Visuomotor adaptation of voluntary step initiation in older adults

It has been suggested that feedforward planning of gait and posture is diminished in older adults. Motor adaptation is one mechanism by which feedforward commands can be updated or fine-tuned. Thus, if feedforward mechanisms are diminished in older adults, motor adaptation is also likely to be limited. The purpose of the study was to compare the ability of healthy older versus young adults in generating a voluntary stepping motor adaptation in response to a novel visual sensory perturbation. We recorded stepping movements from 18 healthy older and 18 young adults during baseline and adaptation stepping blocks. During baseline, the stepping target remained stationary; in adaptation, a visual perturbation was introduced by shifting the target laterally during mid-step. We compared adaptation between groups, measured by improvements in endpoint accuracy and movement duration. Older adults adapted stepping accuracy similarly to young adults (accuracy improvement: 29.7 ± 27.6% vs. 37.3 ± 22.9%, older vs. young group respectively, p = 0.375), but showed significant slowness during movement. Thus older adults were able to achieve accuracy levels nearly equivalent to younger adults, but only at the expense of movement speed, at least during the early adaptation period (movement duration: 1143.7 ± 170.6 ms vs. 956.0 ± 74.6 ms, p < 0.001). With practice, however, they were able to reduce movement times and gain speed and accuracy to levels similar to young adults. These findings suggest older adults may retain the ability for stepping adaptations to environmental changes or novel demands, given sufficient practice.     

Development and reliability of a measure evaluating dynamic proprioception during walking with a robotized ankle-foot orthosis,and its relation to dynamic postural control

BackgroundProprioception is important for proper motor control. As the central nervous system modulates how sensory information is processed during movement (sensory gating), proprioceptive tests performed at rest do not correlate well with performance during dynamic tasks such as walking. Proprioception therefore needs to be assessed during movement execution.Objectives1) To develop a test evaluating the ability to detect movement errors during walking, and its test-retest reliability; 2) to quantify the relationship between proprioceptive threshold (obtained with this new test) and performance in a standardized dynamic balance task.MethodThirty healthy subjects walked on a treadmill while wearing a robotized ankle-foot orthosis (rAFO) for 2 bouts of 6 min on 2 evaluation sessions (test-retest reliability). Force perturbations resisting ankle dorsiflexion during swing were applied to the ankle via the rAFO (150 ms duration, variable amplitude). Participants pushed a button when they detected the perturbations. The Star Excursion Balance Test (SEBT) was used to evaluate dynamic balance.AnalysisAngular differences between perturbed and non-perturbed gait cycles were used to quantify movement error. Detection threshold was defined as the minimal movement error at which 50% of the perturbations were perceived. Intraclass correlation coefficients (ICCs) estimated test-retest reliability, and Pearson coefficients were used to determine the correlation between detection threshold and SEBT.ResultsDetection threshold was 5.31 ± 2.12°. Good reliability (ICC = 0.70) and a moderate to strong correlation to SEBT (r = −0.57 to −0.76) were found.ConclusionForce perturbations produced by the robotized AFO provides a reliable way of evaluating proprioception during walking.     

An evaluation of 3D head pose estimation using the Microsoft Kinect v2

The Kinect v2 sensor supports real-time non-invasive 3D head pose estimation. Because the sensor is small, widely available and relatively cheap it has great potential as a tool for groups interested in measuring head posture. In this paper we compare the Kinect's head pose estimates with a marker-based record of ground truth in order to establish its accuracy. During movement of the head and neck alone (with static torso), we find average errors in absolute yaw, pitch and roll angles of 2.0 ± 1.2°, 7.3 ± 3.2° and 2.6 ± 0.7°, and in rotations relative to the rest pose of 1.4 ± 0.5°, 2.1 ± 0.4° and 2.0 ± 0.8°. Larger head rotations where it becomes difficult to see facial features can cause estimation to fail (10.2 ± 6.1% of all poses in our static torso range of motion tests) but we found no significant changes in performance with the participant standing further away from Kinect – additionally enabling full-body pose estimation – or without performing face shape calibration, something which is not always possible for younger or disabled participants. Where facial features remain visible, the sensor has applications in the non-invasive assessment of postural control, e.g. during a programme of physical therapy. In particular, a multi-Kinect setup covering the full range of head (and body) movement would appear to be a promising way forward.     

