Genetic and epigenetic differences associated with environmental gradients in replicate populations of two salt marsh perennials.

While traits and trait plasticity are partly genetically based, investigating epigenetic mechanisms may provide more nuanced understanding of the mechanisms underlying response to environment. Using AFLP and methylation-sensitive AFLP, we tested the hypothesis that differentiation to habitats along natural salt marsh environmental gradients occurs at epigenetic, but not genetic loci in two salt marsh perennials. We detected significant genetic and epigenetic structure among populations and among subpopulations, but we found multilocus patterns of differentiation to habitat type only in epigenetic variation for both species. In addition, more epigenetic than genetic loci were correlated with habitat in both species. When we analysed genetic and epigenetic variation simultaneously with partial Mantel, we found no correlation between genetic variation and habitat and a significant correlation between epigenetic variation and habitat in Spartina alterniflora. In Borrichia frutescens, we found significant correlations between epigenetic and/or genetic variation and habitat in four of five populations when populations were analysed individually, but there was no significant correlation between genetic or epigenetic variation and habitat when analysed jointly across the five populations. These analyses suggest that epigenetic mechanisms are involved in the response to salt marsh habitats, but also that the relationships among genetic and epigenetic variation and habitat vary by species. Site-specific conditions may also cloud our ability to detect response in replicate populations with similar environmental gradients. Future studies analysing sequence data and the correlation between genetic variation and DNA methylation will be powerful to identify the contributions of genetic and epigenetic response to environmental gradients.

Within-genotype epigenetic variation enables broad niche width in a flower living yeast.

Niche theory is one of the central organizing concepts in ecology. Generally, this theory defines a given species niche as all of the factors that effect the persistence of the species as well as the impact of the species in a given location (Hutchinson 1957; Chase 2011). Many studies have argued that phenotypic plasticity enhances niche width because plastic responses allow organisms to express advantageous phenotypes in a broader range of environments (Bradshaw 1965; Van Valen 1965; Sultan 2001). Further, species that exploit habitats with fine-grained variation, or that form metapopulations, are expected to develop broad niche widths through phenotypic plasticity (Sultan & Spencer 2002; Baythavong 2011). Although a long history of laboratory, greenhouse and reciprocal transplant experiments have provided insight into how plasticity contributes to niche width (Pigliucci 2001), recent advances in molecular approaches allow for a mechanistic understanding of plasticity at the molecular level (Nicotra et al. 2010). In particular, variation in epigenetic effects is a potential source of the within-genotype variation that underlies the phenotypic plasticity associated with broad niche widths. Epigenetic mechanisms can alter gene expression and function without altering DNA sequence (Richards 2006) and may be stably transmitted across generations (Jablonka & Raz 2009; Verhoeven et al. 2010). Also, epigenetic mechanisms may be an important component of an individual's response to the environment (Verhoeven et al. 2010). While these ideas are intriguing, few studies have made a clear connection between genome-wide DNA methylation patterns and phenotypic plasticity (e.g. Bossdorf et al. 2010). In this issue of Molecular Ecology, Herrera et al. (2012) present a study that demonstrates epigenetic changes in genome-wide DNA methylation are causally active in a species' ability to exploit resources from a broad range of environments and are particularly important in harsh environments.

Plant phenotypic plasticity in a changing climate.

Climate change is altering the availability of resources and the conditions that are crucial to plant performance. One way plants will respond to these changes is through environmentally induced shifts in phenotype (phenotypic plasticity). Understanding plastic responses is crucial for predicting and managing the effects of climate change on native species as well as crop plants. Here, we provide a toolbox with definitions of key theoretical elements and a synthesis of the current understanding of the molecular and genetic mechanisms underlying plasticity relevant to climate change. By bringing ecological, evolutionary, physiological and molecular perspectives together, we hope to provide clear directives for future research and stimulate cross-disciplinary dialogue on the relevance of phenotypic plasticity under climate change.

Has the evolution of complexity in the amphibian papilla influenced anuran speciation rates?

