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PubMed1999

Jaw reflexes evoked by mechanical stimulation of teeth in humans.

Jaw reflexes evoked by mechanical stimulation of teeth in humans. The reflex response of jaw muscles to mechanical stimulation of an upper incisor tooth was investigated using the surface electromyogram (SEMG) of the masseter muscle and the bite force. With a slowly rising stimulus, the reflex response obtained on the masseter SEMG showed three different patterns of reflex responses; sole excitation, sole inhibition, and inhibition followed by excitation. Simultaneously recorded bite force, however, exhibited mainly one reflex response pattern, a decrease followed by an increase in the net closing force. A rapidly rising stimulus also induced several different patterns of reflex responses in the masseter SEMG. When the simultaneously recorded bite force was analyzed, however, there was only one reflex response pattern, a decrease in the net closing force. Therefore, the reflex change in the masseter muscle is not a good representative of the net reflex response of all jaw muscles to mechanical tooth stimulation. The net response is best expressed by the averaged bite force. The averaged bite force records showed that when the stimulus force was developing rapidly, the periodontal reflex could reduce the bite force and hence protect the teeth and supporting tissues from damaging forces. It also can increase the bite force; this might help keep food between the teeth if the change in force rate is slow, especially when the initial bite force is low.

Adult↗
PubMed2001

Reflex and intrinsic changes induced by fatigue of human elbow extensor muscles.

Fatigue-induced changes in intrinsic and reflex properties of human elbow extensor muscles and the underlying mechanisms for fatigue compensation were investigated. The elbow joint was perturbed using small-amplitude and pseudorandom movement patterns while subjects maintained steady levels of mean joint extension torque. Intrinsic and reflex properties were identified simultaneously using a nonlinear delay differential equation model. Intrinsic joint properties were characterized by measures of joint stiffness, viscous damping, and limb inertia and reflex properties characterized by measures of dynamic and static reflex gains. Fatigue was induced using 15 min of intermittent voluntary isometric (submaximal) exercise, and a rest period of 10 min was taken to allow the fatigued muscles to recover from acute fatigue effects. Identical experimental and data analysis procedures were used before and after fatigue. Our findings were that after fatigue, joint stiffness was significantly reduced at higher torque levels, presumably reflecting the reduced force-generating capacity of fatigued muscles. Conversely, joint viscosity was increased after fatigue potentially because of the reduced crossbridge detachment rate and prolonged relaxation associated with intracellular acidosis accompanying fatigue. Static stretch reflex gain decreased significantly at higher torque levels after fatigue, indicating that the isometric fatiguing exercise might be associated with a preferential change in properties of spindle chain fibers and bag(2) fibers. For matched pre- and postfatigue torque levels, dynamic reflexes contributed relatively more torque after fatigue, displaying higher dynamic reflex gains and larger dynamic electromyographic responses elicited by the controlled small-amplitude position perturbations. These changes appear to counteract the fatigue-induced reductions in joint stiffness and static reflex gain. The compensatory responses could be partly due to the effects of increasing the number of active motoneurons innervating the fatiguing muscles. This shift in operating point gave rise to significant compensation for the loss of contractile force. The compensation could also be due to fusimotor adjustment, which could make the dynamic reflex gain much less sensitive to fatigue than intrinsic stiffness. In short, the reduced contribution from intrinsic stiffness to joint torque was compensated by increased contribution from dynamic stretch reflexes after fatigue.

Adult↗
PubMed2003

Guanylyl cyclase receptors mediate cardiopulmonary vagal reflex actions of ANP.

