Flexor Carpi Radialis H-reflex Research Articles

Monitoring Spinal Nerve Function With H-Reflexes

H-reflexes have been used in the clinical neurophysiology laboratory for some time to assess patients with neuromuscular disorders. There are only a few reports for the application of H-reflexes for intraoperative neurophysiologic monitoring. The goals of this article are to review the intraoperative neurophysiologic monitoring of spinal nerve root function with H-reflexes. The following will be reviewed: (1) Introduction to H-reflexes, (2) pathophysiology of spinal nerve root function, (3) neurophysiologic basis of H-reflexes, (4) gastrocnemius H-reflex, (5) flexor carpi radialis H-reflex, (6) anesthetic technique and research, and (7) intraoperative applications of H-reflexes. H-reflexes are single sweep real-time recordings that provide immediate feedback to the surgeon. They can be used to monitor not only sensory and motor spinal nerve root function but also peripheral sensory and motor nerves, plexus, and postsynaptic spinal cord gray matter function.

Upper-extremity H-reflex measurement post-stroke: Reliability and inter-limb differences

ObjectiveTo establish test–retest reliability of flexor carpi radialis (FCR) H-reflexes in non-disabled and stroke participants. We also investigated inter-limb differences and effects of chronicity post-stroke compared to non-disabled group and age-related effects in the non-disabled group. MethodsSixteen chronic stroke and twenty-two non-disabled participants were recruited. Bilateral FCR H-reflexes were tested on two separate days by stimulating the median nerve and recording surface electromyography responses. FCR recruitment curves were plotted for H-reflex (H) and motor (M) waves and normalized as a percentage of maximal M-wave (ordinate) and motor threshold (abscissa). StatisticsIntraclass correlation coefficients [two-way mixed model-ICC (1, 2)], one-way ANOVA, Bland–Altman plots, standard error of measurement (SEM), and smallest real difference (SRD). ResultsICCs ranged from 0.55 to 0.95 (stroke) and 0.69–0.88 (non-disabled). SEM% (% of the mean) ranged from 9% to 24% (stroke) and 18–38% (non-disabled); SRD% ranged from 18% to 66% (stroke) and 6% to 50% (non-disabled). H-reflex amplitude and slope were greater in the paretic vs. non-paretic arm post-stroke (p=0.07 and 0.01, respectively) and the paretic arm vs. non-disabled participants (p=0.007 and 0.002, respectively). Stroke participants with longer chronicity (mean 9.4years) revealed a significantly greater Hslp/Mslp on the paretic side compared to shorter chronicity (2.5years; p=0.05). Mean Hslp/Mslp was significantly greater in the young (mean 29years) compared to the older group (62years; p=0.045). ConclusionsThese results establish reliability of FCR H-reflexes in stroke and non-disabled participants. SEM and SRD measurements can be used to interpret recovery patterns and longitudinal effects of therapeutic interventions. SignificanceFCR H-reflex amplitude and slope can be reliably measured and used to investigate neurophysiological mechanisms of motor recovery post-stroke.

Robotic-assisted stepping modulates monosynaptic reflexes in forearm muscles in the human

Although the amplitude of the Hoffmann (H)-reflex in the forelimb muscles is known to be suppressed during rhythmic leg movement, it is unknown which factor plays a more important role in generating this suppression-movement-related afferent feedback or feedback related to body loading. To specifically explore the movement- and load-related afferent feedback, we investigated the modulation of the H-reflex in the flexor carpi radialis (FCR) muscle during robotic-assisted passive leg stepping. Passive stepping and standing were performed using a robotic gait-trainer system (Lokomat). The H-reflex in the FCR, elicited by electrical stimulation to the median nerve, was recorded at 10 different phases of the stepping cycle, as well as during quiet standing. We confirmed that the magnitude of the FCR H-reflex was suppressed significantly during passive stepping compared with during standing. The suppressive effect on the FCR H-reflex amplitude was seen at all phases of stepping, irrespective of whether the stepping was conducted with body weight loaded or unloaded. These results suggest that movement-related afferent feedback, rather than load-related afferent feedback, plays an important role in suppressing the FCR H-reflex amplitude.