For anurans, increasing complexity of the inner ear has been correlated with speciation rates. The evolution of a complex amphibian papilla (AP) is thought to have facilitated speciation by extending the range of frequencies over which mating calls may diverge. Although this example has been proposed to represent a key innovation, the mechanism by which the AP is thought to promote speciation makes the questionable assumption that anurans generally use the AP for detection of their mating calls. This study uses mating calls from 852 species to test this assumption. Surprisingly, the calls of most species are not detected by the AP but by a second organ, the basilar papilla (BP). This refutes the role of AP complexity in facilitating call divergence and hence, speciation. Future research into the evolution of acoustically mediated reproductive isolation should focus instead on the BP as it may play a more critical role in anuran speciation.

A task-orientated intervention enhances walking distance and speed in the first year post stroke: a randomized controlled trial.

OBJECTIVE: To evaluate the efficacy of a task-orientated intervention in enhancing competence in walking in people with stroke. DESIGN: Two-centre observer-blinded stratified block-randomized controlled trial. SETTING: General community. SUBJECTS: Between May 2000 and February 2003, 91 individuals with a residual walking deficit within one year of a first or recurrent stroke consented to participate. INTERVENTIONS: The experimental intervention comprised 10 functional tasks designed to strengthen the lower extremities and enhance walking balance, speed and distance. The control intervention involved the practice of upper extremity activities. Subjects in both groups attended sessions three times a week for six weeks. MAIN MEASURES: Six-minute walk test (SMWT), 5-m walk (comfortable and maximum pace), Berg Balance Scale, timed 'up and go'. RESULTS: At baseline, subjects in the experimental (n = 44) and control (n = 47) groups walked an average distance of 209 m (SD = 126) and 204 m (SD =131), respectively, on the SMWT. Mean improvements of 40 m (SD =72), and 5 m (SD =66) were observed following the experimental and control interventions, respectively. The between-group difference was 35 m (95% confidence interval (CI) 7, 64). Significant between-group effects of 0.21 m/s (95% CI 0.12, 0.30) and of 0.11 m/s (95% CI 0.03, 0.19) in maximum and comfortable walking speed, respectively, were observed. People with a mild, moderate or severe walking deficit at baseline improved an average of 36 (SD =96), 55 (SD = 56) and 18 m (SD = 23), respectively, in SMWT performance following the experimental intervention. CONCLUSIONS: Study findings support the efficacy of a task-orientated intervention in enhancing walking distance and speed in the first year post stroke, particularly in people with moderate walking deficits.

Multi-scale genetic analysis of Uniola paniculata (Poaceae): a coastal species with a linear, fragmented distribution.

Geographic and fine-scale population genetic structures of Uniola paniculata, the dominant coastal dune grass in the southeastern USA, were examined. The linear, naturally fragmented distribution of this native perennial was hypothesized to lead to high genetic structure and lower genetic diversity at the margin of the species range. The extensive ramet production and low seed germination of this species were also expected to cause populations to be dominated by a few large clones. At 20 sites throughout the range of the species, leaf tissue was collected from 48 individuals. Clonal structure was examined using leaf tissue collected from an additional 60 individuals, each in four patches at two sites. Starch gel electrophoresis was used to resolve 27 allozyme loci. The results indicated that Uniola had greater genetic structure (G(ST) = 0.304) than most other outcrossing species, indicating moderate barriers to gene flow. There was a weak but significant positive relationship between genetic distance and geographic distance, supporting an isolation-by-distance model of gene flow. There were no obvious disjunctions between regions. Genetic diversity (H(e)) was relatively uniform throughout most of the range of the species but was lower in all western Gulf of Mexico populations. Clonal diversity varied both within and among sites, but clones were often small, suggesting that sexual reproduction and recruitment from seeds are important factors maintaining genetic diversity.

Locomotor rehabilitation in a complex virtual environment.