Atrial natriuretic peptide (ANP) potentiates vagal cardiopulmonary reflexes due to chemosensory (Bezold-Jarisch [B-J] reflex) or mechanosensory (ramp baroreflex) activation. The ANP receptor mediating these actions is unknown. We examined the role of particulate guanylyl-cyclase (pGC) receptors in ANP-induced enhancement of cardiopulmonary vagal reflexes. Cardiopulmonary baroreceptor reflex function was assessed by bradycardic responses to ramp blood pressure rises after rapid intravenous methoxamine (100 micro g/kg bolus dose). The B-J reflex was evoked by 3 intravenous doses of serotonin (1 to 10 micro g/kg). In conscious, chronically instrumented rats (n=9), these tests were performed on each animal during randomized infusions of rat ANP (150 ng/kg per minute IV), saline (270 micro L/h IV), the pGC receptor antagonist HS-142-1 (3 mg/kg IV), or combined HS-142-1+ANP treatment. HS-142-1 alone attenuated normal B-J reflex (by 33+/-8%, P<0.05) but not ramp baroreflex responses. As we showed previously, ANP enhanced baroreflex and B-J reflex bradycardia (by approximately 140% and approximately 30%, respectively, P<0.05), compared with saline infusion. These ANP effects were completely blocked by HS-142-1, demonstrating that the cardiopulmonary vagal reflex actions of ANP occurred through pGC natriuretic peptide receptors. Additionally, we have provided evidence for the first time that pGC natriuretic peptide receptors are essential for the full expression of the B-J reflex but not for that of cardiopulmonary vagal baroreflexes. This tonic interaction between pGC natriuretic peptide receptors and cardiopulmonary chemosensitive receptors may be important during pathophysiological activation of B-J reflex, such as with myocardial infarction.

Animals↗
PubMed1991

Salt-induced plasticity in cardiopulmonary baroreceptor reflexes in salt-resistant hypertensive patients.

To investigate the effects of salt loading on cardiopulmonary and arterial baroreceptor reflexes, 34 hypertensive patients underwent two 4-day periods with different dietary sodium intakes (70 and 370 meq/day). The patients were classified as salt-sensitive or salt-resistant depending on whether the mean arterial pressure value obtained on day 4 of high salt intake did or did not increase by 8% or more. In 22 patients cardiopulmonary and carotid baroreceptor reflexes were assessed during each dietary period by measuring the reflex responses to the application of -10 mm Hg lower body negative pressure and of +60 mm Hg increase in neck tissue pressure. Salt-resistant patients (n = 16) retained less sodium than salt-sensitive patients (n = 6) and showed a reduction in plasma norepinephrine and forearm vascular resistance during high sodium intake, whereas the salt-sensitive patients did not. During low sodium diet, no significant differences could be detected in the reflex responses to cardiopulmonary and carotid baroreceptor unloading between the two groups. High salt diet, however, potentiated the gain of cardiopulmonary baroreceptor reflex, which was expressed as the increase in plasma norepinephrine or forearm vascular resistance per millimeter of mercury decrease in pulmonary capillary wedge pressure, only in the salt-resistant hypertensive patients. In addition, the atrial natriuretic factor response to changes in pulmonary capillary wedge pressure was significantly enhanced by high salt intake only in the salt-resistant hypertensive patients. The reflex responses to carotid baroreceptor unloading were unaffected by salt loading in either group. In the remaining 12 patients, the hemodynamic effects of graded lower body negative pressure (-5, -10, -15 mm Hg) and neck tissue positive pressure (+30, +45, +60 mm Hg) were tested for both diets. Again, high salt intake significantly potentiated the cardiopulmonary baroreceptor reflex gain, expressed as the slope of the linear correlation between the changes in forearm vascular resistance (mm Hg/ml/min/100 g) and pulmonary capillary wedge pressure (mm Hg), in salt-resistant (from 3.8 +/- 0.9 to 7.2 +/- 1.0, p less than 0.05) but not in salt-sensitive patients (from 4.2 +/- 0.9 to 3.2 +/- 0.6, NS). In conclusion, the present study demonstrates that high salt diet potentiates cardiopulmonary baroreceptor reflexes and enhances atrial natriuretic factor response in salt-resistant but not in salt-sensitive hypertensive patients. The salt-induced plasticity of cardiopulmonary baroreceptor reflexes may exert a protective effect against the development of salt-induced hypertension by augmenting the reflex vasodilatory response to volume expansion.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1991

Cardiovascular reflexes and hypertension.

