Treadmill Aerobic Training Improves Glucose Tolerance and Indices of Insulin Sensitivity in Disabled Stroke Survivors

BACKGROUND AND PURPOSE

Insulin resistance and glucose intolerance are highly prevalent after stroke, contributing to worsening cardiovascular disease risk and a predisposition to recurrent stroke. Treadmill exercise training (T-AEX) increases aerobic capacity (Vo(2) peak) in chronic stroke patients, suggesting intensity levels that may be adequate to improve glucose metabolism. We compared the effects of a progressive T-AEX intervention to an attention-matched stretching intervention (CONTROL) on glucose tolerance and indices of insulin sensitivity in stroke survivors.

METHODS

Participants had hemiparetic gait after remote (>6 months) ischemic stroke. They were randomized to 6-month T-AEX or a duration matched reference CONTROL program of supervised stretching exercises. Main outcome measures were glucose and insulin responses during a 3-hour oral glucose tolerance test (OGTT).

RESULTS

Forty-six subjects (T-AEX=26, CONTROL=20) completed OGTT testing before and after the interventions. T-AEX increased Vo(2) peak (+15% versus -3% Delta, P<0.01) compared with CONTROL. There were significant reductions in fasting insulin (-23% versus +9% Delta, P<0.05) and the total integrated 3-hour insulin response (-24% versus +3% Delta, P<0.01) in T-AEX compared with CONTROL. In patients with abnormal glucose tolerance at baseline, T-AEX resulted in a significant 14% decrease in 3-hour glucose response (n=12, P<0.05). Fifty-eight percent of T-AEX participants with abnormal baseline OGTT (7 of 12) improved glucose tolerance status at 2 hours compared with <10% (1 of 11) of impaired CONTROLS (P<0.05).

CONCLUSIONS

These preliminary findings suggest that progressive aerobic exercise can reduce insulin resistance and prevent diabetes in hemiparetic stroke survivors. Larger clinical trials are needed to definitively establish the use of structured exercise training for stimulating metabolic improvement poststroke.

Microvascular tissue plasminogen activator is reduced in diabetic neuropathy

BACKGROUND

Abnormalities of endogenous fibrinolysis are linked to diabetic macrovascular disease; whether key vascular endothelial regulatory proteins, such as tissue plasminogen activator (tPA), are altered in diabetic neuropathy microvasculature is unknown. This neuropathologic case: control study investigates the hypothesis that tPA expression is regionally deficient in microvessels in human diabetic neuropathy.

METHODS

tPA and von Willebrand factor (vWF), a vascular endothelial cell marker, are detected on vascular endothelium by immunoperoxidase methods with specific antibodies on formalin fixed paraffin embedded sural nerve biopsies from six diabetic and six axonal neuropathy control nerves without vasculopathy. The proportion of microvessels in each nerve region expressing tPA is determined by the ratio of tPA positive vessels/total vWF positive vessels on serial sections.

RESULTS

tPA expression is lower in diabetic neuropathy cases compared to controls in all regions, including epineurial (62.4 +/- 8.6% vs 91.0 +/- 1.6%, p < 0.02) and endoneurial microvessels (51.7 +/- 7.1% vs 91.5 +/- 2.9%, p < 0.001).

CONCLUSIONS

These results demonstrate a four- to sixfold increase in the number of peripheral nerve microvessels lacking immunodetectable tissue plasminogen activator in the epineurial and endoneurial vessels in diabetes, suggesting that impaired endogenous fibrinolysis might contribute to microvascular ischemia in human diabetic neuropathy.

Cardiovascular risk in survivors of stroke

BACKGROUND

Stroke survivors are at significant risk for recurrent stroke and cardiovascular disease. Inadequately managed modifiable risk factors increase the threat of recurrent stroke, development of new comorbidities, and double the risk of premature mortality. The purpose of this study was to determine the prevalence of modifiable cardiovascular risk factors in stroke survivors who completed a research screening evaluation for entry into exercise rehabilitation studies. The sample collected between January 2001 and June 2005 evaluated 364 community-dwelling men and women aged 34 to 88 years living in Baltimore, Maryland.

METHODS

Each participant's risk profile was evaluated from data obtained during a medical history and physical examination and from laboratory analysis of a fasting blood sample. Current practice guidelines were used to define risk categories.

RESULTS

Ninety-nine percent of participants had at least one suboptimally controlled risk factor. Ninety-one percent had two or more concurrent risk factors inadequately treated. Eighty percent of the participants had prehypertension or hypertension, 67% were overweight or obese, 60% had suboptimal low-density lipoprotein, 45% had impaired fasting glucose, 34% had low high-density lipoprotein, and 14% were current smokers, while reportedly receiving routine medical care.

