Efficacy of Acute Intermittent Hypoxia on Physical Function and Health Status in Humans with Spinal Cord Injury: A Brief Review

Gait Recovery in Spinal Cord Injury: A Systematic Review with Metanalysis Involving New Rehabilitative Technologies

Gait recovery is a fundamental goal in patients with spinal cord injury to attain greater autonomy and quality of life. Robotics is becoming a valid tool in improving motor, balance, and gait function in this patient population. Moreover, other innovative approaches are leading to promising results. The aim of this study was to investigate new rehabilitative methods for gait recovery in people who have suffered spinal cord injuries. A systematic review of the last 10 years of the literature was performed in three databases (PubMed, PEDro, andCochrane). We followed this PICO of the review: P: adults with non-progressive spinal cord injury; I: new rehabilitative methods; C: new methods vs. conventional methods; and O: improvement of gait parameters. When feasible, a comparison through ES forest plots was performed. A total of 18 RCTs of the 599 results obtained were included. The studies investigated robotic rehabilitation (n = 10), intermittent hypoxia (N = 3) and external stimulation (N = 5). Six studies of the first group (robotic rehabilitation) were compared using a forest plot for 10MWT, LEMS, WISCI-II, and SCIM-3. The other clinical trials were analyzed through a narrative review of the results. We found weak evidence for the claim that robotic devices lead to better outcomes in gait independence compared to conventional rehabilitation methods. External stimulation and intermittent hypoxia seem to improve gait parameters associated with other rehabilitation methods. Research investigating the role of innovative technologies in improving gait and balance is needed since walking ability is a fundamental issue in patients with SCI.

Considerations about Hypoxic Changes in Neuraxis Tissue Injuries and Recovery

Hypoxia represents the temporary or longer-term decrease or deprivation of oxygen in organs, tissues, and cells after oxygen supply drops or its excessive consumption. Hypoxia can be (para)-physiological-adaptive-or pathological. Thereby, the mechanisms of hypoxia have many implications, such as in adaptive processes of normal cells, but to the survival of neoplastic ones, too. Ischemia differs from hypoxia as it means a transient or permanent interruption or reduction of the blood supply in a given region or tissue and consequently a poor provision with oxygen and energetic substratum-inflammation and oxidative stress damages generating factors. Considering the implications of hypoxia on nerve tissue cells that go through different ischemic processes, in this paper, we will detail the molecular mechanisms by which such structures feel and adapt to hypoxia. We will present the hypoxic mechanisms and changes in the CNS. Also, we aimed to evaluate acute, subacute, and chronic central nervous hypoxic-ischemic changes, hoping to understand better and systematize some neuro-muscular recovery methods necessary to regain individual independence. To establish the link between CNS hypoxia, ischemic-lesional mechanisms, and neuro-motor and related recovery, we performed a systematic literature review following the" Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA") filtering method by interrogating five international medical renown databases, using, contextually, specific keywords combinations/"syntaxes", with supplementation of the afferent documentation through an amount of freely discovered, also contributive, bibliographic resources. As a result, 45 papers were eligible according to the PRISMA-inspired selection approach, thus covering information on both: intimate/molecular path-physiological specific mechanisms and, respectively, consequent clinical conditions. Such a systematic process is meant to help us construct an article structure skeleton giving a primary objective input about the assembly of the literature background to be approached, summarised, and synthesized. The afferent contextual search (by keywords combination/syntaxes) we have fulfilled considerably reduced the number of obtained articles. We consider this systematic literature review is warranted as hypoxia's mechanisms have opened new perspectives for understanding ischemic changes in the CNS neuraxis tissue/cells, starting at the intracellular level and continuing with experimental research to recover the consequent clinical-functional deficits better.

