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Biomedical subjects

O I Kolev

Publications and source records attributed to O I Kolev.

11 recordsLinked to original sources
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

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↗