therapeutic approaches targeting skeletal muscle plasticity after sci
DESCRIPTION
Therapeutic Approaches Targeting Skeletal Muscle Plasticity after SCI. Chris Gregory Assistant Professor Department of Health Sciences & Research Medical University of South Carolina Health Science Specialist Research Service Ralph H. Johnson VAMC July 17, 2012. - PowerPoint PPT PresentationTRANSCRIPT
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Therapeutic Approaches Targeting Skeletal Muscle Plasticity after SCI
Chris Gregory
Assistant ProfessorDepartment of Health Sciences &
ResearchMedical University of South Carolina
Health Science SpecialistResearch Service
Ralph H. Johnson VAMC
July 17, 2012
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Disclosure of PI-RRTC Grant
• James S. Krause, PhD, Holly Wise, PhD; PT, and Emily Johnson, MHA have disclosed a research grant with the National Institute of Disability and Rehabilitation Research.
• The contents of this presentation were developed with support from an educational grant from the Department of Education, NIDRR grant number H133B090005. However, those contents do not necessarily represent the policy of the Department of Education, and you should not assume endorsement by the Federal Government.
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Accreditation• The Medical University of South Carolina is accredited by the Accreditation
Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians. The Medical University of South Carolina designates this live activity for a maximum of 1.0 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.
• In accordance with the ACCME Essentials &Standards, anyone involved in planning or presenting this educational activity will be required to disclose any relevant financial relationships with commercial interests in the healthcare industry. This information is listed below. Speakers who incorporate information about off-label or investigational use of drugs or devices will be asked to disclose that information at the beginning of their presentation.
• The Center for Professional Development is an approved provider of the continuing nursing education by the South Carolina Nurses Association an accredited approver by the American Nurses Credentialing Center’s Commission on Accreditation
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Disclosure of Presenter
• Chris Gregory, PhD, PT, has disclosed research grants with the Department of Veteran’s Affairs, American Heart Association, South Carolina Spinal Cord Injury Research Fund and NIH/NINDS.
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Axon Regeneration
Prevent 2°Damage
Create Bridges
Replace Dead Cells
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Outline
• Skeletal muscle adaptations following SCI– Acute vs. Chronic
• Secondary Health Conditions associated with alterations in skeletal muscle after SCI
• Effects of exercise training on skeletal muscle after SCI
• Health-related benefits of exercise in persons with SCI
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Skeletal Muscle
Spinal Cord Injury
Secondary Conditions:NIDDMCVD
ObesityDyslipidemiaDecreased fitness
Osteoporosis
↓ Bone Density ↓ CV Function
Physical Inactivity / Muscle Unloading
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Secondary conditions following SCI
Increased risk of cardiovascular disease (Kocina, 1997)
Leading cause of death after 20 yr DOI~90% > risk of heart attack relative to un-injured~228% > mortality risk from CVD46% of patients over 30 die from CVDDecreased HDL
Increased risk of NIDDM (Bauman, 2000)
~4x incidence of NIDDM after SCI ~65% have impaired CHO metabolism vs 15% in un-injured population
Decreased bone density~50% reduced in 100% of population
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• Complete injury– Absence of sensory and motor function in the lowest sacral
segment
• Incomplete injury– Partial preservation of sensory and/or motor function below
the neurologic level
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ASIA Impairment Scale:
• A No motor or sensory function in the lowest sacral segment
• B Sensory but not motor function is preserved in the lowest sacral segment
• C Less than ½ of the key muscles below the (single) neurological level have a grade 3 or better
• D At least ½ of the key muscles below the (single) neurological level have a grade 3 or better
5 – Normal strength4 – Full ROM with < normal strength against resistance3 – Full ROM against gravity 2 – Movement with gravity eliminated 1 – Palpable contraction but no movement0 – Total paralysis
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Hillegass and Dudley 1999
Able-bodied male C5 complete SCI male
Skeletal muscle adaptations following “Chronic” SCI
Severe Muscle Atrophy (60-75%)
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Quadriceps muscle CSA and total quadriceps muscle volume in SCI and able-bodied (AB) individuals.
