Two-dimensional coherence for measurement of asymmetry in postural steadiness.

Two-dimensional magnitude squared coherence (2D-MSC) is developed to compare the two-valued time series which represent the center of pressure (COP) under each foot. A sinusoidal multiple taper spectral estimator is used to reduce bias and improve spectral resolution. The measure is applied to evaluate symmetry in the dual-plate postural steadiness time series obtained from healthy young and elderly volunteers, and patients with Huntington's Disease (HD), a group in which asymmetries in postural steadiness are anticipated. The results demonstrate that the 2D-MSC is a robust measure of inter-limb coordination that may be of value in studies of aging and neurologic disease.

Ballistocardiogram artifact reduction in the simultaneous acquisition of auditory ERPS and fMRI.

Electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) are now being combined to analyze brain function. Confounding the EEG signal acquired in the MR environment is a ballistocardiogram artifact (BA), which is predominantly caused by cardiac-related body movement. The objective of this study was to develop and evaluate a method for reducing these MR-induced artifacts to retrieve small auditory event-related potentials (ERPs) from EEG recorded during fMRI. An algorithm for BA reduction was developed that relies on timing information obtained from simultaneous electrocardiogram (ECG) recordings and subsequent creation of an adaptive BA template. The BA template is formed by median-filtering 10 consecutive BA events in the EEG signal. The continuously updated template is then subtracted from each BA in the EEG. The auditory ERPs are obtained through signal averaging of the remaining EEG signal. Experimental and simulated ERP data were estimated to assess effectiveness of the BA reduction. Simulation showed that the algorithm reduced BA without significantly altering the morphology of a signal periodically inserted in the EEG. Auditory ERP data, obtained in a 1.5-T scanner during a passive auditory oddball paradigm and processed with the BA reduction algorithm, were comparable to data recorded in a mock scanner outside the magnetic field with the same experimental paradigm. It is concluded that through adequate reduction of the BA, relatively small auditory ERPs can be acquired in the MR environment.

Autonomic nervous system evaluation of patients with vasomotor rhinitis.

OBJECTIVE: To demonstrate the utility of quantitative neurological laboratory testing of autonomic nervous system dysfunction and to apply this methodology to further study the relation of chronic vasomotor (nonallergic) rhinitis to the autonomic nervous system. METHODS: It has been suspected that vasomotor rhinitis is due either to a hyperactive parasympathetic nervous system or an imbalance between it and the sympathetic nervous system. The exact relation has not been determined. Recently neurological laboratories have been developed in which a battery of tests can be performed to determine reactivity of the autonomic nervous system. RESULTS: Autonomic nervous system testing was performed on 19 patients with symptoms fulfilling the diagnostic criteria for vasomotor rhinitis and the results were compared with 75 sex- and age-matched control subjects. Patients with vasomotor rhinitis had significant abnormalities of their sudomotor, cardiovagal, and adrenergic subscores. Their composite autonomic scale score was significantly impaired at 2.43, as compared with 0.11 for controls (P < .005). CONCLUSION: Autonomic nervous system dysfunction is significant in patients with vasomotor rhinitis. Possible factors that trigger this dysfunction including nasal trauma and extraesophageal manifestations of gastroesophageal reflux are discussed.

Too many treatments for Parkinson's disease: how should they be used?

Surgical ablation for Parkinson's disease was abandoned in the 1970s after successful clinical trials of L-DOPA and L-DOPA/decarboxylase inhibitor combinations and early dopamine receptor agonists were added to prolong a viable therapeutic window beyond 5 years. The development of newer agonists with variations in receptor subtype specificity and new enzyme inhibitors with combinations of central and peripheral effects have continued to attract attention as therapeutic alternatives. Treatment options are now coming full circle with a rebirth of stereotactic neurosurgical alternatives to a wide variety of pharmacologic paradigms. The authors propose a rationale for selecting differing treatment options within historical perspective and modern treatment goals using both medical and surgical alternatives.

Progressive polyradiculoneuropathy in diabetes: correlation of variables and clinical outcome after immunotherapy.

