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PubMed1990

Interlimb coordination of stance in children: divergent modulation of spinal reflex responses and cerebral evoked potentials in terms of age.

EMG responses in the gastrocnemius (GM) and tibialis anterior muscles (TA) of both legs together with cerebral evoked potentials (CP), were recorded following perturbations of stance on a treadmill with split belts, in two age groups of children. Unilateral displacements were followed by ipsilateral short latency and bilateral long latency EMG responses. The CP was similar in both tasks. When displacements were simultaneously induced in opposite directions, a significant reduction in the long latency components of EMG responses occurred, while the amplitude of the CP was maximal in this condition. In the older children the CP and long latency EMG responses were larger and the short latency reflex potentials smaller in all conditions compared to the younger children. It is concluded that (1) CP and EMG responses reflect a divergent modulation of a given somatosensory input; (2) developmental changes are reflected in alterations in the amplitude of CP and EMG responses; (3) there is no evidence of transcortically mediated muscle responses.

Aging↗
PubMed1999

Personal computer supported eight channel surface stimulator for paraplegic walking: first results.

Today functional electrical stimulation (FES) is used among other treatments to restore hand and arm function, to restore mobility of the lower extremities, for phrenic pacing, and in cardiomyoplasty. Common to all FES applications is that they require careful setup of stimulation parameters. To improve these tasks, personal computer (PC) based software for stimulation parameter evaluation and data acquisition was written. First, the described software was used to mobilize paraplegic patients in conjunction with an 12C bus controlled 8 channel surface stimulator. Electrodes were placed on each leg on the m. quadriceps and m. gluteus for hip and knee extension and the peroneal nerve to elicit flexion reflex. The fourth channel was used to correspond to subjects' individual needs. The stimulation patterns for standing up, walking, and sitting down easily could be set up and optimized by adjusting up to 128 stimulation parameters in a task-specific way.

Electric Stimulation Therapy↗
PubMed1995

The role of haptic cues from rough and slippery surfaces in human postural control.

Haptic information is critically important in complex sensory-motor tasks such as manipulating objects. Its comparable importance in spatial orientation is only beginning to be recognized. We have shown that postural sway in humans is significantly reduced by lightly touching a stable surface with a fingertip at contact force levels far below those physically necessary to stabilize the body. To investigate further the functional relationship between contact forces at the hand and postural equilibrium, we had subjects stand in the tandem Romberg stance while being allowed physically supportive (force contact) and non-physically supportive (touch contact) amounts of index fingertip force on surfaces with different frictional characteristics. Mean sway amplitude (MSA) was reduced by over 50% with both touch and force contact of the fingertip, compared to standing without fingertip contact. No differences in MSA were observed when touching rough or slippery surfaces. The amplitude of EMG activity in the peroneal muscles and the timing relationships between fingertip forces, body sway and EMG activity suggested that with touch contact of the finger or with force contact on a slippery surface long-loop "reflexes" involving postural muscles were stabilizing sway. With force contact of the fingertip on a rough surface, MSA reduction was achieved primarily through physical support of the body. This pattern of results indicates that light touch contact cues from the fingertip in conjunction with proprioceptive signals about arm configuration are providing information about body sway that can be used to reduce MSA through postural muscle activation.

Adult↗
PubMed1994

Orthotopic cardiac transplantation reverses abnormal reflex regulation of the microvasculature in the lower leg.

OBJECTIVE: The aim was to investigate the effect of cardiac transplantation on reflex control of lower leg subcutaneous blood flow. METHODS: The reflex regulation of subcutaneous blood flow of the lower leg was studied in 11 patients following orthotopic cardiac transplantation, in 11 patients with severe congestive heart failure (New York Heart Association functional class III or IV), and in 11 healthy subjects. Four patients were studied before and after cardiac transplantation. Cause of heart failure was classified as idiopathic dilated cardiomyopathy in all heart failure patients and in all the cardiac transplant patients before transplantation. Blood flow was measured by the local 133xenon washout method in the supine position and during 45 degrees head up tilt. RESULTS: When performing head up tilt without activation of the local nervous venoarteriolar axon reflex in patients with congestive heart failure, the relative subcutaneous blood flow increased abnormally, by 50(SD 25)%, but in patients after cardiac transplantation a normal decrease was seen [-28(13)%, p < 0.001]. The responses in the transplant group were similar to those observed in normal controls with a decrease in blood flow [-32(15)%; NS]. Head up tilt with simultaneous activation of the local venoarteriolar axon reflex increased blood flow [31(22)%] in patients with heart failure as compared to the decrease in blood flow found in the transplants [-44(17)%, p < 0.001]. The decrease of blood flow was not significantly different between the transplant group and control subjects [-53(19)%; NS]. CONCLUSIONS: These results indicate that abnormal reflex regulation in severe congestive heart failure with peripheral vasodilation of the lower leg during orthostasis is reversed and even normalised after cardiac transplantation. The haemodynamic consequence may be a regaining of an oedema-protective mechanism that eliminates the stress (capillary hypertension) on the microcirculation seen in severe heart failure.

