Dose-related effect of triazolam on postural sway.

Measurement of clinically relevant benzodiazepine drug effects at hypnotic and anxiolytic doses has been difficult because most measures are subjective, difficult to interpret, or relate to anesthetic doses. A potentially useful measure of drug effect is postural sway, which is a manifestation of the corrective mechanisms associated with the maintenance of upright posture. Postural sway was measured over 8 hours, with a biomechanics force platform, in six healthy male volunteers who received triazolam, 0.125, 0.250, or 0.375 mg, or placebo in a randomized double-blind study. Our results show a dose-dependent increase in postural sway measured as the elliptical area or the 95% confidence ellipse for the area covered by the subjects' sway. After triazolam, 0.250 and 0.375 mg, the area under the sway-time curve and peak effect increased significantly compared with placebo (p less than 0.05). The number of losses of balance when subjects stood on one foot also showed a significant increase with increased dose (p less than 0.05). The rate of loss of balance was positively correlated with the extent of postural sway (r = 0.802; p less than 0.001). The extent of sway when the subjects were drug free predicted this increase in a subject's postural sway with triazolam. Thus at hypnotic or anxiolytic doses of triazolam, computer-assisted force platform measures of sway provide a clinically relevant measure of drug effect. Measurement of drug-induced postural sway may be useful in persons at risk for falls, such as the elderly.

Clinical determinants of biomechanics platform measures of balance in aged women.

The cross-sectional associations between clinical variables and biomechanics platform measures of balance (sway) were determined in a random sample of 50 aged single women living in high rise apartment buildings. A history of falling in the previous year was associated with increased areas of sway. Increased body mass was associated with decreased velocity of sway. Poor near, but not far, visual acuity was associated with increased areas of sway. A postural drop of 10 mmHg or more in diastolic pressure was associated with increased velocity of sway. The associations between these variables and the balance measures persisted after adjustment for age and each other to adjust for potential confounding. Slower hand reaction times and poor hearing were associated with increased areas of sway, but these associations were removed after adjustment for age and near visual acuity. There were no associations between any of the balance measures and postural changes in systolic pressure and heart rate. There were no associations between balance measures and base of support. The observed associations, if causal, can aid in development and testing of effective interventions to improve balance and prevent falls in the elderly.

Increased baseline sway contributes to increased losses of balance in older people following triazolam.

OBJECTIVE: Although it has been stated frequently that older people are more sensitive to benzodiazepines, the relative roles of impaired baseline performance, impaired elimination, and altered responsiveness have not been defined. We evaluated postural sway and plasma triazolam concentrations after administration of placebo and triazolam 0.375 mg in both young and older healthy subjects. DESIGN: Double-blind placebo-controlled trial. PARTICIPANTS: Nine young and nine older healthy men. INTERVENTION: All subjects received triazolam 0.375 mg or placebo on different study days, which were separated by at least 48 hours. MEASUREMENTS: Postural sway, visual analog scale of drowsiness, and plasma triazolam levels. RESULTS: The older subjects swayed more during triazolam than did the younger subjects, and this resulted in an increased number of losses of balance. This difference appeared to be caused by greater baseline sway in the older subjects rather than higher concentrations or increased responsiveness. A subset of older people had a much greater number of losses of balance during triazolam than did the rest of the subjects, and these individuals could be identified from their baseline sway. CONCLUSIONS: In this study, the increase in drug effect seen in the older subjects was of similar magnitude to that of the young, but it resulted in greater postural sway after drug administration than was seen in the young. The higher postural sway and the corresponding increased instability seen in the older subjects may put these older persons at increased risk of drug-related falls. This study also suggests that it should be possible to develop techniques that will identify individuals at particular risk of drug-induced postural instability.

Effect of loss of balance on biomechanics platform measures of sway: influence of stance and a method for adjustment.

