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PubMed2002

Effect of gravity and posture on lung mechanics.

The volume-pressure relationship of the lung was studied in six subjects on changing the gravity vector during parabolic flights and body posture. Lung recoil pressure decreased by approximately 2.7 cmH(2)O going from 1 to 0 vertical acceleration (G(z)), whereas it increased by approximately 3.5 cmH(2)O in 30 degrees tilted head-up and supine postures. No substantial change was found going from 1 to 1.8 G(z). Matching the changes in volume-pressure relationships of the lung and chest wall (previous data), results in a decrease in functional respiratory capacity of approximately 580 ml at 0 G(z) relative to 1 G(z) and of approximately 1,200 ml going to supine posture. Microgravity causes a decrease in lung and chest wall recoil pressures as it removes most of the distortion of lung parenchyma and thorax induced by changing gravity field and/or posture. Hypergravity does not greatly affect respiratory mechanics, suggesting that mechanical distortion is close to maximum already at 1 G(z). The end-expiratory volume during quiet breathing corresponds to the mechanical functional residual capacity in each condition.

Adult↗
PubMed2007

Eye, head, and body coordination during large gaze shifts in rhesus monkeys: movement kinematics and the influence of posture.

Coordinated movements of the eye, head, and body are used to redirect the axis of gaze between objects of interest. However, previous studies of eye-head gaze shifts in head-unrestrained primates generally assumed the contribution of body movement to be negligible. Here we characterized eye-head-body coordination during horizontal gaze shifts made by trained rhesus monkeys to visual targets while they sat upright in a standard primate chair and assumed a more natural sitting posture in a custom-designed chair. In both postures, gaze shifts were characterized by the sequential onset of eye, head, and body movements, which could be described by predictable relationships. Body motion made a small but significant contribution to gaze shifts that were > or =40 degrees in amplitude. Furthermore, as gaze shift amplitude increased (40-120 degrees ), body contribution and velocity increased systematically. In contrast, peak eye and head velocities plateaued at velocities of approximately 250-300 degrees /s, and the rotation of the eye-in-orbit and head-on-body remained well within the physical limits of ocular and neck motility during large gaze shifts, saturating at approximately 35 and 60 degrees , respectively. Gaze shifts initiated with the eye more contralateral in the orbit were accompanied by smaller body as well as head movement amplitudes and velocities were greater when monkeys were seated in the more natural body posture. Taken together, our findings show that body movement makes a predictable contribution to gaze shifts that is systematically influenced by factors such as orbital position and posture. We conclude that body movements are part of a coordinated series of motor events that are used to voluntarily reorient gaze and that these movements can be significant even in a typical laboratory setting. Our results emphasize the need for caution in the interpretation of data from neurophysiological studies of the control of saccadic eye movements and/or eye-head gaze shifts because single neurons can code motor commands to move the body as well as the head and eyes.

Animals↗
PubMed2005

Electromyographic activity of dorsal neck muscles in squirrel monkeys during rotations in an upright or upside down posture.

Electromyographic (EMG) activity was recorded from occipitoscapularis, semispinalis, and splenius neck muscles in five alert squirrel monkeys during 0.25-Hz rotations about horizontal axes oriented at 22.5 degrees intervals, including pitch, roll, and intermediate axes. The animals were oriented in either upright or upside down posture. In the upright posture, all monkeys exhibited compensatory EMG activity with maximal activation during rotations about axes between pitch in the pitch forward direction and contralaterally directed roll. Response timing varied across animals with EMG peaks ranging from near pitch forward head velocity to near pitch forward head position. When the head was upside down, response dynamics and directionality were altered to varying degrees in different monkeys. The greatest change in response to head inversion was seen in the monkey that had response phases closest to head position, the least in the animal with phases closest to head velocity. The monkey with EMG response peaks closest to position phase showed nearly 180 degrees inversion of responses when the head was upside down, suggesting that in this monkey a righting reflex mediated by utricular signals was activated in the upside down posture. The monkey with EMG response peaks closest to velocity phase may have lacked a righting response and exhibited only a canal-mediated compensatory vestibulocervical reflex in both upright and upside down postures. The results suggest that reflex contraction of neck muscles in response to passive head rotation includes an interplay of compensatory and righting responses that varies from animal to animal.

