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Search Results: 1 - 10 of 402046 matches for " Frederick M. Ivey "
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Over-ground walking in Parkinson’s disease: A pilot study utilizing a portable metabolic analyzer  [PDF]
Alyssa D. Stookey, Frederick M. Ivey, Jessica E. Hammers, Lisa M. Shulman, Karen Anderson, Leslie I. Katzel
Health (Health) , 2012, DOI: 10.4236/health.2012.431170
Abstract: Alterations in gait biomechanics are common during early stages of Parkinson’s disease (PD), potentially elevating energy requirements of walking and leading to impaired economy of gait. Although gait economy is traditionally assessed during treadmill walking with simultaneous ox-ygen consumption (VO2) monitoring, treadmill gait mechanics, particularly in PD, may be different from over-ground walking mechanics, possibly providing a distorted picture of true gait economy. Currently, no studies have directly examined the energy cost of over-ground walking in PD patients. The purpose of this study was to test the feasibility of measuring energy expenditure during over-ground walking in mild to moderate PD using portable gas exchange monitoring technology. Additionally, we sought to determine whether energy expenditure, as assessed through VO2 measures, related to disease severity for PD. Seventeen PD patients underwent separate 6-minute walk (6MW) tests both with and without the COSMED K4b2 portable oxygen monitoring system. Gait economy was calculated as measured VO2 during 6MW divided by the predicted VO2 for non-PD age-matched subjects, according to a standard estimation equation utilizing ground speed. Distance covered during the 6MW with the portable system (420 ± 12 meters) was highly correlated (r = 0.96, p < 0.001) to distance without the system (442 ± 135 meters) indicating that the lightweight equipment did not confound walking ability in these participants. Mean VO2 during the 6MW (16.0 ± 5.5 mL/kg/min) was 74% of mean VO2 peak for this sample, and 16 out of 17 subjects had impaired gait economy. The degree of gait economy impairment was not related to scores on either UPDRS total or motor. Our results demonstrate that PD patients use extraordinarily high percentage of VO2 peak for normal floor walking, and show impaired gait economy relative to prediction equations. Interestingly, the degree of elevated energy expenditure during gait did not relate to disease severity.
Reduced Cardiorespiratory Fitness after Stroke: Biological Consequences and Exercise-Induced Adaptations
Sandra A. Billinger,Eileen Coughenour,Marilyn J. MacKay-Lyons,Frederick M. Ivey
Stroke Research and Treatment , 2012, DOI: 10.1155/2012/959120
Abstract: Evidence from several studies consistently shows decline in cardiorespiratory (CR) fitness and physical function after disabling stroke. The broader implications of such a decline to general health may be partially understood through negative poststroke physiologic adaptations such as unilateral muscle fiber type shifts, impaired hemodynamic function, and decrements in systemic metabolic status. These physiologic changes also interrelate with reductions in activities of daily living (ADLs), community ambulation, and exercise tolerance, causing a perpetual cycle of worsening disability and deteriorating health. Fortunately, initial evidence suggests that stroke participants retain the capacity to adapt physiologically to an exercise training stimulus. However, despite this evidence, exercise as a therapeutic intervention continues to be clinically underutilized in the general stroke population. Far more research is needed to fully comprehend the consequences of and remedies for CR fitness impairments after stroke. The purpose of this brief review is to describe some of what is currently known about the physiological consequences of CR fitness decline after stroke. Additionally, there is an overview of the evidence supporting exercise interventions for improving CR fitness, and associated aspects of general health in this population. 1. Introduction Little is known about the biology surrounding decrements in cardiorespiratory (CR) fitness after stroke, but evidence has gradually begun to track the damage caused to multiple physiological systems by stroke-related chronic inactivity [1–8]. Collectively, these changes negatively impact morbidity and mortality prospects and contribute to reduced quality of life [9]. Because CR fitness is a measure that quantifies the ability of the heart, lungs, blood vessels, and skeletal muscles to work together to deliver oxygen and remove metabolic byproducts during exercise, it is indirectly reflective of broad categories of cardiovascular, metabolic, and functional health. Most often, CR fitness is measured using a metabolic cart for gas analysis and exercise equipment (e.g., treadmill, recumbent stepper, or cycle ergometer) to determine peak oxygen-consuming capacity (VO2 peak) and is quantified during exercise to complete exhaustion [10–16]. CR fitness varies according to age, gender, physical activity levels, body composition, and the absence or presence of chronic disease or disability. In the poststroke population, the literature suggests that CR fitness is reduced by as much as 50% when compared to age-matched
Impaired Economy of Gait and Decreased Six-Minute Walk Distance in Parkinson's Disease
Leslie I. Katzel,Frederick M. Ivey,John D. Sorkin,Richard F. Macko,Barbara Smith,Lisa M. Shulman
Parkinson's Disease , 2012, DOI: 10.1155/2012/241754
