FES systems that are controlled via voluntary effort from the user

Of central interest to this thesis are the systems that are controlled via voluntary effort from the user. These include systems controlled by EMG, EEG and voluntary movement of the upper limb itself. These systems are described and reviewed below:

a) EMG triggered systems

EMG triggered ES is one of the techniques that allows voluntary control from the users. In general, EMG triggered systems start stimulation if the voluntary EMG signals reach a specific threshold and terminate stimulation once it drops below this threshold. Another EMG triggered system that controls grasping has been developed (Saxena, Nikolic, & Popovic, 1995). The system records the EMG signals from wrist

27 extensors, and once the voluntary contractions of wrist extensors exceed a specific threshold (next-state function), the stimulation of finger and thumb flexors will turn on.

Figure 2.11: State machine control of Saxena, Nikolic et al.’s EMG triggered system (Saxena et al., 1995). The system detects voluntary EMG signals from wrist extensors, and stimulation of the finger and thumb extensors will produce hand opening when the EMG signals exceed a specific threshold.

Another example of a system using EMG signals as control inputs is the STIWELL med4 (Rakos, Hanh, Uher, & Edenhofer, 2007). This system provides the user with two EMG channels for measuring muscle activation and up to four stimulation channels. Exceeding a threshold will activate stimulation to the target muscle groups. The system can provide pre-programmed functional tasks (e.g. hand to mouth). EMG triggered systems that employ a proportional control strategy allow the control of electrical stimulation intensity, to be proportional to the magnitude of voluntary EMG signals. Muraoka has developed an EMG controlled system, which is called the integrated volitional control electrical stimulator (IVES), for the elicitation of wrist and fingers extension (Muraoka, 2001; Yamaguchi et al., 2011). The IVES activates stimulation of muscles at a specific intensity level, and makes the intensity level proportional to the voluntary EMG signals. In another word, the level of users’ wrist and fingers extension will be in proportion to the amplitude of voluntary EMG signals recorded from a target muscle.

The EMG triggered systems are believed to improve arm/hand motor functions during stroke recovery (Bolton, Cauraugh, & Hausenblas, 2004). However, the limitations to

Hand close (State 1)

Hand open (State 2) EMG signals are exceeding

a specific threshold

EMG signals are going below a specific threshold

28 the EMG triggered system are: 1) a minimum voluntary muscle contraction is required (Bolton et al., 2004; Saxena et al., 1995); 2) reliable surface EMG data is limited in people with paretic upper limbs, especially in dynamic conditions. The interpretation of surface EMG data becomes significantly complex in dynamic conditions. The factors such as force output, muscle fiber length and relative position of surface EMG electrodes and source occurring during dynamic tasks will all affect the changes of surface EMG signals (Gazzoni, 2010; Yamaguchi et al., 2011).

b) EEG triggered systems

EEG triggered systems also allow voluntary control by the user (Lauer, Peckham, & Kilgore, 1999; Pfurtscheller et al., 2005; Scherberger, 2009). The EEG signals typically record the brain activity by using the surface scalp electrodes at several sites over specific brain regions (Lauer et al., 1999; Sinkjaer et al., 2003). Lauer, Peckham et al. developed an EEG based control system that allows control of hand opening and closing. The system records EEG signals and converts such signals into the command signals. Two thresholds (a high threshold and a low threshold) have been preset. If the EEG signals go above the high threshold, this generates the command signals for activating stimulation of the muscles, which are responsible for hand closure. When the EEG signals go below the high threshold, command signals for stop closing are generated. Such stimulation stops and the hand stops closing. In order to activate the stimulation of muscles responsible for hand opening, the EEG signals need to go below the low threshold, which generates command signals to go from hand closed to hand open.

29 Figure 2.12: State machine control of Lauer, Peckham et al.’s EEG triggered system

(Lauer et al., 1999). The system records EEG signals and converts these into command signals, which are used to control hand opening and closing.

Most of the current EEG triggered systems use non-invasive EEG electrodes. The non-invasive EEG electrodes can only provide indirect neural signals and only have a limited information transfer rate capacity (Scherberger, 2009). In addition, the current EEG triggered systems, require subjects to complete a great amount of training before using EEG triggered systems (Scherberger, 2009).

c) Motion-triggered systems

The current motion triggered systems typically use shoulder motion (P. Hunter Peckham et al., 2001; P. Hunter Peckham & Knutson, 2005), wrist motion (Prochazka et al., 1997; Prochazka, Wieler, Kenwell, & Gauthier, 1996), contra lateral hand motion (Jayme S. Knutson et al., 2009) or head motion (P. H. Peckham, Mortimer, & Marsolais, 1980) as the control source to the FES system. The typical examples of motion triggered systems are described as follows.

Hand close (state 2) Hand open

(state 1)

EEG signals are going below a high threshold

EEG signals are exceeding a high threshold

Hand stop closing (state 3) EEG signals are going below a

30 Jayme S. Knutson et al., (2007) developed a new contralaterally controlled functional electrical stimulation (CCFES) treatment which aims to restore finger and thumb extension (see figure 2.13). The system employs a proportional control motion triggered system, with the degree of paretic hand opening proportional to the voluntary opening of the contralateral unimpaired hand (Jayme S. Knutson, Harley, Hisel, & Chae, 2007; Jayme S. Knutson et al., 2009). The authors claim the CCFES system requires no residual hand movement of patients and less occupational therapist time due to self-administration of CCFES use.

Figure 2.13: A glove with sensors detects the degree of unaffected hand opening, and stimulation of the finger and thumb extensor muscles will produce proportional

opening of affected hand (Jayme S. Knutson et al., 2009)

Another example was the Bionic Glove, first developed in 1989 (Prochazka et al., 1997; Prochazka et al., 1996). The Bionic Glove FES system is designed for producing functions of hand grasping and opening for C6/7 spinal cord injury (SCI) patients (Dejan Popovic et al., 1999). The typical Bionic Glove usually has a wrist position sensor, which is used for detecting voluntary wrist movement. Such signals collected from wrist position sensors are used as the reference to the control of FES. Voluntary wrist flexion to a specific preset angle activates stimulation and result in hand opening. Conversely, wrist extension to another preset angle activates stimulation of specific muscles and produces a pinch grip (see figure 2.14). However, due to the requirement of voluntary wrist movement, the Bionic Glove is only suitable for patients with C6/7 SCI. The two main effects of daily use of the Bionic Glove

Affected arm Unaffected arm

31 were (1) increasing of grasp force; and (2) increasing of the range of movements of finger joints (Dejan Popovic et al., 1999).

Figure 2.14: The Bionic Glove. (a) The adhesive electrodes are placed on the muscles that will be activated. (b) The wrist position sensor is used for detect the voluntary

movement of wrist. (c) When the wrist flexes to a preset angle, the stimulation is activated to the muscles for production of hand opening. (d) When wrist extends to

another preset angle, the stimulation is activated to the muscles for production of pinch grip (Prochazka et al., 1997)

Motion triggered systems allow voluntary control of stimulation to the target muscles, via voluntary movement of the upper limb itself. Many motion triggered systems are effective for restoration of upper limb functions (Jayme S. Knutson et al., 2009; P. Hunter Peckham et al., 2001; P. Hunter Peckham & Knutson, 2005; Prochazka et al., 1997).