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PubMed2006

Postural balance changes in on-duty firefighters: effect of gear and long work shifts.

OBJECTIVE: The objective of this study was to investigate the impact of long work shifts and turnout gear, including the self-contained breathing apparatus (SCBA) on firefighters' postural stability. METHODS: Sixteen firefighters were assessed using a portable forceplate system at the fire station. Postural sway parameters were recorded at the beginning of the work shift and repeated until the work shift ended. RESULTS: Task had the greatest impact on postural stability for all sway parameters. Turnout gear, with and without SCBA, improved postural stability. Postural stability decreased as firefighters spent more time on duty. CONCLUSIONS: Prolonged work shifts may be an important contributor to the high prevalence of slips and falls among firefighters. In all, the results indicate that many aspects of the firefighters' job may adversely impact their postural stability and potentially increase the risk of falling.

Adult↗
PubMed2006

The consequences of increasing age and duration of injury upon the wheelchair posture of men with tetraplegia.

It has been suggested that postural problems experienced by people with spinal cord injury may increase with greater age and duration of injury; however, there has been little documentation of the magnitude of changes and their time course. Our study was conducted to measure the wheelchair posture of 30 participants with long and short duration of tetraplegia due to spinal cord injury as compared to 30 age-matched able-bodied participants. Posture measurements were derived from the relationships of bony landmarks which were recorded by photography. Results suggest that increasing age and duration of spinal cord injury are associated with more extreme pelvic angle and forward head posture. Thoracic kyphosis, as indicated by chest angle, was the main postural distinction between participants with tetraplegia and able-bodied participants. The kyphosis was not significantly greater in those with longer duration injury. Proactive intervention to prevent late onset postural problems is recommended.

Adult↗
PubMed2005

Maternal posture for cephalic version of breech presentation: a review of the evidence.

BACKGROUND: Maternal posture is commonly recommended to promote cephalic version of breech presentation during pregnancy, but the few studies conducted to examine the efficacy of this obstetric practice are inconclusive. The purpose of this systematic review was to evaluate the research evidence base for postural management of breech presentation. METHODS: This review critically examined the research on maternal posture for breech presentation using guidelines from the third United States Preventive Services Task Force. Database searches were conducted of Ovid Medline, Cumulative Index of Nursing and Allied Health Literature, PubMed, and Cochrane Database of Systematic Reviews, using the keywords "pregnancy," "maternal posture," "maternal position," "postural management," "breech," "presentation." Hand searches were conducted on reference citations from databases, and all research articles, commentaries, and reports of clinical cases were included. RESULTS: Conceptual and methodological issues in the individual studies posed threats to internal validity in each study. Interpretation of the nonsignificant results in the research reports is debatable because the randomized controlled trials were underpowered, and flaws in each study challenged validity of the results. Meta-analysis of previous findings may be inappropriate. CONCLUSIONS: Further research based on explicit theory and improved methods, including sufficient sample size, is needed to determine whether maternal posture promotes cephalic version for pregnant women with breech presentation.

Breech Presentation↗
PubMed1993

Use of a computerized postural sway measurement system for assessing workers exposed to manganese.

1. Computerized postural sway measurement systems have been used recently in human physiology and pharmacology for determining postural stability, but their applicability for the assessment of the effects of exposure to neurotoxic agents is lacking. 2. We have examined the feasibility of using a computerized postural sway measurement system to assess the postural sway parameters of manganese exposed workers compared with a control group. 3. Sway parameter data were collected using a KISLTER multicomponent measuring platform (Type 9281B) connected to VICON motion analysis system for 13 exposed and 16 control subjects. 4. Significant differences in several of the sway parameters (Px, Py--mean distance (mm), from the centre of the platform along the X-axis [anterior-posterior movement] and Y-axis [lateral movement], respectively) between the exposed and control groups were observed even after adjustment for possible confounders. Computerized postural sway measurement system may be a useful method of assessing workers exposed to neurotoxic agents affecting posture.

