Biomedical subjects

C L Vaughan

Publications and source records attributed to C L Vaughan.

At least 19 recordsLinked to original sources

PubMed2006

Non-random fluctuations in power output during self-paced exercise.

OBJECTIVES: To analyse the power output measured during a self-paced 20-km cycling time trial, during which power output was free to vary, in order to assess the level and characteristics of the variability in power output that occurred during the exercise bout. METHODS: Eleven well-trained cyclists performed a 20-km cycling time trial, during which power output was sampled every 200 m. Power spectrum analysis was performed on the power output data, and a fractal dimension was calculated for each trial using the Higuchi method. RESULTS: In all subjects, power output was maintained throughout the trial until the final kilometre, when it increased significantly, indicating the presence of a global pacing strategy. The power spectrum revealed the presence of 1/f-like scaling of power output and multiple frequency peaks during each trial, with the values of the frequency peaks changing over the course of the trial. The fractal dimension (D-score) was similar for all subjects over the 20-km trial and ranged between 1.5 and 1.9. CONCLUSIONS: The presence of an end spurt in all subjects, 1/f-like scaling and multiple frequency peaks in the power output data indicate that the measured oscillations in power output during cycling exercise activity may not be system noise, but may rather be associated with system control mechanisms that are similar in different individuals.

Adult↗

PubMed2004

Three-dimensional point localisation in low-dose X-ray images using stereo-photogrammetry.

A stereo-photogrammetric method for three-dimensional reconstruction of points in low-dose digital X-ray images obtained using a scanner with similar imaging geometry to that of computed tomography scan projection radiography, was analysed. A calibration frame containing 25 radio-opaque markers with known three-dimensional locations was scanned, and the accuracy of reconstruction of the marker positions under varying control point configurations and separation angles was assessed. Errors of less than 1 mm were obtained when nine test points were reconstructed, with 16, 11 and 7 control points at a 90 degrees separation angle, and with 16 and 11 control points at 75 degrees and 60 degrees separation angles. The optimum reconstruction, with a resultant error of 0.68 mm, was found to occur at a separation angle of 90 degrees, with the largest number of control points (16) used to calculate the parameters of the transformation. Extrapolation in the scanning direction beyond the space defined by the control points gave errors of less than 2 mm. This method should be suitable for three-dimensional point reconstruction in applications such as cephalometry, brachytherapy planning and assessment of spinal shape.

Humans↗

PubMed2003

Rectification and non-linear pre-processing of EMG signals for cortico-muscular analysis.

Rectification of the electromyographic (EMG) signal is a commonly used pre-processing procedure that allows detection of significant coherence between EMG and measured cortical signals. However, despite its accepted and wide-spread use, no detailed analysis has been presented to offer insight into the precise function of rectification. We begin this paper with arguments based on single motor unit action potential (AP) trains to demonstrate that rectification effectively enhances the firing rate information of the signal. Enhancement is achieved by shifting the peak of the AP spectrum toward the lower firing rate frequencies, whilst maintaining the firing rate spectra. A similar result is obtained using the analytic envelope of the signal extracted using the Hilbert transform. This argument is extended to simulated EMG signals generated using a published EMG model. Detection of firing rate frequencies is obtained using phase randomised surrogate data, where the original EMG power spectrum exceeds the averaged rectified surrogate spectra at integer multiples of firing rate frequencies. Model simulations demonstrate that this technique accurately determines grouped firing rate frequencies. Extraction of grouped firing rate frequencies prior to coherency analyses may further aid interpretation of significant cortico-muscular coherence findings.

Action Potentials↗

PubMed2003

Eye feature extraction for diagnosing the facial phenotype associated with fetal alcohol syndrome.