Flexor Carpi Radialis H-Reflex Modulation During Spinal Loading and Unloading With Varied Forearm Postures

Flexor carpi radialis (FCR) H-reflex is usually recorded with the patient in lying or sitting postures while the forearm is positioned in supination or pronation to detect C7 radiculopathy. Its amplitude is smaller during forearm supination compared with pronation for unclear reasons and its recordings during postural loading conditions (i.e., sitting or lying) have not been previously reported. The purpose of this study was to examine FCR H-reflex recordings during varied cervical spine loadings and forearm positions. The FCR maximum H-reflex amplitude was recorded from 15 healthy participants during lying, free-sitting and sitting-with-load while the forearm was positioned in either supination or pronation. Four traces were averaged for each combination of conditions. Two-way repeated-measure analysis of variances (2 x 3) was used to examine the statistical differences. The average FCR H-reflex amplitude was significantly greater during free-sitting and sitting-with-load compared with the lying body position. The average FCR H-reflex amplitude was significantly greater when the forearm was positioned in pronation compared with supination. The increase in FCR H-reflex amplitude (augmentation) during forearm pronation and sitting postures compared with supination and lying may have been the result of combined neural and mechanical effects. These results encourage FCR H-reflex recordings during sitting with the forearm in pronation.

Inhibitory Effects of Circumferential Pressure on Flexor Carpi Radialis H-Reflex in Adults with Neurological Deficits

The effects of circumferential air-splint pressure on the flexor carpi radialis H-reflex in 22 participants with cerebrovascular accident and 5 with spinal cord injury were examined. H-reflexes were assessed by measuring the peak-to-peak amplitude change before, during, and after circumferential pressure was applied to the forearm. 12 H-reflexes (H/M ratio: M = 25%; SD = 14) were recorded before pressure application to obtain a baseline value for comparison of data. A pneumatic 34-cm air splint inflated to 51-60 mmHg provided pressure around the forearm. H-reflex recordings were taken at 1, 3, and 5 min. during and 1 min. after application of pressure. A one-way analysis of variance with repeated measures was applied to compare pressure and postpressure measurements against the baseline value. Tukey multiple-comparison tests were used when significant F ratios were noted. Analysis indicated H-reflex amplitudes decreased significantly at 1, 3, and 5 min. during pressure and quickly returned to baseline when pressure was released. The study suggests air splints decreased the H-reflex in participants with neurological deficits and may be used in the upper extremity temporarily to reduce muscle activity associated with neurological dysfunction.

Impact of transcranial direct current stimulation on spinal network excitability in humans

Transcranial direct current stimulation (tDCS) when applied over the motor cortex, modulates excitability dependent on the current polarity. The impact of this cortical modulation on spinal cord network excitability has rarely been studied. In this series of experiments, performed in healthy subjects, we show that anodal tDCS increases disynaptic inhibition directed from extensor carpi radialis (ECR) to flexor carpi radialis (FCR) with no modification of presynaptic inhibition of FCR Ia terminals and FCR H-reflex recruitment curves. We also show that cathodal tDCS does not modify spinal network excitability. Our results suggest that the increase of disynaptic inhibition observed during anodal tDCS relies on an increase of disynaptic interneuron excitability and that tDCS over the motor cortex in human subjects induces effects on spinal network excitability. Our results highlight the fact that the effects of tDCS should be considered in regard to spinal motor circuits and not only to cortical circuits.

85. Flexor carpi radialis H-reflex is absent after total C7 nerve transection

85. Flexor carpi radialis H-reflex is absent after total C7 nerve transection

The Effects of Circumferential Air-Splint Pressure on Flexor Carpi Radialis H-Reflex in Subjects without Neurological Deficits

