September 2013

Document Type


Degree Name



Dept. of Biomedical Engineering


Oregon Health & Science University


The Institute of Medicine reports that “50 to 70 million Americans chronically suffer from a disorder of sleep and wakefulness.” Many of these individuals have sleep apnea which is thought to occur in 24% of middle aged men and 9% of middle aged women. It has been estimated that approximately 80% of individuals with moderate to severe sleep apnea syndrome have not been diagnosed. Unfortunately, even those suspected to have this sleep disorder can expect on average to wait several months for diagnosis and treatment due to the inadequate prevalence of overnight polysomnography (PSG). Polysomnography is the gold standard for detecting sleep disorders. However, an overnight PSG is expensive and obtrusive. Patients admitted for PSG are wired up to several devices. Typically, electrodes are placed on both legs, on the chest, by the eyes, on the chin, and on the scalp. Respiratory induced plethysmography belts are placed around the chest and abdomen. A pulse oximeter is attached to one finger. A nasal pressure cannula and a thermistor are inserted into the nose with the tubing wrapped behind the ears and taped to the face in order to stay in place. Then the patient, who is already having a difficult time sleeping, is asked to sleep normally in a strange bed while being recorded with both video and audio. I am interested in being able to unobtrusively monitor sleep, either during PSG or in patients’ own homes outside of PSG. Over the years, several devices have been developed to ‘unobtrusively’ detect respiration while an individual is lying in bed. However, the majority of these devices are either placed on top of or just under the mattress. I theorize that these devices would either disrupt the sleep of the patient or be disrupted by the patient during routine bed sheet changes. Load cells, however, can be placed completely under the bed in a manner that they would rarely, if ever, come in contact with the patient. In this dissertation, I report the work that I have done to characterize the frequency of response and damping characteristics of the bed/mattress system for several different mattress types. I also describe a novel method for detecting and monitoring the breathing of an individual lying on the bed using a center of pressure signal derived from the load cell data. Finally, I present results showing the ability of the load cell system to be used in the detection and diagnosis of sleep apnea. The load cell system has potential to replace obtrusive breathing sensors in the sleep lab and to be used as a prescreening tool for patients suspected of having sleep apnea. This technology is currently patent pending.




School of Medicine



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