Cognitive impairment in asymptomatic carotid artery stenosis is associated with abnormal segments in the Circle of Willis

OBJECTIVE

Our group has previously demonstrated that patients with asymptomatic carotid artery stenosis (ACAS) demonstrate cognitive impairment. One proposed mechanism for cognitive impairment in patients with ACAS is cerebral hypoperfusion due to flow-restriction. We tested whether the combination of a high-grade carotid stenosis and inadequate cross-collateralization in the Circle of Willis (CoW) resulted in worsened cognitive impairment.

METHODS

Twenty-four patients with high-grade (≥70% diameter-reducing) ACAS underwent carotid duplex ultrasound, cognitive assessment, and 3D time-of-flight magnetic resonance angiography (MRA). The cognitive battery consisted of nine neuropsychological tests assessing four cognitive domains: learning and recall, attention and working memory, motor and processing speed, and executive function. Raw cognitive scores were converted into standardized T-scores. A structured interpretation of the MRA images was performed with each segment of the CoW categorized as being either normal or abnormal. Abnormal segments of the CoW were defined as segments characterized as narrowed or occluded due to congenital aplasia or hypoplasia, or acquired atherosclerotic stenosis or occlusion. Linear regression was used to estimate the association between the number of abnormal segments in the CoW, and individual cognitive domain scores. Significance was set to p<0.05.

RESULTS

The mean age of the patients was 66.1 + 9.6 (mean + SD) years and 79.2% (n=19) were male. A significant negative association was found between the number of abnormal segments in the CoW and cognitive scores in the learning and recall (β = -6.5, p = 0.01), and attention and working memory (β = -7.0, p = 0.02) domains. There was a trend suggesting a negative association in the motor and processing speed (β = -2.4, p = 0.35) and executive function (β = -4.5, p = 0.06) domains that did not reach significance.

CONCLUSION

In patients with high-grade ACAS, the concomitant presence of increasing occlusive disease in the CoW correlates with worse cognitive function. This association was significant in the learning and recall and attention and working memory domains. While motor and processing speed and executive function also declined numerically with increasing abnormal segments in the CoW, the relationship was not significant. Since flow restriction at a carotid stenosis compounded by inadequate collateral compensation across a diseased CoW worsens cerebral perfusion, our findings support the hypothesis that cerebral hypoperfusion underlies the observed cognitive impairment in patients with ACAS.

Lower limb vertical stiffness and frontal plane angular impulse during perturbation-induced single limb stance and their associations with gait in individuals post-stroke

After stroke, deficits in paretic single limb stance (SLS) are commonly observed and affect walking performance. During SLS, the hip abductor musculature is critical in providing vertical support and regulating balance. Although disrupted paretic hip abduction torque production has been identified in individuals post-stroke, interpretation of previous results is limited due to the discrepancies in weight-bearing conditions. Using a novel perturbation-based assessment that could induce SLS by removing the support surface underneath one limb, we aim to investigate whether deficits in hip abduction torque production, vertical body support, and balance regulation remain detectable during SLS when controlling for weight-bearing, and whether these measures are associated with gait performance. Our results showed that during the perturbation-induced SLS, individuals post-stroke had lower hip abduction torque, less vertical stiffness, and increased frontal plane angular impulse at the paretic limb compared to the non-paretic limb, while no differences were found between the paretic limb and healthy controls. In addition, vertical stiffness during perturbation-induced SLS was positively correlated with single support duration during gait at the paretic limb and predicted self-selected and fast walking speeds in individuals post-stroke. The findings indicate that reduced paretic hip abduction torque during SLS likely affects vertical support and balance control. Enhancing SLS hip abduction torque production could be an important rehabilitation target to improve walking function for individuals post-stroke.

Muscle Properties, Gross Motor Performance, and Quality of Life in Children With Sickle Cell Disease

PURPOSE

To explore muscle properties, gross motor performance, and quality of life (QoL) in children with sickle cell disease (SCD) compared with controls and to assess relationships among these outcomes.

METHODS

A cross-sectional study of 24 children assessed muscle properties including: knee extension strength by dynamometry; vastus lateralis (VL) and rectus femoris (RF) muscle thickness by ultrasonography; and VL and RF neuromuscular activation (rate of muscle activation [RoA]) by electromyography (EMG). Gross motor performance and QoL were assessed by standardized tests and questionnaires.

RESULTS

Children with SCD had impaired knee extension strength, VL EMG RoA, gross motor performance, and QoL compared with children without SCD. Relationships among muscle properties, gross motor performance, and QoL were identified.

CONCLUSIONS

These findings indicate that comprehensive muscle properties, gross motor performance, and QoL assessments should be considered to support and develop individualized physical therapy plans for children with SCD.

Lower Limb Vertical Stiffness and Frontal Plane Angular Impulse during Perturbation-Induced Single Limb Stance and Their Associations with Gait in Individuals Post-Stroke

Background

After stroke, deficits in paretic single limb stance (SLS) are commonly observed and affect walking performance. During SLS, the hip abductor musculature is critical in providing vertical support and regulating balance. Although disrupted paretic hip abduction torque production has been identified in individuals post-stroke, interpretation of previous results is limited due to the discrepancies in weight-bearing conditions.

Objective

To investigate whether deficits in hip abduction torque production, vertical body support, and balance regulation remain during SLS when controlling for weight-bearing using a perturbation-based assessment, and whether these measures are associated with gait performance.

Methods

We compared hip abduction torque, vertical stiffness, and frontal plane angular impulse between individuals post-stroke and healthy controls when SLS was induced by removing the support surface underneath one limb. We also tested for correlations between vertical stiffness and angular impulse during perturbation-induced SLS and gait parameters during overground walking.

