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Biomedical subjects

G W Wright

Publications and source records attributed to G W Wright.

At least 19 recordsLinked to original sources
PubMed1993

A comparison of the mechanogram of the ankle jerk in men and women: observations using an adjustable dorsiflexing torque, high inertia mechanical filter and automatic readout system.

An instrument of new design has been constructed to measure the contractions of the calf musculature resulting from a tap on the Achilles tendon. The instrument provides a predetermined and adjustable dorsiflexing torque from a printed motor, but the contractions are virtually isometric as the system is one of high inertia. Peak force, half-contraction time and half-relaxation time are monitored by electronic circuits equipped with digital output meters. Observations have been made on fifty-two male and forty-five female medical students. There were no significant differences in the peak torques generated by the contractions between the men and women students and no difference in the half-contraction times. The half-relaxation times of the women were, however, significantly longer than those of the men (P = 0.0001). In another group of students the EMG discharges following a tendon tap were recorded, there was no significant difference in the duration of the activity in men and women. Observations have also been made on twenty-three male and seventy female subjects whose mean ages were in the mid-sixties. The peak torques generated by the contractions were significantly higher in the women (P = 0.03). There was no difference in the half-contraction times, but the half-relaxation times of the women were significantly longer (P = 0.001). Possible reasons for the differences are discussed.

Adolescent↗
PubMed1991

Neurophysiology of lower-limb function in hemiplegic children.

Equinus in hemiplegic children is multifactorial. In some cases it is due to a short muscle, in others to simple foot-drop, tonic spasticity, rigidity, compensation for a short limb, fixed flexion contracture at the hip, dominantly inherited forefoot deformity, forefoot equinus secondary to chronic toe-walking, or abnormalities of the visco-elastic properties of the muscle, with true intramuscular contracture. This neurophysiological study confirms that hemiplegia in children is not a homogeneous condition. Some have tonic spasticity; some, although stiff, show electrical silence on stretching; some appear to have a short muscle, with no hypertonicity; and others have hypertonicity in relation to position (i.e. rigidity). A short muscle is not always associated with tonic spasticity with reciprocal inhibition. Weakness can occur without spasticity. Speed of movement of toes, ankle and hip is also significantly reduced.

Adolescent↗
PubMed1991

Resonant frequency at the wrist in hypermobile women.

The resonant frequency of the wrist has been measured in sixteen hypermobile and nine normal women at ten levels of peak torque. At the lowest level the results were identical but at the others the hypermobile values were lower. Damping and thixotropy appeared to be normal. In another group the grip strength of hypermobile subjects was similar to that of controls. The possibility that the connective tissue of the musculature of hypermobile subjects is of enhanced compliance is discussed.

Adult↗
PubMed1991

The effects of neuromuscular stimulation on muscle tone at the knee in paraplegia.

Resting muscle tone of the leg was measured in terms of thigh muscle stiffness and knee resonant frequency in muscles of spinal cord injured subjects who had been involved in an electrical neuromuscular stimulation training programme of the thigh muscles over at least 2 months. The thigh circumference of these patients was 6.6% larger than before training commenced (P less than 0.001) and showed increased muscle stiffness and resonant frequency compared to a similar group of paralysed subjects who had not used any neuromuscular stimulation. Resonant frequency and stiffness after the long-term training were similar to those of non-injured controls and therefore the stimulation programme seemed to reverse the effects of paralysis on muscle tone. Short periods of rest (30 min) caused increased muscle stiffness in non-injured controls and paralysed muscles trained by neuromuscular stimulation. Additional 15 min periods of neuromuscular stimulation further increased muscle stiffness in the trained muscles but also in the muscles of paralysed subjects who had no long-term neuromuscular training. In contrast, 15 min sessions of passive movement of the knee decreased muscle stiffness in long-term trained paralysed muscles and untrained paralysed muscles. Knee resonant frequency was also significantly decreased in the trained paralysed muscles. Results show that muscle tone varies depending on the amount of previous movement or rest and that although neuromuscular stimulation of paralysed muscles increases muscle stiffness and knee resonant frequency, it is in fact restoring such properties of the muscle to a state approaching that of non-injured controls.

