344
Brain Research, 559 (1991) 344-346 Elsevier ADONIS 000689939124837M
BRES 24837
Short Communications
Dish
|on of the flex n reflex in spinal cord-injured man and its application in the restoration of
Malcolm Howard Granat 1, Dorothy Joyce Nicol 1, Ronald H. Baxendale 2 and Brian James Andrews 1. 1Bioengineering Unit, Wolfson Centre, University of Strathclyde, Glasgow (U.K.) and 21nstitute of Physiology, The University, Glasgow (U.K.) (Accepted 11 June 1991)
Key words: Reflex; Functional electrical stimulation; C fiber; Gait; Spinal cord-injured
The flexion withdrawal reflex, evoked by surface electrical stimulation, has been used to provide hip flexion for the restoration of gait in paraplegics. A major limitation to its use has been the decrease in the magnitude of the response to repeated stimulation (habituation). In this study it was found that by using high intensity stimulation the response could be dishabituated. It was demonstrated that sufficient hip flexion for functional electrical stimulation-assisted gait was maintained using high intensity pulses in a one-step-ahead controller. The production of locomotion in spinal cord-injured (SCI) subjects using electrical stimulation requires the bracing of the knee during stance phase and the flexion of the hip for swing phase. Flexion of the hip has generally been achieved, with surface electrical stimulation by invoking the flexion withdrawal reflex in a reciprocal gait pattern 3'8. This response has most frequently been evoked by stimulation of the c o m m o n peroneal nerve in the region of the popliteal fossa. This reflex involves hip and knee flexion and ankle dorsiflexion. The major disadvantage of the use of this response is that of habituation L9 which can reduce the amount of hip flexion to zero, thereby limiting the number of steps the subject can take. Dimitrijevic and Nathan 6 found that when the reflex has been habituated by repeated stimulation it could be dishabituated either by stimulating a second site or changing stimulation parameters. Simultaneous or alternate stimulation of a second site was found to have limited functional application as there was little effect on the habituation 2"7. Wall and Woolf H have shown, in the decerebrate rat, and Clarke et al. 4 in the rabbit, that stimulation of the C-fibres can facilitate a flexion reflex. This facilitation was found to last up to 90 min. The present investigations were carried out to: (a) determine if this dishabituating effect was present in SCI man and (b) explore the use of this dishabituating effect
for the control of functional electrical stimulation (FES)assisted gait in SCI patients. The response was elicited by surface stimulation (frequency 25 Hz, pulsewidth 0.3 ms, stimulus train duration 0.5 s repeated every 2 s) of the c o m m o n peroneal nerve using a computer-controlled constant current stimulator. This is referrred to as the test stimulus. Axelgaard circular (32 mm diameter) hydrogel-backed, selfadhesive electrodes were used. A flexible Penny and Giles strain-gauged goniometer was attached to the hip with the subject standing between parallel bars and weight-bearing on the contralateral leg. The signal from the goniometer was amplified and sampled by an analogue to digital (A/D) converter (Amplicon PC26A, 12-bit). The program controlling the stimulator recorded values from the A/D converter together with the stimulation timing sequence at a sampling frequency of 100 Hz. The effect of high intensity conditioning stimulation (duration 5 s, pulsewidth 5 ms and frequency 1 Hz) on the reflex was studied. A separate control trial was first performed using a low intensity conditioning stimulation (duration 5 s, pulsewidth 0.3 ms and frequency 1 Hz). Both the test and the conditioning stimuli were applied at the same site and at the same current amplitude. All tests were performed with the subject standing between parallel bars and weight-bearing on the contralateral leg.
Correspondence: M.H. Granat, Bioengineering Unit, Wolfson Centre, University of Strathclyde, 106 Rottenrow, Glasgow G4 0NW Scotland, U.K.
345
Subject details Subject A: a 21-year-old male with an incomplete lesion at the level of C4/C 5. Subject B: a 43-year-old female with an incomplete lesion at the level of T 6. Results showing the effect of the dishabituating stimuli are presented in Fig. 1. After the 0.3-rns conditioning pulses change in hip angle returned to below or around the initial value (A). A n increase in the response to around the initial values was observed after both series of high intensity stimulation (B). No movement of the limb was recorded from the single 5-ms or 0.3-ms pulses (D) in any of the subjects. The results show that a burst of high intensity stimulation dishabituates the flexion withdrawal response. Low intensity conditioning bursts introduced at the same points and at the same frequency have no similar effect. The dishabituation observed was more marked than that reported previously
Change in hip angle (degrees) 50 -
A
using other dishabituation strategies 6'7. It may be considered that there was not only dishabituation but potentiation of the reflex. For subject A the stimulation of the high intensity conditioning burst was applied at 170 times sensory threshold. The current level was 80 m A and the charge delivered for the single high intensity pulse was 400 pC. This subject had poor pain sensation in his leg and did not report any pain during or after the high intensity conditioning burst. For subject B, after a high intensity conditioning burst, the test stimulus became painful. A burning sensation was also reported by this subject in her lower leg for about 30 min after the test. A diffuse flare reaction was observed underneath and immediately around the area of the electrode. No flare was observed elsewhere in the limb. Dishabituation of the reflex required higher intensity stimulation recruiting smaller diameter fibres than those
Change in hip angle (degrees)
B
50
25
o;.................................................... !................ ,.......... 40
20
60
80
0
20
Stimulus number
Change in hip angle (degrees) 5o
40
Stimulus
C
60
80
number
Change in hip angle (degrees) so
D Test b
50
'°
