FIG. 4:  Opioids have many effects on the respiratory system.  They can inhibit receptors in nerve centers that are centrally or peripherally located.  These include networks that are responsible for generating inspiration and respiratory responses to oxygen (O₂) or carbon dioxide (CO₂), and overall this can lead to a decrease in the respiratory drive and hypoventilation.  In addition, opioids affect the neuromuscular activity that is responsible for upper airway patency, and this can lead to upper airway collapse, particularly in individuals who are vulnerable.  Opioids may also affect the arousal threshold to respiratory challenges, such as hypoxemia or hypercapnia and inspiratory load. 

Altogether, opioids have the potential to affect all aspects of respiration, including the respiratory rate, tidal volume, breathing pattern, upper airway resistance, and as a result, opioids are associated with an array of manifestations of sleep-disordered breathing (SDB).  For example, the SDB associated with opioid use may manifest as obstructive apneas, central apneas, hypoventilation and hypoxemia, ataxic or irregular breathing, or any combination of these.