Influence of Graded Hypercapnia on Endurance Exercise Performance

The aim of this randomized, single-blind, placebo-controlled crossover trial is to determine the effects of graded hypercapnia (0, 2, and 4% inspired CO2) on endurance performance. Twelve healthy and fit young adults (men and women) will complete this study. Participants will perform experimental trials on 3 separate days (one each breathing 0%, 2%, and 4% inspired CO2-all with normal 21% oxygen). During each trial, they will perform 10 minutes of submaximal treadmill walking exercise and then complete a self-paced 2-mile treadmill run time-trial.

Study Overview

• Status: Completed
• Conditions: Hypercapnia
• Intervention / Treatment: Other: Inspired gas

Detailed Description

Participants will undergo baseline measurements of pulmonary function and maximal oxygen uptake (VO2max). They will then complete two familiarization trials, with 10 minutes of submaximal exercise (~40%VO2max) followed by a self-paced 2-mile treadmill time trial. Lastly, they will complete three experimental trials, repeating the same submaximal and time-trial exercise procedures while breathing the test gas (0%, 2%, or 4% CO2-all with normal 21% oxygen). During the experimental trials, arterialized capillary blood samples will be collected at rest breathing room air, at rest breathing the test gas, and during submaximal exercise at 40% VO2max breathing the test gas. The primary outcome is 2-mile treadmill time-trial performance. Secondary outcomes include ventilation, metabolic rate, heart rate, arterialized capillary pH/PCO2/HCO3, perceived exertion, dyspnea, leg discomfort, breathing descriptors, and headache ratings.

• Study Type: Interventional
• Enrollment (Actual): 15
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Massachusetts
    • Natick, Massachusetts, United States, 01760
      • USARIEM

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 16 years to 43 years (Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

Description

Inclusion Criteria:

• Male or female, age 18-45
• In good health as determined by medical screening
• Passed his/her most recent Army Combat Fitness Test (ACFT) (Military Volunteers Only) or performs aerobic exercise at least 2 times per week and able to complete two mile run in ≤ 21 minutes (Civilian Volunteers)
• Willing to not participate in any exercise or drink alcoholic beverages for 24 hours before each study visit.
• Willing to not take part in any strenuous exercise in the 36 hours before each visit.
• Willing not to drink caffeine or eat food until after testing on familiarization and performance testing visits (visits 2-6).
• Willing to maintain a similar dietary pattern in the 2 days before each familiarization and performance visits.
• Have supervisor approval if permanent party military or a federal employee at U.S. Army Natick Soldier System Center
• Able to speak and read English fluently

Exclusion Criteria:

• Females who are pregnant or planning to become pregnant during the study
• Taking dietary supplements, prescriptions, or over the counter medication, other than a contraceptive (unless approved by medical staff & PI)
• Musculoskeletal injuries that compromise ability to run on a treadmill
• Abnormal blood count, presence of abnormal blood chemicals (hemoglobin S or sickle cell traits)
• Smokers or tobacco/nicotine users (unless have quit > 1 month prior)
• Any history of asthma
• Current or recent respiratory tract or sinus infections (< 1 month prior)
• Allergy to skin adhesive
• Any history of migraine or recurrent headaches
• Any history of panic disorder
• Blood donation in the previous 8 weeks
• Positive Covid-19 test within the last month

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Single

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: 4% CO2; Inspired gas containing 4% CO2, 21% O2, balance N2	Other: Inspired gas; Inspired gas content
Experimental: 2% CO2; Inspired gas containing 2% CO2, 21% O2, balance N2	Other: Inspired gas; Inspired gas content
Sham Comparator: 0% CO2; Inspired gas containing 0% CO2, 21% O2, balance N2	Other: Inspired gas; Inspired gas content

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
2 mile self-paced treadmill time trial performance	Time to complete self-paced 2 mile treadmill time trial (min:sec)	30 minutes

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Ventilation rate	Ventilation rate will be assessed using a pneumotachometer [L/min]	30 minutes
Oxygen consumption	Oxygen consumption will be assessed using computerized indirect calorimetry [ml/kg/min]	30 minutes
Heart rate	Heart rate will be assessed using telemetry [beats per min]	30 minutes
Arterialized capillary pH	Arterialized capillary pH will be assessed using a blood gas analyzer [Unitless]	30 minutes
Arterialized capillary pCO2	Arterialized capillary pCO2 will be assessed using a blood gas analyzer [mmHg]	30 minutes
Arterialized capillary HCO3	Arterialized capillary HCO3 will be assessed using a blood gas analyzer [mEq/L]	30 minutes
Rating of perceived exertion	Rating of perceived exertion will be assessed using Borg's 6-20 scale [AU]	30 minutes
Dyspnea	Rating of perceived dyspnea will be assessed using Borg's 0-10 scale [AU]	30 minutes
Leg discomfort	Rating of perceived leg discomfort will be assessed using Borg's 0-10 scale [AU]	30 minutes
Headache	Headache will be assessed using a visual analog scale [AU]	30 minutes
Breathing descriptors	Breathing descriptors will be assessed by having participants check statements that apply to their breathing (e.g., breathing out requires more effort) [unitless]	30 minutes

Collaborators and Investigators

• Sponsor: United States Army Research Institute of Environmental Medicine
• Investigators: Principal Investigator: Benjamin J Ryan, Ph.D., United States Army Research Institute of Environmental Medicine

Study record dates

Study Major Dates

• Study Start (Actual): September 10, 2021
• Primary Completion (Actual): April 14, 2022
• Study Completion (Actual): April 14, 2022

Study Registration Dates

• First Submitted: October 13, 2021
• First Submitted That Met QC Criteria: October 30, 2021
• First Posted (Actual): November 11, 2021

Study Record Updates

• Last Update Posted (Actual): May 31, 2022
• Last Update Submitted That Met QC Criteria: May 24, 2022
• Last Verified: May 1, 2022

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Signs and Symptoms, Respiratory; Hypercapnia
• Other Study ID Numbers: USARIEM

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: No

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No