Behavioural improvement in a minimally conscious state after caloric vestibular stimulation: evidence from two single case studies.

OBJECTIVE: To investigate whether caloric vestibular stimulation, a non-invasive form of neuro-modulation, alters the level of awareness in people residing in a minimally conscious state. DESIGN: Single-case ( n = 2), prospective, controlled (ABAB) efficacy study. SETTING: Tertiary, neuro-rehabilitation inpatient ward within a university hospital. PARTICIPANTS: Two individuals in a minimally conscious state. INTERVENTION: Left ear caloric vestibular stimulation was performed in two four/five-week blocks interleaved with two four/five-week blocks of sham stimulation. Session duration and frequency gradually increased within each block from once per day for 10 minutes (Week 1) to once per day for 20 minutes (Week 2) to 20 minutes twice per day in the remaining weeks. MEASURES: Wessex Head Injury Matrix, JFK Coma Recovery Scale - Revised. RESULTS: Both participants' Wessex Head Injury Matrix scores indicated a transition from involuntary (i.e. mechanical vocalization) to voluntary (i.e. gesture making, selective responses to family members) behaviour that was time-locked to the onset of active stimulation. In one participant, this improvement persisted for at least four weeks after active stimulation, while in the other it diminished two weeks after stimulation. Allied, although less dramatic, changes were seen on the arousal and auditory subscales of the JFK Coma Recovery Scale - Revised. CONCLUSION: The data provide the first evidence that vestibular stimulation may help improve outcome in a low awareness state, although further studies are needed to replicate effect and determine longer-term benefit.

Caloric stimulation with near infrared radiation does not induce paradoxical nystagmus.

Near infrared radiation can be used for warm stimulation in caloric irrigation of the equilibrium organ. Aim of this study was to determine whether near infrared radiation offers effective stimulation of the vestibular organ, whether it is well tolerated by the patients and especially whether it is a viable alternative to warm air stimulation in patients with defects of the tympanic membrane and radical mastoid cavities. Patients with perforations of the tympanic membrane (n = 15) and with radical mastoid cavities (n = 13) were tested both with near infrared radiation and warm dry air. A caloric-induced nystagmus could be seen equally effectively and rapidly in all patients. Contrary to stimulation with warm dry air, no paradoxical nystagmus was observed following caloric irrigation with a warm stimulus (near infrared radiation). Results of a questionnaire showed excellent patient acceptance of near infrared stimulation with no arousal effects or unpleasant feeling. In conclusion, near infrared radiation proved to be an alternative method of caloric irrigation to warm dry air in patients with tympanic membrane defects and radical mastoid cavities. Near infrared radiation is pleasant, quick, contact free, sterile and quiet. With this method an effective caloric warm stimulus is available. If near infrared radiation is used for caloric stimulus no evaporative heat loss occurs.

[Near infrared stimulation of the equilibrium organ--first clinical experiences]. / Nahinfrarotreizung des Gleichgewichtsorgans--erste klinische Erfahrungen.

BACKGROUND: A new method for the stimulation of the organ of equilibrium by means of a broad-scale and monochromatic near infrared emission was developed. This method should be examined within the framework of a pilot study, evaluated and its clinical possible applications examined. PATIENTS AND METHODS: Healthy probands (n = 15), patients with a radical cave of the ear (n = 5), patients with a defect of the tympanic membrane (n = 5) and spontaneous nystagmus (n = 5) were examined. In healthy probands an irritation with broad-scale as well as monochromatic near infrared (NIR) was performed and compared with a water irrigation (44 degrees, 50 ml in 30 seconds). The subjective, local feelings during the application and the appearance of giddiness according to irritation were recorded and the nystagmus was registered by means of videonystagmography. In patients with radical cave of the ear and tympanic membrane defects, a broad-scale NIR-irritation before a comparative irritation with warm air (44 degrees) was performed exclusively. RESULTS: In all healthy probands, a nystagmus reaction could be seen with broad-scale and monochromatic NIR. Compared to the hot water irritation slow phase velocity (SPV) was decreased however registrable by means of Frenzel glasses and electronystagmography during the culmination stage. In patients with radical cave (n = 4) and tympanic membrane defects (n = 3) showing paradoxical nystagmus reaction during hot air irritation, a nystagmus to the site of stimulation resulted by means of light calorisation. In patients with a spontaneous nystagmus an attenuation (n = 1) or inversion (n = 2) could be achieved by NIR-radiation. CONCLUSIONS: The method of the NIR-radiation is suitable in clinical practice for the caloric test proofing warm reaction. Vaporization cold does not occur. The application of heat charm is better proportionable and steerable than during air irritation. The procedure is sterile, noiseless and non-contact. Difficulties in interpretation of results of vestibular tests because of evaporation coldness do not occur.

[A comparison of water and air stimulated bithermal-caloric test and the usefulness of both methods in otologic surgery]. / Porównanie przydatnosci wodnej i powietrznej próby dwukalorycznej w praktyce otochirurgicznej.