CONCLUSIONS

These findings confirm that cardiovascular risk factors remain inadequately managed in stroke survivors, increasing the chance for repeat stroke and cardiovascular event. Systematic assessment of this vulnerable population is imperative at every healthcare encounter.

How does the brain respond to unimodal and bimodal sensory demand in movement of the lower extremity?

Numerous electroencephalography (EEG) studies have shown that neurophysiological signals change in response to visual and sensory adaptations in upper extremity tasks. However, this has not been clearly studied in the lower extremity. In this study, we evaluated how sensory loading affects brain activations related to knee movement. Thirty-two channel EEG was recorded while ten subjects performed knee extension in four different conditions: no weight and no visual target (NWNT), weight affixed to the ankle and no visual target (WNT), no weight and a visual target (NWT), and both weight and target (WT). Surface electromyography (EMG) was recorded from the vastus medialis and vastus lateralis muscles to determine onset of the movement. EEG was epoched from -4.5 s before to 1 s after EMG onset. Epochs were averaged to acquire movement-related cortical potentials (MRCPs) of each task condition. MRCP amplitude during the pre-movement period from -2 s to EMG onset was evaluated at electrodes over motor, sensory, frontal, and parietal areas. The amplitude of the pre-movement potentials for the conditions was different across areas of interest. Over the motor area, NWNT had lower amplitude than any other condition and WT had higher amplitude than any other condition. There was no difference between unimodal NWT and WNT conditions. Mesial frontal and parietal areas showed larger MRCP to the bimodal condition than either unimodal or NWNT conditions. The parietal cortex was the only region that showed a difference between unimodal conditions with greater amplitude for NWT condition. Information concerning added sensory demand is processed by the motor cortex in a way that may be indifferent to the type of modality, but is influenced by the quantity of modalities at the level of the knee. Other brain structures such as parietal and premotor cortices respond based on the modality type to help plan appropriate strategies for motor control in response to sensory manipulations. This suggests that additional task demands in motor training may create a rich sensory environment that may be beneficial in promoting optimal neuromotor recovery.

Reduced cardiovascular fitness and ambulatory function in Black and White stroke survivors

OBJECTIVES

To test the hypothesis that quantitative measures of cardiovascular fitness and ambulatory function differ in Black and White hemiparetic stroke survivors.

DESIGN

Cross-sectional analysis.

SETTING

Outpatient academic medical center.

PARTICIPANTS

Total of 118 hemiparetic stroke survivors.

MAIN OUTCOME MEASURES

Cardiovascular fitness was measured as VO2 peak and ambulatory function using the six-minute walk distance and 30-foot walking velocity in medically screened, community-dwelling stroke survivors.

RESULTS

In 118 subjects (56% Black and 44% White), no differences were seen in 1) VO2 peak between Black or White men (15.0+/-4.3 vs. 15.1+/-3.9 mL/kg/minute) or women (11.5+/-2.7 vs. 12.3+/-3.7 mL/kg/minute); 2) six-minute walk distance between Black or White men (223+/-112 m vs 226+/-132 m) or women (198+/-100 vs 157+/-93 m); or 3) 30-foot walking velocity between Black or White men (0.60+/-0.27 m/second vs 0.61+/-0.31 m/ second) or women (0.50+/-0.21 m/second vs 0.41+/-0.23 m/second).

CONCLUSION

No racial differences were seen in the degree of physical deconditioning in a selected population of community dwelling hemiparetic stroke survivors.

Determinants of Walking Function After Stroke: Differences by Deficit Severity

OBJECTIVES

To investigate the relationship of cardiovascular fitness (Vo(2)peak), neurologic deficits in balance and leg strength, and body composition to ambulatory function after stroke and to determine whether these relationships differ between those with milder versus more severe gait deficits.

DESIGN

Cross-sectional correlation study.

SETTING

Outpatient clinic of an academic medical center.

PARTICIPANTS

Seventy-four people (43 men, 31 women; mean age +/- standard deviation, 64+/-10y) with chronic hemiparetic stroke.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Thirty-foot (9.1-m) walk velocity, 6-minute walk distance, Vo(2)peak, Berg Balance Scale score, bilateral quadriceps eccentric torque, total and regional lean mass, and percentage of fat mass.