Adult↗
PubMed1996

The ambulatory measurement of posture, thigh acceleration, and muscle tension and their relationship to heart rate.

We compared the relative ability of continuous accelerometric, electromyographic (EMG), and hydrostatic posture measurements to discriminate tasks involving variations in motor activity and posture and to predict heart rate (HR) variability. EMG was a more sensitive measure than accelerometry in differentiating the tasks. However, accelerometry and EMG explained comparable amounts of HR variance. The hydrostatic posture was a stable measure that clearly differentiated postures and explained a significant amount of HR variance but less than accelerometry or EMG. Accelerometric and EMG measures of motor activity used either alone or in combination with the hydrostatic posture are valuable in discriminating activities and in controlling for the effects of motor activity and posture on HR during ambulatory measurement.

Adult↗
PubMed1995

Redistribution of body fluids during postural manipulations.

Inter-compartmental body-fluid distribution is contingent upon posture, exercise state and environmental temperature. This investigation aimed at quantifying the distribution of intra- and extravascular fluid volumes during postural manipulations. Fluid shifts were measured in eight males utilizing a simultaneous, radionuclide dilution technique, in which radioiodinated serum fibrinogen, radiochromated erythrocytes, radiobromine and tritiated water were used to measure plasma, red cell, extracellular and total body water volumes. Subjects were exposed to three postural changes [seated (control), supine and standing] for 30 min at an air temperature of 22.0 degrees C, with each posture separated by 30 min seated rest. Total body water content remained stable throughout postural changes (P = 0.842). Relative to seated volumes, BV increased by 89 mL when supine, and decreased by 406 mL while standing (P = 0.003), with such shifts being primarily a result of plasma movement (P = 0.011). Red cell volume changes were not significant. Vascular fluid lost during standing was filtered into the interstitial compartment (P = 0.014), with the extracellular and intracellular volumes remaining unaffected. (P = 0.271 and P = 0.800, respectively). These observations confirmed the influence of posture on inter-compartmental body-fluid distribution. The intravascular fluid loss when standing was caused by the filtration of plasma into the interstitium, while, during supine rest, intravascular volume increased, reflecting fluid flux from the interstitium to the circulation.

Adult↗
PubMed2004

Postural and locomotor control in normal and vestibularly deficient mice.

We investigated how vestibular information is used to maintain posture and control movement by studying vestibularly deficient mice (IsK-/- mutant). In these mutants, microscopy showed degeneration of the cristae of the semicircular canals and of the maculae of the utriculi and sacculi, while behavioural and vestibulo-ocular reflex testing showed that vestibular function was completely absent. However, the histology of Scarpa's ganglia and the vestibular nerves was normal in mutant mice, indicating the presence of intact central pathways. Using X-ray and high-speed cineradiography, we compared resting postures and locomotion patterns between these vestibularly deficient mice and vestibularly normal mice (wild-type and IsK+/-). The absence of vestibular function did not affect resting posture but had profound effects on locomotion. At rest, the S-shaped, sagittal posture of the vertebral column was the same for wild-type and mutant mice. Both held the head with the atlanto-occipital joint fully flexed, the cervico-thoracic junction fully flexed, and the cervical column upright. Wild-type mice extended the head and vertebral column and could walk in a straight line. In marked contrast, locomotion in vestibularly deficient mice was characterized by circling episodes, during which the vertebral column maintained an S-shaped posture. Thus, vestibular information is not required to control resting posture but is mandatory for normal locomotion. We propose that vestibular inputs are required to signal the completion of a planned trajectory because mutant mice continued rotating after changing heading direction. Our findings support the hypothesis that vertebrates limit the number of degrees of freedom to be controlled by adopting just a few of the possible skeletal configurations.

Animals↗
PubMed2003

The effect of changes in the body configuration on anticipatory postural adjustments.

