A simple method to clamp end-tidal carbon dioxide during rest and exercise

Area of Science:

• Exercise Physiology
• Respiratory Regulation
• Biomedical Engineering

Background:

• Carbon dioxide (CO2) is a key regulator of ventilation and cerebral blood flow during physical activity.
• Existing breathing systems face challenges in maintaining stable end-tidal gas concentrations, particularly end-tidal carbon dioxide (PET CO2), during high-intensity exercise.
• Accurate control of PET CO2 is crucial for understanding physiological responses during exercise.

Purpose of the Study:

• To design and validate a simple, inexpensive breathing system for precise control of PET CO2 during exercise.
• To assess the system's efficacy in clamping PET CO2 at a target level across a range of exercise intensities, from rest to maximal work capacity (W(max)).

Main Methods:

• A novel breathing system was developed, utilizing an investigator-controlled titration of a CO2/O2 gas mixture into an open-ended inspiratory reservoir.
• System efficacy was tested on nine fit male subjects performing maximal incremental exercise tests on a cycle ergometer.
• Subjects underwent two trials: a control trial with naturally varying PET CO2 and an experimental trial aiming to clamp PET CO2 at 50 mmHg.

Main Results:

• The developed breathing system successfully maintained PET CO2 at a clamped level of 51 ± 2 mmHg throughout the exercise protocol (rest, W(max)).
• This stable PET CO2 was achieved despite significant, exercise-induced fluctuations in ventilation (ranging from 27-185 L min(-1)) and CO2 production (ranging from 0.3-5.5 L min(-1)).

Conclusions:

• The developed breathing system offers a simple, cost-effective solution for controlling PET CO2 during exercise.
• This system enables accurate manipulation and maintenance of PET CO2, facilitating research into exercise physiology and respiratory control.