Abstract: Changes in the biomechanics of gait may alter the energy requirements of walking in Parkinson's Disease (PD). This study investigated economy of gait during submaximal treadmill walking in 79 subjects with mild to moderate PD and the relationship between gait economy and 6-minute walk distance (6?MW). Oxygen consumption (VO2) at the self-selected treadmill walking speed averaged 64% of peak oxygen consumption (VO2 peak). Submaximal VO2 levels exceeded 70% of VO2 peak in 30% of the subjects. Overall the mean submaximal VO2 was 51% higher than VO2 levels expected for the speed and grade consistent with severe impairment in economy of gait. There was an inverse relationship between economy of gait and 6MW ( , ) and with the self-selected walking speed ( , ). Thus, the impairment in economy of gait and decreased physiologic reserve result in routine walking being performed at a high percentage of VO2 peak. 1. Introduction Walking capacity is central to the performance of many activities of daily living. Difficulty with walking is one of the cardinal symptoms of Parkinson’s Disease (PD). Alterations in the biomechanics of gait, such as decreased stride length, increased stride length variability, and reduced gait speed, are common even in early stages of PD [1–3]. Most often, PD patients attempt to compensate for short steps by increasing gait cadence, thereby potentially altering energy requirements. This higher energy cost of movement is often referred to as a lower economy of gait and is a function of abnormal gait patterns that accompany aging and neurological disability. Reduced economy of gait has been associated with impaired function and fatigue in non-PD populations [4–9], but there is currently scant information on how parkinsonian gait affects energy expenditure or economy of gait using direct measures of oxygen consumption [10]. Further, little is known about the relationship between economy of gait and mobility. Hence, the purpose of this study was to investigate economy of gait during submaximal treadmill walking in mild to moderate PD, and the relationship between economy of gait and the distance covered during the 6-minute walk (6?MW). 2. Methods 2.1. Subjects Participants for this study were recruited from the University of Maryland Parkinson’s Disease Center and the Baltimore VA Medical Center neurology clinics as part of an exercise intervention trial in PD [11]. Inclusion criteria were (1) diagnosis of levodopa-responsive PD characterized by 2 of 3 cardinal signs (resting tremor, bradykinesia, rigidity), (2) Hoehn and Yahr (HY) [12] stage
The Unified Parkinson’s Disease Rating Scale as a predictor of peak aerobic capacity and ambulatory function
Frederick M. Ivey, PhD,Leslie I. Katzel, MD, PhD,John D. Sorkin, MD, PhD,Richard F. Macko, MD
Journal of Rehabilitation Research and Development , 2012, DOI: 10.1682/jrrd.2011.06.0103
Abstract: The Unified Parkinson’s Disease Rating Scale (UPDRS) is a widely applied index of disease severity. Our objective was to assess the utility of UPDRS for predicting peak aerobic capacity (VO2 peak) and ambulatory function. Participants (n = 70) underwent evaluation for UPDRS (Total and Motor ratings), VO2 peak, 6-minute walk distance (6MW), and 30-foot self-selected walking speed (SSWS). Using regression, we determined the extent to which the Total and Motor UPDRS scores predicted each functional capacity measure after adjusting for age and sex. We also tested whether adding the Hoehn and Yahr scale (H-Y) to the model changed predictive power of the UPDRS. Adjusted for age and sex, both the Total UPDRS and Motor UPDRS subscale failed to predict VO2 peak. The Total UPDRS did weakly predict 6MW and SSWS (both p < 0.05), but the Motor UPDRS subscale did not predict these ambulatory function tests. After adding H-Y to the model, Total UPDRS was no longer an independent predictor of 6MW but remained a predictor of SSWS. We conclude that Total and Motor UPDRS rating scales do not predict VO2 peak, but that a weak relationship exists between Total UPDRS and measures of ambulatory function.
Impact of Serum Nutritional Status on Physical Function in African American and Caucasian Stroke Survivors
Monica C. Serra,Charlene E. Hafer-Macko,Frederick M. Ivey,Richard F. Macko,Alice S. Ryan
Stroke Research and Treatment , 2014, DOI: 10.1155/2014/174308
Abstract: Background. The purpose of this study is to compare serum nutritional profiles in chronic stroke survivors to a representative sample of US Adults (NHANESIII) and determine whether these serum markers differed by race and impact physical function in stroke. Methods. Fasting serum samples were collected for analysis of lipids, uric acid, and albumin in 145 African American (AA) and 111 Caucasian (C) stroke survivors (age: 60 ± 1 years [mean ± SEM]). A six-minute walk was performed in a subset of stroke survivors (N = 134). Results. Triglycerides were higher and HDL-cholesterol and albumin lower in C than AA women stroke survivors (Ps < 0.05). Uric acid was lower in C than AA stroke survivors (P < 0.05). Compared to NHANESIII, HDL-cholesterol, albumin, and hemoglobin generally were lower (Ps < 0.05) and lipids were more favorable in stroke (Ps < 0.01). Uric acid was related to six-minute walk performance among a subset of stroke survivors (P < 0.05). Conclusion. In stroke, racial differences exist with regard to serum nutritional risk, but these differences are similar to that observed in the general population. Regardless of race, nutritional risk appears elevated above that of the general population with regard to many of the serum markers. As a modifiable biomarker, uric acid should be monitored closely as it may provide insight into the functional risk of stroke survivors. 1. Introduction Both suboptimal or excessive caloric intake and poor dietary quality affect nutritional risk and may hinder recovery from stroke. In as little as six months following discharge from an initial stroke incident, ~41% of survivors are at nutritional risk, based upon patient interviews regarding appetite, digestion, mobility, and swallowing difficulties [1]. Another study shows that 11% of stroke survivors with initial motor deficits and communication impairment still require feeding assistance six months after stroke [2]. Further, we have previously shown that well into the chronic phase of stroke recovery (>6 months), survivors are obese and have greater intramuscular fat relative to muscle area in their affected limb [3], indicating imbalanced dietary intake relative to energy expenditure. While these data suggest that poor caloric intake exists in chronic stroke, little data are currently available regarding diet quality in stroke. Difficulties with speech and cognition may interfere with obtaining accurate dietary records to assess dietary quality in those chronically disabled by stroke. However, several serum biomarkers commonly found on general comprehensive
On isometric and minimal isometric embeddings
Thomas Ivey,J. M. Landsberg
Mathematics , 1995,
Abstract: In this paper we study critial isometric and minimal isometric embeddings of classes of Riemannian metrics which we call {\it quasi-$k$-curved metrics}. Quasi-$k$-curved metrics generalize the metrics of space forms. We construct explicit examples and prove results about existence and rigidity.