Both arterial baroreceptor reflexes and cardiopulmonary reflexes are modified in human hypertension. The arterial baroreceptor reflex regulation of heart rate, when tested by both vasoactive drug injection and the neck chamber technique, has been shown to be reset and blunted. Arterial baroreceptor reflex control of blood pressure, studied by the neck chamber technique, has been found to be reset to more effectively buffer increases in blood pressure than blood pressure falls, but without any loss of overall reflex sensitivity. Cardiopulmonary reflexes, tested by passive leg raising and by application of lower body negative pressure, are also blunted, and their dysfunction involves not only control of peripheral vasoconstriction but also that of renin release. These readjustments of arterial and cardiopulmonary reflexes make buffering of blood pressure falls or of blood volume changes less effective in hypertension. These readjustments appear to be a consequence, rather than a cause, of hypertension. In particular, the blunting of cardiopulmonary reflexes is induced more by left ventricular hypertrophy than by hypertension. It is very marked in hypertensive patients with echocardiographic evidence of left ventricular hypertrophy and very significantly improves when left ventricular hypertrophy is made to regress by prolonged antihypertensive therapy; significant blunting of cardiopulmonary reflexes has also been found in young athletes with marked left ventricular hypertrophy but normal blood pressure. Whether structural changes in the carotid and aortic wall and possibly in the heart are equally important in the readjustment of arterial baroreceptor reflexes is incompletely clarified at the moment, although there are indications that functional and structural modifications may both be involved.

Animals↗
PubMed2002

Oral and pharyngeal reflexes in the mammalian nervous system: their diverse range in complexity and the pivotal role of the tongue.

The oral cavity and pharynx are anatomically separate but functionally integrated regions of the head. The two regions are involved in complex motor responses that include feeding, chewing, swallowing, speech, and respiration. The multiple sensory receptors that innervate these two regions provide the first link in reflexes that control muscles of the entire head, upper gastrointestinal tract, and airway. Most of the reflexes affect the diversity of muscles that compose the tongue, which is vital to all stages of feeding and which continually affects the patency of the airway. Oral-pharyngeal reflexes are evident in the mammalian fetus and continually emerge as the animal or human matures. Some of the first reflexes in the oral region are geared toward nourishment. As the central nervous system matures and the oral and pharyngeal regions develop morphologically, new reflexes develop. Many of these reflexes are protective both of the tissue in the oral cavity, such as the tongue, and of the upper airway in preventing aspiration. While simple reflexes can be evoked in isolation, most reflexes combine with more complex oral and pharyngeal responses such as chewing and vocalization. Oral-pharyngeal reflexes demonstrate a range in complexity. Some sensory stimuli will evoke a series of responses, as is often evident in the infant, and other stimuli will evoke a complex multiple-level recruitment of muscles in a sequence, as in pharyngeal swallowing. Certain sensory inputs evoke an entire motor behavior pattern, such as taste avoidance or facial expression. The oral-pharyngeal reflexes are critical to maintaining life and ultimately serve functions that the oral and pharyngeal regions have in common, such as communication, feeding, and breathing.

Animals↗
PubMed1999

Reflex and muscular adaptations in rat soleus muscle after hindlimb suspension.

Reflex, mechanical and histochemical adaptations of the soleus muscle following 3 weeks of hindlimb suspension (HS) were measured in the rat. HS transformed the soleus muscle fibre type composition from predominantly slow, type I, to approximately equal proportions of fast, type II and slow fibres. Consistent with this transformation was an increase in the maximum shortening velocity, V(max), and a decrease in the stiffness of the series elastic component. Disuse also produced muscle atrophy and a resultant decrease in twitch and tetanic force. Reflex responses of the ankle extensors were also obtained at 5 and 9 weeks of age for six control rats (C group) and six rats subjected to HS for 3 weeks (HS group). The soleus reflexes to a mechanical tap applied to the Achilles tendon (T reflex) and to an electrical stimulation of the sciatic nerve (H reflex) were measured. The maximal amplitude of these reflexes (T(max) and H(max)) were normalised to the maximal direct motor response (M(max)) and the T(max)/H(max) ratio was also calculated to give an index of the relative adaptations of the peripheral and central components of the reflex pathway. The HS group showed significantly higher H reflex gains than the C group, possibly due to changes in synaptic efficiency after HS. Conversely, the HS group presented strongly inhibited T reflexes and negative gains for the T(max)/H(max) ratios. This result indicated a reduced spindle solicitation after HS, which may reflect changes in the spindle sensitivity itself, but it could also be due to the decrease in stiffness of the musculo-tendinous elements in series with the muscle spindles. Such mechanical changes may play an important part in the decreased T reflex responses.