Adult↗
PubMed1975

The click-evoked post-auricular myogenic response in normal subjects.

The presence of the posterior auricular myogenic reflex was infectigated in healthy subjects. Click stimuli were delivered alternately to each ear and both ipsilateral and contralateral responses were recorded simultaneously. Smiling and head down position increased the number of responses. With this method, in contrast to previous findings, it was possible to demonstrate bilateral auditory reception in 89% of the 45 subjects studied.

Acoustic Stimulation↗
PubMedDate not supplied

Temperature in mice after ethanol: effect of probing and regain of righting reflex.

The handling involved in rectally probing a mouse in order to measure body temperature is a stress which results in an increase in body temperature. However, after an injection of ethanol the fall in body temperature caused by ethanol is exacerbated by probing. In mice, decreases in temperature following probing are ethanol-dose dependent and can be generated on both the falling and rising phases of the ethanol induced change in temperature. The effect of probing can be observed when the mice are under the hypnotic influence of ethanol, and regain of righting reflex itself is followed by a fall in temperature. The resumption of motor activity in undisturbed mice following an hypnotic dose of ethanol also is accompanied by a fall in temperature. Therefore, the drop in temperature observed in any of these procedures which involve moving the mice may be attributable to the disruption of heat conservation rather than a stress interaction.

Animals↗
PubMed1997

[Clinical features and utricular dysfunction in patients with benign paroxysmal positional vertigo].

We report the clinical features in patients with benign paroxysmal positional vertigo (BPPV), who met the following criteria; (1) a history of brief episodes of positional vertigo, and (2) a characteristic torsional paroxysmal positional nystagmus that was observed visually. The mean age of onset was 55 years. There was no sex predominance. In most patients, positional vertigo disappeared within 2 months. We then used the eccentric rotatory test to examine the patients otolithic function. In the eccentric rotatory test, a patient is rotated around an axis located behind his head (eccentric rotation, ECR). We have demonstrated that the enhancement of vestibulo-ocular reflex (VOR) gain in ECR can be used as an index of the utricular function. Enhancement of VOR gain was observed in ECR to the lower ear in positional vertigo, but not to the uppermost ear. The findings suggest an imbalance in utricular function in patients with BPPV. Otoconia dislodged from the deranged utricle may be a source of canalolithiasis/cupulolithiasis.

Adult↗
PubMed2000

Dynamic foot orthoses. Principles and application.

Previous research has identified areas under the foot where stimulation evokes specific tonic reflexes. The term "tonic" is used because these reflex movements occur slowly, as if tonus or tension were accumulating, in contrast to the abrupt phasic response of a tendon jerk. The concept of tonic reactions has now been incorporated into the design of dynamic foot orthoses to help provide improved orthotic treatment with a better functional outcome. This article describes the background of this technique, briefly describes the manufacture of the dynamic orthosis, and outlines some of its uses.

Equipment Design↗
PubMed1986

Visual, vestibular and voluntary contributions to human head stabilization.

We have investigated the ability of humans to stabilize their heads in space and assessed the influence of mental set and the relative importance of visual and vestibular cues. Ten normal subjects and 3 patients with bilateral vestibular loss were studied. Subjects were fixed firmly to the chair of a turntable facing a screen on which was projected a target spot. A 'gunsight' spot generated by a small projector fixed to the head provided feedback of head position. Four conditions were studied (1) Gunsight (GU): subjects were instructed to stabilize the head in space by superimposing the 'gunsight' spot on the fixed target spot while chair position was displaced according to a random pattern with a bandwidth from 0-1 Hz. (2) Imagined gunsight (IGU): identical to condition 1 except that the subject was blindfolded and so had to imagine the target position. (3) Mental arithmetic (MA): subjects did mental arithmetic while the chair was displaced. (4) Visual tracking (VT): subjects were instructed to track the target spot with the 'gunsight' spot while the chair was fixed and the target spot driven to follow the chair displacement trajectory used in conditions 1, 2 and 3. In GU normal subjects stabilized their head position extremely well (mean HEAD/CHAIR gain = 0.81). Significant stabilization was present in IGU although the gain (mean gain = 0.61) was reduced compared to GU. There was very little stabilization in MA (mean gain = 0.12). In VT, subjects tracked the target with about the same gain (mean gain = 0.68) as in IGU. By comparison, the vestibular patients could not perform IGU, for which their performance (mean gain = 0.08) was similar to MA (mean gain = 0.06). In GU (mean gain = 0.54), their performance was attributable to visual tracking (mean gain in VT = 0.50). For the frequency bandwidth in which subjects were tested, the results show that: When subjects were distracted by mental arithmetic, the contribution to head stability of the short latency cervico-collic (CCR) and vestibulo-collic (VCR) reflexes is negligible. As expected, vision plays an important role in stabilizing the head. Equally important are long latency stabilizing mechanisms whose onset times (140 ms) are shorter, but still comparable to that of vision. The latter mechanisms are of vestibular origin and their influence is under voluntary control so as to permit augmenting head stability compared to what it would be if vision acted alone.

