Biomedical subjects

I Pyykkö

Publications and source records attributed to I Pyykkö.

232 records · Page 13Linked to original sources

PubMedDate not supplied

Clinical evaluation of dysrhythmia of postrotatory nystagmus.

Postrotatory responses of nystagmus were analysed in an exponential model by utilizing linear regression analysis. Four nystagmus qualities (velocity and duration of slow and fast phases) were studied in 10 patients with vestibular peripheral lesions, 10 patients with frontal lobe lesions and 10 patients with brain-stem lesions, together with 10 control subjects. In addition, pauses during the responses were quantified. Patients with frontal lobe lesions differed from other groups by scoring higher values of slow phase velocity and by exhibiting more pauses. The time constant was significantly shorter in patients with brain-stem lesion than in any other group. As regards other qualities, e.g. slow phase duration and fast phase velocity, or duration, no differences were observed. The pathological dysrhythmia may therefore be presented as changes in the gain and time constant of slow phase velocity as well as in pauses during nystagmus. Since all these changes may be encountered in normal subjects, one should be cautious in interpreting these changes as being pathological in each individual case.

Adult↗

PubMedDate not supplied

Intrabeat relationship of postrotatory nystagmus in normal subjects.

Intrabeat relationships between duration, amplitude and velocity of the slow phase of nystagmus and between amplitudes of the fast and slow phase of nystagmus were analysed from postrotatory responses in 10 normal subjects, using linear regression analysis. For 5 subjects, the tests were repeated five times. Highly significant correlation was found between velocity and amplitude of the slow phase in 9 of 10 subjects, whereas in one subject it was less significant. All subjects exhibited a significant correlation between velocity and duration of the slow phases. These intrabeat relationships were repeatable and representative for each individual. Highly significant correlation was found between amplitudes of the slow and fast phases of nystagmus in all subjects. No interindividual differences in these variables could be observed. The results indicate that the end-point of the slow phase of vestibular nystagmus in darkness is controlled by positional and durational corollary circuitries. The positional signal in displacement circuitry is probably derived by integration of the velocity signals from the labyrinths. The durational circuitry is presumably more dominant at high nystagmus velocities in order to permit sufficient time for fixation.

Adult↗

PubMedDate not supplied

Intrabeat relationship of postrotatory nystagmus in patients with neurological disorders.

The intrabeat relationships between velocity, amplitude and duration of the slow phase of nystagmus as well as between amplitudes of slow vs. fast phase of nystagmus were analysed during a postrotatory nystagmus response by using linear regression analysis. Three groups of patients were studied, each consisting of 10 subjects with lesions either in the peripheral vestibular system, in the frontal lobe, or in the brain stem. Irrespective of the site of the lesion, all groups exhibited the same response pattern: a reduction in amplitude control of the end-point of nystagmus and an increase in durational control. The most prominent changes were observed in patients with brain-stem lesion in whom the durational control of the slow phase of nystagmus was constant, with a mean slow phase duration of 150 to 250 ms in the case of 3 to 4 fast phases per second. No alterations were observed in the relationship between amplitude of slow vis-à-vis fast phase. The results indicate that analysis of intrabeat relationship may provide additional data on the side of the disorder affecting the vestibular system.

Adult↗

PubMedDate not supplied

Transdermally administered scopolamine vs. dimenhydrinate. I. Effect on nausea and vertigo in experimentally induced motion sickness.

The effect of transdermally administered scopolamine (TTS-scopolamine) (2.5 cm2 surface area, one and two patches) and dimenhydrinate (100 mg) on experimental motion sickness was examined in 16 healthy volunteers in a randomized double-blind study. Nausea was induced by Coriolis manoeuvre and vertigo by calorization of the ear. In all subjects, scopolamine was found in urine in concentrations indicating adequate absorption of the drug. One TTS-scopolamine, two TTS-scopolamine and dimenhydrinate caused a statistically significant reduction in nausea when compared with placebo. Dimenhydrinate was somewhat more effective against nausea than one TTS-scopolamine. Vertigo was significantly reduced after dimenhydrinate and two TTS-scopolamine. Side effects of both drugs were negligible, though gait disturbances and vertigo could occur occasionally after two TTS-scopolamine. No dose-response relationship was found between the urinary excretion of scopolamine and alleviation of nausea. Dimenhydrinate and TTS-scopolamine are both effective against motion sickness, the latter provided it is applied 6 to 8 hours before exposure to the stimulus causing the motion sickness.

Adult↗

PubMedDate not supplied

Transdermally administered scopolamine vs. dimenhydrinate. II. Effect on different types of nystagmus.

The effects of transdermally administered scopolamine (TTS-scopolamine) (release rate 5 micrograms/h, one and two patches) and dimenhydrinate (100 mg) on caloric, angular acceleration induced and optokinetic nystagmus were examined in 16 volunteers in a randomized double-blind study. All drugs induced a statistically significant decrease in maximum velocity of caloric nystagmus, as compared with placebo. In the rotatory test, two TTS-scopolamine and dimenhydrinate reduced the vestibular gain significantly. No changes were observed in time constant. In the optokinetic test, all drugs tended to reduce the responses, but a statistically significant reduction was found only after two TTS-scopolamine. The results indicate that the drugs effective against motion sickness reduce the nystagmic response, which at least partly explains the mode of action of the drugs. The target organ of the drugs is presumably the vestibular nucleus, where vestibular and visual impulses are integrated to ensure optimal gain for vestibular orientation reflexes.