Virtual reality (VR) technology offers a new and safe way to increase practice time and provide the varied environments and constraints needed to optimize locomotor training. Our specific objectives are (1) to create a virtual environment (VE) coupled with a self-paced treadmill for locomotor training; (2) to compare temporal and distance measurements of gait during treadmill walking while looking at different scenarios of VE; and (3) to develop a protocol optimized for the training of locomotor disorders after stroke. A motorized treadmill was mounted on a six-degree-of-freedom motion platform. VEs were created using commercial software (SoftImage) and projected on a large screen, while system control was administered through the CAREN software (Motek BV). The instantaneous treadmill speed and scene progression were servo-controlled. Preliminary results show that healthy subjects are able to have full control of their own walking speed both on the treadmill and within the virtual scene, while experiencing a strong sense of presence. A street crossing training protocol has been developed for locomotor training. It is expected that locomotor training with increasingly complex VEs will allow persons with stroke to increase progressively their locomotor capacity, as required and entrained by the VE.

Quantitative motor assessment in myotonic dystrophy.

OBJECTIVE: To establish baseline data, using a quantitative motor evaluation protocol, prior to a prospective longitudinal study of the natural history of muscular involvement in myotonic dystrophy (DM). DESIGN/METHODS: We conducted a cross-sectional study using a protocol consisting of manual muscle testing (MMT), quantitative muscle testing (QMT), and timed functional testing (TFT) on 50 definite DM patients (27 men, 23 women), aged 16 to 67 years. The relationships between MMT, QMT and TFT scores and disease duration were examined using linear regression analysis. RESULTS: The muscle weakness was symmetric and the neck flexors and the distal muscles of upper and lower extremities were weaker than proximal muscles. Using MMT scores, the average strength decline was 0.95% per year and was similar for men and women. The strength decline was significantly more rapid for distal muscles than for proximal muscles. Quantitative muscle testing scores documented a strength decline per year of disease duration of 1.2-1.6% for the hip flexors and of 2.0-3.0% for the hand grip flexors. CONCLUSIONS: We observed significant linear relationships between the scores generated by this protocol and disease duration. These data illustrate the distal to proximal progression of muscular involvement in DM, a pattern of progression well-recognized by the clinicians. The follow-up assessment of a large DM cohort in a longitudinal study will establish whether this quantitative protocol provides sensitive measures of the disease progression.

Mechanisms of disturbed motor control in ankle weakness during gait after stroke.

This study investigated the role of paresis, excessive antagonist coactivation, increased muscle-tendon passive stiffness and spasticity in the reduced stance phase plantarflexor moment (Mmax) and swing phase dorsiflexion during gait (DFmax) in subjects with a recent (<6 months post-stroke) hemiparesis (patients). The gait pattern of the paretic and non-paretic sides was evaluated in 30 patients (aged 57.8+/-10.8 years), whereas only one side was evaluated in 15 healthy controls (aged 59.1+/-9.8 years) while walking at natural and very slow speeds. Peak plantarflexor moment (Mmax) and peak medial gastrocnemius (MG) activation during the stance phase, as well as peak dorsiflexion angle (Dfmax) and peak tibialis anterior (TA) activation during the swing phase, were retained for analysis. In addition, a coactivation index and a plantarflexor spasticity index were calculated for both the stance and the swing phase, and plantarflexor passive stiffness was evaluated on an isokinetic dynamometer. The results showed that Mmax on the paretic and non-paretic sides were both reduced compared with control values at natural speed. This reduction was combined to a low MG activation (paresis) on the paretic side. On the non-paretic side, the reduced plantarflexor moment was related to excessive coactivation levels. The swing phase Dfmax tended to be reduced (not significantly) on the paretic side of the patients compared with control values. This reduction was neither associated with excessive antagonist coactivation nor to plantarflexor hyperactive stretch reflexes, but rather to an increased plantarflexor passive stiffness. In some of the patients, however, an increased TA activation that overcame the plantarflexor passive stiffness allowed for normal DFmax values. The functional consequences of the disturbed mechanisms of motor control observed in both the paretic and non-paretic sides are discussed.