Victims of fetal alcohol syndrome (FAS) exhibit a unique facial phenotype that is emphasised in diagnosis. Among the characteristic facial features, several occurring in the region of the orbits can be evaluated quantitatively using distance measurements. An algorithm is described for automatic extraction and measurement of eye features from stereo photographs. The algorithm was applied to photographs of 46 six-seven-year-old children. The approach relies on peak and valley maps and integral projection functions, to locate the eyes and extract the iris, and genetic algorithms to fit cubic splines to the upper and lower eyelids. Measurements obtained automatically using this algorithm were compared with measurements obtained manually from the photographs. Mean absolute differences between automatic and manual measurements were less than 1 mm for palpebral fissure length (PFL) and interpupillary distance (IPD). Absolute differences were less than 1 mm for 80.4% of PFLs and 100% of IPDs. Inner canthal distance and outer canthal distance did not compare favourably with manual measurements.

Algorithms↗

PubMed2003

EMG amplitude in maximal and submaximal exercise is dependent on signal capture rate.

This study analysed the effect of different electromyographic (EMG) capture rates during maximal voluntary contraction, submaximal and maximal dynamic cycling activity on EMG amplitude and signal characteristics. Ten healthy subjects participated in this study. Peak power output (PPO) and maximal isometric force output (MVC) were measured, followed by a progressive cycle ride on a cycle ergometer. Electromyographic (EMG) data were simultaneously captured during the MVC and cycling activities at frequencies of 32, 64, 128, 256, 512, 1024 and 1984 Hz. Significant differences in amplitude were found (p < 0.01) between MVC, submaximal (SUB) and maximal cycling activities (PWATT) for all capture rates. Asymptote values for IEMG amplitude occurred at EMG capture rates of 1604 +/- 235.6 Hz during MVC, 503.1 +/- 236.2 Hz during PWATT and 326.2 +/- 105.4 Hz during SUB cycling activity and were significantly different (p < 0.01). No significant differences were found for force/EMG ratios between PWATT and MVC at 1984 Hz capture rates (3.8 +/- 1.7 N/V vs 2.5 +/- 0.9 N/V) while significant differences occurred at 32 Hz capture rate (6.2 +/- 3.8 vs 16.0 +/- 8.0; p < 0.01). Low correlations were found between EMG activity captured at 1984 Hz during PWATT and lean thigh volume (r = 0.36) and MVC (r = 0.32). Asymptote values found on this study suggest that data captured below 326 Hz for SUB, 503 Hz for PWATT and 1604 Hz for MVC are not reliable. Therefore apparatus capturing EMG data at low frequencies from these values cannot be used for quantitative data analyses.

Adult↗

PubMed2002

A stereo-photogrammetric method to measure the facial dysmorphology of children in the diagnosis of fetal alcohol syndrome.

In diagnosing a child with fetal alcohol syndrome (FAS), anthropometric measurements of the face are conventionally performed by highly trained dysmorphologists using a hand-held ruler. This renders the screening of large populations of children for the facial features characteristic of FAS very time-consuming and costly. This study proposes a new, cost-effective, and non-intrusive method to measure in three dimensions the facial dysmorphology of children using stereo-photogrammetry. The face of each child is photographed in a control frame simultaneously by a pair of high-resolution digital cameras mounted 1.04 m from the child and 0.26 m apart. Software has been developed to calibrate the images and to compute the three-dimensional object-space coordinates of any point on the face from a measurement of the point on each of the images. The palpebral fissure lengths, inner canthal-, and interpupillary distances of 44 subjects were measured in this manner independently by two investigators and compared with measurements obtained by clinical specialists in the conventional manner. There was found to be no statistically significant difference between palpebral fissure lengths determined using the two techniques (paired Student's t-test p-values are 0.29 and 0.18, respectively). It has also been demonstrated that facial measurements can be performed with greater consistency from a pair of stereo photographs than direct measurements from live subjects.

Anthropometry↗

PubMed2001

Functional roles of ankle and hip sagittal muscle moments in able-bodied gait.