Olive J L et al. J Appl Physiol 2003;94:701-708
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Skeletal muscle adaptations following “Chronic” SCI
Control
SCI
Conversion to predominately fast fibers
Martin et al. 1992 Gregory et al. 2003
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~66%
~36%
Bickel et al 2004
Muscle Fatigue
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Olive J L et al. J Appl Physiol 2003;94:701-708
Muscle Fatigue
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PCr recovery curves following NMES for (A) control and (B) SCI individual.
Muscle Fatigue
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Muscle Injury
Bickel et al 20042 ± 1 % 25 ± 6 %
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Long-term SCI
Specific Tension - force per unit area.Torque (Nm) = 3.74 x stimulated CSA (cm2) - 14.37, (R2 = 0.93, p < 0.05)
Bickel et al. 2004
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“Chronic” SCI Muscle
• Severe muscle atrophy
• Conversion to predominately fast fibers.
• Increased fatigability
• Increased susceptibility to injury
• Force generating capacity (relatively) maintained
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Individuals years after SCI have been reported to have muscles that are small, highly fatigable and susceptible to damage; but still produce adequate force relative to their size.
(Grimby 1976, Rochester et al. 1995, Hillegass and Dudley 1999 )
Able-bodied male C5 complete SCI male
Skeletal muscle adaptations following “Chronic” SCI
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Pre-injury 12 weeks post-injury
“Classic” Brown-Sequard syndrome
Skeletal muscle adaptations following “Acute” SCI
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Muscle Atrophy
MRI - 6, 12, 24 weeks after injury
Thigh Muscles
- Hamstring (-14%)
- Adductors (-16%)
- Quadriceps (-16%)
Castro et. al. 1999a
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Muscle Atrophy
MRI - 6, 12, 24 weeks after injury
Shank Muscles
- TA (5% decrease, NS)
- Soleus (-12%)
- Gastrocnemius (-24%)
Castro et. al. 1999a
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Muscle Atrophy
QF -42%
Hamstring -44%
Adductor -31%
Gastroc -46%
Soleus -32%
TA -20%
SCI vs. Controls
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55
60
65
70
75
80
% C
SA
of
AB
0 10 20 30 40 50 60
Time (weeks after injury)
EMS
Dudley et al. 1999
Muscle Atrophy
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Fiber type
Castro et. al. 1999b
* Data from m. Vastus Lateralis
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Enzyme changes
Castro et. al. 1999b
CSA
SDH
GPDH
SDH - Kreb’s cycle (aerobic)
GPDH - glycolytic enzyme (anaerobic)
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Muscle Fatigue
Increased muscle fatigue after SCI despite the alterations in muscle
Castro et al 1999b Bickel et al 2004
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“Acute” SCI Muscle
• Muscle specific atrophy
• Change in fiber type composition.• (IIa to IIx)
– No decrease in % slow muscle in first 6 months
• Energy supply/energy demand apparently unaltered.
• Fatigability is increased compared to controls
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Relative differences in individual muscle CSA between the more-affected limb following incomplete SCI vs. control subjects.
Muscle AtrophyIncomplete SCI
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“Chronic” SCI Bone
SCI results in a dramatic loss of bone and a marked increase in fracture incidence
Dauty et al. 2000; Modelesky et al. 2004
- Chronic SCI results in a 50-70% demineralization and is correlated with duration of injury
- Following complete SCI, bone loss proceeds at a rate of ~1% per week for the first 6-12 months- Microgravity = 0.25% /week- Bed rest = 0.1% /week- Menopause 3-5% /year
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“Chronic” SCI Bone
SCI results in a dramatic loss of bone and a marked increase in fracture incidence
Modelesky et al. 2004
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“Chronic” SCI Bone
SCI results in a dramatic loss of bone and a marked increase in fracture incidence
SCI Control
Distal Femur
Proximal Tibia
Modelesky et al. 2004
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“Chronic” SCI Bone
SCI: r = 0.90 and 0.83Modelesky et al. 2004
Relationship between muscle volume and cortical bone volume and BMC remains strong
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Femoral artery diameter
Peak blood flow
Vascular Response to SCI
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In the next several decades, a cure for SCI is a realistic possibility. Without a means to preserve the musculoskeletal integrity of paralyzed lower limbs, people injured today with SCI will be "inappropriate candidates" for reintroduction to
standing and walking, should a cure be found.