Locomotor-specific measure of spasticity of plantarflexor muscles after stroke.

OBJECTIVES: To study the stretch reflex excitability (spasticity) of the plantarflexor muscles during gait in patients with hemiparesis and to study the relationships of spasticity during gait with spasticity at rest and gait speed. DESIGN: Cross-sectional, descriptive. SETTING: Rehabilitation center. PARTICIPANTS: Convenience sample of 30 patients (58 +/- 11yr) with hemiparesis (<6mo poststroke) and 15 healthy controls (59 +/- 8yr). INTERVENTIONS: Patients walked at natural speed, healthy subjects at very slow speed for 10 gait cycles. Electromyographic activation of the medial gastrocremius was recorded by using surface electrodes. A 2-dimensional video camera system with reflective markers was used to acquire kinematics of the lower limbs. MAIN OUTCOME MEASURES: Electromyography-lengthening velocity slopes, calculated from measures obtained during the lengthening periods of the medial gastrocnemius muscle during the stance and the swing phases. Measured spatisticity (Modified Ashworth Scale [MAS]), static strength (ankle clonus), and motor control (Fugl-Meyer test). RESULTS: Velocity-sensitive electromyographic responses, indicative of hyperactive stretch reflexes, were found on the paretic side during the stance phase of gait (in 66% of the patients), but not on the nonparetic side or in controls. In many patients, velocity-sensitive responses coexisted with low plantarflexor activation levels during the stance phase. No clear patterns of response were measured during the swing phase in either group. Spasticity during gait in the patients was found to be positively related (r = .47, p < .01; r = .57, p < .001) to spasticity at rest (MAS; ankle clonus), whereas it was found to be negatively related to gait speed (r = -.47 to -.53, p < .01). CONCLUSIONS: The validity of the present method is supported by the fact that it is locomotor-specific and that it allowed for a good discrimination between spastic and nonspastic limbs, as well as between stance and swing phases of the gait cycle. The results also support plantarflexor spasticity as a factor contributing to the poor locomotor performance after stroke.

Responsiveness and predictability of gait speed and other disability measures in acute stroke.

OBJECTIVES: To identify the most responsive method of measuring gait speed, to estimate the responsiveness of other outcome measures, and to determine whether gait speed predicts discharge destination in acute stroke. DESIGN: A prospective cohort study. SETTING: Five acute-care hospitals. PATIENTS: Fifty subjects with residual gait deficits after a first-time stroke. INTERVENTIONS: Five- (5mWT) and 10-meter walk tests (10mWT) at comfortable and maximum speeds, with 2 evaluations conducted an average +/- standard deviation (SD) of 8 +/- 3 and 38 +/- 5 days poststroke. MAIN OUTCOME MEASURE: Standardized response mean (SRM = mean change/SD of change) was used to estimate responsiveness for each walk test, the Berg Balance Scale, the Barthel Index, the Stroke Rehabilitation Assessment of Movement (STREAM), and the Timed Up and Go (TUG). RESULTS: The SRMs were 1.22 and 1.00 for the 5mWT, and.92 and.83 for the 10mWT performed at a comfortable and maximum pace, respectively. The SRMs for the Berg Balance Scale, the Barthel Index, the STREAM, and the TUG were 1.04,.99,.89, and.73, respectively. The probability of discharge to a rehabilitation center for persons walking at < or = 0.3m/s or > 0.6m/s at the first evaluation was.95 and.22, respectively. CONCLUSIONS: The 5mWT at a comfortable pace is recommended as the measure of choice for clinicians and researchers who need to detect longitudinal change in walking disability in the first 5 weeks poststroke.

Walking speed over 10 metres overestimates locomotor capacity after stroke.

