Biomedical subjects

W F Brown

Publications and source records attributed to W F Brown.

At least 19 recordsLinked to original sources

PubMed2005

Estimation of feeding value of four tropical forage species at two stages of maturity.

The feeding value of four tropical grasses was assessed through voluntary intake and digestibility studies using yearling Brahman x British steers (average BW = 256 +/- 34 kg). The digestibility of OM was estimated using total fecal collection (TFC), in vitro OM digestibility (IVOMD), and by estimating fecal production using insoluble acid detergent fiber (IADF) as an indigestible marker. The four grasses consisted of bahiagrass (Paspalum notatum), limpograss (Hemarthria altissima), bermudagrass (Cynodon dactylon), and stargrass (Cynodon spp.). Grass was harvested at two stages of maturity (approximately 4 and 10 wk). Forages were ground (5 to 10 cm) and offered to steers ad libitum. Forage treatments were assigned randomly to steers over eight 28-d periods and repeated over two consecutive years. Total forage offered and refused was determined during a 14-d sample collection period. For determination of fecal output, steers were placed into metabolism crates for 7 d. Composited samples of forage offered, forage refused, and feces of each steer at each period were analyzed for DM, OM, NDF, ADF, IADF, IVOMD, and CP. All digestibility results were calculated on an OM basis. There were year x grass x maturity interactions (P < 0.01) for all measures of forage quality, except CP. Increased maturity resulted in a 37.8% decrease (P < 0.001) in CP concentration when averaged across all forages. Four-week bermudagrass contained the greatest (P < 0.05) concentration of CP compared with all other grasses at both maturities, except 4-wk stargrass. Bahiagrass IVOMD did not differ among 4- and 10-wk maturities in both years; however, the IVOMD content of both stargrass and bermudagrass decreased (P < 0.05) when these forages matured from 4 to 10 wk. Apparent OM digestibility, determined by TFC, was greater (P < 0.05) than OM digestibility determined by IVOMD and IADF for all forages except bahiagrass, for which IADF did not differ from TFC. In Year 1, OM intake (OMI) of 10-wk limpograss was less (P < 0.05) than all other 4-wk forages. In Year 2, voluntary OMI of 10-wk limpograss was less (P < 0.05) than all grass x maturity combinations, except for 10-wk bermudagrass. These data suggest that important differences exist in changes in nutrient quality associated with increased maturity in tropical forages. Among the forages assessed in this study, bahiagrass seems to better retain nutrient quality when maturing from 4 to 10 wk.

Age Factors↗

PubMed2001

Contractile properties of human motor units in health, aging, and disease.

The primary function of skeletal muscle is to produce force for postural control and movement. Although the contractile properties of the whole muscle are useful functional indicators, they do not accurately reflect the heterogeneity of the constituent motor units (MUs) and their changes in health and disease. However, data on the contractile properties of human MUs, in comparison to other animal species, are relatively sparse. This, in part, is due to greater methodological challenges of in vivo studies of MUs in the human. The purpose of this review is to critically appraise the methods used in humans; to describe the normative data from different muscle groups; to discuss differences between data from healthy humans and other animal species; and, last, to characterize changes of the MU contractile properties in aging, disease, and in response to intervention. Because the spike-triggered averaging technique can only be used to study the twitch properties, other methods were subsequently developed to measure a wider range of contractile properties. Although there is general agreement between human data and those from other animal species, major differences do exist. Potential reasons for these discrepancies include true biological differences, but differences in the techniques used may also be responsible. Although limited, measurement of MU contractile properties in humans has provided insight into the changes associated with aging and motoneuronal diseases and provides a means of gauging their adaptive capacity for training and immobilization.

Aging↗

PubMed2001

Urea and(or) feather meal supplementation for yearling steers grazing limpograss (Hemarthria altissima var. 'Floralta') pasture.

