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Biomedical subjects

J D Brooke

Publications and source records attributed to J D Brooke.

At least 19 recordsLinked to original sources
PubMed1992

Movement features and H-reflex modulation. I. Pedalling versus matched controls.

Modulation of soleus H-reflex magnitude over a cycle of leg movement and the adjustment of controls to account for it were explored. During pedalling, H-reflex magnitudes in all nine subjects were highest in the power producing phase and lowest in recovery. Stimulation intensity was standardized. Compared to sitting, these reflexes were significantly depressed (P less than 0.05). The sitting condition was modified in one experiment, so that the angles of the limb joints and the contraction level of soleus were matched to their values, measured at 13 equi-spaced points, around the pedal cycle. This matching resulted in some modulation of the H-reflex around the pedal cycle, when sitting. When the contraction of tibialis anterior was added to these changes to the seated control, this modulation came closer to that seen during movement. Movement-specific modulation of the reflex was now harder to identify. These data raise the question of whether the three features presently used for matching are causative in the movement modulation of the soleus H-reflex and whether they represent effects arising from centrally descending or peripheral sources.

Adult↗
PubMed1992

Movement features and H-reflex modulation. II. Passive rotation, movement velocity and single leg movement.

Modulation of soleus H-reflex magnitudes during pedalling, and their approximation when seated with appropriate joint positions and contractile activity was demonstrated in the previous paper. The present study investigated the modulation of H-reflexes during (A) pedalling movement in the absence of contractile activity, (B) different movement velocities and (C) movement of a single limb. Using a customized tandem cycle ergometer, seated subjects with trunk supported relaxed their leg muscles and allowed their legs to be rotated. Their feet were supported on the pedals with the ankle braced. Reflexes were collected at four phases in the movement cycle (with some at 13 phases) and with speeds of 5-60 revolutions per min (cycle times from 12 to 1 s). The results showed that (i) reflex magnitude substantially decreased with limb rotation (P less than 0.05). The degree of inhibition was dependent on the phase position. (ii) Increasing speed of passive rotation increased the inhibition at all positions, but was most pronounced near the fullest flexion of hip and knee. When subjects actively pedalled, the relationship between speed and inhibition remained. (iii) When the contralateral leg was moved and the target leg was stationary, crossed projection of reflex inhibition was clear. (iv) The reflex gain measured during active pedalling of one leg was similar to that observed during two legged pedalling. Again, a crossed effect from the contralateral leg could be observed. We conclude that the net influence of discharge from movement-elicited afference is inhibitory on this reflex path and that the reflex modulation during pedalling arises from overlaid sources.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Modulation of human short latency reflexes between standing and walking.

Inhibition of the magnitude of soleus muscle homonymous (H) reflexes occurs in humans when walking, compared to standing. The current study asked, (1) was the task modulation of Ia reflexes limited to soleus muscle, (2) was there support for attributing a presynaptic source to the inhibition in humans and (3) did an oligosynaptic short latency reflex show similar task modulation? In 3 subjects, H reflexes were evoked in vastus medialis and soleus, at 4 levels of contraction in the target muscle, with constant stimulus intensity when walking and standing. The reflex magnitudes in both muscles were significantly inhibited during the contractions for walking, compared to standing. Such inhibition also occurred in H reflexes of tibialis anterior muscle. An excitatory oligosynaptic reflex was then evoked in vastus medialis, through low intensity stimulation of the common peroneal nerve during walking and standing. The mean amplitudes of this reflex were not significantly different (P less than 0.05) between the two conditions, at any contraction level. The depression of quadriceps H reflexes, compared to the oligosynaptic reflexes through the same quadriceps motoneuronal pool in the same task, strongly suggested that the inhibition of H reflexes arose at other sites besides the motoneuronal cell body and proximal dendrites. We conclude that Ia H reflexes of various leg muscles of humans are inhibited when walking but that this does not generalize to the oligosynaptic short latency reflex between the anterior shank and thigh.

Adult↗
PubMed1990

Vibration insensitivity of a short latency reflex linking the lower leg and the active knee extensor muscles in humans.

