Motor unit firing rate modulation is more impaired during flexion synergy-driven contractions of the biceps brachii in chronic stroke.

Following a hemiparetic stroke, individuals exhibit altered motor unit firing patterns during voluntary muscle contractions, including impairments in firing rate modulation and recruitment. These individuals also exhibit abnormal muscle coactivation through multi-joint synergies (e.g., flexion synergy). Here, we investigate whether motor unit firing activity during flexion synergy-driven contractions of the paretic biceps brachii differs from that of voluntary contractions and use these differences to predict changes in descending motor commands. To accomplish this, we characterized motor unit firing patterns of the biceps brachii in individuals with chronic hemiparetic stroke during voluntary isometric elbow flexion contractions in the paretic and non-paretic limbs, as well as during contractions driven by voluntary effort and by flexion synergy expression in the paretic limb. We observed significant reductions in motor unit firing rate modulation from the non-paretic to paretic limb (non-paretic - paretic: 0.14 pps/%MVT, 95% CI: [0.09 0.19]) that were further reduced during synergy-driven contractions (voluntary paretic - synergy driven: 0.19 pps/%MVT, 95% CI: [0.14 0.25]). Moreover, using recently developed metrics, we evaluated how a stroke-induced reliance on indirect motor pathways alters the inputs that motor units receive and revealed progressive increases in neuromodulatory and inhibitory drive to the motor pool in the paretic limb, with the changes greatest during synergy-driven contractions. These findings suggest that an interplay between heightened neuromodulatory drive and alterations in inhibitory command structure may account for the observed motor unit impairments, further illuminating underlying neural mechanisms involved in the flexion synergy and its impact on motor unit firing patterns post-stroke.

Understanding the Interaction of Transcranial Direct Current Stimulation and Visual Feedback During an Ankle Movement Task.

BACKGROUND: Transcranial direct current stimulation (tDCS) has been demonstrated to facilitate motor performance in healthy individuals; however, results are variable. The neuromodulatory effects of tDCS during visuomotor tasks may be influenced by extrinsic visual feedback. However, this interaction between tDCS and visual feedback has not been explored for the lower limb. Hence, our objective was to explore if tDCS over the primary lower limb motor cortex differentially facilitates motor performance based on the availability of visual feedback. METHODS: Twenty-two neurotypical adults performed ankle plantarflexion and dorsiflexion movements while tracking a sinusoidal target. Spatiotemporal, spatial, and temporal error were calculated between the ankle position and target. Participants attended two sessions, a week apart, with (Stim) and without (No-Stim) anodal tDCS. Sessions were divided into two blocks containing randomized visual feedback conditions: full, no, and blindfold. During Stim sessions, the first block included the application of tDCS to the lower limb M1. RESULTS: Spatiotemporal and spatial error increased as feedback faded (p < .001). A two-way repeated-measures analysis of variance showed a significant interaction between tDCS and visual feedback (p < .05) on spatiotemporal error. Post hoc analyses revealed a significant improvement in spatiotemporal error when visual feedback was absent (p < .01). Spatial and temporal errors were not significantly affected by stimulation or visual feedback. DISCUSSION: Our results suggest that tDCS enhances spatiotemporal ankle motor performance only when visual feedback is not available. These findings indicate that visual feedback may play an important role in demonstrating the effectiveness of tDCS.

Understanding factors contributing to participant satisfaction in stroke walking recovery clinical trials.

