Your body is an incredibly dynamic, adaptive system that rapidly responds to changes in its internal environment. The respiratory system demonstrates this concept elegantly in its seamless, autonomous response to increased physical activity during exercise. To maintain blood gas and acid levels, the pulmonary system increases ventilation and blood perfusion to match rates of metabolism in exercising skeletal muscle.
Arterial Blood Gas
Skeletal muscles increase their strength and rate of contraction during exercise. During vigorous exercise, these muscles consume greater levels of oxygen. This change might shift the cells into anaerobic metabolism, which increases the production of lactic acid. Initially, this leads to an increase in blood carbon dioxide levels, as the secreted acid is converted into this gaseous waste product. Despite these changes, arterial blood gas levels remain relatively constant during exercise, thanks to the initial adaptations in pulmonary ventilation.
During the initial stages of exercise, lung ventilation increases dramatically. According to the 2004 article “Physiological Effects of Exercise," this rapid rise in ventilation can be attributed to neural signals sent from your limbs, joints and muscles. As the stretch receptors in these peripheral tissues detect changes in skeletal muscle activity, electrical impulses are generated and travel to the motor center of the brain, thus stimulating increases in lung volume and rate of respiration.
To exchange gas effectively in this situation, the perfusion of blood to the lungs must increase in proportion to ventilation. During exercise, increases in cardiac output lead to more lung capillaries receiving blood, thus enabling them to participate in gas exchange. Furthermore, the pulmonary arteries, which direct blood from the heart into the lungs, will dilate to facilitate these increases in blood flow. The end result is higher rates of blood perfusion throughout the lungs, allowing your body to maximize oxygen absorption and carbon dioxide removal.
Staying in Balance
The physiological adaptations occurring in your lungs during exercise enable your body to perform at maximum capacity. All the changes that are occurring are designed to maintain homeostasis, or a chemical balance, throughout the body. Without such a responsive pulmonary system, your blood would exhibit dramatic swings in pH and blood gas levels, both of which are not conducive to a healthy exercise experience. These initial responses highlight the importance of warming up before an intense workout; this will prime your cardiopulmonary system to support your muscles throughout your exercise routine.
- "Continuing Education in Anaesthesia, Critical Care and Pain: Physiological Effects of Exercise"; Deborah Burton et al; 2004
- “Physiology (fourth edition)”; Linda Costanzo; 2007
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