The study indirectly investigated the afferent source of a human lower limb reflex that spans two joints and may link limb muscular activity during movement. Low threshold (motor nerve threshold (MT) to 1.6 MT) single, 1 msec, pulses were delivered to the common peroneal nerve at caput fibula. Heteronymous excitatory responses were observed in the elctromyogram of the knee extensor muscle vastus medialis (VM), when the latter was prior contracted. The briefest latency for the VM reflex was 24.2 msec. The distal belly and tendon of the tibialis anterior muscle were vibrated for 20 min at a frequency of 105 Hz, amplitude 1-2 mm, to inhibit the reflex potential evoked by group Ia afferent fibres from that muscle. This significantly reduced the amplitude of the group Ia mediated Hoffmann (H) reflex in TA. Such vibration did not depress the amplitude of the heteronymous reflex to VM, when initially the latter was at peak amplitude or at its mid-range for amplitude. Reflex latency, threshold, and stimulation current for peak expression suggested that group II fibres were unlikely to be the major initiators of the reflex. The results support the view that this human reflex is primarily Ib mediated.

Action Potentials↗
PubMed1990

Movement modulation of a short latency reflex linking the lower leg and the knee extensor muscles in humans.

Movement modulation of a heteronymous short latency spinal reflex was investigated with transcutaneous, low threshold, stimuli to the common peroneal nerve, during leg pedalling in humans. Electromyographic (EMG) electrodes on the skin over the quadriceps muscles revealed an excitatory response at a minimum latency of 22.8 msec. Samples were obtained at 5 phases in the cycle of pedal crank rotation, and for stimulus intensities to evoke both maximal, and submaximal, reflexes in quadriceps. Over the pedal cycle, the peak-to-peak magnitude of the reflex, in the 3 quadriceps muscles studied, was deeply modulated, including an areflexive phase. The reflex magnitude was linearly dependent on the ongoing EMG activity in quadriceps. It could be fully re-initiated if contractions were produced out of phase in pedalling. The slopes of the regression lines of reflex magnitude (as % maximum reflex) on contraction level (% maximum voluntary contraction) when pedalling (1.05 (r = 0.86, P less than 0.01], and with isometric contractions in the same subjects seated (1.03 (r = 0.69, P less than 0.01], were very similar, with similar thresholds. This contrasts with the inhibition of soleus H reflexes during human gait. The present heteronymous reflex, acting between limb segments, is modulated coincident with ongoing contraction level in the target muscle.

Adult↗
PubMed1989

Papillary mesenchymal bodies: a histologic finding useful in differentiating trichoepitheliomas from basal cell carcinomas.

To distinguish a basal cell carcinoma (BCC) from a trichoepithelioma can be difficult even for an experienced dermatopathologist. Previously reported differentiating histologic features are relative criteria that may be shared by both tumors. In a review of 30 consecutive cases each of trichoepitheliomas, keratotic BCC, and routine BCC, classic criteria were compared with papillary mesenchymal body formation. Papillary mesenchymal bodies are distinct fibroblastic aggregations that represent abortive attempts to form the papillary mesenchyme responsible for hair induction. Papillary mesenchymal bodies were observed in 93% of all trichoepitheliomas, 7% of all keratotic BCC, and 0% of all routine BCC. Hair bulb formation was observed in 30% of trichoepitheliomas and in none of the BCC. We conclude that papillary mesenchymal body formation is an easily recognizable histologic criterion that is more reliable in differentiating these two tumors than standard criteria, including epidermal connections, keratinization, calcification, foreign body reaction, fibrosis, stromal retraction, tumor mucin, ulceration, frondlike epithelial pattern, and the inflammatory response.

Basal Cell Carcinoma↗
PubMed1989

Effect of knee joint angle on a heteronymous Ib reflex in the human lower limb.

Altered efficacy, from change in receptor discharge with different positions of the knee, was investigated in a heteronymous Ib reflex of the human leg. The electrical stimulus was low threshold, to the common peroneal nerve. The divergence of the group I afferents was studied in the electromyograms (EMGs) of ipsilateral and contralateral thigh muscles. The stimulus evoked ipsilateral, short latency, excitation in the three quadriceps muscles studied and inhibition in the knee flexor semitendinosus (ST), with prior contraction of target muscles. This excitation and inhibition did not alter when studied over the range of the knee joint. The stimulus did not evoke responses in contralateral thigh muscles, contracted or relaxed. It is concluded that (1) any change in convergence from discharge of receptors, during extension of the limb, is small and sub-threshold, and (2) this spinal proprioceptive level of neural control appears to be directed primarily to the single limb.

Adult↗
PubMed1988

A technique for electrically induced perturbation of rhythmic leg movement.