The effects of predictability on inter-limb postural synchronization prior to bouts of postural instability

Anticipatory balance control optimizes balance reactions to postural perturbations. Predictive control is dependent on the ability of the central nervous system to modulate gain in accordance with specific task demands. Inter-limb synchronization is a sensitive measure of individual limb contributions to balance control and may reflect the coordination of gain modulation in preparation for instability. The purpose of the study was to determine whether gain modulation in advance of predictable bouts of instability was reflected in the extent of inter-limb synchronization. Two adjacent force plates were used to collect center of pressure (COP) data from 12 healthy young adults (27.5 ± 3.4 years). Participants prepared for internal and external balance perturbations using a cueing paradigm with three auditory warning tones followed by an imperative tone. Perturbations were delivered in blocked and randomized conditions with two perturbation magnitudes (small and large). Inter-limb synchrony was calculated using the cross-correlation function of the COP excursions from the left and right foot for three seconds prior to perturbation onset in the anteroposterior (AP) and mediolateral (ML) direction. Inter-limb synchrony decreased in the AP and ML directions as perturbation magnitude became more unpredictable. The need to take a step or not knowing whether a step was required prior to postural instability reduced ML inter-limb synchrony. No differences were found between internal and external perturbations. Modulation of postural set was evident in the extent of inter-limb synchrony.     

Effect of age on the ability to recover from a single unexpected underfoot perturbation during gait: Kinematic responses

A sudden underfoot perturbation can present a serious threat to balance during gait, but little is known about how humans recover from such perturbations or whether their response is affected by age. We tested the hypothesis that age would not affect the stepping responses to a nominal 10 degree inversion or eversion of the stance foot during gait. Twenty-three healthy young (22.7 ± 3.35 yrs) and 18 healthy old adults (68.0 ± 7.19 yrs) performed 60 walking trials along a 6-m level walkway at a normal gait speed. In 16 of these trials, a single medial (MP) or lateral (LP) perturbation was randomly administered once under the left or right foot. Recovery step width (SW), step length (SL), trunk kinematics and walking speed were measured optoelectronically. Repeated-measures analysis of variance and post hoc t-tests were used to test the hypotheses. The results show that a MP or LP altered the recovery SL (p = 0.005) and age affected the number of recovery steps (p = 0.017), as well as the first recovery SW and SL (p = 0.013 and p = 0.031, respectively). Both MP and LP caused young adults to have wider SW (p < 0.02) and shorter SL (p < 0.005) without changing trunk movement during their first recovery step. Older adults, however, significantly changed lateral trunk inclination during the first recovery step, decreased their fourth recovery SL (p < 0.001). We conclude that young adults adjust the step kinematics of as many as four recovery steps following this perturbation, a response that was delayed and significantly weaker in older adults who instead exhibited an immediate torso inclination consistent with a hip response strategy.     

Reflex ankle stiffness is inversely correlated with natural body sway

We aimed to determine whether effective ankle stiffness (EAS), measured during slow unperceived perturbations of stance, is related to natural anterior–posterior body sway. Because the perturbations are not perceived, any neural component of the response to perturbation is assumed to be “reflex”, in the broad sense of an involuntary response to a stimulus. Subjects stood on a force platform for three 10-min trials. EAS was obtained from the average slope (Δτ/Δα) of the relation between ankle torque (τ) and ankle angle (α), recorded during repeated perturbations delivered at the waist by a weak spring. EAS was normalised using the subject's “load stiffness” (LS), calculated from mass (m) and height (h) above the ankle joint (m·g·h). Sway was obtained from fluctuations in ankle angle prior to perturbation. Variation in EAS and sway between subjects provided spread of data for correlation. There were no significant changes in EAS or sway across trials. All subjects had higher EAS than LS and mean EAS (1124 N m/rad) was significantly greater (p < 0.01) than mean LS (531 N m/rad). There was a strong significant inverse correlation between mean sway and mean normalised EAS (r = −0.68, p = 0.03). We conclude that the body, in response to slow unperceived perturbations, simulates an inverted pendulum with a stiffness of about twice LS and that EAS is largely generated by neural modulation of postural muscles. The inverse correlation between EAS and body sway suggests that the reflex mechanisms responding to perturbation also influence the extent of natural sway.     