Adult↗
PubMed1990

Purification of a cellular (granulocyte) and an extracellular (serum) phospholipase A2 that participate in the destruction of Escherichia coli in a rabbit inflammatory exudate.

A granule-associated phospholipase A2 from rabbit polymorphonuclear leukocytes and a closely similar phospholipase A2 from rabbit serum have been purified to near homogeneity by ion-exchange and reverse-phase chromatography. The cellular (polymorphonuclear leukocyte) phospholipase A2 has been purified greater than 100,000-fold and the extracellular (serum) phospholipase A2 approximately 60,000-fold. The NH2-terminal amino acid sequence of the ascitic fluid phospholipase A2 that we have recently purified from inflammatory exudates produced in rabbits is nearly identical (15 of 16 residues) to that of the polymorphonuclear leukocyte phospholipase A2 and completely identical (19 of 19 residues) to that of the purified serum phospholipase A2. The functional properties of these three phospholipases A2 are indistinguishable. Each enzyme is active against Escherichia coli killed by the bactericidal/permeability-increasing protein of polymorphonuclear leukocyte, a property shared only by a subset of phospholipases A2. The presence of structurally and functionally very closely similar phospholipases A2 in the cellular and extracellular compartments of an inflammatory exudate is consistent with the apparent role of these enzymes in the destruction of certain microbial invaders during the acute inflammatory response.

Amino Acid Sequence↗
PubMed1989

Muscle tone around the human knee in paraplegia.

The thigh muscle tone of non-injured subjects and complete injury paraplegics has been investigated using torques, generated by a printed motor, to move the knee. The dynamic measure of resonant frequency (related to stiffness) together with a static measure of stiffness have shown the legs of non-injured subjects to respond non-linearly to decreasing torques. However, the complete paraplegics' legs did not respond non-linearly but showed constant resonant frequency and stiffness over the range of torques. Peak velocity at resonance (inversely related to damping) gradually increased with increasing torques in both groups. In addition, at a chosen baseline torque of 0.7 N m, resonant frequency and muscle stiffness were significantly lower and peak velocity significantly higher in the paraplegics compared to the non-injured subjects. Contrary to expectations the thigh muscles in established, complete paraplegia showed a lack of tonic EMG activity. In addition, whilst phasic stretch responses were occasionally seen there was no tonic activity in relation to continued stretch. Since muscles atrophy after paralysis, the smaller muscle bulk may contribute to the lower muscle tone.

Adult↗
PubMed1989

Biodynamics of the wrist in rheumatoid arthritis--the enigma of stiffness.

The wrist has been moved rhythmically in the horizontal plane by sinusoidal torques provided by a printed motor. Measurements have been made on normal subjects and subjects with rheumatoid arthritis. Both groups exhibited a resonance, the oscillations being greatest when the applied torque was of certain frequency. In both groups the resonant frequency fell to approximately the same constant value when the torque was raised. While the main relationships were similar a somewhat lower torque resulted in the lowering of resonant frequency in the patients. The relationship between applied torque and peak velocity at resonance was also studied. For a given torque the motion was greater in the patients. No objective signs of increased viscous or elastic stiffness were demonstrable at the wrist in patients with rheumatoid arthritis.

Arthritis, Rheumatoid↗
PubMed1988

Postural thixotropy at the human hip.

In these experiments the person relaxed on his back with one leg free to swing in the horizontal plane into abduction or adduction; the weight was taken by a cord attached to the ceiling over the hip joint. Records of acceleration following a displacement showed a series of decrementing swings which could last for more than 10 s. The imposition of sinusoidal torques generated by a printed motor showed that the system was non-linear for when small torques were used the resonant frequency rose indicating stiffening. The use of a biasing force to move the mean position of the leg showed that the stiffening was not related to any particular position and was the result of the low level of movement. Under certain conditions the stiffening could be abolished by larger active or passive movements. Even a single active or passive movement could be effective. Such a history-dependent compliance was an indication of postural thixotropy. It was present and apparently normal in patients with artificial joints. Reasons are given for believing that the effects are a reflection of muscle properties.