OBJECTIVE: The main objectives of this study on able-bodied gait were (a) to identify the main functions of the ankle and hip muscle moments and their contribution to support and propulsion tasks, and (b) to illustrate the interaction between the ankle and hip moment activities. DESIGN: Twenty young, able-bodied male subjects walked along a 13 m path at a freely chosen speed. BACKGROUND: Functional contributions of the ankle and hip muscles and their interactions in achieving support and propulsion tasks during gait are still subject to controversy. METHODS: Principal component analysis was applied as a curve structure detection method to identify the main functional characteristics of the ankle and hip muscle moments. The first two principal components which contained over 70% and 85%, respectively, of the information in the ankle and hip moment curves revealed their functional tasks. Ankle versus hip moment plots was used to illustrate the interactions between muscles acting at the hip and ankle in the sagittal plane. Correlation coefficient and covariance calculations quantified the interaction between the ankle and hip moments. RESULTS: The first principal component revealed that the main role of the ankle and hip is to keep the body from collapsing. The second principal component is associated with the functional contribution of both ankle plantarflexors and hip flexors during the propulsion phase (50-60% of the gait cycle). High coordination (r=0.82) between the ankle and hip moments was observed. CONCLUSION: Maintaining body support against gravity was identified as the first functional task of the ankle plantarflexors and hip extensors, while contribution to propulsion was recognised as the second major role for the ankle plantarflexors and hip flexors. RELEVANCE: Identifying the main roles of the muscles acting at the hip and ankle during able-bodied walking provides better insight into how pathological gait should be evaluated.

Adult↗

PubMed2000

Spectral compression of the electromyographic signal due to decreasing muscle fiber conduction velocity.

Spectral compression of the electromyographic (EMG) signal, due largely to decreasing muscle fiber conduction velocity, is commonly used as an indication of muscle fatigue. Current methods of estimating conduction velocity using characteristic frequencies such as the median frequency of the power spectrum, are based on an assumption of uniform spectral compression. To examine changes in the EMG frequency spectrum during fatigue, muscle fiber conduction velocity was measured during sustained, isometric contractions of the biceps brachii. Compression of the EMG power and amplitude spectra was simultaneously examined using the median frequency and an alternative method-the spectral distribution technique. The spectral distribution technique consistently gave a better estimate of the relative change in muscle fiber conduction velocity than either of the median frequencies. This was further examined using a physiologically based EMG simulation model, which confirmed these findings. The model indicated that firing statistics can significantly influence spectral compression, particularly the behavior of characteristic frequencies in the vicinity of the firing rates. The relative change in the median frequency, whether of the amplitude or frequency spectrum, was consistently greater than the relative change in conduction velocity. The most accurate indication of the relative change in conduction velocity was obtained by calculating the mean shift in the midfrequency region of the EMG amplitude spectrum using the spectral distribution technique.

Action Potentials↗

PubMed1999

Effect of dopamine denervation and dopamine agonist administration on serine phosphorylation of striatal NMDA receptor subunits.

Sensitization of striatal N-methyl-d-aspartate (NMDA) receptors has been implicated in the pathogenesis of the response alterations associated with dopaminomimetic treatment of parkinsonian animals and patients. To determine whether serine phosphorylation of NMDA receptor subunits by activation of Ca2+/calmodulin-dependent protein-kinase II (CaMKII) contributes to this process, we examined the effects of unilateral nigrostriatal ablation with 6-hydroxydopamine and subsequent treatment with levodopa, SKF 38393 (D1-preferring dopamine agonist), or quinpirole (D2-preferring agonist) on motor responses and phosphorylation states. Three weeks of twice-daily levodopa administration to rats shortened the duration of their rotational response to levodopa or SKF 38393 challenge, but prolonged the duration of quinpirole-induced rotation. At the same time, levodopa treatment elevated serine phosphorylation of striatal NR2A (p<0.02), but not that of NR2B subunits, without associated changes in subunit protein levels. Chronic treatment with SKF 38393 increased NR2A (p<0.0001) but decreased NR2B (p<0.004) serine phosphorylation. In contrast, chronic quinpirole treatment had no effect on NR2A but increased NR2B phosphorylation (p<0.0001). The acute intrastriatal injection of the CaMKII inhibitor KN93 (1.0 micrograms) not only normalized the levodopa-induced motor response alterations but also attenuated the D1 and D2 receptor-mediated serine phosphorylation of NR2A and NR2B subunits, respectively (p<0.02). These results suggest that a CaMKII-mediated rise in serine phosphorylation of NMDA receptor subunits induced by intermittent stimulation of D1 or D2 dopaminergic receptors contributes to the apparent enhancement in striatal NMDA receptor sensitivity and thus to the dopaminergic response plasticity in levodopa-treated parkinsonian rats.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1998

Enhanced tyrosine phosphorylation of striatal NMDA receptor subunits: effect of dopaminergic denervation and L-DOPA administration.

