Editorial: Neurological, neurophysiological, psychological and psychiatric effects of high altitude and hypoxia

Psychiatric Mental disorders show a prevalence of 30-40% in the general population (Steel et al., 2014), and neurological symptoms such as headache or dizziness are among the most common presenting symptoms in emergency care. Despite their high prevalence, neurological symptoms outside of headache and high altitude cerebral edema have only been investigated to a limited extent during hypoxia and high altitude (HA) exposure (Wilson et al., 2009). HA can also affect higher cortical functions leading to cognitive disturbances (Falla et al. 2021). The effect of hypoxia and HA on the development of psychiatric symptoms is even less investigated (Hüfner et al. 2019). This contrasts sharply with the increasing number of individuals traveling to HA for leisure or occupational purposes as well as recent advances to use (intermittent) hypoxia as a treatment for various symptoms and conditions (Burtscher et al. 2023).The aim of the current research topic was to collect studies on the neurological, neurophysiological, psychological and psychiatric effects of hypoxia and HA in order to advance research in the field and bring together researchers from different specialities involved in hypoxia and HA research. Within the research topic we report the results of two controlled studies performed under laboratory conditions. Such studies performed in controlled environments help greatly to clarify our understanding of physiological and pathophysiological mechanisms at HA, since HA field studies are often performed under challenging conditions and thus often involve small sample sizes or confounding factors. Importantly, reporting guidelines for HA field studies have been established in recent years (Brodmann Maeder et al., 2018) and have proven useful when conducting and reporting research from HA field studies (Hüfner et al., 2021).Alain Riveros-Rivera et al. report on the sex differences of daytime napping at simulated altitude of 2660 m or 4000 m asl in normobaric hypoxia compared to normoxia (https://doi.org/10.3389/fphys.2022.899636). Fifteen healthy volunteers underwent a polysomnography, hematological and cognitive evaluation around a 90 min midday nap. Napping in hypoxic conditions compared to normoxia lead to electrocardiogram changes (RR interval shortening) suggesting sympathetic activation in a sex-dependent way (men had a longer RR intervals than women). The sympathetic activation was also evident with the increase of epinephrine and cortisol levels. Periodic breathing, that has been linked to a longer RR interval during sleep at high altitude (Insalaco et al. 2016), occurred mostly in males in the investigated daytime nap and was present in only one woman with polycystic ovary syndrome suggesting a link to the testosterone level. The study suggests that napping in hypoxic conditions differentially affects sleep architecture, cardiac autonomic modulation, and respiratory pattern in men and women, which could lead to more individualized recommendations during HA exposure.Stefania Pighin et al. assessed the effect of mild hypoxia on risk taking behaviour (https://doi.org/10.3389/fphys.2022.960773). Twenty-five healthy individuals were investigated in an adequately powered, single-blinded, and counterbalanced study design during mild normobaric hypoxia exposure (FiO2: 14.1%) and normoxia. The decision-making task was incorporated after 20 minutes of hypoxia/normoxia exposure. The participants were hypoxaemic with about ~10% blood oxygen desaturation and had an elevated heart rate. In the hypoxic condition the participants were prone to taking higher risks in the betting task although there was no effect on the gains. The study highlights that hypoxia and probably also HA exposure affect cognition and can also have an influence the decision-making capacity of climbers with possible effects on health and safety.Florian Frank et al. review the role and mechanisms of hypoxia in the pathophysiology of migraine and propose how this could give new insights into the mechanisms underlying of migraine and other primary and secondary headaches (| https://doi.org/10.3389/fphys.2022.994469). Specifically, the authors propose that normobaric hypoxia could be used as a "human model" for the induction of migraine as well as aura symptoms.The perspective article by Jiuhong You et al. reviewsed whether and how hyperbaric oxygen preconditioning could affect prevent acute HA diseases. Possible mechanisms include protection of the blood-brain barrier, an inhibition of inflammatory responses, the induction of hypoxia-inducible factor as well as an increase in antioxidant activity. After analysing the existing literature the authors acknowledge the potential of hyperbaric oxygen precondition in preventing HA diseases, but also point out that the optimal protocol still needs to be established and additional well-controlled and designed investigations are needed (https://doi.org/10.3389/fphys.2023.1019103). Protection strategies seems to target intervention on blood-brain barrier, inhibition of the inflammatory responses, induction of the hypoxia-inducible factor as well as an increase in antioxidant activity. Despite that the strategies has been addressed in different papers in the existing literature, the topics seems to need further investigations (https://doi.org/10.3389/fphys.2023.1019103).In a separate contribution also involving also editors of this research topic, Hüfner et al. (https://doi.org/10.3389/fpsyt.2023.1221047) discuss how psychotic symptoms occurring at HA can potentially be classified in the existing diagnostic categories of the ICD-10 (World Health Organisation, 1992) or Diagnostic Statistical Manual of Mental Disorders (American Psychiatric Association, 2022) such as delirium or brief psychotic disorder. The authors specifically discuss the entity of isolated HA psychosis which consists of psychotic symptoms at HA without any other discernible psychopathological signs and symptoms (Hufner et al., 2018). In their hypothesis and theory article the The authors proposediscuss whether specific diagnostic criteria are needed for isolated HA psychosis and offer possible suggestions. that possibly it will be necessary in the future to establish new diagnostic criteria for this entity and also make a suggestion what such criteria might look like in their perspective and hypothesis article.The articles collected in this research topic provide new data and perspectives on neurological, neurophysiological, psychological and psychiatric effects of HA and hypoxia. This research topic offers insights and suggestions to the design and execution of future studies to more comprehensively understand, predict, and treat the individual's response to hypoxia and HA exposures. The effect HA and hypoxia on individuals with pre-existing neurological or pre-existing mental disorders is still insufficiently covered in this research topic as well as in the current medical literature. Gathering evidence based data also in these populations will help to reduce the stigma associated with neurological and especially mental disorders in the mountaineering community and other populations exposed to hypoxia or HA, and subsequently lead to an improvement in medical care and patient safety.As a future outlook we propose that it will be important to address the effects of hypoxia and HA in individuals with pre-existing neurological or psychiatric conditions since we have identified this as an important gap in the current medical literature which we were not able to sufficiently address within this research topic. Such insights will also help to reduce the stigma associated with neurological and psychiatric disorders in the mountaineering community and other populations intermittently or continuously exposed to hypoxia or HA, subsequently leading to an improvement in medical care and patient safety.

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