1
|
Balbinot G, Li G, Wiest MJ, Pakosh M, Furlan JC, Kalsi-Ryan S, Zariffa J. Properties of the surface electromyogram following traumatic spinal cord injury: a scoping review. J Neuroeng Rehabil 2021; 18:105. [PMID: 34187509 PMCID: PMC8244234 DOI: 10.1186/s12984-021-00888-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Accepted: 05/27/2021] [Indexed: 12/23/2022] Open
Abstract
Traumatic spinal cord injury (SCI) disrupts spinal and supraspinal pathways, and this process is reflected in changes in surface electromyography (sEMG). sEMG is an informative complement to current clinical testing and can capture the residual motor command in great detail-including in muscles below the level of injury with seemingly absent motor activities. In this comprehensive review, we sought to describe how the sEMG properties are changed after SCI. We conducted a systematic literature search followed by a narrative review focusing on sEMG analysis techniques and signal properties post-SCI. We found that early reports were mostly focused on the qualitative analysis of sEMG patterns and evolved to semi-quantitative scores and a more detailed amplitude-based quantification. Nonetheless, recent studies are still constrained to an amplitude-based analysis of the sEMG, and there are opportunities to more broadly characterize the time- and frequency-domain properties of the signal as well as to take fuller advantage of high-density EMG techniques. We recommend the incorporation of a broader range of signal properties into the neurophysiological assessment post-SCI and the development of a greater understanding of the relation between these sEMG properties and underlying physiology. Enhanced sEMG analysis could contribute to a more complete description of the effects of SCI on upper and lower motor neuron function and their interactions, and also assist in understanding the mechanisms of change following neuromodulation or exercise therapy.
Collapse
Affiliation(s)
- Gustavo Balbinot
- KITE-Toronto Rehabilitation Institute, University Health Network, Toronto, ON, M5G 2A2, Canada.
| | - Guijin Li
- KITE-Toronto Rehabilitation Institute, University Health Network, Toronto, ON, M5G 2A2, Canada
- Institute of Biomedical Engineering, University of Toronto, Toronto, Canada
| | - Matheus Joner Wiest
- KITE-Toronto Rehabilitation Institute, University Health Network, Toronto, ON, M5G 2A2, Canada
| | - Maureen Pakosh
- Library & Information Services, Toronto Rehabilitation Institute, University Health Network, Toronto, Canada
| | - Julio Cesar Furlan
- KITE-Toronto Rehabilitation Institute, University Health Network, Toronto, ON, M5G 2A2, Canada
- Rehabilitation Sciences Institute, University of Toronto, Toronto, Canada
- Department of Medicine, Division of Physical Medicine and Rehabilitation, University of Toronto, Toronto, Canada
- Division of Physical Medicine and Rehabilitation, Toronto Rehabilitation Institute, University Health Network, Toronto, Canada
- Institute of Medical Sciences, University of Toronto, Toronto, Canada
| | - Sukhvinder Kalsi-Ryan
- KITE-Toronto Rehabilitation Institute, University Health Network, Toronto, ON, M5G 2A2, Canada
- Rehabilitation Sciences Institute, University of Toronto, Toronto, Canada
- Department of Physical Therapy, University of Toronto, Toronto, Canada
| | - Jose Zariffa
- KITE-Toronto Rehabilitation Institute, University Health Network, Toronto, ON, M5G 2A2, Canada
- Institute of Biomedical Engineering, University of Toronto, Toronto, Canada
- Rehabilitation Sciences Institute, University of Toronto, Toronto, Canada
- Edward S. Rogers Sr. Department of Electrical and Computer Engineering, University of Toronto, Toronto, Canada
| |
Collapse
|
2
|
Meyer C, Hofstoetter US, Hubli M, Hassani RH, Rinaldo C, Curt A, Bolliger M. Immediate Effects of Transcutaneous Spinal Cord Stimulation on Motor Function in Chronic, Sensorimotor Incomplete Spinal Cord Injury. J Clin Med 2020; 9:E3541. [PMID: 33147884 PMCID: PMC7694146 DOI: 10.3390/jcm9113541] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Revised: 10/22/2020] [Accepted: 10/30/2020] [Indexed: 12/15/2022] Open
Abstract