Animals↗
PubMed1986

Central programming of postural movements: adaptation to altered support-surface configurations.

We studied the extent to which automatic postural actions in standing human subjects are organized by a limited repertoire of central motor programs. Subjects stood on support surfaces of various lengths, which forced them to adopt different postural movement strategies to compensate for the same external perturbations. We assessed whether a continuum or a limited set of muscle activation patterns was used to produce different movement patterns and the extent to which movement patterns were influenced by prior experience. Exposing subjects standing on a normal support surface to brief forward and backward horizontal surface perturbations elicited relatively stereotyped patterns of leg and trunk muscle activation with 73- to 110-ms latencies. Activity began in the ankle joint muscles and then radiated in sequence to thigh and then trunk muscles on the same dorsal or ventral aspect of the body. This activation pattern exerted compensatory torques about the ankle joints, which restored equilibrium by moving the body center of mass forward or backward. This pattern has been termed the ankle strategy because it restores equilibrium by moving the body primarily around the ankle joints. To successfully maintain balance while standing on a support surface short in relation to foot length, subjects activated leg and trunk muscles at similar latencies but organized the activity differently. The trunk and thigh muscles antagonistic to those used in the ankle strategy were activated in the opposite proximal-to-distal sequence, whereas the ankle muscles were generally unresponsive. This activation pattern produced a compensatory horizontal shear force against the support surface but little, if any, ankle torque. This pattern has been termed the hip strategy, because the resulting motion is focused primarily about the hip joints. Exposing subjects to horizontal surface perturbations while standing on support surfaces intermediate in length between the shortest and longest elicited more complex postural movements and associated muscle activation patterns that resembled ankle and hip strategies combined in different temporal relations. These complex postural movements were executed with combinations of torque and horizontal shear forces and motions of ankle and hip joints. During the first 5-20 practice trials immediately following changes from one support surface length to another, response latencies were unchanged. The activation patterns, however, were complex and resembled the patterns observed during well-practiced stance on surfaces of intermediate lengths.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1994

Effect of neck posture on the activation of feline neck muscles during voluntary head turns.

1. To determine whether neck posture affects the usage of neck muscles during a specific motor task, we recorded the electromyographic (EMG) patterns of neck muscles in four cats, which made horizontal, head-turning movements to fixate eccentrically placed targets. In some trials, the cervical column was oriented vertically whereas in other trials, the cervical column was oriented more horizontally. 2. During horizontal head movements, five muscles (obliquus capitis inferior, splenius, levator scapulae, complexus, and biventer cervicis) displayed activation patterns that were consistent from cat to cat and did not change when the cats adopted a different neck posture. Most of these muscles are large, superficial muscles that attach to the skull and span many cervical joints. 3. Posturally dependent patterns of activation were observed in five other neck muscles (semispinalis cervicis, longissimus capitis, levator scapulae ventralis, scalenus anterior, and obliquus capitis superior). Most of these muscles lie deeper and more laterally within the neck musculature and generally span fewer cervical joints than the muscles that displayed invariant patterns of activation. 4. These results suggest that the set of invariantly activated muscles may compose part of a basic motor program that is triggered during head movements in the horizontal plane. This motor program appears to be modified by the selective activation of ancillary muscles, which are recruited in a manner related to the neck posture. The deep positioning of the ancillary muscles may permit them to regulate the mobility of the cervical column and to adjust the net muscular force applied across the neck to the skull. Organizing the motor output in this manner might simplify the task of computing the appropriate patterns of neck-muscle activation.

Animals↗
PubMed1998

Parietal cortex and spatial-postural transformation during arm movements.

Cells in the parietal motor areas 5, MIP, and 7b have spatially tuned activity during movements. Lesions, however, do not disrupt visual reaching or learned nonspatial movement selection. The role of such parietal cells in sensorimotor coordinate transformations is unclear. The present experiment investigates whether the parietal motor areas are concerned with the following: 1) the transformation between the desired position in space of the hand and the limb's postural configuration during movement and 2) interjoint coordination. Six macaque monkeys were trained to reach in the dark. Spatial-postural transformations assume a simple form in the absence of vision and so may be most easily studied when animals reach in the dark. A lesion was placed in the parietal cortex that included areas 5, MIP, and 7b of three macaques. The simple relation between hand position and limb postural configuration seen in controls was disrupted after the lesion. The intercoordination of movements of the hand with those of the rest of the arm was also affected. The lesion did not affect the range or velocity of joint movements or the curvature of the hand's trajectory. The cell activity in parietal areas 5, MIP, and 7b may not be essential for the transformation between retinocentric representation of the target and shoulder centered representations of the desired position of the hand, but it is essential for both the subsequent transformation between desired hand position and the postural configuration of the arm and for interjoint integration.