This paper describes a method for adjusting biomechanics platform measures of sway for loss of balance. Area and velocity measures of sway were determined in forty-seven elderly women, in double and single leg stance, first with their eyes open, then closed. Subjects were rarely able to complete 10 s trials during single leg stances. Therefore, a method was developed for eliminating data associated with loss of balance. Monitoring changes in vertical force and velocity by computer, those points exceeding trial specific thresholds associated with loss of balance were truncated. In double leg stances, loss of balance increased area measures by 0.3%, but did not effect velocity measures. In contrast, the loss of balance increased area measures by 0-3%, but did not effect velocity measures. In contrast, the loss of balance experienced by most subjects in single leg stance exaggerated area measures by 16-38%, and velocity measures by up to 10%. In double leg stances the correlations between unadjusted area measures and area measures adjusted for loss of balance ranged from 0.98 to 1.00. In single leg stances, the correlations for the area measures ranged from 0.69 to 0.89. The correlations between adjusted and unadjusted velocity measures were 1.00 and 0.93 for the double and single leg stances respectively. Although the question of which sway measure is best remains unanswered, this study provides useful data for future research. First, it demonstrates a method for modifying area representations of the center of pressure excursions for the effects of loss of balance.(ABSTRACT TRUNCATED AT 250 WORDS)

A quantitative and qualitative description of electromyographic linear envelopes for synergy analysis.

The muscular synergy patterns of human locomotion can be described by the phasic activity of electromyographic linear envelopes (LE) and the interphasic spatio-temporal relations. To represent the phasic activity, the LE is modeled as the summation of Gaussian pulses of various lengths. The parameters of interest are the temporal features: time, duration, and amplitude of the phases of activity. A maximum likelihood approach to the parameter estimation for a mixture of normal distributions is adopted for extracting the temporal features. Based on the derived temporal features, a set of relational descriptors can be defined to describe the spatio-temporal relations between the multichannel phasic activities. The strength of this approach is not only that the phasic activity of LE can be quantitatively represented accurately, but also that the resulting synergy patterns can be easily interpreted by observers.

Acoustical properties of speech as indicators of depression and suicidal risk.

Acoustic properties of speech have previously been identified as possible cues to depression, and there is evidence that certain vocal parameters may be used further to objectively discriminate between depressed and suicidal speech. Studies were performed to analyze and compare the speech acoustics of separate male and female samples comprised of normal individuals and individuals carrying diagnoses of depression and high-risk, near-term suicidality. The female sample consisted of ten control subjects, 17 dysthymic patients, and 21 major depressed patients. The male sample contained 24 control subjects, 21 major depressed patients, and 22 high-risk suicidal patients. Acoustic analyses of voice fundamental frequency (Fo), amplitude modulation (AM), formants, and power distribution were performed on speech samples extracted from audio recordings collected from the sample members. Multivariate feature and discriminant analyses were performed on feature vectors representing the members of the control and disordered classes. Features derived from the formant and power spectral density measurements were found to be the best discriminators of class membership in both the male and female studies. AM features emerged as strong class discriminators of the male classes. Features describing Fo were generally ineffective discriminators in both studies. The results support theories that identify psychomotor disturbances as central elements in depression and suicidality.

Reaction force patterns of injured and uninjured knees during walking and pivoting.

A precise knowledge of the biomechanical alterations produced by anterior cruciate ligament (ACL) damage would aid in selecting appropriate therapeutic intervention and monitoring rehabilitation. In an attempt to assess dynamic knee joint function, we compared the ground reaction force (GRF) and vertical couple patterns during walking and pivoting from an ACL-deficient population with those from a separate uninjured population. Statistical methods were used to quantitate the differences between the two populations for each force pattern in each functional task and to delineate the intervals of the force patterns in each functional task during which significant differences existed between the two populations. Our results indicate that significant differences exist between the GRF and vertical couple patterns of ACL-deficient subjects and uninjured subjects, but that onset and duration of these differences during stance phase vary among force components and tasks. The processing scheme extracts significant differences in the GRF and vertical couple patterns that would be lost in a comparison of a few pattern descriptors. Our results suggest that the vertical couple should be evaluated during assessment of pivoting maneuvers and show promise of providing useful information for assessment of knee dysfunction.