The purposes of this study were to investigate the effects of circumferential pressure on flexor carpi radialis (FCR) H-reflex in subjects without neuromuscular deficits and to evaluate the skin's contribution to this effect. FCR H-reflex was assessed in 43 subjects by measuring the peak-to-peak amplitude change before, during, and after circumferential pressure was applied to the forearm. Twelve H-reflexes (H/M ratio: M = 25%, SD = 14) were recorded before pressure application to obtain a baseline value (H(baseline)) to which all data were compared. A pneumatic 15 to 20-cm air splint inflated to 51-60 mmHg provided the pressure around the forearm. H-reflex recordings were taken at 1, 3, and 5 min. during (H(pressure)) and after pressure application. A second smaller study (placebo), in which the air splint was inflated to 0 mmHg, was conducted in 5 subjects to ensure that changes in reflex amplitudes were not a result of cutaneous effects. Two types of responses were observed in the FCR H-reflex following pressure application. One group of subjects significantly increased in H-reflex amplitude while another group decreased in H-reflex amplitude when compared to H(baseline). Regression analysis found that H(max) explained 37.2% of the variance when controlling for H(baseline). Subjects with larger H(max) showed an increase in H(pressure) while subjects with lower H(max) showed decreases in H(pressure) The placebo study revealed no differences in H-reflex amplitude from baseline values, implying that skin stimulation from the air splint has no role in the effects observed. The dichotomous result indicates that pressure influences the upper extremity differently than it does the lower extremity in certain individuals. Clinicians, using circumferential pressure as a therapeutic modality to lower muscle activity of the upper extremity, need to be cognizant that pressure may have contrasting effects on their patients.

Changes in corticomotor excitability of forearm muscles in relation to static shoulder positions

We examined whether the recruitment properties of the corticospinal pathway to forearm muscles are influenced by variations of the shoulder joint angle. Flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles motor evoked potentials (MEPs) in response to transcranial magnetic stimulation were examined during different static positions of shoulder joint in the horizontal plane: from 30° abduction to 30° adduction. We found that at 30° shoulder adduction, maximum slope and plateau phase of the ECR and FCR input–output relationship (i.e., relation between MEP size and stimulus intensity) were significantly higher and lower than at 30° abduction of the shoulder joint, respectively. Intracortical inhibition (ICI) and intracortical facilitation (ICF) of the FCR were assessed using a paired-magnetic pulse paradigm. A significant decrease in ICF was observed after changing shoulder position from 30° abduction to 30° adduction. On the contrary, no variation in the amount of ICI occurred in relation to the same changes in shoulder position. FCR H-reflex to electrical stimulation of median nerve at elbow did not differ significantly between the two shoulder positions. We conclude that shoulder position influences the recruitment efficiency (gain) of the corticospinal volleys to motoneurones of forearm muscles. It is proposed that activity of peripheral receptors signaling static shoulder position influences corticomotor excitability of forearm muscles mainly at cortical level, although C3–C4 propriospinal system could be also involved. It is proposed that the above changes in corticomotoneuronal excitability to forearm muscles as function of shoulder joint position are part of a global proximal–distal synergy operating throughout reaching movements.

Diurnal changes in the amplitude of the Hoffmann reflex in the human soleus but not in the flexor carpi radialis muscle

Changes in the reflex amplitude throughout the day have been observed in non-human mammals. The present experiment tested whether diurnal fluctuations also occur in humans. Hoffmann reflex (H-reflex) amplitude was measured in soleus and flexor carpi radialis (FCR) muscles from the data collected over a 12-h period between 7:00-9:00 a.m. and 7:00-9:00 p.m. At 4-h intervals, M/H recruitment curves were obtained, and two measures of H-reflex excitability were calculated. The maximal H-reflex (H (max)) was calculated as the average of the three largest H-reflexes. H-reflexes were also sampled from the ascending limb of the M/H recruitment curve (H (A), n=10), with a corresponding M-wave of 5% M (max). All values were normalized to the maximal M-wave (M (max)). Soleus H-reflex amplitude and plantar flexion maximal voluntary isometric contraction force (MVIC) were significantly smaller (p<0.05) in the morning (H (max)=57.2% M (max), H (A)=42.3%, M (max), MVIC=162.1 Nm) than in the evening (H (max)=69.1% M (max), a 20.1% increase, H (A)=54.1% M (max), a 27.4% increase and MVIC=195.8 Nm, a 20.8% increase). In contrast, FCR H-reflex amplitude and FCR MVIC were unchanged across all testing sessions. The data show that diurnal fluctuations are present in the amplitude of the human soleus but not in the FCR H-reflex. Diurnal fluctuation in the human soleus H-reflex amplitude must be considered when interpreting H-reflex data, especially when a repeated measures design spanning several days is utilized.

