Surgery – Diagnostic testing – Detecting muscle electrical signal
Reexamination Certificate
2001-07-09
2003-07-22
Marmor, II, Charles A. (Department: 3736)
Surgery
Diagnostic testing
Detecting muscle electrical signal
C060S587000
Reexamination Certificate
active
06597944
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to medical monitoring devices and, in particular, it relates to a monitor for the detection of disorders of nocturnal skeletal muscle activity.
It is known that nocturnal skeletal muscle activity disorders are a common medical problem. Two such syndromes of this nature are bruxism (nocturnal teeth grinding) and Periodic Leg Movement Syndrome (PLMS).
Surveys show that over 5% of the adult population suffer from bruxism. In this condition, ongoing involuntary grinding of the teeth damages healthy enamel on the chewing surfaces of the teeth (possibly even causing stress fractures), and may cause damage to the tempero-mandibular joint. As such, Bruxism is a far more destructive process than is dental caries. However, only a minority of patients suffering from bruxism are aware of their condition. Usually, the patient is completely unaware of this disorder, and does not seek medical or dental attention until irreversible damage to their dentition has occurred necessitating extensive restorative treatment or tooth extraction. “Clenching” is a common variation of bruxism, and involves the non-purposeful closing of teeth in the chewing position. Both bruxism and clenching can occur during the day, but in most cases occur at night during sleep.
Periodic Leg Movement Syndrome (PLMS) is a common sensorimotor sleep disorder in which repeated involuntary, highly regular, jerky movements occur periodically, every 20 to 40 seconds, in one or both legs during sleep. PLMS may occur as an isolated phenomenon, but more often is associated with other sleep disorders such as Restless Leg Syndrome (RLS), narcolepsy, or sleep apnea. Surveys show that about 1% of the population over 40 years of age have either PLMS or RLS, and that the prevalence of the disorder increases with age. PLMS may also be associated with systemic diseases such as iron deficiency anemia, kidney failure, diabetes, rheumatoid arthritis, and peripheral neuropathy. PLMS and RLS may lead to severe sleep disruption and excessive daytime somnolence. As such, the patient may easily fall asleep during working hours, such as when the patient is driving a car or a truck
Definitive diagnosis of bruxism can be achieved by recording jaw muscle electromyographic (EMG) signals during sleep. So too, PLMS is best diagnosed by monitoring the EMG activity of the Tibialis Anterior (calf) muscle while the patient is sleeping. Both such EMG studies are often part of an in-lab, full night, formal sleep study. In such a study, the patient is required to sleep for a whole night in a controlled environment (a “sleep laboratory”) while connected to multiple monitoring devices, which continuously measure such physiological parameters as respiratory effort, nasal and oral airflow, brain electrical activity (EEG), Tibialis Anterior or jaw muscle EMG activity, heart rate and rhythm (ECG), and blood oxygen saturation. These parameters are recorded on paper or stored in a memory bank for later analysis. A trained sleep technician is required to oversee the study so as to ensure that all parameters are recorded properly. The data is then analyzed, either manually or by specialized software, to produce a “hypnogram” which describes the nature of the patients sleep. Indices in the hypnogram, such as a “bruxism index” and a “leg movement index”, are then used, by a sleep specialist, to diagnose the patients pathology, and its severity.
Bruxism is initially treated with an “occlusal splint” bite guard, or by biofeedback techniques, however ongoing monitoring of the efficacy of treatment is necessary so as to determine if and when more aggressive medical or dental intervention is required. PLMS is managed with medications such as benzodiazepines, anti-dopaminergic agents, or opioids. Multiple trials of therapy may be necessary before the optimal drug and dosage is found, and a medication that is initially effective may lose its efficacy with repeated use. Thus PLMS, too, requires ongoing monitoring of the efficacy of treatment.
The formal sleep study as a means of diagnosing and following-up patients with sleep-related problems, however, suffers from several deficiencies and limitations:
1. The study requires the use of multiple medical monitoring devices and the continuous presence of a trained technician. It is thus labor intensive to perform, and requires the use of multiple, expensive, resources. As such, sleep laboratories themselves are a limited resource, each containing only a limited number of beds. This is particularly problematic as studies are often conducted on “suspicious” patients, in whom the outcome is frequently negative. In such patients, for whom there was no need for the study at all, a limited screening study may have been sufficient to exclude sleep pathology. In addition, the study price often prohibits repeating studies on a regular basis for purposes of patient follow-up, and prohibits performing multiple studies for the screening of large populations.
2. The patient is asked to sleep in an unnatural sleep environment, which may itself affect his sleep patterns.
3. The patient is inconvenienced by having to be in a hospital setting for a night.
4. There is no patient privacy.
In order to overcome some of these drawbacks, the performance of home studies by means of ambulatory systems has become popular. These studies utilize miniature ambulatory recorders, and are sometimes limited to a relatively small number of information recording channels. The patient is prepared for the study at the sleep lab, and returns home with all sensors appropriately attached. Alternatively, a technician may come to the patient's home, or the patient may attach the sensors by himself after receiving appropriate instruction from a technician. The study is then conducted in the patient's home, as he sleeps in his own bed, and the recorded data stored in a memory device. In the morning the recorder and memory device are returned to the sleep lab for data downloading to an analysis station. Some of these ambulatory systems can correct for some data recording problems, by adjusting the gain or filtering during data recording or when post-processing the data. Alternatively, the study can be monitored from the sleep lab via a modem.
Although ambulatory sleep-monitoring systems are much more convenient to the patient, and considerably less expensive than formal, in-lab, sleep studies, all current ambulatory sleep-monitoring systems suffer from several deficiencies:
1. Performance of the study still requires the participation of a trained technician (for the purposes of either attaching the monitoring device or instructing the patient how to do so) and the participation of a formal sleep laboratory (for the purposes of downloading and analyzing the test results, and maintaining the equipment necessary for the performance of the test). Such tests are thus still labor and resource intensive.
2. As analysis of the recorded data is performed off-line in the sleep laboratory, the ambulatory monitoring device must be able to store all registered data in a suitable memory storage device, until such data can be downloaded. Alternatively, if the data is relayed to the sleep laboratory in real time, a modem and telephone line are necessary. Current ambulatory devices are therefore relatively complex and expensive to manufacture. As such, ambulatory studies are still too expensive to perform on a regular basis (currently approximately $500 per study), thus precluding their widespread use as a screening tool or for purposes of frequent patient follow-up. In addition, the cost of such studies does not justify their use on “difficult” patients, such as mental health patients or small children, in whom the likelihood of technical failure of the study is high.
There is therefore a need for a nocturnal skeletal muscle activity disorder screening system that is suitable for widespread use for patient screening and follow-up. Such a system should be sufficiently simple to implement as to allow patients to perf
Friedman Mark M.
Marmor, II Charles A.
S.L.P. Ltd.
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