Analysis of vocal tract characteristics for near-term suicidal risk assessment.

OBJECTIVES: Among the many clinical decisions that psychiatrists must make, assessment of a patient's risk of committing suicide is definitely among the most important, complex and demanding. One of the authors reviewing his clinical experience observed that successful predictions of suicidality were often based on the patient's voice independent of content. The voices of suicidal patients exhibited unique qualities, which distinguished them from non-suicidal patients. In this study we investigated the discriminating power of lower order mel-cepstral coefficients among suicidal, major depressed, and non-suicidal patients. METHODS: Our sample consisted of 10 near-term suicidal patients, 10 major depressed patients, and 10 non-depressed control subjects. Gaussian mixtures were employed to model the class distributions of the extracted features. RESULTS AND CONCLUSIONS: As a result of two-sample ML classification analyses, first four mel-cepstral coefficients yielded exceptional classification performance with correct classification scores of 80% between near-term suicidal patients and non-depressed controls, 75% between depressed patients and non-depressed controls, and 80% between near-term suicidal patients and depressed patients.

Evaluation of linear diaphragm-chest expansion models for magnetic resonance imaging motion artifact correction.

The efficacy of Fourier analysis, autoregressive with exogenous input (ARX) and adaptive models to estimate diaphragm position from respiratory belt signal (a measure of chest expansion) was evaluated for the purpose of correcting respiratory motion artifacts in magnetic resonance imaging (MRI). Respiratory belt signal and diaphragm position data were obtained simultaneously during one-dimensional MRI scans with sampling intervals of 100 ms for 128 s (1280 samples). The models were trained using the first 512 data samples for the Fourier method and the first 640 samples for the ARX and adaptive methods. The remaining samples were used as a test set for evaluating the models. Both ARX and adaptive methods produced more accurate results than the Fourier method as reflected by the normalized mean square error (NMSE) and correlation coefficient (R) between the estimated and actual diaphragm position during normal breathing (P < 0.05). However, all three models had difficulty modeling diaphragm positions during breathing plateaus.

Exercise and balance in aged women: a pilot controlled clinical trial.

A pilot controlled trial was conducted to determine the feasibility of testing an exercise program as a means of improving balance in aged women. A random sample of 50 women more than 65 years old was recruited from two apartment buildings. The buildings were randomized to serve as exercise and control sites. The 24 exercisers did not differ significantly from the 26 controls except that they were better educated and had better vision. The median compliance was 85% of requested sessions attended by the exercisers. Follow-up measures were obtained in 92% and 81% of the exercise and control groups, respectively. The outcome variables studied were changes in sway (areas and velocity of the center of force as measured using a biomechanics platform) in four stances with eyes open or closed, on two feet, or on one foot. After 16 weeks, in stances on one foot, exercisers had smaller areas compared to controls with eyes open, but larger areas with eyes closed. Subgroup analysis indicated that compliance with the exercise program was a determinant of degree of change in the area measures. The inconsistent effect of exercise on area measures of sway in this study may be due to (a) lack of statistical power to detect between-group differences, (b) inadequate compliance with the exercise program, (c) baseline differences between the two groups at randomization, and (d) ineffective or inadequate duration of the exercise program. We conclude that controlled clinical trials to study the effect of exercise on balance measures in community-dwelling elderly women are feasible.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of biomechanics platform measures of balance and videotaped measures of gait with a clinical mobility scale in elderly women.

Performance on the clinical mobility index developed by Tinetti (9) was compared with biomechanics platform measures of sway and videotaped measures of gait in a sample of 43 community-dwelling aged women. Area measures of sway, but not velocity, were associated with performance on the mobility index. When standing on one leg with eyes open, the correlation coefficients for radial area per second with the mobility indices ranged from -0.59 to -0.64 (p less than .001). Knee range of motion and stride length correlated with performance on the mobility index. Knee range of motion correlation coefficients ranged from 0.47 to 0.54 (p less than .001), whereas the range was 0.62 to 0.68 (p less than .001) for stride length. These data demonstrate that biomechanics platform measures of sway and videotaped measures of gait are associated with subject performance on a clinical mobility index and may themselves also be predictive of persons susceptible to falling.

