The Influence of Cerebral Blood Flow and Alkalosis on Neuromuscular Function During Environmental Stress
试验速览
- 阶段
- 4 期
- 状态
- 已完成
- 入组人数
- 8
- 试验地点
- 1
- 主要终点
- Resting motor threshold
研究概览
简要总结
Environmental stress, such as low oxygen availability (hypoxia), has been associated with impaired neuromuscular performance; however, the mechanisms associated with these performance decrements remain unclear. While the majority of research suggests that the observed fatigue is related to the central nervous system, the influence of changes in cerebral blood flow (CBF) and associated changes in cerebral pH (partial pressure of carbon dioxide; PCO2) remains unexamined. In response to hypoxic stress, humans hyperventilate to maintain oxygen consumption, resulting in a hypocapnia mediated decrease in CBF and cerebral alkalosis (decreased PCO2). Previous research suggests that hyperventilation induces changes in neural excitability and synaptic transmission; however, it remains unclear if these changes are related to hypocapnia mediated decrease in CBF or cerebral alkalosis or both.
The purpose of the proposed research program is to examine the influence of changes in CBF and cerebral alkalosis on neuromuscular function during environmental stress. The research program will consist of 2 separate projects, summarized below in a table outlining the proposed protocols and resultant physiological manipulations. During each manipulation, neuromuscular function will be evaluated and compared to baseline (normoxic) conditions using a repeated measures design.
The research program will consist of 2 separate projects. Project 1 will examine the changes in CBF and alkalosis by using (a) indomethacin (decrease CBF; no change PCO2) and (b) hypocapnia (decrease CBF; decrease PCO2). Using a similar experimental design, Project 2 will examine the change in CBF and alkalosis during hypoxia by using (a) poikilocapnic hypoxia (decrease PO2; decrease CBF; decrease PCO2), (b) isocapnic hypoxia (decrease PO2; no change CBF; no change PCO2) and (c) isocapnic hypoxia + indomethacin (decrease PO2; decrease CBF; no change PCO2). During each manipulation, neuromuscular function will be evaluated and compared to baseline (normoxic) conditions using a repeated measures design.
Therefore, Project 1 will examine the separate and combined effect of changes in CBF and cerebral alkalosis on neuromuscular function independent of environmental manipulations. Subsequently, Project 2 will examine neuromuscular function during hypoxia while controlling CBF and cerebral alkalosis. It is hypothesized that changes in PCO2 and therefore, changes in cerebral alkalosis will contribute to neuromuscular fatigue independent of changes in CBF and oxygen availability.
研究设计
- 研究类型
- Interventional
- 分配方式
- Randomized
- 干预模型
- Single Group
- 主要目的
- Basic Science
- 盲法
- Single (Participant)
入排标准
- 年龄范围
- 18 Years 至 25 Years（Adult）
- 性别
- Male
- 接受健康志愿者
- 是
入选标准
- •18 to 25 yrs old; healthy males
排除标准
- •diagnosed medical condition; NSAID allergy; smoker; high altitude exposure; implants
研究组 & 干预措施
Drug
Indomethacin 1.2 mg kg 1 dose
干预措施: Indomethacin (Drug)
Placebo
flour capsule
干预措施: Placebo (Drug)
结局指标
主要结局
Resting motor threshold
时间窗: Change from baseline 90-minutes
Motor evoked potentials are recorded from muscles following transcranial magnetic stimulation of motor cortex. The resting motor threshold is defined as the minimum stimulation intensity required to elicit a motor evoked potential. Resting motor threshold will be quantified in millivolts.
H-Reflex Amplitude
时间窗: Change from baseline 90-minutes
The H-Reflex is an indirect measure of motor neuron excitability. Initially, a maximal M-wave (M-max) will be elicited by stimulating (1 ms in duration; 15 s between stimuli) the median nerve incrementally (2 V increments) until the largest waveform is observed. The peak-to-peak amplitude of this waveform is considered M-max. Using similar procedures as above, a sub-maximal M-wave of 5% M-max will be elicited and the amplitude of the resultant H-reflex (a small waveform observed following the submaximal M-wave) will be calculated. The amplitude of the H-reflex will be quantified in milllivolts.
Maximal Voluntary Contraction
时间窗: Change from baseline 90-minutes
During maximal voluntary contraction (MVC) testing, the participants' right arm will be secured in a custom made device used to isolate forearm flexion and to measure force production by the flexor carpi radialis muscle. Participants will be asked to produce a 5-second MVC and will be verbally encouraged to maintain maximal force production throughout the duration of the contraction. MVC will be quantified as the maximum force production in newton meters.
H-reflex latency
时间窗: Change from baseline 90-minutes
The H-Reflex is an indirect measure of motor neuron excitability. Initially, a maximal M-wave (M-max) will be elicited by stimulating (1 ms in duration; 15 s between stimuli) the median nerve incrementally (2 V increments) until the largest waveform is observed. The peak-to-peak amplitude of this waveform is considered M-max. Using similar procedures as above, a sub-maximal M-wave of 5% M-max will be elicited and the amplitude of the resultant H-reflex (a small waveform observed following the submaximal M-wave) will be calculated. The onset latency of the H-reflex will be quantified in milliseconds.
Voluntary Activation
时间窗: Change from baseline 90-minutes
The level of neural drive to muscle during contraction is termed voluntary activation and will be estimated by interpolation of a single supramaximal motor evoked potential during the 5-second MVC contraction. If extra force is evoked by the 'superimposed' stimulus then either the stimulated axons were not all recruited voluntarily or they were discharging at sub-tetanic rates. Therefore, voluntary activation will be quantified as the amplitude of maximal voluntary force production, relative to the amplitude of the supramaximal MEP.
次要结局
- Middle Cerebral Artery Blood Flow Velocity(Change from baseline 90-minutes)
- Brachial Artery Blood flow(Change from baseline 90-minutes)
- Internal Carotid Artery Blood Flow(Change from baseline 90-minutes)
- Blood pressure(Change from baseline 90-minutes)
- Pulse oximetry(Change from baseline 90-minutes)
- Heart Rate(Change from baseline 90-minutes)
- End-Tidal Gas Concentrations(Change from baseline 90-minutes)