Higher Peak Velocity Research Articles

Coalescence with Droplets Caused Acceleration of the Liquid Movement in Microchannels

The coalescence between liquid flow and droplets is usually encountered in liquid filling or some new microdevices; a deep understanding of its underlying mechanism is required. In this work, therefore, the dynamic behaviors of this atypical phenomenon in microchannels were visually investigated with droplets generated by photothermally induced evaporation and condensation. The effects of droplet quantity and position, inlet pressure, and microchannel size were also explored. Experimental results showed that the coalescence accelerated the liquid movement as a result of lowered pressure at the interface. Parametric studies indicated that large droplet quantity and small distance between the inlet and droplets yielded a large velocity increment ratio as a consequence of lowered liquid pressure at the interface and increased pressure gradient, respectively. A high peak velocity increment but with low velocity increment ratio was obtained at high inlet pressure because of high liquid flow velocity. Moreover, the microchannel with a small size yielded a strong acceleration rate of the liquid movement because of more obvious capillary action in the small channel. Results obtained will be helpful for the design and operation of those kinds of microdevices that may face this atypical phenomenon.

Thrombin Generation in Zebrafish

Introduction Recently, the whole blood calibrated automated thrombogram (CAT) was miniaturized enabling the measurement of thrombin generation (TG) in a limited volume (5 µl) of whole blood. Consequently, this approach may be used to determine TG in small lab animals. Zebrafish are readily available test animals for genetic research. However, their small size has been a hurdle in thrombosis and hemostasis research since most assays require large amounts of plasma. In this study we verified the possibility to measure TG in zebrafish using our newly developed miniaturized whole blood assay.Methods For TG, 5 µl of whole blood was mixed with 5 µl of buffer containing a rhodamin-based thrombin-sensitive P2Rho substrate (final concentration (fc) 300 µM). 5 µl of this mixture was put on a paper disk and covered with mineral oil to prevent evaporation. Calibration was done as described previously (Ninivaggi et al. Clin Chem 2012) by adding 5 µl of whole blood to 5 µl of a mixture containing P2Rho (fc 300 µM), a2M-thrombin calibrator (fc 100 nM) and citrate (fc 9,8 mM). Fluorescence was detected with a fluorometer (485/538 nm).Results Due to their limited blood volume, it is impossible to perform both a TG and calibrator measurement on the same fish. Since calibrator measurements performed on blood from different fish demonstrated acceptable variation (CV calibrator slopes < 15%), the average calibrator slope was used for calculations. The calculated TG parameters from 2 independent experiments are depicted in Table 1. TG measured in individual fish showed the same amount of inter-individual variation as in humans. Striking differences with human TG parameters were the short lag time, high peak and high velocity index. Moreover a further analysis of the fibrin network of the clot, by means of scanning electron microscopy (SEM), showed a much denser network composed of thinner fibers compared to humans.Table 1Thrombin generation parameters and their coefficient of variance (CV) in zebrafish in two independent experiments.Experiment 1(n=4)Experiment 2(n=9)MeanCVMeanCVPeak ETP (nM.min)575.6819.69689.7124.91Peak (nM)1573.1629.581668.0514.46Lag time (min)0.270.000.4910.92Time to peak (min)1.085.301.3711.49Velocity (nM/min)4002.3338.213826.3517.04Conclusion These results demonstrate the feasibility of measuring TG in whole blood collected from zebrafish. Consequently, zebrafish may be used as a in vivo model to test the effect of (novel) anticoagulant therapeutics on thrombin generation and serve as a model organism for mechanistical research in thrombosis and haemostasis. DisclosuresNo relevant conflicts of interest to declare.

Binocular advantage for prehension movements performed in visually enriched environments requiring visual search.

