Neuromuscular fatigability at high altitude: Lowlanders with acute and chronic exposure, and native highlanders

Accelerating healing at high altitudes: Oxygen and bFGF delivery through nanoparticle-loaded gel dressings

High altitude environment is mainly characterized by low oxygen. Due to persistent hypoxia, nonhealing wounds are common in high-altitude areas. Moreover, Basic fibroblast growth factor (bFGF) is a versatile biologically active substance that has crucial impact on wound healing. Given the limited availability of atmospheric oxygen and reduced blood oxygen saturation in high-altitude area, and the challenge that arises from direct oxygen and bFGF delivery to wounds through the traumatized vascular structure, it necessitates an innovative solution for local and permeable delivery of oxygen and bFGF. In this study, we present a strategy that involves revamping traditional gel-based wound dressings through the incorporation of nanoparticles encapsulating oxygen and bFGF, engineered to facilitate the localized delivery of dissolved oxygen and bFGF to wound surfaces. The prospective evaluation of this delivery technique's therapeutic impacts on epithelial, endothelial and fibroblasts cells can be materialized. Further experiment corroborated these effects on a high-altitude wounds' murine model. Given its biocompatibility, efficacy, and utility, we posit that NOB-Gel exhibits remarkable translational potential for managing and hastening the healing process of an array of clinical wounds, more so for wounds inflicted at high altitudes.

Curcumin-mediated enhancement of lung barrier function in rats with high-altitude-associated acute lung injury via inhibition of inflammatory response

BACKGROUND

Exposure to a hypobaric hypoxic environment at high altitudes can lead to lung injury. In this study, we aimed to determine whether curcumin (Cur) could improve lung barrier function and protect against high-altitude-associated acute lung injury.

METHODS

Two hundred healthy rats were randomly divided into standard control, high-altitude control (HC), salidroside (40 mg/kg, positive control), and Cur (200 mg/kg) groups. Each group was further divided into five subgroups. Basic vital signs, lung injury histopathology, routine blood parameters, plasma lactate level, and arterial blood gas indicators were evaluated. Protein and inflammatory factor (tumor necrosis factor α (TNF-α), interleukin [IL]-1β, IL-6, and IL-10) concentrations in bronchoalveolar lavage fluid (BALF) were determined using the bicinchoninic acid method and enzyme-linked immunosorbent assay, respectively. Inflammation-related and lung barrier function-related proteins were analyzed using immunoblotting.

RESULTS

Cur improved blood routine indicators such as hemoglobin and hematocrit and reduced the BALF protein content and TNF-α, IL-1β, and IL-6 levels compared with those in the HC group. It increased IL-10 levels and reduced pulmonary capillary congestion, alveolar hemorrhage, and the degree of pulmonary interstitial edema. It increased oxygen partial pressure, oxygen saturation, carbonic acid hydrogen radical, and base excess levels, and the expression of zonula occludens 1, occludin, claudin-4, and reduced carbon dioxide partial pressure, plasma lactic acid, and the expression of phospho-nuclear factor kappa.

CONCLUSIONS

Exposure to a high-altitude environment for 48 h resulted in severe lung injury in rats. Cur improved lung barrier function and alleviated acute lung injury in rats at high altitudes.

High altitude hypoxia and oxidative stress: The new hope brought by free radical scavengers

Various strategies can be employed to prevent and manage altitude illnesses, including habituation, oxygenation, nutritional support, and medication. Nevertheless, the utilization of drugs for the prevention and treatment of hypoxia is accompanied by certain adverse effects. Consequently, the quest for medications that exhibit minimal side effects while demonstrating high efficacy remains a prominent area of research. In this context, it is noteworthy that free radical scavengers exhibit remarkable anti-hypoxia activity. These scavengers effectively eliminate excessive free radicals and mitigate the production of reactive oxygen species (ROS), thereby safeguarding the body against oxidative damage induced by plateau hypoxia. In this review, we aim to elucidate the pathogenesis of plateau diseases that are triggered by hypoxia-induced oxidative stress at high altitudes. Additionally, we present a range of free radical scavengers as potential therapeutic and preventive approaches to mitigate the occurrence of common diseases associated with hypoxia at high altitudes.

Male and Female Mitochondria Respond Differently after Exercising in Acute Hypoxia

The use of hypoxic devices among athletes who train in normobaric hypoxia has become increasingly popular; however, the acute effects on heart and brain metabolism are not yet fully understood. This study aimed to investigate the mitochondrial bioenergetics in trained male and female Wistar rats after acute hypoxia training. The experimental plan included exercising for 30 min on a treadmill in a Plexiglas cage connected to a hypoxic generator set at 12.5% O2 or in normoxia. After the exercise, the rats were sacrificed, and their mitochondria were isolated from their brains and hearts. The bioenergetics for each complex of the electron transport chain was tested using a Clark-type electrode. The results showed that following hypoxia training, females experienced impaired oxidative phosphorylation through complex II in heart subsarcolemmal mitochondria, while males had an altered ADP/O in heart interfibrillar mitochondria, without any change in oxidative capacity. No differences from controls were evident in the brain, but an increased electron transport system efficiency was observed with complex I and IV substrates in males. Therefore, the study's findings suggest that hypoxia training affects the heart mitochondria of females more than males. This raises a cautionary flag for female athletes who use hypoxic devices.