The most commonly used method of testing the responses of the labyrinths is Water Stimulated Bithermal-Caloric Test of Fitzgerald-Hallpike. Before planning an otiatric surgery it is necessary to support by documentary evidence the responses of the vestibular organ in the ear planned to be operated on, however, irrigation with water may cause damage to structures of the ear and may intensify symptoms of the diseases and eventually make the treatment more difficult. In some centers where Water Stimulated Bithermal-Caloric Test were used alone, or a combination of air and water stimulated caloric test were performed, it seemed to be difficult to compare the results of both tests. In this study I tried to establish parameters of stimuli obtained in the Air Stimulated Bithermal-Calorics test that evoked nystagmus, similar to those obtained in the Fitzgerald-Hallpike water stimulated test. It was determined that the duration of nystagmus in both water and air stimulated bithermal-caloric tests were identical when the temperature of "cold" air wave was 26 degrees C, whereas "warm" air wave had the temperature of 48 degrees C and the time of stimulation for both tests was 80 seconds.

[Thermographic detection of heat radiation in caloric vestibular function tests]. / Thermographischer Nachweis der Wärmestrahlung bei der kalorischen Vestibularisprüfung.

BACKGROUND: Since Bárány; caloric irrigations in the external ear canal have been used for unilateral stimulation of the peripheral vestibular system. However, the mechanism of heat transfer from the auditory canal to the vestibular organ is not completely known. From the physical point of view, three mechanisms may be discussed: heat conduction via the bone, convection via the middle ear gas, or radiation. Feldmann et al. (1991) singled out radiation as a very important factor in this regard. Using high-resolution thermography, we were able to "see" radiation almost directly in temporal bone experiments. METHODS: Using the system of infrared thermovision specially adapted for close-up studies, the effect of calorization can be observed and documented in colored planar thermograms. Fresh temporal bone specimens had to be prepared so as to permit simultaneous observation of the tympanic membrane and the medial tympanic wall. RESULTS: Changes in temperature were readily visible during experimental caloric tests: turning blue indicated cooling and red indicated warming. In the caloric test with 44 degrees C or 30 degrees C water, changes in color of the eardrum appeared immediately. At the very same time, however, an area of the medial tympanic wall also changed color. This velocity of transfer cannot be attained by conduction or convection: heat radiation is the only possible explanation. This could only be demonstrated at the very onset of the reaction; subsequent thermograms became more and more diffuse. In this stage the heat transfer may also be effected by conduction and/or convection. CONCLUSIONS: Thermography demonstrates that radiation is a very important factor in heat transfer; at least in the initial phase of calorization.

Vestibular function in the fetal sheep.

Little is known about the functional development of the vestibular system before birth. The purpose of this study was to determine whether vestibular response to caloric stimulation could be elicited in the fetal sheep in utero. Late gestational fetal sheep (n = 6) were instrumented through a midline hysterotomy. Copper caloric probes were inserted into the right bulla and beneath the left facial skin. Electrodes were placed in the skull for monitoring of electro-ocular activity. At least 3 days after surgery the probes were irrigated with water (100 ml/minute) at body temperature, 46 degrees C, and 6 degrees C. Cold water infusion of the bulla consistently produced well-recognized, slow-phase deviations followed by saccades directed contralaterally, findings consistent with vestibular nystagmus. The direction of the response reversed with warm water irrigation. The response was absent with irrigation at fetal body temperature. Only random eye movements were observed in response to caloric stimulation of the facial skin, regardless of water temperature. These results demonstrate that the sheep vestibular system is functioning prenatally. The importance of vestibular function for normal fetal brain maturation may be revealed in future studies using this animal model.

Closed-loop caloric, harmonic acceleration and active head rotation tests: norms and reliability.

Norms and test-retest data from 20 persons with normal hearing and balance function were obtained for bithermal caloric (BC) using a closed-loop irrigator, sinusoidal harmonic acceleration (SHA) and active head rotation (AHR) tests. Each subject was tested twice with each test, with at least 24 hours between retest. Results of BC testing indicate that a unilateral weakness of 30% should be present to confidently identify a significant inter-ear difference when using a closed-loop irrigator for stimulus. Test-retest correlations of unilateral weakness were extremely poor, reflecting the potential for considerable variability with this test. With the exception of asymmetry measures at 0.01 and 0.02 Hz, SHA gain, phase, and asymmetry are very similar to previously published norms. Test-retest correlations were generally better than BC correlations, with phase measures having the highest test-retest correlations. AHR norms were obtained in three conditions, with eyes open and starting at a stationary target (AHR-EO), with eyes closed (AHR-EC), and with eyes open and fixated on a target moving synchronously with the head (AHR-FX). AHR-EO mean gain and phase were slightly less than that reported by other researchers, possibly as a result of differences in analysis algorithms, and had the poorest test-retest correlations. AHR-EC gain and phase were much more variable than AHR-EO between subjects, but showed very high test-retest correlations. AHR-FX gain, phase, and asymmetry are similar to those reported previously and have slightly better test-retest correlations than AHR-EO.