So What?
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Is it possible to elicit changes in muscle and bone years after SCI?
Early studies suggest an inability to increase muscle size in subjects years after injuryOther studies do report modest muscle hypertrophy (0-15%) following NMES cycling
Is this enough?Limitations?
Program design
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Aerobic/endurance exercise does not
Resistance exercise increases muscle size &
strength
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SCI - Resistance Training
2 days/week x 6 months
Electrical stimulation (30 Hz trains of 450 µsec biphasic pulses)
4 sets of 10 knee extensions Resistance - cuff weights
All training performed at subjects’ homes
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55
60
65
70
75
80
% C
SA
of
AB
0 10 20 30 40 50 60
Time (weeks after injury)
EMS
Dudley et al. 1999
4 sets of 102 days per week for 8 weeksTotal contractions = 640
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Molecular signals
Effects of (NMES)-induced exercise on the expression and/or accumulation of mRNA for components of the muscle insulin-like growth factor (IGF)-I system
Bickel et al 2003
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After 6 months of training: Subjects were using between 14 - 30 pounds for resistance at the ankle. QF muscle size increased ~60% in both thighs.
Before 6 Months3 Months
SCI - Resistance Training“Chronic”
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n = 5
*p < 0.05, 3 Mo. Vs. Before
‡ p<0.05, 6 Mo. vs. 3 Mo.
Average AB muscle size (Castro et al. 1999)
RIGHT THIGH LEFT THIGH
SCI - Resistance Training“Chronic”
34
49
58
37
52
62
Mahoney et al 2005
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Left Thigh Muscle CSA
0
10
20
30
40
50
60
70
80
S1 S2 S3 S4 S5 Mean
Mu
sc
le C
SA
(c
m2)
BEFORE
AFTER
SCI - Resistance Training“Chronic”
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FIGURE 1 . Axial MR Images of thigh (A) and knee extensors skeletal muscles (B) and %IMF (C) before and after RT + diet versus diet groups.
Gorgey et al., Med & Sci Sports & Exer. 44(1):165-174
SCI - Resistance Training“Chronic”
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Health-related consequences of increasing muscle mass
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Electrically stimulated RT significantly lowered plasma glucose response during OGTT (n=5)
0
30
60
90
120
150
180
0 60 90 120
Pla
sm
a g
luco
se
(mg/d
l)
SCI - Resistance Training“Chronic”
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Body composition Pre Post
Total (lb) 153.22 ± 9.32 157.76 ± 9.11*
Muscle (lb) 96.8 ± 5.61 100.0 ± 5.47*
Bone (lb) 6.03 ± 0.37 5.99 ± 0.39
Fat (lb) 50.42 ± 5.10 51.78 ± 4.98
Neural factors
Motor score 46.35 ± 4.90 49.35 ± 5.31*
Sensory score 91.59 ± 11.32 97.88 ± 11.52*
Metabolic factors
HDL cholesterol (mg/dL) 34.27 ± 2.00 30.56 ± 2.11*
LDL cholesterol (mg/dL) 102.65 ± 6.20 105.54 ± 5.49
Total cholesterol (mg/dL) 157.91 ± 6.36 156.32 ± 6.65
Triglyceride (mg/dL) 104.92 ± 26.90 101.07 ± 25.46
CRP (mg/L) 15.92 ± 1.57 12.94 ± 0.78*
IL-6 (pg/ml) 4.91 ± 1.10 3.79 ± 0.52*
TNF-α (pg/ml) 11.82 ± 0.63 11.31 ± 0.62*
SCI - Resistance Training“Chronic”
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Fig. 1. Absolute bone mineral density (BMD) for control (■) and for the left (□) and right (▨) sides of subjects with SCI before training. The three regions are statistically different from each other, both for the control and SCI subjects (p < .05). The lower bone densities in the SCI subjects are also significantly different from control subjects in all three regions (indicated by the asterisk above the bars). The BMD expressed as a percentage of control values are indicated at the bottom of the bars
SCI - Resistance Training“Chronic”
