Hypercapnic hypoxia as a rehabilitation method for patients after ischemic stroke

INTRODUCTION

Experimental studies on animals have demonstrated a higher neuroprotective efficacy of hypercapnic hypoxia compared to normocapnic hypoxia. Respiratory training with hypercapnic hypoxia has shown a positive impact on the functional state of the nervous system in children with cerebral palsy (CP). It can be presumed that the combined effect of moderate hypercapnia and hypoxia will be promising for clinical application within the context of early rehabilitation after ischemic stroke.

METHODS

A randomized triple-blind placebo-controlled study was conducted on 102 patients with ischemic stroke, aged 63.07 ± 12.1 years. All patients were diagnosed with ischemic stroke based on neuroimaging criteria and/or clinical criteria within the 48-72 hour timeframe. The experimental group (n = 50) underwent daily respiratory training with hypercapnic hypoxia (FetCO2 5-6%, FetO2 15-16%) using the 'Carbonic' device for 7-11 sessions of 20 minutes each day during the treatment process. The control group (placebo, n = 52) underwent training on a similar device modified for breathing atmospheric air. Neurological examinations were conducted on all patients before the study and on the day after completing the training course.

RESULTS

The standard treatment demonstrated effectiveness in terms of neurological status scales in both groups. Intermittent exposure to hypercapnic hypoxia proved more effective in improving neurological function indicators in patients compared to the placebo group: NIHSS scale scores were 40% lower than in the placebo group (p < 0.001); mRS scale scores were 35% lower (p < 0.001); B-ADL-I and RMI indices were higher by 26% (p < 0.01) and 36% (p < 0.001), respectively; MoCA scale results were 13% higher (p < 0.05); HADS and BDI-II scale scores were lower by 35% (p < 0.05) and 25% (p < 0.05), respectively. The increase in MMSE scale scores in the intervention group was 54% higher (p < 0.001), and MoCA scale scores increased by 25% (p < 0.001).

CONCLUSION

Respiratory training with hypercapnic hypoxia improves the functional state of the nervous system in patients with ischemic stroke. After conducting further clarifying studies, hypercapnic hypoxia can be considered as an effective method of neurorehabilitation, which can be used as early as 48-72 hours after the onset of stroke.

Molecular Mechanisms of Neuroprotection after the Intermittent Exposures of Hypercapnic Hypoxia

The review introduces the stages of formation and experimental confirmation of the hypothesis regarding the mutual potentiation of neuroprotective effects of hypoxia and hypercapnia during their combined influence (hypercapnic hypoxia). The main focus is on the mechanisms and signaling pathways involved in the formation of ischemic tolerance in the brain during intermittent hypercapnic hypoxia. Importantly, the combined effect of hypoxia and hypercapnia exerts a more pronounced neuroprotective effect compared to their separate application. Some signaling systems are associated with the predominance of the hypoxic stimulus (HIF-1α, A1 receptors), while others (NF-κB, antioxidant activity, inhibition of apoptosis, maintenance of selective blood-brain barrier permeability) are mainly modulated by hypercapnia. Most of the molecular and cellular mechanisms involved in the formation of brain tolerance to ischemia are due to the contribution of both excess carbon dioxide and oxygen deficiency (ATP-dependent potassium channels, chaperones, endoplasmic reticulum stress, mitochondrial metabolism reprogramming). Overall, experimental studies indicate the dominance of hypercapnia in the neuroprotective effect of its combined action with hypoxia. Recent clinical studies have demonstrated the effectiveness of hypercapnic-hypoxic training in the treatment of childhood cerebral palsy and diabetic polyneuropathy in children. Combining hypercapnic hypoxia with pharmacological modulators of neuro/cardio/cytoprotection signaling pathways is likely to be promising for translating experimental research into clinical medicine.

Novel Approaches to the Establishment of Local Microenvironment from Resorbable Biomaterials in the Brain In Vitro Models

The development of brain in vitro models requires the application of novel biocompatible materials and biopolymers as scaffolds for controllable and effective cell growth and functioning. The "ideal" brain in vitro model should demonstrate the principal features of brain plasticity like synaptic transmission and remodeling, neurogenesis and angiogenesis, and changes in the metabolism associated with the establishment of new intercellular connections. Therefore, the extracellular scaffolds that are helpful in the establishment and maintenance of local microenvironments supporting brain plasticity mechanisms are of critical importance. In this review, we will focus on some carbohydrate metabolites-lactate, pyruvate, oxaloacetate, malate-that greatly contribute to the regulation of cell-to-cell communications and metabolic plasticity of brain cells and on some resorbable biopolymers that may reproduce the local microenvironment enriched in particular cell metabolites.

The Role of microRNAs in Epigenetic Regulation of Signaling Pathways in Neurological Pathologies

In recent times, there has been a significant increase in researchers' interest in the functions of microRNAs and the role of these molecules in the pathogenesis of many multifactorial diseases. This is related to the diagnostic and prognostic potential of microRNA expression levels as well as the prospects of using it in personalized targeted therapy. This review of the literature analyzes existing scientific data on the involvement of microRNAs in the molecular and cellular mechanisms underlying the development of pathologies such as Alzheimer's disease, cerebral ischemia and reperfusion injury, and dysfunction of the blood-brain barrier.

