Background: Physiological variables provide critical insights into the integrated control of the cardiorespiratory system, reflecting the body's real-time responses to internal and external perturbations. Visualizing the exchange of information between different components of the cardiorespiratory system is beneficial for monitoring individuals in various clinical settings and extreme environments. This study aimed to develop a non-invasive method, using principles of information theory, to visualize the flow of information between physiological variables, with a focus on the integrated cardiorespiratory responses to different physiological stressors. Methods: Heart rate, respiratory rate, minute ventilation, respiratory frequency, tidal volume, capillary oxygen saturation (SpO2), end-tidal oxygen, and end-tidal carbon dioxide concentrations were recorded from 22 healthy participants. Transfer entropy, which reflects measures of causal relationships between parallel time-series, was used to compute the flow of information between cardiorespiratory signals into network maps. Network mapping was performed after rest in a control condition and following exposure to the isolated and combined effects of normobaric hypoxia (FIO2: 0.12), moderate intensity cycling exercise (100W), and overnight sleep deprivation. For each intervention, 10-minute segments of physiological signals (from minutes 5 to 15 after the commencement of hypoxia and/or exercise) were used for analysis. Results: Each physiological stressor was associated with a distinctive pattern of information flow between physiological variables. Hypoxia led to the engagement of SpO2 a hub in the network, facilitating the exchange of information with end-tidal oxygen concentration and heart rate. Sleep deprivation was associated with a shift in the flow of information from SpO2 to other nodes, such as respiratory rate, during hypoxia. During exercise, heart rate emerged as the central node for receiving information, while SpO2 acted as the primary node disseminating information to other nodes. Increased connectivity within the networks was observed during exercise alone or when combined with other stressors. Conclusion: This non-invasive network mapping technique visualizes the interaction of various cardiorespiratory variables following exposure to physiological stressors. By mapping normative responses, this approach may help identify outliers associated with various disease states. ### Competing Interest Statement The authors have declared no competing interest.

Short duration heat acclimation (HA) (≤5 daily heat exposures) elicits incomplete adaptation compared with longer interventions, possibly due to the lower accumulated thermal "dose." It is unknown if matching thermal "dose" over a shorter timescale elicits comparable adaptation to a longer intervention. Using a parallel-groups design, we compared: 1) "condensed" HA (CHA; n = 17 males) consisting of 4 × 75 min·day-1 heat exposures [target rectal temperature (Trec) = 38.5 °C] for two consecutive days, with 2) "traditional" HA (THA; n = 15 males) consisting of 1 × 75 min·day-1 heat exposure (target Trec = 38.5°C) for eight consecutive days. Physiological responses to exercise heat stress, hypoxia, and normoxic exercise performance were evaluated pre- and postintervention. Thermal (Trec over final 45 min: CHA = 38.45 ± 0.17°C, THA = 38.53 ± 0.13°C, P = 0.126) and cardiovascular strain were not different during interventions, indicating similar thermal "dose," although CHA had lower sweating rate, higher starting Trec, and greater inflammation, gastrointestinal permeability, and renal stress (P < 0.05). However, CHA elicited an array of thermophysiological adaptations that did not differ from THA [reduced indices of peak thermal (e.g., Δ peak Trec CHA = -0.28 ± 0.26°C, THA = -0.36 ± 0.17°C, P = 0.303) and cardiovascular strain, inflammation, and renal stress; blood and plasma volume expansion; improved perceptual indices], although improvements in resting thermal strain (e.g., Δ resting Trec CHA = -0.14 ± 0.21°C, THA = -0.35 ± 0.29°C, P = 0.027) and sweating rate were less with CHA. Both interventions improved aspects of hypoxic tolerance, but effects on temperate normoxic exercise indices were limited. The diminished thermal strain was well-maintained over a 22-day decay period. In conclusion, CHA could represent a viable acclimation option for time-restricted young healthy males preparing for a hot, and possibly high-altitude, environment.NEW & NOTEWORTHY This study has shown, for the first time, that a novel condensed heat acclimation program can elicit an array of thermophysiological adaptations, many of which do not differ from traditional heat acclimation. These findings suggest that accumulated thermal "dose" is an important factor contributing to the adaptive responses to heat stress and that condensed heat acclimation may represent a viable option for time-restricted individuals (e.g., military personnel, firefighters, and athletes) preparing to enter a hot environment.