The paper describes electrical circuitry which replaces a mechanical brake, for perturbation of the contractile load of the legs during pedalling. The turning flywheel of an ergometer is connected to an alternator, with the electrical load provided by a power resistor connected across the output terminals. A 12-V battery provides the field current. Through variable resistors the field current is altered under microprocessor control, providing different steady-state loads when pedalling and also sudden transient changes of load. The point of change in load in the movement cycle can be accurately selected. The ergometer is instrumented for accurate measurement of pedal crank position, crank angular velocity and reaction force at the foot, to provide a physical description of the evoked steady states and transients, using microprocessor controlled sampling. The results show that the technique has application to the study of the range of reflex responses within a movement cycle and also to the more complex restoration of a movement pattern over a number of cycles. It is applicable to investigation of normal and diseased states.

Electronics↗
PubMed1987

Response synergies over a single leg when it is perturbed during the complex rhythmic movement of pedalling.

Previous studies report that perturbing the posture of humans evokes specific patterns of muscular synergies in the legs. This study investigated the pattern of muscular responses of a whole limb when it was rapidly perturbed in the phase of extending during stationary pedalling. Subjects were instructed to resist. Accordingly, we anticipated increased extensor activity at knee and ankle to overcome the perturbation. This did not occur in the initial responses, appearing at latencies of 85-132 ms (mean = 104 ms). In contrast, there was facilitation in tibialis anterior, and the knee extensors vastus medialis and rectus femoris, together with profound inhibition of the ankle extensors soleus and lateral gastrocnemius. The anticipated extensor response across the limb appeared in the subsequent pattern of electromyogram (EMG) activity, with latencies ranging from 121 to 195 ms (mean = 168 ms), together with a large increase in propulsive force on the pedal. The difference in EMG patterns and latencies between initial and subsequent synergies was used to separate the responses into an earlier 'prevolitional' and a later 'volitional' component.

Adult↗
PubMed1987

A multivariate solution for cyclic data, applied in modelling locomotor forces.

The variability in dependent biological data (measured as forces at the human foot during pedalling) was reduced, by principal components analysis, to two major components which, combined, accounted for 46% of the variability observed in sets of 26 observations per cycle. On the basis of weightings over the cycle, the components were interpreted as due to Power Production and to Phase Switch from power-generation to recovery. Force measurements were made for three frequencies of leg pedalling (1.00, 1.66, and 2.33 Hz at 10 N ergometer resistance). For each principal component, the mean (or summed) deviation over 75 consecutive cycles was found to increase linearly (p less than 0.05) with velocity of leg movement, by 7% and 85% respectively. Analysis of autocorrelations over cycles of movement showed that, in contrast to the strong interconnections of force measures within a cycle of movement, between-cycle dependence was very low. The statistical technique described provides a useful descriptive and inferential method for analyzing dependent cyclic data. The resulting model of the locomotor forces generated at the foot implies that control of power output is substantially for one cycle of a limb and that variability of force increases at the point when the leg switches from power-generation to recovery.

Analysis of Variance↗
PubMed1987

Human group I excitatory projections from ankle dorsiflexors to quadriceps muscle.

A short latency projection of group I afferent fibers from ankle dorsiflexors to knee extensor muscles has been categorized as species specific to humans. However, the effects of the pathway have only been inferred from conditioning homonymous reflexes in relaxed muscle. This study focused directly on the responses evoked in the electromyogram of the heteronymous muscles when active, in two experiments. In the first, preferential activation of group I afferents of ankle dorsiflexors, by electrical stimulation of the common peroneal nerve, excited both vastus medialis (mean latency, 26.3 ms) and rectus femoris (mean latency, 33.5 ms). No excitation or inhibition in either muscle was associated with stimulation of the tibial nerve. The second experiment compared vastus medialis responses with common peroneal nerve stimulation during three different movement conditions in which the muscle was equally contracted: rhythmic isotonic (pedalling); episodic isotonic; isometric contraction. Responses were identified in all three active states, with no significant differences in amplitude or latency. No responses were seen in the relaxed muscle.

Adult↗
PubMed1986

Magnitude of the H reflex of the soleus substantially exceeds the myotatic response from rapid dorsiflexion of the ankle joint.

We compared the magnitude of short-latency EMG responses in the soleus after electrical stimulation and after muscle stretch. The peak to peak amplitudes and areas of such stretch-evoked responses, following initial rotation velocities to 200 degrees/s, did not extend beyond the lower part of the H reflex range (evoked electrically). The disparity suggests caution in the use of electrical stimulation of group 1 afferent fibers when a study is to be made of normal human movement.

