During  a PSG (polysomnography) (a sleep study), a person with sleep apnea shows breathing interruptions followed by drops/reductions in blood oxygen and increases in blood carbon dioxide level. In adults, a pause must last 10 seconds to be scored as an apnea. However, in young children, who normally breathe at a much faster rate than adults, shorter pauses may still be considered apneas. Hypopneas in adults are defined as a 30% reduction in air flow for more than ten seconds, followed by oxygen-saturation declines of at least 3% or 4% per the AASM standards. and/or EEG arousal. The Apnea-Hypopnea Index (AHI) is expressed as the number of apneas or hypopneas per hour of sleep.As noted above, in central sleep apnea, the cessation of airflow is associated with the absence of physical attempts to breathe; specifically, polysomnograms reveal correlation between absence of rib cage and abdominal movements and cessation of airflow at the nose and lips. By contrast, in obstructive sleep apnea, pauses are not correlated with the absence of attempts to breathe and may even be correlated with more effortful breathing in an instinctive attempt to overcome the pressure on the affected persons airway. If the majority of a sleep-apnea patients apneas/hypopneas are central, their condition is classified as central; likewise, if the majority are obstructive, their condition is classified as obstructive.
CPAP and BiPAP devices can trigger central Apneas in those with obstructive sleep apnea requiring the use of an ASV (adaptive servo ventilation) device, which is also the proper machine for those who have central sleep apnea or mixed/complex apnea. Epidemiology
Central sleep apnea is less prevalent than obstructive sleep apnea. In one study, CSA is stated to have a prevalence of 0.9% in comparison to OSA.There are many factors that increase the risk of developing CSA. Chronic opioid use produces a mean prevalence in central sleep apnea development of 24%. An estimate of 10% of chronic kidney disease (CKD) patients have a CSA diagnosis. Cohort studies of stroke patients show a 70% development rate of CSA within 72 hours of the stroke event, although CSA was detected in less than 17% after 3 months of follow-up. Another cohort study from the Sleep Heart Healthy study showed incidence of CSA in heart failure patients to be 0.9%. Infancy
Central sleep apnea is common in preterm, newborn, and infancy stages but a decrease in risk is found with aging and maturity of the central nervous system. Underlying neurological disorders are the most common cause of CSA in full term infants. Of the apnea related events in preterm infants born at less than 29 weeks, 25% are central in origin. Childhood
CSA is less common after 2 years of age. The prevalence of CSA in healthy children aging 10 to 18 years is 30%. Children with underlying medical conditions fall under a prevalence rate of 4-6%.