OBJECTIVE: To examine 10-m comfortable walking speed and 6-minute distance in healthy individuals and individuals after stroke and to assess the level of disability associated with poor walking endurance after stroke. DESIGN: Descriptive study in which comfortable walking speed over 10 m and distance covered in 6 minutes (6-minute walk test) were compared between healthy subjects and subjects after stroke. SUBJECTS: Twelve healthy subjects and 14 subjects after stroke. MAIN OUTCOME MEASURES: Walking speed and 6-minute distances were compared between groups. In addition, for each group, actual distance walked in 6 minutes was compared with the distance predicted by the 10-m walking speed test and the distance predicted by normative reference equations. RESULTS: Subjects after stroke had significant reductions in 10-m speed and 6-minute distance compared with healthy subjects (p < 0.05). Subjects after stroke were not able to maintain their comfortable walking speed for 6 minutes, whereas healthy subjects walked in excess of their comfortable speed for 6 minutes. The average distance walked in 6 minutes by individuals after stroke was only 49.8+/-23.9% of the distance predicted for healthy individuals with similar physical characteristics. CONCLUSION: In our subjects after stroke, walking speed over a short distance overestimated the distance walked in 6 minutes. Both walking speed and endurance need to be measured and trained during rehabilitation.

Coactivation during gait as an adaptive behavior after stroke.

The aims of the present study were to quantify the impairment in ankle coactivation on the paretic and non-paretic sides of subjects with hemiparesis and to examine the relationship of ankle coactivation with postural instability, motor deficit of the paretic lower extremity and locomotor performance. Electromyography of the medial gastrocnemius (MG) and tibialis anterior (TA) muscles were recorded bilaterally during gait in 30 subjects (62.1+/-9.9 years) who had suffered a recent stroke (<6 months) as well as on one side of 17 healthy controls (59.3+/-9.1 years) walking at very slow speed. Ankle muscle coactivation was calculated by dividing the time of overlap between MG and TA signals (threshold of 20 microV) by the duration of the gait phases of interest: stance, swing, first and second double support sub-phases and single support sub-phase. The time spent in single support and the peak plantarflexor moment of force on the paretic side were used to measure, respectively, postural stability and dynamic strength of the paretic plantarflexors. The subjects with hemiparesis demonstrated less coactivation on the paretic side during the single support sub-phase (p<0.01) and more coactivation during first and second double support sub-phases on the non-paretic side (p<0.001) compared to control values. The patients with coactivation patterns that differed the most from controls were the patients with the more severe impairments and disabilities. While the reduced coactivation on the paretic side may contribute to poor postural stability and poor locomotor performance, the presence of excessive coactivation on the non-paretic side when both limbs were in ground contact may be an adaptation to help maintain postural stability during gait.

Preparatory adjustments during gait initiation in 4-6-year-old children.

The preparatory adjustments related to gait initiation in a group of six children (4-6 years old) were studied in comparison to a group of six adults (50-61 years old). Muscle activity, ground reaction forces and body kinematics were recorded during the initiation of gait in subjects standing with one foot on each of two forceplates. Like adults, children had consistent anticipatory activations of the tibialis anterior (TA) muscle accompanied by center of pressure (COP) displacements, but the relative magnitude of both the backward COP displacement and concomitant initial TA activation burst were lower (P<0.03 and P<0.001 respectively) in children. The latter findings were associated with a lower rate of forward progression in children (P=0.01), and a lack of significant covariance between the backward shift and forthcoming velocity. In contrast, the preparatory adjustments in the medio-lateral (M/L) direction were prominent in children. Larger M/L peak force rates in children (P=0. 01) were associated with an earlier (P=0.007) weight transfer to the stance limb; moreover, children initiated gait from a wider (P=0.04) base of support and had a trajectory of the total COP that was lateral rather than posterior like in adults. The consistent preparatory adjustment responses indicate that the motor program for initiating gait is functional at this age. The prominence of the preparatory adjustments in the M/L direction together with a reduced magnitude of the responses in the antero-posterior direction suggest that the anticipatory behavior for initiating gait develops first in the frontal plane and that more walking experience and better postural stability are required to fully achieve the adult-like control of the gait initiation process.