Task dependent gain regulation of spinal circuits projecting to the human flexor carpi radialis

In humans, the flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles act as antagonists during wrist flexion-extension and as functional synergists during radial deviation. In contrast to the situation in most antagonist muscle pairs, Renshaw cells innervated by the motor neurons of each muscle inhibit the motoneurons, but not Ia inhibitory interneurons, of the opposite motor pool. Here we compared gain regulation of spinal circuits projecting to FCR motoneurons during two tasks: flexion and radial deviation of the wrist. We also investigated the functional consequences of this organisation for maximal voluntary contractions (MVCs). Electromyographic (EMG) recordings were taken from FCR, ECR longus and ECR brevis using fine-wire electrodes and electrical stimulation was delivered to the median and radial nerves. Ten volunteers participated in three experiments. 1. To study the regulation of the Renshaw cell-mediated, inhibitory pathway from ECR to FCR motoneurons, forty stimuli were delivered to the radial nerve at 50% of the maximal M-wave amplitude for ECR brevis. Stimuli were delivered during both isometric wrist flexions and radial deviation actions with an equivalent EMG amplitude in FCR (approximately 5% wrist flexion MVC). 2. To explore the homonymous Ia afferent pathway to FCR motoneurons, 50 stimuli were delivered to the median nerve at intensities ranging from below motor threshold to at least two times that which evoked a maximal M-wave during wrist flexion and radial deviation (matched FCR EMG at approximately 5% wrist flexion MVC). 3. EMG amplitude was measured during MVCs in wrist flexion, extension and radial deviation. There was no significant difference in the inhibition of FCR EMG induced via ECR-coupled Renshaw cells between radial deviation and wrist flexion. However, the mean FCR H-reflex amplitude was significantly (P<0.05) greater during wrist flexion than radial deviation. Furthermore, EMG amplitude in FCR and ECR brevis was significantly (P<0.05) greater during MVCs in wrist flexion and extension (respectively) than radial deviation. ECR longus EMG was significantly greater during MVCs in radial deviation than extension. These results indicate that the gain of the Renshaw-mediated inhibitory pathway between ECR and FCR motoneurons is similar for weak flexion and radial deviation actions. However, the gain of the H-reflex pathway to FCR is greater during wrist flexion than radial deviation. Transmission through both of these pathways probably contributes to the inability of individuals to maximally activate FCR during radial deviation MVCs.

Reciprocal inhibition and corticospinal transmission in the arm and leg in patients with autosomal dominant pure spastic paraparesis (ADPSP)

The pathophysiological mechanisms underlying the development of spasticity are not clear, but the excitability of the disynaptic reciprocal inhibitory pathway is affected in many patients with spasticity of different origin. Patients with genetically identified autosomal dominant pure spastic paraparesis (ADPSP) develop spasticity and paresis in the legs, but usually have no symptoms in the arms. Comparison of the spinal and supraspinal control of the legs and arms in these patients may therefore provide valuable information about the pathophysiology of spasticity. In the present study, we tested the hypothesis that one of the pathophysiological mechanisms of spasticity in these patients is abnormal corticospinal transmission and that this may lead to decreased reciprocal inhibition. Ten patients and 15 healthy age-matched control subjects were investigated. The patients were all spastic in the legs (with hyperactive tendon reflexes, increased muscle tone and Babinski sign), but had no neurological symptoms in the arms (except for one patient). Disynaptic reciprocal Ia inhibition of flexor carpi radialis (FCR) and soleus (SOL) motoneurons was measured (as the depression of the background FCR and SOL EMG activity and as the short latency inhibition of the FCR and SOL H-reflex evoked by radial and peroneal nerve stimulation). In addition, the latency of motor evoked potentials (MEPs) in the FCR muscle and the tibialis anterior (TA) muscle was measured. In the patients, the mean reciprocal inhibition was normal in the arms, while it was significantly decreased in the leg compared with the healthy subjects. In the patients, the average latency of MEPs in the FCR muscle was normal, while the latency to the MEP in TA muscle was significantly longer than that found in healthy subjects. Four patients, however, differed from the other patients by having significant reciprocal inhibition in the leg and a significantly shorter latency of TA MEPs than found in the other patients. The six patients without reciprocal inhibition in the leg instead had significant short latency facilitation of the SOL H-reflex and a longer TA MEP latency than seen in the healthy subjects and in the four patients with retained reciprocal inhibition. These findings support the hypothesis that disynaptic reciprocal inhibition and short latency facilitation are involved in the development of spasticity and, furthermore, they suggest a positive correlation between impairment of corticospinal transmission and decrease of reciprocal inhibition/appearance of reciprocal facilitation.