Adult↗
PubMed1989

Compensatory eye movements during head and body rotation in infants.

Eye movements were measured in 2- and 4-month-old infants during rotation in the light and in the dark using a specially constructed infant seat that was rotated sinusoidally at 0.1, 0.25 and 0.5 Hz. As in adults, the phase of the vestibulo-ocular reflex (VOR) was nearly compensatory with respect to head position, and the gain values were generally in the range between 0.4 and 1.4. There were two types of phases for the cervico-ocular (COR) responses: compensatory and anticompensatory. The gain of the COR was 4-6 times larger than that reported for adults. In addition, it was both frequency- and age-dependent. These characteristics of the COR may reflect developmental processes in the infant nervous system. The interaction of the two reflexes (VOR + COR) gave responses similar to when the VOR was elicited alone. The subjects' use of a fixation light raised the gain of the VOR and VOR + COR to about 1.67 and 1.44, respectively. These values were higher than most gains reported for adults. However, they were close to what was predicted (1.53) for the experimental conditions wherein fixation was on a target 25 cm in front of the eyes.

Eye Movements↗
PubMedDate not supplied

Reflex contributions to the assessment of the vertical.

On the ground the vertical directions "up" and "down" have significance in relation to the strategy for avoiding collision of the skull with the planet. Voluntary acts to this end may be based on the experienced result of reflexly generated motor commands. Relevant receptors lie in the otolith organs of the labyrinth, but the head is seldom steady in waking life. A revised scheme of labyrinth reflexes on the limbs--"downhill limbs extend"--replaces the classical scheme of Magnus. Interactions with neck reflexes according to this scheme serve to stabilize the trunk. In an orbiting spacecraft the pattern of afferent signals from the labyrinth differs from that on the ground, and predictions based on the new scheme are to be tested in the project "Operation Push-Pull" proposed for ESRO's Spacelab. Other activities of the Council of Europe's Working Party on Aerospace Physiology and Medicine are briefly described.

Aerospace Medicine↗
PubMed1999

Evidence for fusimotor drive in stroke patients based on muscle spindle thixotropy.

To study fusimotor function in stroke patients, we compared the amplitude of stretch reflexes elicited in flexor carpi radialis (FCR) after contraction of FCR with the wrist held flexed ('hold-short') or extended ('hold-long'). Seven subjects with impaired hand function and spasticity due to stroke, and seven healthy subjects were investigated. Surface electrodes recorded electromyographic activity of wrist flexors and extensors while subjects performed isometric wrist flexions with the wrist alternately in 15 degrees of flexion or extension. After contractions the wrist was moved passively to the mid-position, and stretch reflexes were elicited via controlled mechanical taps delivered over the FCR tendon. For both groups, the amplitude of the stretch reflex was greater after 'hold-short' than 'hold-long' contractions. This finding is consistent with the 'after-effects' of intrafusal fibre activation, and suggests that fusimotor neurones are activated during voluntary contractions of the paretic limb, just as in the limb of a healthy subject.

Adult↗
PubMed1999

Beta-adrenergic blockers and vasovagal episodes during shoulder surgery in the sitting position under interscalene block.

UNLABELLED: Shoulder surgery is often performed with patients in the sitting position under interscalene block anesthesia. Vasovagal episodes, characterized by a sudden decrease in heart rate and/or blood pressure, have a reported incidence of 17%-24% in this setting. We performed a retrospective study to determine whether there was an association between the use of beta-adrenergic blockers and the incidence of these episodes. Of the 150 patients identified, 20 (13.3%) had a vasovagal event. Similar proportions of patients had received a beta-adrenergic blocker in the group who had a vasovagal event compared with those who did not (20% vs 18%; P = 0.95). No other differences could be identified. We conclude that vasovagal episodes occur frequently in this setting with no identifiable risk factors. Beta-adrenergic blockers were not associated retrospectively with either an increased or decreased incidence of these episodes. The most likely mechanism involves the Bezold-Jarisch reflex. IMPLICATIONS: In this retrospective study of 150 patients who underwent shoulder surgery in the sitting position under interscalene block, we found a 13% incidence of vasovagal episodes. Unlike a previous study, this was not affected by the use of beta-blockers. A randomized, prospective study is necessary to clarify this issue.

