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Biomedical subjects

Per-Anders Fransson

Publications and source records attributed to Per-Anders Fransson.

10 recordsLinked to original sources
PubMed2006

Subjective visual tilt and lateral instability after vestibular deafferentation.

CONCLUSION: Defective utricular function, reflected by deviation of the perceived visual horizontal or vertical, cannot by itself explain increased postural sway in the lateral direction for patients with unilateral vestibular deafferentation (uVD). OBJECTIVE: It is not known why some patients with chronic uVD report distressing unsteadiness while others do not. The objective of this study was to test the hypothesis that impaired utricular compensation, reflected by pathologic tilt in the subjective visual horizontal and vertical (SVH-V) test, would affect postural control in the lateral direction after uVD. PATIENTS AND METHODS: The SVH-V was tested in 28 patients 6 months after translabyrinthine surgery for unilateral vestibular schwannoma, and correlated with posturography results. RESULTS: No increase in lateral and anterior-posterior sway, or the quotients between them, or for Romberg quotients, was found with increasing SVH-V tilt.

Adult↗
PubMed2005

Posturography can be used to screen for primary orthostatic tremor, a rare cause of dizziness.

OBJECTIVE: Primary orthostatic tremor is a rare neurologic condition of unknown origin characterized by a 10- to 20-Hz tremor in the legs while standing. Patients with primary orthostatic tremor usually complain of dizziness and unsteadiness that is relieved if they sit down or start to walk around. These patients might be referred to neurotology clinics. Previously, the only way to make the diagnosis has been by means of surface electromyographic recordings from the lower limbs during standing. The authors wanted to study whether posturography can be used to screen for primary orthostatic tremor. STUDY DESIGN: Retrospective case review. SETTING: Balance clinic at a tertiary referral center. PATIENTS: From September 2000 to August 2002, 701 patients were investigated at the authors' balance clinic. INTERVENTION: Static posturography on a force platform with 50-Hz sampling frequency. Recordings were made during 120 seconds of quiescent stance with open or closed eyes. MAIN OUTCOME MEASURE: Fast-Fourier transformation (FFT) analysis of recorded torque in the fore-to-aft direction to quantify the spectral power distribution in the range of 0 to 25 Hz. Visual inspection of power spectrum plots was performed. RESULTS: Five patients (0.7%) were identified (1 man and 4 women; mean age, 56 yr; age range, 36-73 yr) with narrow peaks at 8.5 to 18 Hz in the power spectra of their posturographic recordings. Surface electromyographic recordings during standing confirmed their diagnosis of primary orthostatic tremor. CONCLUSION: Analysis of power spectra from posturographic recordings is a simple, quick method to screen for primary orthostatic tremor. The condition might be more common than previously assumed. It is important to identify patients with primary orthostatic tremor because they might be misdiagnosed and left without treatment.

Adult↗
PubMed2004

Ipsilesional visual field dependency for patients with vestibular schwannoma.

Vestibular schwannoma patients have a non-homogenous vestibular function and compensation, and might rely more on visual cues for balance control. Using the rod and frame test, visual field dependence was investigated in 17 patients with vestibular schwannoma who had a normal subjective visual horizontal and vertical (0.8 +/- 1.4 degrees). Findings were correlated with tumor size, age, and other parameters of vestibular compensation and compared with field dependency results of 28 healthy subjects. Vestibular schwannoma patients showed greater deviation in the rod and frame test when the frame was tilted towards the lesioned ear (mean 8.2 +/- 4.9 degrees), than towards the healthy ear (mean 5.5 +/- 6.0 degrees; p=0.013). The results indicate a unilateral visual field dependency for patients with vestibular schwannoma that predicts the lesioned side.

Adult↗
PubMed2004

Idiosyncratic compensation of the subjective visual horizontal and vertical in 60 patients after unilateral vestibular deafferentation.

OBJECTIVE: To investigate long-term compensation mechanisms of utricular function after translabyrinthine surgery for vestibular schwannoma. Correlations between the subjective visual horizontal (SVH) and subjective visual vertical (SVV) and other parameters of vestibular compensation were studied. The correlation between the SVH and SVV was also investigated to see whether these measurements are compatible for patients. MATERIAL AND METHODS: Sixty consecutive patients were investigated 3 months before and 6 months after surgery by means of electronystagmography and SVH and SVV tests. Tumor size was measured using MRI. RESULTS: The SVH and SVV increased significantly towards the ipsilesional side postoperatively. Preoperative tilt correlated with age. Postoperative tilt correlated weakly with preoperative caloric sensitivity and inversely with tumor size. The correlation between the SVH and SVV was high both before and after surgery (r(s) > 0.74; p < 0.001). CONCLUSIONS: The long-term compensation of static tilt perception was dependent on age and not on dynamic canal functions. We propose an idiosyncrasy in the SVH and SVV compensation after unilateral vestibular deafferentation, incongruous with the general course of vestibular compensation. The results suggest a probable dependence on non-vestibular information, i.e. proprioception, in facilitating compensation of static vestibular deficits. The similarity between the SVH and SVV measurements confirms that either test can be used clinically for patients with vestibular lesions.