Results

During the perturbation-induced SLS, lower hip abduction torque, less vertical stiffness, and increased frontal plane angular impulse were observed at the paretic limb compared to the non-paretic limb, while no differences were found between the paretic limb and healthy controls. Vertical stiffness during perturbation-induced SLS was positively correlated with single support duration during gait at the paretic limb and predicted self-selected and fast walking speeds in individuals post-stroke.

Conclusions

Reduced paretic hip abduction torque during SLS likely affects vertical support and balance control. Enhancing SLS hip abduction torque production could be an important rehabilitation target to improve walking function for individuals post-stroke.

Hip Abductor Power and Velocity: Reliability and Association With Physical Function

ABSTRACT

Lanza, MB, Jin, KH, Karl, H, Myers, J, Ryan, E, and Gray, VL. Hip abductor power and velocity: reliability and association with physical function. J Strength Cond Res 37(2): 284-290, 2023-Muscle power, defined as the ability of the muscle to produce torque quickly, has received little attention and may be critical for understanding physical function and performance. Hip abductors' capacity to produce power through both torque and velocity is important for different human activities; hence, a reliable assessment of hip abduction is critical. The first aim of the study was to assess the intersession reliability of hip abductor muscles maximal torque and submaximal power and power during standing hip abduction in young adults using pneumatic resistance. A secondary aim was to investigate whether there was a relationship between hip abductor maximal torque and submaximal power and velocity with clinical assessments of strength and power in young adults. The subjects (n = 24; 26.0 ± 3.7 years) visited the laboratory 2 times. In the first visit, the subjects performed on a pneumatic resistance machine 1-repetition maximum (1RM) and submaximal tests (40, 60, and 70% of 1RM) of the hip abductors and clinical tests of lower-extremity strength and power (The 30-second chair stand test [30CST]; and stair climb power test). During the second visit, all tests were repeated except the clinical tests. One-repetition maximum torque and submaximal power and velocity (at all levels) had excellent reliability (intraclass correlation coefficient ≥ 0.943) with absolute reliability of 13.5% up to 28.3%. The agreement between days from Bland-Altman plots for power and velocity was near 0 for all levels. Hip abduction velocity had a significant positive correlation with 30CST at 60% (r = 0.416; p = 0.048) and 70% of 1RM (r = 0.442; p = 0.035). In conclusion, we showed an excellent intersession reliability of the hip abductor muscles 1RM torque and submaximal power and velocity using pneumatic resistance. Furthermore, we demonstrated that hip abduction velocity might be important for the performance of the 30CST.

Quantifying muscle strength, size, and neuromuscular activation in adolescent and young adult survivors of musculoskeletal sarcoma: Identifying correlates and responses to functional strengthening

BACKGROUND

Medical and surgical treatment for musculoskeletal sarcoma (MSS) place survivors at risk for impairments in muscle properties including muscle strength, muscle size, and neuromuscular activation. The purpose of this study was to explore muscle properties, gross motor performance, and quality of life (QoL) and the changes in response to a 6-week functional strengthening intervention (PT-STRONG) in MSS survivors of childhood cancer (CCS).

METHODS

Eight lower extremity MSS CCS (13-23 years old) performed baseline testing and three completed PT-STRONG. Participants completed measurements of knee extension strength using handheld dynamometry, vastus lateralis (VL) and rectus femoris (RF) muscle thickness using ultrasonography at rest, and neuromuscular activation using electromyography during strength testing and a step-up task. Participants also completed gross motor and QoL assessments.

RESULTS

Compared with the non-surgical limb, MSS CCS had lower surgical limb knee extension strength, VL muscle thickness, and RF step-up muscle rate of activation (RoA). Compared with normative values, MSS CCS had decreased bilateral knee extension strength, gross motor performance, and physical QoL. Positive correlations among muscle strength, muscle thickness, and gross motor performance were identified. After PT-STRONG, MSS CCS had improvements in VL muscle thickness, VL and RF RoA duing step-up, gross motor performance, and physical QoL.

CONCLUSIONS

Positive association between larger muscle thickness with greater knee extension strength, and higher knee extension strength with better gross motor performance indicate that comprehensive physical therapy assessment and interventions that identify and target impairments in muscle properties to guide clinical decision making should be considered for MSS CCS into survivorship.

Ultrasound measures of muscle thickness and subcutaneous tissue from the hip abductors: Inter- and intra-rater reliability

BACKGROUND

Ultrasound imaging is important in many fields such as medicine, sports, and health sciences to assess parts of muscle structure (e.g., muscle thickness [MT]) or composition (subcutaneous tissue [Sub_T]).

OBJECTIVE

The aim of the present study was to investigate the intra- and inter-rater reliability of MT and Sub_T measurements of the hip abductor muscles gluteus medius (GM) and tensor fascia latae (TFL).

DESIGN

Cross-sectional study.

METHOD

Twenty young adults participated in the study. Intra-rater reliability was established by measuring the same two images twice by the same rater, while inter-rater reliability was assessed between two raters by measuring the same two images for each muscle. For both intra- and inter-rater reliability, the reliability of the TFL and GM outcomes (MT- Sub_T) were determined by the intraclass correlation coefficient (ICC), coefficient of variation (CV), standard error of the measurement (SEM), and Bland-Altman plots.

RESULTS

For intra-rater reliability, variables of both muscles showed an excellent ICC (≥0.90), lower CV and SEM, and bias near zero. Inter-rater reliability also showed an excellent ICC for both variables and muscles (≥0.81) with lower CV, SEM, and bias.