Adrenergic beta-Antagonists↗
PubMed1983

Murine auto- and cross-tolerance to volatile anaesthetics.

Auto-tolerance and cross-tolerance to halothane, isoflurane and enflurane were tested on 36 mice divided into three equal groups. Each group was first exposed to increasing concentrations of either of the three anesthetics on 13 occasions. The concentration at which each mouse lost its righting reflex during successive exposures in a rotating cage was noted. Cross-tolerance was assessed by comparing the number of mice which had lost their righting reflexes during their first exposure to a given anaesthetic agent to the number which lost it after having been exposed to another anaesthetic. All animals developed auto-tolerance to halothane, isoflurane and enflurane. Cross-tolerance was noted only between mice exposed to isoflurane and enflurane and between mice exposed to halothane and subsequently anaesthetized with isoflurane, but not vice versa.

Animals↗
PubMed1991

Excitation of the extraocular muscles in decerebrate cats during the vestibulo-ocular reflex in three-dimensional space.

(1) Vestibulo-ocular reflex excitation of the six extraocular muscles was studied by recording their electromyographic activity in decerebrate cats during oscillations about horizontal and vertical axes, at frequencies from 0.07 to 4 Hz. Animals were oriented in many different positions and rotated about axes that lay in the horizontal, frontal, or sagittal planes defined by our coordinate system. (2) The strengths of modulation (gains) of the responses of all extraocular muscles were a sinusoidal function of the orientation of the rotation axis within a coordinate plane, and this function was nearly independent of rotation frequency. (3) The responses were used to determine an axis of maximal excitation for each of the extraocular muscles by the vestibulo-ocular reflex. Antagonistic muscle pairs were found to have best axes in nearly opposite directions, confirming their operation as pairs. (4) Excitation of the medial and lateral rectus could be explained by input from the paired horizontal semicircular canals, with essentially no convergent input from vertical canals. (5) Excitation of the vertical rectus and oblique muscles could be explained by convergent inputs from the vertical canals with little or no horizontal canal input.

Animals↗
PubMed1993

Nystagmus responses in normal subjects during eccentric sinusoidal rotation.

Earth vertical axis rotation provides a method of stimulating the horizontal semicircular canals. By placing subjects off from the axis of rotation, the otolith organs may also be stimulated by additional linear acceleration forces. In the present study, we compared the rotation with subjects placed on axis to those placed in an eccentric position, either facing outward or turned 90 degrees facing the direction of the rotation. When the subject was facing outward, sinusoidal eccentric rotation at 0.64 Hz produced a significantly higher vestibulo-ocular reflex (VOR) gain than did on-axis rotation. No increase in VOR gain was observed during eccentric rotation with the subject facing the direction of the rotation. These findings suggest that the gain enhancement due to eccentric rotation is a result of tangential linear acceleration, probably sensed by the utriculus. This study raises the possibility of using eccentric rotation for the diagnosis of the patients with otolith dysfunction.

Acceleration↗
PubMedDate not supplied

Effect of the character of autonomic response and the emotional and personality features of a human being on reactions of the vestibular system.

A moderate degree (R = 0.37-0.45) of correlation between the values of vestibular reactivity, autonomic response, and emotional and personality characteristics was revealed. A conclusion was made that the following features of the background functional organization of the vestibular system, autonomic and emotional and personality characteristics are space sickness predictors: (1) a high coefficient of enhancement of the vestibuloocular reflex (VOR) and its asymmetry with an excess of the physiological norm limits, (2) the presence of depressive manifestations, (3) the impulsive and autistic personality type, and (4) a relative sympathetic deficit and/or increased parasympathetic effects at rest and when engaged in activity. [Translated from Fiziologiya Cheloveka, vol. 25, no. 5, 1999 Sep-Oct, p. 57-63]

Adult↗
PubMed1980

Relationship between the head's and the body's center of gravity during normal standing.

An apparatus for the recording of head movements has been developed and a basic study was performed to determine the normal values of head movement and to estimate the significance of the head movement as a righting reflex. The locus traced by the head closely resembled that of the center of gravity, though shorter in overall length. The head also moves more slowly than the center of gravity. The phase delay of its movement was observed during standing with eyes closed. These results suggest that the head's movement is controlled by the body's center of gravity and that the latter moves in order to keep the head steady, maintaining the eyes in normal position.

Adolescent↗