Differential joint coordination in the tasks of standing up and sitting down

We studied similarities and differences in the use of goal-equivalent patterns of joint coordination to stand up and sit down from different support surfaces, performed without vision. Sagittal plane motion of major body segments was measured and joint angles for the left upper and lower extremities and the trunk were calculated. We used a modeling strategy relating motion in the redundant space of the joints to motion of individual performance variables, such as the center of mass (CM) or head, and determined how the variability of joint combinations across trials was structured; i.e. variations in joint combinations leading to a consistent value of a performance variable (goal-equivalent variability) and variations resulting in variability of the performance variable (non goal-equivalent variability). We found the variability of joint combinations to be selectively channeled into goal-equivalent directions, leading to stable horizontal motion of the CM and of the head, during both standing up and sitting down. In contrast, when evaluating the effect of joint combination variability on the control of vertical CM motion, we found differences in the variability components between standing up and sitting down. In general, more variable vertical CM motion occurred. An important finding was an enhanced use of goal-equivalent joint combinations under challenging task conditions, whether standing up or sitting down.     

人体坐下站起过程中平衡功能评估及训练系统软件的设计与实现

本研究针对脑卒中偏瘫患者的平衡功能定量评估的需求,设计一种针对坐下站起过程中各阶段平衡功能评估及训练的系统软件,该软件配合坐位站起平衡功能训练仪使用。软件采用面向对象编程技术,应用VS2010(Microsoft Visual Studio2010)开发平台编写,可实时获得人体在坐下站起过程中的各评估参数,包括左右臀前后最大压力、左右足底平均压力、伸展期时间、伸展前期时间、左右侧最大和平均压力及站起时的最大加速度等。结合图形和数字实时显示及虚拟现实技术,对人体坐下站起的各阶段进行平衡功能评估和训练,通过视觉、听觉反馈,使训练更具趣味性。经过测试应用,结果表明,该系统软件运行稳定可靠,具有针对性的评估并结合实时可观测的压力曲线及大量的评估参数,可使评估结果更快速更有效。     

Soleus activity in post-stroke subjects: Movement sequence from standing to sitting

Introduction. The beginning of the movement sequence from standing to sitting requires the modulation of plantar flexors activity, including the soleus muscle (SOL), to allow the forward translation of the tibia in relation to the foot, preserving its antigravity function.

Purpose. To analyze the SOL activity during the initial phase of standing to sitting in stroke subjects.

Methods. Two groups of ten subjects each participated in this study, one composed of healthy subjects and the other with subjects with a history of stroke. Electromyographic activity (EMGa) of SOL was analyzed in the ipsilateral (IPSI) and contralateral (CONTRA) limb to side lesion in stroke subjects, and in one limb in healthy subjects during the initial phase of standing to sitting. A force plate was used to identify the movement sequence phase.

Results. The mean values of SOL EMGa were higher in healthy subjects than the ones obtained in the IPSI and CONTRA limb in stroke subjects. Significant differences were only observed between the IPSI and healthy limb (p?=?0.035).

Conclusion. When compared to the healthy subjects, stroke subjects showed a decreased SOL EMGa in the IPSI limb, which suggests that therapeutic decisions must consider the need to promote a better postural control also in the IPSI limb.     

Standing up to the challenge of standing: a siphon does not support cerebral blood flow in humans

Model studies have been advanced to suggest both that a siphon does and does not support cerebral blood flow in an upright position. If a siphon is established with the head raised, it would mean that internal jugular pressure reflects right atrium pressure minus the hydrostatic difference from the brain. This study measured spinal fluid pressure in the upright position, the pressure and the ultrasound-determined size of the internal jugular vein in the supine and sitting positions, and the internal jugular venous pressure during seated exercise. When the head was elevated approximately 25 cm above the level of the heart, internal jugular venous pressure decreased from 9.5 (SD 2.8) to 0.2 (SD 1.0) mmHg [n = 15; values are means (SD); P < 0.01]. Similarly, central venous pressure decreased from 6.2 (SD 1.8) to 0.6 (SD 2.6) mmHg (P < 0.05). No apparent lumen was detected in any of the 31 left or right internal veins imaged at 40 degrees head-up tilt, and submaximal (n = 7) and maximal exercise (n = 4) did not significantly affect internal jugular venous pressure. While seven subjects were sitting up, spinal fluid pressure at the lumbar level was 26 (SD 4) mmHg corresponding to 0.1 (SD 4.1) mmHg at the base of the brain. These results demonstrate that both for venous outflow from the brain and for spinal fluid, the prevailing pressure approaches zero at the base of the brain when humans are upright, which negates that a siphon supports cerebral blood flow.     