CONCLUSION

Therefore, these results provide strong evidence of a reliable measure of MT and Sub_T from GM and TFL. The present study provides health care professionals and researchers increased confidence in using 2D ultrasound to assess the hip abductors muscles reliably.

Neuromechanical control of impact absorption during induced lower limb loading in individuals post-stroke

Decreased loading of the paretic lower limb and impaired weight transfer between limbs negatively impact balance control and forward progression during gait in individuals post-stroke. However, the biomechanical and neuromuscular control mechanisms underlying such impaired limb loading remain unclear, partly due to their tendency of avoiding bearing weight on the paretic limb during voluntary movement. Thus, an approach that forces individuals to more fully and rapidly load the paretic limb has been developed. The primary purpose of this study was to compare the neuromechanical responses at the ankle and knee during externally induced limb loading in people with chronic stroke versus able-bodied controls, and determine whether energy absorption capacity, measured during induced limb loading of the paretic limb, was associated with walking characteristics in individuals post-stroke. Results revealed reduced rate of energy absorption and dorsiflexion velocity at the ankle joint during induced limb loading in both the paretic and non-paretic side in individuals post-stroke compared to healthy controls. The co-contraction index was higher in the paretic ankle and knee joints compared to the non-paretic side. In addition, the rate of energy absorption at the paretic ankle joint during the induced limb loading was positively correlated with maximum walking speed and negatively correlated with double limb support duration. These findings demonstrated that deficits in ankle dorsiflexion velocity may limit the mechanical energy absorption capacity of the joint and thereby affect the lower limb loading process during gait following stroke.

Systematic Review of the Importance of Hip Muscle Strength, Activation, and Structure in Balance and Mobility Tasks

OBJECTIVE

The aim of this systematic review was to identify the associations of the hip abductor muscle strength, structure, and neuromuscular activation on balance and mobility in younger, middle-aged, and older adults.

DATA SOURCES

We followed PRISMA guidelines and performed searches in PubMed, Embase, CINAHL, and Physiotherapy Evidence Database.

STUDY SELECTION

Study selection included: (1) studies with patients aged 18 years or older and (2) studies that measured hip abduction torque, surface electromyography, and/or muscle structure and compared these measures with balance or mobility outcomes.

DATA EXTRACTION

The extracted data included the study population, setting, sample size, sex, and measurement evaluated.

DATA SYNTHESIS

The present systematic review is composed of 59 research articles including a total of 2144 young, middle-aged, and older adults (1337 women). We found that hip abductor strength is critical for balance and mobility function, independent of age. Hip abductor neuromuscular activation is also important for balance and mobility, although it may differ across ages depending on the task. Finally, the amount of fat inside the muscle appears to be one of the important factors of muscle structure influencing balance.

CONCLUSIONS

In conclusion, a change in all investigated variables (hip abduction torque, neuromuscular activation, and intramuscular fat) appears to have an effect during balance or mobility tasks across age ranges and may elicit better performance. Future studies are necessary to confirm the effect of these variables across age ranges and the effects of interventions.

The effects of stroke on weight transfer before voluntary lateral and forward steps

There is a higher rate of falls in the first year after a stroke, and the ability to step in different directions is essential for avoiding a fall and navigating small spaces where falls commonly occur. The lateral transfer of weight is important for stabilizing the body before initiating a step. Hence, understanding the ability to control lateral weight transfer (WT) in different step directions might help understand falls in individuals with stroke. The present study aimed to compare the WT characteristics (onset time, duration, mediolateral center of pressure (ML COP) velocity, and ML COP displacement) and hip abduction torque preceding a lateral and forward voluntary step between individuals with stroke (paretic and non-paretic leg) and controls. Twenty individuals with stroke and ten controls performed voluntary choice reaction tests in the lateral and forward directions. Ten trials (five on each side-right and left) were performed for each step direction. The overall primary findings were that (1) the WT before a lateral step was shorter and initiated earlier, with a larger ML COP displacement and greater hip abductor torque in the stepping leg than the forward step, (2) there was greater hip abductor produced in the stance leg before a forward step than a lateral step, (3) the WT before the lateral step took longer to initiate and was slower to execute in individuals with stroke regardless of the leg (4) the WT before the forward step had more differences in the paretic than the non-paretic leg. Thus, for the first time, it was shown that the WT characteristics and hip abduction torque during the WT are different according to step direction and also appear to be impaired in individuals with stroke. These results have implications for understanding the direction that individuals with stroke are more susceptible to being unable to recover balance and are at risk of falling.

Lack of association between cognitive impairment and systemic inflammation in asymptomatic carotid stenosis

BACKGROUND

Asymptomatic carotid atherosclerotic stenosis (ACAS) is associated with cognitive impairment. Systemic inflammation occurs in patients with systemic atherosclerosis and is also associated with cognitive impairment. The goal of this study was to determine if cognitive impairment in patients with ACAS is the result of systemic inflammation.

METHODS

A cross-sectional analysis of 104 patients (63 patients with ACAS, 41 controls) with cognitive function and inflammatory biomarker assessments was performed. Venous blood was assayed for proinflammatory biomarkers (IL-1β, IL-6, IL-6R, IL-8, IL-17, tumor necrosis factor-α, matrix metalloproteinase [MMP]-1, MMP-2, MMP-7, MMP-9, vascular cell adhesion molecule, and high-sensitivity C-reactive protein). The patients also underwent comprehensive cognitive testing to compute five domain-specific cognitive scores per patient. We first assessed the associations between carotid stenosis and cognitive function, and between carotid stenosis and systemic inflammation in separate regression models. We then determined whether cognitive impairments persisted in patients with carotid stenosis after accounting for inflammation by adjusting for inflammatory biomarker levels in a combined model.