Adaptation, Physiological↗
PubMed1992

Inhibitory reflex during bronchoconstrictions induced by histamine and Ascaris suum antigen.

We investigated the involvements of sympathetic and nonadrenergic nervous systems in the inhibitory reflex following bronchoconstriction in dogs. Inhalations of a 0.00125% solution of histamine and Ascaris suum antigen (3 mg protein) to the bronchial side induced reflex tracheal constriction following bronchoconstriction. An intra-arterial infusion of 5 micrograms/min of atropine to the tracheal site changed the reflex tracheal constrictions by histamine and antigen inhalations into tracheal dilatations. The reflex tracheal dilatations were abolished by the combination of intra-arterial propranolol (100 micrograms) and transections of both the bilateral superior laryngeal nerves and the spinal cord at the C1 level. The reflex tracheal constrictions induced by histamine and antigen inhalations were increased with 100 micrograms propranolol. Furthermore, the reflex tracheal constrictions were enhanced by the combination of 100 micrograms propranolol and transection of the spinal cord. These findings indicate that during the constriction of the bronchial smooth muscle, not only a reflex tracheal constriction mechanism but also one of reflex dilatation operates and that the latter reflex response may be mainly mediated by the sympathetic nerves, with partial involvement of the nonadrenergic nerves. This inhibitory reflex may attenuate asthmatic bronchoconstriction.

Administration, Inhalation↗
PubMed1997

Effects of central nervous stimulants on spino-bulbo-spinal reflex potentials in cats.

Effects of central nervous stimulants on the spino-bulbo-spinal reflex potential were evaluated in anesthetized intact cats, and compared with those on segmental spinal reflex potentials in anesthetized spinal cats. In spinal cats, strychnine augmented polysynaptic reflex potential, picrotoxin inhibited dorsal root reflex potential, aminopyrine potentiated mono- and poly-synaptic reflex potentials but inhibited dorsal root reflex potential, and 4-aminopyridine potentiated all the three types of segmental reflex potentials. A combination of fenbufen, a non-steroidal antiinflammatory agent, and enoxacin, a new quinolone antimicrobial, inhibited all the three types of segmental reflex potentials. In contrast, all these drugs consistently produced an augmentation of the spino-bulbo-spinal reflex potential in anesthetized intact cats. From these findings, we suggest that the spino-bulbo-spinal reflex potential may be used as an electrophysiological parameter for the evaluation of central nervous stimulants.

Action Potentials↗
PubMed1976

[The central neural mechanism of the gastric motility in the dog's medulla oblongata on the vagal inhibitory and excitatory reflexes (author's transl)].

The influences of the vagal inhibitory and excitatory reflexes on the gastric motor centers in the dog's medulla oblongata were investigated. Dogs were anaesthetized with Nembutal, and supplemented Gallamine at need. The brain stem was transected on the level of inferior colliculi of midbrain, the spinal cord transected on the level of between C1 and C2. Bilateral splanchnic nerves were also severed. Electrical activities from the inhibitory and excitatory areas in medulla oblongata were recorded by using a concentric circle electrode which was inserted into medulla oblongata from the dorsal surface of it. Following results were obtaind. 1) Electrical activities of the gastric inhibitory areas were classifed into three types (see Table 1). Type I: The augmentation of electrical activities of the gastric inhibitory areas during theinhibitory reflex were associated with the diminution of them during the exictatory reflex. Type II: Although electrical activities of the gastric inhibitory areas were augmented during the inhibitory reflex, any changes of them were not obtained during the excitatory reflex. Type III: Any changes of electrical activities of the gastric inhibitory areas were not obtained during both inhibitory and excitatory reflexes. 2) Electrical activities of the gastric excitatory areas were classified into two types (see Table 2). Type I: The diminution of electrical activites of the gastric excitatory areas during the inhibitory reflex were associated with the augmentation of them during the excitatory reflex. Type II: Although any changes of electrical activities of the gastric excitatory areas were not observed during the inhibitory reflex, they were augmented during the excitatory reflex.