ABSTRACTIntroductionCold water swimming has increased in popularity and women wish to swim throughout pregnancy. There is a lack of evidenced‐based guidance to make decisions about the safety of immersion in cold water during pregnancy.MethodsClosed social media groups were asked for specific questions in relation to cold water swimming and pregnancy. This highlighted concerns including water temperature, risks to the mother and fetus, and water quality. To find evidence‐based answers, a series of meetings brought together clinicians and researchers with expertise in cold water physiology, exercise physiology, fertility, obstetrics, neonatology, midwifery, water epidemiology, public health and representatives from the Open Water Swimming Society and an Open Water swimming social enterprise.ResultsPublished data were examined via a scoping review process and four studies and eight reports were identified. Recommendations were made with evidence graded (mostly grade 4 expert opinion).ConclusionResearch gaps highlight the need for research to enable accurate advice to determine whether it is safe for pregnant women to swim outdoors in cold water.

Evidence suggests that anthropogenic climate change is accelerating and is affecting human health globally. Despite urgent calls to address health effects in the context of the additional challenges of environmental degradation, biodiversity loss and ageing populations, the effects of climate change on specific health conditions are still poorly understood. Neurological diseases contribute substantially to the global burden of disease, and the possible direct and indirect consequences of climate change for people with these conditions are a cause for concern. Unaccustomed temperature extremes can impair the systems of resilience of the brain, thereby exacerbating or increasing susceptibility to neurological disease. In this Perspective, we explore how changing weather patterns resulting from climate change affect sleep — an essential restorative human brain activity, the quality of which is important for people with neurological diseases. We also consider the pervasive and complex influences of climate change on two common neurological conditions: stroke and epilepsy. We highlight the urgent need for research into the mechanisms underlying the effects of climate change on the brain in health and disease. We also discuss how neurologists can respond constructively to the climate crisis by raising awareness and promoting mitigation measures and research — actions that will bring widespread co-benefits. Evidence suggests that anthropogenic climate change is accelerating, with serious consequences for human health. This Perspective explores how the effects of climate change, such as extreme temperatures, altered weather patterns and increased air pollution, interact with the brain, and discusses how neurologists can respond constructively to the climate crisis.

Visualizing the exchange of information between different components of the cardiorespiratory system is essential for understanding physiological control and is valuable for monitoring individuals in various clinical settings and extreme environments. Network physiology is a multidisciplinary field that explores the collective behaviour of physiological systems, offering a novel approach to understanding these complex interactions. The present study aimed to develop a non-invasive method to visualize the cardiorespiratory network under control conditions and after isolated or combined exposure to hypoxia, exercise and sleep-deprivation (total or partial). Using transfer entropy, a measure of causal relationships between time-series data, network maps were generated to illustrate information flow between 10 min parallel cardiorespiratory signals, namely, heart rate, respiratory rate, minute ventilation, tidal volume, capillary oxygen saturation ( S p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_2}}}$ ), end-tidal O2 and end-tidal CO2 concentrations. Twenty-two healthy participants underwent assessments at rest and following normobaric hypoxia ( F I O 2 ${{F}_{{\mathrm{I}}{{{\mathrm{O}}}_2}}}$ : 0.12), moderate intensity cycling (100 W) and overnight sleep-deprivation both in isolation and in combination. The results showed that each stressor generated a distinct pattern of physiological information exchange. Increased connectivity within the networks was observed during exercise alone or when combined with other stressors. During exercise, heart rate emerged as the primary recipient of information, whereas SpO₂ served as the main disseminator. Hypoxia led to the engagement of S p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_2}}}$ as a hub in the network. Sleep-deprivation was associated with a shift in the flow of information between the nodes during hypoxia. This non-invasive approach effectively maps cardiorespiratory interactions, offering potential for assessing integrated network dynamics in health and disease. KEY POINTS: Application of information theory principles can reveal significant bidirectional interactions between different components of the cardiorespiratory system using non-invasively recorded physiological signals. Increased connectivity within the cardiorespiratory networks was observed during moderate exercise alone or when combined with hypoxia and/or sleep-deprivation. During exercise, heart rate became the central node of the cardiorespiratory network for receiving information, whereas peripheral oxygen saturation acted as the main node that sent out information to other nodes. Acute hypoxic challenge or sleep-deprivation was associated with distinctive pattern of information flow in the cardiorespiratory network. This novel network approach can be used to map the adaptive responses to physiological stressors such as exercise, hypoxia and sleep-deprivation.