RESULTS

Short-distance walking correlated significantly with cardiovascular fitness, balance, paretic leg strength, nonparetic leg strength, percentage of body fat, and paretic lean mass but not with nonparetic lean mass. Long-distance walking correlated significantly with cardiovascular fitness, balance, paretic leg strength, nonparetic leg strength, and paretic lean mass but not with percentage of body fat or nonparetic lean mass. Stepwise regression showed that cardiovascular fitness, balance, and paretic leg strength were independently associated with long-distance walking (r(2)=.60, P<.001). Variance in long-distance walking was largely explained by balance for those who walked more slowly (<.48m/s) for short distances (r(2)=.42, P<.001) and by cardiovascular fitness for those who walked more quickly (>.48m/s) for short distances (r(2)=.26, P=.003).

CONCLUSIONS

Short-distance walking after stroke is related to balance, cardiovascular fitness, and paretic leg strength. Long-distance walking ability differs by gait deficit severity, with balance more important in those who walk more slowly and cardiovascular fitness playing a greater role in those who walk more quickly. Improved understanding of the factors that predict ambulatory function may assist the design of individualized rehabilitation strategies across the spectrum of gait deficit severity in those with hemiparetic stroke.

Exercise rehabilitation after stroke

Stroke is a leading cause of disability that results not only in persistent neurological deficits, but also profound physical deconditioning that propagates disability and worsens cardiovascular risk. The potential for exercise-mediated adaptations to improve function, fitness, and cardiovascular health after stroke has been underestimated: it represents an emerging arena in neurotherapeutics. To define the health rationale for cardiovascular (aerobic) exercise, we first outline the impact of debilitating secondary biological changes in muscle and body composition on fitness and metabolic health after stroke. We provide an overview of evidence-based advances in exercise therapeutics, with a focus on task-oriented models that combine a progressive aerobic conditioning stimulus with motor learning to improve multiple physiological domains that determine longitudinal outcomes after stroke. Although progress in development of safe and effective exercise strategies is advancing, fundamental questions regarding dose intensity, prescription to optimize central and peripheral neuromuscular adaptations, and the public health value of exercise in secondary stroke prevention remain unanswered. Key issues steering future research in exercise neurotherapeutics are discussed within the context of initiatives to facilitate translation to community-based studies, requisite for dissemination.

High Prevalence of Abnormal Glucose Metabolism and Poor Sensitivity of Fasting Plasma Glucose in the Chronic Phase of Stroke

BACKGROUND

Cardiovascular disease is the leading cause of death in long-term stroke survivors, and whole-body glucose metabolism is strongly linked to cardiovascular disease risk. This study provides important preliminary information on the prevalence of abnormal glucose metabolism in chronic stroke patients (mean 3 years after stroke) and reports on the utility of screening for abnormalities using fasting plasma glucose (FPG) in this population.

METHODS

Two hundred and sixteen chronic hemiparetic stroke patients were screened for diabetes status by medical history and FPG. A subset (n = 80) was evaluated by oral glucose tolerance test to assess the utility of screening for abnormalities using FPG alone.

RESULTS

Seventy-five of the 216 (35%) had type 2 diabetes by medical history. Another 70 were either diabetic (n = 11) or had impaired fasting glucose (n = 59) based on a single blood draw at the time of screening. FPG among non-diabetic stroke patients had a sensitivity of 49% for predicting abnormalities in the 2-hour glucose level during oral glucose tolerance test. Cumulative results identify 77% as abnormal (impaired or diabetic) on the basis of medical history, fasting plasma glucose, and/or 2-hour glucose level.

CONCLUSIONS

The prevalence of abnormal glucose metabolism is extremely high in chronic stroke and is underestimated on the basis of FPG.

Fatigue After Stroke

Fatigue is common and persistent in stroke survivors, yet it is not known how mobility deficits, fitness, or other factors, such as social support, relate to fatigue severity, or whether subjective fatigue contributes to reduced ambulatory activity. The severity of fatigue in a sample of 53 community-dwelling subjects with chronic hemiparetic stroke was examined, and relationships among fatigue and mobility deficit severity, cardiovascular-metabolic fitness, ambulatory activity, social support, and self-efficacy for falls were identified. Measures included the Fatigue Severity Scale, timed 10-meter walks, the Berg Balance Scale, submaximal and peak VO2, total daily step activity derived from microprocessor-linked Step Activity Monitors, the Medical Outcomes Study Social Support Survey, and the Falls Efficacy Scale. Forty-six percent of the sample had severe fatigue. Fatigue showed no relationship to ambulatory activity. Fatigue severity was associated with the Berg Balance Scale (p < .01) and falls efficacy (p < .01), but not with cardiovascular fitness variables. Patients with elevated fatigue severity scores had lower social support (p < .05) and poorer falls efficacy scores (p < .05) than patients reporting less fatigue. Only falls efficacy was predictive of fatigue severity (r2 = 0.216, p < .01). Further studies are needed to evaluate whether rehabilitation strategies that include not only fitness and mobility interventions, but also social/behavioral and self-efficacy components, are associated with reduced fatigue and increased ambulation.