Vibrotactile tilt feedback improves dynamic gait index: A fall risk indicator in older adults

The purpose of this study was to determine the effectiveness of vibrotactile feedback of body tilt in improving dynamic gait index (DGI) a fall risk indicator in community dwelling older adults. Twelve healthy elderly subjects (three males and nine females, age 79.7 ± 5.4 yrs) were tested in an institutional balance rehabilitation laboratory to investigate changes between the feedback off and on conditions. Subjects were acutely exposed to a vibrotactile display that indicated the magnitude and direction of their body tilt from the vertical. DGI and mediolateral (ML) sway were determined during locomotion with, and without, vibrotactile tilt feedback (VTTF). All subjects were at risk for falls based on their initial DGI Score (range: 15–19, mean 17.4 ± 1.56), which was taken with the vibratory stimulus turned off. Subjects learned to use the trunk tilt information from the vibrotactile feedback vest through 20–30 min of gait and balance training consisting of activities that challenged their balance. Subjects were then retested on the DGI. Statistically significant changes were demonstrated for the DGI total score while using the vibrotactile tilt feedback. DGI total scores improved from 17.1 ± 0.4 to 20.8 ± 0.3 (p < 0.05). We conclude that vibrotactile tilt feedback improves both control of mediolateral sway during gait and dynamic gait index. Both are fall risk indicators for this population.     

Decreased skin temperature of the foot increases gait variability in healthy young adults

We investigated the effects of reduction in plantar skin temperature on gait. Thirty-four healthy subjects (20 men and 14 women; mean age 22.2 ± 2.5 years; mean height 166.8 ± 8.3 cm) walked 16 m under two different conditions – normal conditions (NC) with the skin at a basal temperature, and cold conditions (CC) after cooling of the plantar skin to about 15 °C. Wireless motion-recording sensor units were placed on the back at the level of L3 and on both heels to measure acceleration and angular velocity. Gait velocity and mean stride, stance and swing times were calculated. The variability of lower limb movement was represented by the coefficients of variation (CVs) of stride, stance and swing times, and that of trunk movement was represented by autocorrelation coefficients (ACs) in three directions (vertical: VT; mediolateral: ML; and anteroposterior: AP). Gait velocity was significantly lower under CC conditions than under NC (p < 0.0001). None of the temporal parameters were changed by plantar cooling. However, all parameters of gait variability were significantly worse under CC, and AC-VT, AC-ML, and AC-AP were significantly lower under CC than under NC, even after adjusting for gait velocity (p = 0.0005, 0.0071, and 0.0126, respectively). Our results suggest that reducing plantar skin temperature induces gait variability among healthy young adults. Further studies are now needed to explore the relationship between plantar skin temperature and gait in the elderly.     

Real-time gait event detection for normal subjects from lower trunk accelerations

In this paper we report on a novel algorithm for the real-time detection and timing of initial (IC) and final contact (FC) gait events. We process the vertical and antero-posterior accelerations registered at the lower trunk (L3 vertebra). The algorithm is based on a set of heuristic rules extracted from a set of 1719 steps. An independent experiment was conducted to compare the results of our algorithms with those obtained from a Digimax force platform. The results show small deviations from times of occurrence of events recorded from the platform (13 ± 35 ms for IC and 9 ± 54 ms for FC). Results for the FC timing are especially relevant in this field, as no previous work has addressed its temporal location through the processing of lower trunk accelerations. The delay in the real-time detection of the IC is 117 ± 39 ms and 34 ± 72 ms for the FC, improving previously reported results for real-time detection of events from lower trunk accelerations.     

In-vivo quantification of dynamic hip joint center errors and soft tissue artifact

Hip joint center (HJC) measurement error can adversely affect predictions from biomechanical models. Soft tissue artifact (STA) may exacerbate HJC errors during dynamic motions. We quantified HJC error and the effect of STA in 11 young, asymptomatic adults during six activities. Subjects were imaged simultaneously with reflective skin markers (SM) and dual fluoroscopy (DF), an x-ray based technique with submillimeter accuracy that does not suffer from STA. Five HJCs were defined from locations of SM using three predictive (i.e., based on regression) and two functional methods; these calculations were repeated using the DF solutions. Hip joint center motion was analyzed during six degrees-of-freedom (default) and three degrees-of-freedom hip joint kinematics. The position of the DF-measured femoral head center (FHC), served as the reference to calculate HJC error. The effect of STA was quantified with mean absolute deviation. HJC errors were (mean ± SD) 16.6 ± 8.4 mm and 11.7 ± 11.0 mm using SM and DF solutions, respectively. HJC errors from SM measurements were all significantly different from the FHC in at least one anatomical direction during multiple activities. The mean absolute deviation of SM-based HJCs was 2.8 ± 0.7 mm, which was greater than that for the FHC (0.6 ± 0.1 mm), suggesting that STA caused approximately 2.2 mm of spurious HJC motion. Constraining the hip joint to three degrees-of-freedom led to approximately 3.1 mm of spurious HJC motion. Our results indicate that STA-induced motion of the HJC contributes to the overall error, but inaccuracies inherent with predictive and functional methods appear to be a larger source of error.     

