n = 8 [11°C, 60% RH]). Before and after each programme power at lactate threshold, mechanical efficiency, VO2max, peak power output (PPO) and work done during a 30-minute cycle trial (T30) were determined under temperate conditions (22°C, 50% RH). HA reduced resting (-0.34 ± 0.30°C) and exercising (-0.43 ± 0.30°C) rectal temperature, and increased whole-body sweating (+0.37 ± 0.31 L·hr-1) (all P≤0.001), with no change in CON. Plasma volume increased in HA (10.1 ± 7.2%, P < 0.001) and CON (7.2 ± 6.3%, P = 0.015) with no between-groups difference, whereas exercise heart rate reduced in both groups, but to a greater extent in HA (-20 ± 11 b·min-1) than CON (-6 ± 4 b·min-1). VO2max, lactate threshold and mechanical efficiency were unaffected by HA. PPO increased in both groups (+14 ± 18W), but this was not related to alterations in any of the performance or thermal variables, and T30 performance was unchanged in either group (HA: Pre = 417 ± 90 vs. Post = 427 ± 83 kJ; CON: Pre = 418 ± 63 vs. Post = 423 ± 56 kJ). In conclusion, 11-days HA induces thermophysiological adaptations, but does not alter the key determinants of endurance performance. In trained males, the effect of HA on endurance performance in temperate conditions is no greater than that elicited by exertion and duration matched exercise training in cool conditions.

Understanding the Impact of Initial COVID-19 Restrictions on Physical Activity, Wellbeing and Quality of Life in Shielding Adults with End-Stage Renal Disease in the United Kingdom Dialysing at Home versus In-Centre and Their Experiences with Telemedicine.

Early in the coronavirus-2019 (COVID-19) containment strategy, people with end-stage renal disease (ESRD) were identified as extremely clinically vulnerable and subsequently asked to 'shield' at home where possible. The aim of this study was to investigate how these restrictions and the transition to an increased reliance on telemedicine within clinical care of people living with kidney disease impacted the physical activity (PA), wellbeing and quality of life (QoL) of adults dialysing at home (HHD) or receiving in-centre haemodialysis (ICHD) in the UK. Individual semistructured telephone interviews were conducted with adults receiving HHD (n = 10) or ICHD (n = 10), were transcribed verbatim and, subsequently, thematically analysed. As result of the COVID-19 restrictions, PA, wellbeing and QoL of people with ESRD were found to have been hindered. However, widespread support for the continued use of telemedicine was strongly advocated and promoted independence and satisfaction in patient care. These findings highlight the need for more proactive care of people with ESRD if asked to shield again, as well as increased awareness of safe and appropriate PA resources to help with home-based PA and emotional wellbeing.

Timing of acute passive heating on glucose tolerance and blood pressure in people with type 2 diabetes: a randomized, balanced crossover, control trial.

Type 2 diabetes mellitus (T2DM) is characterized by chronic hyperglycemia and progressive insulin resistance, leading to macro and microvascular dysfunction. Passive heating has potential to improve glucose homeostasis and act as an exercise mimetic. We assessed the effect of acute passive heating before or during an oral glucose tolerance test (OGTT) in people with T2DM. Twelve people with T2DM were randomly assigned to the following three conditions: 1) 3-h OGTT (control), 2) 1-h passive heating (40°C water) 30 min before an OGTT (HOT-OGTT), and 3) 1-h passive heating (40°C water) 30 min after commencing an OGTT (OGTT-HOT). Blood glucose concentration, insulin sensitivity, extracellular heat shock protein 70 (eHSP70), total energy expenditure (TEE), heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) were recorded. Passive heating did not alter blood glucose concentration [control: 1,677 (386) arbitrary units (AU), HOT-OGTT: 1,797 (340) AU, and OGTT-HOT: 1,662 (364) AU, P = 0.28], insulin sensitivity (P = 0.15), or SBP (P = 0.18) but did increase eHSP70 concentration in both heating conditions [control: 203.48 (110.81) pg·mL-1; HOT-OGTT: 402.47 (79.02) pg·mL-1; and OGTT-HOT: 310.00 (60.53) pg·mL-1, P < 0.001], increased TEE (via fat oxidation) in the OGTT-HOT condition [control: 263 (33) kcal, HOT-OGTT: 278 (40) kcal, and OGTT-HOT: 304 (38) kcal, P = 0.001], increased HR in both heating conditions (P < 0.001), and reduced DBP in the OGTT-HOT condition (P < 0.01). Passive heating in close proximity to a glucose challenge does not alter glucose tolerance but does increase eHSP70 concentration and TEE and reduce blood pressure in people with T2DM.NEW & NOTEWORTHY This is the first study to investigate the timing of acute passive heating on glucose tolerance and extracellular heat shock protein 70 concentration ([eHSP70]) in people with type 2 diabetes. The principal novel findings from this study were that both passive heating conditions: 1) did not reduce the area under the curve or peak blood glucose concentration, 2) elevated heart rate, and 3) increased [eHSP70], which was blunted by glucose ingestion, while passive heating following glucose ingestion, 4) increased total energy expenditure, and 5) reduced diastolic blood pressure.

