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Background and aims:Our studies of the standard neurological examination on 66 middleaged (50–64 yrs) and elderly subjects (65–84 yrs) demonstrate that healthy elders have neurological deficits (or “signs”) that are not associated with specific known neurological disease. The purpose of the current study is to describe this loss of neurological function in healthy aging subjects as seen through accumulated subclinical neurological signs present. Methods:Logistic regression is applied to the data on each of six signs. Parameters determined are used to describe the distribution of first occurrence times for each sign. The results are then used to construct a Poisson-like model that describes the accumulation in the number of signs present over time on average. This model is also used to simulate a longitudinal population to explore the variability in the number of signs present over time in an aging population. Results:As the rate of arrival of the signs is heterogeneous, as determined through logistic regression, and the number of signs detected is finite, the resulting distributions of the number of signs over time have a different nature than Poisson. Our results suggest that we can expect to see on average one neurological deficit in healthy people by the age of 62, and that the expected number of deficits increases linearly at the rate of 1 additional sign every 12 years over a wide age range (age 70–90). The distribution of the number of deficits over time is also described. Conclusions:The linearity in the average rate at which signs appear in this population is somewhat of a surprise, in that an increasing (accelerating) rate might be anticipated. In addition to characterizing the neurological exam results in this group, we demonstrate a methodology that allows the comparison of groups and defines a rate of neurological aging.

This article explores whether persons with disabilities using wheelchairs participate to a lesser degree in social activities than persons with disabilities not using wheelchairs. A secondary data analysis of the 1994-1995 National Health Interview Survey on Disability (NHIS-D) Phase II showed that social contacts (calling friends, calling relatives, and seeing relatives) did not differ significantly between the two groups. Social activities (seeing friends, going to church or temple, eating out, and seeing a movie) varied with wheelchair use and personal and environmental characteristics. The findings suggest that wheelchair use is not necessarily synonymous with exclusion, and social participation of wheelchair users is a far more complex phenomenon than commonly thought.

Abstract: Spectral decomposition of variations in heart rate permits noninvasive measurement of autonomic nervous activity in humans and animals. Autonomic metrics based on spectral analysis are useful in monitoring clinical conditions such as diabetic neuropathy and reinnervation in heart transplant patients. A persistent problem in deriving such autonomic measures is the prerequisite of an accurate and unbiased power spectrum of heart rate variability (HRV). Numerous parametric and nonparametric power spectrum estimators have been introduced, each with its own advantages and drawbacks. Estimator bias has received little attention, despite the fact that at least one common HRV spectrum estimator, the autoregressive method, is known to exhibit bias even in idealized circumstances. We introduce an approximately minimum bias, nonparametric, multichannel spectrum estimation procedure for HRV and contemporaneous signals. The procedure, which is designed specifically for irregular sampling, does not require data segmentation and provides statistically consistent, low variance multichannel spectrum estimates. Estimator performance on simulated and clinical data is presented and compared with results from autoregressive models and Welch periodograms with and without compensation for irregular sampling. Results indicate that the proposed method exhibits advantages over conventional HRV spectrum estimators. Relative computational complexity of the proposed method is also considered.

The purpose of this study was to determine whether use of an abdominal binder would affect oxygen uptake, trunk ange of motion, and duration of the stroke phase during wheelchair propulsion. The subjects were six paraplegic wheelchair athletes with T1-T6 injuries and no abdominal muscle function. Each subject performed two trials, one while wearing the binder and one without the binder. Each trial consisted of submaximal and maximal exercise tests conducted on wheelchair rollers. Oxygen uptake was determined by telemetry. Max VO2 values averaged 2.51 1.min −1 while average maximum heart rate values were 190 190 b.min −1. A 3-D video-based motion analysis system was used to obtain kincmatic parameters of wheelchair propulsion. In general, 30 of the cycle time was comprised of the stroke phase, while 70 was comprised of the recovery phase across speeds. There were no statistically significant effects of the abdominal binder on any of the cardiovascular or kinematic variables at submaximal or maximal levels of exercise. Unde the conditions of this laboratory investigation, it appears that an abdominal binder does not alter physiological or selected biomechanical measures in higly trained athletes.

Electrical burns or ischemia (induced by vascular ligation) were produced in the legs of 15 anesthetized dogs to study evolution of tissue changes compared with impedance alterations. After the application of 1-ampere currents at 60 Hz, animals were monitored from 1 to 4 days. Muscle impedance was measured with frequency sweeping to determine tissue destruction. Nuclear magnetic resonance spectroscopy (phosphorus 31) was used to assess metabolic activity, and results were compared to impedance measurements. In burned limbs, 70 reduction in muscle impedance was seen, which corresponds to decreased metabolic activity (absent organic phosphates) and suggests necrosis. Visually viable tissue had impedance decreases of 25 and levels of organic phosphates slightly lower than normal. Relaxation frequencies in dogs with severe burns exceeded 80 kHz; in viable tissue, 30 to 40 kHz (normal 30 kHz). In ischemic muscle, organic phosphates decreased rapidly (1 to 2 hours); impedance changes evolved more slowly (1 day), but they ultimately reached the same degree of severity. Measurement of impedance may be a valuable adjunct in the evaluation of electrical burns, since significant changes strongly suggest nonviability.

Abstract: Fractal and correlation dimensions have been computed for time series obtained from tests of balance (postural steadiness). Although these measures appear to be reliable and differentiate subject groups, it has become clear that random (noise) time series may have finite dimensions and appear to demonstrate dynamics characteristic of nonlinear systems. Consequently, it is necessary to apply a test to distinguish a time series with putative nonlinear dynamics from random noise. A simple predictor was utilized to compare center of pressure (COP) time series with surrogate data constructed to have similar time and frequency domain characteristics. It was found that the original time series was more predictable than the surrogate data, suggesting that the COP data is derived from a nonlinear system.

• In ten monkeys, selective segmental lesions of the dorsal columns at the upper thoracic and middle cervical levels resulted in almost total attenuation of the cortical evoked potential responses to peripheral nerve stimulation. Conversely isolated segmental dorsal column preservation showed intact transmission of the evoked responses at rostral spinal cord, nucleus ventralis posterior lateralis, and cortical levels. Responses recorded from the intralaminar thalamic nuclei in the region of nucleus centrum medianum were unaffected by dorsal column ablation, but were markedly attenuated following bilateral ventral column ablation.