Adult↗
PubMed1985

Locomotor limb synergism through short latency afferent links.

Reports of facilitation of lower limb synergists through afferent stimulation in resting humans lead to study of short latency reflex responses during activity of the legs. Four synergistic muscles of the right leg were examined following electrical stimulation of low threshold afferents of the posterior tibial (PTN) and femoral (FN) nerves. Four males cycled on an ergometer with pedals modified to measure the force applied. Movement frequency was 0.8 Hz with 15 N ergometer resistance for two 6 min trials, one involving PTN and the other FN. Collection of EMGs of soleus, lateral gastrocnemius, vastus medialis and rectus femoris lasted for 200 msec after stimulation, which was triggered when the pedal was 56 degrees beyond top-dead-center. Control EMGs were similarly collected during intervening, non-stimulated, pedal cycles within the same work bout. Collection of force on pedals occurred over the same 200 msec period as well as the following two complete pedal revolutions. From PTN stimulation short latency increase occurred not only in homonymous EMGs but also in heteronymous as distant as rectus femoris. FN stimulation similarly resulted in short latency changes in quadriceps and also in triceps surae. Pedal force changes accompanied the EMGs. M response confounding in many cases resulted in only tentative identification of the reflex force evoked. Little change with stimulation was seen in the force in subsequent cycles. The responses represent a net of pathways which could affect within-limb coordination of muscles during human locomotion and extend previous investigations of Ia projections in spinal cats and resting humans.

Adult↗
PubMed1982

Repetitive skill deterioration with fast and exercise-lowered blood glucose.

Using a computerized system for measurement of the variability of force exerted at 26 points in each pedal revolution during the repetitive habituated task of cycling, healthy adult males 6 times performed for 20 minutes, either (a) 3 hours after a meal (fasting) or when so fasted and then fed glucose (b) immediately before, or (c) 30 minutes before performance. Both light and moderate workloads were used. As expected, blood glucose concentrations fell modestly below basal with exercise under (a) or (c) but not under (b). ANOVA of force mean and variability statistics significantly contrasted the 3 treatments, and 2 linear functions from multivariate analysis showed (a) and (c) to be significantly different from (b). These two treatments depressing blood glucose were more variable in force applied, with altered pattern of average forces, especially for points in the task where changes occurred in the force/time relationship. These points may use more immediate feedback correction. Such deterioration of movement control has significant applied implications and invites study of its neural aetiology.

Adult↗
PubMed1982

Between-minute stability in habituated human skill with modestly lowered blood glucose.

Modestly lowered blood glucose (G) occurs with fasting and exercise, increasing variability in forces applied during repetitions of an habituated cycling task. Its effect was studied on stability of the movement cycle pattern of forces from minute to minute. Forces applied at 26 positions in the movement cycle were correlated with each other over 20 one minute samples. Six young men worked (a) 3 hr post-prandial, or as (a) but terminated by feeding 100 g (G) slurry (b) immediately before or (c) 30 minutes before exercise. For each sample, data were averaged over subjects, feet, exercise loads (100 W; 150 W) and 40 movement cycles. Over all conditions together, the movement cycle forces were strongly patterned, implying control by pre-set neural programs. Evoked depressions of blood G below fasting coincided with significant reduction in this patterning. It is suggested that in neural control circuits with modestly depressed blood G, there may be increased sensitivity to feedback over movement cycles.

Adult↗
PubMed1979

Bimodal relationship of human tremor and shivering on introduction to cold exposure.

Four subjects were exposed to an environmental challenge of -12 degrees C for 15 min in four conditions of exposure: 1) clothed body and clothed arm, 0.5 clo units: 2) clothed body and exposed arm, 0.4 col; 3) exposed body and exposed arm, 0.1 clo: 4) exposed body and clothed arm, 0.2 clo. Core temperature, surface temperature of the right arm, perceived thermal comfort, EMG indicated onset of shivering, and the frequency of tremor using accelerometry were monitored and data collected every 30 s. The results indicate that tremor frequency significantly increases with cold exposure, but that a significant drop in tremor frequency precedes the onset of shivering. It is suggested that pre-shivering tetany occurs prior to the onset of shivering, acts as a load upon the lever of the hand and reduces the oscillation of the limb.

Adult↗