Abstract Background The RNLI “Float to Live” campaign is based on research conducted in indoor pools with experienced open water swimmers. Study 1 investigated whether the RNLI “Float to Live” guidance would enable less experienced individuals to float in realistic open water conditions. Study 2 examined the separate effects of practice and coaching on floating competence. Methods Study 1: Inexperienced water users conducted floats in either still, open fresh (n = 22) or open sea water (n = 13), followed by moving sea (n = 6) or fresh water (n = 5). Participants undertook three 2-min floats in still water wearing swimwear and one clothed float: 1) naïve; 2) following RNLI “Float to live” messaging; 3) individual float coaching; 4) simulated fall wearing summer clothing. In moving sea water, participants undertook two floats equivalent to Floats 3 and 4. In moving fresh water, participants undertook 3 floats: 1) naïve; 2) following “defensive floating” coaching; 3) simulated fall wearing summer clothing. Study 2: Two groups matched for skinfold thickness undertook three 2-min floats in a flume wearing swimwear. PRAC group (n = 12): 1) naïve; 2) following float practice; 3) float coaching; COACH group (n = 11) coaching followed by practice. Floating difficulty, confidence, competence, “efficiency” and perceived exertion were analysed using either a Friedman test or mixed model ANOVA. Results In both fresh water and sea water, participants’ floating competence and confidence increased after viewing the RNLI messaging, it was further improved with individualised float coaching. The additional helpful instructions included: 1) “head back with ears submerged”; 2) “relax”; 3) “breathe normally”; 4) “it is OK if your legs sink”; 5) an accurate description of sculling for “active” floaters that needed it; 6) spread arms and legs for stability. The simulated fall with clothing did not impair floating competence. No difference in floating competence was seen between PRAC and COACH, though confidence may be increased sooner in COACH. Conclusions The RNLI float advice can be applied in realistic open water settings by less experienced water users. Additional content could be included to make the messaging even more effective.

This article seeks to explore the way in which key, specifically situated actors within the UK water rescue community understand and perceive challenges relating to navigating policy and practical challenges inherent to their role. Utilizing Lipsky's notion of the 'street level bureaucrat', focus groups and interviews were undertaken with water rescue practitioners who bridge the gap between high-level strategy implementers and ground-level operational personnel. Utilizing a grounded theory approach, the research uncovered how these operators conceptualize the boundaries in relation to their work, the role of knowledge and knowledge exchange, the nature of the obligation, especially with regard to differences between statutory and voluntary agencies, and in relation to ever-changing public attitudes towards risk and expectations of a right to be rescued. This was underscored by consistent reference to challenges posed by funding, resourcing and the contingent nature of both political will and public interest in their work. The findings, drawing on these uniquely situated actors, emphasized the importance of practitioners interacting with and knowing one another, in addition to having a shared understanding of the water environment on the coast and inland, as being a key means to navigate the 'bureaucracy' of water rescue. The ways in which Lipsky's model can complement contemporary discussions regarding social identity within the emergency response to promote both vertical and horizontal cohesion and clarity are examined.