Deficient ankle control after incomplete spinal cord injury (iSCI) often accentuates walking impairments. Transcutaneous electrical spinal cord stimulation (tSCS) has been shown to augment locomotor activity after iSCI, presumably due to modulation of spinal excitability. However, the effects of possible excitability modulations induced by tSCS on ankle control have not yet been assessed. This study investigated the immediate (i.e., without training) effects during single-sessions of tonic tSCS on ankle control, spinal excitability, and locomotion in ten individuals with chronic, sensorimotor iSCI (American Spinal Injury Association Impairment Scale D). Participants performed rhythmic ankle movements (dorsi- and plantar flexion) at a given rate, and irregular ankle movements following a predetermined trajectory with and without tonic tSCS at 15 Hz, 30 Hz, and 50 Hz. In a subgroup of eight participants, the effects of tSCS on assisted over-ground walking were studied. Furthermore, the activity of a polysynaptic spinal reflex, associated with spinal locomotor networks, was investigated to study the effect of the stimulation on the dedicated spinal circuitry associated with locomotor function. Tonic tSCS at 30 Hz immediately improved maximum dorsiflexion by +4.6° ± 0.9° in the more affected lower limb during the rhythmic ankle movement task, resulting in an increase of +2.9° ± 0.9° in active range of motion. Coordination of ankle movements, assessed by the ability to perform rhythmic ankle movements at a given target rate and to perform irregular movements according to a trajectory, was unchanged during stimulation. tSCS at 30 Hz modulated spinal reflex activity, reflected by a significant suppression of pathological activity specific to SCI in the assessed polysynaptic spinal reflex. During walking, there was no statistical group effect of tSCS. In the subgroup of eight assessed participants, the three with the lowest as well as the one with the highest walking function scores showed positive stimulation effects, including increased maximum walking speed, or more continuous and faster stepping at a self-selected speed. Future studies need to investigate if multiple applications and individual optimization of the stimulation parameters can increase the effects of tSCS, and if the technique can improve the outcome of locomotor rehabilitation after iSCI.
Collapse
Affiliation(s)
- Christian Meyer
- Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, 8008 Zurich, Switzerland; (C.M.); (M.H.); (R.H.H.); (C.R.); (A.C.); (M.B.)
| | - Ursula S. Hofstoetter
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria
| | - Michèle Hubli
- Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, 8008 Zurich, Switzerland; (C.M.); (M.H.); (R.H.H.); (C.R.); (A.C.); (M.B.)
| | - Roushanak H. Hassani
- Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, 8008 Zurich, Switzerland; (C.M.); (M.H.); (R.H.H.); (C.R.); (A.C.); (M.B.)
| | - Carmen Rinaldo
- Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, 8008 Zurich, Switzerland; (C.M.); (M.H.); (R.H.H.); (C.R.); (A.C.); (M.B.)
| | - Armin Curt
- Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, 8008 Zurich, Switzerland; (C.M.); (M.H.); (R.H.H.); (C.R.); (A.C.); (M.B.)
| | - Marc Bolliger
- Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, 8008 Zurich, Switzerland; (C.M.); (M.H.); (R.H.H.); (C.R.); (A.C.); (M.B.)
| |
Collapse
|
3
|
Easthope CS, Traini LR, Awai L, Franz M, Rauter G, Curt A, Bolliger M. Overground walking patterns after chronic incomplete spinal cord injury show distinct response patterns to unloading. J Neuroeng Rehabil 2018; 15:102. [PMID: 30419945 PMCID: PMC6233558 DOI: 10.1186/s12984-018-0436-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Accepted: 10/15/2018] [Indexed: 12/28/2022] Open
Abstract
BACKGROUND Body weight support (BWS) is often provided to incomplete spinal cord injury (iSCI) patients during rehabilitation to enable gait training before full weight-bearing is recovered. Emerging robotic devices enable BWS during overground walking, increasing task-specificity of the locomotor training. However, in contrast to a treadmill setting, there is little information on how unloading is integrated into overground locomotion. We investigated the effect of a transparent multi-directional BWS system on overground walking patterns at different levels of unloading in individuals with chronic iSCI (CiSCI) compared to controls. METHODS Kinematics of 12 CiSCI were analyzed at six different BWS levels from 0 to 50% body weight unloading during overground walking at 2kmh- 1 and compared to speed-matched controls. RESULTS In controls, temporal parameters, single joint trajectories, and intralimb coordination responded proportionally to the level of unloading, while spatial parameters remained unaffected. In CiSCI, unloading induced similar changes in temporal parameters. CiSCI, however, did not adapt their intralimb coordination or single joint trajectories to the level of unloading. CONCLUSIONS The findings revealed that continuous, dynamic unloading during overground walking results in subtle and proportional gait adjustments corresponding to changes in body load. CiSCI demonstrated diminished responses in specific domains of gait, indicating that their altered neural processing impeded the adjustment to environmental constraints. CiSCI retain their movement patterns under overground unloading, indicating that this is a viable locomotor therapy tool that may also offer a potential window on the diminished neural control of intralimb coordination.
