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Biomedical subjects

V Galea

Publications and source records attributed to V Galea.

At least 19 recordsLinked to original sources
PubMed2001

Depletion and sizes of motor units in spinal muscular atrophy.

Motor unit number estimation (MUNE) was applied to the biceps brachii muscles of 13 young patients (age 5--24 years) with spinal muscular atrophy (SMA) and the results compared with those of healthy control subjects matched for age and gender. In the SMA patients, all motor unit (MU) estimates fell below the control range, and there was good correspondence between the values for the two arms in the same subject. No correlation could be found between the MUNEs and the severity of the weakness. This unexpected result was attributed to the presence of small and normal-sized MUs in the muscles of patients, in addition to MUs that appeared to be considerably enlarged. The threefold mean increase in MU potential size was insufficient to compensate for the MU loss. In addition, the study confirmed that there are, on average, approximately 130 MUs in the healthy biceps brachii muscle.

Adolescent↗
PubMed2001

Electrical characteristics of human ankle dorsi- and plantar-flexor muscles. Comparative responses during fatiguing stimulation and recovery.

Changes in muscle excitability were investigated during fatigue and the recovery of human dorsi- and plantar-flexor isometric contractions. The indirectly evoked muscle compound action potentials [tibialis anterior (TA) and soleus (SOL) M-waves] were used as an index of excitability. Ten subjects successfully completed five experiments, spaced at least 1 week apart, in which intermittent tetanic trains at different frequencies of stimulation (0-30 Hz) were used to fatigue the ankle dorsi-flexors. Muscles were rendered ischaemic via a thigh cuff inflated above mean arterial pressure. The effects of ischaemia were examined by repeating the 20-Hz stimulation protocol under non-ischaemic conditions. Five of those subjects also participated in one further session in which the ischaemic plantar-flexors were also fatigued. It was hypothesized that muscle excitability would be preferentially retained in the SOL. Maintenance of excitability in both muscles was possible for 1 min regardless of stimulus frequency; thereafter, stimulation at the highest frequencies induced the greatest decline [30 Hz stimulation; 95.4 (0.5)%, P < 0.01) in the amplitude of the M-wave. The decline in M-wave amplitude was always greater than the decline in M-wave area and occurred at firing rates not normally associated with neuromuscular blockade, implying propagation failure along the sarcolemma. The presence of ischaemia significantly accelerated the decline in both amplitude (78% versus 12%, P<0.01) and area (45% versus no decline, P<0.01) of the M-wave. Recovery was limited when tetanic stimulation ceased but progressed rapidly after circulation was restored. Twitch and tetanic torque declines were significantly different between SOL and TA (fall between rest and fatigue -SOL: 77%, 75.2%; TA: 95.5%, 96.9%, P<0.01, respectively). M-wave changes between the two muscles were not significantly different although the onset of the decline was delayed in the SOL. It is proposed that the observed delay in fatiguing decline was due to the early potentiation in muscle excitability observed in the SOL but not in the TA.

Action Potentials↗
PubMed2001

Use of a cold cathode for percutaneous stimulation of human plantarflexor muscles.

Prolonged, supramaximal stimulation of the soleus muscle is painful to humans. A method is proposed whereby percutaneous, supramaximal stimulation is possible using a cold cathode. Cooling the skin exposed to the stimulating current results in a sufficient anaesthesia of nociceptive cutaneous afferent nerves. This occurs without concomitant cooling of the muscle mass deep to the skin and subcutaneous tissue.

Anesthesia↗
PubMed2001

Enhancing the ability of gait analyses to differentiate between groups: scaling gait data to body size.