Animals↗
PubMed2001

Effect of stance width on multidirectional postural responses.

The effect of stance width on postural responses to 12 different directions of surface translations was examined. Postural responses were characterized by recording 11 lower limb and trunk muscles, body kinematics, and forces exerted under each foot of 7 healthy subjects while they were subjected to horizontal surface translations in 12 different, randomly presented directions. A quasi-static approach of force analysis was done, examining force integrals in three different epochs (background, passive, and active periods). The latency and amplitude of muscle responses were quantified for each direction, and muscle tuning curves were used to determine the spatial activation patterns for each muscle. The results demonstrate that the horizontal force constraint exerted at the ground was lessened in the wide, compared with narrow, stance for humans, a similar finding to that reported by Macpherson for cats. Despite more trunk displacement in narrow stance, there were no significant changes in body center of mass (CoM) displacement due to large changes in center of pressure (CoP), especially in response to lateral translations. Electromyographic (EMG) magnitude decreased for all directions in wide stance, particularly for the more proximal muscles, whereas latencies remained the same from narrow to wide stance. Equilibrium control in narrow stance was more of an active postural strategy that included regulating the loading/unloading of the limbs and the direction of horizontal force vectors. In wide stance, equilibrium control relied more on an increase in passive stiffness resulting from changes in limb geometry. The selective latency modulation of the proximal muscles with translation direction suggests that the trunk was being actively controlled in all directions. The similar EMG latencies for both narrow and wide stance, with modulation of only the muscle activation magnitude as stance width changed, suggest that the same postural synergy was only slightly modified for a change in stance width. Nevertheless, the magnitude of the trunk displacement, as well as of CoP displacement, was modified based on the degree of passive stiffness in the musculoskeletal system, which increased with stance width. The change from a more passive to an active horizontal force constraint, to larger EMG magnitudes especially in the trunk muscles and larger trunk and CoP excursions in narrow stance are consistent with a more effortful response for equilibrium control in narrow stance to perturbations in all directions.

Adult↗
PubMed2001

Contributions of the reticulospinal system to the postural adjustments occurring during voluntary gait modifications.

To test the hypothesis that reticulospinal neurons (RSNs) are involved in the formation of the dynamic postural adjustments that accompany visually triggered, voluntary modifications of limb trajectory during locomotion, we recorded the activity of 400 cells (183 RSNs; 217 unidentified reticular cells) in the pontomedullary reticular formation (PMRF) during a locomotor task in which intact cats were required to step over an obstacle attached to a moving treadmill belt. Approximately one half of the RSNs (97/183, 53%) showed significant changes in cell activity as the cat stepped over the obstacle; most of these cells exhibited either single (26/97, 26.8%) or multiple (63/97, 65.0%) increases of activity. There was a range of discharge patterns that varied in the number, timing, and sequencing of the bursts of modified activity, although individual bursts in different cells tended to occur at similar phases of the gait cycle. Most modified cells, regardless of the number of bursts of increased discharge, or of the discharge activity of the cell during unobstructed, control, locomotion, discharged during the passage of the lead forelimb over the obstacle. Thus, 86.9% of the modified cells increased their discharge when the forelimb ipsilateral to the recording site was the first to pass over the obstacle, and 72.2% when the contralateral limb was the first. Approximately one quarter of the RSNs increased their discharge during the passage of each of the four limbs over the obstacle in both the lead (27.1%) and trail (27.9%) conditions. In general, in any one cell, the number and relative sequencing of the subsequent bursts (with respect to the lead forelimb) was maintained during both lead and trail conditions. Patterns of activity observed in unidentified cells were very similar to the RSN activity despite the diverse population of cells this unidentified group may represent. We suggest that the increased discharge that we observed in these reticular neurons reflects the integration of afferent activity from several sources, including the motor cortex, and that this increased discharge signals the timing and the relative magnitude of the postural patterns that accompany the voluntary gait modification. However, based on the characteristics of the patterns of neuronal activity in these cells, we further suggest that while individual RSNs probably contribute to the selection of different patterns of postural activity, the ultimate expression of the postural response may be determined by the excitability of the locomotor circuits within the spinal cord.

