Biomedical subjects

T Jarchow

Publications and source records attributed to T Jarchow.

4 recordsLinked to original sources

PubMed2003

Perceived horizontal body position in healthy and paraplegic subjects: effect of centrifugation.

The perception of body position is mainly mediated by otolith information and visual cues. It has been shown, however, that proprioceptive sources are also involved. To distinguish between the contributions of the vestibular and nonvisual extra-vestibular information to graviception, we tested the effects of a stimulus that leaves the vestibular input unchanged but modifies the information from sense organs located more caudal along the trunk. This was achieved by bringing subjects into a horizontal ear-down position and rotating them around an earth-vertical axis that coincided with the interaural axis. In this paradigm, through centrifugal force, the stimulation of the vestibular and the putative extravestibular graviceptive organs in the body becomes dissociated. Healthy subjects (n = 14) and paraplegic patients with lesions between T4 and T8 (n = 7) adjusted themselves to the perceived horizontal right-ear down body position under two conditions: one with constant velocity rotation (ROT, velocity =120 degrees /s) around the earth-vertical axis of the turntable, and one without rotation (BASE). Among healthy subjects, the individual differences between BASE and ROT varied widely in both the feet-up or feet-down direction. In contrast, adjustments in paraplegic patients during ROT were always in the feet-down direction compared with BASE. A model with two extravestibular graviceptive sensors could explain our results: one sensor is located rostral to T4, and the other is caudal to T8. A load on the rostral graviceptor is interpreted as a tilt of the body in the feet-up direction and shifts the adjustments of perceived body position feet-down; a load on the caudal receptor is interpreted as a tilt in the feet-down direction and shifts the perceived body position feet-up. During ROT, healthy subjects solve the discrepant inputs of both extravestibular graviceptors in a highly variable manner, while paraplegic subjects show less variability because they are restricted to only the rostral graviceptor.

Adult↗

PubMed1999

The effect of water immersion on postural and visual orientation.

BACKGROUND: The subjective visual vertical (SVV) and the subjective horizontal body position (SHP) perceptually dissociate and may therefore be based on a differential participation of graviceptive references. This study focuses primarily on the effects that are caused by an alteration of somatosensory information on the skin surface induced by water immersion. We expect the SHP to be selectively affected during water immersion while the SVV remains unchanged. METHODS: Four diving subjects took part in the experiments. An underwater apparatus (UWA) allowed for a determination of the SHP and the SVV during water immersion. On land, the adjustments of the SHP and SVV were made in a tilt chair apparatus (TCA). RESULTS: Three of four subjects show a significant head-upward shift between 7 degrees and 20.3 degrees of the SHP when tested under water (p < 0.02). The adjustments of the SVV were compared within corresponding physical roll inclinations and did not differ with the exception of one subject who showed a significant change of the SVV toward the physical vertical. CONCLUSIONS: The SHP and SVV perceptually dissociate on land and, as we determined for the first time, also under water. Water immersion leads to an increased roll tilt perception as measured by the SHP. However, a systematic influence on SVV could not be observed under water thus supporting the assumption that the SVV and SHP depend on gravitoreceptive information that is selectively altered during water immersion.

Adult↗

PubMed1996

Perceived body position and the visual horizontal.

This contribution examines the relation between the subjective visual vertical, the subjective visual horizontal, and the perceived body position of human subjects. Firmly fixed on a tiltable chair with head and torso restrained, 11 healthy subjects were rolled sideways and indicated their subjective horizontal body position. In these positions the subjects were also asked to adjust a luminous line alternately to the vertical and to the horizontal. The adjustments of the subjective horizontal body position cluster around a mean of 96.3 degrees with a remarkably broad range (SD: 19.7 degrees). In the subjective horizontal body position, the luminous line does not appear horizontal when in line with one's own spinal axis. It is set further down by 27.4 degrees on average and, therefore, perpendicular to the subjective visual vertical. This finding supports the idea that the judgement of the own body position and the judgement of the orientation of a seen object respective to gravity are based on different references. Contradictory to other investigations [23,24], is the empirical fact that the individual subjects were not able to adjust the horizontal body position with the reported accuracy (range of mean adjustments 77.5 to 117.6 degrees).

Adult↗

PubMed1996

Can a unilateral loss of otolithic function be clinically detected by assessment of the subjective visual vertical?

Asymmetries in the settings of the subjective visual vertical after unilateral vestibular neurectomy during eccentric centrifugation [3] might provide a clinical test for unilateral otolithic function. This study investigates whether these asymmetries can also be revealed by a technically much easier practicable roll tilt of the subject relative to gravity instead of a roll tilt of the gravitational force on a human centrifuge. Twenty-seven normal subjects and 13 patients before surgery indicated verticality very accurately in the upright position. In 26 degrees roll positions (subjects seated on a slanted chair), they were only slightly more variable with no asymmetries larger than 5.3 and 7.8 degrees in normals and preoperative patients, respectively, between the roll positions toward the healthy and toward the affected ear. One week after surgical unilateral vestibular deafferentation, there was a consistent shift (mean 11.9 degrees) of the subjective vertical toward the affected ear in all patients and in all body positions. When the settings in the two roll tilt positions were referred to the setting in upright position, the group means of the patients were symmetrical although single subjects revealed asymmetries up to 22.4 degrees. Only one of four patients who were tested also during eccentric rotation revealed an important asymmetry with decreased sensitivity for tilts of the gravitational vector toward the affected ear. Measuring the subjective visual vertical assesses only asymmetrical tonic otolithic input, while a simple clinical test for unilateral otolithic sensitivity still has to be found.

Adolescent↗