Measurements of volume changes and venous pressure in the human lower leg during walking and running.

This study investigates whether walking or running prevents the formation of edema in the lower leg. In 18 volunteers changes in calf volume were measured using strain gauge plethysmography during slow (3 km/h) and fast (6 km/h) walking or running (10 km/h) on a treadmill for 20 min each. Venous pressure was measured in a superficial vein near the ankle. Low-pass filtering removed motion artifacts from the signals. Slow walking reduced the calf volume in a biphasic manner: a rapid decrease was followed by a slow decline, lasting from about minute 2 to minute 20, its mean rate being -0.073%/min. Besides a rapid initial decrease, no significant change was observed during fast walking. During running, the calf volume first increased within 7 min to a maximum of 2.5% and subsequently decreased with a mean rate of -0.096%/min. The medians of venous pressure were 84.0, 23.5, 30.4, and 29.5 mmHg during quiet standing, slow and fast walking, and running, respectively. The experimental results prove the hypothesis that walking prevents dependent edema formation. This effect, however, cannot be fully explained by the lowered venous pressures.     

Effect of peak pressure and pressure gradient on subsurface shear stresses in the neuropathic foot

The pressure distribution on the plantar surface of the foot may provide insights into the stresses within the subsurface tissues of patients with diabetes mellitus and peripheral neuropathy (PN) who are at risk for skin breakdown. The purposes of this study were to (1) estimate the stress distribution in the subsurface soft tissue from a measured surface pressure distribution and determine any differences between values in the forefoot and rearfoot, and (2) determine the relationship between maximum shear stress (MSS) (magnitude and depth) and characteristics of the pressure distribution. The measured in-shoe pressure distributions during walking characterized by the peak plantar pressure and maximum pressure gradient on the plantar surface of the feet for 20 subjects with diabetes, PN and history of a mid foot or forefoot plantar ulcer were analyzed. The effects of peak pressure and maximum pressure gradient at the peak pressure location on the stress components in the subsurface soft tissue were studied using a potential function method to estimate the subsurface tissue stress. The calculated MSSs are larger in magnitude and located closer to the surface in the forefoot, where most skin breakdown occurs, compared to the rearfoot. In addition, the MSS (magnitude and depth) is highly correlated with the pressure gradient (r=-0.77 & 0.61) and the peak pressure (r=-0.61 & 0.91). The peak pressure and the maximum pressure gradient obtained from the surface pressure distribution appear to be important variables to identify where MSSs are located in the subsurface tissues on the plantar foot that may lead to skin break down.     

Locomotion pattern and foot pressure adjustments during gentle turns in healthy subjects

People suffering from locomotor impairment find turning manoeuvres more challenging than straight-ahead walking. Turning manoeuvres are estimated to comprise a substantial proportion of steps taken daily, yet research has predominantly focused on straight-line walking, meaning that the basic kinetic, kinematic and foot pressure adaptations required for turning are not as well understood. We investigated how healthy subjects adapt their locomotion patterns to accommodate walking along a gently curved trajectory (radius 2.75 m). Twenty healthy adult participants performed walking tasks at self-selected speeds along straight and curved pathways. For the first time for this mode of turning, plantar pressures were recorded using insole foot pressure sensors while participants’ movements were simultaneously tracked using marker-based 3D motion capture. During the steady-state strides at the apex of the turn, the mean operating point of the inside ankle shifted by 1 degree towards dorsiflexion and that for the outside ankle shifted towards plantarflexion. The largest change in relative joint angle range was an increase in hip rotation in the inside leg (>60%). In addition, the inside foot was subject to a prolonged stance phase and a 10% increase in vertical force in the posteromedial section of the foot compared to straight-line walking. Most of the mechanical change required was therefore generated by the inside leg with hip rotation being a major driver of the gentle turn. This study provides new insight into healthy gait during gentle turns and may help us to understand the mechanics behind some forms of impairment.     

Effect of intrathoracic pressure on pressure-volume characteristics of the lung in man.