Background: Individuals with stroke face a distinct set of challenges, barriers and facilitators that need to be understood to streamline efficacy of stroke clinical trials and improve participant retention. Few long-term stroke rehabilitation trials have evaluated participant perception of their laboratory experience. Methods: We collected data regarding trial satisfaction from 33 individuals with stroke who participated in 12 sessions of treadmill training which included pre, post and follow-up non-invasive brain stimulation and clinical assessments. We evaluated factors such as overall trial satisfaction, burden of testing, perceived benefits, perceived barriers, and perceived support using a participant satisfaction questionnaire (PSQ) that assessed participants' overall trial experience. Results: 97% of our participants found participating in the study to be rewarding and would recommend it to other persons with stroke. Transcranial magnetic stimulation (TMS) testing was found to be the major perceived burden of participation while travelling to the lab was found to be the major perceived barrier to participation. Significant correlations were found between various items of the PSQ and clinical assessments. Conclusions: This study helped us get a preliminary perspective into the benefits and barriers faced by persons with stroke enrolled in a 4-week long clinical trial. We observed that participant satisfaction was driven by various factors including functional status, personal relevance to the research, perceptive physical and mental health improvements, interaction with research personnel, and ease of testing protocols.

The AOA/ACGME Single Accreditation System and Its Immediate and Future Impact on Family Medicine.

BACKGROUND AND OBJECTIVES: The American Osteopathic Association (AOA) agreed to combine its graduate medical education programs with the Accreditation Council for Graduate Medical Education (ACGME) between July 1, 2015 and June 30, 2020 in an initiative called the Single Accreditation System (SAS). The objective of our study was to identify the impact the SAS had on the ACGME, family medicine (FM), and implications for the future of FM. METHODS: We collected and compiled data from the AOA, ACGME, and the National Residency Matching Program (NRMP). Analysis reveals the effects that the addition of former 122 AOA-accredited FM residencies had on the ACGME and FM programs. RESULTS: Several osteopathic FM programs encountered challenges meeting ACGME accreditation standards. As of June 1, 2020, 89 of 122 accreditation applications received initial or continuing accreditation; the others had accreditation issues to resolve. The Osteopathic Recognition program emphasizing training in osteopathic principles and practices was a popular option in FM residencies. Fewer DOs serve as program directors in former AOA-accredited FM residencies. CONCLUSIONS: The SAS has shifted the balance in the percentages of MDs, DOs, and international medical graduates (IMGs) in FM. Trends in FM show that as more DOs enter the NRMP the percent of MDs and IMGs decreases. In the future, it is projected that DOs will outnumber MDs and IMGs in ACGME FM residencies. The 51 new medical schools started between 2010 and 2020 will generate a test for the integration of their graduates into GME. Increased competition for FM residencies is expected.

Estimates of persistent inward currents are reduced in upper limb motor units of older adults.

Ageing is a natural process causing alterations in the neuromuscular system, which contributes to reduced quality of life. Motor unit (MU) contributes to weakness, but the mechanisms underlying reduced firing rates are unclear. Persistent inward currents (PICs) are crucial for initiation, gain control and maintenance of motoneuron firing, and are directly proportional to the level of monoaminergic input. Since concentrations of monoamines (i.e. serotonin and noradrenaline) are reduced with age, we sought to determine if estimates of PICs are reduced in older (>60 years old) compared to younger adults (<35 years old). We decomposed MU spike trains from high-density surface electromyography over the biceps and triceps brachii during isometric ramp contractions to 20% of maximum. Estimates of PICs (ΔFrequency; or simply ΔF) were computed using the paired MU analysis technique. Regardless of the muscle, peak firing rates of older adults were reduced by ∼1.6 pulses per second (pps) (P = 0.0292), and ΔF was reduced by ∼1.9 pps (P < 0.0001), compared to younger adults. We further found that age predicted ΔF in older adults (P = 0.0261), resulting in a reduction of ∼1 pps per decade, but there was no relationship in younger adults (P = 0.9637). These findings suggest that PICs are reduced in the upper limbs of older adults during submaximal isometric contractions. Reduced PIC magnitude represents one plausible mechanism for reduced firing rates and function in older individuals, but further work is required to understand the implications in other muscles and during a variety of motor tasks. KEY POINTS: Persistent inward currents play an important role in the neural control of human movement and are influenced by neuromodulation via monoamines originating in the brainstem. During ageing, motor unit firing rates are reduced, and there is deterioration of brainstem nuclei, which may reduce persistent inward currents in alpha motoneurons. Here we show that estimates of persistent inward currents (ΔF) of both elbow flexor and extensor motor units are reduced in older adults. Estimates of persistent inward currents have a negative relationship with age in the older adults, but not in the young. This novel mechanism may play a role in the alteration of motor firing rates that occurs with ageing, which may have consequences for motor control.