The purpose of this study was to examine the role of binocular vision during a prehension task performed in a visually enriched environment where the target object was surrounded by distractors/obstacles. Fifteen adults reached and grasped for a cylindrical peg while eye movements and upper limb kinematics were recorded. The complexity of the visual environment was manipulated by varying the number of distractors and by varying the saliency of the target. Gaze behavior (i.e., the latency of the primary gaze shift and frequency of gaze shifts prior to reach initiation) was comparable between viewing conditions. In contrast, a binocular advantage was evident in performance accuracy. Specifically, participants picked up the wrong object twice as often during monocular viewing when the complexity of the environment increased. Reach performance was more efficient during binocular viewing, which was demonstrated by shorter reach reaction time and overall movement time. Reaching movements during the approach phase had higher peak velocity during binocular viewing. During monocular viewing reach trajectories exhibited a direction bias during the acceleration phase, which was leftward during left eye viewing and rightward during right eye viewing. This bias can be explained by the presence of esophoria in the covered eye. The grasping interval was also extended by ~20% during monocular viewing; however, the duration of the return phase after the target was picked up was comparable across viewing conditions. In conclusion, binocular vision provides important input for planning and execution of prehension movements in visually enriched environments. Binocular advantage was evident, regardless of set size or target saliency, indicating that adults plan their movements more cautiously during monocular viewing, even in relatively simple environments with a highly salient target. Nevertheless, in visually-normal adults monocular input provides sufficient information to engage in online control to correct the initial errors in movement planning.

Abstract 18623: Evaluation of Left Ventricular Geometry Changes in Patients with Tight Aortic Stenosis Using Multi-detector Computed Tomography

Background: Although aortic stenosis (AS) is a prototype of left ventricular hypertrophy (LVH) due to pressure overloading, patterns of LV geometric changes in patients with tight AS and their potential impact remain to be established. Methods: LV mass index (LVMI), LV end-diastolic volume (LVEDV) and regional LV wall thickness in 16 segments were measured in 147 patients with tight AS (indexed aortic valve area [AVA] &lt; 0.6 cm 2 /m 2 ) using multi-detector computed tomography and compared with those of 32 normal controls. LVH was defined as LVMI &gt;95 th percentile of normal controls and LV remodeling as increased LVM/LVEDV with normal range of LVMI. Asymmetric remodeling or hypertrophy were used for patients with septal wall thickness &gt;1.5 fold compared to the opposite segment. Patients with increased LVMI but normal range of LVM/LVEDV were classified to have eccentric LVH and those with eccentric LVH and decreased LV systolic function were defined to have de-compensation. Results: AS patients with mean indexed AVA of 0.36 ± 0.08 cm 2 /m 2 showed 7 different patterns of LV geometry including normal LV geometry (n=44), remodeling (n=7), asymmetric remodeling (n=7), concentric hypertrophy (n=16), asymmetric hypertrophy (n=23), eccentric hypertrophy (n=38), and de-compensation (n=12). Peak transaortic velocity (r=0.31, p&lt;0.001) and E/E’ (r=0.29, p&lt;0.001) showed positive correlation with LVMI: compared to other groups, patients with LVH (concentric or asymmetric or eccentric) showed higher peak velocity and E/E’ with smaller AVA (all, p&lt;0.001). Despite similar AVA and mean pressure gradient, patients with E/E’ ≥ 15 (n=110) showed different LV remodeling patterns (p=0.028) with higher LVMI (97.8 ± 21.1 vs 86.4 ± 20.2 g/m 2 , p=0.005). Conclusions: Various remodeling patterns of LV geometry were observed in tight AS and individual variation in LVH severity under similar LV pressure overloading could explain different severity of diastolic dysfunction.

Efficacy of Stentless Aortic Bioprosthesis Implantation for Aortic Stenosis with Small Aortic Annulus.

In patients with small aortic annulus, sufficient size of stented aortic bioprosthesis cannot be implanted without additional procedures. In such cases, we use stentless aortic bioprosthesis to obtain sufficient effective orifice area. In this study, we investigated long-term impact of stentless aortic bioprosthesis on clinical outcomes, compared with stented aortic bioprosthesis. We retrospectively investigated 140 patients who underwent aortic valve replacement (AVR) with porcine bioprosthesis for severe aortic stenosis between 1999 and 2010. Patients who had moderate or more aortic regurgitation and who underwent concomitant mitral procedures were excluded. A total of 69 patients (49%) were implanted stentless bioprosthesis (Freestyle group; Medtronic Inc, Minneapolis, Minnesota, United States) and 71 patients (51%) were implanted stented bioprosthesis (Mosaic group; Medtronic Inc). Follow-up was complete in 97.9% patients. Median follow-up period was 4.2 years. Patients in Freestyle group had smaller body surface area, smaller aortic annulus diameter, smaller aortic valve area, larger mean pressure gradient, higher peak velocity across aortic valve, larger left ventricular mass index (LVMI), and lower left ventricular ejection fraction (LVEF). Mean size of implanted prosthesis was larger in Freestyle group. In-hospital mortality was 1.4% in Freestyle group and 2.8% in Mosaic group (p = 0.980). Five-year survival rate was not different between two groups (5-year survival rate was 87.5 ± 4.7% in Freestyle group and 84.1 ± 7.5% in Mosaic group; log rank, p = 0.619). Late New York Heart Association functional class was lower in Freestyle group. Late LVMI and LVEF became similar between two groups. Stentless aortic bioprosthesis is superior in left ventricular remodeling after AVR for aortic stenosis and is especially effective for small aortic annulus.

