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.
Convex or convexity may refer to:

Science and technology
Convex lens, in optics

Mathematics
Convex set, containing the whole line segment that joins points
Convex polygon, a polygon which encloses a convex set of points
Convex polytope, a polytope with a convex set of points
Convex metric space, a generalization of the convexity notion in abstract metric spaces
Convex function, when the line segment between any two points on the graph of the function lies above or on the graph
Convex conjugate, of a function
Convexity (algebraic geometry), a restrictive technical condition for algebraic varieties originally introduced to analyze Kontsevich moduli spaces

Economics and finance
Convexity (finance), second derivatives in financial modeling generally
Convexity in economics
Bond convexity, a measure of the sensitivity of the duration of a bond to changes in interest rates
Convex preferences, an individuals ordering of various outcomes

Other uses
Convex Computer, a former company that produced supercomputers

See also
List of convexity topics
Non-convexity (economics), violations of the convexity assumptions of elementary economics
Obtuse angle
All pages with titles beginning with Convex