What is Tremor:

A basic description of tremor is an involuntary, roughly sinusoidal oscillation of a body part or parts.  While most cases occur in the arms and hands, tremor can also affect the legs, head or just about any other muscle on the body.  Tremor affecting the arms being of most concern, as our hands and arms allow us to perform those tasks vital for an independent life.

Initially tremor may be categorized as either Physiological or Pathological tremor.  Physiological tremor is an 8-12 hz oscillation which is inherent in all human motion. Its amplitude is generally so small however that it only becomes a nuisance in the most intricate of tasks.

Pathological tremor on the other hand occurs as a symptom of numerous diseases such as Parkinson's Disease, Multiple Sclerosis, or as a result of head injury.  Even in a mild form, pathological tremor can make simple tasks such as writing a tedious difficulty.  In its most disabling form termed "intention tremor" (associated with MS), the tremor can occur with sufficient amplitude to obscure any underlying intentional motion.  The effect for the sufferer is that otherwise simple tasks, such as eating, drinking and self care, require enormous effort and often cannot be completed unaided.

Tremor can take on various personalities depending on the cause and many other factors which are far beyond my abilities to understand but which is the topic of much research.

One characterisation used is based on the nature and conditions under which tremor pervades.  The main categories being 

* Postural - tremor occurs when a limb is supporting itself against gravity.
* Rest -tremor occurs when the limb is at rest, for example when a persons hand is lying on their lap.
* The final category and possibly the most annoying is action/intention tremor, which as its name suggests is brought on by goal or activity directed motion.  An example would be an increase in tremor amplitude in a persons arm as they reach to pick up a specific object. 


Medical Tremor treatment:

When a person is initially diagnosed with a disabling form of tremor, the initial course of treatment is usually medication.  At present the most common forms of medication prescribed are what are known as beta blockers, examples are propranolol (Inderal) and the anticonvulsant primidone.  While medication proves successful in some cases, what works for one patient usually will not work for another.  If a successful combination and dosage of medication is found it is usually the result of  a long process of trial and error.

Given the nature of the drugs used to treat tremor, a successful treatment may come at the expense of substantial side effects such as nausea, nightmares and hallucinations.

For severely disabling tremor the next step is one of two forms of invasive surgery.
The first is a thalamotomy, which usually involves the surgical lesioning of parts of the thalamus region of the brain believed responsible for tremor. This is usually only considered in patients with severe, drug-resistant essential tremor and for a very small subset of patients with Parkinson's Disease who have severe, disabling  tremor.  While this has shown to give immediate relief from the symptoms of tremor, postoperative complications including weakness, sensory deficits and confusion are not uncommon.

The other option is thalamic stimulation.  This is a relatively new technique, though the U.S. Food and Drug Administration have recently approved thalamic stimulation as an accepted therapy for suppression of essential tremor or parkinsonian tremor in the upper extremity.  Basically this involves implanting a fine electrode in the thalamic area found to be responsible for the tremor.  After the wire of the electrode leaves the skull, it is tunnelled under the scalp and down the neck to a pulse generator located in the subclavicular region (around your collar bone).  The implanted generator acts much like a modified pacemaker, sending electrical impulses to the electrode in the brain, which are carefully timed to cancel the signal causing tremor.  In the first study of this technique, as many as 88 percent of the patients with Parkinson's Disease had either good or excellent relief from tremor.  It is usually desirable to avoid any form of surgery involving the brain.


Tremor suppression:

Failing drug therapy and avoiding brain surgery, an alternative approach to tremor control is to suppress the tremor using complementary technology (gadgets).  Several gadgets have been designed that filter out or dampen tremor related movements from computer mouse or joystick inputs, allowing the user to control the cursor on the computer screen.  There are also mechanical aids available such as the Neatereater by Michealis Engineering, this is like a little robotic arm which can be attached to a table or wheelchair.  It is designed to support various utensils which can assist in eating and other personal care activities.

While the above techniques have proved quite successful they are all focused on specific tasks and environments.  It is the purpose of my research to develop a device which will control the tremor during a range of every day tasks, thus hopefully restoring some of the independence to the sufferer which was robbed by tremor.  In order for the device to suppress tremor during every day tasks it was decided to make it wearable, in the form of a brace or orthosis.  Possibly the most important issue in the design is that it shouldn't make the wearer feel like Robocop as for most that would be as annoying as the tremor itself.

Research by various groups has shown that velocity dependent resistance, or applying a weight to the affected arm, is capable of substantial tremor suppression.  The problem here is that simply applying a weight to the arm not only suppresses the tremor but also makes doing anything useful very difficult.  For this reason we are trying to develop an intelligent or adaptive device which will hopefully be able to tell the difference between tremor and intentional movements.  It could then apply a resistance which will suppress the tremor and allow intentional movement to go unimpeded.


Design Parameters:

Initially it was decided to focus on tremor suppression at the elbow , as this is the simplest joint on the arm.  Hopefully though, if the device proves successful, the technology developed would be applicable to tremor suppression at the shoulder and wrist.  We need to start with " baby steps".
 
As noted in the section describing tremor, the dynamic characteristics of a sufferers tremor is specific to him/her.  For this reason a tremor suppression orthosis would need to be designed to meet the specific demands of their individual tremor.

From a control or engineering  point of view the most important characteristics of tremor induced motion are listed below.

* The first parameter of concern is the pattern of muscle activation. The two possibilities are alternating and synchronous activation of antagonistic muscle pairs. At the elbow for example this would correspond to the biceps and triceps being activated in an alternating fashion or at the same time. 
* Results have found that frequency (rate at which spasms occur) does not change over time though some drift is to be expected. The base or mean frequency of the tremor is mainly dependent on the cause of the tremor.  Multiple Sclerosis, for example, is characterised by a 2.5-3.5hz oscillation, while essential tremor exhibits a frequency of between 5-7hz.  The amount that the frequency can vary over time is usually found to be sufferer specific. 
* The amplitude or severity of the oscillating motion is the most variable characteristic.  Amplitude not only depends on the cause of the tremor but for some cases on physiological and emotional factors as well.  It is not uncommon for a  tremor to increase in amplitude when the sufferer becomes upset or agitated.  The amplitude can also increase with the amount of effort put into moving the arm.

You may be wondering why I have not mentioned the actual orthosis or elbow brace onto which the system will be mounted and which will interface with the user.  Orthotic design is a highly skilled area and for this reason Mr Dave Allen, Consultant Orthotist (Cappa Hospital, Dublin), has kindly agreed to design and manufacture the orthosis for the project. 

To give a brief summery of  what we plan to do:

Motivation
?Tremor in the hand and arms is the most disabling
?Affects ability to perform simple every day Tasks 
?Devices to date focused on task specific tremor suppression
?Non-adaptive devices tend to inhibit voluntary motion

Main Objective
?Wearable device, for tremor suppression during daily tasks
?Safe and Un-obtrusive operation in daily environments 
?Actively Dissipate Tremor-Related Torque at affected joint
?Adapt to variations in tremor characteristics and environment

Dynamic Requirements
?Initially Focus on Elbow Restricted to 1 angular DOF 
?"Worst case Scenario" , ±8N/m Torque , amplitude of ±15 Degrees
?Adapt to frequency variation of ±1 Hz over range 3-10Hz
?Control applicable to full range Flexion and Extension