The Impact of the ACGME/AOA Single Accreditation System on Osteopathic Surgical Specialties, Residents, and DO Students.

OBJECTIVE: This article examines the outcomes and impact of the AOA/ACGME Single Accreditation System (SAS) on 6 osteopathic surgical specialties, their program directors, residents, and students and how growth in osteopathic medical schools and students affects ACGME surgical training. DESIGN: The study charts the choices of 159 osteopathic surgical residencies regarding the acquisition of ACGME accreditation, decisions made by ACGME Review Committees, and how they affected program leadership, residents, and osteopathic medical students as reflected in results of residency matching programs. SETTING AND PARTICIPANTS: According to the SAS, the osteopathic profession ceded its accreditation operations and have its programs acquire ACGME accreditation between 2015 and 2020 to form a unified accreditation system under the ACGME. RESULTS: More than one-fourth (26%) of eligible osteopathic surgical programs either did not submit an application or voluntarily withdrew from the ACGME accreditation process. For the 118 surgical programs that did achieve ACGME Initial Accreditation, subsequent site visits and Review Committee decisions sparingly granted Continuing Accreditation status. In addition, 49% of the osteopathic applications listed an MD program director. Osteopathic surgical residents encountered few disruptions in transitioning to the ACGME. The full impact of the SAS was felt by osteopathic graduates in 2020 who encountered fewer DO-oriented ACGME programs and the historic trend of established ACGME surgical programs favoring candidates from American allopathic medical schools. As the osteopathic profession continues its rapid growth, competition for surgical training will only increase. CONCLUSIONS: Participation in the SAS resulted in the loss of 41 surgical programs and marked reductions in training positions during a period of rapid osteopathic growth. Results from matching programs indicate that integration of DOs into established ACGME surgical residencies will be a slow, gradual process. The SAS succeeded in creating a unified standard for surgical training yet generated negative consequences on osteopathic surgical training.

The Single Accreditation System: Risks to the Osteopathic Profession.

In August 2014, the American Osteopathic Association (AOA) and the American Association of Colleges of Osteopathic Medicine (AACOM) signed a memorandum of understanding with the Accreditation Council for Graduate Medical Education (ACGME) to create the Single Accreditation System (SAS) for graduate medical education (GME) in the United States. The AOA made the decision that it would close its GME accreditation system in response to dramatic growth in colleges of osteopathic medicine, a shortfall in osteopathic GME positions with increasing dependence on the ACGME system, ACGME policy decisions that adversely impacted osteopathic students, and declining osteopathic student interest in primary care. Osteopathic teaching institutions bore responsibility for meeting ACGME accreditation standards between 2015 and 2020, including determining institutional sponsorship, which program applications to submit, program size, educational leadership, and whether to pursue Osteopathic Recognition. Approximately 692 of 954 (72.5%) eligible osteopathic GME programs in 2014-2015 obtained ACGME accreditation by June 1, 2020. There were sharp reductions in surgical and subspecialty programs and a significant drop of DOs in educational leadership positions. A low percentage of ACGME-accredited programs applied for Osteopathic Recognition. In closing its GME accreditation system and joining the ACGME, the AOA gave up control of its direct relationship with osteopathic residents, fellows, and teaching institutions to gain critical GME opportunities. In this article, the author considers whether this gain will offset the risks taken by the AOA, including decreased DO leadership opportunities and role models, lower than expected interest in Osteopathic Recognition, and possible decreased DO interest in osteopathic organizations and osteopathic specialty board certification. Time and the choices of current and future DO trainees in ACGME programs will determine the future of the osteopathic profession-and whether these risks were worth taking.

Impact of parameter selection on estimates of motoneuron excitability using paired motor unit analysis.