The unique relationship between TDN and CP concentration (low CP relative to TDN) in the whole-plant of 'Floralta' limpograss (Hemarthria altissima) may provide an opportunity for improving cattle performance through protein supplementation. In each of three consecutive years, yearling Brahman x British crossbred steers (initial weight approximately 270 kg) grazed limpograss during the summer and fall (five steers per ha, three pasture replications per treatment) and were fed liquid cane molasses-based supplements (1.4 kg DM daily) alone, or containing urea and(or) hydrolyzed poultry feather meal. In yr 1 and 2, protein supplementation did not influence ADG. In these years, pasture availability was in excess at all times, and visual observations indicated that the upper canopy contained abundant leaf. Pasture samples collected in a manner to simulate grazing had in vitro organic matter disappearance (IVOMD):CP ratios ranging from 6.5 to 8.1, and plasma urea nitrogen concentration in the blood of steers fed no supplemental protein was high (10.6 to 15.9 mg/dL), both not suggestive of a situation where providing a protein supplement might improve animal performance. In yr 3, ADG was improved (P < 0.05) by protein supplementation. Forage availability was in excess at the beginning of the trial but declined significantly as the trial progressed. At the end of the trial, forage IVOMD:CP ratio (11.1) and plasma urea nitrogen values of steers fed no protein supplement (6.6 mg/dL) were both suggestive of a situation where providing supplemental protein might improve animal performance. Grazing management of limpograss pasture can affect canopy composition, thereby influencing cattle response to protein supplementation. In cases where limpograss is moderately grazed resulting in abundant leaf in the grazed horizon, dietary energy:protein ratio can be balanced, and positive responses to protein supplementation may not be observed. Where limpograss is grazed more intensively resulting in greater quantities of stem in the upper pasture canopy, an imbalance of dietary protein (low) relative to energy can develop, increasing the opportunity for enhancing cattle performance through protein supplementation.

Animal Feed↗

PubMed2001

Source and level of energy supplementation for yearling cattle fed ammoniated hay.

Brahman x British crossbred steers were used in growth and digestion trials to evaluate the response of source (corn, sugar cane molasses, or soybean hulls) and feeding rate (0, 1.4, or 2.8 kg DM per steer daily in the growth trials; 0, 15, or 30% of the ration DM in the digestion trial) of energy supplementation in cattle fed ammoniated (4% of forage DM) stargrass (Cynodon nlemfuensis Vanderyst var. nlemfuensis) hay. Cattle on all treatments were fed 0.5 kg cottonseed meal daily. In the growth trials, steers grazed dormant bahiagrass (Paspalum notatum) pasture. Increasing the levels of supplementation decreased hay intake but increased total dietary intake for all diets (P < 0.07). Daily gain and feed efficiency of steers were improved (P < 0.03) with supplementation. Steers supplemented with corn or soybean hulls at 2.8 kg DM/d had a higher ADG (0.92 kg) and gain/feed (0.103) than steers supplemented with molasses (0.78 kg, 0.08, respectively) at the same level. Seven crossbred steers (200 kg) were used in a five-period digestion trial to evaluate apparent OM, NDF, ADF, and hemicellulose digestibility. Apparent OM digestibility of all diets increased linearly (P = 0.02) as the level of supplementation increased. Apparent NDF and ADF digestibility decreased (P < 0.03) as the level of supplementation with corn or molasses increased, whereas increasing the level of soybean hulls in the diet increased (P < 0.06) apparent NDF and ADF digestibility. Four ruminally fistulated crossbred steers (472 kg) were used in a 4 x 4 latin square design to investigate ruminal characteristics with energy supplementation at 30% of ration DM. Ruminal pH in steers supplemented with soybean hulls or corn declined after feeding. Ruminal pH decreased more rapidly with corn supplementation and remained below 6.2 for a longer period of time than with the other diets. Ruminal pH did not change within 24 h after feeding for steers fed the control or molasses diets. No change in total VFA concentration was observed in steers fed molasses or corn. Total ruminal VFA concentration in steers supplemented with soybean hulls increased initially after feeding and then declined within 24 h after feeding. Soybean hulls produced fewer negative associative effects than corn when fed with ammoniated stargrass hay at 2.8 kg DM/d. The reduced gain/feed of steers supplemented with molasses compared to soybean hulls or corn indicates that molasses was not utilized as efficiently as the other energy sources.

Ammonia↗

PubMed2000

Multifocal motor neuropathy improved by IVIg: randomized, double-blind, placebo-controlled study.

OBJECTIVE: To determine the effect of IV immunoglobulin (IVIg) on neurologic function and electrophysiologic studies in multifocal motor neuropathy with conduction block (MMN). BACKGROUND: MMN is characterized by progressive, asymmetric, lower motor neuron weakness and is probably immune-mediated. IVIg treatment has been shown to have beneficial effects in several open-label studies and in one small controlled trial. However, larger randomized controlled studies are lacking. METHODS: The authors recruited 16 patients with MMN. All subjects were given each of two treatments (IVIg [0.4 g/kg/d for 5 consecutive days] or placebo [dextrose or saline]) that were assigned according to a randomized, crossover design under double-blind conditions. Patients were evaluated before and about 28 days after trial treatment for subjective functional improvement, neurologic disability score, grip strength, distal and proximal compound muscle action potential amplitude, and conduction block. RESULTS: Subjective functional improvement with IVIg treatment was rated as dramatic or very good in nine patients, moderate in one, mild in one, and absent in five patients. This improvement was absent after placebo. The neurologic disability score improved by 6.7+/-3.3 points with IVIg treatment, whereas it decreased by 2.1+/-3.0 with placebo (p = 0.038). Grip strength on the weaker side was increased by 6.4+/-1.9 kg with IVIg treatment; it decreased by 1.0+/-0.8 kg with placebo (p = 0.0021). Conduction block worsened by 12.98+/-6.52 % with placebo, but improved by 12.68+/-5.62 % with IVIg treatment (p = 0.037). Conduction block was reversed in five patients with IVIg but not placebo. CONCLUSION: IVIg improved conduction block as well as subjective and objective clinical measures of function in patients with MMN.