Genetic Markers of Fibrinolytic Responses of Older Persons to Exercise Training

We assessed the interactive effect of genetic polymorphisms and exercise training on fibrinolysis in 50 - 75 yr old men (n = 17) and women (n = 28). Subjects had tissue plasminogen activator (t-PA) antigen levels and activity and plasminogen activator inhibitor-1 (PAI-1) activity measured before and after 6 mo of endurance-exercise training. Subject's DNA was typed for the PAI-1 4 G/5 G and t-PA I/D variants. Baseline PAI-1 activity, t-PA activity, and t-PA antigen levels were not different among PAI-1 or t-PA genotype groups. Overall, exercise training did not change PAI-1 activity (- 0.43 +/- 0.81 IU/mL, p = NS), increased t-PA activity (0.37 +/- 0.16 IU/mL, p = 0.02), and decreased t-PA antigen levels (- 0.88 +/- 0.20 ng/mL, p < 0.001). Although the differences in changes with training were not significant among genotype groups, significant t-PA antigen level improvements were evident only in PAI-1 4 G allele carriers and significant t-PA activity increases only in PAI-1 4 G homozygotes. t-PA genotype affected the training-induced t-PA antigen level improvements (p = 0.033) after covarying for gender and baseline t-PA antigen levels, with the smallest and largest reductions in the D homozygotes and I/D heterozygotes, respectively. These findings could have important treatment implications for the use of exercise training to reduce CV disease and thrombotic risk in older men and women.

Hemostatic Activation and Outcome After Recombinant Tissue Plasminogen Activator Therapy for Acute Ischemic Stroke

BACKGROUND AND PURPOSE

Early thrombolytic therapy with intravenous recombinant tissue plasminogen activator (rtPA) improves clinical outcome in acute ischemic stroke (AIS), but impaired endogenous fibrinolysis, thrombin generation, and vascular injury may hamper the efficacy of thrombolysis. We investigated in an exploratory, post hoc analysis the relationship between hemostatic markers and clinical outcomes among patients included in the National Institute of Neurological Disorders and Stroke (NINDS) rtPA Stroke Study.

METHODS

Tissue plasminogen activator (tPA) antigen, thrombin-antithrombin complex (TAT), soluble thrombomodulin, and fibrinogen levels were measured in patients with AIS included in the NINDS rtPA Stroke Study from plasma samples collected at baseline, at 2 hours after treatment, and after 24 hours.

RESULTS

TAT and tPA antigen levels peaked at 2 hours selectively in the rtPA treatment group, whereas fibrinogen levels dropped at 2 hours and remained low after 24 hours (P<0.0001 for interaction effects between time and treatment). At 24 hours, higher levels of tPA antigen were associated with a lower chance of favorable outcome (odds ratio [OR]=0.34; 95% CI, 0.14 to 0.82) selectively in the rtPA group, and higher levels of TAT (OR=1.72; 95% CI, 1.26 to 2.34) in the entire cohort and of thrombomodulin selectively in the rtPA group (OR=4.45; 95% CI, 1.26 to 15.67) were associated with higher 3-month mortality.

CONCLUSIONS

Hemostatic activation after AIS appears to be independently associated with clinical outcome in patients treated with rtPA. However, because we have tested for multiple associations, some may have been identified by chance alone and require further confirmatory studies. On the basis of this exploratory analysis, there is a rationale to investigate the safety and efficacy of protocols in which rtPA is complemented by agents that are antithrombotic and enhance fibrinolysis.

Effects of treadmill exercise on transcranial magnetic stimulation-induced excitability to quadriceps after stroke

OBJECTIVE

To determine characteristics of transcranial magnetic stimulation (TMS)-induced measures of central motor excitability to the paretic and nonparetic quadriceps muscles of chronic hemiparetic stroke patients in the context of a short-term, submaximal bout treadmill exercise.

DESIGN

Cross-sectional.

SETTING

Motor control and gait biomechanics laboratory.

PARTICIPANTS

Convenience sample of 11 patients including cohorts of treadmill untrained (n=8) and trained (n=3) stroke patients with chronic hemiparetic gait.

INTERVENTION

Short-term submaximal treadmill exercise.

MAIN OUTCOME MEASURES

Thresholds, amplitudes and latencies of TMS-induced motor evoked potentials at vastus medialis in paretic and nonparetic lower extremities.

RESULTS

Baseline characteristics of the motor evoked potentials (MEPs) show significantly higher motor thresholds, longer latencies, and reduced amplitudes on the paretic side. In cross-sectional comparisons a group of treadmill-trained patients had greater paretic MEP amplitude changes after treadmill exercise versus paretic MEP responses from a group of untrained patients.