Animals↗
PubMed1993

Patterns of jaw reflexes induced by incisal and molar pressure stimulation in relation to background levels of jaw-clenching force in humans.

Patterns of jaw reflexes induced by periodontal stimulation were examined in ten adults. Surface electromyograms (EMGs) from the masseter and anterior temporal muscles were recorded when pressure stimulation was applied to either an incisor or a molar. Reflex responses to periodontal pressure stimulation varied, depending on the background levels of jaw-clenching force that preceded stimulation (background clenching force, BCF). At low BCF, excitatory reflexes were elicited from the jaw-closing muscles and jaw-clenching force. However, the magnitude of excitatory reflexes varied with the location of the stimulated tooth along the dentition. While excitatory reflexes were induced equally in the masseter and temporal muscles during incisal stimulation, stronger excitatory reflexes were induced in the temporal muscle than in the masseter muscle during molar stimulation. At high BCF, inhibitory reflexes in the jaw-closing muscles and jaw-clenching force were elicited in eight subjects (group A) during periodontal stimulation. However, excitatory reflexes in the muscles and force were elicited in the remaining two subjects (group B). In the subjects of group A, stronger inhibitory reflexes were elicited in the temporal muscle than in the masseter muscle, and jaw-clenching force also decreased during both incisal and molar stimulation. In the subjects of group B, the magnitude of excitatory reflexes decreased with increases in BCF.

Adult↗
PubMedDate not supplied

[Effect of noise on changes in the acoustic reflex].

Acoustic, stapedial reflex represents a response of the m. stapedius to a sonic excitation of supra speech intensity. It is the constitutive part of impendancmetric investigations, it is performed on the same apparatus after tympanometry, and it is the inseparable part in representation of impendancmetric findings. Until now, the most frequently monitored parameters of acoustic reflex of clinical importance are: threshold, amplitude, output and input angle of the reflex curve. The aim of this work was to performed detailed analysis of mentioned parameters in workers exposed to extensive action of industrial noise of known physical characteristics (of different durations) and to establish which changes occurred in these workers, to what extent and under which conditions. Investigations included 173 industrial workers (346 ears), which work in working unit "Forge", where during the working process noise is produced which is above permissible limits and of the unfavorable frequency content. Workers were divided into two groups. The first group consisted of workers who were spending the whole working time in the workroom with noise above permissible limits, the second group consisted of workers who were spending 3 hours of the working time in that workroom, while the control group consisted of workers who were spending the whole working time in that workroom but they did not have any hearing impairment. Workers of the first and the second group had the hearing impairment, which occurred exclusively as a consequence of chronical acoustic trauma. For all the workers the anamnesis was taken, as well as ORL status and audiometric and impendancmetric investigations were performed, namely the tympanometry and acoustic reflex. Results have shown that the acoustic reflex threshold at 500 Hz and at 1000 Hz for the first group (95.10 dB) was increased with respect to the reflex threshold of the second and the control group (84 dB). At higher frequencies of 2000 Hz and 4000 Hz an increase of the reflex threshold was found for the first and the second group (96 dB) with respect to the control group (87 dB). The amplitude of acoustic reflex was increased, at frequencies 500 Hz and 1000 Hz (3.38), with respect to the second group (2.78) and the control group (2.36), and at higher frequencies, this increase is more prominent. The input angle of the reflex curve was, for the first and the second group, within limits 41 degrees to 50 degrees, and for the control group was from 31 degrees to 50 degrees. The output angle was, at majority of ears of the first and the second group, from 26 degrees to 35 degrees, and for the control group it was from 16 degrees to 35 degrees. Acoustic reflex, as the noninvasive method, short term one, objective and simple for application, does not require collaboration of workers, what provides for objectivity of obtained results and what caused that wrongful estimations, impressions and subjective reactions of workers were avoided.

Hearing Loss, Noise-Induced↗
PubMedDate not supplied

The intra-aural muscle reflex in retrocochlear pathology: a model study in the rabbit.