Efficacy of myofeedback therapy in regaining control of lower extremity musculature following stroke.

The short-term efficacy (three months or less) of electromyographic biofeedback on the control and strength of six lower extremity muscles in twenty-two hemiplegic patients was investigated. The analysis of the data shows that patients receiving myofeedback therapy achieve a much larger increase in the control of muscle activity whereas there is no significant difference in the increase in strength.

Comparison of gating methods for the real-time analysis of left ventricular function in nonimaging blood pool studies.

BACKGROUND: Gating methods developed for electrocardiographic-triggered radionuclide ventriculography are being used with nonimaging detectors. These methods have not been compared on the basis of their real-time performance or suitability for determination of load-independent indexes of left ventricular function. This work evaluated the relative merits of different gating methods for nonimaging radionuclude ventriculographic studies, with particular emphasis on their suitability for real-time measurements and the determination of pressure-volume loops. METHODS AND RESULTS: A computer model was used to investigate the relative accuracy of forward gating, backward gating, and phase-mode gating. The durations of simulated left ventricular time-activity curves were randomly varied. Three acquisition parameters were considered: frame rate, acceptance window, and sample size. Twenty-five studies were performed for each combination of acquisition parameters. Hemodynamic and shape parameters from each study were compared with reference parameters derived directly from the random time-activity curves. Backward gating produced the largest errors under all conditions. For both forward gating and phase-mode gating, ejection fraction was underestimated and time to end systole and normalized peak ejection rate were overestimated. For the hemodynamic parameters, forward gating was marginally superior to phase-mode gating. The mean difference in errors between forward and phase-mode gating was 1.47% (SD 2.78%). However, for root mean square shape error, forward gating was several times worse in every case and seven times worse than phase-mode gating on average. CONCLUSIONS: Both forward and phase-mode gating are suitable for real-time hemodynamic measurements by nonimaging techniques. The small statistical difference between the methods is not clinically significant. The true shape of the time-activity curve is maintained most accurately by phase-mode gating.

Relationship between vertical ground reaction force and speed during walking, slow jogging, and running.

OBJECTIVE: To obtain descriptive information between vertical ground reaction force (GRF)-time histories and gait speed, running style, and gender. DESIGN: GRF-time history measurements were obtained from male and female subjects during walking, slow jogging, jogging and running on an indoor platform. BACKGROUND: Previous studies have established GRF descriptor variables for male subjects running at speeds from 3 to 6 m s(-1), but very little descriptive data exists for slower or faster running, nor have previous studies reported GRF descriptors separately for female subjects. METHODS: GRF-time histories were recorded for 13 male and 10 female recreational athletes during walking and slow jogging at speeds between 1.5 and 3.0 m s(-1), and running at speeds between 3.5 and 6.0 m s(-1). Vertical GRF-time data for trials with speeds within 0.2 m s(-1) of the prescribed speed were analysed to determine thrust maximum GRF (F(z)) and loading rate (G(z)). RESULTS: In both male and female subjects, F(z) increased linearly during walking and running from 1.2 BW to approximately 2.5 BW at 6.0 m s(-1), remaining constant during forward lean sprinting at higher speeds. F(z) was linearly correlated to G(z), the latter ranging from 8 to 30 BW s(-1) over this speed range. Slow jogging was associated with a > 50% higher F(z) and G(z) in comparison to walking or fast running. CONCLUSIONS: Similar GRF descriptor data and velocity relationships were obtained for male and female subjects. Impact forces were greatest when the subjects adopted a higher, less fixed centre of gravity during slow jogging. RELEVANCE: These results suggest that vertical GRF norms can be established for male and female subjects alike, and that slow or fast running with a lower, fixed centre of gravity decreases impact forces.