Altered dynamic postural control during gait termination following concussion

Impaired postural control is a cardinal symptom following concussion. Planned gait termination (GT) is a non-novel, dynamic task that challenges postural control in individuals with neurological deficits, and it could be an impactful measure for identifying dynamic postural control impairments following concussion. Therefore, the purpose of this study was to assess acute post-concussion dynamic postural control utilizing a planned GT task. The concussion participants (n = 19, age: 19.0 ± 0.8 years, height: 177.0 ± 10.1 cm, weight: 83.3 ± 20.0 kg) completed five planned GT trials during preseason baseline testing (Baseline) and on Day 1 post-concussion (Day-1). Healthy control participants (n = 19, age: 20.4 ± 1.2 years, height: 173.8 ± 8.9 cm, weight: 80.2 ± 17.6 kg) completed the same trials a week apart. The dependent variables of interest included COP displacement and velocity in the mediolateral (ML) and anteroposterior (AP) axes during the three phases (braking, transitional, stabilization) of planned GT. There were significant interactions observed in both the braking ML and transitional AP displacement (p = 0.042, p = 0.030) and velocity (p = 0.027, p = 0.030). These results suggest a conservative post-concussion motor control strategy during planned GT. Further, these results support the use of dynamic postural control tasks as measures of post-concussion impairments.     

Heat stress impairs proprioception but not running mechanics

ObjectivesTo determine the effects of heat stress on ankle proprioception and running gait pattern.DesignCounterbalanced repeated measures.Methods12 trained runners performed a proprioception test (active movement discrimination) before and immediately after a 30 min, self-paced treadmill run in HOT (39 °C) and COOL (22 °C) ambient conditions. Velocity was imposed during the first and last minute (70% of maximal aerobic velocity, 13.3 ± 0.8 km h⁻¹) for determination of running mechanics and spring–mass characteristics.ResultsRectal (39.7 ± 0.4 vs. 39.4 ± 0.4 °C), skin (36.3 ± 1.1 vs. 31.8 ± 1.1 °C) and average body (38.3 ± 0.2 vs. 36.4 ± 0.4 °C) temperatures together with heart rate (178 ± 8 vs. 174 ± 6 bpm) and thermal discomfort (6.5 ± 0.5 vs. 4.3 ± 1.3) were all higher at the end of the HOT compared to COOL run (all p < 0.05). Distance covered was lower in HOT than COOL (−5.1 ± 3.6%, p < 0.001). Average error during the proprioception test increased after running in HOT (+11%, p < 0.05) but not in COOL (−2%). There was no significant difference for most segmental and joint angles at heel contact, except for a global increase in pelvis retroversion and decrease in ankle dorsi-flexion angles with time (p < 0.05). Step frequency decreased (−2.5 ± 3.6%) and step length increased (+2.6 ± 3.8%) over time (p < 0.05), independently of condition. Spring–mass characteristics remained unchanged (all p > 0.05).ConclusionsHeat stress exacerbates thermal, cardiovascular and perceptual responses, while running velocity was slower during a 30 min self-paced treadmill run. Heat stress also impairs ankle proprioception during an active movement discrimination task, but it has no influence on gait pattern assessed at a constant, sub-maximal velocity.     

