1. Sleep-related expiratory groaning;De Roeck;Sleep Res,1983
2. Catathrenia (nocturnal groaning): a new type of parasomnia;Vetrugno;Neurology,2001
3. Vocalization during episodes of prolonged expiration: a parasomnia related to REM sleep;Pevernagie;Sleep Med,2001
4. The international classification of sleep disorders - revised,2001
5. The International classification of sleep disorders - revised,2005