Adult↗

PubMed2000

Human motor units in health and disease.

Recent advances in clinical neurophysiology have made it possible to non-invasively stimulate single motor axons and determine the physiological characteristics of the associated motor units. Some motor units lend themselves to longitudinal studies of their electrical and contractile characteristics. The former include the conduction velocities of their motor axons and the sizes and shapes of their motor unit action potentials and the latter such contractile characteristics of the motor unit as their contractile speeds, twitch and tetanic tensions, and resistance to fatigue. The feasibility of serially examining the same motor unit has made it possible to study the responses of single motor units to conditioning as well as changes in the responses of single motor units to diseases such as amyotrophic lateral sclerosis. The non-invasive character of these approaches offers an attractive means of studying the responses of single human cells, in these cases motor neurons, in health and disease.

Amyotrophic Lateral Sclerosis↗

PubMed1999

Genotype/phenotype correlations in X-linked dominant Charcot-Marie-Tooth disease.

We have studied the relationship between genotype, clinical phenotype, and pathology in 13 families with dominant X-linked Charcot-Marie-Tooth (CMT) neuropathy. Connexin32 (Cx32) gene mutations were spread throughout the coding region and included eight missense mutations, one 8-bp deletion/4-bp insertion frame shifting mutation, two nonsense mutations, and one deletion of the entire coding sequence. One hundred sixteen affected CMTX patients (53 males and 63 females) and 63 unaffected, at-risk individuals were compared by neurological and electrophysiological examinations and analyzed by gender; nerve biopsies were available from seven index cases. It was found that mutations within all regions of the Cx32 gene coding sequence caused an identical clinical phenotype. Male CMTX patients were affected more severely and showed an age-dependent progression of clinical signs and of the pathology; there was, however, variability in the severity of disease expression, irrespective of age, among males within families of defined genotype. All but 10% of female CMTX patients had only mild signs. Motor nerve conduction velocities were moderately slowed (median nerve MNCV: males 34.5 +/- 6.2 m/sec; females 45.8 +/- 7.3 m/sec), and motor and sensory nerve amplitudes were reduced (median nerve CMAP: males 3.7 +/- 3.7 mV; females 7.8 +/- 3.4 mV), with electromyographic evidence of chronic denervation. Differences were significant between gender and between affected and unaffected individuals. In agreement with the electrophysiological observations, pathological studies showed evidence of paranodal demyelination and of a length-related axonal degeneration in motor and sensory nerve fibers. Correlations between genotype and clinical phenotype suggested that missense mutations located within the second transmembrane domain and/or cytoplasmic loop might be associated with milder clinical phenotype, and therefore might be less disruptive of connexin32 gap junction function. Missense, chain-terminating, or deletion mutations in all other locations of the connexin32 protein caused severe forms of CMTX and disease onset in the first decade. Observed variability of disease severity among males within kinships suggests the influence of other modifying factors.

Charcot-Marie-Tooth Disease↗

PubMed1999

The effects of training through high-frequency electrical stimulation on the physiological properties of single human thenar motor units.

The relative impact of training on motor units (MUs) with differing physiological characteristics remains controversial. To examine this issue, we longitudinally tracked the contractile and electrical characteristics of six human thenar MUs in 2 young healthy subjects before, during, and following an intermittent, high-frequency electrical stimulation program. Responses of MUs with differing baseline physiological characteristics varied widely. While the twitch and maximal tetanic tensions of the slower and fatigue-resistant MUs increased, tensions of the faster and more fatigable MUs declined. The fatigue resistance of the faster and more fatigable MUs, on the other hand, increased while that of the slower MUs remained unchanged. Although electrical stimulation of individual MUs allowed their training to be precisely controlled, it will be of practical importance to determine whether similar divergent MU contractile changes also occur with voluntary training.