Flow characteristics of the proximal pulmonary arteries and vena cava in patients with chronic thromboembolic pulmonary hypertension: correlation between 3.0 T phase-contrast MRI and right heart catheterization.

We aimed to determine the correlation between flow characteristics of the proximal pulmonary arteries and vena cava obtained by 3.0 T phase-contrast magnetic resonance imaging (MRI) and hemodynamic characteristics by right heart catheterization in patients with chronic thromboembolic pulmonary hypertension. Twenty consecutive patients with chronic thromboembolic pulmonary hypertension and 20 sex- and age-matched healthy volunteers were included prospectively. All patients and controls underwent phase-contrast MRI to determine the flow characteristics including peak velocity, mean velocity, and mean blood flow of the proximal pulmonary artery and vena cava. All patients underwent right heart catheterization to determine the hemodynamics. Peak velocity and mean velocity of the proximal pulmonary artery were significantly lower in the patient group. In patients, both peak velocity and mean blood flow were sequentially decreased in the main pulmonary artery, left and right pulmonary arteries, and left and right interlobar pulmonary arteries. Inferior vena cava had higher peak velocity, mean velocity, and mean blood flow than superior vena cava. Peak velocity of the main pulmonary artery correlated with mean and diastolic pulmonary artery pressure. Peak velocity of both inferior and superior vena cava strongly correlated with the pulmonary vascular resistance index (PVRI) (r=-0.68, P < 0.001 and r=-0.74, P < 0.001, respectively). Mean velocity of the main pulmonary artery and right pulmonary artery strongly correlated with PVRI and mean pulmonary artery pressure. Mean velocity of the superior vena cava and mean blood flow of the main pulmonary artery strongly correlated with PVRI and right cardiac work index. Blood flow in the proximal pulmonary artery and vena cava evaluated by phase-contrast MRI correlate with hemodynamic parameters of right heart catheterization and can be used to noninvasively evaluate the severity of chronic thromboembolic pulmonary hypertension and, potentially, to follow up the treatment response.

Peak Velocity Measurements in Tortuous Arteries With Phase Contrast Magnetic Resonance Imaging

Blood flow velocity measurement with phase contrast magnetic resonance imaging (PC-MRI) is widely applied in clinical routine imaging. Usually, velocity and volumetric flow measurements are performed using unidirectional encoding of the through-plane velocity with a 2-dimensional (2D) acquisition. Single-slice acquisitions and measurements with unidirectional encoding, however, may lead to significant errors, especially in tortuous vessels, but might benefit from higher signal-to-noise ratios (SNRs). To evaluate the impact of volumetric acquisition and multidirectional velocity encoding, blood velocity measurements were performed at 3 locations in the distal internal carotid artery with a 3-dimensional, 3-directional time-resolved phase contrast (PC) sequence (4-dimensional [4D]) and a 2D acquisition with 3-directional (2D-3dir) and through-plane velocity encoding (2D-tp) derived from the same sequence. Twenty carotid arteries of 10 healthy volunteers (24-37 years) were evaluated. For each volunteer, 1 4D acquisition and 3 2D 3-directional PC measurements were placed according to a time-of-flight angiography. Unidirectionally encoded through-plane velocities were derived from the multidirectionally encoded 2D scan by discarding the in-plane components. Regions of interest were identified on the slab after postprocessing and visualization for the 4D data set as well as directly on the digital imaging and communications in medicine images for the 2D measurement. Blood flow velocity, volumetric flow, and SNRs were measured at carotid segments C4, C5, and C7 on both sides obtaining 20 values per vessel location. The quantities were tested for significant differences between each modality at all 3 locations with paired t tests. At the segments C5 and C7, the highest peak velocities (PVs) were measured with the 4D sequence, followed by 2D-3dir and 2D tp. The PV differences between the sequences were significant (P < 0.01) at both locations. At the proximal segment of the carotid siphon (C4), the PV values of the 2D-3dir sequence were significantly higher than the ones measured with 2D-tp. The mean PV value of the 4D sequence was located in between 2D-3dir and 2D-tp without significant differences to either of the 2D sequences. Volumetric flow measurements were also significantly different between 2D and 4D acquisitions, but without a discernible trend. The SNR analysis clearly favored 2D over 4D acquisitions because of higher inflow enhancement. The results of the current study show that velocity measurements with a unidirectional encoded through-plane PC sequence lead to a significant underestimation of velocity values in tortuous vessels. In all 3 evaluated segments of the distal internal carotid artery, multidirectional velocity encoding revealed significantly higher PV values than those of unidirectional velocity encoding. These results indicate that multidirectional encoding should be preferred to unidirectional encoding for velocity measurements in tortuous vessels. Furthermore, 4D PC-MRI is superior to 2D-3dir in 2 of 3 locations. However, single-slice measurements with multidirectional velocity encoding have higher SNR and may be an alternative to 4D PC-MRI with a scan time of only approximately 90 seconds per slice.

