Current perception threshold and reaction time in the assessment of sensory peripheral nerve fibers through sinusoidal electrical stimulation at different frequencies

INTRODUCTION: The Perception Sensory Threshold (ST) for sinusoidal current stimuli at 5, 250, and 2,000 Hz is commonly used in the assessment of peripheral nerve fibers (C, Aδ, and Aβ, respectively). However, the neuroselectivity of these frequencies is far from consensus. In addition, Reaction Time (RT) measurements suggest that 2,000 Hz stimuli excite Aβ-fibers, 250 Hz Aβ- or Aδ-fibers, as well as 5 Hz Aβ-, Aδ- or C-fibers. Therefore, we suppose that the sinusoidal current neuroselectivity may be better observed if ST and RT parameters are jointly evaluated. In addition, we have investigated whether there are other sets of frequencies that could be used. METHODS: Thus this work investigates ST and RT for stimuli with frequency ranging from 1 to 3,000 Hz, on 28 healthy subjects aged from 19 to 44 years old (27.1±5.49). ST and RT dissimilarity among different frequencies was evaluated applying bi-dimensional Fisher Quadratic Discriminant. RESULTS: The lowest classification error (3.6%) was obtained for 1, 250, and 3,000 Hz. Error for 5, 250, and 2,000Hz was 16.7%. Stimulation frequency at 1 Hz evoked more sensations related to C-fibers (53% of reports) than to Aβ-fibers (36%). However, this behavior did not repeat itself at 5 Hz (only 21% of perceptions were related to C-fibers against 64% to Aβ-fibers). Sensations related to Aβ-fibers prevailed for the highest frequencies presented to the subjects (2,000 Hz - 82% and 3,000 Hz - 93%). Mean RT values showed a decreasing trend with frequency. CONCLUSION: These results suggest that frequencies 1, 250, and 3,000 Hz are more neuroselective than 5, 250, and 2,000 Hz for the evaluation of peripheral sensitive fibers. Furthermore, they show RT usefulness

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 127, April 1974

This special bibliography lists 279 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1974

The Isolation of Human Rod and Cone Photoreceptor Activity combining Electroretinography and Silent Substitution Techniques

Aims: The electroretinogram (ERG) can be used to independently assess the function of rod and cone photoreceptors within the human retina. The work in this thesis sought to investigate an alternative method of recording the ERG, using the silent substitution paradigm (Estevez and Spekreijse 1982). The aims are separated into two parts, firstly, the isolation and characterisation of the non-dark adapted rod photoreceptor response, and secondly, characterising the ERG response from L-, M- and S-cones. Methods: Rod, L-, M- and S-cone isolating as well as non-isolating sinusoidal flicker and transient square-wave stimuli were generated on a 4 primary LED ganzfeld stimulator to elicit ERGs from non-dark adapted participants with normal and compromised rod or cone function. Results: The results from the rod experiments showed that ERGs elicited by rod isolating silent substitution stimuli exhibit low-pass temporal frequency response characteristics with an upper response limit of 30Hz and saturate beyond 1000ph Td. Responses are optimal between 5 – 8 Hz and between 10-100 photopic Td. There is a significant correlation between the response amplitudes obtained with the silent substitution method and current standard clinical protocols. The results from the cone experiments showed that the L-, M- and S-cone stimulation produced ERGs with very different morphologies. L- and M-cone stimulation is of limited use as an objective measure of colour vision deficiency. Conclusion: Silent substitution provides an effective method for the isolation of human rod and cone photoreceptor function in subjects when stimuli are used within appropriate parameter ranges

Effect of wrist activity on median nerve function

Background - Hand intense occupational activities have been associated with an increase in the incidence of carpal tunnel syndrome (CTS). CTS is characterized by an impairment of median nerve function. To date, a dose-response relationship between wrist activity and median nerve performance has not been documented. Since repetitive hand/wrist activity in the workplace has significant implications, it is important to establish a scientific basis for the aetiology of work-related carpal tunnel syndrome. Methods -- In a laboratory environment, twenty-seven clinically confirmed asymptomatic female subjects performed continuous repetitive wrist motion in the flexion-extension plane during which an angle of 120 degrees was subtended about the neutral wrist position. Four levels of wrist activity, corresponding with 0 (static), 22 (Iow), 38 (medium) and 49 (high) repetitions per minute, were prescribed. Wrist motion was recorded using a state-of-the-art 3D electromagnetic tracking system (HumanTRAC). Mathematical descriptors of wrist kinematics, including cycle time, amplitude, angular velocity and angular acceleration, were calculated. Sensory median nerve response to imposed physical stressors was monitored antidromically and recorded using a clinical electroneurometer every ten minutes throughout the simulated work activities. Near-nerve skin temperature was recorded at three sites along the distal sensory branch of the median nerve every twenty minutes. Results - After adjusting for changes in near-nerve skin temperature, a significant within-subject effect of duration of exposure (time) was detected. Sensory median nerve conduction velocity differed statistically by 2.1 ms-1 between the static and high wrist activity conditions after 120 minutes of exposure, signifying adverse effects on nerve conduction that are uniquely attributable to repetitive hand motion. Wrist activity measures of mean angular acceleration presented a highly significant association with nerve performance, where nerve conduction decreased as wrist activity increased. Using regression analysis, a maximum safe wrist-workload exposure limit of 0.91 repetitions per minute is proposed. Limitations of this result are discussed. A biomechanical model is presented to calculate the effect of physical risk factors on tendon forces at the wrist. This model offers a method by which findings of the study can be employed for workplace exposure surveillance and development of ergonomic workstation design recommendations. Conclusions -- Across the study population of clinically asymptomatic female participants, a change in median nerve performance was observed. This significant effect was evoked due to imposed physical stressors. A dose response relationship between work intensity, exposure time and median nerve conduction velocity was demonstrated. The research explored in this thesis presents a foundation for the future development of a "Dynamic Median Nerve Stress Test". This test would involve the performance of a repetitive motion activity of the wrist during which changes in the function of the median nerve are closely monitored. The Dynamic Median Nerve Stress Test might prove to be valuable both as a provocative clinical test as well as an important research tool

