Breathing is controlled through the respiratory centre which is formed by a group of nerves in the medulla. Rate and depth of breathing is manged autonomically in this respiratory rhythmicity centre to ensure adequate supply of Oxygen and removal of Carbon Dioxide as per the body’s needs. Chemoreceptors within the body respond to changes in the partial pressure of Oxygen (PO2), Carbon Dioxide (PCO2), and blood acidity. If there are slight changes in the partial pressures or acidity levels, this informs the respiratory centre, and signals are sent to alter the respiratory rate. For example, if CO2 and acidity is rising, chemoreceptors will detect this, sending a signal for an increased respiratory rate. The increased respiratory rate allows for more oxygen supply and removal of carbon dioxide, allowing the balance of partial pressures and acidity to return to normal.  

An individual can override the autonomic process with voluntary controlled respirations for completing activities such as talking, singing, shouting, and so on.

Breathing Mechanics 

Inspiration occurs through the Diaphragm and External Intercostal muscles contracting. This increases the space within the lungs, decreasing atmospheric pressure. Air flows into the lungs as the atmospheric pressure tries to normalise within the larger space, bringing in Oxygen. On expiration, the Diaphragm and Intercostal muscles relax, causing the lungs to recoil. This increases atmospheric pressure within the lungs, forcing air out. On normal inspiration around 500 ml of air passes in and out of the lungs. This is known as Tidal Volume (TV).  

Gaseous exchange occurs within the Alveoli, where capillaries surround the Alveolar structures, allowing the transfer of Oxygen and Carbon dioxide.

Through this finely balanced process of respiratory control within the Medulla involving Chemoreceptors measuring blood acidity and PO2/PCO2, and the response of increased respirations through contraction and relaxation of the Diaphragm and Intercostal muscles, homeostasis can be maintained and the body’s requirements met.

Assessing breathing is an important aspect to identify any deficits that may be present, or any worsening symptoms. An initial review of rate, depth, and effectiveness will give you an idea of any potential pathophysiology happening. The clinician can question; is the rate within normal parameters? Is it elevated or decreased indicating an imbalance of PO2/PCO2 or acidity? Is it regular or irregular indicating potential issues with the Medulla respiratory centre? Is the depth adequately perfusing the patient? Are there shallow breaths indicating poor air entry or are they deep and irregular suggesting possible neurological issues? Is the patients’ breathing effective and is there evidence of cyanosis, excessive intercostal, diaphragm, and/or abdominal use to get air in? Are they having use a tripod position to help maintain air entry? Is their Oxygen Saturation (SPO2) maintaining between a healthy normal range, 94-98%, or 88-92% in COPD. All of these questions can help the clinician build an idea if there are potential pathophysiological issues with a patients’ breathing.