Exploring How Low Oxygen Post Conditioning Improves Stroke-Induced Cognitive Impairment: A Consideration of Amyloid-Beta Loading and Other Mechanisms

Cognitive impairment is a common and disruptive outcome for stroke survivors, which is recognized to be notoriously difficult to treat. Previously, we have shown that low oxygen post-conditioning (LOPC) improves motor function and limits secondary neuronal loss in the thalamus after experimental stroke. There is also emerging evidence that LOPC may improve cognitive function post-stroke. In the current study we aimed to explore how exposure to LOPC may improve cognition post-stroke. Experimental stroke was induced using photothrombotic occlusion in adult, male C57BL/6 mice. At 72 h post-stroke animals were randomly assigned to either normal atmospheric air or to one of two low oxygen (11% O2) exposure groups (either 8 or 24 h/day for 14 days). Cognition was assessed during the treatment phase using a touchscreen based paired-associate learning assessment. At the end of treatment (17 days post-stroke) mice were euthanized and tissue was collected for subsequent histology and biochemical analysis. LOPC (both 8 and 24 h) enhanced learning and memory in the 2nd week post-stroke when compared with stroke animals exposed to atmospheric air. Additionally we observed LOPC was associated with lower levels of neuronal loss, the restoration of several vascular deficits, as well as a reduction in the severity of the amyloid-beta (Aβ) burden. These findings provide further insight into the pro-cognitive benefits of LOPC.

Acute intermittent hypoxia enhances regeneration of surgically repaired peripheral nerves in a manner akin to electrical stimulation

The intrinsic repair response of injured peripheral neurons is enhanced by brief electrical stimulation (ES) at time of surgical repair, resulting in improved regeneration in rodents and humans. However, ES is invasive. Acute intermittent hypoxia (AIH) - breathing alternate cycles of regular air and air with ~50% normal oxygen levels (11% O₂), considered mild hypoxia, is an emerging, promising non-invasive therapy that promotes motor function in spinal cord injured rats and humans. AIH can increase neural activity and under moderately severe hypoxic conditions improves repair of peripherally crushed nerves in mice. Thus, we posited an AIH paradigm similar to that used clinically for spinal cord injury, will improve surgically repaired peripheral nerves akin to ES, including an impact on regeneration-associated gene (RAG) expression-a predictor of growth states. Alterations in early RAG expression were examined in adult male Lewis rats that underwent tibial nerve coaptation repair with either 2 days AIH or normoxia control treatment begun on day 2 post-repair, or 1 h ES treatment (20 Hz) at time of repair. Three days post-repair, AIH or ES treatments effected significant and parallel elevated RAG expression relative to normoxia control at the level of injured sensory and motor neuron cell bodies and proximal axon front. These parallel impacts on RAG expression were coupled with significant improvements in later indices of regeneration, namely enhanced myelination and increased numbers of newly myelinated fibers detected 20 mm distal to the tibial nerve repair site or sensory and motor neurons retrogradely labeled 28 mm distal to the repair site, both at 25 days post nerve repair; and improved return of toe spread function 5-10 weeks post-repair. Collectively, AIH mirrors many beneficial effects of ES on peripheral nerve repair outcomes. This highlights its potential for clinical translation as a non-invasive means to effect improved regeneration of injured peripheral nerves.

Effects of body weight-support treadmill training on postural sway and gait independence in patients with chronic spinal cord injury

OBJECTIVE

To examine the effects of a six-week body weight-support treadmill training (BWSTT) program on center-of-mass control and gait independence in chronic, incomplete spinal cord injury (iSCI) patients.

DESIGN

Descriptive.

SETTING

Clinica Los Coihues. Neurorehabilitation center in Santiago, Chile.

PARTICIPANTS

17 chronic iSCI patients and 17 healthy subjects.

OUTCOME MEASURES

An instrumented sway (ISway) test was performed before and after the implementation of a six-week BWSTT program. The standing balance of participants was measured by Normalized jerk (NJ) and root mean square (RMS). These values were used to assess the standing balance of participants, and were correlated with the scores obtained on the Walking Index Spinal Cord Injury (WISCI) II test.

RESULTS

Significant differences were found in standing balance (i.e., through NJ) after the BWSTT program (P = 0.016), but no significant differences were found in RMS values for postural sway (P = 0.693). None of the patients obtained improved WISCI II scores pre- vs. post-intervention.

CONCLUSION

While a BWSTT program can improve center-of-mass control in iSCI patients, no effects were recorded for gait independence.

TRIAL REGISTRATION

National Clinical Trials, registry number NCT02703883.

Links between lower urinary tract symptoms, intermittent hypoxia and diabetes: Causes or cures?