Collapse
Affiliation(s)
| | - Luca Renato Traini
- Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, CH-8008, Zürich, Switzerland
| | - Lea Awai
- Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, CH-8008, Zürich, Switzerland.,Sobell Department of Motor Neuroscience and Movement Disorders, University College London, London, UK
| | - Martina Franz
- Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, CH-8008, Zürich, Switzerland
| | - Georg Rauter
- BIROMED-Lab, Department of Biomedical Engineering, University Basel, Basel, Switzerland
| | - Armin Curt
- Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, CH-8008, Zürich, Switzerland
| | - Marc Bolliger
- Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, CH-8008, Zürich, Switzerland
| |
Collapse
|
4
|
Holanda LJ, Silva PMM, Amorim TC, Lacerda MO, Simão CR, Morya E. Robotic assisted gait as a tool for rehabilitation of individuals with spinal cord injury: a systematic review. J Neuroeng Rehabil 2017; 14:126. [PMID: 29202845 PMCID: PMC5715997 DOI: 10.1186/s12984-017-0338-7] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 11/23/2017] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Spinal cord injury (SCI) is characterized by a total or partial deficit of sensory and motor pathways. Impairments of this injury compromise muscle recruitment and motor planning, thus reducing functional capacity. SCI patients commonly present psychological, intestinal, urinary, osteomioarticular, tegumentary, cardiorespiratory and neural alterations that aggravate in chronic phase. One of the neurorehabilitation goals is the restoration of these abilities by favoring improvement in the quality of life and functional independence. Current literature highlights several benefits of robotic gait therapies in SCI individuals. OBJECTIVES The purpose of this study was to compare the robotic gait devices, and systematize the scientific evidences of these devices as a tool for rehabilitation of SCI individuals. METHODS A systematic review was carried out in which relevant articles were identified by searching the following databases: Cochrane Library, PubMed, PEDro and Capes Periodic. Two authors selected the articles which used a robotic device for rehabilitation of spinal cord injury. RESULTS Databases search found 2941 articles, 39 articles were included due to meet the inclusion criteria. The robotic devices presented distinct features, with increasing application in the last years. Studies have shown promising results regarding the reduction of pain perception and spasticity level; alteration of the proprioceptive capacity, sensitivity to temperature, vibration, pressure, reflex behavior, electrical activity at muscular and cortical level, classification of the injury level; increase in walking speed, step length and distance traveled; improvements in sitting posture, intestinal, cardiorespiratory, metabolic, tegmental and psychological functions. CONCLUSIONS This systematic review shows a significant progress encompassing robotic devices as an innovative and effective therapy for the rehabilitation of individuals with SCI.
Collapse
Affiliation(s)
- Ledycnarf J Holanda
- Neuroengineering Program, Edmond and Lily Safra International Neuroscience Institute, Santos Dumont Institute, Rodovia RN 160, Km 03, 3001 Distrito Jundiaí, Macaíba, 59280-000, Brazil.