Biomechanical Phenomena↗
PubMed1987

A neurological study of hand function of hemiplegic children.

Twenty-five children with hemiplegic cerebral palsy between the ages of five and 15 years were examined in more detail, using a torque generator motor. A significant reduction in distal power, fatiguability and speed of movement was found on the hemiplegic side. Proximal power was relatively well preserved. Muscle tone, as would be expected, was significantly increased on the affected side and this was demonstrated by a significant rise in measured resonant frequency. Phasic spasticity in response to stretch was found on EMG to be much more common than phasic and tonic combined. Hand function correlated well with the loss of distal power and speed of movement. There was wide individual variation in the relationship between increased muscle tone and hand function. Thixotropy was normal in spastic muscles. Use of the unaffected hand had a marked effect on muscle tone and EMG of the affected side.

Adolescent↗
PubMed1987

Inertia, resonant frequency, stiffness and kinetic energy of the human forearm.

The biodynamics of the forearm of a number of relaxed human subjects have been investigated using a printed motor as a torque generator. Oscillation in the horizontal plane at the resonant frequency has been maintained by feed-back of a modified velocity signal. By means of negative position feed-back the stiffness could be artificially increased and the resonant frequency accordingly elevated. From these changes it has been possible to calculate limb inertia and muscle stiffness, treating the limb as a torsion pendulum. The correlation of inertia with the fifth power of limb length has been studied, this relationship being predicted on theoretical grounds. A significant correlation was found between resonant frequency and the square root of the reciprocal of inertia, a relationship also predicted on theoretical grounds. As the limb was kept on resonance the motion was limited solely by the damping. When the rate of oscillation was increased by the use of added stiffness the peak velocity increased, indicating that the damping was reduced. The mean inertia and mean stiffness values for the men were higher than those for the women. The kinetic energy of rapid voluntary movements was greater in men than in women.

Biomechanical Phenomena↗
PubMed1987

Patellar clonus: an autonomous central generator.

The mechanisms underlying clonus are considered in relation to current theories. By the use of a lever attached to a printed motor forces have been applied to the upper edge of the patella, a steady stretching force in suitable hemiplegic patients started the clonic oscillations. With rhythmic forces it has been found that the underlying rhythm is very resistant to entrainment. The oscillation provoked by a steady bias is increased in amplitude but unchanged in frequency when inertia is added to the apparatus. The frequency of clonus at the ankle, patella and wrist is similar. These and other considerations lead to the conclusion that clonus is not due to the self re-excitation of stretch reflexes but to an autonomous central generator.

Electromyography↗
PubMed1986

Control and postural thixotropy of the forearm muscles: changes caused by cold.

The forearm was cooled in water at 5-10 degrees C while wrist biodynamics were investigated. Pronounced loosening following a perturbation (thixotropy) was no longer seen. The wrist became stiffer for large or moderate but not small movements; EMG activity did not increase. Cooling the wrist alone, or opposite forearm, was without effect. The ability to make rapid reciprocating movements was reduced and muscle relaxation time was increased. Single movements were not affected.

Adult↗
PubMed1986

Passive mechanical properties of the wrist and physiological tremor.

Observations on wrist tremor have been made in the horizontal plane using a tremorograph of new design. A small tap to the hand gave rise to a decrementing series of oscillations at about 9 Hz; as these effects were seen in relaxed and in anaesthetised subjects they were not due to neural reflexes. With the fingers partially extended the spontaneous tremor increased markedly and taps again gave rise to a series of oscillations. Under these circumstances there was no modulation of the EMG. It is accordingly concluded that mechanical wrist resonance plays a major role in the forms of tremor studied.

Anesthetics↗