Biomedical subjects
Publications and source records attributed to I Pyykkö.
The eye tracking test is today a well established part of clinical otoneurological examination. In the present paper some applications of the test in evaluating of the level of lesion within the vestibular system are reviewed.
During recent decades a vast amount of literature concerning horizontal optokinetic nystagmus has emerged, regarding which--and especially as regards our own work--this report is intended to consider the clinical value of optokinetic nystagmus.
Postural control is maintained by sensory feedback from visual, vestibular and somatosensory receptors. Recently several methods for evaluating postural control have been devised, utilizing an imposed perturbation. Most of these methods use stimuli which simultaneously affect more than one of the sensory feedback loops. In the present paper a posturographic technique is presented with specific loading of the proprioceptive system, using a computer controlled vibratory stimulus and computerized analysis of the results.
A review of the treatment of vestibular disorders with drugs is presented. In animal experiments, administration of certain drugs, e.g. alcohol, barbiturates and chlorpromazine, retards the vestibular compensation, while others, e.g. caffeine, amphetamine and ACTH, accelerate the compensation. In compensated animals, some drugs produce overcompensation and some decompensation. A double-blind, randomized trial of the effect of scopolamine and dimenhydrinate in patients with vertigo of varying origin showed, as compared with placebo, that these drugs did not significantly alleviate the vestibular imbalance. The reason for the poor efficacy of the treatment may have been overcompensation of vestibular function loss and adverse effects caused by the drugs. Care should be taken that the drugs used do not retard the vestibular compensation caused by the central nervous system.
The present study was carried out to determine whether impulse noise and simultaneous exposure to noise and vibration can aggravate sensory neural hearing loss (SNHL) among forest (N = 199) and shipyard (N = 171) workers. The average level of exposure to noise outside the used earmuffs and the average exposure over time were nearly equal for the two groups. The impulsiveness of the noise and the average exposure level inside the earmuffs were measured with a miniature microphone. The hearing threshold of the workers was measured at 4 kHz and then estimated according to Robinson's model to compare the observed and expected hearing loss. The impulsiveness of the noise was greater both outside and inside the earmuffs in shipyard work than in forest work. The average SNHL was higher than predicted for the shipyard workers and about the same as predicted for the forest workers. The total exposure level inside the earmuffs was influenced by the total wearing time. The low frequencies of the chain-saw noise were not attenuated sufficiently by the earmuffs to protect the workers' hearing. The present study suggests that exposure to impulse noise increases the risk of SNHL, but that simultaneous exposure to hand-arm vibration and noise does not.
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Many subjects have a negative spike in the beginning of a saccade in electro-oculographic signals. The amplitude of the spike depends on the location of the electrodes. The spike distorts the saccades and causes errors in the parameters. The saccade spike can assist in the identification of small saccades. A syntactic technique based on formal languages and parsing is presented which looks for spikes from the electro-oculographic signal. For calculation of the algorithm, saccades from the photoelectric signal have been concurrently recorded and compared with the electro-oculographic signal.
A detailed analysis of risk factors for the development of sensory-neural hearing loss (SNHL) was carried out on 122 forest workers. These forest workers were selected from a larger group (n = 217) by restricting the age range to 30-55 years. The hearing threshold of the left ear at 4000 Hz was measured and the effect of age, exposure, systolic and diastolic blood pressure (DBP), presence of vibration-induced white finger (VWF), tobacco smoking and use of earmuffs were evaluated in multiple linear regression analysis. Robinson's nonlinear model was used to evaluate the rate of hearing loss. Aging was the major risk factor and it explained 15.4% of the variance of the SNHL. The presence of VWF was the second most important single risk factor and explained a further 5.2% of the SNHL. Elevation of DBP correlated significantly with SNHL and explained an additional 4.1% of the SNHL. These main factors were able to explain about 26% of the spread of SNHL. Additional factors in the analysis, e.g. smoking, systolic blood pressure, did not significantly contribute to the genesis of SNHL. When Robinson's model was applied to the SNHL data, on a group basis, we did not observe any exaggerated risk of hearing loss due to combination of noise and vibration. In combined exposure subjects with VWF as well as subjects with enhanced DBP will run a higher risk for SNHL.
A computer analysis of slow and fast phase of velocity of nystagmus is presented. Several methodological factors are known to affect the computation of velocities, such as sampling frequencies, cutoff frequencies of the differentiation method, and resolution in bits of analog-digital conversion. A simulated signal without noise was first applied in nystagmus data in order to study maximum velocities at the theoretical level. Electro-oculographic postrotational nystagmus movements were then examined to test theoretical results. It was shown that the sampling frequency ought to be 400 Hz at least, the cutoff frequency about 70 Hz, and the resolution of analog-digital conversion 12 bits or higher.