Action Potentials↗

PubMed1999

The relationship of motor unit size, firing rate and force.

OBJECTIVE: Using a clinical electromyographic (EMG) protocol, motor units were sampled from the quadriceps femoris during isometric contractions at fixed force levels to examine how average motor unit size and firing rate relate to force generation. METHODS: Mean firing rates (mFRs) and sizes (mean surface-detected motor unit action potential (mS-MUAP) area) of samples of active motor units were assessed at various force levels in 79 subjects. RESULTS: MS-MUAP size increased linearly with increased force generation, while mFR remained relatively constant up to 30% of a maximal force and increased appreciably only at higher force levels. A relationship was found between muscle force and mS-MUAP area (r2 = 0.67), mFR (r2 = 0.38), and the product of mS-MUAP area and mFR (mS-MUAP x mFR) (r2 = 0.70). CONCLUSIONS: The results support the hypothesis that motor units are recruited in an orderly manner during forceful contractions, and that in large muscles only at higher levels of contraction ( > 30% MVC) do mFRs increase appreciably. MS-MUAP and mFR can be assessed using clinical EMG techniques and they may provide a physiological basis for analyzing the role of motor units during muscle force generation.

Action Potentials↗

PubMed1998

Longitudinal study of the contractile and electrical properties of single human thenar motor units.

Serial motor unit number estimates have shed important light on the extent and rates of motoneuron losses in aging and amyotrophic lateral sclerosis. However, the estimates alone provide few clues to the health and functional status of surviving motor units. A reliable means for assessing the functional status of the surviving motor units would therefore by a welcome addition to our present tools for studying motor units. Examining the physiological properties of samples of motor units drawn at intervals during the course of a motoneuronal disease suffers from the important limitation that the samples may not be representative of one another. The latter problem could be circumvented by serially studying the same motor units. This study describes a noninvasive technique capable of longitudinally tracking the contractile and electrical properties of specific single thenar motor units in healthy subjects, in some instances over several years. The technique proved to be reasonably reliable and provided information on a wide range of contractile and electrical properties of motor units. Such an approach could serve as a potentially powerful and sensitive means of studying the life histories of single motor units in aging, diseases of the motoneuron, and in the latter instances, the responses of the motoneurons to treatment.

Action Potentials↗

PubMed1998

The usefulness of central motor conduction studies in the localization of cord involvement in cervical spondylytic myelopathy.

Cervical spondylytic myelopathy (CSM) is common. Magnetic resonance imaging (MRI), although sensitive, often reveals extensive and sometimes clinically irrelevant findings. The purpose of this study was to investigate the usefulness of central motor conduction studies in localizing the rostral level of cord involvement in 6 patients with CSM. Central motor conduction was assessed using high-voltage stimulation for the spinal roots and magnetoelectrical stimulation for the motor cortex, recording from "marker muscles" innervated by successively higher cervical cord segments. Abnormal central motor conduction affected all subjects at C8-T1, 5 subjects at C7, but none at the C5-C6 levels. The MRI showed abnormalities at multiple levels as high as C4. Our results suggest that central motor conduction studies are helpful in localizing the clinically relevant levels of spinal cord compression in CSM and correlate well with motor abnormalities on clinical examination.

Adult↗

PubMed1998

Firing rate analysis using decompostion-enhanced spike triggered averaging in the quadriceps femoris.

Electromyographic signals detected from the quadriceps femoris during various constant force contractions were decomposed to identify individual motor unit discharges and mean firing rates (FRs). Subject and group mean FRs were calculated for each force level. Mean FR values and FR variability increased with force. Individual, subject, and group mean FRs showed slight increases until 30% of maximum voluntary contraction and larger increases thereafter. Findings are discussed in relation to motor unit recruitment, frequency modulation, and fatigue.

Action Potentials↗

PubMed1998

A longitudinal study of the pathophysiological changes in single human thenar motor units in amyotrophic lateral sclerosis.

The sequence of pathophysiological changes in amyotrophic lateral sclerosis (ALS) at the single motor unit (MU) level is not well understood. Using a recently described technique, a comprehensive range of physiological properties in two thenar MUs in ALS were intensively studied. In the first MU, despite a marked decline in the ability of the subject to voluntarily recruit the MU, the physiological properties of this MU remained remarkably stable over a 2-year period. In contrast, the physiological properties of the other MU declined rapidly over 5 months despite the fact that this MU could be recruited with ease throughout the study period. These differences between the progressively dysfunctional changes in these two MUs illustrates the value of such longitudinal studies of specific MUs in improving our understanding of the evolution of changes in single motoneurons in ALS. The broader application of longitudinally tracking the pathophysiological changes of the surviving MUs may prove to be a sensitive measure of disease progression and in evaluating the effectiveness of treatments.