A network physiology approach to oxygen saturation variability during normobaric hypoxia.

NEW FINDINGS: What is the central question of this study? What is the physiological interpretation of SpO2 fluctuations observed during normobaric hypoxia in healthy individuals? What is the main finding and its importance? There is a significant flow of information between SpO2 and other cardio-respiratory time series during graded hypoxia. Analysis of the pattern of SpO2 variations has potential for non-invasive assessment of the engagement of respiratory control system in health and disease. ABSTRACT: Peripheral capillary oxygen saturation ( SpO2 ) exhibits a complex pattern of fluctuations during hypoxia. The physiological interpretation of SpO2 variability is not well understood. In this study, we tested the hypothesis that SpO2 fluctuation carries information about integrated cardio-respiratory control in healthy individuals using a network physiology approach. We explored the use of transfer entropy in order to compute the flow of information between cardio-respiratory signals during hypoxia. Twelve healthy males (mean (SD) age 22 (4) years) were exposed to four simulated environments (fraction of inspired oxygen ( FIO2 ): 0.12, 0.145, 0.17, and 0.2093) for 45 min, in a single blind randomized controlled design. The flow of information between different physiological parameters ( SpO2 , respiratory frequency, tidal volume, minute ventilation, heart rate, end-tidal pressure of O2 and CO2 ) were analysed using transfer entropy. Normobaric hypoxia was associated with a significant increase in entropy of the SpO2 time series. The transfer entropy analysis showed that, particularly at FIO2 0.145 and 0.12, the flow of information between SpO2 and other physiological variables exhibits a bidirectional relationship. While reciprocal interactions were observed between different cardio-respiratory parameters during hypoxia, SpO2 remained the main hub of this network. SpO2 fluctuations during graded hypoxia exposure carry information about cardio-respiratory control. Therefore, SpO2 entropy analysis has the potential for non-invasive assessment of the functional connectivity of respiratory control system in various healthcare settings.

Scapular Dyskinesis Is Not an Isolated Risk Factor for Shoulder Injury in Athletes: A Systematic Review and Meta-analysis.

BACKGROUND: Scapular dyskinesis has been considered a risk factor for athletic shoulder injury; however, findings in the prospective literature have demonstrated mixed results. PURPOSE: To determine if scapular dyskinesis increases the risk of shoulder injury in athletes. STUDY DESIGN: Meta-analysis. METHODS: A systematic search was conducted on the MEDLINE, CINAHL Plus, SPORTDiscus, and Embase databases to identify prospective studies examining scapular dyskinesis and shoulder injury risk in athletes. Studies were included if they assessed participants using a dynamic scapular assessment at baseline and monitored for the development of shoulder injury. Data from the studies were subject to meta-analysis using the Mantel-Haenszel method to produce a pooled risk ratio. RESULTS: Seven studies were eligible for inclusion, resulting in 212 shoulder injuries observed across 923 athletes. Scapular dyskinesis was present in 46% of participants, and these athletes had an injury rate of 25%. The presence of scapular dyskinesis displayed a trend to increase the risk of shoulder injury, but this was not statistically significant (risk ratio, 1.07; 95% CI, 0.85-1.34; P = .59). CONCLUSION: Scapular dyskinesis was not significantly associated with the development of shoulder injury in athletes. REGISTRATION: CRD42019133089 (PROSPERO).