Adolescent↗
PubMed2003

Phobic postural vertigo: body sway during vibratory proprioceptive stimulation.

Phobic postural vertigo patients might rely more on proprioceptive than visual cues to regulate stance. We tested 14 phobic postural vertigo patients and 24 healthy subjects with posturography during quiet stance and periods of vibratory proprioceptive calf muscle stimulation, both with eyes open and closed. During quiet stance phobic postural vertigo patients showed higher torque variance than healthy subjects, especially above 0.1 Hz. Vibratory proprioceptive stimulation increased the differences between healthy subjects and phobic postural vertigo patients. The patients were less able to use vision to counteract vibration-induced movements. Phobic postural vertigo patients are more sensitive to proprioceptive disturbances than healthy subjects are, and less apt to use visual information to control upright stance. This might be part of an anxious mode of balance control.

Adult↗
PubMed2003

Postural control adaptation during galvanic vestibular and vibratory proprioceptive stimulation.

The objective for this study was to investigate whether the adaptation of postural control was similar during galvanic vestibular stimulation and during vibratory proprioceptive stimulation of the calf muscles. Healthy subjects were tested during erect stance with eyes open or closed. An analysis method designed to consider the adaptive adjustments was used to evaluate the motion dynamics and the evoked changes of posture and stimulation response. Galvanic vestibular stimulation induced primarily lateral body movements and vibratory proprioceptive stimulation induced anteroposterior movements. The lateral body sway generated by the galvanic stimulation was proportionally smaller and contained more high-frequency movements (> 0.1 Hz) than the anteroposterior body sway induced by the vibratory stimulation. The adaptive adjustments of the body sway to the stimulation had similar time course and magnitude during galvanic and vibratory stimulation. The perturbations induced by stimulation were gradually reduced within the same time range (15-20 s) and both kinds of stimulation induced a body leaning whose direction was dependent on stimulus. The similarities in the adjustment patterns suggest that postural control operates in the same way independent of the receptor systems affected by the disturbance and irrespective of whether the motion responses were induced in a lateral or anteroposterior direction.

Adaptation, Physiological↗
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

Visual influence on postural control, with and without visual motion feedback.

Body sway was investigated in 20 healthy subjects to determine whether visual input must contain motion feedback information from the surroundings in order to influence postural control. Posturography was used to record body sway under the following visual conditions: eyes open with or without a restricted visual field; eyes open in ganzfield white light; eyes open in darkness with a head-fixed visual target; eyes open in darkness; and eyes closed in darkness. Stance was perturbed by means of a pseudorandomly applied vibratory stimulation to the calf muscles. Least sway was found with eyes open in an unrestricted visual field but increased in a restricted visual field. Greatest sway was found without visual motion feedback, i.e. under the following conditions: eyes closed; eyes open in darkness; eyes open in ganzfield white light; and with a head-mounted fixation point. Sway was significantly (p < 0.05) greater with eyes open in darkness compared with eyes closed during the initial 50 s with perturbations. After 150 s, sway was almost identical under the four test conditions without visual motion feedback. Standing with eyes open in darkness was initially a disadvantage compared with having the eyes closed. The postural control system may be programmed to expect visual feedback information when the eyes are open, which may delay changes in postural strategy.

Adaptation, Physiological↗
PubMedDate not supplied

Large vestibular evoked myogenic potentials in response to bone-conducted sounds in patients with superior canal dehiscence syndrome.

Dehiscence of the superior semicircular canal is a 'new' vestibular entity. Among these patients, the vestibular evoked myogenic potentials (VEMP) in response to air-conducted sounds are large. In the present study, VEMP in response to bone-conducted sounds were studied in 5 normal subjects, in 3 patients after (unilateral) labyrinthectomy and in 4 patients with (unilateral) superior canal dehiscence syndrome. The bone-conducted sound stimulus was a 250- and a 500- tone burst delivered monaurally on the mastoid using standard bone conductors. Among the normals, bone-conducted sounds delivered monaurally caused VEMP bilaterally. There was, however, a transcranial attenuation for the 500-Hz stimulus, but less so for the 250-Hz stimulus. Among the patients with labyrinthectomy there were VEMP on the healthy side, but not on the lesioned side, irrespective of whether the bone-conducted sounds were presented behind the healthy or the operated ear. Among the patients with superior canal dehiscence syndrome, the VEMP on the affected side were larger than on the healthy side. This suggests that there is also vestibular hypersensitivity for bone-conducted sounds in these patients.

Adult↗