Lumbar plexus in patients with chronic inflammatory demyelinating polyneuropathy: Evaluation with 3D nerve-sheath signal increased with inked rest-tissue rapid acquisition of relaxation enhancement imaging (3D SHINKEI)

PurposeTo evaluate whether 3D SHINKEI in the lumbar plexus could identify patients with chronic inflammatory demyelinating polyneuropathy (CIDP).Materials and methodsTwenty-one patients with CIDP and 15 non-CIDP patients were studied in this retrospective study. The SNR, contrast-to-noise ratio (CNR), contrast ratio (CR) and the size of the lumbar ganglions and roots were measured. Statistical analyses were performed with Mann-Whitney U test and receiver operating characteristics (ROC) analysis.ResultsThe SNRs of the ganglions and roots were larger in patients with CIDP (8.30 ± 4.87 and 8.24 ± 4.92) than in non-CIDP patients (4.95 ± 2.05 and 5.08 ± 1.97, P < 0.0001, respectively). The CNRs of the ganglions and roots were larger in patients with CIDP (40.79 ± 43.19 and 37.16 ± 48.31) than in non-CIDP patients (25.90 ± 10.41 and 18.37 ± 32.83, P < 0.0001, respectively). The CRs of the ganglions and roots were larger in patients with CIDP (0.74 ± 0.13 and 0.66 ± 0.17) than in non-CIDP patients (0.72 ± 0.12 and 0.50 ± 0.17, P = 0.004 and P < 0.0001, respectively). The sizes of the ganglions and the roots were larger in patients with CIDP (6.62 ± 1.81 mm and 5.76 ± 3.24 mm) than in non-CIDP patients (5.23 ± 1.17 mm and 4.24 ± 1.11 mm, P < 0.0001, respectively). ROC analysis showed the best diagnostic performance with the CNR of the roots.ConclusionPatients with CIDP could be distinguished from controls on 3D SHINKEI.     

Whole-body biomechanical load in running-based sports: The validity of estimating ground reaction forces from segmental accelerations

ObjectivesUnlike physiological loads, the biomechanical loads of training in running-based sports are still largely unexplored. This study, therefore, aimed to assess the validity of estimating ground reaction forces (GRF), as a measure of external whole-body biomechanical loading, from segmental accelerations.MethodsFifteen team-sport athletes performed accelerations, decelerations, 90° cuts and straight running at different speeds including sprinting. Full-body kinematics and GRF were recorded with a three-dimensional motion capture system and a single force platform respectively. GRF profiles were estimated as the sum of the product of all fifteen segmental masses and accelerations, or a reduced number of segments.ResultsErrors for GRF profiles estimated from fifteen segmental accelerations were low (1–2 N kg⁻¹) for low-speed running, moderate (2–3 N kg⁻¹) for accelerations, 90° cuts and moderate-speed running, but very high (>4 N kg⁻¹) for decelerations and high-speed running. Similarly, impulse (2.3–11.1%), impact peak (9.2–28.5%) and loading rate (20.1–42.8%) errors varied across tasks. Moreover, mean errors increased from 3.26 ± 1.72 N kg⁻¹ to 6.76 ± 3.62 N kg⁻¹ across tasks when the number of segments was reduced.ConclusionsAccuracy of estimated GRF profiles and loading characteristics was dependent on task, and errors substantially increased when the number of segments was reduced. Using a direct mechanical approach to estimate GRF from segmental accelerations is thus unlikely to be a valid method to assess whole-body biomechanical loading across different dynamic and high-intensity activities. Researchers and practitioners should, therefore, be very cautious when interpreting accelerations from one or several segments, as these are unlikely to accurately represent external whole-body biomechanical loads.     

The effects of acute experimental hip muscle pain on dynamic single-limb balance performance in healthy middle-aged adults

Middle-aged adults with painful hip conditions show balance impairments that are consistent with an increased risk of falls. Pathological changes at the hip, accompanied by pain, may accelerate pre-existing age-related balance deficits present in midlife. To consider the influence of pain alone, we investigated the effects of acute experimental hip muscle pain on dynamic single-limb balance in middle-aged adults. Thirty-four healthy adults aged 40–60 years formed two groups (Group-1: n = 16; Group-2: n = 18). Participants performed four tasks: Reactive Sideways Stepping (ReactSide); Star Excursion Balance Test (SEBT); Step Test; Single-Limb Squat; before and after an injection of hypertonic saline into the right gluteus medius muscle (Group-1) or ∼5 min rest (Group-2). Balance measures included the range and standard deviation of centre of pressure (CoP) movement in mediolateral and anterior-posterior directions, and CoP total path velocity (ReactSide, Squat); reach distance (SEBT); and number of completed steps (Step Test). Data were assessed using three-way analysis of variance. Motor outcomes were altered during the second repetition of tasks irrespective of exposure to experimental hip muscle pain or rest, with reduced SEBT anterior reach (−1.2 ± 4.1 cm, P = 0.027); greater step number during Step Test (1.5 ± 1.7 steps, P < 0.001); and slower CoP velocity during Single-Limb Squat (−4.9 ± 9.4 mms⁻¹, P = 0.024). Factors other than the presence of pain may play a greater role in balance impairments in middle-aged adults with hip pathologies.     