RESULTS

Patients with ACAS and control patients differed in age, race, coronary artery disease prevalence, and education. Stenosis patients had worse cognitive scores in two domains: learning and memory (P = .05) and motor and processing speed (P = .002). Despite adjusting for inflammatory biomarker levels, patients with ACAS still demonstrated deficits in the domains of learning and memory and motor and processing speed.

CONCLUSIONS

Although systemic atherosclerosis-induced inflammation is a well-recognized cause for cognitive impairment, our data suggest that it is not the primary underlying mechanism behind cognitive impairments seen in ACAS. Cognitive impairments in learning and memory and motor and processing speed seen in patients with ACAS persist after adjusting for systemic inflammation. Thus, alternative mechanisms should be explored to account for the observed functional impairments.

The Efficacy of Targeted Exercise on Gross Motor and Neuromuscular Performance in Survivors of Childhood Leukemia: A Pilot Study

OBJECTIVES

This quasi-experimental study examined the efficacy of targeted exercise training on gross motor performance and neuromuscular impairments in survivors of childhood acute lymphoblastic leukemia (ALL CCS).

MATERIALS AND METHODS

Ten ALL CCS (median age: 10 years; range: 6-14 years) performed a 6-week training program three times per week (five in-person sessions), including a warm-up, total body stretching, progressive jump rope training, and a cool down. Gross motor performance (test of gross motor proficiency) and lower extremity rate of muscle activation (electromyography), joint torques (motion capture and force plate), and jump height (motion capture) were measured during a countermovement jump at baseline and post-training.

RESULTS

Post-training, ALL CCS demonstrated improvements in body coordination, strength and agilty, bilateral coordination, running speed and agility, and strength gross motor performance (mean change: 1.6-8.1; p < 0.05), the rate of muscle activation of the tibialis anterior and vastus lateralis muscles (mean change: 0.58-0.75; p < 0.05), hip and ankle joint torques (mean change: 0.07; p < 0.05), and jump height (mean change: 0.05; p < 0.05).

CONCLUSION

This study demonstrated that targeted exercise training can improve gross motor performance and neuromuscular impairments in ALL CCS post-medical treatment.

Single-Leg Vertical Hop Test Detects Greater Limb Asymmetries Than Horizontal Hop Tests After Anterior Cruciate Ligament Reconstruction in NCAA Division 1 Collegiate Athletes

BACKGROUND

Knee function deficits may persist after anterior cruciate ligament reconstruction (ACLR). Return to sport (RTS) testing batteries assess recovery after ACLR and can guide RTS progression, but the ideal test components are debatable. The single leg vertical hop for height (SLVH) test using a commercially available jump mat may provide a valuable assessment of knee function.

HYPOTHESIS/PURPOSE

The purpose of this study was to compare the limb symmetry index (LSI) of SLVH to horizontal hop testing in a cohort of National Collegiate Athletic Association (NCAA) Division 1 collegiate athletes after ACLR. The hypothesis was the SLVH would elicit significantly lower LSI than horizontal hop tests.

STUDY DESIGN

Cross-Sectional Study.

METHODS

Eighteen National Collegiate Athletic Association (NCAA) Division 1 collegiate athletes (7 males, 11 females) at 7.33 ± 2.05 months after ACLR were included in this retrospective study. LSI was calculated for single hop for distance (SHD), triple hop for distance (THD), cross-over hop for distance (CHD), timed 6-meter hop (T6H), and SLVH. A repeated measures ANOVA was performed to identify differences in LSI for each test. Spearman's Rho correlation coefficient was calculated to examine the relationship between LSIs for each test.

RESULTS

The LSI for SLVH (84.48% ± 11.41%) was significantly lower than LSI for SHD (95.48 ± 8.02%, p = 0.003), THD (94.40 ± 3.70%, p = 0.002), CHD (95.85 ± 7.00, p = 0.007), and T6H (97.69 ± 6.60%, p = 0.001). The correlation of LSI between SLVH and the horizontal hop tests was weak and non-significant for SHD (rs = 0.166, p = 0.509), CHD (rs = 0.199, p = 0.428), and T6H (rs = 0.211, p = 0.401) and moderate and non-significant for THD (rs = 0.405, p = 0.096).

CONCLUSIONS

Individuals after ACLR had lower LSI on the SLVH than on horizontal hop tests and weak to moderate correlations between the tests suggest SLVH detects performance deficits not identified by the horizontal hop tests.

LEVEL OF EVIDENCE

3.

Hip Abductor and Adductor Rate of Torque Development and Muscle Activation, but Not Muscle Size, Are Associated With Functional Performance

