[Bilateral peripheral vestibulopathy]. / Dvustoronnyaya perifericheskaya vestibulopatiya.

Bilateral vestibulopathy is a relatively widespread and at the same time rarely diagnosed cause of chronic postural instability. Numerous toxic factors, dysmetabolic, autoimmune and neurodegenerative processes can lead to this condition. The main clinical manifestations of bilateral vestibulopathy are balance disorders and visual disturbances (oscillopsia), which can significantly increase the risks of falls in such patients. In addition, cognitive and affective disorders, which also reduce the quality of life in patients with bilateral vestibulopathy, have been described and actively studied in recent years. The diagnosis of bilateral vestibulopathy is based on the results of a clinical neurovestibular study, including a dynamic visual acuity test and a Halmagyi test. A video head impulse test, a bithermal caloric test and a sinusoidal rotation test are used as instrumental methods confirming the dysfunction of the peripheral vestibular system. However, they are still not widespread in neurological practice. Treatment of bilateral vestibulopathy is reduced to vestibular rehabilitation. Encouraging results have been obtained in a number of studies using galvanic vestibular stimulation and the use of vestibular implants. In addition, cognitive rehabilitation methods are currently being developed, which presumably can also improve compensation for bilateral vestibular loss.

Heart rate and blood pressure effects during caloric vestibular testing.

OBJECTIVES: To determine whether the caloric vestibular test causes significant changes in heart rate and mean arterial blood pressure. MATERIALS AND METHODS: Changes in heart rate and mean arterial blood pressure before and after caloric irrigation were compared with the degree of nystagmus (as measured by maximum slow phase velocity) and the patient's subjective dizziness (scored from 0 to 10). A cardiologist reviewed each patient's heart rate and mean arterial blood pressure changes. Patients' anxiety levels were also assessed. RESULTS: Eighteen patients were recruited. There were no adverse events in any patient. There were no overall significant differences between the heart rate and mean arterial pressure before and after each irrigation. There was a significant correlation between the maximum slow phase velocity and patients' subjective dizziness scores. CONCLUSION: Heart rate and mean arterial blood pressure are not significantly influenced by the caloric vestibular test. This preliminary study will enable patients with stable cardiovascular disease to be recruited for further risk determination.

Temporary phantom limbs evoked by vestibular caloric stimulation in amputees.

OBJECTIVE: Relationships between the vestibular system and the body schema have been suggested but never demonstrated in amputees. We studied the effects of vestibular stimulation on body representation in amputees focusing on the phantom limb phenomenon. METHOD: Prospective study in 31 amputated subjects of one or several limbs before the age of 16 years. The amputees underwent a caloric vestibular stimulation test, ipsilateral (n = 31) and contralateral (n = 8) to the side of amputation. Amputees were asked to report their perceptions spontaneously and to answer open questions. Four types of perceptions were analyzed: normal phantom, deformed phantom, painful phantom, and no phantom, before, during, and after the vestibular stimulation test. Data were compared between the two groups for pre- and post-test perceptions (chi2 test). RESULTS: Vestibular caloric stimulation provoked temporary perception of a normal phantom limb in 16 of 17 amputees who previously did not experience phantoms. For 12 of 12 amputees who currently experienced deformed or painful phantom limbs, caloric stimulation led to temporary replacement of the abnormal phantom with a non-painful normal phantom. CONCLUSIONS: The phenomena observed: 1) throw light on assumed mechanisms controlling construction of static and dynamic engrams used to produce the body schema; 2) complete the neuromatrix theory proposed to explain the phantom limb phenomenon; and 3) suggest that the vestibular system triggers the procedure of reconstruction of the global body schema.

Effects of caloric stimulation on respiratory frequency and heart rate and blood pressure variability.