-'
Brain Research, 559 (1991) 344-346 Elsevier ADONIS 000689939124837M
BRES 24837
Short Communications
Dish
|on of the flex n reflex in spinal cord-injured man and its application in the restoration of
Malcolm Howard Granat 1, Dorothy Joyce Nicol 1, Ronald H. Baxendale 2 and Brian James Andrews 1. 1Bioengineering Unit, Wolfson Centre, University of Strathclyde, Glasgow (U.K.) and 21nstitute of Physiology, The University, Glasgow (U.K.) (Accepted 11 June 1991)
Key words: Reflex; Functional electrical stimulation; C fiber; Gait; Spinal cord-injured
The flexion withdrawal reflex, evoked by surface electrical stimulation, has been used to provide hip flexion for the restoration of gait in paraplegics. A major limitation to its use has been the decrease in the magnitude of the response to repeated stimulation (habituation). In this study it was found that by using high intensity stimulation the response could be dishabituated. It was demonstrated that sufficient hip flexion for functional electrical stimulation-assisted gait was maintained using high intensity pulses in a one-step-ahead controller. The production of locomotion in spinal cord-injured (SCI) subjects using electrical stimulation requires the bracing of the knee during stance phase and the flexion of the hip for swing phase. Flexion of the hip has generally been achieved, with surface electrical stimulation by invoking the flexion withdrawal reflex in a reciprocal gait pattern 3'8. This response has most frequently been evoked by stimulation of the c o m m o n peroneal nerve in the region of the popliteal fossa. This reflex involves hip and knee flexion and ankle dorsiflexion. The major disadvantage of the use of this response is that of habituation L9 which can reduce the amount of hip flexion to zero, thereby limiting the number of steps the subject can take. Dimitrijevic and Nathan 6 found that when the reflex has been habituated by repeated stimulation it could be dishabituated either by stimulating a second site or changing stimulation parameters. Simultaneous or alternate stimulation of a second site was found to have limited functional application as there was little effect on the habituation 2"7. Wall and Woolf H have shown, in the decerebrate rat, and Clarke et al. 4 in the rabbit, that stimulation of the C-fibres can facilitate a flexion reflex. This facilitation was found to last up to 90 min. The present investigations were carried out to: (a) determine if this dishabituating effect was present in SCI man and (b) explore the use of this dishabituating effect
for the control of functional electrical stimulation (FES)assisted gait in SCI patients. The response was elicited by surface stimulation (frequency 25 Hz, pulsewidth 0.3 ms, stimulus train duration 0.5 s repeated every 2 s) of the c o m m o n peroneal nerve using a computer-controlled constant current stimulator. This is referrred to as the test stimulus. Axelgaard circular (32 mm diameter) hydrogel-backed, selfadhesive electrodes were used. A flexible Penny and Giles strain-gauged goniometer was attached to the hip with the subject standing between parallel bars and weight-bearing on the contralateral leg. The signal from the goniometer was amplified and sampled by an analogue to digital (A/D) converter (Amplicon PC26A, 12-bit). The program controlling the stimulator recorded values from the A/D converter together with the stimulation timing sequence at a sampling frequency of 100 Hz. The effect of high intensity conditioning stimulation (duration 5 s, pulsewidth 5 ms and frequency 1 Hz) on the reflex was studied. A separate control trial was first performed using a low intensity conditioning stimulation (duration 5 s, pulsewidth 0.3 ms and frequency 1 Hz). Both the test and the conditioning stimuli were applied at the same site and at the same current amplitude. All tests were performed with the subject standing between parallel bars and weight-bearing on the contralateral leg.
Correspondence: M.H. Granat, Bioengineering Unit, Wolfson Centre, University of Strathclyde, 106 Rottenrow, Glasgow G4 0NW Scotland, U.K.
345
Subject details Subject A: a 21-year-old male with an incomplete lesion at the level of C4/C 5. Subject B: a 43-year-old female with an incomplete lesion at the level of T 6. Results showing the effect of the dishabituating stimuli are presented in Fig. 1. After the 0.3-rns conditioning pulses change in hip angle returned to below or around the initial value (A). A n increase in the response to around the initial values was observed after both series of high intensity stimulation (B). No movement of the limb was recorded from the single 5-ms or 0.3-ms pulses (D) in any of the subjects. The results show that a burst of high intensity stimulation dishabituates the flexion withdrawal response. Low intensity conditioning bursts introduced at the same points and at the same frequency have no similar effect. The dishabituation observed was more marked than that reported previously
Change in hip angle (degrees) 50 -
A
using other dishabituation strategies 6'7. It may be considered that there was not only dishabituation but potentiation of the reflex. For subject A the stimulation of the high intensity conditioning burst was applied at 170 times sensory threshold. The current level was 80 m A and the charge delivered for the single high intensity pulse was 400 pC. This subject had poor pain sensation in his leg and did not report any pain during or after the high intensity conditioning burst. For subject B, after a high intensity conditioning burst, the test stimulus became painful. A burning sensation was also reported by this subject in her lower leg for about 30 min after the test. A diffuse flare reaction was observed underneath and immediately around the area of the electrode. No flare was observed elsewhere in the limb. Dishabituation of the reflex required higher intensity stimulation recruiting smaller diameter fibres than those
Change in hip angle (degrees)
B
50
25
o;.................................................... !................ ,.......... 40
20
60
80
0
20
Stimulus number
Change in hip angle (degrees) 5o
40
Stimulus
C
60
80
number
Change in hip angle (degrees) so
D Test b
50
'°
-'