Determination of esophageal probe insertion length based on standing and sitting height

The present study derives simple formulas for the prediction of optimal insertion length of an esophageal temperature-sensitive probe from the measurements of either standing or sitting height. The formulas assume that the optimal site for an esophageal temperature probe is in the region of the esophagus bounded by the left ventricle and aorta, corresponding to the level of the eighth and ninth thoracic vertebrae (T8 and T9, respectively). An esophageal probe was constructed of polyethylene tubing containing 1-cm segments of alternating radiopaque and nonradiopaque tubing in the distal 20 cm of the probe. The probe was inserted through a nostril into the esophagus of 20 subjects (12 males and 8 females) of various heights (range 163-194.6 cm) and weights (range 52.2-100.8 kg), and lateral chest radiograms were obtained for determination of the insertion length of the probe (L) required to situate the probe in the retrocardiac esophagus. Analysis of the radiograms demonstrated that, at the level of the intervertebral disc between T8 and T9, the probe was below the tracheal bifurcation and close to the left ventricle. The distance from the nasal flare to this level showed a good correlation with the subject's stretched stature (r2 = 0.71) and sitting height (r2 = 0.86). The following equations were derived to predict the placement of the esophageal probe at the T8/T9 level based on standing height: L (CM) = 0.228 x (standing height) - 0.194, and sitting height: L (cm) = 0.479 x (sitting height) - 4.44.     

Letter fluency: psychometric properties and Dutch normative data

Normative data were collected for a Dutch version of the Controlled Oral Word Association Test (COWAT) in 200 healthy subjects between 17 and 89 years of age. The COWAT is a letterfluency task that is widely used in clinical neuropsychology. Fluency is an important aspect of executive functioning. The psychometric properties of the Dutch version of the test were largely comparable to those of the original COWAT. Its reliability is 0.80, and its scores are significantly related to level of education and/or vocabulary, but not to age or gender. A regression formula is provided by which the raw scores can be corrected for level of education.     

Scaling up and down: movement ecology for microorganisms

Movement is critical for the fitness of organisms, both large and small. It dictates how individuals acquire resources, evade predators, exchange genetic material, and respond to stressful environments. Movement also influences ecological and evolutionary dynamics at higher organizational levels, such as populations and communities. However, the links between individual motility and the processes that generate and maintain microbial diversity are poorly understood. Movement ecology is a framework linking the physiological and behavioral properties of individuals to movement patterns across scales of space, time, and biological organization. By synthesizing insights from cell biology, ecology, and evolution, we expand theory from movement ecology to predict the causes and consequences of microbial movements.     

Falciparum malaria: sticking up, standing out and out-standing

Cytoadherence is believed to be fundamental for the survival of Plasmodium falciparum in vivo and, uniquely, is a major determinant of the virulence of this parasite. Despite the widely professed importance of cytoadhesion in the development of severe disease, there are a number of aspects of this highly complex process that remain poorly understood. Recent progress in the understanding of cytoadhesive phenomena was discussed extensively at the Molecular Approaches to Malaria conference, Lorne, Australia, 2-5 February 2000. Here, Brian Cooke, Mats Wahlgren and Ross Coppel consider just how far we have progressed during the past 30 years and highlight what is still missing in our understanding of the mechanisms and clinical relevance of this apparently vital process.     

Energy features in spontaneous up and down oscillations

Spontaneous brain activities consume most of the brain’s energy. So if we want to understand how the brain operates, we must take into account these spontaneous activities. Up and down transitions of membrane potentials are considered to be one of significant spontaneous activities. This kind of oscillation always shows bistable and bimodal distribution of membrane potentials. Our previous theoretical studies on up and down oscillations mainly looked at the ion channel dynamics. In this paper, we focus on energy feature of spontaneous up and down transitions based on a network model and its simulation. The simulated results indicate that the energy is a robust index and distinguishable of excitatory and inhibitory neurons. Meanwhile, one the whole, energy consumption of neurons shows bistable feature and bimodal distribution as well as the membrane potential, which turns out that the indicator of energy consumption encodes up and down states in this spontaneous activity. In detail, energy consumption mainly occurs during up states temporally, and mostly concentrates inside neurons rather than synapses spatially. The stimulation related energy is small, indicating that energy consumption is not driven by external stimulus, but internal spontaneous activity. This point of view is also consistent with brain imaging results. Through the observation and analysis of the findings, we prove the validity of the model again, and we can further explore the energy mechanism of more spontaneous activities.     

