Continuous positive airway pressure (CPAP), Bilevel Continuous Positive Airway Pressure (BiPAP), or similar machines can be used nightly at home to effectively manage sleep-related breathing disorders such as apnea. In milder cases, oral appliances may be effective alternate treatments. For mild cases in obese people, weight reduction may be sufficient, but it is usually recommended as an adjunct to CPAP treatment since sustaining weight loss is difficult. In some cases, upper airway surgery, generally performed by an otolaryngologist/head & neck surgeon or occasionally an oral and maxillofacial surgeon, is indicated. The treatments prevent airway collapse, which interrupts breathing during sleep. A 2001 study published by Hans-Werner Gessmann in the Journal of Sleep Medicine and Sleep Psychology found that patients who practiced a series of electrical stimulations of suprahyoidal tongue muscles for 20 minutes a day showed a marked decline in sleep apnea symptoms after two months. Patients experienced an average of 36% fewer apnea episodes after successfully completing the treatments.