Sensitization of striatal N-methyl-D-aspartate receptors (NMDAR) has been linked to events leading to the motor response changes associated with the administration of dopaminomimetics to parkinsonian animals and patients. To determine whether tyrosine phosphorylation of NMDAR subunits contributes to the apparent long-term enhancement in synaptic efficacy of these receptors, we examined the effect of unilateral nigrostriatal dopamine system ablation with 6-hydroxydopamine followed by twice-daily treatment with l-DOPA on the phosphorylation state of rat striatal NR2A and NR2B subunits. Three weeks of intermittent l-DOPA administration produced a shortening in the duration of the rotational response to dopaminergic challenge and other changes mimicking those occurring in patients with Parkinson's disease. Concurrently, tyrosine phosphorylation of NR2A and especially of NR2B subunits increased ipsilateral to the lesion (20+/-5% and 46+/-7% of intact striatum, respectively; p<0.01) without attendant changes in subunit protein levels. Selective blockade of NR2B subunits with ACEA 10-1244, but not of NR2A subunits with MDL 100,453, reversed the l-DOPA-induced response alterations. The intrastriatal injection of a tyrosine kinase inhibitor, genistein, at a dose (2.0 microg) that normalized the response shortening, attenuated the NR2A and NR2B phosphorylation increase by about 12% and 24%, respectively (p<0.01). Taken together, these results suggest that augmented tyrosine phosphorylation of NR2B subunits, alone or in combination with the smaller rise in NR2A subunit phosphorylation, contributes to the apparent enhancement in striatal NMDAR sensitivity and thus to the plastic alterations in dopaminergic responses in l-DOPA-treated parkinsonian rats.

Animals↗

PubMed1998

Gait assessment of fixed ankle-foot orthoses in children with spastic diplegia.

OBJECTIVE: To evaluate the effectiveness of ankle-foot orthoses (AFOs) in spastic diplegic cerebral palsy patients for whom orthoses were indicated to control equinus or pes planovalgus deformities. DESIGN: A retrospective, cross-sectional assessment was performed on diplegic subjects who had suitable barefoot and AFO gait trials on the same day. PATIENTS: Thirty-five subjects with a mean age of 8.7 yrs were included. Eighteen wore braces to control equinus and 17 to control pes planovalgus and crouch. OUTCOME MEASURES: Gait data assessed in all subjects included temporal-distance factors and sagittal kinematics. Force plate data to determine joint moments and powers were obtained in 20. Repeated measures analysis of variance was used to compare across conditions and indications. RESULTS: The cohort demonstrated increased velocity (10 cm/sec; p < .001), stride length (10 cm; p < .001), and percent single-limb support (1.8%; p < .002) using AFOs compared with barefoot gait. In braces, ankle excursion was reduced (p < .0001), while pelvic, hip, and knee excursions were increased to account for the temporal changes (p < .009). Effects were similar in both indication groups. In neither indication group did the AFO significantly alter knee position in stance. Kinetic analysis showed a reduction of abnormal power burst (p < .05) in early stance and an increase in late stance ankle moment (p < .05) with AFOs. Differences in gait characteristics and bracing effects are shown for both indication groups. CONCLUSION: Compared with barefoot gait, AFOs enhanced gait function in diplegic subjects. Benefits resulted from elimination of premature plantar flexion and improved progression of foot contact during stance. Effects on proximal joint alignment were not significant.

Adolescent↗

PubMed1998

Gait before and 10 years after rhizotomy in children with cerebral palsy spasticity.