| | - Patrícia M M Silva
- Neuroengineering Program, Edmond and Lily Safra International Neuroscience Institute, Santos Dumont Institute, Rodovia RN 160, Km 03, 3001 Distrito Jundiaí, Macaíba, 59280-000, Brazil
| | - Thiago C Amorim
- Neuroengineering Program, Edmond and Lily Safra International Neuroscience Institute, Santos Dumont Institute, Rodovia RN 160, Km 03, 3001 Distrito Jundiaí, Macaíba, 59280-000, Brazil
| | - Matheus O Lacerda
- Federal University of Rio Grande do Norte, Av. Sen. Salgado Filho Lagoa Nova, Natal, 59078-970, Brazil
| | - Camila R Simão
- Federal University of Rio Grande do Norte, Av. Sen. Salgado Filho Lagoa Nova, Natal, 59078-970, Brazil.,Anita Garibaldi Center of Education and Research in Health, Santos Dumont Institute, Rodovia RN 160, Km 02, 2010 Distrito Jundiaí, Macaíba, 59280-970, Brazil
| | - Edgard Morya
- Neuroengineering Program, Edmond and Lily Safra International Neuroscience Institute, Santos Dumont Institute, Rodovia RN 160, Km 03, 3001 Distrito Jundiaí, Macaíba, 59280-000, Brazil.,Anita Garibaldi Center of Education and Research in Health, Santos Dumont Institute, Rodovia RN 160, Km 02, 2010 Distrito Jundiaí, Macaíba, 59280-970, Brazil
| |
Collapse
|
5
|
Schrafl-Altermatt M, Dietz V, Bolliger M. Effect of Locomotor Training on Exhaustion of Leg Muscle Activity in Chronic Complete Spinal Cord Injury. J Neurotrauma 2017; 34:2375-2378. [PMID: 27736315 DOI: 10.1089/neu.2016.4627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The aim of this study was to evaluate the effect of a continuous locomotor training on leg muscle electromyographic (EMG) exhaustion during assisted stepping movements in a patient with motor complete spinal cord injury (SCI). EMG exhaustion and loss of potentials starts to develop in untrained patients at ∼6 months after injury. In the trained patient examined in this study, exhaustion was also observed but occurred with a delay of several months. In contrast to an untrained patient, no more EMG exhaustion was observed in the very chronic stage. At this time (12 years after injury) a basic locomotor pattern of leg muscle activity of reduced amplitude could still be elicited, but it was resistant to exhaustion and unchanged in amplitude after 12 min of assisted stepping. It is suggested that fatigue-resistant motor units prevail at this stage and can still be activated during stepping as a result of the training.
Collapse
Affiliation(s)
| | - Volker Dietz
- Spinal Injury Center, Balgrist University Hospital , Zürich, Switzerland
| | - Marc Bolliger
- Spinal Injury Center, Balgrist University Hospital , Zürich, Switzerland
| |
Collapse
|
6
|
Recruitment of Polysynaptic Connections Underlies Functional Recovery of a Neural Circuit after Lesion. eNeuro 2016; 3:eN-NWR-0056-16. [PMID: 27570828 PMCID: PMC4999536 DOI: 10.1523/eneuro.0056-16.2016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Revised: 07/14/2016] [Accepted: 07/18/2016] [Indexed: 11/21/2022] Open
Abstract
The recruitment of additional neurons to neural circuits often occurs in accordance with changing functional demands. Here we found that synaptic recruitment plays a key role in functional recovery after neural injury. Disconnection of a brain commissure in the nudibranch mollusc, Tritonia diomedea, impairs swimming behavior by eliminating particular synapses in the central pattern generator (CPG) underlying the rhythmic swim motor pattern. However, the CPG functionally recovers within a day after the lesion. The strength of a spared inhibitory synapse within the CPG from Cerebral Neuron 2 (C2) to Ventral Swim Interneuron B (VSI) determines the level of impairment caused by the lesion, which varies among individuals. In addition to this direct synaptic connection, there are polysynaptic connections from C2 and Dorsal Swim Interneurons to VSI that provide indirect excitatory drive but play only minor roles under normal conditions. After disconnecting the pedal commissure (Pedal Nerve 6), the recruitment of polysynaptic excitation became a major source of the excitatory drive to VSI. Moreover, the amount of polysynaptic recruitment, which changed over time, differed among individuals and correlated with the degree of recovery of the swim motor pattern. Thus, functional recovery was mediated by an increase in the magnitude of polysynaptic excitatory drive, compensating for the loss of direct excitation. Since the degree of susceptibility to injury corresponds to existing individual variation in the C2 to VSI synapse, the recovery relied upon the extent to which the network reorganized to incorporate additional synapses.
