<prompt> Severe Obstructive sleep apnea is defined as AHI of greater than15 eventshour20 eventshour25 eventshour30 eventshour  <response>: Obstructive Sleep ApneaHypopnea Syndrome Quantification and Severity scaleApnea-hypopnea index : Number of apnea plus hypopnea per hour of sleepRespiratory disturbance index : Number of apneas plus hypopnea plus RERAs per hour of sleepMild OSAHSAHI of 5-14 eventshourModerate OSAHSAHI of 15-29 eventshourSevere OSAHSAHI of 30 eventshourReference: Harrison;s Principles of Internal Medicine; 19th edition; Chapter 319; Sleep Apnea 