OBJECT: Selective dorsal rhizotomy is a neurosurgical procedure performed for the relief of spasticity in children with cerebral palsy, but its long-term functional efficacy is still unknown. The authors sought to address this issue by means of an objective, prospective study in which quantitative gait analysis was used. METHODS: Eleven children with spastic diplegia (mean age at initial surgery 7.8 years) were evaluated preoperatively in 1985 and then at 1, 3, and at least 10 years after surgery. For comparison, 12 age-matched healthy individuals were also studied. Retroreflective targets were placed over the hip, knee, and ankle joints, and each individual's gait was videotaped. The video data were subsequently entered into a computer for extraction and analysis of the gait parameters. An analysis of variance yielded a significant time effect (p < 0.05), and post hoc comparisons revealed differences before and after surgery and with respect to the healthy volunteers. The knee and hip ranges of motion (59 degrees and 44 degrees, respectively, for healthy volunteers) were significantly restricted in children with spastic diplegia prior to surgery (41 degrees and 41 degrees, respectively), but were within normal limits after 10 years (52 degrees and 45 degrees, respectively). The knee and hip midrange values (31 degrees and 3 degrees, respectively, for healthy volunteers), indicative of posture, were significantly elevated preoperatively (42 degrees and 15 degrees) and increased sharply at 1 year (56 degrees and 18 degrees), but by 10 years they had decreased to within normal limits (36 degrees and 9 degrees). Step length and velocity improved postoperatively but were not within the normal range after 10 years. Ten years after surgery these patients not only had increased ranges of motion, but also used that movement at approximately a normal midrange point. CONCLUSIONS: Selective dorsal rhizotomy is an effective method for alleviating spasticity. Furthermore, the authors provide evidence to show that lasting functional benefits, as measured by improved gait, can also be obtained.

Adolescent↗

PubMed1997

Anterior cruciate ligament reconstruction and joint dynamics during stair climbing.

Athletes with anterior cruciate ligament (ACL) deficiencies exert decreased knee extension moments during level walking (quadriceps avoidance gait), and yet within a few months of ACL reconstruction they are often expected to return to competitive sport. To investigate this issue further, 10 normal subjects and seven ACL deficient patients were evaluated both pre- and post-operatively (mean follow-up of 6 months), and each performed multiple trials ascending a staircase which consisted of three steps. Bilateral joint angles, moments, powers, and work were measured and the data were ensemble averaged and statistically analyzed (repeated measures ANOVA with significance level set at 0.05). Anterior-posterior knee laxity decreased significantly (from 7.9 mm to 5.8 mm) while subjective knee function also improved following ACL reconstruction (knee score increased from 70.4 to 88.5). Pre-operatively, there were no statistically significant differences in biomechanical parameters between the patients' ACL-deficient and intact sides and the normal subjects. Post-operatively, however, statistically significant reductions were seen for the peak moment (91.9 vs 22.5 Nm), power (181 vs 84 W), and work performed (28.0 vs -5.6 J) at the injured knee, which was also the knee from which the patellar tendon graft had been harvested. These reductions were accommodated by significant increases in excursion, moment, and power at the contralateral ankle joint. The results indicate that while the ACL reconstruction were successful in restoring anterior-posterior knee stability, the decrease in knee power and work performed post-operatively by the injured (i.e., donor) knee suggests that donor site morbidity may need to be critically evaluated over a long-term period.

Adolescent↗

PubMed1997

Fuzzy clustering of children with cerebral palsy based on temporal-distance gait parameters.

Temporal-distance parameters for 88 children with the spastic diplegia form of cerebral palsy (CP) are grouped using the fuzzy clustering paradigm. The two features chosen for clustering are stride length and cadence which are normalized for age and leg length using a model based on a population of 68 neurologically intact children. Using information provided by the neurologically intact population and cluster validity techniques, five clusters for the children with cerebral palsy are identified. The five cluster centers represent distinct walking strategies adopted by children with cerebral palsy. Utilizing just four easily obtained parameters--stride length, cadence, leg length and age--and a small number of simple equations, it is possible to classify any child with spastic diplegia and to generate an individual's membership values for each of the five clusters. The clinical utility of the fuzzy clustering approach is demonstrated with pre- and post-operative test data for subjects with cerebral palsy (one neurosurgical and one orthopaedic) where changes in membership of the five clusters provide an objective technique for measuring improvement. This approach can be adopted to study other clinical entities where different cluster centers would be established using the algorithm provided here.

