Breathing is a vital function that is controlled by the rhythmic firing of neurons in a few specific brain regions deep in the brainstem. These brain regions in the medulla also receive signals from a complex network of sensors for blood oxygen, carbon dioxide and acidity, as well as from other higher level brain regions, to ultimately control the signaling sent to the diaphragm and external intercostal muscles involved in expansion (inspiration; inhalation) and contraction (expiration; exhalation) of the lungs.
As discussed in this section, several types of breathing disorders result from changes in neuronal signaling to the muscles that control the patency of the upper airway (size of the airway opening) in the throat. During sleep, breathing disorders often occur because certain muscles, especially those controlling the upper airway, have less muscle tone and are weaker during sleep, causing the airway to partially (snoring) or completely collapse, resulting in obstructive sleep apnea.
However, sleep apnea can also be due to loss or reduction of neural signaling to the lungs (called central sleep apnea or CSA), and can be quite prevalent in certain diseases. For example, individuals with congestive heart failure have a high prevalence of CSA and those individuals have a poorer disease prognosis compared to heart failure patients without sleep apnea. Other, less prevalent breathing disorders are due to genetic mutations that affect the respiratory rhythm generating neuronal groups (RETT syndrome, congenital central hypoventilation syndrome), or are due to degeneration of these neurons during age-related diseases, as seen in some patients with Parkinson’s disease or Multiple System Atrophy.
Various drugs, such as opiate painkillers or anesthetics, can negatively affect the neuronal signaling that controls breathing, resulting in drug-induced respiratory depression.
Sleep apnea and respiratory depression, as well as the other less prevalent breathing disorders, are significant unmet clinical indications that would benefit from safe, effective medications which served to normalize breathing in affected patients.