Task-related circuit training improves performance of locomotor tasks in chronic stroke: a randomized, controlled pilot trial.

OBJECTIVE: To evaluate the immediate and retention effects of a 4-week training program on the performance of locomotor-related tasks in chronic stroke. DESIGN: Randomized, controlled pilot study with 2-month follow-up. SETTING: Rehabilitation center. SUBJECTS: A convenience sample consisting of 12 chronic stroke subjects was used. Subjects were randomly assigned to the experimental or the control group. Three subjects withdrew from the study. INTERVENTION: Both experimental and control groups participated in exercise classes three times a week for 4 weeks. The exercise class for the experimental group focused on strengthening the affected lower limb and practicing functional tasks involving the lower limbs, while the control group practiced upper-limb tasks. MAIN OUTCOME MEASURES: Lower-limb function was evaluated by measuring walking speed and endurance, peak vertical ground reaction force through the affected foot during sit-to-stand, and the step test. RESULTS: The experimental group demonstrated significant immediate and retained (2-month follow-up) improvement (p < or = .05) compared with the control group in walking speed and endurance, force production through the affected leg during sit-to-stand, and the number of repetitions of the step test. CONCLUSION: The pilot study provides evidence for the efficacy of a task-related circuit class at improving locomotor function in chronic stroke.

Contribution of passive stiffness to ankle plantarflexor moment during gait after stroke.

OBJECTIVE: To measure the contribution of passive stiffness to the ankle plantarflexor moment during gait in subjects with hemiparesis early after stroke. The relationship of passive stiffness with gait speed was also examined. DESIGN: Cross-sectional, descriptive. PATIENTS AND OTHER PARTICIPANTS: A sample of convenience of 14 patients (54.7+/-10.9 yrs) with a hemiparesis for less than 5 months and 11 healthy controls (50.6+/-11.6 yrs). MAIN OUTCOME MEASURES: The contribution of passive stiffness to the plantarflexor moment during gait was obtained using moment-angle slope (stiffness) values. Total plantarflexor stiffness was measured during gait, and passive stiffness was measured during passive dorsiflexion imposed by an isokinetic dynamometer at velocities and ranges of movement matched with values recorded during the plantarflexor lengthening period of the stance phase. The contribution of passive stiffness was obtained by dividing the passive stiffness (dynamometer) by the total plantarflexor stiffness (gait). RESULTS: On the paretic side, passive stiffness contributed more (16.8%; range 2.9% to 49.6%) to total plantarflexor stiffness during gait compared (p<.01) with both the nonparetic side (7.3%) and control values (5.9%). This increased contribution on the paretic side resulted from a large muscle-tendon passive stiffness, a decreased active muscle contribution, or both. Although in some patients the increased passive component led to the development of a total plantarflexor stiffness that was within normal values, it did not in others either because the active component was very small or because limited dorsiflexion during the stance phase prevented the passive component tension to develop. The contribution of passive stiffness was not significantly (p>.05) related to gait speed in both the patients and the controls. CONCLUSIONS: The increased contribution of passive stiffness to total plantarflexor moment during gait likely acts as an adaptation for a defective muscle active component, helping ankle push-off at the end of the stance phase. Although this mechanism is effective in most of the patients, it cannot come into action if the dorsiflexion movement during the stance phase is prevented, for instance, by enhanced stretch reflexes.

Abstinence promotion and the provision of information about contraception in public school district sexuality education policies.