Cyclic h-reflex modulation in resting forearm related to contractions of foot movers, not to foot movement.

During rhythmic voluntary oscillations of the foot, the excitability of the H-reflex in the Flexor Carpi Radialis (FCR) muscle of the resting prone forearm increases during the foot plantar-flexion and decreases during dorsiflexion. It is known that, when the two extremities are moved together, isodirectional (in-phase) coupling is the preferred form of movement association. Thus the above pattern of the H-reflex excitability modulation may favor the preferred coupling between the two limbs. To gain some clues about its origin, FCR H-reflex excitability was tested before and after modifying the phase relations between the activation [electromyogram (EMG)] of foot movers and foot movement, either by loading of the foot or by changing the movement frequency. After foot loading, the movement cycle was consistently delayed with respect to the onset of the EMG in Soleus (Sol) or Tibialis Anterior (TA) muscles. Simultaneously, the FCR H-reflex modulation advanced by that same amount with respect to the foot movement, thus remaining phase-locked to the EMG onsets. Similarly, when movement frequency was varied step-wise between 1.0 and 2.0 Hz, the foot movement was progressively delayed with respect to both the EMG onset (Sol and TA) and the FCR H-reflex modulation, so that the phase relation between the motor command to the foot and the H-modulation in the forearm remained constant. These results suggest that modulation of H-reflex in the forearm is tied to leg muscle contraction, rather than to foot kinematics, and point to a central, rather than kinesthetic, origin for the modulation.

Excitability changes in human corticospinal projections to forearm muscles during voluntary movement of ipsilateral foot.

Excitability of the H-reflex in the relaxed flexor carpi radialis (FCR) muscle was tested during voluntary oscillations of the ipsilateral foot at five evenly spaced delays during a 600 ms cycle. In some experiments the H-reflex was conditioned by transcranial magnetic stimulation (TMS). With the hand prone, the amplitude of the FCR H-reflex was modulated sinusoidally with the same period as the foot oscillation, the modulation peak occurring in coincidence with contraction of the foot plantar-flexor soleus and the trough during contraction of the extensor tibialis anterior. When the H-reflex was facilitated by TMS at short latency (conditioning-test interval: -2 to -3.5 ms), the modulation was larger than that occurring with an unconditioned reflex of comparable size. This suggests that both the peripheral and the corticospinal components of the facilitated response were modulated in parallel. When the H-reflex was tested 40-60 ms after conditioning, i.e. during the cortical "silent period" induced by TMS, no direct effect was produced on the reflex size but the foot-associated modulation was deeply depressed. These results suggest that the reflex modulation may depend on activity fluctuations in the cortical motor area innervating the forearm motoneurones. It is proposed that when the foot is rhythmically oscillated, along with the full activation of the foot cortical area a simultaneous lesser co-activation of the forearm area produces a subliminal cyclic modulation of cervical motoneurones excitability. Should the two limbs be moved together, the time course of this modulation would favour isodirectional movements of the prone hand and foot, indeed the preferential coupling observed when hand and foot are voluntarily oscillated.

Changes in the excitability of the H-reflex in wrist flexors related to the prone or supine position of the forearm in man

The effect of the forearm position, prone vs. supine, on the excitability of the H-reflex in flexor carpi radialis (FCR) muscle was tested in nine adult volunteers by comparing the recruitment profiles of the H and M waves. The H-reflex size, normalized to the maximal M response, was lower when the forearm was supine than when it was prone, with an average reduction of about 50% over most of the H-recruitment curve. In three wrist positions, intermediate between prone and supine, the amount of reflex attenuation was related to the prono-supination angle. Control experiments excluded that the changes in the H reflex excitability were due to displacements of the stimulating or recording electrodes.

