Vestibular Disorders. Группа авторов

for significant spontaneous nystagmus [12] may also improve the sensitivity of the results, though further investigation is needed.

      Air versus Water Calorics

Compared with water caloric irrigation systems, air caloric systems have some practical benefits: they tend to be more portable than water systems, they reach the desired testing temperatures more rapidly, and they do not require a nearby water source. In addition, air calorics can be performed safely even when a tympanic membrane perforation or other contraindications to water calorics (e.g., presence of mastoid cavity) are present [17]. These factors have likely contributed to the adoption of air caloric systems in many centers.

However, some questions have been raised about the use of air as a caloric stimulus; to date, no standards for air calorics have been approved by the American National Standards Institute (ANSI) [18]. One concern with air calorics is the potential for unexpected sources of variability. Even the size of the speculum that is used can influence the SPV values obtained; smaller speculums (2.5 mm) generate nystagmus that is nearly twice that of the SPV values generated with larger (4 mm) speculums on average [19]. It appears that the speculum size has an impact on the speed of the air flow as it enters the ear canal.

The general consensus in the literature indicates that air calorics yield unilateral weakness values that are comparable to water calorics [20–22]. However, the literature also indicates that the average SPV values obtained with water as the caloric medium are significantly larger than the values obtained with air [20, 22–24]. This raises questions about whether air and water caloric mediums should be considered as interchangeable when the response magnitudes achieved from the two techniques are clearly different. Moreover, from a statistical standpoint, small differences between SPV values are amplified when the average SPV values are lower overall, an element of Jongkees’ formula [25] that makes lower SPV values more vulnerable to skewed results. Indeed, one study comparing water and air caloric media found that almost 6% of the normal group had abnormal caloric results with air while none had abnormal results with water [20]. Recent publications investigating water and air as caloric mediums have identified new considerations and potential approaches that may help in generating equivalent responses across the two approaches [19, 21].

      Posturography

      Posturography pertains to the functional evaluation of postural control and stability, which is largely mediated by the interaction between sensory systems (visual, vestibular, somatosensory), and can be assessed in both static and dynamic conditions. Approaches to posturography vary from simple bedside clinical tests to computerized systems that can quantify postural control/stability over various static and dynamic conditions (e.g., computerized dynamic posturography; CDP). Though CDP is considered the “gold standard” for posturography, the large size and high cost of CDP has limited the number of centers that are equipped with it.

      Considerations for Future Research

An in-depth discussion of the areas within the posturography literature that are in need of further exploration, standardization, and consensus, of which there are many, falls outside the scope of this chapter. However, recent advances within posturography cannot be explored as a topic without acknowledging the need to fill the many gaps within the literature. Comprehensive reviews of these issues have been published in recent years [26, 27].

Concerns about the validity and reliability of the various applications of posturographic measurements have been raised consistently over the years. The approaches and analysis techniques that exist for posturography vary widely [28] and further complicate attempts to find agreement within the literature. There is little consensus regarding the best approaches for assessment or interpretation [26]. Recent publications have also identified an assortment of factors that may significantly impact findings based on posturographic testing, including the instructions given to the patient prior to testing [29], the patient’s stance [30], stability of the platform for CDP [31], the type of balance pad used [32], and the time of day the testing takes place [33]. While most of these factors are likely to stay reasonably stable across time for an individual patient, or even for all patients within a given center, these findings emphasize that even subtle factors may further hamper our ability to make comparisons between studies.

Posturography has not yet been shown to be effective as a diagnostic tool for any disorder, including disorders of balance; the results are non-localizing and there is significant overlap between the results of patients with normal and abnormal vestibular functions [34, 35]. Of the investigations that have looked at posturography for diagnosis, most are retrospective and do not include calculations of sensitivity and specificity [27]. Work is needed to better separate abnormal populations from normal controls if posturography is to be used for diagnostic purposes in the future.

      A search of the Pubmed database using the term “posturography” reveals that mentions of posturography have tripled in the past 5 years compared with the previous 5 years. While caution is required when determining the dependence on posturographic results until there is more agreement within the literature, there is hope that continued research efforts will answer some important questions related to posturography and will lead to the standardization of approaches and analysis techniques.

      Technological Innovations

The most apparent recent advance within the realm of posturography has been the drive to validate lower cost alternatives to traditional force-plate systems. In particular, the Nintendo Wii Balance Board (WBB), an accessory for the Wii video game console that contains pressure sensors, has inspired a surge in publications looking at the validity of the system for quantifying posturography, so far the results are very encouraging [36–38]. However, other researchers have expressed concern that the WBB may not be an appropriate alternative to traditional force-plates in some instances [39–41].

Currently, the most promising application of the