Leverage, Default Risk, and the Cross-Section of Equity and Firm Returns  [PDF]
Frederick M. Hood III
Modern Economy (ME) , 2016, DOI: 10.4236/me.2016.714143
Abstract: I examine the two components of default risk and how they relate to stock returns, size, and book-to-market. High default risk firms do not necessarily have high levels of systematic asset risk. I show that the two components of default risk, asset volatility and leverage, are negatively related. I provide evidence that leverage differences across firms are not reflected in equity betas. Therefore, I construct firm returns using estimates of firm’s debt returns. The results indicate that a large part of the value premium and some of the size premium can be explained by differences in leverage across firms.
Finite-gap Solutions of the Vortex Filament Equation: Isoperiodic Deformations
Annalisa M. Calini,Thomas A. Ivey
Physics , 2006, DOI: 10.1007/s00332-007-9002-x
Abstract: We study the topology of quasiperiodic solutions of the vortex filament equation in a neighborhood of multiply covered circles. We construct these solutions by means of a sequence of isoperiodic deformations, at each step of which a real double point is "unpinched" to produce a new pair of branch points and therefore a solution of higher genus. We prove that every step in this process corresponds to a cabling operation on the previous curve, and we provide a labelling scheme that matches the deformation data with the knot type of the resulting filament.
The triage dilemma: opening Pandora's box... ever so slowly
Frederick M Burkle
Critical Care , 2010, DOI: 10.1186/cc8215
Abstract: In reality, intensive care units with their professional staff and high-tech equipment represent a major limiting factor for most communities. The most plausible scenario for a viral pathogen of greater severity and lethality is that emergency departments and hospital wards will be deluged with critical care patients, the challenge being how to provide 'opportunities for survival' by transferring some semblance of critical care services and expertise to these 'non-critical care' settings. Discipline-directed triage management protocols will only be as important as the manner in which these tertiary level algorithms can be integrated into a larger system-wide triage scheme that begins at the primary triage care level and ends with whatever additional resources a regional support system can mobilize. Many 'uncomfortable but real' decisions that have not, to date, been operationalized at the local level will be made.Triage management requires an infrastructure, such as health emergency operations centers (HEOCs), where central triage committees, operationalized ethical resources, palliative care guidance, data collection and analysis, and communication capacities provide high-level situational awareness for simultaneously initiating triage and modifying protocols at all health facilities and their individual triage teams [5]. While attempts to provide independent hospital-centric plans are noble, they do not solve what ultimately requires an integrated population-based system-wide solution [6].Triage is an imperfect but necessary 'art and science' whether based on good clinical judgment or informed by protocols that attempt to direct resources to those most likely to benefit. Critical care studies opened Pandora's box. What follows requires much more input from other disciplines and society itself. Although it may first seem like one is trespassing professional boundaries, the investment in integrated preparedness and effective surge strategies, including system-wide t
The Proper Motion, Parallax, and Origin of the Isolated Neutron Star RX J185635-3754
Frederick M. Walter
Physics , 2000, DOI: 10.1086/319058
Abstract: The isolated neutron star RX J185635-3754 is the closest known neutron star to the Sun. Based on HST WFPC2 obervations over a 3 year baseline, I report its proper motion (332 +/- 1 mas/yr at a position angle of 100.3 +/- 0.1 degrees) and parallax (16.5 +/- 2.3 mas; 61 pc). This proper motion brings the neutron star from the general vicinity of the Sco-Cen OB association. For an assumed neutron star radial velocity between -55 and -60 km/s, the runaway O star zeta Oph, the Upper Sco OB association, and the neutron star come into spatial coincidence between 0.9 and 1.0 million years ago. RX J185635-3754 may be the remnant of the original primary of the zeta Oph system. If so, the space velocity suggests that the neutron star received a kick of about 200 km/s at birth.
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