CONTEXT: For more than two decades, abstinence from sexual intercourse has been promoted by some advocates as the central, if not sole, component of public school sexuality education policies in the United States. Little is known, however, about the extent to which policies actually focus on abstinence and about the relationship, at the local district level, between policies on teaching abstinence and policies on providing information about contraception. METHODS: A nationally representative sample of 825 public school district superintendents or their representatives completed a mailed questionnaire on sexuality education policies. Descriptive and multivariate analyses were conducted to identify districts that had sexuality education policies, their policy regarding abstinence education and the factors that influenced it. RESULTS: Among the 69% of public school districts that have a district-wide policy to teach sexuality education, 14% have a comprehensive policy that treats abstinence as one option for adolescents in a broader sexuality education program; 51% teach abstinence as the preferred option for adolescents, but also permit discussion about contraception as an effective means of protecting against unintended pregnancy and disease (an abstinence-plus policy); and 35% (or 23% of all U.S. school districts) teach abstinence as the only option outside of marriage, with discussion of contraception either prohibited entirely or permitted only to emphasize its shortcomings (an abstinence-only policy). Districts in the South were almost five times as likely as those in the Northeast to have an abstinence-only policy. Among districts whose current policy replaced an earlier one, twice as many adopted a more abstinence-focused policy as moved in the opposite direction. Overall, though, there was no net increase among such districts in the number with an abstinence-only policy; instead, the largest change was toward abstinence-plus policies. CONCLUSIONS: While a growing number of U.S. public school districts have made abstinence education a part of their curriculum, two-thirds of districts allow at least some positive discussion of contraception to occur. Nevertheless, one school district in three forbids dissemination of any positive information about contraception, regardless of whether their students are sexually active or at risk of pregnancy or disease.

PIP: Descriptive and multivariate analyses were conducted to identify districts that had sexuality education policies, their policy regarding abstinence education and the factors that influenced it. A nationally representative sample of 825 public school district superintendents or their representatives completed a mailed questionnaire on sexuality education policies. Results revealed that 69% of public school districts have a district-wide policy to teach sexuality education, of which 14% have a comprehensive policy that treats abstinence as one option for adolescents in a broader sexuality education program; 51% teach abstinence as the preferred option for adolescents, but also permit discussion about contraception as an effective means of protecting against unintended pregnancy and disease; and 35% teach abstinence as the only option outside of marriage, with discussion of contraception either prohibited entirely or permitted only to emphasize its shortcomings. A growing number of US public school districts have made abstinence education a part of their curriculum; however, two-thirds allow at least some positive discussion of contraception to occur.

A ventricular assist device powered by conditioned skeletal muscle.

BACKGROUND: We are developing and testing a new ventricular assist device (VAD) to be powered by conditioned skeletal muscle. METHODS: To evaluate the VAD hardware and to develop a muscle training regimen, 8 calves have been used in studies in which the right latissimus dorsi muscle was employed. The experiments were carried out to an approximately 4-month duration. RESULTS: There was significant conversion of type II (fast twitch) to type I (slow twitch) muscle fibers. This did not correlate well, however, with device performance. The device stroke volumes ranged from approximately 17 to 90 cc. This variability of outcome occurred despite the fact that identical hardware, surgical procedures, and training regimens were employed. CONCLUSIONS: The results from the first eight studies lead us to speculate that perfusion may be important even when the muscle is working at pressures much lower than systemic blood pressure levels. In an attempt to augment tissue perfusion, we plan to investigate thermally induced angiogenesis as a possible mechanism for increasing blood flow to the tissue.

Gait in stroke: assessment and rehabilitation.

This article discusses the assessment and treatment of gait disorders after stroke. After consideration of the effects (of the disturbed motor control resulting from stroke) on the gait movements and the expected rate of recovery of walking capacity, different methods of assessment are considered. Emphasis is placed on selecting the appropriate measurement tool according to the individual's level of function. Also, the need to measure walking performance under different environmental constraints and the importance of instrument responsiveness to change over the range of walking disabilities are discussed. Task-related training with the opportunity for large amounts of practice is recommended to improve walking performance after stroke.

Lessons from recent nosocomial epidemics.

This review describes important examples of recent nosocomial infection epidemics. Current trends suggest that emerging problems in nosocomial infections include increased nosocomial epidemics in out-of-hospital settings, contamination of medical devices and products, and antimicrobial resistance. Increased attention should be focused on outbreak investigations in these areas.