Effects of acute hypoxia on postural and kinetic tremor

Investigating Sea-Level Brain Predictors for Acute Mountain Sickness: A Multimodal MRI Study before and after High-Altitude Exposure

BACKGROUND AND PURPOSE

Acute mountain sickness is a series of brain-centered symptoms that occur when rapidly ascending to high altitude. Predicting acute mountain sickness before high-altitude exposure is crucial for protecting susceptible individuals. The present study aimed to evaluate the feasibility of predicting acute mountain sickness after high-altitude exposure by using multimodal brain MR imaging features measured at sea level.

MATERIALS AND METHODS

We recruited 45 healthy sea-level residents who flew to the Qinghai-Tibet Plateau (3650 m). We conducted T1-weighted structural MR imaging, resting-state fMRI, and arterial spin-labeling perfusion MR imaging both at sea level and high altitude. Acute mountain sickness was diagnosed for 5 days using Lake Louise Scoring. Logistic regression with Least Absolute Shrinkage and Selection Operator logistic regression was performed for predicting acute mountain sickness using sea-level MR imaging features. We also validated the predictors by using MR images obtained at high altitude.

RESULTS

The incidence rate of acute mountain sickness was 80.0%. The model achieved an area under the receiver operating characteristic curve of 86.4% (sensitivity = 77.8%, specificity = 100.0%, and P < .001) in predicting acute mountain sickness At sea level, valid predictors included fractional amplitude of low-frequency fluctuations (fALFF) and degree centrality from resting-state fMRI, mainly distributed in the somatomotor network. We further learned that the acute mountain sickness group had lower levels of fALFF in the somatomotor network at high altitude, associated with smaller changes in CSF volume and higher Lake Louise Scoring, specifically relating to fatigue and clinical function.

CONCLUSIONS

Our study found that the somatomotor network function detected by sea-level resting-state fMRI was a crucial predictor for acute mountain sickness and further validated its pathophysiologic impact at high altitude. These findings show promise for pre-exposure prediction, particularly for individuals in need of rapid ascent, and they offer insight into the potential mechanism of acute mountain sickness.

Neuropsychological, Neurocognitive, Vestibular, and Neuroimaging Correlates of Exposure to Repetitive Low-Level Blast Waves: Evidence From Four Nonoverlapping Samples of Canadian Breachers

INTRODUCTION

We assessed the utility of a battery of neuropsychological, neurocognitive, physiological (balance, ataxia, postural tremor), and neuroimaging measures for studying the effects of blast waves in breachers-a population repeatedly exposed to low-level blast during military training and operations.

MATERIALS AND METHODS

Data were collected from four nonoverlapping samples, in the course of similarly structured 4-day breacher training exercises in successive years involving a combination of indoor and outdoor blast events. In all cases, self-report and neuropsychological measures were administered once at baseline (i.e., 1 day before the start of training). In years 1-2, neurocognitive and physiological measures were administered daily before and after training. In years 3-4, neurocognitive data were collected once at baseline. In Year 4, we introduced 3 modifications to our design. First, in addition to breachers, we also collected data from sex-and age-matched military controls at the same time points. Second, we assessed balance, ataxia, and postural tremor immediately following blast exposure "in the field," enabling us to quantify its acute effects. Third, structural magnetic resonance imaging (MRI) scans were acquired before and after the 4-day training exercise to explore differences between breachers and controls at baseline, as well as possible training-related changes using voxel-based morphometry. These design modifications were made to enable us to test additional hypotheses in the context of the same training exercise.

RESULTS

At baseline, scores on the "Rivermead Post Concussion Symptoms Questionnaire," "RAND SF-36" (physical functioning, role limitation due to physical health, social functioning, energy/fatigue, general health), and "Short Musculoskeletal Function Questionnaire" distinguished breachers from controls. Also at baseline, the MRI data revealed that there was greater regional gray matter volume in controls compared to breachers in the right superior frontal gyrus. Balance, ataxia, and postural tremor did not exhibit sensitivity to the acute effects of blast in the field, nor did neurocognitive measures to its cumulative or daily effects.

CONCLUSION

Our exploratory results suggest that self-report neuropsychological measures and structural MRI hold promise as sensitive measures for quantifying the long-term, cumulative effects of blast exposure in breachers. We discuss the limitations of our study and the need for prospective longitudinal data for drawing causal inferences regarding the impact of blast exposure on breachers' health and performance.