Short interspike intervals and double discharges of anconeus motor unit action potentials for the production of dynamic elbow extensions

Incidence of double discharges (DDs; >100 Hz) and short interspike intervals (ISIs; >50 to <100 Hz) is reported to vary widely among different muscles and tasks, with a higher incidence in motor unit (MU) trains of fast muscles and for the production of fast contractions in humans. However, it is unclear whether human muscles with a large composition of slower motor units exhibit DDs or short ISIs when activated with maximal synaptic drive, such as those required for maximal velocity dynamic contractions. Thus the purpose of this study was to determine the effect of increasing peak contraction velocity on the incidence of DDs and short ISIs in the anconeus muscle. Seventeen anconeus MUs in 10 young males were recorded across dynamic elbow extensions ranging from low submaximal velocities (16% of maximal velocity) up to maximal velocities. A low incidence of DDs (4%) and short ISIs (29%) was observed among the 583 MU trains recorded. Despite the low incidence in individual MU trains, a majority (71% and 94%, respectively) of MUs exhibited at least one DD or short ISI. The number of short ISIs shared no variance with MU recruitment threshold (R(2) = 0.02), but their distribution was skewed toward higher peak velocities (G = -1.26) and a main effect of peak elbow extension velocity was observed (P < 0.05). Although a greater number of short ISIs was observed with increasing velocity, the low incidence of DDs and short ISIs in the anconeus muscle is likely related to the function of the anconeus as a stabilizer rather than voluntary elbow extensor torque and velocity production.

Hemodynamic Impact of Transcatheter Aortic Valve Deployment Configuration.

