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Biomedical subjects

O I Kolev

Publications and source records attributed to O I Kolev.

15 recordsLinked to original sources
PubMed2001

Postural reflexes evoked by tapping forehead and chest.

We investigated whether a tap with a reflex hammer to the forehead can elicit responses in the leg muscles and whether vestibular stimulation is the crucial prerequisite for eliciting these responses. We also measured the postural changes caused by the tap and by the compensatory, presumably reflex-like reactions of the subject. Tap-evoked activity of leg muscles was easily elicited during upright stance in normal subjects and was also seen in two subjects without vestibular function. The pattern of muscle activation clearly showed a counteraction to the tap-evoked perturbation of stance. Taps applied to the chest elicited similar reflexes. Since these two conditions imply a different activation of the vestibular apparatus, the vestibular input alone cannot account for the observed leg muscle reflexes. We suggest that multisensory reflex pathways that integrate vestibular and proprioceptive inputs account for these reflexes.

Adult↗
PubMed2000

The human vertical optokinetic afternystagmus and the effect of gravity during pitch tilt.

BACKGROUND: Findings concerning human vertical optokinetic afternystagmus (VOKAN) are often not consistent and in some cases even contradictory. METHOD: VOKAN was studied in nine normal subjects using corneo-retinal potential technique and an infrared video camera detection apparatus (ISCAN). VOKAN responses were measured at three angles of pitch head (and body) tilt: 0 degrees (upright), 90 degrees (supine) and 135 degrees (45 degrees below horizontal). The optokinetic stimulus was stripe movement with a velocity of 60 degrees/s. RESULTS: Upward slow phase velocity (SP-Up) VOKAN was evoked in 6/9 subjects (67%) at 0 degrees tilt and at 90 degrees tilt, and in 4/9 (44%) at 135 degrees tilt. Downward slow phase velocity (SP-Down) VOKAN was elicited in 3/9 subjects (33%) at 0 degrees tilt; in 2/9 subjects (22%) at 90 degrees tilt and in 0/9 subjects (0%) at 135 degrees tilt. CONCLUSION: The pitch tilt, as a gravity effect, influences significantly on the appearance and the duration of VOKAN.

Adult↗
PubMed1999

Central nervous system impairment in diabetic patients.

The aims of this study were to investigate the function of the central motor control system in interaction with the vestibular and auditory systems (measured by H-reflex changes in response to vestibular and acoustic stimulations) in diabetics without clinical data for CNS impairment, in order to establish whether the disease affects these CNS mechanisms; and to assess this approach in detecting subclinical CNS diabetic pathology. The results show the same mode of change of H-reflex amplitude in response to acoustic and vestibular stimulations in diabetics as in normal subjects. However the degree of facilitation and inhibition was significantly (p < 0.001) higher in diabetics which indicates subclinical CNS dysfunction. Therefore it was concluded that the test is useful in early diagnosis of the diabetic CNS impairment.

Acoustic Stimulation↗
PubMed1997

Cold caloric microcirculatory reflex disturbance in patients with Parkinson's disease.

The basal skin microcirculatory blood flow and its change in response to a cold caloric stimulus (cold water, 5 degrees C, exposure of one foot for 30 s) were investigated in nine patients with Parkinson's disease (PD) and nine normal subjects (controls). The results revealed a significant (p < 0.001) difference between the groups. In the controls there was a strong decrease in the red cell flux (RCF) on cold water exposure, while eight of the nine PD patients revealed no detectable change in RCF; in one patient only there was a less pronounced reaction. It was concluded that the regulation of the microcirculatory blood flow was affected in PD patients; the cold caloric reflex was attenuated or absent but there was no difference in the basal microcirculatory blood flow compared to normal subjects.

Aged↗
PubMed1997

Responses in skin microcirculation to vestibular stimulation before and during motion sickness.

BACKGROUND: Observation of physiological changes during motion sickness is required to quantify the degree of sickness. The review of the literature does not show unifying results. An objective symptom of motion sickness is facial pallor. It reflects changes in skin microcirculation which have not been measured so far. METHODS: Eleven healthy volunteers susceptible to motion sickness were subjected to eccentric vertical axis rotation. The dynamics and the correspondence of the changes in skin blood flow in two segments, forehead and finger, were measured by laser Doppler flowmeter. RESULTS AND CONCLUSIONS: The difference in the microcirculatory skin blood flow across the phases of motion sickness is significant for the forehead but not for the fingertip: the established dynamics of the forehead blood flow during motion sickness will be of benefit in quantifying the degree of sickness; there is no correlation between the blood flow changes in both measured areas; the rhythmic blood flow fluctuation increases during motion sickness; there is a difference between the blood flow responses to vestibular stimulation before the appearance of motion sickness and in the course of the sickness. Laser Doppler flowmetry is a reliable method in quantifying the degree of motion sickness.

Adult↗
PubMed1997

Vertical optokinetic nystagmus and after-responses during backward tilt.