Heat acclimation improves sweat gland function and lowers sweat sodium concentration in an adult with cystic fibrosis.

We present novel data concerning the time-course of adaptations and potential benefits of heat acclimation for people with cystic fibrosis (pwCF), who are at greater risk of exertional heat illness. A 25-year-old male (genotype: delta-F508 and RH117, forced expiratory volume in 1-second: 77% predicted and baseline sweat [Na+]: 70 mmol·L - 1), who had previously experienced muscle cramping during exercise in ambient heat, underwent 10-sessions of heat acclimation (90-min at 40°C and in 40% relative humidity). Adaptations included; lower resting core temperature (-0.40°C) and heart rate (-6 beats·min-1), plasma volume expansion (+6.0%) and, importantly, increased sweat loss (+370 mL) and sweat gland activity (+12 glands·cm2) with decreased sweat [Na+] (-18 mmol·L - 1). Adaptations were maintained for at least 7-days, with no evidence of cramping during follow-up exercise-heat stress testing. These data suggest pwCF may benefit from heat acclimation to induce sudomotor function improvements, particularly reductions in sweat [Na+], however, further research is required.

Effects of Normobaric Hypoxia on Oxygen Saturation Variability.

Background: The study is the first to evaluate the effects of graded normobaric hypoxia on SpO2 variability in healthy individuals. Materials and Methods: Twelve healthy males (mean [standard deviation] age 22 [4] years) were exposed to four simulated environments (fraction of inspired oxygen [FIO2]: 0.12, 0.145, 0.17, and 0.21) for 45 minutes, in a balanced crossover design. Results: Sample entropy, a tool that quantifies the irregularity of pulse oximetry fluctuations, was used as a measure of SpO2 variability. SpO2 entropy increased as the FIO2 decreased, and there was a strong significant negative correlation between mean SpO2 and its entropy during hypoxic exposure (r = -0.841 to -0.896, p < 0.001). In addition, SpO2 sample entropy, but not mean SpO2, was correlated (r = 0.630-0.760, p < 0.05) with dyspnea in FIO2 0.17, 0.145, and 0.12 and importantly, SpO2 sample entropy at FIO2 0.17 was correlated with dyspnea at FIO2 0.145 (r = 0.811, p < 0.01). Conclusions: These findings suggest that SpO2 variability analysis may have the potential to be used in a clinical setting as a noninvasive measure to identify the negative sequelae of hypoxemia.

Thirst-guided participant-controlled intravenous fluid rehydration: a single blind, randomised crossover study.

BACKGROUND: Dehydration is common in hospitals and is associated with increased mortality and morbidity. Clinical assessment and diagnostic measures of dehydration are unreliable. We sought to investigate the novel concept that individuals might control their own intravenous rehydration, guided by thirst. METHODS: We performed a single-blind, counterbalanced, randomised cross-over trial. Ten healthy male volunteers of mean age 26 (standard deviation [sd] 10.5) yr were dehydrated by 3-5% of their baseline body mass via exercising in the heat (35°C, 60% humidity). This was followed by a 4 h participant-controlled intravenous rehydration: individuals triggered up to six fluid boluses (4% dextrose in 0.18% sodium chloride) per hour in response to thirst. Participants undertook two blinded rehydration protocols which differed only by bolus volume: 50 ml (low volume [LV]) or 200 ml (high volume [HV]). Each hour during the rehydration phase, plasma osmolality (pOsm) was measured and thirst score recorded. Nude body mass was measured at baseline, after dehydration, and after the rehydration phase. RESULTS: In both conditions, the mean dehydration-related body mass loss was 3.9%. Thirst score was strongly associated with pOsm (within-subject r=0.74) and demand for fluid decreased as pOsm corrected. In the HV condition, participants rapidly rehydrated themselves (mean fluid delivered 3060 vs 981 ml in the LV condition) to body mass and pOsm no different to their euhydrated state. CONCLUSION: Healthy individuals appear able to rely on thirst to manage intravenous fluid intake. Future work must now focus on whether patient-controlled intravenous fluids could represent a paradigm shift in the management of hydration in the clinical setting. CLINICAL TRIAL REGISTRATION: NCT03932890.

Cognitive performance is associated with cerebral oxygenation and peripheral oxygen saturation, but not plasma catecholamines, during graded normobaric hypoxia.