A number of factors are likely to play a major role in the process of generation of anticipatory postural adjustments (APAs). Among them are the magnitude and direction of an expected perturbation, properties of a voluntary action associated with the perturbation, and features of the postural task such as a body's configuration prior to the action. The aim of this study was to analyze the effect of body configuration on APAs. Experiments were performed on 8 healthy subjects performing fast bilateral shoulder extension movements while standing. Body configuration was modified by instructions to the subjects to stand vertically or with a forward upper body bend varying from 15 to 60 degrees. The electrical activity of postural muscles and displacements of the center of pressure were recorded. Results indicated that APAs were modified with changes in the angular position of the upper body. Decreased anticipatory activation was seen in rectus abdominis and rectus femoris, while increased anticipatory inhibition was observed in erecteor spinae and biceps femoris across conditions with forward bend. As a result, the total anticipatory activity of muscles in a muscle pair in series with a forward bend showed only slight modulation as compared to vertical posture. These results suggest that the CNS uses reorganization of the anticipatory activity of postural muscles by compensating for the changes in APAs of individual muscles in a muscle pair in such a way that the overall anticipatory activity of the muscle pair stays unchanged. Such compensation in counteracting the expected mechanical effects of the perturbation is used to accommodate both changes in the length of postural muscles and diminished stability of the body due to forward bend.

Adaptation, Physiological↗
PubMed1994

Development of posture in prone and supine positions during the prenatal period in low risk preterm infants.

The development of posture in the prone and supine positions was studied longitudinally in 10 low risk preterm infants between 31 and 39 weeks' postmenstrual age whose subsequent neurological development at 18 months old was normal. The infants were observed from one week after birth until the expected date of delivery. All postures were analysed according to the procedures described by Prechtl et al. There were large intraindividual and interindividual differences in posture in terms of the duration and incidence of the two positions. There was no age specific preferred posture found in either position. The posture duration in the prone position was longer than that in the supine position, but overall flexed and abducted posture were observed more often in the former. Turning of the head to the right side was also observed more often in the prone than in the supine position.

Female↗
PubMed2000

Effect of exposure to lead on postural control in workers.

OBJECTIVES: To examine the effect of lead on postural control of workers who have been exposed to lead. METHODS: 63 Male, lead battery workers mean (SD) age 41.0 (7.4) were compared with 48 age matched male controls after excluding those with acute or chronic diseases. Exposed workers had mean (SD) past blood lead concentrations of 37.5 (9.2) micrograms/dl and 11.2 (5.7) years of employment. Postural control was measured with a computerised postural sway measurement system which measured both sway and total movements. RESULTS: Workers standing straight with eyes open on the bare plates had sway and total movements which were not notably different from controls. On the other hand increased movements were needed in the exposed workers to maintain stability (the general stability quotient 18.2 (5.4) v 15.4 (4.4) in controls, p < 0.01) when standing directly on the foot-plates with closed eyes,, and with the head tilted (15.0 (3.8) v 11.5 (3.0) in controls, p < 0.001). Exposed workers also had a trend for less ability to synchronize anterior posterior and lateral sway in the stress positions (0.0625) than had non-exposed workers. Significant but low correlations were found between the estimate of the chronic internal dose of lead and three of 10 of the postural control measurements, and present lead blood concentrations and only one of the 10 measurements and (r values ranged from 0.21 to 0.31, p < or = 0.03). CONCLUSIONS: These findings suggest that lead affects postural control in asymptomatic workers. Further studies are warranted to find whether workers with decreased postural control are at increased risk of accidents and the relation, if any, of these measurements with subsequent morbidity.

Adult↗
PubMed1990

Age-related differences in norepinephrine kinetics: effect of posture and sodium-restricted diet.