CONCLUSIONS

These results indicate that treadmill training for 3 months or more may alter responsiveness of the lower-extremity central motor pathways to a short-term treadmill stimulus.

Testing a model of post-stroke exercise behavior

Stroke is the leading cause of disability in older Americans, and survivors tend to be sedentary, thereby risking loss of functional gains achieved during rehabilitation and increasing cardiovascular risk. Studies of motivation to exercise in older adults suggest that self-efficacy and outcome expectations are key determinants of initiation and adherence to exercise programs. This study tested a theoretical model of physical activity in stroke survivors. A survey of exercise beliefs and patterns was sent to National Stroke Association stroke support groups. Responses from 312 stroke survivors (mean age 63 years, 57% female, 70% White) indicated that only 31% exercised four times weekly. Self-efficacy and outcome expectations for exercise, before exercise history, and physician recommendation all directly and indirectly influenced self-reported exercise behavior and accounted for 33% of the total variance in exercise behavior. Model testing supported the theory and the model fit the data. Interventions to strengthen self-efficacy and outcome expectations for exercise, along with reminders for clinicians to encourage regular exercise programs, may increase the likelihood of initiating and maintaining an exercise program, potentially improving physical function and cardiovascular fitness in this population.

Human gender differences in fibrinolytic responses to exercise training and their determinants

Endurance exercise training improves fibrinolysis, but this training-induced adaptation may differ somewhat between men and women. We sought to determine whether the potential gender differences in training-induced changes in selected fibrinolysis measures were related to changes in adiposity and/or plasma lipoprotein lipid levels. Seventeen men and 28 women, 50-75 years old, who were generally overweight to obese, were assessed for plasminogen activator inhibitor-1 (PAI-1) and tissue plasminogen activator (t-PA) activity, t-PA antigen and plasma lipoprotein-lipid levels, and body composition before and after 6 months of endurance exercise training while on a low-fat diet. At baseline, there were no differences in fibrinolytic measures between the men and women. Baseline levels of these fibrinolytic markers in both men and women were primarily related to other fibrinolytic measures and body composition, with a smaller contribution from plasma high-density lipoprotein cholesterol (HDL-C) levels. Exercise training reduced t-PA antigen levels in both men and women, but the reduction was significantly greater in men (-1.6 +/- 0.3 versus -0.5 +/- 0.2 ng ml(-1), P = 0.007). Exercise training decreased PAI-1 activity more in men than in women (-2.6 +/- 1.4 versus +0.9 +/- 0.9 IU ml(-1), P = 0.03). Men and women both showed increased t-PA activity with exercise training to the same extent (+0.38 +/- 0.12 versus +0.36 +/- 0.24 U ml(-1)). The changes in fibrinolytic measures with exercise training in men and women were correlated with changes in other fibrinolytic measures, although in men abdominal fat changes were a strong predictor of fibrinolytic changes with training. These findings suggest that training-induced improvements in endogenous fibrinolysis markers are somewhat greater in men compared to women and may be more strongly associated with abdominal obesity in men.

Treadmill Exercise Rehabilitation Improves Ambulatory Function and Cardiovascular Fitness in Patients With Chronic Stroke

BACKGROUND AND PURPOSE

Physical inactivity propagates disability after stroke through physical deconditioning and learned nonuse. We investigated whether treadmill aerobic training (T-AEX) is more effective than conventional rehabilitation to improve ambulatory function and cardiovascular fitness in patients with chronic stroke.

METHODS

Sixty-one adults with chronic hemiparetic gait after ischemic stroke (>6 months) were randomized to 6 months (3x/week) progressive T-AEX or a reference rehabilitation program of stretching plus low-intensity walking (R-CONTROL). Peak exercise capacity (Vo2 peak), o2 consumption during submaximal effort walking (economy of gait), timed walks, Walking Impairment Questionnaire (WIQ), and Rivermead Mobility Index (RMI) were measured before and after 3 and 6 months of training.

RESULTS

Twenty-five patients completed T-AEX and 20 completed R-CONTROL. Only T-AEX increased cardiovascular fitness (17% versus 3%, delta% T-AEX versus R-CONTROL, P<0.005). Group-by-time analyses revealed T-AEX improved ambulatory performance on 6-minute walks (30% versus 11%, P<0.02) and mobility function indexed by WIQ distance scores (56% versus 12%, P<0.05). In the T-AEX group, increasing training velocity predicted improved Vo2 peak (r=0.43, P<0.05), but not walking function. In contrast, increasing training session duration predicted improved 6-minute walk (r=0.41, P<0.05), but not fitness gains.