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Fatigue before training (6–12 months prior to the initiation of this study), at 8 and 12 weeks, and post-training (18 weeks). Data are illustrated as mean SD. Fatigue decreased as training progressed (P=0.008). Although the pretime point (ie, 0 on the graph) occurred some time before the training program began, the protocol and test administrators were identical for each test administration and subjects had not changed activity levels during the interim period. *P=0.014 for comparison with pretraining. †P=0.016 for comparison with pretraining
SCI - Resistance Training“Chronic”
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Twice weekly, 4 sets of 10 reps of dynamic knee extension
• Quadriceps muscle size increased ~70% in both thighs
• Glucose tolerance was improved
• Bone density increased
• Muscle fatigue was reduced 60%
Health-related consequences of increasing muscle mass
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Low physical fitness is associated with increased risk of CVD mortality in non-injured individuals (Blair et al 1995)
Low physical fitness = Peak VO2 < 20 ml/kg/min
Decrease risk of CVD by 50% by increasing peak VO2 by 7 ml/kg/min8% risk reduction with 1.75 ml/kg
Future Directions
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Peak VO2 measures on SCI patients range from 12-20 ml/kg/min.
Some improvements in peak VO2 realized after cycling, arm ergometry, circuit training and ambulation training (e-stim).
Circuit training (Jacobs et al. 2000) Peak VO2 increased 30%(19 - 24 ml/kg/min)
FES cycling (Pollack et al. 1989) Peak VO2 on increased 17% (1.2 L/min - 1.4 L/min)
Ambulation training VO2 increased 33% (1.2-1.6 L/min)
Future Directions
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Small peripheral muscle mass seemingly limits oxygen consumption (Hopman et al 1998)
For example:Take an AB person and exercise one limb
This would not stress central cardiovascular function because of the limited mass of active muscle
Future Directions
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Muscle mass and peak VO2
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Can NMES resistance exercise increase muscle mass to allow for sufficient training stimulus to evoke large increases in fitness?
Future Directions
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Optimization of Electrical Stimulation Patterns
Future/Current Directions
- Reduce fatigue?- Resistance and aerobic training
Center of RotationMagnetic Brake/ClutchTorque TransducerEncoder Assembly
Interface Box
Flexion/Extension Electrode Pair
Flexion/Extension Electrode Pair
Center of RotationMagnetic Brake/ClutchTorque TransducerEncoder Assembly
Interface Box
Flexion/Extension Electrode Pair
Flexion/Extension Electrode Pair
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Future/Current DirectionsIncomplete SCI
Impaired neuromuscular function limits locomotor ability following incomplete SCI and rehab programs specifically targeting muscular
impairments will attenuate existing deficits and improve walking.
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Future/Current DirectionsIncomplete SCI
Impaired neuromuscular function limits locomotor ability following incomplete SCI and rehab programs specifically targeting muscular
impairments will attenuate existing deficits and improve walking.
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• Progressive RT (2-3x/week, 12 weeks)– 2-3 sets of 6-12 reps (70-85% 1 RM)
• Target: CSA & Strength
• Ballistic Training– 2-3 sets, 12-20 contacts
• Target: Time to peak tension; Power
Future DirectionsIncomplete SCI
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Acknowledgements
Gary Dudley PhD Manning Sabatier PhD
Scott Bickel PT, PhD Chris Black PhD
Mark Bowden PT, PhD Jill Slade PhD
Ed Mahoney PhD Arun Jayaraman PT, PhD
Krista Vandenborne PhD Prithvi Shah PT, PhD
Funding: National Institutes of Health RO1HD40850