Collapse
|
7
|
Nardone R, Trinka E. Reorganization of spinal neural circuitry and functional recovery after spinal cord injury. Neural Regen Res 2015; 10:201-2. [PMID: 25883613 PMCID: PMC4392662 DOI: 10.4103/1673-5374.152368] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/01/2014] [Indexed: 01/06/2023] Open
Affiliation(s)
- Raffaele Nardone
- Department of Neurology, Christian Doppler Klinik, Paracelsus Medical University, Salzburg, Austria; Spinal Cord Injury and Tissue Regeneration Center, Paracelsus Medical University, Salzburg, Austria ; Department of Neurology, Franz Tappeiner Hospital, Merano, Italy
| | - Eugen Trinka
- Department of Neurology, Christian Doppler Klinik, Paracelsus Medical University, Salzburg, Austria; Spinal Cord Injury and Tissue Regeneration Center, Paracelsus Medical University, Salzburg, Austria
| |
Collapse
|
8
|
Modulation of spinal neuronal excitability by spinal direct currents and locomotion after spinal cord injury. Clin Neurophysiol 2013; 124:1187-95. [DOI: 10.1016/j.clinph.2012.11.021] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Revised: 10/29/2012] [Accepted: 11/05/2012] [Indexed: 12/18/2022]
|
9
|
Wang P, Low KH, McGregor AH, Tow A. Detection of abnormal muscle activations during walking following spinal cord injury (SCI). RESEARCH IN DEVELOPMENTAL DISABILITIES 2013; 34:1226-1235. [PMID: 23396198 DOI: 10.1016/j.ridd.2012.12.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Revised: 12/18/2012] [Accepted: 12/19/2012] [Indexed: 06/01/2023]
Abstract
In order to identify optimal rehabilitation strategies for spinal cord injury (SCI) participants, assessment of impaired walking is required to detect, monitor and quantify movement disorders. In the proposed assessment, ten healthy and seven SCI participants were recruited to perform an over-ground walking test at slow walking speeds. SCI participants were given assistance from physiotherapists, if required, while they were walking. In agreement with other research, larger cadence and smaller step length and swing phase of SCI gait were observed as a result of muscle weakness and resultant gait instability. Muscle activation patterns of seven major leg muscles were collected. The EMG signal was processed by the RMS in frequency domain to represent the muscle activation power, and the distribution of muscle activation was compared between healthy and SCI participants. The alternations of muscle activation within the phases of the gait cycle are highlighted to facilitate our understanding of the underlying muscular activation following SCI. Key differences were observed (p-value=0.0006) in the reduced activation of tibialis anterior (TA) in single stance phase and rectus femoris (RF) in swing phase (p-value=0.0011). We can then conclude that the proposed assessment approach of gait provides valuable information that can be used to target and define therapeutic interventions and their evaluation; hence impacting the functional outcome of SCI individuals.
Collapse
Affiliation(s)
- Ping Wang
- Institute for Sports Research, Nanyang Technological University (NTU), Singapore 639798, Republic of Singapore
| | | | | | | |
Collapse
|
10
|
Duysens J, De Groote F, Jonkers I. The flexion synergy, mother of all synergies and father of new models of gait. Front Comput Neurosci 2013; 7:14. [PMID: 23494365 PMCID: PMC3595503 DOI: 10.3389/fncom.2013.00014] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 02/20/2013] [Indexed: 12/22/2022] Open
Abstract
Recently there has been a growing interest in the modular organization of leg movements, in particular those related to locomotion. One of the basic modules involves the flexion of the leg during swing and it was shown that this module is already present in neonates (Dominici et al., 2011). In this paper, we question how these finding build upon the original work by Sherrington, who proposed that the flexor reflex is the basic building block of flexion during swing phase. Similarly, the relation between the flexor reflex and the withdrawal reflex modules of Schouenborg and Weng (1994) will be discussed. It will be argued that there is large overlap between these notions on modules and the older concepts of reflexes. In addition, it will be shown that there is a great flexibility in the expression of some of these modules during gait, thereby allowing for a phase-dependent modulation of the appropriate responses. In particular, the end of the stance phase is a period when the flexor synergy is facilitated. It is proposed that this is linked to the activation of circuitry that is responsible for the generation of locomotor patterns (CPG, “central pattern generator”). More specifically, it is suggested that the responses in that period relate to the activation of a flexor burst generator. The latter structure forms the core of a new asymmetric model of the CPG. This activation is controlled by afferent input (facilitation by a broad range of afferents, suppression by load afferent input). Meanwhile, many of these physiologic features have found their way in the control of very flexible walking bipedal robots.
Collapse
Affiliation(s)
- Jacques Duysens
- Department of Kinesiology, KU Leuven Heverlee, Belgium ; Department of Research, Sint Maartenskliniek Nijmegen, Netherlands
| | | | | |
Collapse
|
11
|
Hubli M, Bolliger M, Limacher E, R. Luft A, Dietz V. Spinal neuronal dysfunction after stroke. Exp Neurol 2012; 234:153-60. [DOI: 10.1016/j.expneurol.2011.12.025] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2011] [Revised: 11/28/2011] [Accepted: 12/15/2011] [Indexed: 10/14/2022]
|