The variation in heart rate (HRV) at rest and during deep breathing (6 cycles a minute) of 88 professional lumber jacks was studied using a computer technique. The traditional indexes of HRV (CV, CVS, MEAN) were calculated and the spectral components of the HRV were also computed. There was a significant difference (p less than 0.001) between the HRV indexes during the deep breathing test in those with the shortest (CV = 10.1 +/- 1.1) and those with the longest (CV V 6.2 +/- 0.4) exposures to vibration. The values of the HRV indexes decreased with age, but multiple regression analysis showed that the total exposure time to vibration had an independent negative association with the HRV. There were significant differences in all the frequency bands (frequency related power, FRP) of the heart rate between those with the longest and those with the shortest exposures. The HRV during a deep breathing test is associated with the activity of the parasympathetic nervous system and is decreased in autonomic neuropathies. Our results suggest that prolonged exposure to the vibration caused by a chain saw has a negative effect on the parasympathetic activity and thus causes autonomic dysfunction.
Electrical brain activity and eye movements were recorded in 10 intact and 6 unilaterally labyrinthectomized rabbits, each with implanted electrodes. The frequency of optokinetic nystagmus (OKN) and a 10-second aggregate of theta waves in the dorsal hippocampus were determined after exposure of the animals to sound, vibration and optokinetic stimulation. Each stimulus used caused significant increases in OKN and theta activity. Vibratory stimuli caused stronger increases in OKN and theta activity than did sound stimuli. Not only was OKN significantly reduced after unilateral labyrinthectomy (UL), but alerting the rabbit with sound or vibration failed to restore the responses to normal, and hippocampal EEG responses to sound, vibration or optokinetic stimulus were significantly reduced. The findings indicate that a visual orientation reflex is normally improved by simultaneous sensory stimulation. Reduced response to stimuli after UL affects not only orientational reflexes but other sensory responses as well, and is accompanied by a reduced state of alertness.
The vibrotactile perception threshold has been evaluated in 20 manual workers not exposed to occupational vibration and in 27 workers using hand-held vibrating tools. Threshold values were evaluated with a Békesy type of vibrometer at frequencies ranging from 8 to 500 Hz. The earliest sign of vibration lesion was a reduction of sensation at frequencies of 125 to 250 Hz, indicating dysfunction in receptors of the fast adapting type II (stage 1 curve), followed in more severe cases by a prominent loss of sensation at all frequencies higher than 65 Hz (stage 2 curve). The stage 3 curve indicated the most severe loss of sensation in which the function of slowly adapting type I receptors, as well as fast adapting type I receptors, was deteriorated; consequently the vibrotactile thresholds at low-, median-, and high-frequency ranges were impaired. The vibrotactile changes corresponded well to numbness and the presence of vibration-induced white finger.
Peripheral neuropathy represents a well-known complication from long-term exposure to vibration. In the present study an experimental model is presented with the purpose of analyzing the formation of intraneural edema following vibration exposure. Vibration (82 Hz, peak-to-peak amplitude 0.21 mm) was induced in the hind limb of rats by the use of vibrating electric motors during 4 h/d for 5 d. Tracer techniques (with albumin Evans blue and horseradish peroxidase) were used to study the permeability of intraneural microvessels after the vibration exposure on day 5. It was found that the vibration trauma in this model induced epineurial edema in the sciatic nerve. It is hypothesized that the formation of intraneural edema may be an important pathophysiological factor in the occurrence of vibration-induced neuropathy.
On the basis of experience accumulated over the past few years, a revision has been made in the currently used Taylor-Pelmear scale for the staging of Raynaud's phenomenon in persons exposed to vibration from hand-held tools, while retaining as much as possible of the well-established advantages of the scale for research and its proved usefulness for clinical and medicolegal purposes. The 0T and 0N stages of symptoms have been omitted, together with the parallel disability scale. A separate staging for neurological disorders connected with the syndrome was proposed and accepted at the workshop "Symptomatology and Diagnostic Methods in the Hand-Arm Vibration Syndrome," held in Stockholm in 1986. The criteria descriptions have been changed so as to minimize their reliance on seasonal factors. The new staging system--a stage 0 and four stages (1-4) with attacks of cold-induced Raynaud's phenomenon--clearly defines the differences in the descriptions of the stage criteria in order to improve their clinical usefulness. A numerical scoring based on the extent and distribution of finger blanching was not, however, introduced, whereas a score based on the number of affected fingers on each hand was proposed, considered, and accepted.
A review of current knowledge on the pathophysiological aspects of peripheral circulatory derangements in the hand-arm vibration syndrome is presented. Hemodynamic measurements indicate that the primary factor in vibration-induced white finger is an increase in peripheral resistance of finger circulation, present after local and general cooling. The reason for this increase is not known, but it is postulated that there is an excess affinity for the efferent receptors of vasoactive substances and that this affinity is potentiated during local cooling of the digits.
An analysis of electroneurographic studies of workers who operate hand-held vibrating power tools reveals that, when controlled for polyneuropathy and the effects of heavy manual work, significantly reduced sensory nerve conduction velocities occur within the hands. This finding is compatible with the available pathophysiological evidence. The detection of this presumed vibration-induced neuropathy and its distinction from compression neuropathies involving a localized primary lesion, such as carpal tunnel syndrome, thus requires a detailed investigation of nerve conduction within the hands. A technique well adapted to the detection of abnormalities in the most peripheral sensory nerve fibers and mechanoreceptors has been developed based on vibrotactile stimulation of a fingertip. The compound action potentials recorded noninvasively at the base of the finger and wrist from healthy male subjects possess peak-to-peak amplitudes of no more than 0.5 and 0.25 microV, respectively.