Bothersome lower urinary tract symptoms (LUTS) manifest as urinary frequency, urgency, incontinence and incomplete bladder emptying. Existing treatments ameliorate but do not eliminate most symptoms, leading to financial and personal burdens attributable to sustained medical therapies that may last a lifetime. The purpose of this review is to highlight evidence of causal associations between LUTS and several common comorbidities, including intermittent hypoxia (IH) concomitant with obstructive sleep apnea (OSA), obesity, metabolic syndrome and type 2 diabetes. Links between these conditions, including therapies targeted to co-occurring complications that have demonstrated benefits for LUTS, suggest compelling avenues of research and also underscore critical gaps in understanding the mechanisms underlying urinary dysfunction. These gaps are prominent in the IH field, where an acknowledged link between OSA and LUTS has gone largely uninvestigated. New tools, models, or reappropriation of existing ones, especially rodent models, is required to parse the associations between IH/OSA, LUTS and obesity/diabetes and to elucidate their underlying, and potentially shared, etiologies.

Low Oxygen Post Conditioning as an Efficient Non-pharmacological Strategy to Promote Motor Function After Stroke

Low oxygen post conditioning (LOPC) has shown promising results in terms of neuroprotection after stroke, but the effects on motor function have not been considered. Cortical stroke targeting the motor and sensory cortex was induced by photothrombotic occlusion and after 48 h allocated to LOPC (11% O₂) for 2 weeks. Motor impairment was assessed using the cylinder and grid walk tests during the exposure period and for two further weeks upon completion of the intervention. Neuroprotection was evaluated by histological and molecular analysis at two time points. Two weeks of LOPC was sufficient to significantly reduce motor deficits and tissue loss after stroke. This functional improvement was associated with increased capillary density, enhanced levels of BDNF, decreased neuronal loss and decreased microglia activation. These improvements, in most instances, were maintained up to 2 weeks after the end of the treatment. To our knowledge, this is the first study to demonstrate that LOPC induces a persistent improvement in motor function and neuroprotection after stroke, and in doing so provides evidence to support a case for considering taking LOPC forward to early stage clinical research.

Effects of intermittent hypoxic training performed at high hypoxia level on exercise performance in highly trained runners

This study exanimated the effects of intermittent hypoxic training (IHT) conducted at a high level of hypoxia with recovery at ambient air on aerobic/anaerobic capacities at sea level and hematological variations. According to a double-blind randomized design, fifteen highly endurance-trained runners completed a 6-weeks regimented training with 3 sessions per week consisting of intermittent runs (6x work-rest ratio of 5':5') on a treadmill at 80-85% of maximal aerobic speed ([Formula: see text]). Nine athletes (hypoxic group, HG) performed the exercise bouts at FI0₂ = 10.6-11.4% while six athletes (normoxic group, NG) exercised at ambient air. Running time to exhaustion at a velocity corresponding to 95% [Formula: see text] significantly increased for HG while no effect was found for NG. Regarding [Formula: see text], no significant effects were found in either training group. In addition, the decline of jumping performances over a 45s-continuous maximal vertical jump test (i.e. anaerobic capacity index) tended to be lower in HG compared to NG. The levels of the studied hematological variables, including erythropoietin and hematocrit, did not significantly change for either HG or NG. These results highlight that our IHT protocol may induce additional effects on aerobic performance without compromising the anaerobic capacity index in highly-trained athletes.

The Use of Simulated Altitude Techniques for Beneficial Cardiovascular Health Outcomes in Nonathletic, Sedentary, and Clinical Populations: A Literature Review

Lizamore, Catherine A., and Michael J. Hamlin. The use of simulated altitude techniques for beneficial cardiovascular health outcomes in nonathletic, sedentary, and clinical populations: A literature review. High Alt Med Biol 18:305-321, 2017.

BACKGROUND

The reportedly beneficial improvements in an athlete's physical performance following altitude training may have merit for individuals struggling to meet physical activity guidelines.

AIM

To review the effectiveness of simulated altitude training methodologies at improving cardiovascular health in sedentary and clinical cohorts.

METHODS

Articles were selected from Science Direct, PubMed, and Google Scholar databases using a combination of the following search terms anywhere in the article: "intermittent hypoxia," "intermittent hypoxic," "normobaric hypoxia," or "altitude," and a participant descriptor including the following: "sedentary," "untrained," or "inactive."