Somatosensory evoked potentials in neonates and infants: developmental and normative data

Fifty-two sets of cortical somatosensory evoked potentials (SEPs) were recorded from 23 normal children between the ages of 1 day and 13 weeks with median nerve stimulation. Two bandpass settings 5–1500 Hz and 30–3000 Hz were used; rate of stimulation was 1.1 Hz and sweep-time was 200 msec. The state of wakefulness was documented, but SEPs were obtained and evaluated independently of the child being awake or asleep during the recording. SEPs were present in every recording. The bandpass 30–3000 Hz best differentiated positive and negative early potentials. The bandpass 5–1500 Hz was helpful in some cases, as late slow waves were recorded with this setting. Normative data were established. Mean values were calculated for 3 age groups: 0–2 weeks, 2–6 weeks and 7–13 weeks. P15 and N20 were the first components seen in the newborn, with the P22 becoming the major component by 2–3 weeks of age. The study indicates that maturation of the somatosensory system is fastest during the first 3 weeks of life.     

Irregular dynamics in up and down cortical states

Complex coherent dynamics is present in a wide variety of neural systems. A typical example is the voltage transitions between up and down states observed in cortical areas in the brain. In this work, we study this phenomenon via a biologically motivated stochastic model of up and down transitions. The model is constituted by a simple bistable rate dynamics, where the synaptic current is modulated by short-term synaptic processes which introduce stochasticity and temporal correlations. A complete analysis of our model, both with mean-field approaches and numerical simulations, shows the appearance of complex transitions between high (up) and low (down) neural activity states, driven by the synaptic noise, with permanence times in the up state distributed according to a power-law. We show that the experimentally observed large fluctuation in up and down permanence times can be explained as the result of sufficiently noisy dynamical synapses with sufficiently large recovery times. Static synapses cannot account for this behavior, nor can dynamical synapses in the absence of noise.     

Oxygen uptake/heart rate relationship in leg and arm exercise, sitting and standing.

The effect of leg exercise and of arm exercise in sitting and standing body positions on energy output and on some cardiorespiratory parameters was studied in seven male subjects. Oxygen uptake (VO2), heart rate (fH), pulmonary ventilation (VE) and respiratory frequency were measured at rest, in the 7-8th min of submaximal work (300, 600, 900 kpm/min), and at maximal effort. Significantly higher Vo2, fH, and VE in arm cranking than in cycling were found at submaximal work loads above 300 kpm/min. Though the maximal work load in arm exercise was 50-60% of that in cycling, Vo2 in arm work was at maximal effort only 22% lower than in leg exercise while the difference in fH was insignificant. No differences were found in arm work between the results obtained at any work level in sitting and standing body positions. The only postural difference in arm work was a 13% higher work load achieved at maximal effort when standing than when sitting. Differences in fH between arm and leg exercise were much smaller for the same Vo2 than for the same work load and were time dependent. While fH quickly leveled off in leg exercise, fH in arm cranking rose steadily during the first 6 min of work which created the fH differences observed in the 7-8 min of submaximal arm arm and leg exercise. At submaximal work levels a tendency to synchronize the respiratory frequency with the frequency of the rotatory movements was more apparent in arm cranking than in cycling.     

Top down and bottom up engineering of bone

The goal of this retrospective article is to place the body of my lab's multiscale mechanobiology work in context of top-down and bottom-up engineering of bone. We have used biosystems engineering, computational modeling and novel experimental approaches to understand bone physiology, in health and disease, and across time (in utero, postnatal growth, maturity, aging and death, as well as evolution) and length scales (a single bone like a femur, m; a sample of bone tissue, mm-cm; a cell and its local environment, μm; down to the length scale of the cell's own skeleton, the cytoskeleton, nm). First we introduce the concept of flow in bone and the three calibers of porosity through which fluid flows. Then we describe, in the context of organ-tissue, tissue-cell and cell-molecule length scales, both multiscale computational models and experimental methods to predict flow in bone and to understand the flow of fluid as a means to deliver chemical and mechanical cues in bone. Addressing a number of studies in the context of multiple length and time scales, the importance of appropriate boundary conditions, site specific material parameters, permeability measures and even micro-nanoanatomically correct geometries are discussed in context of model predictions and their value for understanding multiscale mechanobiology of bone. Insights from these multiscale computational modeling and experimental methods are providing us with a means to predict, engineer and manufacture bone tissue in the laboratory and in the human body.