We used compartmental analysis to study the influence of age on the kinetics of norepinephrine (NE) distribution and metabolism. Plasma NE and [3H]NE levels were measured in 10 young (age 19-33 yr) and 13 elderly (age 62-73 yr) subjects in the basal supine position, during upright posture, and after 1 wk of a sodium-restricted diet. We found that the basal supine release rate of NE into the extravascular compartment, which is the site of endogenous NE release (NE2), was significantly increased in the elderly group (young, 9.6 +/- 0.5; elderly, 12.3 +/- 0.8 nmol.min-1.m-2; means +/- SE; P = 0.016), providing direct evidence for an age-related increase in sympathetic nervous system (SNS) tone. Although upright posture led to a greater increase in plasma NE in the young (0.90 +/- 0.07 to 2.36 +/- 0.16 nM) than in the elderly (1.31 +/- 0.11 to 2.56 +/- 0.31 nM; age group-posture interaction, P = 0.02), the increase in NE2 was similar between the young (9.6 +/- 0.6 to 16.2 +/- 1.5 nmol.min-1.m-2) and the elderly (11.6 +/- 1.4 to 16.1 +/- 2.4 nmol.min-1.m-2; posture effect, P = 0.001; age group-posture interaction, P = 0.15). Thus the increase in SNS tone resulting from upright posture was similar in young and elderly subjects. Plasma NE levels increased similarly in both groups after a sodium-restricted diet (diet effect, P = 0.001; age group-diet interaction, P = 0.23). However, NE2 did not increase significantly in either group (diet effect, P = 0.26), suggesting that SNS tone did not increase after a sodium-restricted diet. Compartmental analysis provides a description of age-related differences in NE kinetics, including an age-related increase in the extravascular NE release rate.

Adult↗
PubMed1982

Effects of posture on flow-volume curve configuration in normal humans.

Tien et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 46: 565-570, 1979) found reproducible details in the configuration of averaged maximal expiratory flow-volume curves and suggested that these details may correspond to sudden relocations of airway choke points. The occurrence of choke points depends on factors affecting local airway pressure-diameter behavior. We postulated that changes in posture as they affect the distribution of lung recoil on airways might change the locations of choke points and thereby alter flow-volume configuration. Twenty normal adults performed five flow-volume curves in each of four postures (standing, supine, right, and left lateral recumbent). Volume was measured with a Krogh spirometer and airflow with a Fleisch No. 4 pneumotachometer. Curves were digitally filtered and plotted relative to upright total lung capacity. Five curves in each posture were averaged at increments of 0.1 l/s of flow and average volumes at given flows were compared using the Student's t test. Significant differences (P less than 0.01) in mean volumes at given flows occurred in all subjects from standing to supine and/or right to left lateral postures. Large changes in configuration were apparent in one of the two postural pairs in eight subjects. We conclude that changes in posture result in significant changes in flow-volume configuration in most normal adults. These findings are consistent with the wave-speed theory of flow limitation and suggest that small changes in local airway stresses can significantly alter the location and motion of airway choke points during forced expiration.

Adult↗
PubMed1986

Scintigraphic evaluation of shape of lung and chest in upright and head-down posture.

We determined the configuration of lungs and chest in six healthy young subjects using anteroposterior and lateral technetium-99m-labeled scintigraphic images obtained in upright and in 90 degree head-down posture at 0, 25, 50, 75, and 100% vital capacity (VC). The lung shape was evaluated from curves relating vertical height vs. cumulative volume of 20 apicodiaphragmatic lung zones of equal height. S-shaped curves were obtained, which, after size normalization, were largely independent of volume or posture (P greater than 0.1). However, the apical zones tended to become relatively wider and the diaphragmatic zones relatively smaller with increasing volume, especially between 0 and 25% VC in upright posture and 0-50% VC in head-down posture. Changing posture from upright to head-down also tended to slightly widen the apical zones and to narrow the diaphragmatic zones, which is in line with a greater intrathoracic penetration of the diaphragm/abdomen. The shape of the chest was evaluated from the ratio of the transverse-thoracic and anteroposterior distances over height. These ratios did not clearly change with posture (P greater than or equal to 0.05) but increased by approximately 30% with decreasing volume (P less than 0.01). The fact that these shape changes of the chest were not accompanied by similar changes in lung shape can be explained mainly by widening of the mediastinum when volume decreases. In conclusion, the shape of the lung and chest are similar in head-down and upright humans, in contrast to the reversal of the apicodiaphragmatic differences in alveolar expansion and in transpulmonary pressure.