RESULTS

1015 articles were returned, of which 26 studies were accepted (4 clinical cohorts, 22 studies used sedentary participants). Simulated altitude methodologies included prolonged hypoxic exposure (PHE: continuous hypoxic interval), intermittent hypoxic exposure (IHE: 5-10 minutes hypoxic:normoxic intervals), and intermittent hypoxic training (IHT: exercising in hypoxia).

CONCLUSIONS

In a clinical cohort, PHE for 3-4 hours at 2700-4200 m for 2-3 weeks may improve blood lipid profile, myocardial perfusion, and exercise capacity, while 3 weeks of IHE treatment may improve baroreflex sensitivity and heart rate variability. In the sedentary population, IHE was most likely to improve submaximal exercise tolerance, time to exhaustion, and heart rate variability. Hematological adaptations were unclear. Typically, a 4-week intervention of 1-hour-long PHE intervals 5 days a week, at a fraction of inspired oxygen (F_IO₂) of 0.15, was beneficial for pulmonary ventilation, submaximal exercise, and maximum oxygen consumption ([Formula: see text]O_2max), but an F_IO₂ of 0.12 reduced hyperemic response and antioxidative capacity. While IHT may be beneficial for increased lipid metabolism in the short term, it is unlikely to confer any additional advantage over normoxic exercise over the long term. IHT may improve vascular health and autonomic balance.

Ferulic Acid Improves Functional Recovery after Acute Spinal Cord Injury in Rats by Inducing Hypoxia to Inhibit microRNA-590 and Elevate Vascular Endothelial Growth Factor Expressions

Spinal cord injury (SCI) is the leading cause of paralysis, disability and even death in severe cases, and neural stem cells (NSCs) transplant has been employed for repairing SCI. Ferulic acid (FA) is able to promote neurogenesis in various stem cell therapies. We aimed to investigate the effect of FA on NSC transplant therapy, and the underlying mechanism, in improving functional recovery in SCI rat model. A rat model of SCI was established, which then received transplant of NSCs with or without FA pre-treatment. Functional recovery of the SCI rats was then evaluated, in terms of spinal cord water content, myeloperoxidase activity and behavioral assessments. Effect of FA in inducing hypoxia in NSCs was also assessed, followed by identifying the hypoxic regulated microRNA and the subsequent target gene. Transplant of FA pre-treated NSCs improved functional recovery of SCI rats to a more significant extent than NSCs without FA pre-treatment. The beneficial effects of FA in repairing SCI was mediated by inducing hypoxia in NSCs, which in turn inhibited microRNA-590 to elevate vascular endothelial growth factor expression. Our findings support the clinical potential of FA in improving efficacy of NSC transplant therapy for treatment of SCI.

Cytoprotective effects of myristicin against hypoxia‑induced apoptosis and endoplasmic reticulum stress in rat dorsal root ganglion neurons

The aim of the present study was to investigate the role of myristicin (Myr; 1‑allyl‑5‑methoxy‑3,4‑methylenedioxybenzene), an active aromatic compound isolated from nutmeg, carrot, basil, cinnamon and parsley, in hypoxia‑induced apoptosis in rat dorsal root ganglion (DRG) neurons. It was observed that Myr significantly enhanced cell viability in hypoxia‑induced DRG neurons in a dose‑dependent manner; the optimal concentration of Myr was 50 µM. Furthermore, Myr reduced the percentage of deoxynucleotidyl transferase‑mediated dUTP nick end‑labeling‑positive neuronal cells and influenced the expression of the pro‑apoptotic gene B‑cell lymphoma 2 (Bcl‑2) associated X protein, the apoptosis protease cleaved caspase‑3 and the anti‑apoptotic gene Bcl‑2, in the hypoxia‑induced group. In addition, Myr protected against hypoxic injury in DRG neurons by inhibiting malondialdehyde and lactate dehydrogenase, however upregulating superoxide dismutase and glutathione peroxidase. Myr reduced the expression of endoplasmic reticulum stress (ERS) markers, including CCAAT/enhancer‑binding protein‑homologous protein, glucose‑related protein 78 and cleaved caspase‑12 in the hypoxia‑induced group. To the best of our knowledge, this is the first demonstration of the activity of Myr against hypoxia‑induced apoptosis in rat DRG neurons via inhibition of the ERS pathway.

