Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4433_Библиотеки_им_академика_М_И_Перельмана

The first detailed description of the caloric test and its underlying mechanism is attributed to Robert Bárány (Baloh, 2002). In his now well-known book published almost a century ago, Bárány (1907) described caloric irrigations administered in the supine position with the head placed at an angle of 30 degrees with respect to the horizontal plane (Figure 12–1A). In this head position, known as the caloric test position, the lateral (horizontal) semicircular canals become aligned with the plane of gravity. In the absence of caloric stimula­tion, no responses are evoked from the lateral canals because the cupula and the surrounding endolymph have the same densities and are not affected by grav­ity. When the external auditory canal is irrigated with a medium that is considerably cooler or warmer than the body temperature, a temperature gradient is generated across the lateral canal of the irrigated ear. According to Bárány, the temperature gradient changes the density of the endolymph on the side of the canal closest to the site of irrigation. If that explanation is correct, warm irrigations in the standard caloric test position should cause the endolymph to become lighter and rise, thus generating an ampullopetal deflection of the cupula. Such a deflection should cause an excitatory response from the lateral canal and generate nystagmus with its fast phases beating toward the irrigated ear (see