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Nod off-switch off

25 April 2013

Researchers in China have presented a device for identifying when a patient is asleep and accordingly to adjust deep brain stimulation (DBS) in Parkinson’s disease sufferers.  The device is worn on the wrist and can communicate with the implanted stimulating system to control its activity.

Beta test

Deep brain stimulation is a neurosurgical treatment for treating various neurological diseases.  It has been used to great effect in treating the symptoms of Parkinson’s disease, with 85% of patients who have received it experiencing significant symptom suppression.

The aim of DBS is to regulate neural activity in the brain to healthy, normal levels.  This neural activity, in the brain and throughout the body, is periodic with frequencies ranging from 0.1 Hz to 100 Hz.  Beta-waves, sitting between 12 Hz and 30 Hz are the frequencies associated with normal waking consciousness.  In the case of Parkinson’s disease, the patient’s so called ‘beta power’ will be significantly higher than normal, and DBS can reduce this to normal levels, thus eliminating the symptoms associated with the disease, such as tremors or difficulty in initiating movement.

The technique is now in clinical use and has had, as mentioned above, huge success in treating the symptoms of Parkinson’s disease.  However, there remain serious problems which need to be addressed.

Overstimulation

While the neurological characteristics of Parkinson’s disease are reasonably universal, different patients require different treatments.  With the current state-of-the-art, only a limited choice of stimulating waveforms are available, which in turn limits the worth of DBS.  Furthermore, only a small section of the brain can be stimulated, which may not be the most effective treatment for a certain patient.

Another problem for researchers in this field is the tendency of Parkinson’s disease to get worse over time.  Unfortunately, current systems are static when, because of this deterioration, there is clearly a need for dynamic or tuneable settings.

Along with such complex medical problems, there is also the issue of energy efficiency.  Like a pace maker, the DBS device uses a battery, which must be replaced every two to five years.  This requires surgery, leading to possible infection and other complications associated with frequent surgery.

Finally, DBS itself can be detrimental to patients’ well-being.  Overstimulation can cause a number of problems, such as impaired attention span and difficulties with procedural learning.  To address this, the authors have proposed to switch off the stimulating device when it is not necessary: when the patient is asleep.

Sleeping it off

Clinical tests have shown that symptoms of Parkinson’s disease - for example, tremors - disappear during sleep.  Therefore, the researchers reason, the DBS system could be switched off during sleep.  Other methods have been suggested to effect this, but did not work in real time.  The device proposed in this issue of Electronics Letters is a real time sleep detector, which can identify when the patient is sleeping and switch off DBS.

It was important to the researchers that the detector not be invasive or intrusive, so they developed a wrist wearable, wireless device, which identifies sleep through the patient’s arm movements.  A sensor records the acceleration behaviour of the wrist, and a model coded into the device can identify sleeping behaviour. Once sleep is confirmed, a radiofrequency transmitter instructs the DBS system to switch off.

The device was tested on Parkinson’s disease patients, where all were given the device but for some it was switched off, and for some it was switch on.  Infrared cameras were used to confirm sleeping behaviour of the patients, and it was found that patients with a switched-on device experienced improved sleeping patterns.

The group’s device also helps to improve power consumption, reducing the frequency of surgery, and they feel that it will also find utility in other medical or healthcare environments, such as night time patient monitoring or as a fall alarm for elderly care homes.

Further reading

This article is based on the Letter: Wireless wrist-wearable wake/sleep identification device for closed-loop deep brain stimulation (new window).

A PDF version (new window) of this feature article is also available.

Journal content

Cover of Electronics Letters, volume 50, issue 25

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Browse or search all papers in the latest or past issues of Electronics Letters on the IET Digital Library.