Biomedical subjects

Arne Tribukait

Publications and source records attributed to Arne Tribukait.

15 recordsLinked to original sources

PubMed2006

The human sense of the head's polarity is influenced by changes in the magnitude of gravity.

The present investigation concerns the integrity of a primary mental function, the egocentric frame of reference and the sense of polarity of one's own head. The visually perceived eye level (VPEL) and the subjective antero-posterior axis of the head were measured by means of a visual indicator in darkness during two stimulus conditions: static pitch (sagittal-plane) tilting in the 1-g environment and gondola centrifugation (2G). It is demonstrated that an increase in the magnitude of the gravitoinertial (G) force, acting in the direction of the head and body long (z) axis, causes a substantial change not only in the VPEL but also in the perceived direction of the antero-posterior axis of the head.

Adult↗

PubMed2006

Motion sickness increases the risk of accidental hypothermia.

Motion sickness (MS) has been found to increase body-core cooling during immersion in 28 degrees C water, an effect ascribed to attenuation of the cold-induced peripheral vasoconstriction (Mekjavic et al. in J Physiol 535(2):619-623, 2001). The present study tested the hypothesis that a more profound cold stimulus would override the MS effect on peripheral vasoconstriction and hence on the core cooling rate. Eleven healthy subjects underwent two separate head-out immersions in 15 degrees C water. In the control trial (CN), subjects were immersed after baseline measurements. In the MS-trial, subjects were rendered motion sick prior to immersion, by using a rotating chair in combination with a regimen of standardized head movements. During immersion in the MS-trial, subjects were exposed to an optokinetic stimulus (rotating drum). At 5-min intervals subjects rated their temperature perception, thermal comfort and MS discomfort. During immersion mean skin temperature, rectal temperature, the difference in temperature between the non-immersed right forearm and 3rd finger of the right hand (DeltaTff), oxygen uptake and heart rate were recorded. In the MS-trial, rectal temperature decreased substantially faster (33%, P < 0.01). Also, the DeltaTff response, an index of peripheral vasomotor tone, as well as the oxygen uptake, indicative of the shivering response, were significantly attenuated (P < 0.01 and P < 0.001, respectively) by MS. Thus, MS may predispose individuals to hypothermia by enhancing heat loss and attenuating heat production. This might have significant implications for survival in maritime accidents.

Adult↗

PubMed2006

Semicircular canal influence on the visually perceived eye level during gondola centrifugation.

BACKGROUND: When exposed to an increased gravitoinertial force, a subject, sitting upright, experiences an illusion of being tilted backwards. This so-called "G-excess illusion" is generally ascribed to the otolith organs. The present study aimed at elucidating how stimulation of the semicircular canals may influence the development of the G-excess illusion. METHODS: The visually perceived eye level (VPEL) was measured by means of a visual indicator in a large swing-out gondola centrifuge. The roll position of the gondola was controlled so that the subject was always upright with respect to the resultant vector of the Earth gravity force and the centrifugal force. Subjects (n = 8) underwent four centrifuge runs (2 G, 5 min), sitting in different positions, i.e., heading forwards, backwards, centripetally, and centrifugally. RESULTS: At the 2-G plateau there was a depression of the VPEL which was initially small but increased with a time constant of 90 +/- 30 s toward an asymptote of -22.0 +/- 6.9 degrees (mean and 1 SD for all positions). The initial depression was significantly smaller for the centripetal (+2.0 +/- 14.6 degrees) than for the centrifugal position (-14.5 +/- 10.4 degrees). However, there was no difference between the forward (-5.6 +/- 4.8 degrees) and backward (-4.0 +/- 4.5 degrees) positions. Initially after deceleration of the centrifuge to 1 G there was still a significant depression of the VPEL (-13.5 +/- 7.9 degrees), decreasing with a time constant of 100 +/- 46 s. CONCLUSIONS: The considerable delay in the otolith-mediated changes in the VPEL is interpreted as due to the absence of adequate canal information for a change in head position. The difference in VPEL between the centripetal and centrifugal positions suggests an influence of canal change-in-position information. However, pitch-plane angular velocity, being of considerable magnitude but of opposite sign for the forward and backward positions, did not influence the VPEL.