An animal model for the evaluation of the acoustic stapedius reflex is described. The intra-aural muscle reflex in the rabbit can be recorded with a technique identical to that used in man. The validity and reproducibility of the measurements are good. Lesions in the reflex pathway were shown to be followed by changes in reflex properties. The type of alteration depended on the location of the damage. Lesions in the dorsal cochlear nucleus were not followed by reflex changes. Lesions in the ventral cochlear nucleus and/or the eighth nerve were followed by a rise of reflex threshold and often, but not always, by reflex decay. Lesions in the midline of the trapezoid body were followed by specific changes in the crossed reflex, whereas the ipsilateral reflex was unaffected. The advantage of making simultaneous ipsilateral and contraleral reflex recordings was pointed out.

Acoustic Stimulation↗
PubMed1983

The acoustic reflex threshold in relation to noise-induced hearing loss.

In 100 consecutive cases with severe noise-induced hearing loss, pure-tone threshold measurements revealed symmetric hearing losses with maximum shifts at 4000 and 6000 Hz. Acoustic reflex measurements showed that few patients had an elevated pathologic reflex threshold. In contrast, we found a depressed acoustic reflex sensation level (i.e., the difference, in decibels, between pure-tone threshold and acoustic reflex threshold) suggesting a cochlear localization of the injury. Consequently, the probability of retro-cochlear involvement was small, or the cochlear component dominated the retro-cochlear one. The relation between the absence of the acoustic reflex and the degree of hearing loss showed that even at a pure-tone threshold of 80 dB HL, 50% of the ears still had an elicitable acoustic reflex. Statistical analysis yielded a significant correlation between acoustic reflex sensation level and speech discrimination, but no such correlation between acoustic reflex threshold and speech discrimination. We suggest that acoustic reflex sensation level should be a complement to the acoustic reflex threshold in order to distinguish between different localizations of sensorineural hearing losses.

Adult↗
PubMed2000

Intrasession and intersession reliability of the soleus H-reflex in supine and standing positions.

The Hoffmann reflex (H-reflex) is a measure of motoneuron pool excitability, which is valuable in determining muscle inhibition caused by joint damage (arthrogenic muscle inhibition). In order to detect changes in H-reflex due to injury, the reliability of such a measurement must be established. The purpose of this study was to establish the intrasession and intersession reliability of soleus H-reflex in a supine and standing position. Thirteen healthy volunteers (age 10 +/- 2.63 yr, height 171.35 +/- 10.19 cm, mass 69.62 +/- 13.03 Kg) with no lower extremity orthopedic or neurological disorders within the past year participated in this study. To determine the intrasession and intersession reliability of this measure in a supine resting position and a one-leg standing position, EMG data were collected from the soleus while the tibial nerve was stimulated in the popliteal space. A high voltage (120-200 V), short duration (1.0 msec) stimulus was automatically triggered, eliciting a reflex twitch detected by surface EMG. Several of these measurements were performed with 20 second rest intervals to find the maximum H-reflex. The maximum H-reflex was located by adjusting the intensity of the stimulus. Once a maximum H-reflex was found, 12 measurements were taken in that position with 20 second rest intervals. These steps were repeated for each position (supine and standing) at the same time for 5 consecutive days. Intrasession reliability was computed using 12 measurement trials (12), 12 measurement trials dropping the high and low score (12x), the first 7 measurement trials dropping the high and low score (7x), and the first 5 measurement trials (5). Intrasession and intersession reliability over five consecutive days was estimated using intraclass correlation coefficients (ICC (3, 1)). The supine intrasession reliability measurements were as follows: 0.932 (12), 0.932 (12x), 0.935 (7x), and 0.932 (5). The standing intrasession reliability was 0.853 (12), 0.852 (12x), 0.865 (7x), and 0.862 (5). The intersession reliability was 0.938 in the supine position and 0.803 in the standing position. These results indicate that the H-reflex measured using our protocol in a supine and standing position is a reliable assessment within sessions and between sessions. Five measurements are sufficient to observe reliable measurements within a single session. Most importantly, this data shows that the H-reflex is a reliable assessment that may be used to measure small changes in motoneuron pool excitability over time.