Understanding the physiological variables that contribute to a functional task provides important information for trainers and clinicians to improve functional performance. The hip abductors and adductors muscles appear to be important in determining the performance of some functional tasks; however, little is known about the relationship of the hip abductor/adductors muscle strength, activation, and size with functional performance. This study aimed to investigate the relationship of maximum torque, rate of torque development (RTD), rate of activation (RoA), and muscle thickness of the hip abductors [tensor fascia latae (TFL) and gluteus medius (GM)] and adductor magnus muscle with the Four Square Step Test (FSST) and the two-leg hop test in healthy young adults. Twenty participants (five males) attended one testing session that involved ultrasound image acquisition, maximal isometric voluntary contractions (hip abduction and hip adduction) while surface electromyography (EMG) was recorded, and two functional tests (FSST and two-leg side hop test). Bivariate correlations were performed between maximum voluntary torque (MVT), RTD at 50, 100, 200, and 300ms, RoA at 0-50, 0-100, 0-200, and 0-300, and muscle thickness with the dynamic stability tests. For the hip abduction, MVT (r=-0.455, p=0.044) and RTD₃₀₀ (r=-0.494, p=0.027) was correlated with the FSST. GM RoA₅₀ (r=-0.481, p=0.032) and RoA₁₀₀ (r=-0.459, p=0.042) were significantly correlated with the two-leg side hop test. For the hip adduction, there was a significant correlation between the FSST and RTD₃₀₀ (r=-0.500, p=0.025), while the two-leg side hop test was correlated with RTD₂₀₀ (r=0.446, p=0.049) and RTD₃₀₀ (r=0.594, p=0.006). Overall, the ability of the hip abductor and adductor muscles to produce torque quickly, GM rapid activation, and hip abductor MVT is important for better performance on the FSST and two-leg hop tests. However, muscle size appears not to influence the same tests.

Moderate aerobic exercise prevents matrix degradation and death in a mouse model of aortic dissection and aneurysm

Thoracic aortic aneurysm and dissection (TAAD) is a deadly disease characterized by intimal disruption induced by hemodynamic forces of the circulation. The effect of exercise in patients with TAAD is largely unknown. β-Aminopropionitrile (BAPN) is an irreversible inhibitor of lysyl oxidase that induces TAAD in mice. The objective of this study was to investigate the effect of aerobic exercise on BAPN-induced TAAD. Upon weaning, mice were given either BAPN-containing water or standard drinking water and subjected to either conventional cage activity (BAPN-CONV) or forced treadmill exercise (BAPN-EX) for up to 26 wk. Mortality was 23.5% (20/85) for BAPN-CONV mice versus 0% (0/22) for BAPN-EX mice (hazard ratio 3.8; P = 0.01). BAPN induced significant elastic lamina fragmentation and intimal-medial thickening compared with BAPN-untreated controls, and aneurysms were identified in 50% (5/10) of mice that underwent contrast-enhanced CT scanning. Exercise significantly decreased BAPN-induced wall thickening, calculated circumferential wall tension, and lumen diameter, with 0% (0/5) of BAPN-EX demonstrating chronic aortic aneurysm formation on CT scan. Expression of selected genes relevant to vascular diseases was analyzed by qRT-PCR. Notably, exercise normalized BAPN-induced increases in TGF-β pathway-related genes Cd109, Smad4, and Tgfβr1; inflammation-related genes Vcam1, Bcl2a1, Ccr2, Pparg, Il1r1, Il1r1, Itgb2, and Itgax; and vascular injury- and response-related genes Mmp3, Fn1, and Vwf. Additionally, exercise significantly increased elastin expression in BAPN-treated animals compared with controls. This study suggests that moderate aerobic exercise may be safe and effective in preventing the most devastating outcomes in TAAD.NEW & NOTEWORTHY Moderate aerobic exercise was shown to significantly reduce mortality, extracellular matrix degradation, and thoracic aortic aneurysm and dissection formation associated with lysyl oxidase inhibition in a mouse model. Gene expression suggested a reversal of TGF-β, inflammation, and extracellular matrix remodeling pathway dysregulation, along with augmented elastogenesis with exercise.

Untangling biomechanical differences in perturbation-induced stepping strategies for lateral balance stability in older individuals

When recovering balance from a lateral perturbation, younger adults tend to stabilize balance with a single lateral sidestep while older adults often take multistep responses. Using multiple steps to recover balance is consistently associated with increased fall risk, altered body center of mass (CoM) control and instability. The aim of this study was to compare the spatio-temporal stepping characteristics and the margin of stability (MoS) of single lateral sidesteps (LSS1) with the first and second steps of a two-step protective step sequence. Two-step sequences begin with either a cross-over step to the front or back, or a medial step followed by a lateral sidestep. Seventy-one older adults received random lateral waist-pull perturbations to either side. We hypothesized that LSS1 would be more stable (larger MoS) than either step in a two-step sequence. With some exceptions, utilizing a two-step sequence was associated with a reduced CoM velocity and distance between the base of support and CoM and decreased stability in the frontal plane following limb loading of the first and second step. There were no differences in the time available to arrest the extrapolated CoM at the end of a single lateral sidestep or the final step of a two-step sequence. Two-step sequences involving a cross-over step include more complex stepping trajectories and also challeng stability in the sagittal plane requiring a multidimensional balance correction. These results indicate important step type differences in center of mass control in recovering balance with a single lateral sidestep as opposed to a two-step sequence among older adults.

Asymptomatic carotid artery stenosis is associated with cerebral hypoperfusion

OBJECTIVE

We have shown that almost 50% of patients with asymptomatic carotid stenosis (ACS) will demonstrate cognitive impairment. Recent evidence has suggested that cerebral hypoperfusion is an important cause of cognitive impairment. Carotid stenosis can restrict blood flow to the brain, with consequent cerebral hypoperfusion. In contrast, cross-hemispheric collateral compensation through the Circle of Willis, and cerebrovascular vasodilation can also mitigate the effects of flow restriction. It is, therefore, critical to develop a clinically relevant measure of net brain perfusion in patients with ACS that could help in risk stratification and in determining the appropriate treatment. To determine whether ACS results in cerebral hypoperfusion, we developed a novel approach to quantify interhemispheric cerebral perfusion differences, measured as the time to peak (TTP) and mean transit time (MTT) delays using perfusion-weighted magnetic resonance imaging (PWI) of the whole brain. To evaluate the utility of using clinical duplex ultrasonography (DUS) to infer brain perfusion, we also assessed the relationship between the PWI findings and ultrasound-based peak systolic velocity (PSV).

