Caffeine Enhances Intermittent Hypoxia-Induced Gains in Walking Function for People with Chronic Spinal Cord Injury

Motor-evoked potentials in the human upper and lower limb do not increase after single 30-min sessions of acute intermittent hypoxia

Acute intermittent hypoxia (AIH) can induce sustained facilitation of motor output in people with spinal cord injury (SCI). Most studies of corticospinal tract excitability in humans have used 9% fraction inspired oxygen ([Formula: see text]) AIH (AIH-9%), with inconsistent outcomes. We investigated the effect of single sessions of 9% [Formula: see text] and 12% [Formula: see text] AIH (AIH-12%) on corticospinal excitability of a hand and leg muscle in able-bodied adults. Ten naïve participants completed three sessions on separate days comprising 15 epochs of 1 min of AIH-9%, AIH-12%, or sham (SHAM-21%) followed by 1 min of room air (21% [Formula: see text]) in a randomized crossover design. Motor-evoked potentials (MEPs; n = 30, ∼1 mV) elicited at rest by transcranial magnetic stimulation and maximal M-waves (Mmax) evoked by peripheral nerve stimulation were measured from the first dorsal interosseous (FDI) and tibialis anterior (TA) muscles at baseline and at ∼0, 20, 40, and 60 min post intervention. AIH-9% induced the greatest reduction in peripheral oxygen saturation (to 85% vs. 93% and 100% in AIH-12% and SHAM-21%, respectively; P < 0.001) and the greatest increase in ventilation [by 22% vs. 12% and -3% in AIH-9%, AIH-12%, and SHAM-21%, respectively (P < 0.001)]. There was no difference in MEP amplitudes (%Mmax) after any of the three conditions (AIH-9%, AIH-12%, SHAM-21%) for both the FDI (P = 0.399) and TA (P = 0.582). Despite greater cardiorespiratory changes during AIH-9%, there was no evidence of corticospinal facilitation (tested with MEPs) in this study. Further studies could explore variability in response to AIH between individuals and other methods to measure motor facilitation in people with and without spinal cord injuries.NEW & NOTEWORTHY This is the first study that tests whether acute intermittent hypoxia (AIH) induces motor output facilitation in humans after two different doses of AIH (9% and 12% [Formula: see text]) and the reproducibility of participant responses after a repeat AIH intervention at 9% AIH. There was no motor output facilitation in response to either dose of AIH. The results question the effectiveness of a single 30-min session of AIH in inducing motor output facilitation, tested in this way.

BREATHE DMD: boosting respiratory efficacy after therapeutic hypoxic episodes in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a fatal genetic neuromuscular disorder, characterised by progressive decline in skeletal muscle function due to the secondary consequences of dystrophin deficiency. Weakness extends to the respiratory musculature, and cardiorespiratory failure is the leading cause of death in men with DMD. Intermittent hypoxia has emerged as a potential therapy to counteract ventilatory insufficiency by eliciting long-term facilitation of breathing. Mechanisms of sensory and motor facilitation of breathing have been well delineated in animal models. Various paradigms of intermittent hypoxia have been designed and implemented in human trials culminating in clinical trials in people with spinal cord injury and amyotrophic lateral sclerosis. Application of therapeutic intermittent hypoxia to DMD is considered together with discussion of the potential barriers to progression owing to the complexity of this devastating disease. Notwithstanding the considerable challenges and potential pitfalls of intermittent hypoxia-based therapies for DMD, we suggest it is incumbent on the research community to explore the potential benefits in pre-clinical models. Intermittent hypoxia paradigms should be implemented to explore the proclivity to express respiratory plasticity with the longer-term aim of preserving and potentiating ventilation in pre-clinical models and people with DMD.

Randomized controlled trial of intermittent hypoxia in Parkinson's disease: study rationale and protocol

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disease for which no disease-modifying therapies exist. Preclinical and clinical evidence suggest that repeated exposure to intermittent hypoxia might have short- and long-term benefits in PD. In a previous exploratory phase I trial, we demonstrated that in-clinic intermittent hypoxia exposure is safe and feasible with short-term symptomatic effects on PD symptoms. The current study aims to explore the safety, tolerability, feasibility, and net symptomatic effects of a four-week intermittent hypoxia protocol, administered at home, in individuals with PD.