CONCLUSIONS

T-AEX improves both functional mobility and cardiovascular fitness in patients with chronic stroke and is more effective than reference rehabilitation common to conventional care. Specific characteristics of training may determine the nature of exercise-mediated adaptations.

Elevated Tumor Necrosis Factor-α in Skeletal Muscle After Stroke

BACKGROUND AND PURPOSE

Tumor necrosis factor-alpha (TNF-alpha), an inflammatory cytokine negligibly expressed in normal muscle, is elevated in selected metabolic conditions characterized by muscle wasting and insulin resistance. Inflammation is fundamental to stroke pathogenesis. Stroke patients have gross muscular atrophy and high prevalence of diabetes and insulin resistance. Yet, no previous studies examined TNF-alpha expression in hemiparetic skeletal muscle. This study investigates whether TNF-alpha mRNA levels are elevated in paretic compared with nonparetic leg muscles of chronic ischemic stroke patients and age-matched controls.

METHOD

Total RNA extracted from bilateral vastus lateralis muscle biopsies from n=20 hemiparetic stroke patients and n=9 healthy controls was reverse transcribed to cDNA, then TNF-alpha transcripts were amplified by real-time quantitative polymerase chain reaction. TNF-alpha mRNA concentrations were normalized against acidic ribosomal phosphoprotein, housekeeping gene.

RESULTS

TNF-alpha mRNA levels were 2.8-fold higher in paretic compared with control leg muscle (6.28+/-1.86 versus 2.28+/-0.67; P<0.03) and 1.6-fold higher in nonparetic leg (3.71+/-1.02; P<0.11) compared with controls. There was a trend for higher TNF-alpha mRNA in paretic compared with nonparetic leg.

CONCLUSIONS

Findings demonstrate increased TNF-alpha expression in paretic leg muscle, suggesting inflammatory pathways are accelerated in stroke muscle. Further studies are under way to determine whether intramuscular TNF-alpha contributes to atrophy and metabolic abnormalities after stroke.

Promoter polymorphisms in the nitric oxide synthase 3 gene are associated with ischemic stroke susceptibility in young black women

BACKGROUND AND PURPOSE

Endothelial nitric oxide exerts a variety of protective effects on endothelial cells and blood vessels, and therefore the nitric oxide synthase 3 gene (NOS3) is a logical candidate gene for stroke susceptibility.

METHODS

We used the population-based Stroke Prevention in Young Women case-control study to assess the association of five NOS3 polymorphisms in 110 cases (46% black) with ischemic stroke and 206 controls (38% black), 15 to 44 years of age. Polymorphisms included 3 single nucleotide polymorphisms (SNPs) in the promoter region (-1468 T>A, -922 G>A, -786 T>C), 1 SNP in exon 7 (G894T), and 1 insertion/deletion polymorphism within intron 4.

RESULTS

Significant associations with both the -922 G>A and -786 T>C SNPs with ischemic stroke were observed in the black, but not the white, population. This association was attributable to an increased prevalence of the -922 A allele (OR=3.0, 95% CI=1.3 to 6.8; P=0.005) and the -786 T allele (OR=2.9, 95% CI=1.3 to 6.4; P=0.005) in cases versus controls. These 2 SNPs were in strong linkage disequilibrium (D'=1.0), making it impossible to determine, within the confines of this genetic study, whether 1 or both of these polymorphisms are functionally related to NOS3 expression. Two sets of haplotypes were also identified, 1 of which may confer an increased susceptibility to stroke in blacks, whereas the other appears to be protective.

CONCLUSIONS

Promoter variants in NOS3 may be associated with ischemic stroke susceptibility among young black women.

Reduced Ambulatory Activity After Stroke: The Role of Balance, Gait, and Cardiovascular Fitness

OBJECTIVES

To determine ambulatory activity in a sample of community-dwelling people with chronic hemiparetic stroke and to examine whether deficits in balance and gait and cardiovascular and metabolic fitness are key determinants of ambulatory activity levels.

DESIGN

Descriptive correlational.

SETTING

Home and community.

PARTICIPANTS

Twenty-eight men and 22 women (N=50) over the age 45 years with more than 6 months of hemiparetic gait after ischemic stroke.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Ambulatory activity (total daily step activity), mobility deficit severity (Berg Balance Scale [BBS] scores, timed 10-m walks), and cardiovascular fitness (energy costs of hemiparetic gait, peak exercise capacity [VO2peak]).

