Breathing is a fundamental process of the body. Naturally, it is an involuntary function that is controlled by the autonomic nervous system. However, respiration itself is an active process since it requires the contraction of thoracic (chest) muscles such as the external intercostal muscles and the diaphragm (lower band-like muscle of the respiratory system). As multicellular organisms we have conscious control over our skeletal muscles, and thus we are able to exercise control of our own breathing regardless of the body’s involuntary capability to breathe on its own. The process of inhalation (taking in air) entails the contraction of the external intercostal muscles which increases the front-to-back width of the thoracic cavity (ribcage) and thereby induces a pressure drop in the lungs, allowing air and oxygen to flow in. Exhalation occurs as the external intercostal muscles and the diaphragm relax so that the thoracic cavity returns to its pre-inspiratory state. This way, the lungs experience a rise in pressure and in turn, carbon dioxide and air are forced outward.
Breathing is an autonomous function. We progress from breathing deeply as infants to more shallowly as we age and we attribute this to stress because stress hormones such as epinephrine and cortisol are known for increasing the rate of respiration. An infant breathes noticeably deeply in comparison to its mother and that is attributed to their differences in stress exposure. An extreme example of the body’s reaction to stress is how the autonomic sympathetic nervous system is likely to evaluate cliff diving as a high stress situation and increase heart rate and respiration accordingly. So as general stress, such as educational or career-related pressure, creates heavier burden on an individual, it would make sense for their breathing to be shallower. Infants do not experience the same stress and are able to continue breathing deeply. Shallow breathing poses the risk of inadequate carbon dioxide release from the body. If high concentrations of carbon dioxide remain in circulation, blood may become more acidic or the carbon dioxide may block oxygen from binding to hemoglobin and impair the gas exchange process to ultimately cause asphyxiation.