Comments on: Electromyographic signature of isometric squat in the highest refuge in Europe

We read with particular interest the study by Rua et al. (Eur J Transl Myol 33 (3) 11637, 2023 doi: 10.4081/ejtm.2023.11637) on the electromyographic (EMG) activity of the quadriceps muscle during squat at high-altitude. It offers interesting insights into how neural factors might alter muscle function during a multi-joint low-intensity motor task with sustained contraction after trekking under hypoxic conditions. However, the methodological processes and procedures used in the study could bias the interpretation of the outcomes. Therefore, we outline the procedural considerations that should be taken into account in further studies aimed at investigating the potential changes in quadriceps EMG activity during the squat as a result of trekking at high-altitude.

Electromyographic signature of isometric squat in the highest refuge in Europe

Reports of electromyography during hypoxic exercise are contrasting, due to protocol and muscle diversity. This work aimed to investigate alterations in muscle activation and myoelectrical fatigue during exercise at high-altitude in those muscles primarily involved in trekking. Twelve young adults balanced by gender and age were tested at low (1,667 m) and high (4,554 m, "Capanna Margherita", Italy) altitude, during an isometric squat lasting 60 seconds. High-density surface electromyography was performed from the quadriceps of right limb. The root mean square (RMS), median frequency with its slope, and muscle fiber conduction velocity (MFCV) were computed. Neither males nor females showed changes in median frequency (Med: 36.13 vs 35.63 Hz) and its slope (Med: -9 vs -12 degree) in response to high-altitude trekking, despite a great inter-individual heterogeneity, nor differences were found for MFCV. RMS was not significantly equivalent, with greater values at low altitude (0.385 ± 0.104 mV) than high altitude (0.346 ± 0.090 mV). Unexpected results can be due either to a postural compensation of the whole body compensating for a relatively greater effort or to the inability to support muscle activation after repeated physical efforts.  Interesting results may emerge by measuring simultaneously electromyography, muscle oxygenation and kinematics comparing trekking at normoxia vs hypoxia.

The benefits of early continuous renal replacement therapy in critically ill patients with acute kidney injury at high-altitude areas: a retrospective multi-center cohort study

Severe hypoxia would aggravate the acute kidney injury (AKI) in high-altitude areas and continuous renal replacement therapy (CRRT) has been used to treat critically ill patients with AKI. However, the characteristics and outcomes of CRRT in critically ill patients at AKI in high altitudes and the optimal timing of CRRT initiation remain unclear. 1124 patients were diagnosed with AKI and treated with CRRT in the ICU, comprising a high-altitude group (n = 648) and low-altitude group (n = 476). Compared with the low-altitude group, patients with AKI at high altitude showed longer CRRT (4.8 vs. 3.7, P = 0.036) and more rapid progression of AKI stages (P < 0.01), but without any significant minor or major bleeding episodes (P > 0.05). Referring to the analysis of survival and kidney recovery curves, a higher mortality but a lower possibility of renal recovery was observed in the high-altitude group (P < 0.001). However, in the high-altitude group, the survival rate of early CRRT initiation was significantly higher than that of delayed CRRT initiation (P < 0.001). The findings showed poorer clinical outcomes in patients undergoing CRRT for AKI at high altitudes. CRRT at high altitudes was unlikely to increase the adverse events. Moreover, early CRRT initiation might reduce the mortality and promote renal recovery in high-altitude patients.

The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits

The purpose of this study was to examine how two common methods of continuous hypoxaemia impact the activity of intracortical circuits responsible for inhibition and facilitation of motor output, and spinal excitability. Ten participants were exposed to 2 h of hypoxaemia at 0.13 fraction of inspired oxygen (F I O 2 ${F_{{\mathrm{I}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol) and 80% of peripheral capillary oxygen saturation (S p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol) using a simulating altitude device on two visits separated by a week. Using transcranial magnetic and peripheral nerve stimulation, unconditioned motor evoked potential (MEP) area, short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF), and F-wave persistence and area were assessed in the first dorsal interosseous (FDI) muscle before titration, after 1 and 2 h of hypoxic exposure, and at reoxygenation. The clamping protocols resulted in differing reductions inS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ by 2 h (S p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol: 81.9 ± 1.3%,F I O 2 ${F_{{\mathrm{I}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol: 90.6 ± 2.5%). Although unconditioned MEP peak to peak amplitude and area did not differ between the protocols, SICI duringF I O 2 ${F_{{\mathrm{I}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping was significantly lower at 2 h compared toS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping (P = 0.011) and baseline (P < 0.001), whereas ICF was higher throughout theF I O 2 ${F_{{\mathrm{I}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping compared toS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping (P = 0.005). Furthermore, a negative correlation between SICI andS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ (rrm  = -0.56, P = 0.002) and a positive correlation between ICF andS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ (rrm  = 0.69, P = 0.001) were determined, where greater reductions inS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ correlated with less inhibition and less facilitation of MEP responses. Although F-wave area progressively increased similarly throughout the protocols (P = 0.037), persistence of responses was reduced at 2 h and reoxygenation (P < 0.01) during theS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol compared to theF I O 2 ${F_{{\mathrm{I}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol. After 2 h of hypoxic exposure, there is a reduction in the activity of intracortical circuits responsible for inhibiting motor output, as well as excitability of spinal motoneurones. However, these effects can be influenced by other physiological responses to hypoxia (i.e., hyperventilation and hypocapnia). NEW FINDINGS: What is the central question of this study? How do two common methods of acute hypoxic exposure influence the excitability of intracortical networks and spinal circuits responsible for motor output? What is the main finding and its importance? The excitability of spinal circuits and intracortical networks responsible for inhibition of motor output was reduced during severe acute exposure to hypoxia at 2 h, but this was not seen during less severe exposure. This provides insight into the potential cause of variance seen in motor evoked potential responses to transcranial magnetic stimulation (corticospinal excitability measures) when exposed to hypoxia.