Neurophysiological Responses to Rest and Fatiguing Exercise in Severe Hypoxia in Healthy Humans

The central nervous system is highly sensitive to reductions in oxygen availability but the neurophysiological responses in healthy human lowlanders are not well understood. In severe hypoxia, whole-body exercise tolerance is impaired and neuromuscular fatigue, defined as any exercise-induced reduction in the ability of a muscle to generate force or power, reversible by rest, may be largely due to cerebral perturbations. The primary aim of this thesis was to determine the mechanisms of exercise-induced neuromuscular fatigue and the related neurophysiological responses to acute, chronic and intermittent severe hypoxia in healthy humans. In acute severe hypoxia (AH), exercise tolerance was, in part, mediated by a hypoxia-sensitive source of central fatigue, measured as a decrease in voluntary activation (VA) of the knee extensors (Study 1 – 4). This coincided with a significant challenge to systemic (arterial oxygen saturation [SpO2] ≈ 70%, Study 1 - 4) and cerebral oxygen availability at end-exercise (Study 3 - 4). The rate of development of peripheral locomotor muscle fatigue was blunted at task failure in AH in comparison to normoxia (Study 1 – 2). Corticospinal excitability and the neuromuscular mechanisms of fatigue were measured after a prolonged (two-week) exposure to high altitude in Study 3 (5260 m above sea level, Mount Chacaltaya, Bolivia). This was the first study to show that acclimatisation to chronic severe hypoxia (CH) alleviates the development of supraspinal fatigue induced by whole-body exercise in AH. This occurred in parallel to an improved cerebral oxygen delivery and cerebral oxygenation. Interestingly, the neurophysiological responses at rest in CH were characterised by an increased corticospinal and muscle membrane excitability. The peripheral contribution to neuromuscular fatigue was not attenuated following acclimatisation to high altitude. In study 4, a two-week protocol of intermittent hypoxia (IH) attenuated exercise-induced supraspinal fatigue measured in AH and substantially improved constant-power cycling in severe hypoxia. Total haemoglobin mass was unaltered by IH, but arterial oxygen content was improved due to an increase in SpO2, secondary to an enhanced ventilatory response to exercise. Peripheral locomotor muscle fatigue was lower following IH, which may be related to exercise training in hypoxia. Although corticospinal excitability was unchanged following a single 2-h exposure to severe hypoxia, repeated exposures of IH resulted in a transient increase in motor cortex excitability without changes in intracortical inhibition. (Study 5). In conclusion, in acute severe hypoxia, whole-body exercise tolerance is impaired through oxygensensitive mechanisms which exacerbate central fatigue. The acute response can be alleviated following both chronic and intermittent severe hypoxia

Exercise-induced fatigue in severe hypoxia following an intermittent hypoxic protocol

PURPOSE: Exercise-induced central fatigue is alleviated following acclimatisation to high altitude. The adaptations underpinning this effect may also be induced with brief, repeated exposures to severe hypoxia. The purpose of this study was to determine whether (i) exercise tolerance in severe hypoxia would be improved following an intermittent hypoxic (IH) protocol and (ii) exercise-induced central fatigue would be alleviated following an IH protocol.METHODS: Nineteen recreationally-active males were randomised into two groups who completed ten 2-h exposures in severe hypoxia (IH: PIO2 82 mmHg; n=11) or normoxia (control; n=8). Seven sessions involved cycling for 30 min at 25% peak power (W˙peak) in IH, and at a matched heart rate in normoxia. Participants performed baseline constant-power cycling to task failure in severe hypoxia (TTF-Pre). After the intervention, the cycling trial was repeated (TTF-Post). Pre- and post-exercise, responses to transcranial magnetic stimulation and supramaximal femoral nerve stimulation were obtained to assess central and peripheral contributions to neuromuscular fatigue.RESULTS: From pre- to post-exercise in TTF-Pre, maximal voluntary force (MVC), cortical voluntary activation (VATMS) and potentiated twitch force (Qtw,pot) decreased in both groups (all p < 0.05). Following IH, TTF-Post was improved (535 ± 213 s vs. 713 ± 271 s, p < 0.05) and an additional isotime trial was performed. After the IH intervention only, the reduction in MVC and VATMS was attenuated at isotime (p < 0.05). No differences were observed in the control group.CONCLUSION: Whole-body exercise tolerance in severe hypoxia was prolonged following a protocol of IH. This may be related to an alleviation of the central contribution to neuromuscular fatigue

Aristotle on Joint Perception and Perceiving that We Perceive

While most interpreters take the opening of De Anima III 2 (“Since we perceive that we see and hear […]”) to be an oblique reference to some sort of conscious awareness, I argue that Aristotle intends to explain what I call ‘joint perception’: when conjoined with Aristotle’s subsequent claim that perceiving and being perceived are the same activity, the metaperception underpins the perception of a unified object. My interpretation is shown to have a more satisfactory account of the aporiai that follow. While I argue that the immediate focus of the metaperceptual account is joint perception, it may also be applicable to other kinds of complex (i.e. non-special) perception, which I briefly consider in the closing section.While most interpreters take the opening of De Anima III 2 (“Since we perceive that we see and hear […]”) to be an oblique reference to some sort of conscious awareness, I argue that Aristotle intends to explain what I call ‘joint perception’: when conjoined with Aristotle’s subsequent claim that perceiving and being perceived are the same activity, the metaperception underpins the perception of a unified object. My interpretation is shown to have a more satisfactory account of the aporiai that follow. While I argue that the immediate focus of the metaperceptual account is joint perception, it may also be applicable to other kinds of complex (i.e. non-special) perception, which I briefly consider in the closing section

Services used by perinatal substance-users with child welfare involvement: a descriptive study

Abstract Background Substance use during pregnancy often leads to involvement in the child welfare system, resulting in multiple social service systems and service providers working with families to achieve successful child welfare outcomes. The Vulnerable Infants Program of Rhode Island (VIP-RI) is a care coordination program developed to work with perinatal substance-users to optimize opportunities for reunification and promote permanency for substance-exposed infants. This paper describes services used by VIP-RI participants and child welfare outcomes. Methods Data collected during the first four years of VIP-RI were used to identify characteristics of program participants, services received, and child welfare outcomes: closed child welfare cases, reunification with biological mothers and identified infant permanent placements. Descriptive Results Medical and financial services were associated with positive child welfare outcomes. Medical services included family planning, pre- and post-natal care and HIV test counseling. Financial services included assistance with obtaining entitlement benefits and receiving tangible support such as food and clothing. Conclusions Findings from this study suggest services that address basic family needs were related to positive child welfare outcomes. The provision of basic services, such as health care and financial assistance through entitlement benefits and tangible donations, may help to establish a foundation so mothers can concentrate on recovery and parenting skills. Identification of services for perinatal substance users that are associated with more successful child welfare outcomes has implications for the child welfare system, treatment providers, courts and families.</p