Quasi-static pressure-volume (P-V) curves in normal seated human subjects were determined with pressure at the airway opening (Pa0) set below (negative pressure), above (positive pressure), or equal to ambient pressure. Dynamic compliance (Cdyn) during controlled continuous negative pressure breathing (CNPB) was also studied. Quasi-static P-V curves at negative pressure were decreased in slope, reflected a decrease in total lung capacity, and intersected the P-V curve obtained at ambient Pa0. At positive pressure the P-V curves showed an increase in slope and an increase in total lung capacity. During CNPB a fall in Cdyn was found. The fall in Cdyn was rapid and persisted for the duration of CNPB. Cdyn promptly returned to control levels when Pa0 was adjusted to ambient pressure.     

Diurnal changes in xylem pressure and mesophyll cell turgor pressure of the lianaTetrastigma voinierianum: The role of cell turgor in long-distance water transport

Summary Long-term xylem pressure measurements were performed on the lianaTetrastigma voinierianum (grown in a tropical greenhouse) between heights of 1 m and 9.5 m during the summer and autumn seasons with the xylem pressure probe. Simultaneously, the light intensity, the temperature, and the relative humidity were recorded at the measuring points. Parallel to the xylem pressure measurements, the diurnal changes in the cell turgor and the osmotic pressure of leaf cells at heights of 1 m and 5 m (partly also at a height of 9.5 m) were recorded. The results showed that tensions (and height-varying tension gradients) developed during the day time in the vessels mainly due to an increase in the local light intensity (at a maximum 0.4 MPa). The decrease of the local xylem pressure from positive, subatmospheric or slightly above-atmospheric values (established during the night) to negative values after daybreak was associated with an almost 1 1 decrease in the cell turgor pressure of the mesophyll cells (on average from about 0.4 to 0.5 MPa down to 0.08 MPa). Similarly, in the afternoon the increase of the xylem pressure towards more positive values correlated with an increase in the cell turgor pressure (ratio of about 1 1). The cell osmotic pressure remained nearly constant during the day and was about 0.75–0.85 MPa between 1 m and 9.5 m (within the limits of accuracy). These findings indicate that the turgor pressure primarily determines the corresponding pressure in the vessels (and vice versa) due to the tight hydraulic connection and thus due to the water equilibrium between both compartments. An increase in the transpiration rate (due to an increase in light intensity) results in very rapid establishment of a new equilibrium state by an equivalent decrease in the xylem and cell turgor pressure. From the xylem, cell turgor, and cell osmotic pressure data the osmotic pressure (or more accurately the water activity) of the xylem sap was calculated to be about 0.35–0.45 MPa; this value was apparently not subject to diurnal changes. Considering that the xylem pressure is determined by the turgor pressure (and vice versa), the xylem pressure of the liana could not drop to — in agreement with the experimental results — less than -0.4 MPa, because this pressure corresponds to zero turgor pressure.     

The Relationships between Foot Arch Volumes and Dynamic Plantar Pressure during Midstance of Walking in Preschool Children

Objectives

The purpose of this study was to examine the correlation between the foot arch volume measured from static positions and the plantar pressure distribution during walking.

Methods

A total of 27 children, two to six years of age, were included in this study. Measurements of static foot posture were obtained, including navicular height and foot arch volume in sitting and standing positions. Plantar pressure, force and contact areas under ten different regions of the foot were obtained during walking.

Results

The foot arch index was correlated (r = 0.32) with the pressure difference under the midfoot during the foot flat phase. The navicular heights and foot arch volumes in sitting and standing positions were correlated with the mean forces and pressures under the first (r = −0.296∼−0.355) and second metatarsals (r = −0.335∼−0.504) and midfoot (r = −0.331∼−0.496) during the stance phase of walking. The contact areas under the foot were correlated with the foot arch parameters, except for the area under the midfoot.

