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

This study is not yet open for participant recruitment. (see Contacts and Locations)
Verified May 2013 by Brock University
Sponsor:
Information provided by (Responsible Party):
Stephen Cheung, Brock University
ClinicalTrials.gov Identifier:
NCT01848665
First received: May 3, 2013
Last updated: NA
Last verified: May 2013
History: No changes posted
  Purpose

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.


Condition Intervention Phase
Healthy Males
Neuromuscular Function
Drug: Indomethacin
Phase 4

Study Type: Interventional
Study Design: Allocation: Randomized
Intervention Model: Single Group Assignment
Masking: Single Blind (Subject)
Primary Purpose: Basic Science
Official Title: The Influence of Cerebral Blood Flow and PETCO2 on Neuromuscular Function During Passive Heat Stress

Resource links provided by NLM:


Further study details as provided by Brock University:

Primary Outcome Measures:
  • Resting motor threshold [ Time Frame: Change from baseline 90-minutes ] [ Designated as safety issue: No ]
    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 [ Time Frame: Change from baseline 90-minutes ] [ Designated as safety issue: No ]
    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.

  • Maximal Voluntary Contraction [ Time Frame: Change from baseline 90-minutes ] [ Designated as safety issue: No ]
    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 [ Time Frame: Change from baseline 90-minutes ] [ Designated as safety issue: No ]
    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 [ Time Frame: change from baseline 90-minutes ] [ Designated as safety issue: No ]
    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.


Secondary Outcome Measures:
  • Middle Cerebral Artery Blood Flow Velocity [ Time Frame: Change from baseline 90-minutes ] [ Designated as safety issue: No ]
    Middle cerebral artery (MCA) blood flow velocity will be measured non-invasively by a 2-MHz transcranial Doppler (TCD) ultrasound probe, attached bilaterally to a comfortable headband and secured anterior to the zygomatic arch, rostral of the pinna. Doppler probes will be paced over the temporal windows (near the ear) and will remain in place throughout the duration of the experimental protocol. MCA velocity will be quantified in cm/s.

  • Blood Pressure [ Time Frame: Change from baseline 90-minutes ] [ Designated as safety issue: No ]
    Beat by beat blood pressure will be calculated from the blood pressure waveform using finger photoplethysmography (Nexfin, bmeye), with a finger cuff placed directly over the middle finger on the left hand. Blood pressure will be quantified in mmHg.

  • Heart rate [ Time Frame: Change from baseline 90-minutes ] [ Designated as safety issue: No ]
    Heart rate will be measured by electrocardiogram. Heart rate will be quantified in beats per minute.

  • End-tidal Gas concentrations [ Time Frame: change from baseline 90-minutes ] [ Designated as safety issue: No ]
    The end-tidal concentrations of oxygen and carbon dioxide will be measured and reported in mmHg.

  • Rectal Temperature [ Time Frame: change from baseline 90-minutes ] [ Designated as safety issue: No ]
    Rectal temperature will be measured in degrees Celsius

  • Skin Temperature [ Time Frame: change from baseline 90-minutes ] [ Designated as safety issue: No ]
    skin temperature will be measured in degrees Celsius


Estimated Enrollment: 10
Study Start Date: May 2013
Estimated Primary Completion Date: August 2014 (Final data collection date for primary outcome measure)
Arms Assigned Interventions
Experimental: Drug Drug: Indomethacin

  Eligibility

Ages Eligible for Study:   18 Years to 45 Years
Genders Eligible for Study:   Male
Accepts Healthy Volunteers:   Yes
Criteria

Inclusion Criteria:

  • 18 to 45 yrs old; healthy males

Exclusion Criteria:

  • diagnosed medical condition; NSAID allergy; smoker; high altitude exposure; implants
  Contacts and Locations
Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study. To learn more about this study, you or your doctor may contact the study research staff using the Contacts provided below. For general information, see Learn About Clinical Studies.

Please refer to this study by its ClinicalTrials.gov identifier: NCT01848665

Contacts
Contact: Stephen Cheung, PhD 905 688-5550 ext 5662 scheung@brocku.ca

Locations
Canada, Ontario
Brock University Not yet recruiting
St Catharines, Ontario, Canada, L2S 3A1
Contact: Stephen Cheung, PhD    905 688-5550 ext 5662    scheung@brocku.ca   
Sponsors and Collaborators
Brock University
  More Information

No publications provided

Responsible Party: Stephen Cheung, Professor, Brock University
ClinicalTrials.gov Identifier: NCT01848665     History of Changes
Other Study ID Numbers: EEL 073.3
Study First Received: May 3, 2013
Last Updated: May 3, 2013
Health Authority: Canada: Health Canada

Additional relevant MeSH terms:
Heat Stress Disorders
Wounds and Injuries
Indomethacin
Gout Suppressants
Antirheumatic Agents
Therapeutic Uses
Pharmacologic Actions
Tocolytic Agents
Reproductive Control Agents
Physiological Effects of Drugs
Cyclooxygenase Inhibitors
Enzyme Inhibitors
Molecular Mechanisms of Pharmacological Action
Anti-Inflammatory Agents, Non-Steroidal
Analgesics, Non-Narcotic
Analgesics
Sensory System Agents
Peripheral Nervous System Agents
Anti-Inflammatory Agents
Cardiovascular Agents
Central Nervous System Agents

ClinicalTrials.gov processed this record on July 26, 2014