OBJECTIVE: Noninvasive estimation of motoneuron excitability in human motoneurons is achieved through a paired motor unit analysis (ΔF) that quantifies hysteresis in the instantaneous firing rates at motor unit recruitment and de-recruitment. The ΔF technique provides insight into the magnitude of neuromodulatory synaptic input and persistent inward currents (PICs). While the ΔF technique is commonly used for estimating motoneuron excitability during voluntary contractions, computational parameters used for the technique vary across studies. A systematic investigation into the relationship between these parameters and ΔF values is necessary. APPROACH: We assessed the sensitivity of the ΔF technique with several criteria commonly used in selecting motor unit pairs for analysis and methods used for smoothing the instantaneous motor unit firing rates. Using high-density surface EMG and convolutive blind source separation, we obtained a large number of motor unit pairs (5409) from the triceps brachii of ten healthy individuals during triangular isometric contractions. MAIN RESULTS: We found an exponential plateau relationship between ΔF and the recruitment time difference between the motor unit pairs and an exponential decay relationship between ΔF and the de-recruitment time difference between the motor unit pairs, with the plateaus occurring at approximately 1 s and 1.5 s, respectively. Reduction or removal of the minimum threshold for rate-rate correlation of the two units did not affect ΔF values or variance. Removing motor unit pairs in which the firing rate of the control unit was saturated had no significant effect on ΔF. Smoothing the filter selection had no substantial effect on ΔF values and ΔF variance; however, filter selection affected the minimum recruitment and de-recruitment time differences. SIGNIFICANCE: Our results offer recommendations for standardized parameters for the ΔF approach and facilitate the interpretation of findings from studies that implement the ΔF analysis but use different computational parameters.

Properties of Motor Units of Elbow and Ankle Muscles Decomposed Using High-Density Surface EMG.

Analyses of motor unit activity provide a window to the neural control of motor output. In recent years, considerable advancements in surface EMG decomposition methods have allowed for the discrimination of dozens of individual motor units across a range of muscle forces. While these non-invasive methods show great potential as an emerging technology, they have difficulty discriminating a representative sample of the motor pool. In the present study, we investigate the distribution of recruitment thresholds and motor unit action potential waveforms obtained from high density EMG across four muscles: soleus, tibialis anterior, biceps brachii, and triceps brachii. Ten young and healthy control subjects generated isometric torque ramps between 10-50% maximum voluntary torque during elbow or ankle flexion and extension. Hundreds of motor unit spike trains were decomposed for each muscle across all trials. For lower contraction levels and speeds, surface EMG decomposition discriminated a large number of low-threshold units. However, during contractions of greater speed and torque level the proportion of low threshold motor units decomposed was reduced, resulting in a relatively uniform distribution of recruitment thresholds. The number of motor units decomposed decreased as the contraction level and speed increased. The decomposed units showed a wide range of recruitment thresholds and motor unit action potential amplitudes. In conclusion, although surface EMG decomposition is a useful tool to study large populations of motor units, results of such methods should be interpreted in the context of limitations in sampling of the motor pool.

Meeting ACGME Standards Under a Unified Accreditation System: Challenges for Osteopathic Graduate Medical Education Programs.

In 2014, the American Osteopathic Association (AOA) and the American Association of Colleges of Osteopathic Medicine signed a memorandum of understanding (MOU) with the Accreditation Council for Graduate Medical Education (ACGME) to create a unified accreditation system for graduate medical education (GME) under the ACGME. The AOA will cease to accredit GME programs on June 30, 2020. By then, AOA-accredited programs need to apply for and achieve ACGME initial accreditation. The terms of the MOU also made it advantageous for some formerly nonteaching hospitals to establish AOA programs, chiefly in primary care, as a step toward future ACGME accreditation.In transitioning AOA programs to the ACGME system, hospitals with osteopathic GME can expect to encounter challenges related to major differences between AOA and ACGME standards. The minimum numbers of residents for ACGME programs in most specialties are greater than those for AOA programs, which will require hospitals that may already be at their federal caps to add additional residency positions. ACGME standards are also more faculty- and staff-intensive and require additional infrastructure, necessitating additional financial investments. In addition, greater curricular specificity in ACGME standards will generate new educational and financial challenges.To address these challenges, hospitals may need to reallocate resources and positions among their current AOA programs, reducing the number of programs (and specialties) they sponsor. It is expected that a number of established and new AOA programs will choose not to pursue ACGME accreditation or will fail to qualify for ACGME initial accreditation.