Heart rate variability (HRV), blood pressure variability (BPV) and respiratory frequency were measured by power spectrum techniques in six normal humans (25-34 years old) and one labyrinthine-defective patient (33 years old) during cold (30 degrees ) vestibular caloric stimulation. Caloric stimuli were delivered intermittently for 2 min, under two different breathing conditions: (1) spontaneous breathing and (2) breathing paced with a metronome (0.25 Hz). During the spontaneous breathing condition, in the normal subjects, the caloric stimuli induced a significant increase in the absolute magnitude of the power spectrum density of the high frequency component (0.15-0. 40 Hz) of HRV and the total bandwidth (0.04-0.4 Hz) of mean BPV. These responses were related to a shift in the weighted average of the respiration frequency on the respiration spectrum, from a median value of 0.27 Hz (range, 0.17-0.29 Hz) during baseline to 0.31 Hz (0. 26-0.31 Hz) following caloric stimulation. This change was not observed in the labyrinthine-defective patient, who had weighted averages of 0.37 Hz and 0.34 Hz, respectively. No significant changes in the normalised units of the low frequency component (0. 04-0.15 Hz) or the high frequency component (0.04-0.4 Hz) of HRV and BPV were observed. During the paced breathing condition, no consistent effect on HRV or BPV was evident. For both breathing conditions, the proportions of HRV and BPV power linearly independent from respiration did not show any caloric-induced change. This study shows that caloric vestibular stimulation produces changes in HRV and BPV by modifying the respiratory pattern.

Comparison between air and water caloric tests in children.

The caloric test represents an essential part of each procedure evaluating vestibular function. The use of water has many contraindications: tympanic perforation, external otitis and mastoid diseases. Sometimes, nausea can make test execution very difficult. Several authors contributed to the study and diffusion of the caloric test for the evaluation of labyrinthine function using different types of otoalcorimeters. We compared two methods in the child--generally intolerant to the water test--and the results obtained were adapted to a mathematical model of air and water caloric nystagmus. Twenty-seven normal children, aged between 5 and 14 years, subdivided into three age groups (5-7, 8-10 and 11-14 years), underwent the water caloric test (250 cm3 at 31 and 43 degrees C for 40 s) and then the air test, together with another nine subjects undergoing only the air test (flow-rate 8 l/min at 25 and 49 degrees C) on different days. The comparison between the two stimulation methods showed a statistically significant difference (P < 0.002) between maximum slow speed component (max SSC) in degrees per second (degrees/s) of water (4.74 degrees/s) and air (2.98 degrees/s). The results of two caloric tests and the interindividual and intraindividual analysis of our electronystagmographic results are in agreement with the data obtained by other authors in studies on adults. Therefore, notwithstanding the differences between the two stimulation methods, the air caloric test can be applied in a larger number of cases, it is better tolerated and can thus be used even in children for the study of labyrinthine function.

Balancing the caloric-induced nystagmus velocity with cold air and water.

A useful alternative to the traditional water caloric is to use an air stimulus. However, the caloric test has not been standardized and a range of parameters are being used in different audiology clinics. The aim of this study was to determine cold air parameters that resulted in a similar slow-component eye velocity to that for water irrigation. Twelve normal subjects underwent caloric testing using air temperatures in the range 18-33 degrees C. The duration and air-flow rate were held constant at 60 s and 5 l/min. A water irrigation at 30 degrees C for 30 s and delivering 150 ml resulted in a mean slow-component eye velocity of 17 degrees/s. An equal response was obtained with an air temperature of 21.0 degrees C. Further work is required to find equivalent air and water responses for other combinations of parameters.

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.

Air caloric test with continuous thermal change.

A new technique was designed for vestibular testing with an air caloric stimulator. With this technique, the temperature threshold necessary to induce caloric nystagmus was measured as air temperature decreased at a constant rate (from 37 degrees C). As a pilot study, an air caloric test with continuous thermal change was done at 6 different rates of decrease: 0.01, 0.03, 0.05, 0.1, 0.15 and 0.2 degrees C/s. The rate of 0.05 degrees C/s gave the smallest standard deviation for temperature threshold in normal subjects. This deviation had the narrowest normal limits of all ordinary caloric tests when the coefficient of variation was compared (standard deviation/mean x 100). No discomfort was observed during or after the air caloric test with continuous thermal change at this rate.

Clinical experience with a short-acting caloric test.

The prolonged labyrinthine stimulation produced by the conventional caloric irrigation is uncomfortable and fatiguing to patients and necessitates an undesirable waiting period between applications of the test. The present report describes the use of a short-acting caloric test, and an analysis of all available data on 100 consecutive patients evaluated with this procedure. Because the labyrinthine stimulus produced by the new method is short-acting and because the stimulus was applied at reduced intensity in patients who were more sensitive, the new procedure was well tolerated even when five or more irrigations were used. It was found convenient to repeat irrigations when results were uncertain, thereby ensuring a more reliable assessment of vestibular function.