The H-Reflex Changes During Wrist Flexion and Wrist Extension

The aim of this study was to find the optimal H-reflex testing conditions regarding the wrist position and forearm muscle contractions. We investigated the effects of weak (at 10% and 20 % of maximal voluntary contraction) isometric wrist flexion and wrist extension on the Hreflex amplitudes in flexor carpi radialis (FCR). In addition, the H-reflexes during passive wrist flexion and passive wrist extension were also evaluated and compared with that at the neutral wrist position. Thus, the factors regarding contractions and mechanical properties to the changes of FCR H-reflex could be scrutinized. The H-reflex amplitudes were significantly different in the seven experimental conditions used in this study, while M-responses were not. Compared to resting neutral wrist position, the H-reflex amplitudes were significantly larger during 10% and 20% wrist flexion. On the contrary, the H-reflex amplitudes during passive and active wrist extensions were all smaller and significantly different from those at neutral positions. However, the H-reflex amplitudes during passive wrist flexion could not be distinguished from that at neutral position. The results indicated that wrist flexion itself exerted a major excitatory input on the alpha motoneurons, while the wrist extension was the contrary. In addition, passive stretch of FCR significantly reduced the H-reflex amplitude, though the passive flexion of the wrist had no effect. This study showed that the FCR H-reflex was strongly modulated in the wrist isometric contraction; high during wrist flexion, and low during wrist extension. This may be functionally important. The results also indicated that minimal tonic contraction (10% MVC) in the wrist flexion position was sufficient to obtain the best test condition. These findings also extend the diagnostic and therapeutic utility of H-reflex testing. In order to maximize the value of reflex studies, the effects of contraction level and joint position must be taken into consideration when setting the test conditions.

Treatment based on H-reflexes testing improves disability status in patients with cervical radiculopathy

Postural modification in patients with lumbosacral radiculopathy either causes further H-reflex suppression, indicating increased root compression, or it effects recovery, indicating decompression of the spinal root. The posture that effects maximum recovery of the H-reflex amplitude is called optimum spinal posture (OSP) and is suggested as a therapeutic exercise to decompress the compromised nerve root. The focus of this study was to identify the OSP that effects the maximum recovery of the flexor carpi radialis (FCR) H-reflex and to study its effect on the disability status in patients with cervical radiculopathy. Fourteen patients (46 +/- 12 y) with confirmed symptoms of C7 radiculopathy for the previous 6 months volunteered for the study. The FCR H-reflex was elicited by electrical stimulation of the median nerve at the cubital fossa (0.5 ms, 0.2 pps at H-max). Signals from the FCR muscle were recorded using a Cadwell 5200A EMG unit. The FCR H-reflex was recorded in natural sitting position with the head in natural position and in the OSP. Four traces of the H-reflex were recorded and averaged. The disability status was evaluated, using the Neck Disability Index (NDI), before exercising in the OSP and after 2 days of exercise in the OSP. Paired t-test and Spearman's correlation coefficients were used. The H-reflex amplitude and latency were significantly different in the OSP and with the head in a natural position (P < 0.004; P < 0.011). Larger reflex amplitude and shorter latency were recorded in the OSP. The NDI scores were considerably improved after exercising in the OSP (P < 0.001). Spearman's correlation coefficient showed negative association between the H-reflex amplitude and the NDI scores (r = -0.64 to -0.54; P < 0.05). Exercising in the OSP increased the H-reflex amplitude and decreased latency of the compromised cervical root. It resulted in decreasing the disability status in this group of patients.

Cervical root compression monitoring by flexor carpi radialis H-reflex in healthy subjects.

One-group, pretest-postest experimental research with repeated measures. To determine the effect of head postural modification on the flexor carpi radialis H-reflex in healthy subjects. H-reflex testing has been reported to be useful in evaluating and treating patients with lumbosacral and cervical radiculopathy. The idea behind this technique is that postural modification can cause further H-reflex inhibition, indicating more compression of the impinged nerve root, or recovery, indicating decompression of the root. Such assumptions cannot be supported unless the influence of normal head postural modification on the H-reflex in healthy subjects is studied. Twenty-two healthy subjects participated in this study (14 men, 8 women; mean age, 39 +/- 9 years). The median nerve of the subjects at the cubital fossa was electrically stimulated (0.5 msec; 0.2 pulses per second [pps] at H-max), whereas the flexor carpi radialis muscle H-reflex was recorded by electromyography. The H-reflexes were recorded after the subject randomly maintained the end range of head-forward flexion, backward extension, rotation to the right and the left, lateral bending to the right and the left, retraction and protraction. These were compared with the H-reflex recorded during comfortable neutral positions. Data were recorded after the subject maintained the position for 30 seconds, to avoid the effect of dynamic postural modification on the H-reflex. Four traces were recorded in each position. During recording, the H-reflex was monitored by the M-response to avoid any changes in the stimulation-recording condition. Repeated multivariate analysis of variance was used to evaluate the significance of the difference among the H-reflex, amplitude, and latency, in various head positions. The H-reflex amplitude showed statistically significant changes (P < 0.001) with head postural modification. All head positions, except flexion, facilitated the H-reflex. Extension, lateral bending, and rotation toward the side of the recording produced higher reflex facilitation than the other positions. These results indicate that H-reflex changes may be caused by spinal root compression-decompression mechanisms. It may also indicate that relative spinal root decompression occurs in most head-neck postures except forward flexion. Head postural modification significantly influences the H-reflex amplitude but not the latency. This indicates that the H-reflex is a more sensitive predictor of normal physiologic changes than are latencies. The H-reflex modulation in various head positions may be-caused by relative spinal root compression-decompression mechanisms.