Osteopathic Students' Graduate Medical Education Aspirations Versus Realities: The Relationship of Osteopathic Medicine and Primary Care.

Osteopathic medicine is closely identified with primary care. The mission statements of a majority of colleges of osteopathic medicine (COMs) mention the goal of producing primary care physicians. By far, there are more family medicine and internal medicine residency programs in the American Osteopathic Association graduate medical education (GME) system than programs for any other specialty. In addition, the osteopathic profession is embarking on a new direction to ensure COM graduates are trained as practice-ready primary care physicians. In counterpoint to the osteopathic profession's emphasis on primary care, the majority of entering and graduating osteopathic medical students express preferences for residencies in non-primary care specialties. When graduating students confront their GME options, however, they discover their choices for non-primary care specialties are limited. Currently, approximately two-thirds of COM graduates end up in a primary care residency. The creation of a unified GME accreditation system under the Accreditation Council for Graduate Medical Education (ACGME) may further consolidate the osteopathic identity with primary care: Osteopathic training institutions may reduce the number of non-primary care programs they offer, which would allow them to increase enrollment in primary care programs to meet ACGME standards and remain below their Medicare caps. Additionally, in the National Resident Matching Program Match, selection patterns by program directors for competitive non-primary care residencies currently favor U.S. MDs. Therefore, while osteopathic students enter COMs aspiring to careers in non-primary care specialties, they are encountering a GME environment that offers them a shrinking number of alternatives.

The Educational Model of Private Colleges of Osteopathic Medicine: Revisited for 2003-2013.

Trends in the development of new private colleges of osteopathic medicine (COMs) described by the author in 2003 have accelerated in the ensuing decade. During 2003 to 2013, 10 new COMs as well as 2 remote teaching sites and 4 new branch campuses at private institutions were accredited, leading to a 98% increase in the number of students enrolled in private COMs. The key features of the private COM educational model during this period were a reliance on student tuition, the establishment of health professions education programs around the medical school, the expansion of class size, the creation of branch campuses and remote teaching sites, an environment that emphasizes teaching over research, and limited involvement in facilities providing clinical services to patients. There is institutional ownership of preclinical instruction, but clinical instruction occurs in affiliated hospitals and medical institutions where students are typically taught by volunteer and/or adjunct faculty.Between 2003 and 2013, this model attracted smaller universities and organizations, which implemented the strategies of established private COMs in initiating new private COMs, branch campuses, and remote teaching sites. The new COMs have introduced changes to the osteopathic profession and private COM model by expanding to new parts of the country and establishing the first for-profit medical school accredited in the United States in modern times. They have also increased pressure on the system of osteopathic graduate medical education, as the number of funded GME positions available to their graduates is less than the need.

The impact of osteopathic physicians' participation in ACGME-accredited postdoctoral programs, 1985-2006.

Between 1985 and 2006, the number of osteopathic physicians (DOs) training in Accreditation Council for Graduate Medical Education (ACGME) postdoctoral (i.e., residency and fellowship) programs increased by 5,352 (419%). In 2006, more than two of every three DOs (6,629 of 9,618) in postdoctoral training were in an ACGME program. The integration of osteopathic physicians into these programs was facilitated by several factors. The most important of these was a noted growth in the number and types of ACGME programs and a consistent number of U.S. MD graduates (USMDs) from schools accredited by the Liaison Committee on Medical Education (LCME). From 1985 to 2006, the number of all physicians in ACGME programs, both DO and MD, grew by 30,365 (41%). DOs were most often selected for specialties less populated by USMDs, chiefly family and internal medicine and pediatrics.Growth patterns in LCME medical schools project an increase in the national class size to accommodate 3,400 more students by 2012, a 21% increase. The development of new colleges of osteopathic medicine (COMs) and expansion in existing ones is expected to generate 5,227 first-year students in 2012, an increase of 1,380 students (36%) over 2006 numbers. The overwhelming majority of these anticipated new COM graduates cannot be accommodated in American Osteopathic Association postdoctoral programs because of limited capacity. As these additional LCME graduates move into their postdoctoral training, educational opportunities for DOs are expected to decline and competition is expected to become stiffer. The window of opportunity for DOs in ACGME programs that opened in the last two decades will gradually start to close.