NEW FINDINGS: What is the central question of this study? What are the mechanisms responsible for the decline in cognitive performance following exposure to acute normobaric hypoxia? What are the main findings and their importance? We found that (1) performance of a complex central executive task (n-back) was reduced at FIO2 0.12; (2) there was a strong correlation between performance of the n-back task and reductions in SpO2 and cerebral oxygenation; and (3) plasma adrenaline, noradrenaline, cortisol and copeptin were not correlated with cognitive performance. ABSTRACT: It is well established that hypoxia impairs cognitive function; however, the physiological mechanisms responsible for these effects have received relatively little attention. This study examined the effects of graded reductions in fraction of inspired oxygen ( FIO2 ) on oxygen saturation ( SpO2 ), cerebral oxygenation, cardiorespiratory variables, activity of the sympathoadrenal system (adrenaline, noradrenaline) and hypothalamic-pituitary-adrenal axis (cortisol, copeptin), and cognitive performance. Twelve healthy males [mean (SD), age: 22 (4) years, height: 178 (5) cm, mass: 75 (9) kg, FEV1 /FVC ratio: 85 (5)%] completed a four-task battery of cognitive tests to examine inhibition, selective attention (Eriksen flanker), executive function (n-back) and simple and choice reaction time (Deary-Liewald). Tests were completed before and following 60 min of exposure to FIO2 0.2093, 0.17, 0.145 and 0.12. Following 60 min of exposure, response accuracy in the n-back task was significantly reduced in FIO2 0.12 compared to baseline [82 (9) vs. 93 (5)%; P < 0.001] and compared to all other conditions at the same time point [ FIO2 0.2093: 92 (3)%; FIO2 0.17: 91 (6)%; FIO2 0.145: 85 (10)%; FIO2 12: 82 (9)%; all P < 0.05]. The performance of the other tasks was maintained. Δaccuracy and Δreaction time of the n-back task was correlated with both Δ SpO2 [r(9) = 0.66, P < 0.001 and r(9) = -0.36, P = 0.037, respectively] and Δcerebral oxygenation [r(7) = 0.55, P < 0.001 and r(7) = -0.38, P = 0.045, respectively]. Plasma adrenaline, noradrenaline, cortisol and copeptin were not significantly elevated in any condition or correlated with any of the tests of cognitive performance. These findings suggest that reductions in peripheral oxygen saturation and cerebral oxygenation, and not increased activity of the sympathoadrenal system and hypothalamic-pituitary-adrenal axis, as previously speculated, are responsible for a decrease in cognitive performance during normobaric hypoxia.

A multidisciplinary consensus on dehydration: definitions, diagnostic methods and clinical implications.

Background: Dehydration appears prevalent, costly and associated with adverse outcomes. We sought to generate consensus on such key issues and elucidate need for further scientific enquiry. Materials and methods: A modified Delphi process combined expert opinion and evidence appraisal. Twelve relevant experts addressed dehydration's definition, objective markers and impact on physiology and outcome. Results: Fifteen consensus statements and seven research recommendations were generated. Key findings, evidenced in detail, were that there is no universally accepted definition for dehydration; hydration assessment is complex and requires combining physiological and laboratory variables; "dehydration" and "hypovolaemia" are incorrectly used interchangeably; abnormal hydration status includes relative and/or absolute abnormalities in body water and serum/plasma osmolality (pOsm); raised pOsm usually indicates dehydration; direct measurement of pOsm is the gold standard for determining dehydration; pOsm >300 and ≤280 mOsm/kg classifies a person as hyper or hypo-osmolar; outside extremes, signs of adult dehydration are subtle and unreliable; dehydration is common in hospitals and care homes and associated with poorer outcomes. Discussion: Dehydration poses risk to public health. Dehydration is under-recognized and poorly managed in hospital and community-based care. Further research is required to improve assessment and management of dehydration and the authors have made recommendations to focus academic endeavours. Key messages Dehydration assessment is a major clinical challenge due to a complex, varying pathophysiology, non-specific clinical presentations and the lack of international consensus on definition and diagnosis. Plasma osmolality represents a valuable, objective surrogate marker of hypertonic dehydration which is underutilized in clinical practice. Dehydration is prevalent within the healthcare setting and in the community, and appears associated with increased morbidity and mortality.