Transcatheter aortic valve (TAV) replacement holds promise for a large number of patients who otherwise have limited or no treatment options. However, it also poses various challenges, due to its unique disease treatment mechanism. Successful TAV deployment and function are heavily reliant on the tissue-stent interaction [1,2]. For patients with aortic stenosis, heavy calcium deposition on the valve leaflets and the aortic root can also cause distortion of TAV geometries, resulting in a valve of an elliptical shape [3–5] instead of a nominal circular shape. In a recent study by Schultz et al. [5], the geometry and apposition of the TAV after implantation in 30 patients with aortic stenosis were evaluated using multislice computed tomography. The results indicated that none of the TAV frames reached exactly nominal designed dimensions. The difference between the orthogonal smallest and largest diameters of TAV cross section at the ventricular end was 4.4 mm, which was clearly an asymmetric elliptical shape [5]. In this study, we sought to develop computational models of valve hemodynamics under clinically relevant deployment scenarios.The geometry of a “generic” TAV has been described in detail [6]. It is a thin pericardial bioprosthetic valve with similar design features to TAVs used commercially. This model has been extended previously to the development of elliptical valves, with eccentricities of 0.3, 0.5, and 0.68 and alignment of either the major or minor axis of the ellipse to a native commissure [7]. In the current study, the open configuration for each of these elliptical models was obtained using abaqus finite element simulation (Fig. 1(a)). The leaflets were attached to a circular mounting ring (Fig. 1(b)) and then sealed in a 38-mm tube (Fig. 1(c)) in preparation for import into computational fluid dynamics (CFD) software using Hypermesh (Altair Engineering, Troy, MI).The CFD software star-CCM+ was used, with a polyhedral mesh and boundary conditions of 30 liters per minute (LPM) mass flow at the inlet and 100 mmHg pressure at the outlet. A Newtonian fluid was used, with a viscosity of 0.0035 Pa-s and a density of 1056 kg/m3. Turbulence was modeled by specifying intensity and length scale for the k-ε model.The sealed geometry was also used to fabricate physical models through additive manufacturing, which were then used for experimental validation using steady forward flow at 30 LPM. A centerline probe was advanced upstream, measuring pressure at 1-mm spacing.For the baseline circular valve, a peak transvalvular pressure of 10.92 mmHg was simulated (Fig. 2), which correlated to an effective orifice area (EOA) of 2.93 cm2. In a long-axis view, the peak centerline velocity was 2.16 m/s and the peak turbulent kinetic energy (TKE) was 0.30 J/kg. We observed that EOA dropped for more elliptical conditions, particularly when the minor axis of the ellipse was aligned with the TAV commissures. The changes in flow were also observed as higher transvalvular pressure, higher peak velocity, and higher TKE as compared with the baseline circular condition.Experimental pressure versus axial position curves can be used to validate steady-flow models. Best turbulence modeling was obtained for 10% turbulent intensity and a length scale of 4.6 mm. TAV ellipticity tended to cause increased EOA with higher peak velocity. These models may be used in the future to investigate more complicated clinical scenarios.The authors gratefully acknowledge the funding provided by the NSF, NIH, and Edwards Lifesciences, Inc.

Reduced effects of tendon vibration with increased task demand during active, cyclical ankle movements

Tendon vibration can alter proprioceptive feedback, one source of sensory information which humans can use to produce accurate movements. However, the effects of tendon vibration during functional movement vary depending on the task. For example, ankle tendon vibration has considerably smaller effects during walking than standing posture. The purpose of this study was to test whether the effects of ankle tendon vibration are predictably influenced by the mechanical demands of a task, as quantified by peak velocity. Twelve participants performed symmetric, cyclical ankle plantar flexion/dorsiflexion movements while lying prone with their ankle motion unconstrained. The prescribed movement period (1, 3 s) and peak-to-peak amplitude (10°, 15°, 20°) were varied across trials; shorter movement periods or larger amplitudes increased the peak velocity. In some trials, vibration was continuously and simultaneously applied to the right ankle plantar flexor and dorsiflexor tendons, while the left ankle tendons were never vibrated. The vibration frequency (40, 80, 120, 160 Hz) was varied across trials. During trials without vibration, participants accurately matched the movement of their ankles. The application of 80 Hz vibration to the right ankle tendons significantly reduced the amplitude of right ankle movement. However, the effect of vibration was smaller during more mechanically demanding (i.e., higher peak velocity) movements. Higher vibration frequencies had larger effects on movement accuracy, possibly due to parallel increases in vibration amplitude. These results demonstrate that the effects of ankle tendon vibration are dependent on the mechanical demand of the task being performed, but cannot definitively identify the underlying physiological mechanism.

Vascular Health in Kawasaki Disease

The objective of our study was to compare the indices of vascular health in Kawasaki disease (KD) patients to those of control subjects. The literature on peripheral vascular health after KD is conflicting. Subjects were patients 11 to 29 years of age with the onset of KD >12 months before the study visit (n= 203) andhealthy control subjects (n= 50). We measured endothelial function (using the Endothelial Pulse Amplitude Testing index), intima-media thickness (IMT) of the right common carotid artery (RCCA) and the left common carotidartery (LCCA), and fasting lipid profile and C-reactive protein (CRP). KD patients were classified according totheir worst-ever coronary artery (CA) status: group I, always normal CAs (n= 136, 67%); group II, CA z-scores≥2 but<3 (n= 20, 10%); group III, CA aneurysm z-scores≥3 but<8 mm (n= 40, 20%); and group IV, giant CAaneurysm, defined as≥8 mm (n= 7, 3%). At a median of 11.6 years (range, 1.2 to 26 years) after KD onset, compared with controls, KD patients had a higher peak velocity in the LCCA (p= 0.04) and higher pulsatility index of both the RCCA and LCCA (p= 0.006 and p= 0.05, respectively). However, there were no differences in the Endo-PAT index or carotid IMT or stiffness. Themean IMT of the LCCA tended to differ across the KD subgroups and control group (p= 0.05), with a higher mean in group IV. Otherwise the KD subgroups and control group had similar vascular health indexes. In contrast to some earlier reports, our study of North American children and young adults demonstrated that KDpatients whose maximum CA dimensions were either always normal or mildly ectatic have normal vascular health indexes, providing reassurance regarding peripheral vascular health in this population.