METHODS

Structural and PWI of the brain and magnetic resonance angiography of the carotid arteries were performed in 20 patients with ≥70% ACS. DUS provided the PSV, and magnetic resonance angiography provided plaque geometric measures at the stenosis. Volumetric perfusion maps of the entire brain from PWI were analyzed to obtain the mean interhemispheric differences for the TTP and MTT delays. In addition, the proportion of brain volume that demonstrated a delay in TTP and MTT was also measured. These proportions were measured for increasing severity of perfusion delays (0.5, 1.0, and 2.0 seconds). Finally, perfusion asymmetries on PWI were correlated with the PSV and stenosis features on DUS using Pearson's correlation coefficients.

RESULTS

Of the 20 patients, 18 had unilateral stenosis (8 right and 10 left) and 2 had bilateral stenoses. The interhemispheric (left-right) TTP delays measured for the whole brain volume identified impaired perfusion in the hemisphere ipsilateral to the stenosis in 16 of the 18 patients. More than 45% of the patients had had ischemia in at least one half of their brain volume, with a TTP delay >0.5 second. The TTP and MTT delays showed strong correlations with PSV. In contrast, the correlations with the percentage of stenosis were weaker. The correlations for the PSV were strongest with the perfusion deficits (TTP and MTT delays) measured for the whole brain using our proposed algorithm (r = 0.80 and r = 0.74, respectively) rather than when measured on a single magnetic resonance angiography slice as performed in current clinical protocols (r = 0.31 and r = 0.58, respectively).

CONCLUSIONS

Interhemispheric TTP and MTT delay measured for the whole brain using PWI has provided a new tool for assessing cerebral perfusion deficits in patients with ACS. Carotid stenosis was associated with a detectable reduction in ipsilateral brain perfusion compared with the opposite hemisphere in >80% of patients. The PSV measured at the carotid stenosis using ultrasonography correlated with TTP and MTT delays and might serve as a clinically useful surrogate to brain hypoperfusion in these patients.

Biomechanical control of paretic lower limb during imposed weight transfer in individuals post-stroke

Background

Stroke is a leading cause of disability with associated hemiparesis resulting in difficulty bearing and transferring weight on to the paretic limb. Difficulties in weight bearing and weight transfer may result in impaired mobility and balance, increased fall risk, and decreased community engagement. Despite considerable efforts aimed at improving weight transfer after stroke, impairments in its neuromotor and biomechanical control remain poorly understood. In the present study, a novel experimental paradigm was used to characterize differences in weight transfer biomechanics in individuals with chronic stroke versus able-bodied controls

Methods

Fifteen participants with stroke and fifteen age-matched able-bodied controls participated in the study. Participants stood with one foot on each of two custom built platforms. One of the platforms dropped 4.3 cm vertically to induce lateral weight transfer and weight bearing. Trials involving a drop of the platform beneath the paretic lower extremity (non-dominant limb for control) were included in the analyses. Paretic lower extremity joint kinematics, vertical ground reaction forces, and center of pressure velocity were measured. All participants completed the clinical Step Test and Four-Square Step Test.

Results

Reduced paretic ankle, knee, and hip joint angular displacement and velocity, delayed ankle and knee inter-joint timing, increased downward displacement of center of mass, and increased center of pressure (COP) velocity stabilization time were exhibited in the stroke group compared to the control group. In addition, paretic COP velocity stabilization time during induced weight transfer predicted Four-Square Step Test scores in individuals post-stroke.

Conclusions

The induced weight transfer approach identified stroke-related abnormalities in the control of weight transfer towards the paretic limb side compared to controls. Decreased joint flexion of the paretic ankle and knee, altered inter-joint timing, and increased COP stabilization times may reflect difficulties in neuromuscular control during weight transfer following stroke. Future work will investigate the potential of improving functional weight transfer through induced weight transfer training exercise.

Lateral Perturbation-Induced and Voluntary Stepping in Fallers and Nonfallers After Stroke

OBJECTIVE

A loss of balance poststroke from externally induced perturbations or during voluntary movements is often recovered by stepping. The purpose of this study was to characterize stepping behavior during lateral induced waist-pull perturbations and voluntary steps in community-dwelling fallers and nonfallers with chronic stroke.

METHODS

This study used a cohort design. Thirty participants >6 months poststroke were exposed to 24 externally triggered lateral waist-pull perturbations and 20 voluntary steps. Balance tolerance limit (BTL) (transition from single to multiple steps) and first step type were determined for the waist-pull perturbations. Step parameters of initiation time, velocity, first step length, and clearance were calculated at and above BTL and for the voluntary steps. Hip abductor/adductor torque, foot cutaneous sensation, and self-reported falls that occurred 6 months prior were evaluated.

RESULTS

Twelve participants were classified retrospectively as fallers and 18 as nonfallers. Fallers had a reduced BTL and took more medial first steps than nonfallers. Above BTL, no between-group differences were found in medial steps. At BTL, the nonparetic step clearance was reduced in fallers. Above BTL, fallers took longer to initiate a paretic and nonparetic step and had a reduced nonparetic step length and clearance compared with nonfallers. There was a between-group difference in step initiation time for voluntary stepping with the paretic leg (P < .05). Fallers had a reduced paretic abductor torque and impaired paretic foot cutaneous sensation.

CONCLUSION

A high fall rate poststroke necessitates effective fall prevention strategies. Given that more differences were found during perturbation-induced stepping between fallers and nonfallers, further research assessing perturbation-induced training on reducing falls is needed.

IMPACT

Falls assessments should include both externally induced perturbations along with voluntary movements in determining the fall risk.