OBJECTIVE: To quantify the progression of diabetic polyradiculoneuropathy-a condition in which immune factors have been implicated-after immunotherapy. METHODS: The study evaluated 15 consecutive patients with this condition. All patients were older than 40. Four had type I diabetes and six were women. The duration of pre-existing diabetes varied from 2 to 20 years. The clinical presentation was dominated by painful progressive motor weakness, with or without exacerbation of sensory symptoms. The weakness involved all limbs, but was often asymmetric. RESULTS: Electrophysiological testing showed a predominantly axonal polyneuropathy, with more recent denervating polyradiculopathy. Analysis of CSF showed increased protein in 14 and oligoclonal bands in five. Quantitative autonomic tests showed abnormalities in all patients. Sural nerve biopsy was performed in 14 patients; all showed fibre loss and segmental demyelination, four had occasional onion bulbs, and 10 showed various inflammatory infiltrates. After immunomodulating therapy, there was no further deterioration and clinical improvement occurred in all patients. Sweat responses, cardiovascular reflexes, and sural nerve fibre density correlated best with functional outcome. There was no significant difference between plasmapheresis and intravenous gammaglobulin. CONCLUSION: Immunotherapy may improve this condition, but only certain variables correlate with rapid therapeutic response.

Neural basis of endogenous and exogenous spatial orienting. A functional MRI study.

Whole-brain functional magnetic resonance imaging (MRI) was used to examine the neural substrates of internally (endogenous) and externally (exogenous) induced covert shifts of attention. Thirteen normal subjects performed three orienting conditions: endogenous (location of peripheral target predicted by a central arrow 80% of the time), exogenous (peripheral target preceded by noninformative central cue). Behavioral results indicated faster reaction times (RTs) for valid than for invalid trials for the endogenous condition but slower RTs for valid than for invalid trials for the exogenous condition (inhibition of return). The spatial extent and intensity of activation was greatest for the endogenous condition, consistent with the hypothesis that endogenous orienting is more effortful (less automatic) than exogenous orienting. Overall, we did not observe distinctly separable neural systems associated with the endogenous and exogenous orienting conditions. Both exogenous and endogenous orienting, but not the control condition, activated bilateral parietal and dorsal premotor regions, including the frontal eye fields. These results suggest a specific role for these regions in preparatory responding to peripheral stimuli. The right dorsolateral prefrontal cortex (BA 46) was activated selectively by the endogenous condition. This finding suggests that voluntary, but not reflexive, shifts of attention engage working memory systems.

Analysis of gait abnormalities in Huntington disease.

OBJECTIVE: To evaluate patterns of successful gait strategy in Huntington disease (HD) at various stages of illness to improve fall avoidance and maintenance of independence. DESIGN: Repeated measurements of gait kinematic parameters and joint performance during gait cycles of six HD patients compared to 30 age-matched controls. SETTING: A standard gait laboratory. SUBJECTS: Six HD patients, rank-ordered for disease severity from minimal chorea to generalized dystonia, selected because they were ambulatory despite 3 to 17 years' disease duration. One patient was from a nursing home (walked with assistance) and five were living independently, either alone or with a working spouse who was the caregiver. MAIN OUTCOME MEASURES: Standardized gait evaluations (retroreflective markers on standard bony landmarks) from five video angles, fed into digitizer to computer-generate joint angles and standard gait kinematic parameters. RESULTS: Wide variability in gait kinematic parameters and joint interaction plots (phase plane and angle-angle plots) was observed between individuals and successive trials of the same limb, tending to increase with disease severity. Joint interaction plots show that random, highly variable distractions from planned trajectories are more apparent distally. CONCLUSIONS: Chorea in HD does not appreciably affect the center of gravity during ambulation, and the consistency of gait profiles at heel strike shows that the ultimate target is achieved in each step despite random and frequent variability during the gait cycle.

A rate-controlled indentor for in vivo analysis of residual limb tissues.

A tissue tester was designed to enable rate-controlled indentation of the bulk soft tissues of lower extremity residual limbs. The tissue tester employs a digital linear actuator that implements rate-controlled indentation, and a load cell that measures the reaction force resulting from tissue indentation. Viscoelastic phenomena such as preconditioning, hysteresis and force relaxation can be assessed, and the effect of varying indentation rates on soft tissue stiffness can be investigated. The device accommodates indentor excursions up to 30 mm, indentation at rates of 0 to 10 mm/s, reaction forces up to 44 N, and multiple loading/unloading cycles. The tissue tester is controlled via a notebook personal computer with a PCMCIA data acquisition card. The tissue testing trials are automated and the entire test system is portable and amenable for use in a clinical or research environment. System output consists of force-displacement curves from cyclic loading, and force-time curves following ramped-step indentation. The mean indentor positioning error was 0.071 (+/-0.75)% of the desired displacement. This error varied as a function of indentation and was approximately independent of the indentation rate. Indentation rates were accurate to within 0.94(+/-0.68)% of the desired value and also varied with indentation. Indentation of a viscoelastic foam yielded force-displacement curves that were consistent with that obtained from an Instron universal testing machine.

