1. Physiological Response to Exercise with Naturally-Occurring
Carbon Dioxide Exposure
Megan Johnson, Robert Shute, Dustin Slivka
University of Nebraska at Omaha, School of Health and Kinesiology, Omaha, NE
Exercise Physiology Lab
AIMS
METHODS
ABSTRACT
Aim: To determine the impact of exposure to naturally-elevated carbon dioxide levels on the physiological response to exercise.
In the control trials, carbon dioxide in the chamber will be monitored and maintained at 300 ppm using the CO2 scrubber.
In the experimental trials, CO2 levels will be allowed to rise naturally with expiration from the subjects and the lab technicians present, with monitoring and recording using the CO2 meter.
The chamber will be held constant for temperature (20ºC), relative humidity (60%), and oxygen (20.9%) levels.
Throughout each 60-minute exercise trial and 30-minute recovery, the following will be monitored for each subject: heart rate, end-tidal CO2, respiration rate, pulse oximetry, blood pressure, cardiac output, tissue oxygenation, and rating of perceived exertion
Differences in physiological data will be analyzed via repeated measures two-way ANOVA (time x trial).
BACKGROUND: Carbon dioxide (CO2) plays a normal part in gas exchange and acid-base equilibrium in the human body. With added stress or exposure, CO2 levels can accumulate in the blood and tissues, causing hypercapnia. Research has shown that exposure to CO2 at 40,000 ppm will cause cardio-respiratory burden, both at rest and during exercise. Lower levels may still cause changes under conditions of added stress, but this has not been elucidated. Preliminary data from our laboratory chamber suggests physiological changes at levels of CO2 reaching 8,000 ppm during experiments with exercising subjects. Without a CO2 scrubber, the heavy breathing from exercising subjects will build up CO2 in the chamber. PURPOSE: The purpose of this study is to explore whether exposure to incremental carbon dioxide levels of up to 20,000 ppm in the environmental chamber result in different physiological responses to exercise and recovery when compared to controlled CO2 levels resembling normal air at 300 ppm. METHODS: Subjects will perform two randomized cycling trials for 1 hour at 65% of the power output associated with their VO2peak. Trials will follow up with resting recovery for 30 minutes in the same condition. One trial will be in naturally-elevated (up to 20,000 ppm) CO2 and one in normal (300 – 400 ppm) CO2. Cardiovascular and respiratory measures will be taken throughout both trials to determine the physiological response to elevated CO2 during vigorous exercise.
Figure 1. (left) Cycling in environmental chamber
Figure 2. (right) Oxymon near-infrared spectrometer on vastus lateralis
METHODS
Eighteen recreationally active subjects between the ages of 19 and 35 will complete three visits to the Exercise Physiology Laboratory (1 descriptive and 2 experimental trials).
During the initial visit, body composition will be determined through hydrodensitometry. Subjects will also perform a graded exercise test until volitional exhaustion on an electronically braked cycle ergometer and expired gases will be measured using a metabolic cart to evaluate VO2peak.
Experimental trials will consist of exercise and recovery periods in the environmental chamber. They will be performed in a blinded, randomized, counterbalanced order using the following conditions: Normal/control CO2 (300 ppm) and Elevated CO2 (2,000 – 20,000 ppm).
For both control and experimental trials, participants will cycle at for 60 minutes on the cycle ergometer. Exercise intensity will be set to 65% of the power output associated with their VO2peak.
INTRODUCTION
Without use of a CO2 scrubber, the environmental chamber will accumulate excess CO2 which may affect the physiology of exercising subjects.
Normal CO2 in the environment is usually around 300 ppm.
Elevated CO2 exposure, depending on volume and time, can cause physiological changes, including increased respiration rate and heart rate. Significant physiological effects of CO2 occur during exercise at approximately 4,000 ppm.
In previous studies in the chamber, physiological response varied from in vivo high altitude experiments. This could be due to hypercapnia.
More research is needed to understand cardio-respiratory changes during high intensity exercise in a chamber with rising CO2 levels.
Figure 3. Carbon dioxide scrubber Figure 4. Environmental chamber.
IMPLICATIONS
Chamber studies control variables for environmental conditions such as hypoxia and high altitude; these require management of confounding variables like hypercapnia.
The results of this study will clarify implications of CO2 buildup in the environmental chamber, which will allow interpretation of physiological data obtained from experimentation.
This work will be supported by a UNO Graduate Research and Creative Activity (GRACA) grant and the Great Plains IDeA-CTR grant U545GM