Adolescent↗

PubMed1996

Abduction-adduction moments at the knee during stair ascent and descent.

To examine the relative magnitude of the knee abduction-adduction moments during stair climbing, ten normal subjects (average weight 660 N, leg length 0.962 m, height 1.74 m) were studied during repeated trials of stair ascent and descent. Data were collected using a four-camera video system and two forces plates incorporated within a flight of three stairs. The inverse dynamics approach was used to calculate internal moments at the knee, and these moments were normalized in magnitude (to percent body weight and leg length) and time (percent stance). The primary findings were: (1) knee joint moments were similar in shape and magnitude for the first and second steps during both stair ascent and descent; (2) the abduction knee moments, although comparable in magnitude (25-45 Nm), were statistically smaller than the extension moments (60-85 Nm) for stair ascent and descent; and (3) the moment patterns were exclusively abductor throughout stance, indicating that the ground reaction vector always passed medial to the knee joint center. Although the knee abduction-adduction moment is not in the primary plane of motion, its magnitude should not be ignored when trying to understand the stability and function of the knee during stair climbing.

Adult↗

PubMed1995

Fundamental patterns of bilateral muscle activity in human locomotion.

Human gait is characterized by smooth, regular and repeating movements but the control system is complex: there are many more actuators (i.e. muscles) than degrees of freedom in the system. Statistical pattern-recognition techniques have been applied to examine muscle activity signals, but these have all concentrated exclusively on unilateral gait. We report here the application of factor analysis to the electromyographic patterns of 16 muscles (eight bilateral pairs) in ten normal subjects. Consistent with our prior work, we have established two factors, named loading response and propulsion, which correspond with important phases in the gait cycle. In addition, we have also discovered a third factor, which we have named the coordinating factor, that maintains the phase shift between the left and right sides. These findings suggest that the central nervous system solves the problem of high dimensionality by generating a few fundamental signals which control the major muscle groups in both legs.

Adult↗

PubMed1995

Effect of foot-progression angle on hip joint moments during gait.

Loosening has emerged as the most serious long-term complication of total hip replacement and torsional loading of the femoral implant has been implicated as a possible cause. In an effort to explore a strategy for minimizing this risk, the following hypothesis was tested: the foot-progression angle has a significant effect on the resultant hip moments, and particularly the internal-external rotation moment, during level walking. Twelve normal subjects performed a total of nine trials: three in which they walked normally with the right foot pointing approximately straight ahead; three in which they were told to walk with the foot internally rotated approximately 30 degrees; and three in which the foot was externally rotated about 30 degrees. The inverse dynamics approach was used to integrate the body segment parameter, kinematic and force plate data, and to solve for the resultant moment at the right hip joint. In all three conditions--foot straight, foot in, and foot out-the subjects walked at the same average speed of 1.5 (+/- 0.3) ms-1. For the flexion-extension moment (where the maximum flexion moment of 95 Nm was in good agreement with other published data), there was no significant difference between the three foot orientation conditions. For the abduction-adduction moment, the foot straight condition exhibited the classic double peak pattern with a maximum abductor moment of 57 Nm, and there was no statistically significant difference between the three curves.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Muscle response to heavy resistance exercise in children with spastic cerebral palsy.

Fourteen ambulatory children with spastic diplegia participated in a bilateral quadriceps strengthening program in an attempt to decrease the amount of knee crouch during gait. Each child exercised three times a week for six weeks using free ankle weights at a load of 65 per cent of maximum. A normal comparison group of 25 children was also tested under identical conditions. Children with cerebral palsy were significantly weaker in the quadriceps and hamstrings muscle groups than controls. Quadriceps strength increased significantly at all three angles of knee flexion as a result of the weight-training program and did not differ statistically from normal at the end of the program. Quadriceps weakness was shown to be a factor in crouch gait; restoring strength through resistance exercise may be a useful adjunct in the treatment of cerebral palsy.

Adolescent↗