Acceleration↗

PubMed2006

Roll-tilt perception during gondola centrifugation: influence of steady-state acceleration (G) level.

BACKGROUND: Spatial disorientation is an important problem in aviation. The significance of the C level for illusions elicited from the semicircular canals is not clear. The aim of the present investigation was to elucidate how a gravitoinertial force, acting in parallel with the subject's long (z) axis, may influence the magnitude and persistence of canal-induced tilts of the subjective visual horizontal (SVH) present after acceleration in a gondola centrifuge. METHODS: The SVH was measured by means of an adjustable luminous line in darkness. Two series of experiments were performed. In series 1, the SVH was measured in 13 subjects at 1.1 G, 1.7 G, and 2.5 G. In series 2, it was measured in 8 subjects at 2.5 G and 4.5 G. RESULTS: After acceleration of the centrifuge the SVH was tilted relative to the gravitoinertial horizontal. The direction of tilt was compensatory to the gondola inclination. In series 1 the initial SVH tilt was: 16.2 +/- 7.0 degrees (1.1 G), 24.2 +/- 10.2 degrees (1.7 G), and 27.1 +/- 13.9 degrees (2.5 G). In series 2 it was: 27.6 +/- 14.6 degrees (2.5 G), and 31.2 +/- 18.8 degrees (4.5 G). The gain for this response, defined as the ratio between the initial tilt and the inclination of the gondola, was: 0.65 +/- 0.28 (1.1 G), 0.45 +/- 0.19(1.7 G), 0.41 +/- 0.21 (2.5 G) (series 1); and 0.42 +/- 0.22 (2.5 G), and 0.40 +/- 0.24 (4.5 G) (series 2). Thus, an increase from 1.1 G to 1.7 G caused a reduction in the gain, but at G levels beyond 1.7 G there was no further decrease. The time constant for exponential decay tended to increase with the G level. It was: 61 +/- 31 s (1.1 G), 84 +/- 36 s (1.7 G), 89 +/- 42 s (2.5 G) (series 1); and 67 +/- 49 s (2.5 G), and 101 +/- 73 s (4.5 G) (series 2). CONCLUSION: It appears that otolithic stimulation via an increased gravitoinertial force vector, acting in parallel with the head and body long axis, does not substantially influence the magnitude of the canal-mediated sensation of roll-tilt after acceleration in a swing-out gondola centrifuge. Nor does it reduce the duration of this sensation.

Acceleration↗

PubMed2006

Subjective visual horizontal in the upright posture and asymmetry in roll-tilt perception: independent measures of vestibular function.

The subjective visual horizontal (SVH) was measured in the upright position and at 10, 20, and 30 degrees of head and body tilt to the right and left. Normal subjects (n=25) were tested on two separate occasions with an interval of 1-14 days. Test variables considered were the SVH in the upright position, the perception of tilt to the right and left, calculated on the basis of the SVH in the upright and tilted positions, and the asymmetry in tilt perception. There was no correlation between the perception of tilt to the right and to the left r=0.10). Neither was there any correlation between the SVH in the upright position, representing a resting asymmetry, and the asymmetry in tilt perception, i.e. the response asymmetry (r=0.17). However, for each variable, there was a high correspondence between data obtained at test and retest (r ranged from 0.68 to 0.89, p<0.001), suggesting that the independence between variables is not due to noise. Findings are discussed taking into consideration the possible roles of otoliths and semicircular canals in the formation of the SVH. In an attempt to explain the independence between the two measures of asymmetry it is hypothesized that while the otoliths must be essential for the perception of static lateral tilt, the SVH in the upright position to a considerable degree reflects semicircular canal function.

Adult↗

PubMed2005

Morphological characteristics of the human macula sacculi.