A new method for measuring AFO deformation,tibial and footwear movement in three dimensional gait analysis

Solid ankle-foot orthoses (AFOs) are designed to immobilise the ankle but numerous studies have measured a considerable ankle range of motion (ROM) in AFO users. Measurement of ankle kinematics may be affected by soft-tissue artefact (STA) of the knee marker, deformation of the AFO or tibial movement within the AFO. A new model based on the Conventional Gait Model (CGM) was developed to calculate these effects. Although movement of the AFO within the shoe should not affect the measured ankle joint angle the model also allows an estimation of this movement.Seven children (13 limbs) with spastic diplegic cerebral palsy were assessed to present the benefits of the new model compared to the CGM. STA of the knee marker was estimated to result in a 1.5° overestimation of total ankle ROM (from 8.2° to 9.7°). STA error was strongly related to angle of knee flexion (r = 0.82) with an average maximum error of 3.8°. AFO deformation contributed approximately two thirds of the ankle ROM (6.0 ± 4.3°) with the remaining third from tibial movement relative to the AFO (2.8 ± 0.9°). Movement of the AFO within the footwear was very small (1.8 ± 0.8°). A strong positive relationship (r = 0.9) was found between body mass (kg) and AFO deformation which was statistically significant (p < 0.001). This is the first model to attempt to quantify different contributions to ankle dorsiflexion measured during gait analysis of people wearing AFOs.     

Ocular dominance and balance performance in healthy adults

PurposeTo evaluate the effect of ocular dominance on balance performance in healthy adult subjects.MethodsOcular dominance was determined in 24 healthy subjects using the hole-in-the-paper test. Balance function was evaluated by computerized dynamic platform posturography (CDPP). Sway index (SI), antero-posterior sway (APS) and lateral sway (LS) were served as outcome parameters.ResultsThe outcome parameters did not differ significantly between dominant and non-dominant eye fixation both in static and angular balance tests (SI—5.47 ± 0.42, 6.23 ± 0.52, p = 0.146 and 18.4 ± 1.07, 19.11 ± 1.15, p = 0.142, respectively; APS—?2.26 ± 4.68, ?5.1 ± 4.6, p = 0.082 and ?1.94 ± 3.33, ?3.64 ± 2.6, p = 0.48, respectively; LS—?1.21 ± 1.46, ?1.12 ± 1.66 p = 0.94 and ?1.98 ± 1.16, ?1.55 ± 1.39, p = 0.69, respectively).ConclusionsOcular dominance does not seem to affect postural function in the monovision and far viewing condition.     

Aluminium salt-based antiperspirant coated prosthesis liners do not suppress local sweating during moderate intensity exercise in hot and temperate conditions

ObjectiveTo determine whether coating prosthesis liners with a 5% aluminium zirconium tetrachlorohydrate antiperspirant solution (AZCH) reduces local sweating on the thigh.DesignDouble-blinded counter-balanced crossover designMethodsFourteen able-bodied participants (age: 28 ± 5 y; body mass: 73.9 ± 7.9 kg, height: 1.73 ± 0.09 m; peak oxygen consumption [VO_2peak]: 50.7 ± 9.1 mlO₂⋅ kg⁻¹⋅ min⁻¹) simultaneously wore a prosthesis liner on each leg, one treated with AZCH and one untreated, for four days prior to running at 50% of VO_2peak for 60 min in a temperate (23.7 ± 0.7 °C and 42.2 ± 2.6% relative humidity) or hot (34.0 ± 1.6 °C and 40.8 ± 6.1% relative humidity) environment. Rectal temperature (T_re) and whole-body sweat rates (WBSR) were measured to characterize thermal strain. Local sweat rate (LSR) was measured bilaterally underneath the liners, continuously, and heat-activated-sweat gland density (HASGD) was measured bilaterally every 15 min.ResultsIn temperate condition, the mean change in T_re was 1.2±0.4 °C and WBSR was 723 ± 129 g⋅ h⁻¹, whereas in the hot condition, change in T_re was 1.2±0.5 °C and WBSR was 911 ± 231 g⋅ h⁻¹. In the temperate condition, AZCH treatment did not alter LSR (treated: 0.50±0.17 mg·cm^–2 min^–1, untreated: 0.50±0.17 mg·cm^–2 min^–1; P = 0.87) or HASGD (treated: 54±14 glands·cm^–2, untreated 55±14 glands·cm^–2; P = 0.38). In the hot condition, AZCH treatment paradoxically increased LSR (treated: 0.88 ± 0.38 mg·cm^–2 min^–1, untreated: 0.74 ± 0.28 mg·cm^–2 min^–1; P = 0.04) but not HASGD (treated: 52 ± 17 glands·cm^–2, untreated: 48 ± 19 glands·cm^–2; P = 0.77).ConclusionThese results indicate coating prosthesis liners with 5% AZCH is ineffective at reducing local sweating.     