Effects of diabetes and aging on posture and acceleration thresholds during lateral translations

Research objectives. One source of falls in the elderly may be an inability to sufficiently adjust to transient postural perturbations or slips. Identifying useful predictors of fall potential, as well as factors that affect the ability of an individual to detect a movement of the standing support surface may provide insight into postural stability and methods to increase stability in elders. To do this, acceleration thresholds to short, precise, lateral platform translations and the resultant psychophysical responses of adults with early Type 2 diabetes to age-matched controls and young adults were measured. Methods. Using an innovative SLIP-FALLS platform, short (1, 2, 4, 8,and 16mm) lateral perturbations were presented to 21 individuals—9 young adults, 6 neurologically intact elder adults, and 6 elders with diabetes using a two-alternative forced choice (2AFC) protocol. All subjects underwent lower-limb nerve conduction velocity determination, air conduction velocity testing, Semmes-Weinstein monofilament thresholds, the Mini Mental Status Exam, and reaction time tests to touch, tone and high acceleration, 4mm super-threshold perturbations. Results. All three groups had significantly different thresholds at all small (\u3c4mm) movement lengths, with the diabetic neuropathy group having a markedly higher acceleration threshold (P \u3c 0.001); the healthy elderly, which, in turn, had markedly higher thresholds than young adults. Patients with neuropathy had significantly higher reaction times to platform movements and touches to the plantar sole, but not for auditory tones. Both elderly groups had a significantly higher reaction time to superthreshold platform movement than did young adults. Sensory tests revealed slower nerve conduction velocities, higher air conduction velocities, and lower cognitive ability in the diabetic group. Conclusions. A marked decrease in perception of very small moves due to aging and diabetic neuropathy could well have a detrimental effect on postural control mechanisms. The higher prevalence of falls in the elderly and elderly diabetics may be due to decreased perceptual ability, slower nerve conduction velocities, and slowing reaction times compounded by larger amounts of imparted energy needed for detection of a slipping event

The utility of latency and spectral analysis methods in evoked potential recordings from patients with hepatic encephalopathy

Evoked potentials (EPs) are small phasic potentials that are elicited in conjunction with sensory, motor and cognitive events. EP variables have been assessed in patients with cirrhosis but in general, methods were inadequately standardized and study populations incompletely characterized, leading to some studies questioning the validity of EP’s in diagnosing and monitoring hepatic encephalopathy, while other studies indicated that there is only a low positive yield with these investigations. Few studies have attempted tri-modal sensory and cognitive recordings. Recorded waveforms may demonstrate altered morphology while possessing broadly normal latencies. Since EP analysis is usually performed solely in the time domain, latency measurements do not therefore highlight morphological changes to the waveform and so abnormalities may go unreported. The aim of this study was twofold (i) to measure sensory and cognitive EPs in patients with cirrhosis in relation to their neuropsychiatric status and (ii) to address frequency content in relation to neuropsychiatric status by examining EPs with two spectral techniques, the Fourier Transform (FT) and the Power Spectral Density Estimate (PSD). Seventy patients with biopsy–proven cirrhosis were classified using clinical, psychometric and EEG criteria as unimpaired or as having minimal or overt hepatic encephalopathy (HE). Forty-eight healthy individuals served as controls. Visual (VEPs), brainstem auditory (BAEPs) somatosensory (SSEPs) and cognitive auditory (P300) EPs were recorded under standardized conditions. Significant latency differences were observed in sensory EPs between patients and controls with patient subgroups differences being less significant. The cognitive auditory P300 however, distinguished the patient subpopulations from one another. Frequency shifts are observed in all EP modalities with significant differences also occurring between patient groups. The sensitivity and specificity of the frequency-domain is comparable to that of the time-domain. Paired EP investigations analysed by latency indicate BAEP and P300 best discriminate any degree of encephalopathy; in the frequency domain it is the VEP combined with SEP and in the time-frequency domain it is the SEP. These findings suggest that EPs, when performed as a bank of multimodal tests and with spectral analysis, could provide a sensitive and specific method for the diagnosis and monitoring of hepatic encephalopathy

Aerospace medicine and biology. A continuing bibliography with indexes, supplement 235, August 1982

This bibliography lists 201 reports, articles and other documents introduced into the NASA Scientific and Technical Information system in July 1982