METHODS/DESIGN

This is a two-armed double-blinded randomized controlled trial involving 40 individuals with mild to moderate PD. Participants will receive 45 min of normobaric intermittent hypoxia (fraction of inspired oxygen 0.16 for 5 min interspersed with 5 min normoxia), 3 times a week for 4 weeks. Co-primary endpoints include nature and total number of adverse events, and a feasibility-tolerability questionnaire. Secondary endpoints include Movement Disorders Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part II and III scores, gait tests and biomarkers indicative of hypoxic dose and neuroprotective pathway induction.

DISCUSSION

This trial builds on the previous phase I trial and aims to investigate the safety, tolerability, feasibility, and net symptomatic effects of intermittent hypoxia in individuals with PD. Additionally, the study aims to explore induction of relevant neuroprotective pathways as measured in plasma. The results of this trial could provide further insight into the potential of hypoxia-based therapy as a novel treatment approach for PD.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT05948761 (registered June 20th, 2023).

Acute Intermittent Hypoxia Did Not Alter Pain Sensitivity or Pain Intensity Ratings for Individuals with Chronic Low Back Pain: A Pilot Study

Aims and Objective

The purpose of this pilot study was to explore whether AIH produces changes in pain sensitivity or in reports of self-reported pain intensity for individuals with low back pain.

Methods

In a quasi-experimental, cross-over design we compared participants (n = 9) exposed to normal room air and hypoxia using a commercially available gas blender. The treatment period consisted of 5 consecutive days of randomly assigned to AIH or room air. For the participants initially randomized to AIH there was cross-over to receive 5 more consecutive days of room air. Therefore, this design allowed for between group and within subject assessment of AIH effects. Pain sensitivity was assessed with quantitative sensory testing (QST) for posterior superior iliac spine pressure threshold, plantar thermal threshold, and peak pain ratings. Self-reported pain intensity for low back pain was assessed via the Brief Pain Inventory.

Results

There were no between group differences for AIH and room air in pain sensitivity or self-reported pain intensity. In the within subject analyses larger effect sizes favoring AIH were detected for plantar measures of pain sensitivity but not for self-reported pain intensity.

Conclusion

This study, while presenting null findings, describes an initial step in determining whether AIH can be used to increase pain relief. Based on this pilot study we offer guidance for future research including study design, AIH dosage, participant selection, and using AIH in combination with non-pharmacologic treatments.

Serum Caffeine Concentration at the Time of Traumatic Brain Injury and Its Long-Term Clinical Outcomes

Caffeine is one of the most widely consumed psychoactive drugs in the general population. It has a neuroprotective effect in degenerative neurological disorders; however, the association between caffeine and traumatic brain injury (TBI) outcomes is contradictory. The objective of this study was to evaluate the association between serum caffeine concentration at the time of injury and long-term functional outcomes of patients with TBI visiting the emergency department (ED). This was a prospective multi-center cohort study including adult patients with intracranial injury confirmed by radiological examination, who visited five participating EDs within 72 h after TBI. The main exposure was the serum caffeine level within 4 h after injury, and the study outcome was a favorable functional recovery at 6 months after injury. Multi-variable logistic regression analysis adjusted for potential confounders was performed to calculate adjusted odds ratios (AORs) with 95% confidence intervals (CIs). Among the 334 study participants, caffeine was not detected in 102 patients (30.5 %). In patients with identifiable caffeine level, serum caffeine level was categorized into tercile groups; low (0.01-0.58 μg/mL), intermediate (0.59-1.66 μg/mL), and high (1.67-10.00 μg/mL). The proportions of patients with a 6-month favorable functional recovery were 56.9% in the no-caffeine group, 79.2% in the low-caffeine group, 75.3% in the intermediate-caffeine group, and 66.7% in the high-caffeine group (p = 0.006). In multi-variable logistic regression analysis, the low- and intermediate-caffeine groups were significantly associated with a higher probability of 6-month favorable functional recovery compared with the no-caffeine group [AORs (95% CI): 2.82 (1.32-6.02) and 2.18 (1.06-4.47], respectively. This study showed a significant association between a serum caffeine concentration of 0.01 to 1.66 μg/mL and good functional recovery at 6 months after injury compared with the no-caffeine group of patients with TBI with intracranial injury. These results suggest the possibility of using serum caffeine level as a potential biomarker for TBI outcome prediction and of using caffeine as a therapeutic agent in the clinical care of patients with TBI.