Asymptomatic carotid stenosis is associated with mobility and cognitive dysfunction and heightens falls in older adults

BACKGROUND

Atherosclerosis of the carotid bifurcation with plaque formation causes asymptomatic carotid artery stenosis (ACAS), which may also be associated with cerebral hypoperfusion. Cerebral hypoperfusion adversely affects multiple aspects of mobility and cognition. This study tests the hypothesis that community-dwelling older adults with a 50% or greater diameter-reducing ACAS will have mobility and cognitive impairments that heighten their risk for falls.

METHODS

Eighty community-dwelling adults completed a mobility assessment (Short Physical Performance Battery, Berg Balance Scale, Four Square Step Test, Dynamic Gait Index, Timed Up and Go, and gait speed), self-reported physical function (Activities-Specific Balance Confidence, SF-12 Physical Function Component), and cognitive tests (Mini-Mental State Examination). Falls were recorded for the past 6 months. Standardized carotid ultrasound examination classified participants into no stenosis (<50% diameter reduction) (n = 54), moderate stenosis (50%-69%) (n = 17), and high-grade stenosis (70%-99%) (n = 9) groups. Linear and logistic regression analyses determined the associations between these measures and the degree of stenosis (three groups).

RESULTS

Logistic regression analysis showed their degree of stenosis was associated with reductions in mobility (Short Physical Performance Battery [P = .008], Berg Balance Scale [P = .0008], Four Square Step Test [P = .005], DGI [P = .0001], TUG [P = .0004], gait speed [P = .02]), perceived physical function (ABC [P < .0001], SF-12 Physical Function Component [P < .0001]), and cognition (MMSE [P = .003]). Adults with moderate- and high-grade stenosis had a greater incidence of falls compared with those without stenosis (relative risk, 2.86; P = .01). Results remained unchanged after adjustment for age, sex and cardiovascular risk factors.

CONCLUSIONS

ACAS is associated with impaired mobility and cognition that are accompanied with increased fall risk. These impairments increased with worsening severity.

Stepping characteristics during externally induced lateral reactive and voluntary steps in chronic stroke

BACKGROUND

Stepping is critical for responding to perturbations, whether externally induced or self-initiated. Falls post-stroke is equally likely to happen from either mechanism. The objective of the study was, to examine lateral stepping performance during waist-pull induced reactive steps and voluntary choice reaction time steps in chronic stroke and controls.

METHODS

In this cross-sectional study participants with chronic stroke (N = 10) and age- and gender-matched controls (N = 10) performed reactive and voluntary lateral steps. Step initiation time, global step length, step clearance, and step velocity were calculated. Other measures for reactive step included, Balance tolerance limit (perturbation magnitude when recovery transitioned from single to multiple steps), and step type. The Community Balance & Mobility Scale, and hip abductor and adductor isokinetic asymmetry torque ratio were assessed.

RESULTS

The paretic and non-paretic leg were combined since step characteristics did not differ. Step (voluntary vs. reactive) by group (stroke vs. controls) was significant for step initiation time. The stroke group took longer initiating a voluntary step (P = 0.004). Reactive and voluntary steps were executed slower (P = 0.041), with a reduced step length (P = 0.028) by the stroke group. The stroke group had a lower balance tolerance limit (P = 0.01) and took reactive medial steps more frequently (P = 0.001). The Community Balance & Mobility Scale (P > 0.001), and hip abductor and adductor asymmetry torque ratio (P > 0.001; P = 0.015) was reduced in the stroke group.

SIGNIFICANCE

Our findings indicate individuals post-stroke are slower initiating and executing reactive and voluntary steps. Though the reactive step timing is less impaired, this may be a method for enhancing faster voluntary movements and training reactive balance.

Control of lateral weight transfer is associated with walking speed in individuals post-stroke

Restoring functional gait speed is an important goal for rehabilitation post-stroke. During walking, transferring of one's body weight between the limbs and maintaining balance stability are necessary for independent functional gait. Although it is documented that individuals post-stroke commonly have difficulties with performing weight transfer onto their paretic limbs, it remains to be determined if these deficits contributed to slower walking speeds. The primary purpose of this study was to compare the weight transfer characteristics between slow and fast post-stroke ambulators. Participants (N=36) with chronic post-stroke hemiparesis walked at their comfortable and maximal walking speeds on a treadmill. Participants were stratified into 2 groups based on their comfortable walking speeds (≥0.8m/s or <0.8m/s). Minimum body center of mass (COM) to center of pressure (COP) distance, weight transfer timing, step width, lateral foot placement relative to the COM, hip moment, peak vertical and anterior ground reaction forces, and changes in walking speed were analyzed. Results showed that slow walkers walked with a delayed and deficient weight transfer to the paretic limb, lower hip abductor moment, and more lateral paretic limb foot placement relative to the COM compared to fast walkers. In addition, propulsive force and walking speed capacity was related to lateral weight transfer ability. These findings demonstrated that deficits in lateral weight transfer and stability could potentially be one of the limiting factors underlying comfortable walking speeds and a determinant of chronic stroke survivors' ability to increase walking speed.