The surface morphology of 20 human maculae sacculi is presented. Individual data on the total area, shape and the relative area of the pars superior are given. The mean area of 14 adult maculae was (mean +/- SD) 2.35 +/- 0.31 mm2. The ratio between the length and width of the macula was 2.54 +/- 0.28. The pars superior was significantly larger than the pars inferior. The percentage of pars superior was 56.4 +/- 4.7. As regards the shape of the macula, there was a large interindividual variability. The findings are discussed, taking into consideration comparative anatomy as well as spatial orientation.

Acoustic Maculae↗

PubMed2005

Drift in ocular torsion during sustained head tilt.

PURPOSE: A head tilt towards the shoulder (roll) induces an ocular counter-roll (OCR), i.e. torsion in the opposite direction to the head. How this counter-rolled position is maintained during a static head tilt is in debate. In a previous study, we reported an OCR-increasing drift subsequent to the head tilt. This finding is in contrast to other reports where no such response was found. The primary aim of this study was to repeat the experiment during a prolonged head-tilt test and to describe the OCR characteristics. A secondary aim was to investigate the influence of spatial visual cues on OCR. METHODS: Five male subjects performed a head tilt (30 degrees ) towards the right shoulder while the eye position was recorded during a 10-minute interval. In test 1, the subjects viewed a target with no cues for spatial orientation. The same head-tilt paradigm was repeated in test 2 with a visual target with spatial cues. Two samples of data were extracted from the start and the end of the recordings for statistical analysis. RESULTS: Subsequent to the head tilt, a slow OCR-increasing drift in the opposite direction to the head roll was found in all subjects. On average, this drift lasted for 30 sec (+/- 5) in test 1 and for 55 sec (+/- 18) in test 2. The drift was then found to change its direction, i.e. the eyes were rotated in the same direction as the head roll. When measured after 10 minutes, the OCR was significantly decreased. CONCLUSIONS: The OCR during static head tilt is not constant. During the first minute there is a gradually increasing OCR. Thereafter, the amplitude of the OCR decreases gradually. These changes are influenced to some extent by spatial visual cues. Possible mechanisms are adaptive responses in otolithic afferents as well as central nervous memory functions related to the semicircular canal system.

Adult↗

PubMed2005

Drift in ocular counterrolling during static head tilt.

A decreasing drift of the counter-rolled eye position (OCR) during head tilt was recently described. The underlying mechanism is not known. OCR in eleven healthy subjects was recorded (Search coil, Skalar) during a head tilt paradigm in two test conditions. The head was tilted with a velocity below (test 1) and above (test 2) detection threshold for the semicircular canals (SC) and held static for eight minutes. A significant drift of OCR was revealed in test 2 (P = .0006, ANOVA) and close to significant in test 1 (P = .07). No statistical difference was found between the two test conditions. The results suggest that the OCR drift was not caused by the SC complex merely.

Adaptation, Physiological↗

PubMed2005

Perception of the head transversal plane and the subjective horizontal during gondola centrifugation.

The subjective visual horizontal (SVH) and the subjective head transversal plane (STP) were measured by means of an adjustable luminous line in darkness during centrifuging. Subjects (N = 10) were seated upright, facing forward in a swing-out gondola. After acceleration of the centrifuge to 2G (vectorial sum of the earth's gravity and the centrifugal force; gondola inclination 60 degrees), subjects had to set the line either so that it was perceived as gravitoinertially horizontal (SVH) or so that it was perceived as parallel with the transversal ("horizontal") plane of the head (STP). Initially after acceleration, the SVH was tilted with respect to the gravitoinertial horizontal of the gondola (M = 16.6 degrees). This tilt was compensatory with respect to the gondola inclination. However, the STP was tilted in the opposite direction (M = 12.4 degrees), which might suggest a vestibular-induced distortion of the mental representation of one's own body. Similar results were obtained when measuring the subjective visual vertical (SVV) and the subjective midsagittal plane (SSP) in 5 subjects. The perceived roll angle (obtained as SVH-STP or SVV-SSP) was considerably larger than had previously been reported. Time constants for exponential decay of the tilt of the SVH or SVV were often 2-3 min, indicating a memory for semicircular canal information on changes in head orientation--a position-storage mechanism.

Adult↗

PubMed2005

On the role of otoliths and semicircular canals in spatial orientation: Dynamics of the visually perceived eye level during gondola centrifugation.