Conclusions

The foot arch index measured in a static position could be a functional index to predict the dynamic foot functions when walking. The foot arch is a factor which will influence the pressure distribution under the foot. Children with a lower foot arch demonstrated higher mean pressure and force under the medial forefoot and midfoot, and lower contact areas under the foot, except for the midfoot region. Therefore, children with flatfoot may shift their body weight to a more medial foot position when walking, and could be at a higher risk of soft tissue injury in this area.     

Stump-socket pressure in lower extremity prostheses

The pressures existent at the interface between stump and socket were obtained for two subjects equipped with above the knee prostheses. The effects of leg alignment changes and the passage of time are detailed in terms of local dynamic pressures experienced while walking.

Local instantaneous pressures vary from 0 to 50 psi as a function of location, subject and gait phase. Highest pressures are obtained at the socket brim. Alignment changes produce but small pressure changes. Maximum donning pressures equal those in walking: standing pressures are less than half of peak walking pressures.     

Influence of extravascular pressure on changes induced in vascular resistance in the small intestine by elevated venous pressure

The influence of the extravascular pressure on the size of the increase in vascular resistance after elevation of venous outflow pressure (venous-vasomotor response) was studied in an intestinal segment, perfused at a constant rate, in anaesthetized dogs. If pressure in the lumen of the intestine was elevated (spontaneously, pharmacologically, mechanically) or pressure in the plethysmograph was raised, venous-vasomotor responses were either smaller or absent. When pressure in the intestinal lumen was raised, blood volume increments produced in the segment by elevated venous pressure were significantly smaller than those observed in the presence of resting pressure. The presence of a venous-vasomotor response was correlated to the quantitative relationship between the extravascular and the venous pressure. Its induction was dependent on whether the outflow venous pressure was higher than the pressure values in the intestinal lumen or the plethysmograph; in that case it developed to an extent corresponding to the increment in transmural vascular pressure.     

Heart rate and arterial pressure variability in humans during different orthostatic load.

The influence of posture on the rhythms in blood pressure, heart rate and respiration was tested by means of spectral analysis in 14 healthy subjects. During squatting, standing and sitting, the finger blood pressure was recorded by the non-invasive Penáz technique together with cardiac intervals and respiratory movements. The power spectra obtained from five-minute samples showed that the respiratory components of cardiac interval and pulse pressure were reduced significantly in standing. Compared to squatting, a significant increase of total power in the medium frequency band (0.05-0.15 Hz) for cardiac interval, diastolic and mean pressure could be detected.     

Determining the centre of pressure during walking and running using an instrumented treadmill

In this paper, a new method of determining spatial and temporal gait parameters by using centre of pressure (CoP) data is presented. A treadmill is used which was developed to overcome limitations of regular methods for the analysis of spatio-temporal gait parameters and ground reaction forces during walking and running. The design of the treadmill is based on the use of force transducers underneath a separate left and right plate, which together form the treadmill walking surface. The results of test procedures and measurements show that accurate recordings of vertical ground reaction force can be obtained. These recordings enable a separate analysis of vertical ground reaction forces during double support phases in walking, and the analysis of changes in the centre of pressure (CoP) position during subsequent foot placements. From the CoP data, temporal gait parameters (e.g. duration of left/right support and swing phases) and spatial gait parameters (i.e. left/right step lengths and widths) can be derived.     

Speed training with body weight unloading improves walking energy cost and maximal speed in 75- to 85-year-old healthy women.