Increasing speed to improve arm movement and standing postural control in Parkinson's disease patients when catching virtual moving balls

Research has shown that moving targets help Parkinson's disease (PD) patients improve their arm movement while sitting. We examined whether increasing the speed of a moving ball would also improve standing postural control in PD patients during a virtual reality (VR) ball-catching task. Twenty-one PD patients and 21 controls bilaterally reached to catch slow-moving and then fast-moving virtual balls while standing. A projection-based VR system connected to a motion-tracking system and a force platform was used. Dependent measures included the kinematics of arm movement (movement time, peak velocity), duration of anticipatory postural adjustments (APA), and center of pressure (COP) movement (movement time, maximum amplitude, and average velocity). When catching a fast ball, both PD and control groups made arm movements with shorter movement time and higher peak velocity, longer APA, as well as COP movements with shorter movement time and smaller amplitude than when catching a slow ball. The change in performance from slow- to fast-ball conditions was not different between the PD and control groups. The results suggest that raising the speed of virtual moving targets should increase the speed of arm and COP movements for PD patients. Therapists, however, should also be aware that a fast virtual moving target causes the patient to confine the COP excursion to a smaller amplitude. Future research should examine the effect of other task parameters (e.g., target distance, direction) on COP movement and examine the long-term effect of VR training.

The relationship between cognitive impairment and cerebral blood flow changes after transient ischaemic attack

Objective: The associations between cognitive impairment following the initial onset of transient ischaemic attack (TIA) and the parameters of altered cerebral blood flow and high-sensitivity C-reactive protein (HsCRP) level are unclear.Methods: A total of 97 first-time TIA patients aged 69·94±4·02 years (38–75 years; M:F, 50:47) hospitalized between March 2010 and July 2011 were compared to 100 healthy control patients aged 66·56±12·15 years (45–80 years; M:F, 60:40). Cognitive function was quantified by Montreal Cognitive Assessment (MoCA). Intracranial blood flow was measured using transcranial Doppler ultrasound, and HsCRP levels were assessed using the Spearman correlation coefficient. Relationships between both values and MoCA scores were examined.Results: Transient ischaemic attack patients exhibited declined cognitive function manifested as impaired verbal fluency (97·93%), memory recall (91·75%), abstraction (84·53%), and visuospatial/executive abilities (79·38%). To a lesser degree, TIA patients also evidenced abnormalities in attention (50·52%), naming (20·62%), and orientation (20·62%). Furthermore, MoCA scores significantly correlated with high HsCRP levels and low vascular systolic peak velocities (P<0·001). Vascular systolic peak velocities were high in nine patients (9·23%) and low in 57 patients (58·76%). Thus, cognitive impairment was closely related to HsCRP levels and intracranial blood flow velocities.Conclusion: Post-TIA cognitive impairment may result from atherosclerosis and reduced blood flow to the brain. Cognitive impairment, transcranial Doppler-visualized changes, and elevated HsCRP levels are important diagnostic indicators of TIA. Markers provided by cognitive evaluation of TIA patients following the initial onset of TIA may allow clinicians to better predict and prevent adverse vascular events.

The physiological and biomechanical contributions of poling to roller ski skating