Thermal effects of laser stapedectomy in an animal model: CO2 versus KTP.

Although use of the laser for stapedectomy has become common in recent years, controversy remains regarding whether the CO2 or visible-spectrum lasers (argon and KTP) are best suited for this operation. The main concern has been the potential for thermal injury to the inner ear with the visible-spectrum lasers attributable to their absorption characteristics. To further investigate this issue, the author performed 20 laser stapedectomies on adult chinchillas. Following placement of a 0.127-mm-diameter copper/constantan thermocouple (sampling at 12 Hz) beneath the footplate on the medial wall of the vestibule via a distant fenestration site, thermal changes with a micromanipulator-based CO2 and fiberoptic KTP system were compared. This was the first live animal model comparison of these two lasers. There was no statistical difference in the mean temperature elevation between the two systems (P = 0.395).

Measures of postural steadiness: differences between healthy young and elderly adults.

Measures of postural steadiness are used to characterize the dynamics of the postural control system associated with maintaining balance during quiet standing. The objective of this study was to evaluate the relative sensitivity of center-of-pressure (COP)-based measures to changes in postural steadiness related to age. A variety of time and frequency domain measures of postural steadiness were compared between a group of twenty healthy young adults (21-35 years) and a group of twenty healthy elderly adults (66-70 years) under both eyes-open and eyes-closed conditions. The measures that identified differences between the eyes-open and eyes-closed conditions in the young adult group were different than those that identified differences between the eye conditions in the elderly adult group. Mean velocity of the COP was the only measure that identified age-related changes in both eye conditions, and differences between eye conditions in both groups. The results of this study will be useful to researchers and clinicians using COP-based measures to evaluate postural steadiness.

Effect of an abdominal binder during wheelchair exercise.

The purpose of this study was to determine whether use of an abdominal binder would affect oxygen uptake, trunk range 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 open circuit spirometry while heart rate was determined by telemetry. Max VO2 values averaged 2.51 l.min-1 while average maximum heart rate values were 190 b.min-1. A 3-D video-based motion analysis system was used to obtain kinematic 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. Under the conditions of this laboratory investigation, it appears that an abdominal binder does not alter physiological or selected biomechanical measures in highly trained athletes.

Vascular effects of spinal cord stimulation in the monkey.

Because of clinical reports suggesting beneficial effects of electrical stimulation in peripheral vascular disease, studies have been conducted in the monkey. Regional blood flow was measured prior to, during and following the application of electrical currents to the spinal cord. The flow measurements were made using radioactive microspheres. In addition, tissue temperatures and venous and arterial concentrations of epinephrine and norepinephrine were measured. The results show that electrical stimulation increases blood flow to the skin and muscle. It is hypothesized that the effect is due to sympathetic inactivation secondary to the application of electrical currents.

Fibrillation induced at powerline current levels.

Electrical fibrillation of the human heart results in many unfortunate deaths. Because little information is available on short duration high current fibrillation, current levels below 1 and 50 A were used to induce ventricular fibrillation in hogs. Application times ranged between 16 ms and 3 s. Fibrillation was only produced when currents were applied during the T-wave period of the cardiac cycle. However, only 50 percent of the current application during the T-wave caused fibrillation. The total body resistance of the hogs was also measured at the high voltages and currents. The average resistance for 90 current applications was 284 omega. Trends in the data show that the total resistance decreases for increasing voltage, for increasing electrode size, and for current applications following the first current application.

Measure of tissue resistivity in experimental electrical burns.

Studies were conducted in 14 mongrel dogs to compare resistivities in normal muscle with those from muscle subjected to electrical burns. One-ampere, 60-Hz currents were passed between the hind limbs of the dogs producing injury in three measurement regions of the gracilis muscle. Histology, heart rate, body temperature, arterial and pulmonary artery pressure, cardiac output, hematocrit, leukocyte counts, fibrinogen levels, and platelet levels were determined. Muscle resistivity associated with severe tissue necrosis was 70% lower than control values. Resistivity in tissue showing edema and minimal necrosis decreased 20 to 40% from control values. Muscle showing only edema had a 10 to 30% decrease in resistivity.