This randomized controlled study was designed to prove the hypothesis that a novel approach to high-speed interval training, based on walking on a treadmill with the use of body weight unloading (BWU), would have improved energy cost and speed of overground walking in healthy older women. Participants were randomly assigned to either the exercise group (n = 11, 79.6 +/- 3.7 yr, mean +/- SD) or the nonintervention control group (n = 11, 77.6 +/- 2.3 yr). During the first 6 wk, the exercise group performed walking interval training on the treadmill with 40% BWU at the maximal walking speed corresponding to an intensity close to heart rate at ventilatory threshold (T(vent) walking speed). Each session consisted of four sets of 5 min of walking (three 1-min periods at T(vent) walking speed, with two 1-min intervals at comfortable walking speed in between each period at T(vent) walking speed) with 1-min interval between each set. Speed was increased session by session until the end of week 6. BWU was then progressively reduced to 10% during the last 6 wk of intervention. After 12 wk, the walking energy cost per unit of distance at all self-selected overground walking speeds (slow, comfortable, and fast) was significantly reduced in the range from 18 to 21%. The exercise group showed a 13% increase in maximal walking speed and a 67% increase in mechanical power output at T(vent) after the training program. The novel "overspeed" training approach has been demonstrated to be effective in improving energy cost and speed of overground walking in healthy older women.     

Estimation of microbial cell concentration in suspension culture by the osmotic pressure measurement of culture broth

Summary A method for estimating microbial cell concentration in suspension cultures even under heterogeneous conditions was developed on the basis of changes in osmotic pressure of the medium. During batch cultivation of Saccharomyces cerevisiae and Candida brassicae, there was a linear relationship between increase in cell concentrations (X) and the difference between osmotic pressure change in the broth (P_c) and the osmotic pressure increase due to product accumulation (P_p) regardless of the product (ethanol) concentration in the broth. A linear relationship between (X) and (P_c — P_p) was also observed when medium containing solid substrate (wheat germ) was used. An enzymatic method for separating cells from the solids was developed and cell concentrations in broths containing solid substrates could be measured accurately. During the batch production of bialaphos (a herbicide) by Streptomyces hygroscopicus using a medium containing solid substrates, the cell concentration could also be estimated by the developed methods.     

Estimating the complete ground reaction forces with pressure insoles in walking

This study presented a method to estimate the complete ground reaction forces from pressure insoles in walking. Five male subjects performed 10 walking trials in a laboratory. The complete ground reaction forces were collected during a right foot stride by a force plate at 1000Hz. Simultaneous plantar pressure data were collected at 100Hz by a pressure insole system with 99 sensors covering the whole plantar area. Stepwise linear regressions were performed to individually reconstruct the complete ground reaction forces in three directions from the 99 individual pressure data until redundancy among the predictors occurred. An additional linear regression was performed to reconstruct the vertical ground reaction force by the sum of the value of the 99 pressure sensors. Five other subjects performed the same walking test for validation. Estimated ground reaction forces in three directions were calculated with the developed regression models, and were compared with the real data recorded from force plate. Accuracy was represented by the correlation coefficient and the root mean square error. Results showed very good correlation in anterior-posterior (0.928) and vertical (0.989) directions, and reasonable correlation in medial-lateral direction (0.719). The root mean square error was about 12%, 5% and 28% of the peak recorded value. Future studies should aim to generalize the methods or to establish specific methods to other subjects, patients, motions, footwear and floor conditions. The method gives an extra option to study an estimation of the complete ground reaction forces in any environment without the constraints from the number and location of force plates.     

Changes in lung volume and upper airway using MRI during application of nasal expiratory positive airway pressure in patients with sleep-disordered breathing