Changes in excitability of the flexor carpi radialis H-reflex following tactile stimulation of the index fingertip

Adequate stimulation of cutaneous afferents from the fingertip evokes a short-latency inhibition followed by a long-lasting excitation in human flexor carpi radialis (FCR) motoneurones. Changes in excitability of flexor motoneurones were investigated in 11 subjects by means of the H-reflex conditioning technique. The index fingertip, immobilised on a flat table, was stimulated by a small probe mounted on an electromagnetic vibrator. Contact time and tactile perception threshold (PT) were monitored throughout the experiment. In all subjects, tactile stimulation of the skin covering the index pulp, with 10 ms long square pulses, at an intensity of 2-2.5 PT, produced an inhibition starting at a conditioning-test interval of 15 ms and lasting about 2 ms. This was followed by a powerful facilitation lasting more than 10 ms. Excitation appeared just at tactile threshold, whereas threshold for inhibition was about 2 PT. Similar effects were observed after mechanical stimulation of the skin covering the dorsal aspect of the index, close to the nail. Local anaesthesia of the finger pulp drastically reduced both the inhibition and the facilitation of FCR H-reflex. By contrast, electrical stimulation of the index digital nerves, by means of ring electrodes, was always ineffective in modifying the excitability of the FCR H-reflex. It is proposed that inhibition and excitation of FCR H-reflex are caused by activation of oligosynaptic pathways fed by cutaneous afferents; however, it cannot be excluded that joint receptors and primary endings of small hand muscles may contribute in part to the late excitation. The pathways described might play an essential role in modulation and control of exploratory movements and object manipulation, actions that need tactile information to regulate muscle force.

NECK RETRACTION INCREASED CERVICAL H-REFLEX AND DECREASED NECK PAIN.

1392 Neck exercises are the central treatment protocol for patients with neck pain. Extension, flexion or retraction movements have been prescribed based on patients self report of pain. The purpose of this study was to evaluate the use of the flexor carpi radialis (FCR) H-reflex in determining cervical root compression and decompression during neck retraction and correlate the finding with neck pain. Twelve subjects (20-40y) with confirmed symptoms of neck pain for more than 6 months volunteered for the study. The FCR H-reflex was elicited by electrical stimulation of the median nerve at the cubital fossa(0.5 ms., 0.2 pps at H-max) using bipolar surface electrodes. Signal was recorded from the FCR muscle using 500-2000 gain and 10-10,000 Hz bandpass. Pain intensity of the neck (evaluated by visual analog scale) and the H-reflex were recorded before and after A-upright sitting, B- 20min of reading and C- 20 repetitions of neck retractions. The peak to peak amplitude and the deflection latency were measured and averaged for 4 reflex representations. One way ANOVA and Spearman correlation were used for statistics. Results showed significant decrease in the H-reflex amplitude after reading and significant increase after neck retractions (p<0.001). No measurable changes were recorded in the H-reflex latency (p<0.34). Neck pain intensity was significantly increased after reading and decreased after neck retraction(p<0.001). Changes in the H-reflex amplitude and pain intensity during different testing conditions were strongly correlated (r=0.85- -0.82). These results imply a cervical root decompression during neck retractions and suggest it for effective therapy. They also confirm the objective utility of the FCR H-reflex for on line evaluation of patients with neck pain.