Adult↗
PubMed2005

3He MRI-based assessment of posture-dependent regional ventilation gradients in rats.

A recently developed method for quantitative assessment of regional lung ventilation was employed for the study of posture-dependent ventilation differences in rats. The measurement employed hyperpolarized (3)He MRI to detect the build-up of the signal intensity after increasing numbers of (3)He breaths, which allowed for computation of a regional ventilation parameter. A group of six anesthetized rats was studied in both supine and prone postures. Three-dimensional maps of the ventilation parameter were obtained with high spatial resolution (voxel volume approximately 2 mm(3)). Vertical (dorsal-ventral) gradients of the ventilation index, defined as the regional ventilation normalized by the average ventilation within the whole lung, were investigated. Variations in the regional distribution of the ventilation parameter, as well as of the ventilation index, could be detected, depending on the posture of the rats. In supine posture, ventilation was elevated in the dependent parts of the lungs, with a linear gradient of the ventilation index of -0.11 +/- 0.03 cm(-1). In prone posture, the distribution of ventilation was more uniform, with a significantly (P < 0.001) smaller gradient of the ventilation index of -0.01 +/- 0.02 cm(-1). It is concluded that the (3)He MRI-based method can detect and quantify regional ventilation gradients in animals as small as the rat and that these gradients depend on prone or supine posture of the animal.

Administration, Inhalation↗
PubMed2002

Spatial distribution of ventilation and perfusion in anesthetized dogs in lateral postures.

We aimed to assess the influence of lateral decubitus postures and positive end-expiratory pressure (PEEP) on the regional distribution of ventilation and perfusion. We measured regional ventilation (VA) and regional blood flow (Q) in six anesthetized, mechanically ventilated dogs in the left (LLD) and right lateral decubitus (RLD) postures with and without 10 cmH(2)O PEEP. Q was measured by use of intravenously injected 15-microm fluorescent microspheres, and VA was measured by aerosolized 1-microm fluorescent microspheres. Fluorescence was analyzed in lung pieces approximately 1.7 cm(3) in volume. Multiple linear regression analysis was used to evaluate three-dimensional spatial gradients of Q, VA, the ratio VA/Q, and regional PO(2) (Pr(O(2))) in both lungs. In the LLD posture, a gravity-dependent vertical gradient in Q was observed in both lungs in conjunction with a reduced blood flow and Pr(O(2)) to the dependent left lung. Change from the LLD to the RLD or 10 cmH(2)O PEEP increased local VA/Q and Pr(O(2)) in the left lung and minimized any role of hypoxia. The greatest reduction in individual lung volume occurred to the left lung in the LLD posture. We conclude that lung distortion caused by the weight of the heart and abdomen is greater in the LLD posture and influences both Q and VA, and ultimately gas exchange. In this respect, the smaller left lung was the most susceptible to impaired gas exchange in the LLD posture.

Aerosols↗
PubMed2006

Muscle synergy organization is robust across a variety of postural perturbations.

We recently showed that four muscle synergies can reproduce multiple muscle activation patterns in cats during postural responses to support surface translations. We now test the robustness of functional muscle synergies, which specify muscle groupings and the active force vectors produced during postural responses under several biomechanically distinct conditions. We aimed to determine whether such synergies represent a generalized control strategy for postural control or if they are merely specific to each postural task. Postural responses to multidirectional translations at different fore-hind paw distances and to multidirectional rotations at the preferred stance distance were analyzed. Five synergies were required to adequately reconstruct responses to translation at the preferred stance distance-four were similar to our previous analysis of translation, whereas the fifth accounted for the newly added background activity during quiet stance. These five control synergies could account for > 80% total variability or r2 > 0.6 of the electromyographic and force tuning curves for all other experimental conditions. Forces were successfully reconstructed but only when they were referenced to a coordinate system that rotated with the limb axis as stance distance changed. Finally, most of the functional muscle synergies were similar across all of the six cats in terms of muscle synergy number, synergy activation patterns, and synergy force vectors. The robustness of synergy organization across perturbation types, postures, and animals suggests that muscle synergies controlling task-variables are a general construct used by the CNS for balance control.

