The respiratory system, in coordination with the cardiovascular system, makes it possible for your body to do work. While the heart is responsible for an increase in circulating blood, the lungs are responsible for the increased exchange of carbon dioxide for oxygen. Upon physical activity, there are certain changes that occur that involve the respiratory system.
Gas
To fully understand how the exchange of carbon dioxide and oxygen occurs, you must first understand the anatomy of the lungs and red blood cells. Carbon dioxide is the product of metabolism that occurs to produce energy. As the blood flows through the working muscles, it takes away the carbon dioxide and gives the muscle cells oxygen. Blood flow continues into the lungs, where the carbon dioxide is disposed of and the red blood cells pick up fresh oxygen.
Anatomy and Mechanics
The respiratory muscles make it possible to move air in and out. During rest the diaphragm and intercostal muscles slowly and passively move air in and out. However, during exercise, other muscles such as the sternocleidomastoid, scalenes and trapezius help to lift the ribs and clavicles to further increase space for air. These muscles are known as the accessory inspiratory muscles. In addition, exhaling becomes a forced movement during exercise. The intercostals pull the ribs down and in while the abdominal muscles increase pressure, forcing the diaphragm up.
Measuring Breath
Exercise dramatically increases the rate of ventilatory air flow through the lungs. Tidal volume and breathing frequency increase as a response to exercise in order to maintain gas exchange. Tidal volume is the amount of air that you can inhale and exhale per breath. Breathing frequency is the amount of breaths per minute. In a normal, healthy person tidal volume is 0.5 L, or liters, per breath at rest. However, during exercise this amount can increase eight times greater than rest and can reach a maximum of 4 L per breath. Breathing frequency is about 12 breaths per minute at rest. During exercise, this number can increase four times, to a maximum of around 48 breaths per minute.
Neural Regulation
The motor cortex of the brain signals the respiratory center to increase ventilation. This is why if you even anticipate exercise, your breathing may increase. Other mechanisms called chemoreceptors give feedback to the brain regarding blood pH and carbon dioxide and oxygen inside of the blood. The brain will change breathing rates based on this feedback. If pH or oxygen is below the set point or if carbon dioxide is above the set point, changes in breathing mechanics and blood flow will occur.
References
- "Anatomy and Physiology"; Kenneth S. Saladin; 2004
- "Exercise Physiology"; George A. Brooks, Thomas D. Fahey, Kenneth M. Baldwin; 2005