RESULTS

Mean ambulatory activity profiles were extremely low (2837 steps/d vs reported 5000-6000 steps/d in sedentary older adults). Ambulatory activity levels were strongly associated with BBS scores (r=.581, P<.001) and self-selected floor walking velocity (r=.554, P<.001). Participants also had profound cardiovascular deconditioning (mean VO2peak, 11.7+/-2.8 mL.kg(-1).min(-1)). The energy costs of hemiparetic gait were high (8.7+/-1.7 mL.kg(-1).min(-1)), representing 76% of physiologic fitness reserve. Although the relationships of economy of gait and VO2peak to ambulatory activity was not statistically significant, both the VO2peak and the physiologic fitness reserve, as expressed by fractional utilization, were strongly related to balance (r=.374, P=.02; r=-.430, P< .01, respectively.) The BBS predicted 30% of the variance in ambulatory activity.

CONCLUSIONS

Ambulatory activity levels and cardiovascular fitness in patients with chronic stroke are extremely low. Mobility deficits, particularly in balance, are associated with low ambulatory activity. Balance-related inactivity may be an important factor in deconditioning. Further studies are needed to better understand whether task-oriented exercise enhances balance and whether increases in daily ambulatory activity yield improved cardiovascular fitness in chronic stroke survivors.

Steps After Stroke

Background and Purpose— Nearly two thirds of stroke survivors have deficits impairing ambulatory recovery. Conventional mobility outcome measures such as timed walks and functional independence measure (FIM) do not quantify free-living ambulatory behavior. This study compared step activity monitoring (SAM) with established instruments to assess ambulatory recovery across the outpatient subacute stroke rehabilitation phase.

Methods— We measured FIM mobility subscale, SAM-derived daily steps, Stroke Impact Scale (SIS) mobility scores, and timed walks in 11 subjects after discharge from inpatient rehabilitation and again 3 months later.

Results— Significant improvement was measured in free-living step activity (mean gain 80%; P =0.001) but not with timed walks ( P =0.4), FIM ( P =0.08), or SIS mobility scales ( P =0.3).

Conclusions— Microprocessor-linked SAM is a sensitive indicator of ambulatory recovery that measures improvements not captured by other conventional outcome instruments.

Brain activation of lower extremity movement in chronically impaired stroke survivors

Lower extremity paresis poses significant disability to chronic stroke survivors. Unlike for the upper extremity, cortical adaptations in networks controlling the paretic leg have not been characterized after stroke. Here, the hypotheses are that brain activation associated with unilateral knee movement in chronic stroke survivors is abnormal, depends on lesion location, and is related to walking ability. Functional magnetic resonance imaging of unilateral knee movement was obtained in 31 patients 26.9 months (mean, IQ range: 11.3-68.1) after stroke and in 10 age-matched healthy controls. Strokes were stratified according to lesion location. Locomotor disability (30 ft walking speed) did not differ between patient groups (9 cortical, 12 subcortical, 10 brainstem lesions). Significant differences in brain activation as measured by voxel counts in 10 regions of interest were found between controls and patients with brainstem (P = 0.006) and cortical strokes (P = 0.002), and between subcortical and cortical patients (P = 0.026). Statistical parametric mapping of data per group revealed similar activation patterns in subcortical patients and controls with recruitment of contralateral primary motor cortex (M1), supplementary motor area (SMA), and bilateral somatosensory area 2 (S2). Cortical recruitment was reduced in brainstem and cortical stroke. Better walking was associated with lesser contralateral sensorimotor cortex activation in brainstem, but stronger recruitment of ipsilateral sensorimotor and bilateral somatosensory cortices in subcortical and cortical patients, respectively. A post hoc comparison of brainstem patients with and without mirror movements (50%) revealed lesser recruitment of ipsilateral cerebellum in the latter. Subcortical patients with mirror movements (58%) showed lesser bilateral sensorimotor cortex activation. No cortical patient had mirror movements. The data reveal adaptations in networks controlling unilateral paretic knee movement in chronic stroke survivors. These adaptations depend on lesion location and seem to have functional relevance for locomotion.

Accelerometer monitoring of home- and community-based ambulatory activity after stroke

OBJECTIVES

To investigate the utility of a novel microprocessor-linked Step Watch Activity Monitor (SAM) to quantify ambulatory activity after stroke and to evaluate the validity and reliability of conventional accelerometers to measure free-living physical activity in this population.

DESIGN

Cross-sectional with repeated measures of 2 separate 48-hour recordings in 17 persons wearing an ankle-mounted SAM and Caltrac, a hip-mounted mechanical accelerometer.

SETTING

Home and community.

PARTICIPANTS

Seventeen subjects with chronic hemiparetic gait after stroke.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

The SAM derived stride counts per day and Caltrac estimated the daily caloric expenditure of physical activity.