One goal of gait analysis is to distinguish clearly between a set of abnormal gait values measured from a patient referenced to a comparable population. However, the comparable population is often composed of individuals of various heights and weights, which increases inter-subject gait value variation which reduces the ability of a statistical test to identify a set of gait data outcomes with evaluative properties. Therefore, scaling gait data, based on subject leg length and mass, is commonly used to decrease the inter-subject variation but the efficacy of these methods is unknown. In this paper each of eight scaling strategies (none, ad hoc, dimensionless numbers, and five connected strategies based on similarity, dimensional analysis and muscle properties) were used to modify a set of gait data outcomes acquired from 10 individuals spanning a wide range of height (1.33-1.96 m) and mass (42.3-148.8 kg). These data were then examined to select that strategy and those scaling factors which maximally reduced inter-subject variation. The ad hoc, dimensionless numbers, and dynamic/mechanical/elastic (diameter of a limb (D) proportional to it's length (L) to the 1.5 power; time proportional to L(2) D(-1)) scaling strategies reduced the global inter-subject gait data outcome variation to 44% of its un-scaled value. Considering ten commonly reported gait data outcomes (temporal and spatial (stride time, stride length, progression velocity), kinematic (angles in the sagittal and frontal planes, angles in the transverse plane), external kinetic (ground reaction force and moment), and internal kinetic (joint force, moment, and power)) these three scaling strategies provided the largest number of minimum inter-subject variations (10, 10, and 9, respectively). Reduced inter-subject variation in gait data outcomes increases the ability of a statistical tool to detect a difference between a patient and a comparable group. With a statistically significant difference a clinician can then decide if this patient's gait pattern clinically deviates from that of the comparable group and an appropriate intervention warranted. The ad hoc, dimensionless numbers, and the dynamic/mechanical/elastic scaling strategies all reduce maximally the inter-subject variation in gait data outcomes.

Adolescent↗
PubMed2001

Use of orthoses lowers the O(2) cost of walking in children with spastic cerebral palsy.

PURPOSE: The aim of this study was to assess the effects of hinged ankle foot orthoses (AFO) on the metabolic and cardiopulmonary cost of walking and gross motor skills of children with cerebral palsy (CP). METHODS: Ten habitual users of hinged AFO with spastic diplegic CP (9.01 yr +/- 2.10) participated in the study. Expired gas and heart rate (HR) were measured during sitting and with AFO on and off during steady state treadmill walking at three speeds: 3 km.h(-1), comfortable walking speed (CWS), and 90% of their fastest walking speed (FWS). Comfortable and fastest ground walking speed and Gross Motor Function Measure scores were also assessed with AFO on and off and analyzed with ANOVA. Because not all children could walk at all speeds on the treadmill, an ANOVA was performed on data for children who walked at 3 km.h(-1) and CWS (N = 8 for HR; N = 9 for pulmonary ventilation and metabolic variables) and a t-test on data at 90% of FWS (N = 9 for HR; N = 8 for pulmonary ventilation and metabolic variables). RESULTS: When children wore their AFO net oxygen uptake (L.min(-1), absolute--sitting values) was significantly (P < 0.05) reduced by 8.9% at 3 km.h(-1) and by 5.9% at 90% of FWS. Net pulmonary ventilation (L.min(-1)) was significantly (P < 0.05) lower with AFO on by 10.3% but only at 3 km.h(-1). AFO did not affect net HR (beats.min(-1)) nor the respiratory exchange ratio at any speed, nor any physiologic variable at CWS, nor gross motor skills. CONCLUSIONS: Use of hinged AFO reduces the oxygen and ventilatory cost of walking in children with spastic diplegic CP.

Ankle Joint↗
PubMed2000

Developmental apraxia arising from neonatal brachial plexus palsy.

