Читать книгу Vestibular Disorders - Группа авторов - Страница 45

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].