Intermittent Hypoxic Training at Lactate Threshold Intensity Improves Aiming Performance in Well-Trained Biathletes with Little Change of Cardiovascular Variables

The main objective of this research was to evaluate the efficacy of intermittent hypoxic training (IHT) on aiming performance and aerobic capacity in biathletes. Fourteen male biathletes were randomly divided into a hypoxia group (H) (n = 7), which trained three times per week in a normobaric hypoxic environment (FiO₂ = 16.5%, 2000 m a.s.l.) with lactate threshold intensity (LT) determined in hypoxia, and a control group (C) (n = 7), which exercised under normoxic conditions with LT intensity determined in normoxia. The training program included three weekly microcycles, followed by three days of recovery. The main part of the interval workout consisted of four 7 min (1^st week), 8 min (2^nd week), or 9 min (3^rd week) running bouts at treadmill separated by 2 minutes of active recovery. After the warm-up and during the rest between the bouts, the athletes performed aiming to the target in the standing position with a sporting rifle (20 s). The results showed that the IHT caused a significant (p < 0.05) increase in retention time in the target at rest (RT9_rest) by 14.4% in hypoxia, whereas RT postincremental test (RT9_post) increased by 27.4% in normoxia and 26.7% in hypoxia. No significant changes in this variable were found in group C. Additionally, the capillary oxygen saturation at the end of the maximal effort (SO_{2capillary max}) in hypoxia increased significantly (p < 0.001) by ∼4% after IHT. The maximal workload during the incremental test (WR_max) in normoxia also increased significantly (p < 0.001) by 6.3% after IHT. Furthermore, in absolute and relative values of VO_2max in normoxia, there was a propensity (p < 0.07) for increasing this value by 5% in group H. In conclusion, the main findings of this study showed a significant improvement in resting and postexercise aiming performance in normoxia and hypoxia. Furthermore, the results demonstrated beneficial effects of the IHT protocol on aerobic capacity of biathletes.

The effect of changes in joint angle on the characteristics of physiological tremor

INTRODUCTION

Physiological tremor, as a whole, can be influenced by changes in muscle activity. However, the origin of low-frequency physiological tremor oscillations has yet to be conclusively determined. It is possible that by experimentally manipulating muscular activity, a better determination of the origin of those low-frequency oscillations can be achieved. It was demonstrated that changes in joint angle modify characteristics of muscular activity. As such, we hypothesize that changes in wrist-joint angle will alter the characteristics of low-frequency physiological tremor oscillations.

OBJECTIVE

Assess the influence of changes in joint angle of the wrist on characteristics of physiological finger tremor.

METHODS

Physiological finger tremor was recorded (n = 25) using a laser displacement system while the arm and hand were supported. The relative angle between the dorsum of the hand and the forearm was altered between conditions (135°, 180°, 225° and 270°), while the hand and the finger remained parallel to the ground. EMG of the extensors and flexors were also recorded.

RESULTS

Tremor amplitude was significantly altered by changes in wrist-joint angle. This was especially the case for lower frequency oscillations. In addition, electromyography properties of forearm muscles were also significantly modified by changes in wrist-joint angles.

CONCLUSIONS

This study demonstrates that changes in wrist-joint angle modify the characteristics of physiological finger tremor. This should be taken into account when interpreting tremor data as well as when developing tools to minimize tremor.

Chin tremor in full-term neonate after hypoxia

CONTEXT

Newborns may present a range of motor phenomena that are not epileptic in nature. Chin tremor is an unusual movement disorder that typically starts in early childhood and may be precipitated by stress and emotion. Its pathophysiology has not been fully elucidated.

CASE REPORT

We describe a full-term newborn that, immediately after neonatal anoxia, presented body and chin tremors that were unresponsive to anti-epileptic drugs. Subsequent neurological evaluation revealed signs of pyramidal tract damage and chin tremor triggered by percussion and crying. We discuss the hypothesis that the anatomopathological abnormality may lie at the level of the higher cortical centers or midbrain.

CONCLUSIONS

Further studies are needed in order to gain greater comprehension of neonatal tremors. Recognition of the various etiological possibilities and consequent management of treatable causes is essential for care optimization.