OBJECTIVE: To determine whether motor unit activation is impaired in patients with persisting disability arising from neonatal brachial plexus palsy (NBPP). BACKGROUND: In NBPP patients, the authors previously found more extensive muscle reinnervation than might have been anticipated from the clinical examination. METHODS: Motor skills were tested in a group of nine boys and seven girls with prior NBPP, who then underwent physiologic investigation of proximal and distal muscles in their affected and unaffected arms. The latter tests comprised measurements of maximal evoked muscle compound action potential (M-wave) amplitude, maximal voluntary torque, twitch torque, and twitch interpolation. A group of 17 children of similar ages served as control subjects. RESULTS: In the NBPP group, motor skills were diminished and voluntary torque was reduced relative to M-wave amplitude and twitch torque. Moreover, interpolated twitches could be demonstrated in some NBPP patients but not in control subjects. CONCLUSION: Persisting disability in NBPP patients is due, at least in part, to impaired motor unit activation. The authors suggest that the impairment is a form of developmental apraxia caused by defective motor programming in early infancy.

Action Potentials↗
PubMed1997

Loss of twitch torque following muscle compression.

With the elbow flexed, compression of the human biceps brachii has been found to reduce twitch torque, with an approximately linear relationship being observed between the loss of torque and the applied pressure (up to 45 kPa). The decline in torque could no longer be demonstrated when the biceps muscle was stretched, by extending the elbow from a flexed position. The loss of torque in the flexed position appeared to be due to an inability of muscle sarcomeres to bulge sufficiently to take up the series elasticity at the fiber ends.

Adult↗
PubMed1996

Potentiation and depression of the M wave in human biceps brachii.

1. The effects of repeated excitation on the compound action potential, or M wave, of mammalian muscle fibres have been investigated in the human biceps brachii. 2. During continuous indirect stimulation at 10 and 20 Hz the mean voltage-time area of the M wave doubled within the first minute, while the mean peak-to-peak amplitude increased by approximately half. The enlargement of the M wave was sustained during stimulation at 10 Hz but not at 20 Hz. Stimulation at 3 Hz caused a small increase which was significant for M wave amplitude only. 3. When the 20 Hz stimulation was performed under ischaemic conditions, the M wave first enlarged and then gradually declined. After 20 Hz stimulation was discontinued, the M wave increased in size; in the ischaemic experiments the release of the cuff produced a further, rapid augmentation. In both the ischaemic and non-ischaemic experiments, the amplitudes and areas of the M waves during the recovery period became significantly larger than the resting values (range, 15-60% at the endplate zone). 4. The mean muscle fibre impulse conduction velocity decreased to less than half the resting value during 20 Hz stimulation, with or without ischaemia, and then increased above the resting value during recovery. 5. On the basis of previous experiments in animals, the augmentation of the M wave was attributed to enhanced electrogenic Na(+)-K+ pumping, and the biceps brachii appeared to be an excellent preparation for studying the time course of this enhancement.

Action Potentials↗
PubMed1996

Changes in motor unit estimates with aging.

Elderly persons usually exhibit some degree of muscle atrophy, together with a reduction in voluntary strength, but there is still argument concerning the nature of the cellular events involved. This issue was reexamined by estimating the numbers and relative sizes of motor units in three limb muscles, using a fully automated system (Galea et al., 1993). In 79 healthy volunteers aged 20-98 years, estimations of motor unit numbers were performed on the thenar, biceps brachii, and extensor digitorum brevis muscles. Motor unit populations were noted to decrease significantly with age in the distal muscles but appeared to remain constant in the biceps. The excitable muscle fiber mass, as reflected in the peak-to-peak amplitude and area of the maximum M-wave, was diminished in all three muscles. Although the area of the average motor unit action potential was not significantly different between groups, the ratio of this potential to the M-wave area increased with increasing age. The results suggest that muscle deterioration in the elderly is due to a combination of changes in the muscle fibers and in their nerve supply and that the extent may differ between proximal and distal muscles.

Action Potentials↗
PubMed1994

Pseudofacilitation: a misleading term.