Acceleration↗

PubMedDate not supplied

The relationship of optokinetic nystagmus to pursuit eye movements, vestibular nystagmus and to saccades in humans. A clinical study.

The relationship of mean velocity of optokinetic nystagmus (OKN) to pursuit eye movements (PEM), to vestibular nystagmus and to voluntary saccades was analysed in 10 patients with peripheral vestibular lesions and in 30 patients with central vestibular lesions. PEM and vestibular nystagmus were significantly correlated to OKN, suggesting that a common neural pathway is used in the generation of these eye movements. Weak or no correlation was found between saccadic peak velocity and slow phase velocity of OKN. Using multiple linear regression analysis, it was found that 78.5% of the variation in the slow-phase velocity of OKN could be explained by a synthesis of PEM and vestibular test data. PEM test data were more powerful than those of vestibular nystagmus in deduction of OKN. The possible appearance of slow build-up of OKN could not be deduced from the reduction of PEM. Hence, the relationship between PEM and OKN in man is not a simple linear one, but is more complex.

Adolescent↗

PubMedDate not supplied

Velocity and asymmetry of optokinetic nystagmus in the evaluation of vestibular lesions.

Optokinetic nystagmus (OKN) at a constant stimulus velocity of 90 degrees/s was studied in 50 healthy subjects and three different groups of patients: 10 with vestibular neuritis (VN), 17 with unilateral infratentorial lesion (UI) and 13 patients with bilateral infratentorial lesion (BI). Among healthy subjects, OKN decreased with age in those over 42 and 44 years for maximum and mean velocity, respectively. The maximum velocity of OKN discriminated between the healthy subjects and the groups of patients rather better than did mean velocity of OKN. Asymmetry of either mean or maximum velocity contributed only marginally to correct group assignment. By subjecting test data on velocity and asymmetry variables to linear discriminant function analysis, 80% of subjects could be correctly classified as healthy/not healthy, and 64% assigned to the correct group according to diagnosis. Analysis of OKN data satisfactorily discriminated BI and UI patients from VN patients and healthy subjects, and is thus useful in assessing infratentorial vestibular lesions.

Adolescent↗

PubMedDate not supplied

Significance of pressor input from the human feet in anterior-posterior postural control. The effect of hypothermia on vibration-induced body-sway.

The importance to postural control of the mechanoreceptors of the soles was investigated in thirteen healthy subjects. Body-sway velocity was evaluated before and after exposing the subject's feet to hypothermia, and when calf muscles were exposed to vibration at frequencies between 20 and 100 Hz. Subjects were tested both with eyes open and closed. Body-sway velocity was found to increase significantly during hypothermia of the feet. The difference in body-sway between hypothermal and normothermal conditions was less prominent when the subject's eyes were open though the difference was significant in both cases. The present results indicate the importance of the mechanoreceptors of the soles to postural control and elucidate their interaction with compensatory visual input in maintaining postural control. These findings also suggest, that factors affecting pressor input should be taken into consideration when assessing patients with complaints of dysequilibrium.

Adult↗

PubMedDate not supplied

An expert system for the computer-aided diagnosis of dizziness and vertigo.

We have developed an expert system to assist in the diagnostic work-up of otoneurological cases. Our otoneurological expert system ONE takes advantage of both patient history and clinical measurement data in order to supply all possible information about the patient's symptoms and other findings. This paper presents ONE after its initial stage of development, which included tests with numerous patients.

Adult↗

PubMedDate not supplied

An essay on power of expert systems versus human expertise.

In connection with several recent studies of medical informatics, the usefulness and use of expert systems have been both criticized and defended. We have examined the issue of the inference power of expert systems compared to that of human experts. At an abstract level we have shown that there is no doubt that expert systems could successfully complement human experts within strictly limited and well-defined specialties, and actually be of reasonable aid in diagnosis, provided that the expert systems have been correctly and effectively elaborated. Also practical experiments were conducted with our recently implemented expert system.

Brain Diseases↗

PubMedDate not supplied

The use of hearing protectors among forest, shipyard and paper mill workers in Finland--a longitudinal study.

From 1953 to 1995 the usage rate of hearing protective devices (HPD) was tracked at a paper mill, a shipyard, and in selected areas of forestry work. For each work period, observations were made of HPD use among workers. In the paper mill, the usage rate increased steadily from 1965. In 1990, 39% of workers used HPDs full-time. At the shipyard, the usage rate remained low up to the mid-1980s, but thereafter the proportion of full-time users rose to 70%. A similar trend was noted in forest workers, with the full-time use at 97% by the 1990s. Due to the increased usage rate in all measured industries, the mean effective noise level at the ear has decreased to below 85 dB.

Cross-Sectional Studies↗

PubMedDate not supplied

Measurements of postural stability: development of a force platform and some excitation systems.