Adult↗
PubMed1999

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

BACKGROUND: 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. SUBJECTS AND METHODS: 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. DATA ANALYSIS: Paired t-test and Spearman's correlation coefficients were used. RESULTS: 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). CONCLUSION: 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.

Activities of Daily Living↗
PubMed2003

Intrasession and intersession reliability of the quadriceps Hoffmann reflex.

The Hoffmann reflex (H-reflex) is a resting electromyographic (EMG) measurement of motoneuron pool recruitment. While the soleus H-reflex has been studied extensively, the study of the quadriceps H-reflex has been limited for various reasons. To date no data exist regarding the reliability of this measurement within and between sessions over an extended period of time. The purpose of this study was to establish quadriceps H-reflex reliability over a four-week period consisting of 6 testing sessions. Eleven neurologically sound volunteers (age: 20 +/- 2 yr, height: 181.9 +/- 9.9 cm; mass: 84.2 +/- 17.8 Kg) participated in this study. Subjects were prepared for EMG surface electrodes over the vastus medialis and medial malleolus (ground). A stimulating bar electrode was placed over the femoral nerve, and a stimulus was delivered at 20 sec intervals with increasing amplitude to obtain a peak quadriceps H-reflex. Ten peak H-reflex measurements were recorded for each session. The stimulator amplitude was increased further to obtain the peak efferent motor response (M-response) for normalization of peak H-reflex measurements. The procedure was repeated at 1 hr, 24 hr, 1, 2, and 3 weeks following the initial session. Intraclass correlation coefficients (ICC (2.1) and ICC (3.1)) were calculated using normalized peak H-reflex measurements. Strong reliability was detected within a session (10 trials ICC (2.1) = 0.957, ICC (3.1) = 0.970; 5 trials ICC (2.1) = 0.961, (ICC (3.1) = 0.970). ICC (2.1) calculations yielded strong reliability between the first and second (1 hr) session (0.956) but moderate reliability between days 1 and 2 (0.787) and between all session over 4 weeks (0.756). ICC (3.1) calculations were also computed to determine the reliability for the fixed selection of sessions. This calculation yielded strong reliabilities between days 1 and 2 (0.969) and between all sessions over 4 weeks (0.911). Within a measurement session quadriceps H-reflex measurements are very reliable, and we recommend 5 trials to establish a measurement. Between measurement sessions these data provide evidence of strong reliability for these fixed sessions (ICC (3.1)), and generalized evidence for moderate reliability over a 4-week period has also been provided (ICC (2.1)). These data provide valuable information for the researcher and practitioner as to the reliability of this measurement in detecting changes in the neuromuscular system.

Adult↗
PubMed2004

Change of stretch reflex threshold in spasticity: effect of botulinum toxin injections.

Spasticity is a disorder of hypertonus associated with neurological diseases, characterized by a decrease in stretch reflex threshold. Stretch reflex threshold of wrist flexors has been recorded in subjects affected by forearm spasticity due to acute neurological lesions, occurred from one to sixty-one months before. In all the subjects a decreased stretch reflex threshold was recorded and a negative correlation between stretch reflex threshold and time of the disease resulted. In five subjects affected by mild spasticity the velocity stretch reflex threshold was tested one-three months after stroke and then six months later. In three cases a further decrease in stretch reflex threshold was recorded. Sixteen subjects affected by heavy forearm spasticity (quantified by Ashworth scale), were treated with Botulinum toxin injections to reduce spasticity. Fourteen of 16 subjects were responsive to the antispastic therapy: a decrease of at least 1 point in the Ashworth scale was detected after the treatment. In all the responsive cases an increase of stretch reflex threshold was recorded. The results confirm that the stretch reflex threshold is decreased in spastic muscles; it decreases progressively in time after the acute lesion. In addition, these results demonstrate that the decreased stretch reflex threshold can be reversed with Botulinum toxin injections. It is known that Botulinum toxin reduce the presynaptic release of Acetylcholine of neuromuscular synapses, but there are experimental evidences that it acts even on spindle's fibres, decreasing the sensitivity of intrafusal muscle fibres. This effect explains how Botulinum toxin increases the stretch reflex threshold in spastic muscles.

Action Potentials↗