The possible causes of the transient enlargement of muscle compound action potentials during repetitive stimulation ("pseudofacilitation") are considered. The phenomenon cannot be due to mechanical artefact, while hypersynchronization of the muscle fiber action potentials, the usual explanation, can only make a minor contribution. A more convincing explanation, for which there is now experimental evidence, is that the muscle fibers undergo hyperpolarization, due to the intramuscular release of norepinephrine and consequent stimulation of the electrogenic Na+,K(+)-pump. Defective phosphorylation of the Na+,K(+)-pump is a possible cause of the transient weakness and myotonia in myotonic dystrophy.

Action Potentials↗
PubMed1993

Motor unit populations in healthy and diseased muscles.

The numbers of functioning motor units can be estimated in proximal and distal muscles of human limbs by an electrophysiological technique in which the mean sizes of the motor unit potentials are compared with the maximum M-waves of the same muscles. Although manual methods of estimation have been used successfully in the past, the introduction of automated techniques has brought considerable advantages, including greater objectivity and reduced contamination of the results by "alternation." In healthy subjects, the intrinsic muscles of the hand have approximately 100 motor units each, and the biceps brachii muscle has only slightly more. With advancing age, there is a loss of motor units, which appears to be more pronounced in distal muscles. The motor unit estimating methodology has been found to be of value in the diagnosis and assessment of patients suspected of having muscle denervation. In amyotrophic lateral sclerosis, the mean rate of motor unit loss is swift, whereas in late-onset cases of spinal muscular atrophy, the reduction in the motor unit population does not appear to progress. In only the most rapidly deteriorating cases of post-polio syndrome is it possible to demonstrate further loss of motor units. In all of these denervating disorders, and in peripheral neuropathies, the importance of collateral reinnervation as a compensatory mechanism is emphasized.

Adaptation, Physiological↗
PubMed1991

The numbers and relative sizes of motor units estimated by computer.

A fully automated system is described for estimating the numbers and relative sizes of functioning motor units in proximal and distal muscles of the arm and leg. In this system, a computer controls the motor nerve stimulation, and analyzes the potentials evoked from the muscles; a subprogram searches for instances of "alternation." In 33 healthy volunteers, aged 21 to 56 years, the median-innervated thenar muscles of one hand were tested 2 to 3 times; the mean motor unit estimate was 228 +/- 93 SD. For similar numbers of biceps brachii, extensor digitorum brevis, and vastus medialis muscles, the respective mean values were 113 +/- 40, 131 +/- 45, and 229 +/- 108 units. The reproducibility of the method was such that the overall coefficient of variation, for the normalized results from the 121 muscles studied, was 22%. The reliability of the automated method was doubled if 3 estimates, rather than one, were performed on each muscle. Comparisons of the results obtained by automated and "manual" methods indicated that the computer-derived values tended to be lower by approximately 33%.

Action Potentials↗
PubMed1990

Regional bone mineral measurements.

Total body dual-photon transmission scanning was performed in 9 control persons, 15 athletes and in 5 patients with eating disorders. Total body bone mineral mass was measured, with a reproducibility of 2%; for regional bone mineral mass the reproducibility was 4%. The fraction of total bone mineral in the spines and heads of women is greater than in men. Patients with eating disorders have a smaller fraction of total body mineral in the pelvis than female controls. Weight lifters have a significantly greater mineral mass in the trunk region than other athletes and male controls. These and other differences are consistent with the conclusion that total body dual-photon absorptiometry allows quantitation of the distribution of mineral within the skeleton.

Absorptiometry, Photon↗
PubMed1990

Body composition by photon absorptiometry.

Whole-body dual photon measurements of body composition were made in 9 controls, 15 athletes and 5 patients with eating disorders. Measurements of lean body mass, mineral mass and fat mass were accurate. Lean body mass and fat mass were measured with reliabilities of about 0.8 kg while for total body bone mineral mass, the reliability was about 60 g. Women had a smaller lean body mass and a greater fat mass than men. Women with eating disorders had the same body composition as males. Measurements of body composition by dual photon absorptiometry are safe and reliable.

Absorptiometry, Photon↗