Physiological and Pathological Remodeling of Cerebral Microvessels

There is growing evidence that the remodeling of cerebral microvessels plays an important role in plastic changes in the brain associated with development, experience, learning, and memory consolidation. At the same time, abnormal neoangiogenesis, and deregulated regulation of microvascular regression, or pruning, could contribute to the pathogenesis of neurodevelopmental diseases, stroke, and neurodegeneration. Aberrant remodeling of microvesselsis associated with blood-brain barrier breakdown, development of neuroinflammation, inadequate microcirculation in active brain regions, and leads to the dysfunction of the neurovascular unit and progressive neurological deficits. In this review, we summarize current data on the mechanisms of blood vessel regression and pruning in brain plasticity and in Alzheimer's-type neurodegeneration. We discuss some novel approaches to modulating cerebral remodeling and preventing degeneration-coupled aberrant microvascular activity in chronic neurodegeneration.

Inhibition of Apoptosis is a Potential Way to Improving Ischemic Brain Tolerance in Combined Exposure to Hypercapnia and Hypoxia

We compared the intensity of apoptosis in the peri-infarction area of the brain after isolated and combined exposure to hypoxia and hypercapnia prior to focal ischemic stroke modeling. Hypoxia and hypercapnia reduced the number of TUNEL-positive cells in the peri-infarction area, and their combination was most effective in comparison with effects of isolated exposures. The maximum neuroprotective effect of combined exposure to hypoxia and hypercapnia in comparison with isolated exposures was determined by inhibition of apoptosis in the peri-infarction zone.

Stress of the Endoplasmic Reticulum of Neurons in Stroke Can Be Maximally Limited by Combined Exposure to Hypercapnia and Hypoxia

We studied the expression of chaperone GRP-78 and transcription factor NF-kB during the development of ischemic tolerance of the brain after combined and isolated exposure to hypoxia and hypercapnia. Combined exposure to hypoxia and hypercapnia maximally increased the expression of chaperone GRP-78 and transcription factor NF-kB, while the formation of ischemia-induced tolerance under conditions of hypercapnic hypoxia can be associated with activation of adaptive stress mechanisms in the endoplasmic reticulum. Under these conditions, hypercapnia in combination with hypoxia is a priority factor for activation of GRP-78 and transcription factor NF-kB.

[Hypercapnia--alternative hypoxia signal incentives to increase HIF-1α and erythropoietin in the brain]

Investigated the role of hypercapnic component in the mechanism of activation of HIF-1α and increase the synthesis of erythropoietin in the combined and the isolated impact of hypoxia and hypercapnia. It was found that the content of proteins of interest significantly increases both in isolated hypoxia and hypercapnia, and at their combined effect. Moreover, the hypercapnic hypoxia causes maximum activation of the synthesis and accumulation of erythropoietin HIF-1α, and permissive hypercapnia enhances their content more than hypoxic exposure.

[OPTIMAL HYPERCAPNIC HYPOXIA CONDITIONS FOR INCREASING RESISTANCE TO ACUTE HYPOXIA]

The study was focused on finding an optimal length of hypercapnia-hypoxia sessions of training resistance to acute hypoxia and looking for benefits from reoxygenation intervals and intermittent training over daytime. It turned out that 3 days of a 5-minute hypercapnia-hypoxia session per day improved resistance to acute hypoxia explicitly and that a 30-minute session increased resistance to the highest rate. Two training sessions per day are no better than one session. Hypercapnia-hypoxia training with reoxygenation intervals are the least effective in comparison to the other modes of training.

[The role of adenosine Al receptors and mitochondrial K+ATP channels in the mechanism of increasing the resistance to acute hypoxia in the combined effects of hypoxia and hypercapnia]

We studied the role of the role of mitoK+ATp channels and Al-adenosine receptor in the mechanism of increasing the resistance to acute hypoxia after hypoxic, hypercapnic and hypercapnic-hypoxic preconditioning. It is shown that mitochondrial ATP-sensitive potassium channels and Al-adenosine receptors, an important mechanism of preconditioning have a high value to increase the resistance to acute hypoxia/ischemia in the combined effect of hypoxia and hypercapnia. However, with regard to the adenosine receptor, this mechanism is realized without the participation hypercapnic component, which apparently starts neuroprotection without activation of the adenosine Al receptors.

[The role of VEGF, HSP-70 and protein S-100B in the potentiation effect of the neuroprotective effect of hypercapnic hypoxia]

Studied the role of VEGF, HSP-70 and S-100B in potentiating hypercapnia neuroprotective effect of hypoxia. Demonstrated that neuroprotective effects when exposed hypercapnic hypoxia-mediated protein synthesis increased S-100B, mainly due to the action of carbon dioxide, and not oxygen deficiency. Neuroprotective effects of HSP-70 due to hypoxia, but the combined effect of hypoxia and hypercapnia gives a significant increase in the synthesis of HSP-70 in comparison with the isolated effect of hypoxia. Vascularization activated equally as hypoxia and hypercapnia, without adding significant effects in combination. This suggests dominant effect hypercapnia, hypoxia compared in neuroprotection mechanisms related to protein S-100B, but not the protein VEGF, hypercapnia and potentiate the neuroprotective efficacy of hypoxia-related protein HSP-70.

[Comparative efficacy of hypoxia, hypercapnia and hypercapnic hypoxia increases body resistance to acute hypoxia in rats]

The relative efficiency of trainings with isolated hypoxia, hypercapnia and hypoxia in aggregate with hypercapnia in order to enhance the resistance of organism to the effect of an extreme hypoxia was studied. The combined effect of the hypoxia and hypercapnia was shown to influence more greatly in comparison with the effect of an isolated hypoxia. This effect was supported with an increase in the time of the loss position and the time of the animal's life under the condition of an extreme hypoxia. Also it is shown that the hypercapnia in a combination to a hypoxia makes dominating impact on formation of nonspecific resistance as the isolated hypercapnia enlarges indicators of nonspecific resistance, than the isolated hypoxia more effectively.