PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “REFLEX, POSTURAL”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMed1998

Importance of cutaneous postural reflex vasoconstriction in patients with atherosclerotic occlusive disease of the lower extremities.

OBJECTIVE: The present study was designed to measure the cutaneous postural vasoconstrictive reflex (PVR) in normal controls and patients with atherosclerotic occlusive disease of the lower extremities, and to determine its diagnostic and prognostic relevance. EXPERIMENTAL DESIGN: The postural vasoconstrictive reflex was recorded in 34 patients with atherosclerotic occlusive disease of the lower limbs and 27 normal controls, using laser-Doppler flowmetry. Patients also had ankle and toe pressure measurements and transcutaneous oximetry (TcPO2). SETTING: University hospital. RESULTS: The PVR on the pulp of the big toe was 20+/-7 arbitrary perfusion units in normal controls, 9.4+/-12 in patients with claudication, and -19 +/- 5 in patients with rest pain and/or gangrene, who differed from the claudicant and control groups (p=0.001 and 0.0001 respectively). The sensitivity of negative PVR in the big toe was 89% for the diagnosis of rest pain and/or gangrene, and its specificity, 83%. The severity of foot ischaemia and PVR values exhibited a significant inverse correlation (r=-0.56, p<0.0001). All patients with a poor outcome, ie. death and/or major amputation within 100 days of follow-up, had a negative PVR, and all patients with a positive PVR had a good 100-day prognosis without even a minor amputation. CONCLUSIONS: Laser-Doppler provides useful additional information in the assessment of foot ischaemia severity by showing that postural vasoconstriction is impaired in patients with severe atherosclerotic occlusive disease of the lower limbs, resulting in increased skin microcirculatory flow during leg dependency.

Aged↗
PubMedDate not supplied

[Participation of the head of the caudate nucleus of the dog in mechanisms of conditioned reflex postural reorganization].

On the model of instrumental defensive reflexes, components of conditioned postural reorganization were analyzed in 5 dogs before and after preliminary stimulation of the caudate nucleus head (CNH) of the contralateral (with respect to the active limb) hemisphere. The disturbance of normal function of the striatum caused by electric stimulation of CNH or by pathological changes elicited by a prolonged (during two-four years) CNH stimulation led to a significant change in the main mechanisms of posture reorganization: disturbances of the centre of gravity transfer and sharp rise of time of weight redistribution to the supporting limbs. Changes elicited by caudate pathology and by CNH stimulation went in the same direction. It is suggested that disturbances in the initiation of voluntary movement in striate pathology, are mainly caused by disturbances in posture initiation and reorganization, necessary for movement execution.

Animals↗
PubMed1992

Effect of knee joint laxity on long-loop postural reflexes: evidence for a human capsular-hamstring reflex.

The onset latency and discharge amplitude of preprogrammed postural responses were evaluated in order to determine if the structure of synergistic activation could be altered by ligamentous laxity at the knee joint. Twelve subjects with unilateral and one subject with bilateral anterior cruciate ligament (ACL) insufficiency were tested while standing on a moveable platform. External balance perturbations (6 cm anterior or posterior horizontal displacements of the platform) were presented at velocities ranging from 15 to 35 cm/s. Perturbations were presented under the following experimental conditions: unilateral and bilateral stance, knees fully straight or flexed, and with ankle motion restricted or free. These stance, knee position, and ankle motion conditions were introduced to alter the stress transmitted to the knee joint during movement of the support surface. The automatic postural response was recorded from the tibialis anterior (T), quadriceps (Q), and medial hamstrings muscles (H) bilaterally. The normal response to an externally induced backward sway involved the automatic activation of T and Q at latencies of 80 ms and 90 ms respectively. Activation of the hamstrings in the non-injured extremity was not coupled with the postural response. Hamstrings are not typically involved in the correction posterior sway because H activation would tend to pull the center of mass further backwards. However, when the response in the ACL-deficient extremity was compared to the non-injured limb: (1) the automatic postural response in the ACL-deficient extremity was restructured to include hamstrings activation (100 ms latency), (2) H activation time was faster and less variable in the ACL-deficient limb, and (3) the ratio of H/Q discharge amplitude integrated over 100 ms and 200 ms from the onset of EMG activation showed a dominance of hamstring activity during unilateral stance on the lax limb. In addition, H/Q ratios integrated over 200 ms showed dominant hamstring activity in the ACL-deficient limb during bilateral stance. (4) Cross-limb comparisons showed greater normalized IEMG amplitudes for T, H, and Q during unilateral stance on the lax limb. These results suggest that a capsular-hamstring reflex is integrated into the existing structure of a preprogrammed postural synergy in order to compensate for ligamentous laxity. Furthermore, the generalized increase of response gain observed during perturbations of unilateral stance on the lax limb indicates that joint afference can modulate central programming to control localized joint hypermobility. A concept of postural control is discussed with respect to the capsular reflex, joint loading and displacement of the center of gravity.