The visually perceived eye level (VPEL) was measured during gondola centrifugation. Subjects (N = 11) were seated upright, facing motion in a swing-out gondola The head was adjusted so that Reid's baseline was tilted 10 degrees anterior end up. The subjects were requested to adjust the position of a small luminous dot so that it was perceived as gravitationally at eye level. In the 1-g environment, the VPEL was a few degrees below the true gravitational eye level (M = -1.75 degrees, SD = 1.90 degrees). After rapid acceleration of the centrifuge to 2 G (vectorial sum of the earth gravity force and the centrifugal force), there was an exponentially increasing depression of the VPEL. The initial value was -6.4 degrees +/- 5.2 degrees. During 10 min at 2 G, the VPEL approached an asymptotic value of -24.8 degrees +/- 5.4 degrees. The time constant showed a large interindividual variability, ranging from 59 to 1,000 sec (M = 261 sec, median = 147 sec). The findings are discussed, taking into consideration otolith-semicircular-canal interaction, as well as memory functions of the vestibular system.

Adult↗

PubMed2005

Semicircular canal contribution to the perception of roll tilt during gondola centrifugation.

BACKGROUND: Spatial disorientation is an important problem in aviation. The mechanisms behind the sensation of roll tilt during coordinated turns are not well known. The present study aimed at elucidating what kind of semicircular canal information might cause tilts of the subjective horizontal during gondola centrifugation. METHODS: The subjective visual horizontal (SVH) was measured by means of an adjustable visual line in darkness. Subjects (n = 8) underwent four centrifuge runs (2 G, 5 min), sitting in different positions, i.e., heading forwards, backwards, centripetally, and centrifugally. The roll position of the gondola (60 degrees at 2 G) was controlled so that the subject was always upright with respect to the resultant gravitoinertial force vector. Thus, the semicircular-canal stimulus components in yaw, pitch, and roll were varied to some extent independently of each other. RESULTS: For the forward position the SVH was substantially tilted in a direction compensatory with respect to the inclination of the gondola. For the backward position there was also a tendency to a compensatory SVH tilt. In all subjects the magnitude of tilt was larger for the forward position than for the backward. The group means were +20.9 +/- 8.4 degrees and -6.9 +/- 10.5 degrees (positive sign designates a clockwise deviation of the SVH), p < 0.001, n = 8. There were no significant SVH tilts for the centripetal (+6.4 +/- 10.7 degrees) and centrifugal (+2.1 +/- 4.8 degrees) positions. The effects of deceleration of the centrifuge were very small for all positions. CONCLUSION: These findings suggest that the substantial SVH tilt after acceleration heading forwards is not directly related to any single component of semicircular canal stimulation but depends on the ability of the brain to expediently process complex stimulus patterns.

Adult↗

PubMed2004

Function of semicircular canals, utricles and saccules in deaf children.

OBJECTIVE: To study vestibular function in deaf children. MATERIAL AND METHODS: In 36 deaf children the function of the semicircular canals, saccules and utricles was measured by means of caloric testing, recordings of vestibular-evoked myogenic potentials (VEMPs) and measurements of the subjective visual horizontal (SVH) at different body tilts, respectively. RESULTS: In total, 30% of subjects had caloric hypo- or areflexia and 24% had a caloric asymmetry. VEMPs were weak or absent bilaterally in 22% of cases, and asymmetric in 19%. Regarding the utricle, 17% of subjects had a pathologically reduced perception of roll tilt to both sides and 25% had an asymmetry. In total, 30% of subjects were pathologic in all 3 tests and 30% were completely normal. Semicircular canal function correlated best with the function of the saccule. If hearing was better than 90 dB (pure-tone average of 0.5, 1.0 and 2.0 kHz) vestibular function was often normal. For hearing levels of 100-120 dB, otolith function declined significantly. CONCLUSIONS: Vestibular function tends to be preserved up to a point where hearing is nearly extinct. Hearing level correlates more closely with otolith function, especially that of the utricle, than with semicircular canal function.

