Postural reflexes in patients with HIV-1 infection.

OBJECTIVE: We studied whether medium latency (ML) and long latency (LL) postural reflexes, which are abnormal in a number of neurological conditions including basal ganglia disorders, provide an early marker of CNS involvement in HIV-positive patients. METHODS: Leg reflexes were elicited in 9 neurologically normal HIV-positive patients and 10 healthy controls who were standing upright, using toe-up forceplate rotations of varying amplitude (4 degrees and 10 degrees) and predictability (serial and random). RESULTS: For predictable amplitude perturbations, posturally destabilizing ML and stabilizing LL responses in HIV-seropositives did not differ from controls. However, for unpredictable amplitude perturbations, HIV-positive patients inappropriately manifested a mid-size default LL response, in contrast to healthy subjects who showed a maximum size default response. CONCLUSIONS: These results suggest that impaired modulation of LL reflex processing occurs in early stages of HIV infection, prior to the onset of clinical postural instability, and this dysregulation may be influenced by cognitive factors.

Balance in the healthy elderly: posturography and clinical assessment.

OBJECTIVES: To measure balance changes in the healthy elderly using quantitative dynamic posturography. To relate these changes to clinical measures of balance and gait. DESIGN: Elderly subjects screened for health criteria in a longitudinal study were examined using standardized cognitive, neurological, and performance-based tests. Quantitative posturography (Equitest, Neurocom International, Clackamas, Ore) was performed to determine the subject's response to sensory (Sensory Organization Test) and motor perturbations (Motor Coordination Test). SUBJECTS: Thirty-three healthy, old old subjects (> or =80 years; mean+/-SD age, 88+/-5 years) were compared with 15 subjects younger than 80 years (mean+/-SD age, 72+/-3 years). All were free of centrally active medications. RESULTS: The old old had worse quantitative equilibrium scores compared with subjects younger that 80 years when proprioceptive input was inaccurate and visual input was either preserved or completely absent. Old old subjects showed diminished adaptation to repeated platform rotations and fell more frequently during posturography. Quantitative balance measures correlated with age and functional measures of balance (Tinetti Balance Scale score, timed 1 leg standing). CONCLUSIONS: Progressive, functionally evident, age-related quantitative balance changes occur independent of typical geriatric pathological changes. These data should facilitate clinical decisions by allowing the distinction to be made between age-related and pathological changes.

Flexibility of anticipatory postural adjustments revealed by self-paced and reaction-time arm movements.

In standing humans, it is not certain whether anticipatory postural adjustments associated with rapid, voluntary elbow flexion movements (focal movements) originate as a selection from preset synergies or as the result of specific planning of motor commands. We studied these muscle recruitment patterns when the same focal movement was made under behavioral conditions of a self-paced task (SPT) and a reaction-time task (RTT). While standing still, eight normal subjects performed focal movements under the SPT and RTT behavioral conditions and under three different biomechanical conditions: (1) unloaded-upright, (2) loaded-upright (holding a 3800-g metal bar), and (3) unloaded-forward leaning. Anticipatory postural adjustments were quantified using the latency and duration of electromyographic (EMG) data and the center of pressure (COP) displacement data. Postural-kinematic [joint and body center of gravity (COG) motion] data were used to quantify the anticipatory postural program's effectiveness at preventing postural movement. Focal movement kinematics and associated EMG activity differed due to biomechanical but not behavioral (SPT vs. RTT) conditions. The maximum and net displacement of the body COG measurements did not differ between the behavioral conditions. The amplitude, timing, and net movements of lower extremity joints were influenced by the behavioral conditions. However, the behavioral conditions significantly affected the phasing (including order of activation) and duration of anticipatory postural EMG activity and the phasing of COP displacements under certain biomechanical conditions. These findings support the theory that anticipatory postural adjustments are planned in detail.

Clinical correlates of motor performance during paced postural tasks in Parkinson's disease.

Bradykinesia and hypokinesia may both play a significant role in postural instability commonly seen in patients with Parkinson's disease. We investigated which factor--movement time or movement amplitude--is the more significant limiting variable in patients with Parkinson's disease during a paced postural task. We also assessed the effect of antiparkinson medication upon these movement factors and the degree of correlation with changes in clinical performance. Subjects performed paced left-right (L-R) and forward-backward (F-B) continuous weight-shifting tasks at slow, medium and fast paces. Ten Parkinson patients were studied both OFF and ON their usual antiparkinson medication. Ten age-matched healthy controls were also tested and subsequently retested on the same schedule as the patients. Movement times and amplitudes were measured and correlated with clinical changes in UPDRS motor subscores. Parkinson patients performed similar to controls with respect to movement time, but significantly displayed underscaled (reduced) movement amplitude. Movement amplitude improved after antiparkinson medication, but remained significantly less than that of controls. Improvements in L-R movement amplitude correlated with clinical improvements in bradykinesia and postural instability, while improved F-B movement amplitude correlated only with reduced postural instability. We conclude that hypometric movement amplitude, and not abnormal movement time, is the primary abnormality observed in Parkinson patients during a paced postural task. Amplitude underscaling seems antiparkinson medication-dependent and improvement correlates with favorable clinical changes in bradykinesia and postural instability scores.

Biomechanical assessment of quiet standing and changes associated with aging.

The kinematics of standing balance were analyzed in 24 normal subjects, aged 21 to 78 years, to examine differences attributable to age, visual input, and sex. Movements of individual body segments, displacement of the center of gravity (COG), and position of the center of pressure (COP) were measured, and total path length and variability about the mean position were derived from the resulting values. Aging was associated with an increase in variability of the COG, head, and hip, but not in path length. The changes, which may be clinically interpreted as excess postural sway, do not show stability deficits as a consequence of aging. On the contrary, older subjects seem to adopt a postural control strategy that achieves comparable stability during quiet standing. Eye closure increased the anterior-posterior COP path length without corresponding changes in the COG, indicating an increase in small accelerations without associated instability. There was more medial-lateral movement in women than in men. Quantitative electromyographic measures showed that, in general, quiet standing requires very little muscular activity. We conclude that the task of quiet standing produces no evidence of postural instability concurrent with aging. The altered postural control strategy may be less effective when balance is suddenly or severely compromised.

Biomechanical assessment of upright stance in parkinson's disease: a single-subject study.

In order to evaluate the usefulness of biomechanical measures in the clinical assessment of Parkinson's disease, we studied the kinematics of upright stance in a patient with evident fluctuations in clinical state (ON-OFF), which allowed us to optimize experimental control. We determined the total amount of movement and the variability of whole body and body segment kinematics in the vertical, anterior-posterior (A-P), and medial-lateral planes. The total excursion parameter (TEX) represented the co-ordinate path over a 20 s period, and the movement variability parameter (VAR) was calculated based on the standard deviation about the quadratic fit to this path. Discriminant analysis was employed to assess the ability of these parameters to discriminate the patient's clinical state, and statistical reduction of the number of measures was accomplished with a stepwise selection procedure. Measures of shoulder A-P movement and the vertical motion of the centre of gravity (COG) were selected for inclusion in both discriminant functions. The VAR function included only four measures (vertical COG and A-P head, shoulder, and hip), while the TEX function required six measures to discriminate the clinical state. Results obtained with the VAR function were superior to those obtained with TEX, and VAR discriminated the OFF state, a common characteristic of Parkinson's disease, especially well. The results are promising, as the measures appear sensitive to the patient's clinical state even though fluctuation of symptoms was reduced in the latter part of the study by various treatments.