Måns Magnusson

Identification of human postural dynamics

Human postural dynamics was investigated for six healthy subjects using a force platform recording body sway induced by vibrators attached to the calf muscles. The model of body mechanics adopted was that of an inverted pendulum, the dynamics of postural control being assumed to be reflected in the stabilizing forces exerted on the platform by the feet as a result of complex muscular activity subject to state feedback of body sway and position. The approach to signal processing has been that of parametric identification of a transfer function representing the stabilized inverted pendulum. Posture control was quantified in three variables: swiftness, stiffness, and damping. It is shown that the identification fulfils ordinary statistical validation criteria, and it is conjectured that the state feedback parameters identified are suitable for use in assessing ability to maintain posture. >

Postural and symptomatic improvement after physiotherapy in patients with dizziness of suspected cervical origin

OBJECTIVE To assess postural performance in patients with dizziness of suspected cervical origin in whom extracervical causes had been excluded, and to assess the effects of physiotherapy on postural performance and subjective complaints of neck pain and dizziness. DESIGN Prospective, randomized, controlled trial. SETTING Primary care centers and a tertiary referral center. PATIENTS AND SUBJECTS Of 65 referrals, 43 patients were excluded because extracervical etiology was suspected. Of the remaining 22 patients, 17 completed the study (15 women, 2 men, x age 37 yr, range 26-49). The controls were 17 healthy subjects (15 women, 2 men, x age 36 yr, range 25-55). INTERVENTION Physiotherapy based on analysis of symptoms and findings, and aimed to reduce cervical discomfort. Patients were randomized either to receive immediate physiotherapy (n = 9), or to wait 2 months, undergo repeat measurements, and then receive physiotherapy (n = 8). MAIN OUTCOME MEASURES Posturography, measuring velocity and variance of vibration-induced body sway and variance of galvanically induced body sway. Subjective intensity of neck pain (Visual Analog Scale ratings, 0-100), intensity and frequency of dizziness (subjective score 0-4). RESULTS The patients manifested significantly poorer postural performance than did healthy subjects (.05 > p > .0001). Physiotherapy significantly reduced neck pain and intensity and the frequency of dizziness (p < .01), and significantly improved postural performance (.05 > p > .0007). CONCLUSIONS Patients with dizziness of suspected cervical origin are characterized by impaired postural performance. Physiotherapy reduces neck pain and dizziness and improves postural performance. Neck disorders should be considered when assessing patients complaining of dizziness, but alternative diagnoses are common.

Significance of pressor input from the human feet in anterior-posterior postural control. The effect of hypothermia on vibration-induced body-sway

The importance to postural control of the mechanoreceptors of the soles was investigated in thirteen healthy subjects. Body-sway velocity was evaluated before and after exposing the subjects feet to hypothermia, and when calf muscles were exposed to vibration at frequencies between 20 and 100 Hz. Subjects were tested both with eyes open and closed. Body-sway velocity was found to increase significantly during hypothermia of the feet. The difference in body-sway between hypothermal and normothermal conditions was less prominent when the subjects eyes were open though the difference was significant in both cases. The present results indicate the importance of the mechanoreceptors of the soles to postural control and elucidate their interaction with compensatory visual input in maintaining postural control. These findings also suggest, that factors affecting pressor input should be taken into consideration when assessing patients with complaints of dysequilibrium.

Isolated acute vertigo in the elderly; vestibular or vascular disease?