Poling is considered to make a significant contribution to cross-country skiing with the skating technique. To better understand this contribution, the current investigation compared roller ski skating on a treadmill with the so-called G3 skating technique with (G3-P) and without poling (G3-NP). Seven male elite skiers performed 5-min submaximal tests at 8, 12, and 15 km h(-1), as well as an incremental test to exhaustion with both techniques on a 5 % incline. Ventilatory variables were assessed by open-circuit indirect calorimetry and three-dimensional kinematics analyzed using the Qualisys Pro Reflex system. G3-P was associated with approximately 15 % higher peak velocity and 10 % higher peak oxygen uptake than G3-NP in the incremental test (both P < 0.01). All ventilatory variables, as well as heart rate and blood lactate concentration were lower with G3-P as compared to G3-NP at 12 and 15 km h(-1) (all P < 0.01). Gross efficiency (i.e., the ratio of work rate to metabolic rate) at 12 km h(-1) was higher in G3-P (14.9 %) than G3-NP (13.5 %) (P < 0.01). Moreover, with G3-P cycle time and length were both 30 % longer, with correspondingly reduced cycle rates (all P < 0.01). In addition, the ski gliding and swing phases were longer and the angle between the skis smaller with G3-P (both P < 0.01), whereas the push-off time was independent of technique and velocity. Taken together, these results indicate that poling makes an important contribution to propulsion and velocity during ski skating, specifically by enhancing peak oxygen uptake, skiing efficiency and associated biomechanical variables.

The Effect of Flow Acceleration on the Cyclic Variation of Blood Echogenicity Under Pulsatile Flow

It has been shown that the echogenicity of blood varies during a flow cycle under pulsatile flow both in vitro and in vivo. In general, the echogenicity of flowing whole blood increases during the early systole phase and then reduces to a minimum at late diastole. While it has been postulated that this cyclic variation is associated with the dynamics of erythrocyte aggregation, the mechanisms underlying this increasing echogenicity with flow velocity remain uncertain. The effect of flow acceleration has also been proposed as an explanation for this phenomenon, but no specific experiments have been conducted to test this hypothesis. In addition, the influence of ultrasonic attenuation on the cyclic variation of echogenicity requires clarification. In the present study, a Couette flow system was designed to simulate blood flowing with different acceleration patterns, and the flow velocity, attenuation, and backscattering coefficient were measured synchronously from 20%- and 40%-hematocrit porcine whole blood and erythrocyte suspensions using 35-MHz ultrasound transducers. The results showed ultrasonic attenuation exerted only minor effects on the echogenicity of blood under pulsatile flow conditions. Cyclic variations of echogenicity were clearly observed for whole blood with a hematocrit of 40%, but no variations were apparent for erythrocyte suspensions. The echogenicity did not appear to be enhanced when instantaneous acceleration was applied to flowing blood in any case. These findings show that flow acceleration does not promote erythrocyte aggregation, even when a higher peak velocity is applied to the blood. Comparison of the results obtained with different accelerations revealed that the cyclic variation in echogenicity observed during pulsatile blood flow may be jointly attributable to the effect of shear rate and the distribution of erythrocyte on aggregation.

The StartReact Effect on Self-Initiated Movements

Preparation of the motor system for movement execution involves an increase in excitability of motor pathways. In a reaction time task paradigm, a startling auditory stimulus (SAS) delivered together with the imperative signal (IS) shortens reaction time significantly. In self-generated tasks we considered that an appropriately timed SAS would have similar effects. Eight subjects performed a ballistic wrist extension in two blocks: reaction, in which they responded to a visual IS, and action, in which they moved when they wished within a predetermined time window. In 20–25% of the trials, a SAS was applied. We recorded electromyographic activity of wrist extension and wrist movement kinematic variables. No effects of SAS were observed in action trials when movement was performed before or long after SAS application. However, a cluster of action trials was observed within 200 ms after SAS. These trials showed larger EMG bursts, shorter movement time, shorter time to peak velocity, and higher peak velocity than other action trials (P < 0.001 for all), with no difference from Reaction trials containing SAS. The results show that SAS influences the execution of self-generated human actions as it does with preprogrammed reaction time tasks during the assumed building up of preparatory activity before execution of the willed motor action.

Reaching a Better Understanding of the Control of Bimanual Movements in Older Adults

The ability to interact skilfully with the environment is essential for independent living and therefore a critical factor for the aging population. Here we investigate the differences between young and older adults in a bimanual reaching task where the goal is to bring two objects together to the same location with a synchronous placement. Older (mean age 74) and young (mean age 20) adults were asked to pick up two spatially disparate objects, one in each hand, and bring them together to place them in one of three trays laid out in front of them from left to right. The results showed that the older adults were no more detrimentally affected than the young by asymmetric bimanual movements compared to symmetric ones, and both groups completed their movements in the same time. Nevertheless, compared to the young, the older adult group produced reaches characterised by higher peak velocities (although this effect was marginal), shorter hover times, and where the movement distance varied for each hand the scaling of the kinematic profile across the two limbs diverged from that found with younger participants. They then spent longer than the young in the final adjustment phase and during this phase they made more adjustments than the young, and as a result were more synchronous in terms of the final placement of the objects. It seems that the older adults produced reach movements that were designed to reach the vicinity of the tray quite rapidly, after which time they made discreet adjustments to their initial trajectories in order to exercise the precision necessary to place the objects in the tray. These findings are consistent with the idea that older adults have problems using online control (as they wait until they can fixate both objects before making adjustments).