Age-related changes in mediolateral dynamic stability control during volitional stepping

The control of mediolateral dynamic stability during stepping can be particularly challenging for older adults and appears to be related to falls and hip fracture. The specific mechanisms or control challenges that lead to mediolateral instability, however, are not fully understood. This work focussed on the restabilisation phase of volitional forward stepping, subsequent to foot contact, which we believe to be a principal determinant of mediolateral dynamic stability. Twenty younger (age 24 ± 5 years; 50% women) and 20 older participants (age 71 ± 5 years; 50% women) performed three different single-step tasks of various speed and step placement, which varied the challenge to dynamic stability. The trajectory of the total body centre of mass (COM) was quantified. Mediolateral COM incongruity, defined as the difference between the peak lateral and final COM position, and trial-to-trial variability of incongruity were calculated as indicators of dynamic stability. Older adults exhibited increased instability compared to young adults, as reflected by larger COM incongruity and trial-to-trial variability. Such increases among older adults occurred despite alterations in COM kinematics during the step initiation and swing phases, which should have led to increased stability. Task related increases in instability were observed as increased incongruity magnitude and trial-to-trial variability during the two rapid stepping conditions, relative to preferred speed stepping. Our findings suggest that increased COM incongruity and trial-to-trial variability among older adults signify a reduction in dynamic stability, which may arise from difficulty in reactive control during the restabilisation phase.     

Optimal timing of image acquisition for arterial first pass CT myocardial perfusion imaging

PurposeTo determine the optimal timing of arterial first pass computed tomography (CT) myocardial perfusion imaging (CTMPI) based on dynamic CTMPI acquisitions.Methods and materialsTwenty-five patients (59 ± 8.4 years, 14 male)underwent adenosine-stress dynamic CTMPI on second-generation dual-source CT in shuttle mode (30 s at 100 kV and 300 mAs). Stress perfusion magnetic resonance imaging (MRI) was used as reference standard for differentiation of non-ischemic and ischemic segments. The left ventricle (LV) wall was manually segmented according to the AHA 16-segment model. Hounsfield units (HU) in myocardial segments and ascending (AA) and descending aorta (AD) were monitored over time. Time difference between peak AA and peak AD and peak myocardial enhancement was calculated, as well as the, time delay from fixed HU thresholds of 150 and 250 HU in the AA and AD to a minimal difference of 15 HU between normal and ischemic segments. Furthermore, the duration of the 15 HU difference between ischemic and non-ischemic segments was calculated.ResultsMyocardial ischemia was observed by MRI in 10 patients (56.3 ± 9.0 years; 8 male). The delay between the maximum HU in the AA and AD and maximal HU in the non-ischemic segments was 2.8 s [2.2–4.3] and 0.0 s [0.0–2.8], respectively. Differentiation between ischemic and non-ischemic myocardial segments in CT was best during a time window of 8.6 ± 3.8 s. Time delays for AA triggering were 4.5 s [2.2–5.6] and 2.2 s [0–2.8] for the 150 HU and 250 HU thresholds, respectively. While for AD triggering, time delays were 2.4 s [0.0–4.8] and 0.0 s [−2.2–2.6] for the 150 HU and 250 HU thresholds, respectively.ConclusionIn CTMPI, the differentiation between normal and ischemic myocardium is best accomplished during a time interval of 8.6 ± 3.8 s. This time window can be utilized by a test bolus or bolus tracking in the AA or AD using the time delays identified here.