Intruduction –‐ Elderly patients with isolated acute vertigo are commonly encountered in clinical practice, but little is known about the underlying cause of the symptoms. Material & methods –‐ We prospectively studied 24 patients aged 50–75 years with the acute onset of isolated vertigo lasting > 48 h and no abnormality on neurological examination other than nystagmus. The study protocol included neuro‐imaging (MRI 22 patients, CT 2 patients), Doppler sonography, and electro‐oculography. Results— MRI/CT showed the presence of an infarction of the caudal cerebellum in six patients (25%), 3 of whom had a potential cardioembolic source and normal Doppler sonography findings, whereas 3 patients had ipsilateral vertebral artery occlusion and normal cardiac findings. MRI of the posterior fossa was normal in 18 patients. On electro‐oculography, ataxic pursuit eye movements was a characteristic finding in patients with cerebellar infarction, whereas caloric test findings were not discriminative. Conclusion –‐ A caudal cerebellar infarction may easily be misdiagnosed clinically as a labyrinthine disorder, and was found to be the cause in one fourth of patients presenting with isolated acute vertigo.

Significance of pressor input from the human feet in lateral postural control. The effect of hypothermia on galvanically induced body-sway

The significance to human postural control of pressor information from the feet was investigated during vestibular disturbance in seven normal subjects who were exposed to bipolar biaural galvanic stimulation of the vestibular nerves before and after their feet were anaesthetized with hypothermia. The increase in body sway in the lateral plane induced by the galvanic stimulus was enhanced when the feet were anaesthetized, and adaptation of postural control to the galvanic stimulus was delayed. It is concluded that pressor information from the feet contributes significantly to postural control in humans and is important in compensating for vestibular disturbance.

Zebris versus Myrin: a comparative study between a three-dimensional ultrasound movement analysis and an inclinometer/compass method: intradevice reliability, concurrent validity, intertester comparison, intratester reliability, and intraindividual variability.

Study Design. Experimental study. Objectives. To compare two devices for measuring cervical range of motion, a three-dimensional ultrasound motion device (Zebris) and a gravity-reference goniometer (Myrin). Summary of Background Data. Assessment of cervical range of motion is used to evaluate the effect of different treatments, determine impairment, and ascertain the relationship between neck disorders and cervical spine mobility. Methods. Sixty “neck-healthy” volunteers (25 men, 35 women; mean age 38 years, range 22–58 years) performed active maximal movements in flexion–extension, rotation, and lateral flexion. Maximal cervical range of motion was recorded simultaneously with the Zebris and Myrin devices. Intradevice reliability, concurrent validity, intertester comparison, intratester reliability, and intraindividual variability were computed. Results. Our study showed good agreement of full-cycle cervical range of motion measurement between devices, testers, and the test and retest (intraclass correlation [ICC] was >0.90 for intradevice reliability, >0.93 for concurrent validity, and >0.92 for intratester reliability). Method error, assessed with the within-subject coefficient of variation for 95% of the measurements, was 5.4% to 11.1% for intradevice reliability, 4.4% to 7.6% for concurrent validity, 3.6% to 7.6% for intratester reliability, and 5.3% to 9.9% for individual variability. Individual variability did not increase with an increased cervical range of motion. Conclusion. Both devices are reliable and showed good agreement. We conclude that the two techniques can be used interchangeably. Our study supports the continued use of the Myrin—a gravity-reference goniometer in routine clinical orthopedic work. The more sophisticated three-dimensional method adds information and allows evaluation of combined motion in two and three dimensions and is suitable for research.

Diagnostic criteria for Menière's disease

This paper presents diagnostic criteria for Menières disease jointly formulated by the Classification Committee of the Bárány Society, The Japan Society for Equilibrium Research, the European Academy of Otology and Neurotology (EAONO), the Equilibrium Committee of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) and the Korean Balance Society. The classification includes two categories: definite Menières disease and probable Menières disease. The diagnosis of definite Menières disease is based on clinical criteria and requires the observation of an episodic vertigo syndrome associated with low- to medium-frequency sensorineural hearing loss and fluctuating aural symptoms (hearing, tinnitus and/or fullness) in the affected ear. Duration of vertigo episodes is limited to a period between 20 minutes and 12 hours. Probable Menières disease is a broader concept defined by episodic vestibular symptoms (vertigo or dizziness) associated with fluctuating aural symptoms occurring in a period from 20 minutes to 24 hours.