Intermittent hypoxia initiated plasticity in humans: A multipronged therapeutic approach to treat sleep apnea and overlapping co-morbidities

Over the past three decades exposure to intermittent hypoxia (IH) has generally been considered a stimulus associated with a number of detrimental outcomes. However, there is sufficient evidence to link IH to many beneficial outcomes but they have largely been ignored, particularly in the field of sleep medicine in the United States. Recent reviews have postulated that this apparent contradiction is related to the severity and duration of exposure to IH; mild forms of IH initiate beneficial outcomes while severe forms of IH are coupled to detrimental consequences. In the present review we explore the role that IH has in initiating respiratory plasticity and the potential this form of plasticity has to mitigate obstructive sleep apnea (OSA) in humans. In taking this approach, we address the possibility that IH could serve as an adjunct therapy coupled with continuous positive airway pressure (CPAP) to treat OSA. Our working hypothesis is that exposure to mild IH leads to respiratory plasticity that manifests in increased stability of the upper airway, which could ultimately reduce the CPAP required to treat OSA. In turn, this reduction could increase CPAP compliance and extend the length of treatment each night, which might improve the magnitude of outcome measures. Improved treatment compliance coupled with the direct effect that IH has on numerous overlapping conditions (i.e. asthma, chronic obstructive pulmonary disease, spinal cord injury) may well lead to substantial improvements that exceed outcomes following treatment with CPAP alone. Overall, this review will consider evidence from the published literature which suggests that IH could serve as an effective multipronged therapeutic approach to treat sleep apnea and its overlapping co-morbidities.

Chronic intermittent hypoxia and obstructive sleep apnea: an experimental and clinical approach

Obstructive sleep apnea (OSA) is a prevalent sleep disorder considered as an independent risk factor for cardiovascular consequences, such as systemic arterial hypertension, ischemic heart disease, cardiac arrhythmias, metabolic disorders, and cognitive dysfunction. The pathogenesis of OSA-related consequence is assumed to be chronic intermittent hypoxia (IH) inducing alterations at the molecular level, oxidative stress, persistent systemic inflammation, oxygen sensor activation, and increase of sympathetic activity. Overall, these mechanisms have an effect on vessel permeability and are considered to be important factors for explaining vascular, metabolic, and cognitive OSA-related consequences. The present review attempts to examine together the research paradigms and clinical studies on the effect of acute and chronic IH and the potential link with OSA. We firstly describe the literature data on the mechanisms activated by acute and chronic IH at the experimental level, which are very helpful and beneficial to explaining OSA consequences. Then, we describe in detail the effect of IH in patients with OSA that we can consider "the human model" of chronic IH. In this way, we can better understand the specific pathophysiological mechanisms proposed to explain the consequences of IH in OSA.

Intermittent Hypoxia Does not Elicit Memory Impairment in Spinal Cord Injury Patients

There is a critical need for new therapeutic strategies to restore motor function in patients with spinal cord injuries (SCIs), without unwanted effects. Intermittent hypoxia (IH) induces plasticity in spared synaptic pathways to motor neurons below the level of injury, which can be harnessed to elicit motor recovery in incomplete SCI patients. However, there is conflicting evidence regarding the effects of IH on memory function. The aim of this study was to assess episodic verbal and visual memory function with the Complutense verbal learning test (TAVEC) and the Rey-Osterrieth Complex Figure Test (ROCF), respectively, before and after a 4-week protocol of repetitive IH combined with body weight-supported treadmill training (BWSTT) in incomplete ASIA C and D SCI subjects. Subjects received either IH (cycling 9%/21% FiO2 every 1.5 min, 15 cycles per day) or continued normoxia (Nx, 21% FiO2) combined with 45 min of BWSTT for 5 consecutive days, followed by 3 times per week IH and BWSTT for 3 additional weeks. ROCF Z scores between IH plus BWSTT and Nx plus BWSTT were not significantly different (p = .43). Compared with baseline, IH and BWSTT group showed a significantly greater (p < .05) verbal memory performance for immediate, short-term, and long-term recall; however, it was not different from Nx plus BWSTT group in all verbal memory components (p > .05). Our results suggest that a 4-week protocol of moderate IH does not elicit visual or verbal memory impairment. Thus, repetitive IH may be a safe therapeutic approach to incomplete spinal cord injury patients, without deleterious cognitive effects.