The Influence of Cerebral Blood Flow and PETCO2 on Neuromuscular Function During Passive Heat Stress

NCT01848665 | Completed Phase 4

• 1 other identifier: EEL 073.3
• Study Type: interventional
• Target: 8
• Locations: 1 country
• Sites: 1

Brief Summary

Increased core temperature (hyperthermia) has been associated with impaired neuromuscular performance; however, the mechanisms associated with these performance decrements and their potential synergies 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 alkalosis (estimated by end-tidal partial pressure of carbon dioxide; PETCO2) remains unexamined. In response to hyperthermia, humans hyperventilate as means of heat dissipation, resulting in a hypocapnia (reduced PETCO2) mediated decrease in CBF and consequently, cerebral alkalosis (increased cerebral pH). 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 decreased PETCO2 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 passive heat stress. The research project will consist of 3 separate experimental trials: (a) poikilocapnic hyperthermia (increased core temperature; decrease CBF; decrease PETCO2), (b) isocapnic hyperthermia (increased core temperature; no change CBF; no change PETCO2) and (c) isocapnic hyperthermia + indomethacin (increased core temperature; decrease CBF; no change PETCO2). During each manipulation, neuromuscular function will be evaluated and compared to baseline (normothermic) conditions using a repeated measures design. It is hypothesized that changes in PETCO2 and therefore, changes in cerebral alkalosis will contribute to neuromuscular fatigue independent of changes in CBF or increases in core temperature.

Conditions

Healthy Males; Neuromuscular Function

Outcome Measures

Primary Outcomes (5)

• Resting motor threshold

  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.

  Change from baseline 90-minutes

• H-Reflex Amplitude

  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 millivolts.

  Change from baseline 90-minutes

• Maximal Voluntary Contraction

  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.

  Change from baseline 90-minutes

• H-Reflex latency

  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.

  Change from baseline 90-minutes

• Voluntary Activation

  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.

  change from baseline 90-minutes

Secondary Outcomes (6)

• Middle Cerebral Artery Blood Flow Velocity

  Change from baseline 90-minutes

• Blood Pressure

  Change from baseline 90-minutes

• Heart rate

  Change from baseline 90-minutes

• End-tidal Gas concentrations

  change from baseline 90-minutes

• Rectal Temperature

  change from baseline 90-minutes

Study Arms (2)

Drug

EXPERIMENTAL

Indomethacin, 1.2 mg kg 1 dose

Drug: Indomethacin

Placebo

PLACEBO COMPARATOR

generic flour placebo capsule

Drug: Placebo

Interventions

Indomethacin DRUG

Drug

Placebo DRUG

Placebo

Eligibility Criteria

• Age: 18 Years - 45 Years
• Sex: male
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• to 45 yrs old; healthy males

You may not qualify if:

• diagnosed medical condition; NSAID allergy; smoker; high altitude exposure; implants

Sponsors & Collaborators

• Brock University: lead

Study Sites (1)

Brock University

St. Catharines, Ontario, L2S 3A1, Canada

Location

MeSH Terms

Interventions

Indomethacin

Intervention Hierarchy (Ancestors)

Indoles; Heterocyclic Compounds, 2-Ring; Heterocyclic Compounds, Fused-Ring; Heterocyclic Compounds

Study Design

• Study Type: interventional
• Phase: phase 4
• Allocation: RANDOMIZED
• Masking: SINGLE
• Who Masked: PARTICIPANT
• Purpose: BASIC SCIENCE
• Intervention Model: SINGLE GROUP
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Professor

Study Record Dates

• First Submitted: May 3, 2013
• First Posted: May 7, 2013
• Study Start: May 1, 2013
• Primary Completion: June 1, 2015
• Study Completion: December 1, 2016
• Last Updated: January 29, 2018

Record last verified: 2018-01

Locations

CA (1)