RESULTS

SAM data revealed that stroke patients had a mean strides per day +/- standard deviation of 3035+/-1944 and demonstrated a broad range of daily activity profiles (400-6472 strides). SAM test-retest reliability was high across separate monitoring periods (r=.96, P<.001). Although Caltrac also revealed a broad range of daily activity calories (346+/-217 kcal/d; range, 83-1222 kcal/d), reliability was poor (r=.044, P=not significant) and Caltrac accounted for only 64% of the ambulatory activity quantified by the SAM.

CONCLUSIONS

Microprocessor-linked accelerometer monitoring, but not conventional accelerometers, are accurate and highly reliable for quantifying ambulatory activity levels in stroke patients. These findings support the utility of personal status monitoring of ambulatory activity as an outcomes instrument and metric in programs to increase physical activity and cardiovascular health after stroke.

Unilateral Impairment of Leg Blood Flow in Chronic Stroke Patients

BACKGROUND

Previous studies comparing paretic limb blood flow with the unaffected limb have been contradictory and have often omitted comparisons of peak reactive hyperemic flow. Our objective was to perform bilateral measurements of resting and reactive hyperemic blood flow in the lower legs of chronic (>6 months) stroke patients. A secondary purpose was to determine the extent to which any unilateral changes in limb blood flow were a function of decreases in lean tissue mass on the affected side. We hypothesized that the chronic hemiparesis accompanying ischemic stroke creates an altered metabolic environment in the tissues of the affected side that ultimately impairs vasomotor function.

METHODS

The study used a single-visit cross-sectional design. All tests were performed at the Baltimore VA Medical Center. Nineteen chronic hemiparetic stroke patients (15 male, 4 female) who had mild to moderate hemiparetic gait after ischemic stroke were recruited for observation. Bilateral measurements of resting and reactive hyperemic blood flow were made using venous occlusion strain gauge plethysmography. Paired t-tests were used for the between leg comparison. Regression analysis and analysis of covariance were utilized to determine the strength of the relationship between lower leg lean tissue mass and blood flow.

RESULTS

Resting and reactive hyperemic blood flows were significantly reduced in the paretic compared with the non-paretic limb (32 and 35%, respectively, p < 0.001). Lean tissue mass was also significantly lower in the affected limb (p < 0.01). However, neither resting nor reactive hyperemic blood flows were significantly correlated with lower leg lean tissue mass by dual energy X-ray absorptiometry. The difference in blood flow between limbs remained after covarying for lean tissue mass.

CONCLUSION

Hemiparesis causes impairments in vasomotor function under both resting and hyperemic conditions that are independent of the muscle atrophy on the affected side.

Thrombomodulin Ala455Val Polymorphism and the risk of cerebral infarction in a biracial population: the Stroke Prevention in Young Women Study

Background

The genes encoding proteins in the thrombomodulin-protein C pathway are promising candidate genes for stroke susceptibility because of their importance in thrombosis regulation and inflammatory response. Several published studies have shown that the Ala455Val thrombomodulin polymorphism is associated with ischemic heart disease, but none has examined the association with stroke. Using data from the Stroke Prevention in Young Women Study, we sought to determine the association between the Ala455Val thrombomodulin polymorphism and the occurrence of ischemic stroke in young women.

Methods

All 59 hospitals in the greater Baltimore-Washington area participated in a population-based case-control study of stroke in young women. We compared 141 cases of first ischemic stroke (44% black) among women 15 to 44 years of age with 210 control subjects (35% black) who were identified by random digit dialing and frequency matched to the cases by age and geographical region of residence. Data on historical risk factors were collected by standardized interview. Genotyping of the thrombomodulin Ala455Val polymorphism was performed by pyrosequencing.

Results

The A allele (frequency = 0.85) was associated with stroke under the recessive model. After adjustment for age, race, cigarette smoking, hypertension, and diabetes, the AA genotype, compared with the AV and VV genotypes combined, was significantly associated with stroke (odds ratio 1.9, 95% CI 1.1–3.3). The AA genotype was more common among black than white control subjects (81% versus 68%) but there was no significant interaction between the risk genotype and race (adjusted odds ratio 2.7 for blacks and 1.6 for whites). A secondary analysis removing all probable (n = 16) and possible (n = 15) cardioembolic strokes demonstrated an increased association (odds ratio 2.2, 95% CI 1.2–4.2).

Conclusions

Among women aged 15 to 44 years, the AA genotype is more prevalent among blacks than whites and is associated with increased risk of early onset ischemic stroke. Removing strokes potentially related to cardioembolic phenomena increased this association. Further studies are needed to determine whether this polymorphism is functionally related to thrombomodulin expression or whether the association is due to population stratification or linkage to a nearby functional polymorphism.