METHOD: Vertical optokinetic nystagmus (VOKN) and after-responses were detected in nine subjects using the corneo-retinal potential (CRP) technique and an infrared video camera detection apparatus (ISCAN) simultaneously. The ISCAN method produced a much smaller inter-subject variability, a higher linear regression coefficient (0.94) when vertical eye position was regressed against vertical target position (+/- 30 degrees, 5 degrees increments). Detected by ISCAN, VOKN responses were measured at 3 angles of pitch head (and body) tilt: upright (0 degrees), supine (90 degrees), and declined 45 degrees below horizontal (135 degrees). Two stripe velocities (40 degrees.s-1 and 60 degrees.s-1) were used. RESULTS: In six of the nine subjects (67%) and in 40/54 conditions (74%) for all subjects, upward (slow phase velocity up) VOKN gain was greater than downward VOKN gain for both stripe velocities at all tilt angles. The gain for both upward and downward VOKN decreased as stripe velocity increased from 40-60 degrees.s-1, which suggests that both upward and downward VOKN systems were starting to saturate. Across subjects, a mean up-down asymmetry index, I, increased monotonically as the subjects declined. The slope of the monotonic function was greater for 60 degrees.s-1 stripe velocity than for 40 degrees.s-1 stripe velocity. The mean of all subjects' individual asymmetry ratios (ASYM) also increased as tilt increased but the slope of the best fitted regression line was not statistically significantly different from zero (p > 0.05). CONCLUSION: Optokinetic after-responses observed in the present study were of two types: 1) resetting of the eye by a drift, with nystagmus superimposed, from a beating field (eye position) that occurred during optokinetic stimulation; and 2) resetting of the eye without nystagmus superimposed. Upward VOKN produced the greatest number of after-responses. The beating field of VOKN was not correlated with pitch tilt.

Adult↗
PubMed1995

Vestibular and auditory influences on segmental motoneuron excitability--a comparative study.

This study aimed to investigate the vestibular and acoustic influences on segmental motoneuron excitability in the same normals in order to compare the effects of both sensory systems. The results show that both systems exert similar influences on H-reflex in the same subjects. These indicate similarities in the function of motor control and suggest common final pathways of the vestibular and auditory activity to the segmental motoneuron. The alternative effect, facilitation or inhibition, of acoustic and vestibular stimuli on H-reflex is devoted to processing of the labyrinthine activation in the brainstem reticular formation, or to the state of the spinal interneurons.

Acoustic Stimulation↗
PubMed1995

Influence of intense sound stimuli on skin microcirculation.

Sound influences not only the organ of hearing but also other systems including the circulation. The purpose of the present study was to investigate the effect of strong sound on the skin microcirculation of the palmar area of the hand and of the plantar area of the foot, which are areas of dense microvasculature and rich sympathetic innervation. The laser Doppler technique was used for measuring cutaneous red cell flux (RCF). Eighteen normal subjects were studied. The results indicate that a pure tone sound of 1500 Hz, with an intensity of 100 dBA and duration 5 s, applied by earphones caused a significant decrease in RCF in 14 out of 18 subjects in the finger but not in the foot skin. A higher intensity (110 dBA) tone caused a stronger decrease of RCF in the finger. The latency and the duration of the reaction showed a dependence on the intensity of the sound, i.e. the reaction to the stronger stimulus was of shorter latency (p < 0.01) and longer duration (p < 0.05). The duration of the reaction did not show significant change when a longer stimulus of 30 s was applied. Repetitive stimuli evoked habituation (p < 0.05).

Acoustic Stimulation↗
PubMed1992

Vestibular and cardiac reactions to open-sea exposure.

Nineteen healthy male volunteers were exposed to a 72-hour open-sea stay in a lifeboat in order to study whether randomized protracted stimulation of different parts of the vestibular system would cause a decrease of vestibular activity as assessed by unilateral calorization of the horizontal vestibular canal. The influence on the autonomic nervous system was investigated by calculating the heart rate by the R-R intervals at ECG at rest and at maximum speed of the nystagmus slow phase. Calorization and ECG investigations were performed immediately before and after the open-sea exposure. Seven healthy males who were not exposed to the open sea served as controls. They were investigated in the same manner as the test subjects, that is twice, 3 days apart. All test subjects experienced seasickness. After the sea stay, the caloric nystagmus response had decreased significantly more than in the controls. In 7 subjects with the most pronounced vestibular habituation, the resting heart rate decreased significantly after the sea exposure. Caloric stimulation of the labyrinths did not cause any specific change of the heart rate. It is concluded that prolonged open-sea exposure causes vestibular habituation to unilateral labyrinthine stimulation. Furthermore, there are some indications that the mechanism that is responsible for vestibular habituation to some extent influences the function of the autonomic nervous system, resulting in a decreased pulse rate.

Adolescent↗
PubMedDate not supplied

The directions of nystagmus and apparent self-motion evoked by caloric tests and angular accelerations.

