Response of the Respiratory System During Exercise

The primary purpose of the respiratory system is to provide the human body with an exchange of gases from the outside environment to its internal environment. Simply put, the respiratory system removes carbon dioxide from the blood stream and replaces oxygen. The two main gases in the respiratory process, oxygen and carbon dioxide, are exchanged by ventilation and diffusion.2

Pulmonary ventilation is the mechanical movement of air in and out of the lungs due to different atmospheric pressures inside the lungs and the external environment. Diffusion, the movement of molecules from an area of high concentration to an area of low concentration, is what moves the oxygen and carbon dioxide in and out of the bloodstream. Oxygen moves from the lungs to the blood due to the tension being greater in the lungs than the blood. Likewise, carbon dioxide moves from the blood into the lungs due to the tension of carbon dioxide being greater than the tension in blood. This relationship during respiration determines the respiratory exchange ratio (RER). This ratio is the volume of carbon dioxide output (VCO2) and the volume of oxygen consumed (VO2). At rest RER is about 0.8. The closer to 1.0 or higher it gets; the more carbon dioxide is produced. This all, of course, changes with exercise.2

With the initiation of moderate or intense exercise comes an increase in ventilation. VO2 increases exponentially, and then to a steady-state level when exercise is performed at a given work rate. Exercise over a high intensity (>75% VO2) for a long period of time results in an upward drift in oxygen consumption over time and does not reach a steady state. Such instances would be observed in a VO2max test.2

Muscular exercise causes an increase in pulmonary ventilation and also a disturbance in the respiratory exchange ratio. The amount of carbon dioxide molecules being produced increases when an individual participates in a moderate or high intensity workout and increases the RER.1 VO2 characteristics differ at different exercise intensities. Several factors can affect VO2 kinetic responses, such as: age, training level, and pathological conditions.1 Which of course will be discussed in future blogs.

1Bassett, D. R., Howley, E. T. Limiting factors for maximum oxygen uptake and determinants of endurance performance. Med Sci Sports Exercise. 2000; 32(1): 70-84

2Powers, S.K. and Howley, E. T. Exercise Physiology. Theory and Application to Fitness and Performance. 2015; (9): 71-77, 216-239.

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