Type 2 diabetes mellitus (T2DM) is characterised by endothelial dysfunction, leading to increased risk of cardiovascular disease. Emerging evidence suggest that HWI may favourably improve vascular function but data are limited in individual with T2DM. The aim was to investigate whether repeated hot water immersion (HWI) improved macrovascular, microvascular and central haemodynamic function in individuals with T2DM. Fourteen individuals completed a pre-post experimental study where participants were assessed pre- and post-8-10 x 1 h HWI sessions (40 degrees C water) undertaken within a 14-day period. During HWIs, body position was adjusted to clamp rectal temperature at 38.5-39.0 degrees C for the duration of the immersion. Stroke volume index (SVi), cardiac index (Q(center dot) i), resting heart rate (HR), systolic blood pressure (SBP), diastolic BP (DBP), brachial flow-mediated dilation (FMD) and cutaneous microvascular endothelial function (via transdermal iontophoresis) and plasma [nitrate] and [nitrite] (NOX; via ozone chemiluminescence) were assessed pre- and post HWI. Neither brachial FMD measures of macrovascular endothelial function (p = 0.43) or forearm microvascular function (ACh max, p = 0.63; ACh area under curve (AUC), p = 0.63; insulin max, p = 0.51; insulin AUC, p = 0.86) or NOX (p = 0.38) were changed. Q(center dot) i (p < 0.01), SVi (p < 0.02) and resting HR (p < 0.01) were all significantly reduced following the 10-days HWI intervention. SBP was reduced (p = 0.03), whereas DBP was unchanged (p = 0.56). HWI may represent an appropriate intervention to improve Q(center dot) I, SVi and BP in individuals with T2DM, but not macrovascular endothelial or cutaneous microvascular function.

High altitude residents have a lower incidence of type 2 diabetes mellitus (T2DM). Therefore, we examined the effect of repeated overnight normobaric hypoxic exposure on glycaemic control, appetite, gut microbiota and inflammation in adults with T2DM. Thirteen adults with T2DM [glycated haemoglobin (HbA1c): 61.1 ± 14.1 mmol mol-1; aged 64.2 ± 9.4 years; four female] completed a single-blind, randomised, sham-controlled, cross-over study for 10 nights, sleeping when exposed to hypoxia (fractional inspired O2 [ F I O 2 ${{F}_{{\mathrm{I}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ ] = 0.155; ∼2500 m simulated altitude) or normoxic conditions ( F I O 2 ${{F}_{{\mathrm{I}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$  = 0.209) in a randomised order. Outcome measures included: fasted plasma [glucose]; [hypoxia inducible factor-1α]; [interleukin-6]; [tumour necrosis factor-α]; [interleukin-10]; [heat shock protein 70]; [butyric acid]; peak plasma [glucose] and insulin sensitivity following a 2 h oral glucose tolerance test; body composition; appetite indices ([leptin], [acyl ghrelin], [peptide YY], [glucagon-like peptide-1]); and gut microbiota diversity and abundance [16S rRNA amplicon sequencing]. During intervention periods, accelerometers measured physical activity, sleep duration and efficiency, whereas continuous glucose monitors were used to assess estimated HbA1c and glucose management indicator and time in target range. Overnight hypoxia was not associated with changes in any outcome measure (P > 0.05 with small effect sizes) except fasting insulin sensitivity and gut microbiota alpha diversity, which exhibited trends (P = 0.10; P = 0.08 respectively) for a medium beneficial effect (d = 0.49; d = 0.59 respectively). Ten nights of overnight moderate hypoxic exposure did not significantly affect glycaemic control, gut microbiome, appetite, or inflammation in adults with T2DM. However, the intervention was well tolerated and a medium effect-size for improved insulin sensitivity and reduced alpha diversity warrants further investigation. KEY POINTS: Living at altitude lowers the incidence of type 2 diabetes mellitus (T2DM). Animal studies suggest that exposure to hypoxia may lead to weight loss and suppressed appetite. In a single-blind, randomised sham-controlled, cross-over trial, we assessed the effects of 10 nights of hypoxia (fractional inspired O2 ∼0.155) on glucose homeostasis, appetite, gut microbiota, inflammatory stress ([interleukin-6]; [tumour necrosis factor-α]; [interleukin-10]) and hypoxic stress ([hypoxia inducible factor 1α]; heat shock protein 70]) in 13 adults with T2DM. Appetite and inflammatory markers were unchanged following hypoxic exposure, but an increased insulin sensitivity and reduced gut microbiota alpha diversity were associated with a medium effect-size and statistical trends, which warrant further investigation using a definitive large randomised controlled trial. Hypoxic exposure may represent a viable therapeutic intervention in people with T2DM and particularly those unable or unwilling to exercise because barriers to uptake and adherence may be lower than for other lifestyle interventions (e.g. diet and exercise).