Technical data are given for the construction of a low cost transportable force platform to measure postural stability. The measuring elements in the platform are placed between two rigid metal plates to give information about the movements of the center point of force of a standing subject. The system utilizes a microcomputer for data collection, and data analysis routines are used to calculate the movement of the center point of force. Postural perturbation was excited with a vibrating platform, a low frequency noise source and a vibration stimulator for the calf muscles.

Amplifiers, Electronic↗

PubMedDate not supplied

Impulse noise and risk criteria.

Impulse noise causes evidently more severe hearing loss than steady state noise. The additional effect of occupational impulse noise on hearing has been shown to be from 5 to 12 dB at 4 kHz audiometric frequency. Reported cases for compensated for hearing loss are prevalent in occupations where noise is impulsive. For impulse noise two measurement methods have been proposed: the peak level method and energy evaluation method. The applicability of the peak level method is difficult as even the recurrent impulses have different time and frequency characteristics. Various national risk criteria differ from international risk criteria. In France the maximum A-weighted peak level is 135 dB, and in the United Kingdom the C-weighted peak sound pressure is limited to 200 Pa (140 dB). This criterion of unweighted 200 Pa (140 dB) is used in European Union (EU) directive 86/188 and ISO 1999-1990 regardless of the number of impulses. The American Conference of Governmental Industrial Hygienists (ACGIH) has recommended that no exposure in excess of a C-weighted peak sound pressure level of 140 dB should be permitted. At work places these norms do not cause any practical consequences since the impulses seldom exceed 140 dB peak level. In several occupations the impulses are so rapid that they contribute only a minimal amount to the energy content of noise. These impulses can damage the inner ear even though they cause reduced awareness of the hazard of noise. Based to the present knowledge it is evident that there is the inadequacy of the equal energy principle in modelling the risk for hearing loss. The hearing protectors attenuate industrial impulse noise effectively due to the high frequency contents of impulses. Directive regarding the exposure of workers to the risks arising from noise requires that in risk assessment attention should be paid also to impulsive noise. So far there is no valid method to combine steady state and impulse noise. A statistical method for the measurements of industrial impulse noise is needed to get a preferably single number for risk assessment. There is an urgent task to develop risk assessment method and risk criteria for impulsive noise to meet the requirements of the upcoming European Union noise directive.

Adult↗

PubMedDate not supplied

Reduction of gain and time constant of vestibulo-ocular reflex in man induced by diazepam and thiopental.

The effect of intravenous administration of two sedatives, diazepam (0.3 mg/kg) and thiopental (6.0 mg/kg), on the vestibulo-ocular reflex (VOR) in man was investigated on 9 volunteers. The VOR was evoked with a velocity step rotation test and gain and time constant of prerotatory and postrotatory nystagmus were measured. Both drugs reduced VOR gain. Diazepam-induced reduction lasted 8 h and thiopental-induced reduction 1 h. A reduction of the VOR time constant was found lasting about 1 h for both drugs, but with a tendency for the thiopental effect to last longer. These findings, not previously described in man, differ from what has been found in macaques and rabbits injected with diazepam. The reduction of gain and time constant were not correlated with the blood concentration of either drug. The present results suggest that in man the VOR gain and time constant are both reduced by different types of sedatives although with different time courses. On the basis of previously shown effect of alertness on the VOR, it is hypothesized that diazepam and thiopental, besides having a specific effect on central nervous system structures important to the VOR, also induce reduction of the VOR through a general sedation of the CNS.

Adult↗

PubMedDate not supplied

Eye movements in patients with speech dyspraxia.

Saccades, smooth pursuit and angular acceleration induced nystagmus were analysed quantitatively in 10 patients with speech dyspraxia. The saccades were less accurate, had a prolonged reaction time and showed a tendency to reduced peak velocity, though only contralateral to the lesion. Smooth pursuit was imparied, with a reduction in maximum velocity gain. The vestibular responses tended to be hyperactive, indicating facilitated brain-stem reflexes. The findings show that a lesion in the frontal eye field can produce various oculomotor disturbances, in which the triggering of eye movements and their control, and pacing of the various movement sequences are disturbed. In addition, anticipation of a movement pattern requiring volition may be greatly impaired.

Adult↗

PubMedDate not supplied

Vestibular neuronitis. A clinical and electro-oculographic analysis.

Thirty patients, primarily diagnosed as having vestibular neuronitis, were investigated with a test battery consisting of neuro-otological, neuro-ophthalmological, neurological examinations and electro-oculography. Initial routine examination failed to reveal involvement of structures outside the vestibular nerve, whereas neurological evaluation and analysis of the cerebrospinal fluid indicated an intrinsic central nervous system (CNS) disorder in 6 cases. The electro-oculographic analysis revealed abnormalities supporting a 'central' cause of the vertigo in 12 cases. Altogether 13 patients showed signs of a possible intrinsic CNS disorder. Consequently, although routine examination may indicate a diagnosis of vestibular neuronitis, the patient concerned frequently has signs of an intrinsic CNS disorder and not a disorder of the peripheral nerve.

Adult↗