Respiratory Rate in Response to Exercise
Respiratory Rate in Response to Exercise
Upon initiation of exercise, we all experience an increase in our breathing rate. There are several factors that influence this breathing rate and how fast it occurs. The respiratory system consists of Lungs, and the air passage ways which lead air to the lungs. Furthermore, the lungs have within them gas exchanging compartments called alveoli. Its here at the alveoli that the vital exchange of oxygen and carbon dioxide takes place.
Normal respiration rate, which we would all experience throughout the day is a passive process controlled by the respiratory control center within the Medulla Oblongata of the brain. This normal respiration rate remains constant most the day, but with the initiation of exercise there is a dramatic change in the respiratory rate. Although normal respiration rate is controlled by the respiratory control center, there are several other factors which take action during exercise.
As you can see from the graph, there is an initial increase in minute ventilation before the exercise begins. This small increase in minute ventilation is a response to the mere thought of beginning exercise. The thought of beginning exercise sends signals from higher brain centers to the respiratory control center to increase minute ventilation even before exercise begins. This can be seen as the body’s way of getting primed to begin exercise.
After the initiation of exercise, we can see from the graph that there is a quick jump in minute ventilation. Why does minute ventilation rise so quickly, when the carbon dioxide levels in the blood are still fairly normal? This spike in minute ventilation come from signals sent from mechanoreceptors in the skeletal muscle to the respiratory control center in the brain. These mechanoreceptors detect contraction and force application of skeletal muscle. So this signalling from the mechanoreceptors in the skeletal muscle are responsible for the quick jump in minute ventilation at the onset of exercise.
As exercise continues on, other factors begin to influence our minute ventilation. Chemoreceptors, which may detect changes in temperature or concentrations of carbon dioxide and hydrogen ions sends signals to our respiratory control center to increase minute ventilation. As exercise continues, we being to see larger quantities of carbon dioxide in the blood as a bi-product of metabolism. Chemoreceptors near the heart and within the skeletal muscle detect this increase in carbon dioxide and in response increase minute ventilation beyond that of the normal respiratory rate.
After cessation of exercise, minute ventilation does not just return to the normal respiratory rate. Within the blood there remains large quantities of carbon dioxide and hydrogen ions which need to be dealt with. So as you can see from the graph, minute ventilation tapers down back to the normal respiratory rate so as to eliminate the excess carbon dioxide in the blood through respiration. The amount of time this takes depends on the individual and the quantity of carbon dioxide within the blood.
Muscles Involved in Respiration
There are several muscles involved in the process of breathing. At normal respirations rates, breathing is passive; does not require thinking on our part to perform. The diaphragm is the primary muscle involved in respiration; this muscle contracts downwards into the abdomen and protrudes the abdomen outwards slightly under maximal inspiration. Also assisting in inspiration are the intercostal muscles between our ribs which contract and expand during breathing, muscles of the neck which pull up on the clavical and rib cage allowing the thoracic cavity to expand and allow maximum inspiration. The purpose of all muscles involved in inspiration is to expand the thoracic cavity as much as possible during maximum inspiration.
The only muscles which assist in expiration are the muscles of the abdomen. Including, the inner and outer abdominals as well as the external and internal oblique muscles which contract the abdomen and force the lungs to expire air. If you expire as hard as you can you will feel your abdomen contract.