Frequency and degree of change of peak transvalvular pressure gradient determined by two Doppler echocardiographic examinations in newborns and children with valvular congenital aortic stenosis.

The natural history of congenital aortic stenosis (AS) has been described predominantly using data derived from catheterization studies. Because of the inherent selection bias of many of these studies, this study was conducted to determine the course of valvular AS using data from serial echocardiograms, for which this bias is less pervasive. The medical records of 103 patients (mean age 3.3+/-3.8 years at time of diagnosis) with congenital AS were examined, and data from the initial and most recent echocardiograms before any intervention on the aortic valve were recorded. The average change in gradient for the entire study population was +1 mm Hg/patient-year. Forty percent (8 of 20) of patients diagnosed in the newborn period (<2 months) required intervention before 6 months of age, compared with 11% (9 of 83) of those diagnosed after the newborn period who required intervention at any time during the study period (p<0.01). Patients diagnosed at >or=1 year of age were less likely to have acute increases in gradient or need intervention; those older patients whose gradients progressed more rapidly were more likely to have significant (more than mild) aortic insufficiency than those whose gradients did not progress (55% vs 28%, p<0.05). In conclusion, congenital AS is usually a slowly progressive disease. Risk factors for more rapid gradient progression include diagnosis as a neonate and the development of significant aortic insufficiency.

The predicament of osteopathic postdoctoral education.

The growth of colleges of osteopathic medicine (COMs) during the past 20 years has been a catalyst for change and has created new challenges in osteopathic medicine. None of these challenges is more daunting than the task of sustaining an osteopathic graduate medical education (OGME) system that has suffered during this period of rapid development. Notable trends within the osteopathic medicine community since 1990 include allopathic residency programs obtaining OGME accreditation, COM graduates bypassing OGME, repeated major changes in American Osteopathic Association (AOA) accreditation policies, a growing dependence on Accreditation Council for Graduate Medical Education programs to train osteopathic graduates, and a lessening of options for the AOA to effectively direct its OGME system. The predicament is whether COMs can continue to grow without resulting in the demise of the OGME system and a loss of professional identity.

Family medicine's search for manpower: the American Osteopathic Association accreditation option.

In recent years, family medicine has encountered problems recruiting and filling its Accreditation Council for Graduate Medical Education (ACGME)-accredited residencies. In addressing these reverses, one increasingly popular strategy has been to acquire American Osteopathic Association (AOA) accreditation as a way to tap into the growing number of osteopathic graduates. This stratagem is founded on assumptions that parallel-accredited postdoctoral programs are attractive to doctor of osteopathy (DO) graduates, that collaboration with sponsoring colleges of osteopathic medicine (COMs) provides direct access to osteopathic students, and that DOs can play an important role in replacing the increasing scarcity of United States medical graduates who are selecting specialty residencies. Within the past 5 years, nearly 10% of all ACGME family medicine residency programs have voluntarily obtained a second level of accreditation to also qualify as AOA-accredited family medicine residency programs. This strategy has produced mixed outcomes, as noted from the results of the osteopathic matching program. The flood of osteopathic graduates into these parallel-accredited programs has not occurred. In addition, recent AOA policy changes now require ACGME-accredited programs to make a deeper educational commitment to osteopathic postdoctoral education. The most successful ACGME/AOA-accredited programs have been those that are closely affiliated with and in near proximity of a COM and also train osteopathic students in required clerkship rotations.