Action Potentials↗

PubMed1998

Dissociation of the electrical and contractile properties in single human motor units during fatigue.

The surface EMG area often exhibits progressive enlargement during a submaximal fatiguing contraction, but the underlying reasons still remain uncertain. Fatigue-induced changes in the surface-detected motor unit action potentials (S-MUAPs) of 10 human thenar motor units (MUs) with widely differing physiological properties were examined. After 2 min of repetitive 40-Hz stimulation, the size of the S-MUAPs of all MUs increased, the magnitude of which was negatively correlated with their tetanic tension changes. These findings suggest that during muscle fatigue, in addition to reflecting recruitment of new MUs and increases in firing rates of the active MUs, the surface EMG may also be markedly influenced by changes in the S-MUAPs, especially in fast fatigable muscles.

Adult↗

PubMed1998

Quantitation in EMG.

The neuromuscular system may be affected by disorders of the central nervous system as well as other disorders affecting motoneurons, axons, neuromuscular transmission, the sarcolemmal membrane, the contractile elements and other components of the muscle fibers themselves. One or a combination of these possibilities can present in patients in the critical care unit. This paper reviews various qualitative and quantitative methods for assessing the various components of the peripheral contributions to the electrical and force output as well as the central motor drive to motoneurons. These methods all have their own strengths and weaknesses but many are complementary and together, can provide important diagnostic and prognostic information to guide management.

Brain↗

PubMed1997

Multifocal motor neuropathy presenting as ophthalmoplegia.

A 45-year-old man developed ophthalmoplegia and subsequently multiple cranial nerve palsies in association with bibrachial paresis. Investigations revealed evidence of conduction block occurring at a very proximal location (i.e., the spinal roots) and seemingly sparing sensory fibers. Other causes were ruled out and a diagnosis of multifocal motor neuropathy with conduction block (MMN) was suggested. The patient responded to cyclophosphamide. Differentiating features between MMN and chronic inflammatory demyelinating polyradioneuropathy (CIDP) are discussed. This case demonstrates that MMN may rarely present with ophthalmoparesis and also demonstrates that features of MMN and CIDP may overlap.

Brachial Plexus↗

PubMed1997

Decomposition-enhanced spike-triggered averaging: contraction level effects.

Decomposition-enhanced spike-triggered averaging (DE-STA) was applied to the vastus medialis muscle to examine size distributions of surface-detected motor-unit action potentials (S-MUAPs) at various force levels. Using DE-STA, 15-20 S-MUAPs were identified during 5%, 10%, 20%, and 30% of maximum voluntary contraction. Average S-MUAPs showed increase in peak to peak (and negative peak) amplitude with force (In microV): 5% = 37.9 +/- 6.1 (16.6 +/- 2.5), 10% = 44.0 +/- 4.0 (20.4 +/- 1.8), 20% = 80.7 +/- 9.3 (41.3 +/- 4.5), and 30% = 102.5 +/- 10.3 (53.6 +/- 5.0). Test-retest variability of peak to peak (and negative peak amplitude) between repeated trials was 0.10 (0.14), 0.14 (0.14), 0.17 (0.15), and 0.21 (0.20) at 5%, 10%, 20%, and 30% respectively. A relationship was found between the S-MUAP amplitude and force (r2 = 0.78, df = 90, F = 160, P < 0.001). Increase in average S-MUAP amplitude with force suggests that STA performed only at low levels of contraction may result in a biased sampling and small average S-MUAP amplitudes.

Action Potentials↗

PubMed1997

Age-related changes in the twitch contractile properties of human thenar motor units.

The purpose of this study was to examine the effects of aging on the contractile and electrophysiological properties of human thenar motor units (MUs). Percutaneous electrical stimulation of single motor axons within the median nerve was used to isolate and examine the twitch tensions, contractile speeds, and surface-detected MU action potential (S-MUAP) sizes of 48 thenar MUs in 17 younger subjects (25-53 yr) and 44 thenar MUs in 9 older subjects (64-77 yr). A wide range of twitch tensions, contractile speeds, and S-MUAP sizes was observed in both age groups. However, older subjects had significantly larger MU twitch tensions and slower MU twitch contraction and half-relaxation times. These changes were accompanied by increased S-MUAP sizes. These findings suggest that the human thenar MU pool undergoes significant age-related increase in MU size and slowing of contractile speed. Such adaptation may help to overcome previously reported age-related losses of thenar MUs.

Adult↗