Animals↗
PubMed2006

Neural bases of postural control.

The body posture during standing and walking is maintained due to the activity of a closed-loop control system. In the review, we consider different aspects of postural control: its functional organization, the distribution of postural functions in different parts of the central nervous system, and the activity of neuronal networks controlling posture.

Animals↗
PubMed2005

Postural muscle dyscoordination in children with cerebral palsy.

The present paper gives an overview of the knowledge currently available on muscular dyscoordination underlying postural problems in children with cerebral palsy (CP). Such information is a prerequisite for developing successful therapeutic interventions in children with CP. Until now, three children with CP functioning at GMFCS (Gross Motor Function Classification System) level V have been documented. The children totally or partially lacked direction specificity in their postural adjustments and could not sit independently for more than 3 seconds. Some children functioning at GMFCS level IV have intact direction-specific adjustments, whereas others have problems in generating consistently direction-specific adjustments. Children at GMFCS levels I to III have an intact basic level of control but have difficulties in fine-tuning the degree of postural muscle contraction to the task-specific conditions, a dysfunction more prominently present in children with bilateral spastic CP than in children with spastic hemiplegia. The problems in the adaptation of the degree of muscle contraction might be the reason that children with CP, more often than typically developing children, show an excess of antagonistic coactivation during difficult balancing tasks and a preference for cranial-caudal recruitment during during reaching. This might imply that both stereotypies might be regarded as functional strategies to compensate for the dysfunctional capacity to modulate subtly postural activity.

Adaptation, Physiological↗
PubMed2001

Influence of body posture and gravitational forces on shear wave propagation in the skin.

The body posture and gravitational forces govern in part the intrinsic skin tensile strength because they influence the orientation of the dermal fibre networks. Our objective was to assess changes in shear wave propagation in the skin according to the body posture and orientation of the gravitational forces. The study was performed in 30 middle-aged women with a normal body mass index. The Reviscometer was used to assess the mechanical wave propagation on the volar forearm in extension or flexion. Similar measurements were made on the supra-areolar region of the breast when the trunk was in the horizontal or vertical position. Four measurements were made in each of 4 directions at given angles with regard to the body axis. The device gave reproducible data. Shear wave propagation was influenced by the body posture. The intra-individual variability in shear wave velocity according to the directions of measurements increased when the tissues were in a relaxed position. Skin tensile anisotropy increased in a relaxed body posture. Shear wave propagation may be a convenient non-invasive tool to better identify the natural skin tension lines in the skin, thus refining the orientation of incision during cutaneous surgery.

Adult↗
PubMedDate not supplied

Does practice modify the relationship between postural control and the execution of a secondary task in young and older individuals?

BACKGROUND: Numerous daily activities require performing more than one task simultaneously, such as standing while engaging in a conversation. Recent studies have shown that postural control may be degraded when individuals are asked to perform a secondary task and that this effect seems to be more pronounced in older adults. Since various types of secondary tasks have been used in postural control studies, the novelty of the tasks may partly explain why dual-task interference occurs. It is known that novel tasks require greater attentional resources and thus may interfere to a greater extent with the performance of another task. Therefore, by practicing this dual-task situation, interference could perhaps be diminished. Since the dual-tasking efficiency is reduced with aging, practice could be very beneficial to older adults. OBJECTIVES: The main goal of this study was to examine whether practice could modify the changes seen in postural sway when individuals are asked to perform a secondary task while maintaining upright stance and whether older individuals could benefit to a greater extent from practice than would young individuals. The second goal was to examine the dual-task performance in young versus older adults and to determine whether older individuals benefit equally or to a greater extent from practice as compared with young individuals. METHODS: Young and older individuals were asked to stand on a force platform while performing a secondary task or no task. The secondary task condition was repeated six times to examine the effects of practice. RESULTS: Practice did not modify the performance of postural sway, but did lead to an increase in speed of execution of the secondary task for both groups equally. In young participants, the amplitude of sway was decreased, and the frequency of sway was increased, indicating an increased stiffness when performing the cognitive task. Older participants showed increased amplitude of sway and increased frequency of sway in the mediolateral direction only. CONCLUSIONS: Since the dual-task condition was only repeated six times, it could be hypothesized that the effect of practice would be greater, if more trials were added or if more practice sessions were included. More research is needed to verify this hypothesis.

