This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
Severe Obstructive sleep apnea is defined as AHI of greater than 
Select and explain. 
A. 15 events/hour, B. 20 events/hour, C. 25 events/hour, D. 30 events/hour
D: 30 events/hour
Answer: D: 30 events/hour 
Explanation: Obstructive Sleep Apnea/Hypopnea 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 events/hourModerate OSAHSAHI of 15-29 events/hourSevere OSAHSAHI of >= 30 events/hourReference: Harrison&;s Principles of Internal Medicine; 19th edition; Chapter 319; Sleep Apnea