Nasal expiratory positive airway pressure (nEPAP) delivered with a disposable device (Provent, Ventus Medical) has been shown to improve sleep-disordered breathing (SDB) in some subjects. Possible mechanisms of action are 1) increased functional residual capacity (FRC), producing tracheal traction and reducing upper airway (UA) collapsibility, and 2) passive dilatation of the airway by the expiratory pressure, carrying over into inspiration. Using MRI, we estimated change in FRC and ventilation, as well as UA cross-sectional area (CSA), in awake patients breathing on and off the nEPAP device. Ten patients with SDB underwent nocturnal polysomnography and MRI with and without nEPAP. Simultaneous images of the lung and UA were obtained at 6 images/s. Image sequences were obtained during mouth and nose breathing with and without the nEPAP device. The nEPAP device produced an end-expiratory pressure of 4-17 cmH(2)O. End-tidal Pco(2) rose from 39.7 ± 5.3 to 47.1 ± 6.0 Torr (P < 0.01). Lung volume changes were estimated from sagittal MRI of the right lung. Changes in UA CSA were calculated from transverse MRI at the level of the pharynx above the epiglottis. FRC determined by MRI was well correlated to FRC determined by N(2) washout (r = 0.76, P = 0.03). nEPAP resulted in a consistent increase in FRC (46 ± 29%, P < 0.001) and decrease in ventilation (50 ± 15%, P < 0.001), with no change in respiratory frequency. UA CSA at end expiration showed a trend to increase. During wakefulness, nEPAP caused significant hyperinflation, consistent with an increase in tracheal traction and a decrease in UA collapsibility. Direct imaging effects on the UA were less consistent, but there was a trend to dilatation. Finally, we showed significant hypoventilation and rise in Pco(2) during use of the nEPAP device during wakefulness and sleep. Thus, at least three mechanisms of action have the potential to contribute to the therapeutic effect of nEPAP on SDB.     

The relationship between speed, contact time and peak plantar pressure in terrestrial walking of bonobos

The aim of this paper is twofold. Firstly, we investigate whether contact times, as recorded by pedobarographic systems during quadrupedal and bipedal walking of bonobos, can be used to reliably calculate actual velocities, by applying formulae based on lateral-view video recordings. Secondly, we investigate the effect of speed on peak plantar pressures during bipedal and quadrupedal walking of the bonobo. Data were obtained from 4 individuals from a group of bonobos at the Animal Park Planckendael. From our study, we can conclude that both walking speeds calculated from contact times and lower leg length or simply from recorded contact times are good estimators for walking speed, when direct observation of the latter is impossible. Further, it was found that effects of speed on peak plantar pressures and vertical forces are absent or at least subtle in comparison to a large variation in pressure patterns. In bonobos, the same pressure patterns are used at all walking speeds, and, in consequence, we do not expect major changes in foot function.     

Turgor pressure regulation and the orientation of cortical microtubules in Spirogyra cells.

Microtubules (MTs) of cells of Spirogyra sp. were depolymerized by treatment with amiprophos-methyl (APM) for 1 h and then reorganized in 0.30 M mannitol solution. The reorganized MTs after 1.5 h incubation showed an oblique/longitudinal orientation and then became transversely oriented as the incubation was prolonged. During this incubation, the osmotic pressure of cells was measured by the plasmolysis method. The cell osmotic pressure increased with time. The calculated turgor pressure at 1.5 h was 0.11 M (mannitol equivalent) and, at 13.5 h, 0.25 M. Similar changes in MT orientation and recovery of the turgor pressure were also observed in 0.30 M sorbitol solution. These results suggest that the MT orientation may be correlated with the turgor pressure. Among fresh water algae sensitive to a saline environment, this Spirogyra was the first species shown to have a turgor regulating mechanism, although the recovery of turgor pressure was incomplete. The recovery of turgor pressure in mannitol solutions was also observed without APM treatment.     

New insights into the plantar pressure correlates of walking speed using pedobarographic statistical parametric mapping (pSPM)

This study investigates the relation between walking speed and the distribution of peak plantar pressure and compares a traditional ten-region subsampling (10RS) technique with a new technique: pedobarographic statistical parametric mapping (pSPM). Adapted from cerebral fMRI methodology, pSPM is a digital image processing technique that registers foot pressure images such that homologous structures optimally overlap, thereby enabling statistical tests to be conducted at the pixel level. Following previous experimental protocols, we collected pedobarographic records from 10 subjects walking at three different speeds: slow, normal, and fast. Walking speed was recorded and correlated with the peak pressures extracted from the 10 regions, and subsequently with the peak pixel data extracted after pSPM preprocessing. Both methods revealed significant positive correlation between peak plantar pressure and walking speed over the rearfoot and distal forefoot after Bonferroni correction for multiple comparisons. The 10RS analysis found positive correlation in the midfoot and medial proximal forefoot, but the pixel data exhibited significant negative correlation throughout these regions (p<5x10(-5)). Comparing the statistical maps from the two approaches shows that subsampling may conflate pressure differences evident in pixel-level data, obscuring or even reversing statistical trends. The negative correlation observed in the midfoot implies reduced longitudinal arch collapse with higher walking speeds. We infer that this results from pre- or early-stance phase muscle activity and speculate that preferred walking speed reflects, in part, a balance between the energy required to tighten the longitudinal arch and the apparent propulsive benefits of the stiffened arch.     