Adult↗
PubMedDate not supplied

Physical activity and postural control in the elderly: coupling between visual information and body sway.

BACKGROUND: Aging is characterized by a decline in the postural control performance, which is based on a coherent and stable coupling between sensory information and motor action. Therefore, changes in postural control in elderlies can be related to changes in this coupling. In addition, it has been observed that physical activity seems to improve postural control performance in elderlies. These improvements can be due to changes in the coupling between sensory information and motor action related to postural control. OBJECTIVE: The purpose of this study was to verify the coupling between visual information and body sway in active and sedentary elderlies. METHODS: Sixteen sedentary elderlies (SE), 16 active elderlies (AE) and 16 young adults (YA) were asked to stand upright inside a moving room in two experimental conditions: (1) discrete movement and (2) continuous movement of the room. RESULTS: In the continuous condition, the results showed that the coupling between the movement of the room and body sway was stronger and more stable for SE and AE compared to YA. In the discrete condition, SE showed larger body displacement compared to AE and YA. CONCLUSIONS: SE have more difficulty to discriminate and to integrate sensory information than AE and YA indicating that physical activity may improve sensory integration.

Adult↗
PubMed1977

Postural effects on the noninvasive baselines of ventricular performance.

The effects of posture on time-based noninvasive measurements were determined utilizing the sequence supine-sitting-standing in a formal protocol in which observer biases were eliminated by blinding the measurement and calculation phases. Compared to the supine posture, the sitting and standing postures produced significant increases in heart rate, isovolumic contraction time, pre-ejection period and pre-ejection periog/left-ventricular ejection time and significant decreases in ejection time and ejection time index. The response patterns are consistent with their hemodynamic correlates cited in the literature which show increased adrenergic activity and decreased venous return in the sitting and standing postures, the effect on venous return being dominant.

Adult↗
PubMed2004

Relation of postural vasovagal syncope to splanchnic hypervolemia in adolescents.

BACKGROUND: The mechanisms of simple faint remain elusive. We propose that postural fainting is related to excessive thoracic hypovolemia and splanchnic hypervolemia during orthostasis compared with healthy subjects. METHODS AND RESULTS: We studied 34 patients 12 to 22 years old referred for multiple episodes of postural faint and 11 healthy subjects. Subjects were studied in the supine position and during upright tilt to 70 degrees for 30 minutes and subgrouped into S+, historical fainters who fainted during testing (n=24); S-, historical fainters who did not faint during testing (n=10); and control subjects. Supine venous occlusion plethysmography showed no differences between blood flows of the forearm and calf in S+, S-, or control. Cardiac index, total peripheral resistance, and blood volume were not different. Using impedance plethysmography, we assessed blood redistribution during upright tilt. This demonstrated decreased thoracic blood volume and increased splanchnic, pelvic, and leg blood volumes for all subjects. However, thoracic blood volume was decreased in S+ compared with control volume, correlating well with the maximum upright heart rate. Splanchnic volume was decreased in the S+ and S- groups, correlating with the change in thoracic blood volume. Pelvic and leg volume changes were similar for all groups and uncorrelated to thoracic blood volume. CONCLUSIONS: Enhanced postural thoracic hypovolemia and splanchnic hypervolemia are associated with postural simple faint.

Adolescent↗
PubMed1975

Postural changes in left ventricular and mitral valvular dynamics in the systolic click - late systolic murmur syndrome.