Adolescent↗
PubMed1979

Postural reflexes in man.

In 40 adult patients stabilized on the tilt table, no evidence was found that the amount of activity at rest in spastic muscles depends on the position of the head in space. The influence of postural labyrinthine reflexes (Magnus) was not confirmed. The activity in spastic extensor muscles was significantly higher (t greater than 1%) in the prone position. The activity in spastic flexor muscles was higher (t greater than 1%) in the supine position. Extralabyrinthine forces (tonic stretch reflexes and exteroceptive reflexes) are assumed to be decisive in these changes. In the same group of patients, the symmetric deep neck reflexes were examined. The patient actively flexed his head forwards or backwards. Significant increase in the activity at rest in spastic extensor muscles on dorsal flexion of the head in the prone position was found (t greater than 1%). Significant increase in the activity at rest in spastic flexor muscles on ventral flexion of the head in the supine position was also found (t greater than 5%). The phenomena of irradiation are assumed to be decisive in these changes. In another group of 27 adults the asymmetric deep neck reflexes (Magnus and De Kleijn) were examined. The patient actively turned his head either to the left or to the right, while his arms were raised (Hoff-Schilder maneuver). When the degree of rotation of the head was slight, the trunk and arms deviated in the same direction. When the rotation of the head was extreme, and reached behind the shoulder, the trunk and arms often reversed the direction of deviation. The effect of asymmetric deep neck reflexes was not confirmed. Visual perception and the mechanism of focusing are assumed to be decisive in these changes. The head turns toward the object of interest in the visual field by the mechanism of eye-centering (Bender) and influences the position of the trunk and motor patterns of the upper extremities (motor principle "eyes-hand").

Adolescent↗
PubMed2005

Variability of motoneuron activation and the modulation of force production in a postural reflex of the hermit crab abdomen.

The tri-phasic reflex in hermit crab (Pagurus pollicarus) abdomen is triggered by local mechanoreceptors and is essential for postural control. The reflex consists of three stereotypical phases: a brief, high-frequency burst, a transient cessation of firing, and a late-discharge that is much lower in frequency than the initial burst. To better understand the reflex generation of force, variability of motoneuron discharge in each of five parameters of reflex activation was assessed. An intracellular current injection routine was used to correlate each of these parameters with force production. Phase 3 motoneuron firing frequency showed the greatest correlation with force production. Phase 3 spike rate increased as a function of phase 2 duration, but the relationship between phase 2 duration and force produced by the reflex was weak. Junction potential amplitude decreased as phase 2 duration increased, and we hypothesize that this trend counteracts the increased phase 3 frequency, explaining the weak relationship of phase 2 duration and force production. Surprisingly, when phase 3 frequency was held constant and phase 2 was increased in duration, the concurrent decrease in junction potential amplitude did not reduce force production.

Abdomen↗
PubMed1980

Anticipatory postural reflexes in Parkinson's disease and other akinetic-rigid syndromes and in cerebellar ataxia.

We have examined anticipatory postural responses in calf muscles (triceps surae) in response to a small pull to the arm in standing subjects. This stimulus normally evokes a brisk automatic compensatory contraction of the calf muscles. This is not due to calf muscle stretch, for leg movement occurs after the response has appeared. It appears to be driven centrally by input produced by the pull to the arm. Such anticipatory postural responses were present in every one of the 50 normal subjects studied, but were absent or greatly reduced in many patients with Parkinson's disease when compared to age-matched normal subjects, particularly in those exhibiting postural instability. However, a normal anticipatory postural response was elicited in four patients with progressive supranuclear palsy and in a single patient with an akinetic rigid syndrome due to cerebrovascular disease. Cerebellar truncal ataxia only depressed the response in severe cases. We conclude that although these responses may not be necessary to maintain balance, they may be employed in fine adjustment of posture.

Cerebellar Ataxia↗