Effects of postural disturbances with fatigued triceps surae muscles or with 20% additional body weight

One of the main issues for balance control is the ability to generate enough forces to execute motions and uphold stability. This study aimed to investigate whether induced fatigue of the triceps surae muscles and decreased muscle force due to temporary additional body weight affected the ability to withstand balance perturbations. Another aim was to examine whether postural control adaptation over time was able to compensate for the changes induced by fatigue and additional body weight. Eleven normal subjects were exposed to vibratory proprioceptive stimulation during three test conditions; a baseline test during normal condition; when the body weight was increased by 20%, by adding additional weight load; and when the triceps surae muscles were fatigued. The tests were performed both with eyes open and closed. The body movements were evaluated by analyzing the anteroposterior and lateral torques induced towards the supporting surface measured with a force platform. Postural control was substantially affected both by the additional body weight, and by muscle fatigue in the triceps surae muscles. The anteroposterior and lateral body sway were larger both with added weight and fatigued muscles compared with the baseline test during quiet stance. However, the body sway induced by the vibratory stimulation was significantly larger with additional body weight compared with when the triceps surae muscles were fatigued. The differences between the test conditions were mostly pronounced during tests with eyes closed and in the high frequency body sway (>0.1 Hz). Postural control adaptation was able to reduce but not fully compensate for the changes induced by fatigue and additional body weight. Several hypotheses could account for these observations. (1) Fatigued muscles are less sensitive to muscle vibration, (2) muscle fatigue alters the muscle contractile efficiency and thus alters the ability to produce high-frequency, short-latency responses to balance perturbations.

Galvanic vestibular stimulation for analysis of postural adaptation and stability

Human postural dynamics was investigated in 12 normal subjects by means of a force platform recording body sway, induced by bipolar transmastoid galvanic stimulation of the vestibular nerve and labyrinth. The model adopted was that of an inverted segmented pendulum, the dynamics of postural control being assumed to be reflected in the stabilizing forces actuated by the feet as a result of complex muscular activity subject to state feedback of body sway and position. Time-series analysis demonstrates that a transfer function from stimulus to sway-force response with specific parameters can be identified. In addition, adaptation to the vestibular stimulus is demonstrated to exist, and the authors describe this phenomenon using quantification in terms of a postural adaptation time constant in the range of 40-50 s. The results suggest means to evaluate adaptive behavior and postural control in the erect human being which may be useful in the rehabilitation of individuals striving to regain upright stance.<<ETX>>

Treatment of phobic postural vertigo. A controlled study of cognitive-behavioral therapy and self-controlled desensitization.

In balance clinic practice, phobic postural vertigo is a term used to define a population with dizziness and avoidance behavior often as a consequence of a vestibular disorder. It has been described as the most common form of dizziness in middle aged patients in dizziness units. Anxiety disorders are common among patients with vestibular disorders. Cognitive–behavioral therapy is an effective treatment for anxiety disorders, and vestibular rehabilitation exercises are effective for vestibular disorders. This study compared the effect of additional cognitive–behavioral therapy for a population with phobic postural vertigo with the effect of self–administered vestibular rehabilitation exercises.39 patients were recruited from a population referred for otoneurological investigation. Treatment effects were evaluated with the Dizziness Handicap Inventory, Vertigo Symptom Scale, Vertigo Handicap Questionnaire, and Hospital Anxiety and Depression Scale. All patients had a self treatment intervention based on education about the condition and recommendation of self exposure by vestibular rehabilitation exercises. Every second patient included was offered additional cognitive behavioral therapy.Fifteen patients with self treatment and 16 patients with cognitive– behavioral treatment completed the study. There was significantly larger effect in the group who received cognitive behavioral therapy than in the self treatment group in Vertigo Handicap Questionnaire and the Hospital Anxiety and Depression scale and its subscales.Cognitive–behavioral therapy has an additional effect as treatment for a population with phobic postural vertigo.A multidisciplinary approach including medical treatment, cognitive–behavioral therapy and physiotherapy is suggested.