Marked changes in the auscultatory pattern with posture have been noted in patients with mid-systolic clicks and/or late systolic murmurs (MSC-LSM). MSC tend to move earlier in systole and LSM become longer and often louder when patients assume upright posture. Systolic prolapse of the mitral leaflets with mild regurgitation account for MSC-LSM; earlier and greater prolapse with more and prolonged regurgitation associated with a reduced left ventricular volume (LVV) in the upright position would explain the auscultatory changes. Twenty-two patients with MSC-LSM were studied supine and at 45 degrees head-up tilt, recording intracardiac pressures, cardiac outputs, systolic time intervals, and performing LV cineangiography. Systolic prolapse of one or both mitral leaflets was demonstrated in all patients. Left ventricular end-diastolic and end-systolic volumes both decreased significantly at 45 degrees in all sixteen technically satisfactory studies. Greater mitral prolapse was noted upright in 12 of 14 studies with enough sinus beats to judge. The amount of mitral regurgitation was mild in all, and changes in amount from supine to upright posture could not be discerned angiographically. THE FINDINGS, SUGGEST THAT THE AUSCULTATORY CHANGES OCCURRING WITH UPRIGHT POSTURE IN PATIENTS WITH MSC-LSM are related to greater prolapse of the mitral leaflets which is associated with a small LVV in the upright position.

Angiocardiography↗
PubMed1982

Postural changes in pulmonary blood flow in pulmonary hypertension: a noninvasive technique using ventilation-perfusion scans.

To determine whether postural changes in ratio of upper to lower (U:L) zone pulmonary blood flow reflect pulmonary arterial pressures, we used pulmonary perfusion photoscintigraphy to study 12 normal subjects and 10 patients with precapillary pulmonary hypertension (eight classified as "primary" and two as thromboembolic). All patients underwent right-heart catheterization and measurement of pulmonary arterial systolic, diastolic, mean and capillary (wedge) pressures. The distribution of perfusion was then assessed in the supine and erect positions after i.v. injection of technetium-99m-labeled, macroaggregated albumin. Perfusion distribution was corrected for lung volume by xenon-133 equilibrium ventilation scans. In normal subjects, the U:L lung zone perfusion ratio decreased by 70.7 +/- 12.2% with the change in position. The patient group differed (p less than 0.0001) from normal subjects in that there was only a 19 +/- 17.4% shift of U:L ratio with the postural change. The mean pulmonary arterial pressure in the patient groups was 50 +/- 24.2 mm Hg. The postural change in U:L zone ratio correlated significantly with the mean pulmonary arterial pressure (r = -0.84, p less than 0.01) pulmonary arterial systolic (r = -0.83, p less than 0.01) and diastolic pressures (r = -0.72, p less than 0.05) and with the pulmonary vascular resistance (r = -0.74, p less than 0.02). No correlation was found with other hemodynamic, spirometric or blood gas data. We conclude that the postural shift in U:L ratio warrants further exploration as a noninvasive approach for detecting and quantifying pulmonary hypertension.

Adult↗
PubMed2000

Possible locus on chromosome 18q influencing postural systolic blood pressure changes.

We conducted a genome-wide scan for quantitative trait loci influencing the systolic blood pressure, diastolic blood pressure, and pulse responses to a postural challenge in 498 white sibling-pairs from the Hypertension Genetic Epidemiology Network, a multicenter study of the genetic susceptibility to hypertension. All participants were hypertensive (systolic blood pressure >/=140 mm Hg, diastolic blood pressure >/=90 mm Hg, or on antihypertensive medications) with diagnosis before age 60. Blood pressure and pulse were measured by an oscillometric method after a 5-minute rest in a supine position and again immediately on standing. The genome scan included a total of 387 autosomal short-tandem-repeat polymorphisms typed by the National Heart, Lung, and Blood Institute Mammalian Genotyping Service at Marshfield. We used multipoint variance-components linkage analysis to identify possible quantitative trait loci influencing postural change phenotypes after adjusting for sex, age, and use of antihypertensive medications. There was suggestive evidence for linkage on chromosome 18q for the postural systolic blood pressure response (maximum logarithm of the odds score=2.6 at 80 centiMorgans). We also observed a maximum logarithm of the odds score of 1.9 for the systolic blood pressure response and 1.7 for the diastolic blood pressure response on chromosome 6p. The marker that demonstrated the strongest evidence for linkage for the systolic blood pressure response (D18S858) lies within 20 centiMorgans of a marker previously linked to rare familial orthostatic hypotensive syndrome. Our findings indicate that there may be 1 or more genes on chromosome 18q that regulate systolic blood pressure during the physiological recovery period after a postural stressor.

Age Distribution↗

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