Exercise-induced swelling of rat soleus muscle: its relationship with intramuscular pressure

Exercise-induced tissue swelling and its possible consequence for tissue pressure were studied in rat soleus muscle. Rats ran for 75 min on a belt with a 10 degree positive incline. Wet weights of cryofixed soleus muscles were increased at 3 (16%), 6 (28%), 9 (16%), and 24 (16%) h after running compared with those of nonexercised controls. The transient increase in muscle wet weight correlated in time with an increase in muscle volume. Muscle fiber swelling accounted for most of the muscle swelling in absolute terms because of the large proportion (approximately 90%) of the muscle volume composed of fibers, but swelling of the interstitium was about twofold larger than fiber swelling per unit area. Muscle fiber degeneration was most frequently found at the end of the observation period, i.e., 24 h after running. The muscle swelling was not associated with an increase in intramuscular pressure. During the postexercise measuring period (18 min to 24 h after exercise), intramuscular pressures of exercised rats (1.3 +/- 0.3 mm Hg) did not differ significantly from control values (1.0 +/- 0.2 mm Hg). These findings indicate that increased intramuscular pressure is not responsible for the muscle fiber degeneration found in rat soleus muscle 24 h after endurance running.     

Influence of examination stress and psychoemotional characteristics on the blood pressure and heart rate regulation in female students

During the semester and immediately before an examination, changes in the heart rate variability, blood pressure, and state anxiety induced by examination stress, as well as the dependence of these changes on the probabilistic prediction and actual examination mark, were investigated. Before an examination, most students exhibited an increase in state anxiety, diastolic blood pressure, and heart rate; the last of these is connected with an increase in the LF/HF ratio. The behavior of the cardiovascular system of the students (who were females) under psychoemotional stress varied considerably depending on how well they were prepared for the examination and on the subjective prediction of success. The importance of the type of heart rate regulation during the semester for the progress of examination stress was established.     

A force plate based method for the calibration of force/torque sensors

This study describes a novel calibration method for six-degrees-of-freedom force/torque sensors (FTsensors) using a pre-calibrated force plate (FP) as a reference measuring device. In this calibration method, the FTsensor is rigidly connected to a FP and force/torque data are synchronously recorded while a dynamic functional loading procedure is applied by the researcher. Based on these data an accurate calibration matrix for the FTsensor can easily be obtained via least-squares optimization. Using this calibration method, this study further investigated what loading methods are appropriate for the calibration of FTsensors intended for ambulatory measurement of ground reaction forces (GRFs). Seven different loading methods were compared (e.g., walking, pushing while standing on the FTsensor). Calibration matrices were calculated based on the raw data from the seven loading methods individually and all loading methods combined. Performance of these calibration matrices was subsequently compared in an in situ trial. During the in situ trial, five common work tasks (e.g., walking, manual lifting, pushing) were performed by an experimenter, while standing on the FP wearing a "ForceShoe" with two calibrated FTsensors attached to its sole. Root-mean-square differences (RMSDs) between the FTsensor and FP outcomes were calculated over all tasks. Using the calibration matrices based on all loading methods combined resulted in small RMSDs (GRF: <8 N, center of pressure: <2 mm). Using the calibration matrices based on "pushing against manual resistance" resulted in similar RMSDs, proving it to be the best single loading method.