Adolescent↗

PubMed2003

Human vestibular memory studied via measurement of the subjective horizontal during gondola centrifugation.

Measurements of the subjective visual horizontal (SVH) were made in a large swing-out gondola centrifuge. Rotation of the centrifuge was anti-clockwise, as seen from above. Test subjects were seated upright in the gondola, facing forwards. In front of the subject, at a straight-ahead eye-level position, there was a narrow luminous line, which could be rotated, by remote control, about the visual axis. At gravitoinertial force levels of 1.1-1.3G the subjects were asked to indicate, by repeatedly setting the line in darkness, what they perceived as horizontal (the SVH). During gondola centrifugation, the head and body length axis is always parallel with the resultant gravitoinertial force vector (vectorial sum of earth gravity force and the centrifugal force) i.e., the horizontal plane of the head or body does not change with respect to the gravitoinertial horizontal. Hence, the otolith organs, as well as the somatosensory system, continually signal upright position. However, the swing-out of the gondola during acceleration of the centrifuge (25 degrees at 1.1G) is a roll (frontal plane) change-in-position stimulus to the vertical semicircular canals, thus creating an otolith-semicircular canal conflict. After acceleration of the centrifuge, the SVH was initially tilted up to 20 degrees to the right relative to the gravitoinertial horizontal. Since there was no roll-tilt stimulus to gravity receptors, this SVH tilt must be related to stimulation of the semicircular canals. However, it decayed much more slowly than any known effects of angular-velocity stimulation of the semicircular canals. The decay was bi-phasic with two time constants, the smaller in the region of 1-2 min, the other being too large to be reliably estimated on the basis of data collected during only 10 min. This persistence of the SVH tilt suggests a memory for angular changes in roll head position detected by the semicircular canals-a position-storage mechanism. Further, the SVH seems to be dependent on two different mechanisms related to semicircular canal stimulation.

Adult↗

PubMed2003

Vestibular evoked myogenic potentials in response to skull taps for patients with vestibular neuritis.

In recent years it has been demonstrated that loud clicks generate short latency vestibular evoked myogenic potentials (VEMP). It has also been demonstrated that skull tap stimulation evokes similar VEMP. In the present study, the differences between the click-induced and the skull-tap induced VEMP were studied in 18 patients at onset of vestibular neuritis. Gentle skull taps were delivered manually above each ear on the side of the skull and on the forehead midline. The muscular responses were recorded over both sternocleidomastoid muscles using skin electrodes. Abnormal skull tap VEMP were found in the majority of the patients (10/18, 56%). However, only 4/18 (22%) showed asymmetry in the click-induced VEMP. The high percentage of abnormal skull tap VEMP might suggest that this response is not only dependent on the inferior division of the vestibular nerve, because the inferior division of this nerve is usually spared in vestibular neuritis. Moreover, the patients with abnormal skull tap VEMP differed from those with normal VEMP in their settings of the subjective visual horizontal with static head tilt in the roll plane. This might suggest that skull tap VEMP are (also) related to utricular function.

Acoustic Stimulation↗

PubMed2002

Vestibular evoked myogenic potentials in response to laterally directed skull taps.

In recent years it has been demonstrated that loud clicks generate short latency vestibular evoked myogenic potentials (VEMP). It has also been demonstrated that midline forehead skull tap stimulation evokes similar VEMP. In the present study, the influence of skull tap direction on VEMP was studied in 13 normal subjects and in five patients with unilateral vestibular loss. Gentle skull taps were delivered manually above each ear on the side of the skull. The muscular responses were recorded over both sternocleidomastoid muscles using skin electrodes. Among the normals, laterally directed skull taps evoked "coordinated contraction-relaxation responses", i.e. skull taps on one side evoked a negative-positive "inverted" VEMP on that side and a positive-negative "normal" VEMP on the other side. Among patients with unilateral vestibular function loss, skull taps above the lesioned ear evoked similar coordinated contraction-relaxation responses. However, skull taps above the healthy ear did not evoke that type of response. These findings suggest that laterally directed skull taps activate mainly the contralateral labyrinth.

Acoustic Stimulation↗