Patterns of muscle coordination during stepping responses post-stroke

This study compared self-induced stepping reactions of seventeen participants after stroke and seventeen controls. Surface electromyographic (EMG) signals were recorded bilaterally from the soleus (SOL), tibialis anterior (TA), biceps femoris (BF) and rectus femoris (RF) muscles. Principal component analysis (PCA) was used to reduce the data into muscle activation patterns and examine group differences (paretic, non-paretic, control leg). The first principal component (PC1) explained 46.7% of the EMG signal of the stepping leg. Two PCs revealed distinct activation features for the stepping paretic leg: earlier TA onset at step initiation and earlier BF and SOL onset at mid-step. For the stance leg, PC1 explained 44.4% of the EMG signal and significant differences were found in the non-paretic leg compared to paretic (p < 0.001) and control (p < 0.001). In PC1, at step onset the BF and SOL EMG and the RF and TA EMG were increased over the latter half of the step. No PC loadings were distinct for the paretic leg during stance, however differences were found in the non-paretic leg: earlier TA burst and increased BF and SOL EMG at step initiation. The results suggest impairments in the paretic leg when stepping and compensatory strategies in the non-paretic stance leg.

Effects of fast functional exercise on muscle activity after stroke

BACKGROUND

In stroke rehabilitation, considerable emphasis is placed on improving muscle strength with less focus on the speed of movement. Muscle power (product of force and velocity) is essential for balance and mobility but velocity of movement is impaired after stroke.

OBJECTIVE

The purpose of this efficacy study is to determine if a single session of fast functional movements can increase muscle activation and the speed of movement in participants with a subacute stroke.

METHODS

In total, 32 individuals poststroke and 32 age- and sex-matched controls performed a single session of 50 fast squats and steps. Electromyographic (EMG) activity was measured bilaterally in the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and soleus muscles. The average EMG area and the movement speed were calculated over 10 trials. The effect of exercise was determined as the change from the second set (Start) to the last set (End) of 10 trials.

RESULTS

The stroke group had significant increases in EMG area of the TA, BF, and RF during the squatting exercise. There was an increase in EMG area of the RF and BF when the paretic leg was stepping. Improvements in EMG area of the soleus and RF when the paretic leg was in stance accompanied increases in EMG area when the nonparetic leg was stepping. There was a trend for improved movement speed for both exercises.

CONCLUSION

A single session of exercises emphasizing speed of movement can be used to improve muscle activation in persons with mild to moderately severe strokes.

Control of fast squatting movements after stroke

OBJECTIVE

Little is known about how residual motor impairments after stroke affect the motor control of fast movements, particularly those that combine postural control and limb movement. The purpose of this study was to examine the influence of stroke on the motor control of fast squatting movements.

METHODS

Seventeen individuals with hemiparesis and seventeen age- and sex-matched controls performed fast squatting movements. Force platform data, knee acceleration, and electromyographic activity from rectus femoris, biceps femoris, tibialis anterior, soleus, were collected.

RESULTS

Subjects after stroke performed the squats asymmetrically, with reduced velocity and acceleration compared to controls. Subjects with low motor recovery depended on the non-paretic leg to compensate for poor paretic muscle activation whereas subjects with high motor recovery activated muscles in the paretic leg in an adaptive manner, making the movement more symmetrical. Difficulty with postural control was evident by reduced coupling of the timing of the knee movement with the center of pressure excursion.

CONCLUSIONS

Slow performance of squatting movements was accompanied by altered muscle activation, coupled with impaired postural control.

SIGNIFICANCE

Fast squatting movements in standing require appropriate muscle activation and postural control, the latter of which can be measured easily with force platform and accelerometer data.

Peptones from diverse sources: pivotal determinants of bacterial growth dynamics

AIMS

In view of the major problems encountered by microbiologists in obtaining reproducible data on growth dynamics in complex media, we studied the effects of different peptones made from different biological sources and produced by numerous manufacturers.

METHODS AND RESULTS

Peptones (including casein, gelatin, meat, soy and yeast) were assessed as a constituent of the pre-enrichment broth buffered peptone water (BPW). Generation times (g) and yields of Salmonella serovar Typhimurium were significantly affected by the type of peptone employed with yeast peptones generating yields of 7.04 x 10(9) CFU ml(-1) and gelatin peptones producing 0.81 x 10(9) CFU ml(-1). Medium sterilization was also found to have significant effects (P = 0.000) upon subsequent bacterial growth. Filter sterilization of BPW media produced lower generation times compared with those obtained after sterilization by autoclaving. Finally, it was observed that some peptones which produced good growth when inoculated with healthy organisms, showed relatively poor growth when inocula were sublethally injured by heating.

CONCLUSIONS

Variation in peptone as a constituent of BPW has a significant effect on growth and enumeration of bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

Increased consideration with respect to culture media may significantly improve bacterial growth and experimental reproducibility.

Efficacy of a hydroxynaphthoquinone, 566C80, in experimental Pneumocystis carinii pneumonitis

The efficacy of a new class of drugs for Pneumocystis carinii pneumonitis was demonstrated. 566C80, a hydroxynaphthoquinone, administered orally in a dose of greater than or equal to 100 mg/kg of body weight per day prophylactically prevented P. carinii pneumonitis in 90% or more of rats, while all untreated control animals developed pneumonitis. When 566C80 (100 mg/kg per day) was administered for 3 weeks after P. carinii pneumonitis was established, therapy was totally effective and all of the untreated controls had progressive P. carinii pneumonitis. A dose of 566C80 of between 25 and 50 mg/kg per day protected 50% of the rats from P. carinii pneumonitis, and a dose of between 50 and 100 mg/kg per day cured 50% of those treated for P. carinii pneumonitis. Both prophylaxis and treatment with 566C80 were at least as effective as with trimethoprim-sulfamethoxazole. Animals maintained on immunosuppression after completion of treatment remained free of P. carinii, suggesting a killing effect. Clearance of P. carinii was associated with levels of 60 micrograms or more of 566C80 per ml of plasma. This hydroxynaphthoquinone offers promise as an anti-P. carinii drug.