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.

Astronauts in microgravity experience multi-system deconditioning, impacting their inflight efficiency and inducing dysfunctions upon return to Earth gravity. To fill the sex gap of knowledge in the health impact of spaceflights, we simulate microgravity with a 5-day dry immersion in 18 healthy women (ClinicalTrials.gov Identifier: NCT05043974). Here we show that dry immersion rapidly induces a sedentarily-like metabolism shift mimicking the beginning of a metabolic syndrome with a drop in glucose tolerance, an increase in the atherogenic index of plasma, and an impaired lipid profile. Bone remodeling markers suggest a decreased bone formation coupled with an increased bone resorption. Fluid shifts and muscular unloading participate to a marked cardiovascular and sensorimotor deconditioning with decreased orthostatic tolerance, aerobic capacity, and postural balance. Collected datasets provide a comprehensive multi-systemic assessment of dry immersion effects in women and pave the way for future sex-based evaluations of countermeasures.

New FindingsWhat is the central question of this study?Are biomarkers of endothelial function, oxidative stress and inflammation altered by non-freezing cold injury (NFCI)?What is the main finding and its importance?Baseline plasma [interleukin-10] and [syndecan-1] were elevated in individuals with NFCI and cold-exposed control participants. Increased [endothelin-1] following thermal challenges might explain, in part, the increased pain/discomfort experienced with NFCI. Mild to moderate chronic NFCI does not appear to be associated with either oxidative stress or a pro-inflammatory state. Baseline [interleukin-10] and [syndecan-1] and post-heating [endothelin-1] are the most promising candidates for diagnosis of NFCI. Plasma biomarkers of inflammation, oxidative stress, endothelial function and damage were examined in 16 individuals with chronic NFCI (NFCI) and matched control participants with (COLD, n = 17) or without (CON, n = 14) previous cold exposure. Venous blood samples were collected at baseline to assess plasma biomarkers of endothelial function (nitrate, nitrite and endothelin-1), inflammation [interleukin-6 (IL-6), interleukin-10 (IL-10), tumour necrosis factor alpha and E-selectin], oxidative stress [protein carbonyl, 4-hydroxy-2-nonenal (4-HNE), superoxide dismutase and nitrotyrosine) and endothelial damage [von Willebrand factor, syndecan-1 and tissue type plasminogen activator (TTPA)]. Immediately after whole-body heating and separately, foot cooling, blood samples were taken for measurement of plasma [nitrate], [nitrite], [endothelin-1], [IL-6], [4-HNE] and [TTPA]. At baseline, [IL-10] and [syndecan-1] were increased in NFCI (P P = 0.015, respectively) and COLD (P = 0.033 and P = 0.030, respectively) compared with CON participants. The [4-HNE] was elevated in CON compared with both NFCI (P = 0.002) and COLD (P < 0.001). [Endothelin-1] was elevated in NFCI compared with COLD (P < 0.001) post-heating. The [4-HNE] was lower in NFCI compared with CON post-heating (P = 0.032) and lower than both COLD (P = 0.02) and CON (P = 0.015) post-cooling. No between-group differences were seen for the other biomarkers. Mild to moderate chronic NFCI does not appear to be associated with a pro-inflammatory state or oxidative stress. Baseline [IL-10] and [syndecan-1] and post-heating [endothelin-1] are the most promising candidates for diagnosing NFCI, but it is likely that a combination of tests will be required.

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.