Animals↗
PubMed1995

Effect of galvanic vestibular stimulation on human postural responses during support surface translations.

1. We investigated the role of the vestibular system in postural control by combining galvanic vestibular stimulation (0.2-0.5 mA) with platform translations in standing subjects. Vestibular stimulation delivered 500 ms before and continuously during the platform translation produced little change in the earliest center of pressure (COP) and center of mass (COM) movements in response to platform translations, but resulted in large changes during the execution of the postural movement and in the final equilibrium position. 2. Vestibular stimulation produced anterior or posterior shifts in the position of COP and COM, depending on the polarity of the galvanic current. These shifts were larger during platform translations than during quiet stance. The peak of these shifts in COP and COM occurred at 1.5-2.5 s after the onset of platform translation, and increased in magnitude with increasing platform velocity. The final equilibrium positions of COP and COM were also shifted, but these shifts were smaller and not dependent on platform velocity. 3. These results imply that a tonic step of galvanic current to the vestibular system can change the final equilibrium position for an automatic postural response. Furthermore, these results indicate that the vestibular system may play a larger role in interpreting sensory reafference during postural movements, and especially during fast postural movements, than in controlling quiet stance. Finally, these results indicate that the vestibular system does not play a critical role in triggering the earliest postural responses, but it may be critical in establishing an internal reference for verticality.

Adult↗
PubMed1997

Postural control of three-dimensional prehension movements.

This experiment was carried out to test the hypothesis that three-dimensional upper limb movements could be initiated and controlled in the joint space via a mechanism comparing an estimate of the current postural state of the upper arm with a target value determined by one specific inverse static transform converting the coordinates of the object into a set of arm, forearm, and wrist angles. This hypothesis involves two main predictions: 1) despite joint redundancy, the posture reached by the upper limb should be invariant for a given context; and 2) a movement programmed in joint space should exhibit invariant characteristics of the joint covariation pattern as well as a corresponding variable hand path curvature in the task space. To test these predictions, we examined prehension movements toward a cylindrical object presented at a fixed spatial location and at various orientations without vision of the moving limb. Once presented, the object orientation was either kept constant (unperturbed trials) or suddenly modified at movement onset (perturbed trials). Three-dimensional movement trajectories were analyzed in both joint and task spaces. For the unperturbed trials, the task space analysis showed a variable hand path curvature depending on object orientation. The joint space analysis showed that the seven final angles characterizing the upper limb posture at hand-to-object contact varied monotonically with object orientation. At a dynamic level, movement onset and end were nearly identical for all joints. Moreover, for all joints having a monotonic variation, maximum velocity occurred almost simultaneously. For the elbow, the only joint presenting a reversal, the reversal was synchronized with the time to peak velocity of the other joint angles. For the perturbed trials, a smooth and complete compensation of the movement trajectory was observed in the task space. At a static level the upper limb final posture was identical to that obtained when the object was initially presented at the orientation following the perturbation. This result was particularly remarkable considering the large set of comfortable postures allowed by joint redundancy. At a dynamic level, the joints' covariation pattern was updated to reach the new target posture. The initial synergies were not disrupted by the perturbation, but smoothly modified, the different joints' movements ending nearly at the same time. Taken together, these results support the hypothesis that prehension movements are initiated and controlled in the joint space on the basis of a joint angular error vector rather than a spatial error vector.

Adult↗