Effect of therapist-based constraint-induced therapy at home on motor control, motor performance and daily function in children with cerebral palsy: a randomized controlled study

Objective: To determine the effect of therapist-based constraint-induced therapy at home on motor performance, daily function and reaching control for children with cerebral palsy. Design: A single-blinded, randomized controlled trial. Subjects: Forty-seven children (23 boys; 24 girls) with unilateral cerebral palsy, aged 6–12 years, were randomized to constraint-induced therapy (n = 24) or traditional rehabilitation (n = 23). Interventions: Constraint-induced therapy involved intensive functional training of the more affected arm while the less affected arm was restrained. Traditional rehabilitation involved functional unilateral and bilateral arm training. Both groups received individualized therapist-based interventions at home for 3.5–4 hours/day, two days a week for four weeks. Main measures: Motor performance and daily function were measured by the Peabody Developmental Motor Scale, Second Edition and the Pediatric Motor Activity Log. Reaching control was assessed by the kinematics of reaction time, movement time, movement unit and peak velocity. Results: There were larger effects in favour of constraint-induced therapy on motor performance, daily function, and some aspects of reaching control compared with traditional rehabilitation. Children receiving constraint-induced therapy demonstrated higher scores for Peabody Developmental Motor Scale, Second Edition – Grasping (pretest mean ± SD, 39.9 ± 3.1; posttest, 44.1 ± 2.8; P < 0.001), Pediatric Motor Activity Log (pretest, 1.8 ± 0.3; posttest, 2.5 ± 0.3; P < 0.001) and shorter reaction time, normalized movement time (P < 0.001) and higher peak velocity (P = 0.004) of reaching movement. Conclusions: Constraint-induced therapy induced better grasping performance, daily function, and temporal and spatiotemporal control of reaching in children with unilateral cerebral palsy than traditional rehabilitation.

Hemodynamics of Portal Venous Stenosis Before and After Treatment in Pediatric Liver Transplantation: Evaluation with Doppler Ultrasound

AimThe aim of this study was to evaluate portal vein stenosis (PVS) in pediatric liver transplantation (PLT) using Doppler ultrasound (DUS) before and after interventional management for hemodynamic changes. Materials and MethodsFrom 2000 to 2010, we encountered 11 PVS cases among 180 PLT that were evaluated using DUS and computed tomography (CT) angiography (CTA); all underwent portal stenting. DUS was used to monitor portal hemodynamics. For the diagnosis of PVS, we investigated multiple parameters including stenotic size (SS), stenotic ratio (SR) (SR [%] = PRE-SS/PRE [PRE = stenotic size]), portal flow velocity ratio (VR) (VR = VS/PRE [PRE = velocity at prestenotic site; VS = peak velocity at stenotic site]), spleen size, and platelet count. ResultsThe incidence of PVS was 5.6% (11/180). The PV was 2.5 mm using DUS and 2.7 mm using CTA. The average SR was 65% fitting the criterion. Low prestenotic portal flow <12 cm/sec and high peak velocity in the stenotic segment (up to 147 cm/sec) were observed in 6 cases. The VR value was high at 7.5:1 and there was splenomegaly with thrombocytopenia. After portal vein stenting, hyperperfusion occurred might after reopening the stenosis: the flow increased to an average of 34 cm/sec and then flow decreased slowly to a stable level 2 weeks later. The size of the spleen decreased from 17 to 12 cm and the thrombocytopenia also improved with platelet counts increasing from 67 × 103 to 178 × 103/μl at 2 months follow-up. The changes in portal flow, portal vein size, spleen size, and platelet count were significant (P < .05). ConclusionPVS is diagnosed using DUS by increased intrahepatic PV dilatation, peak flow at the stenotic site, discrepant VR. Early portal stenting showed a better prognosis. DUS is essential and effective for hemodynamic monitoring and management of PVS.

Video game use correlates with shorter saccadic reaction times and higher peak velocities

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