PURPOSE: To further investigate the direction of (I) nystagmus and (II) self-motion perception induced by two stimuli: (a) caloric vestibular stimulations and (b) a sudden halt during vertical axis rotation. SUBJECTS AND METHODS: Twelve normal humans received caloric stimulation at 44 degrees C, 30 degrees C, and 20 degrees C while in a supine position with the head inclined 30 degrees upwards. In a second test they were rotated around the vertical axis with the head randomly placed in two positions: tilted 30 degrees forward or tilted 60 degrees backward, at a constant velocity of 90 degrees /sec for 2 minutes and then suddenly stopped. After both tests they were asked to describe their sensations of self-motion. Eye movements were recorded with an infrared video-technique. RESULTS: Caloric stimulation evoked only horizontal nystagmus in all subjects and induced a non-uniform complex perception of angular in frontal and transverse planes (the former dominated) and linear movements along the antero-posterior axis (sinking dominated) of the subject's coordinates. The self-motion was felt with the whole body or with a part of the body. Generally the perception evoked by cold (30 degrees C) and warm (44 degrees C) calorics was similar, although there were some differences. The stronger stimulus (20 degrees C) evoked not only quantitative but also qualitative differences in perception. The abrupt halt of rotation induced self-motion perception and nystagmus only in the plane of rotation. The self-motion was felt with the whole body. CONCLUSION: There was no difference in the nystagmus evoked by caloric stimulation and a sudden halt of vertical axis rotation (in head positions to stimulate the horizontal canals); however, the two stimuli evoked different perceptions of self-motion. Calorics provoked the sensation of self-rotation in the frontal plane and linear motion, which did not correspond to the direction of nystagmus, as well as arcing and a reset phenomenon during angular and linear self-motion, caloric-induced self-motion can be felt predominantly or only with a part of the body, depending on the self-motion intensity. The findings indicate that, unlike the self-motion induced by sudden halt of vertical axis rotation, several mechanisms take part in generating caloric-induced self-motion.

Acceleration↗
PubMedDate not supplied

Visual hallucinations evoked by caloric vestibular stimulation in normal humans.

This study describes a hitherto unknown phenomenon in healthy humans: visual hallucinations evoked by caloric vestibular stimulation. The hallucinations are of elementary type. The following quantitative and qualitative characteristics of the hallucinatory images were measured: latency, duration, location in the visual field, relation to the provoked vertigo, colour of the hallucinatory image and the background, number, size, shape, distance from the eyes, and motion. Two mechanisms are proposed to explain the genesis of these hallucinations. One mechanism is direct: change in the spontaneous activity of the visual system in several levels; the other mechanism is indirect: transient haemodynamic disturbance in the visual system.

Adolescent↗
PubMedDate not supplied

Changes in the gastrointestinal electric pattern to motion sickness in susceptibles and insusceptibles during fasting.

The cardinal symptoms of motion sickness occur in the gastrointestinal system. This study sought to investigate the influence of sickness-provoking motion stimuli on the interdigestive migrating electric complex (IDMEC) of the gastro-intestinal system. Thirteen susceptibles and 14 insusceptibles to motion sickness were subjected to intralumenal recording before and after caloric vestibular stimulations. Motion sickness developed in all subjects. The results indicate that there are no significant differences in the IDMECs of susceptibles and insusceptibles in a state of rest; vestibular stimulation changes the duration of IDMEC phases (P < 0.05 and P < 0.01); IDMEC changes differ slightly between susceptibles and insusceptibles; motion stimuli induce simultaneous nonpropulsive spike activity, which is more frequent in susceptibles (P < 0.01); vestibular stimulation applied during phase III of IDMEC does not provoke vomiting in susceptibles.

Adult↗
PubMedDate not supplied

Changes in interdigestive migrating electric complex induced by motion sickness.

This study aimed to investigate, by means of an intralumenal recording technique, the influence of motion sickness on the interdigestive migrating electric complex (IDMEC) of the gastrointestinal system of susceptible subjects. The results indicate that vestibular stimulations significantly change the duration of IDMEC phases (p < 0.05 and p < 0.01): phase I in both the stomach and duodenum decreases, the duration of phase II and phase III is changed differently in the stomach and in the duodenum.

Adult↗
PubMedDate not supplied

Characteristics of the autonomic response in the visually evoked reflex in humans.

This study aimed (a) to investigate the effect of the visuogenic reflex on the skin microcirculation of the hand and foot, and (b) to compare it to that evoked by thermal stimuli. Fifteen volunteers took part in this study. The laser Doppler technique was used for measuring blood flow (BF). The results showed that a flash of light with a duration of 300 ms caused a significant decrease in BF (mean 38.4 +/- 14.8%) in 10 out of 15 subjects in the hand but not in the foot. The latency was 5.05 +/- 0.7 s and the duration 7.2 +/- 1.8 s. The reaction did not show a significant change when a longer stimulus of 14 s was applied. Repetitive stimuli evoked habituation (p < 0.01). There is significant difference (p < 0.01) between autonomic responses to visuogenic and to calorically evoked reflexes.

Adolescent↗