Positional changes and stabilization of middle ear pressure.

Middle ear pressure has been shown to increase when body position is shifted from the erect to the supine position, which is explained by an increased volume of the middle ear mucosa due to an increased hydrostatic pressure. The increase in the volume of middle ear mucosa consists of a fast major response followed by slow minor increase, which is reflected by a similar pattern in the increase of middle ear pressure. Since many otological experiments may be performed with subjects in the supine position, it is of interest to analyse these changes in middle ear pressure, as results may be affected by changes in middle ear pressure. The present study investigated the middle ear pressure changes due to a shift in body position from sitting to supine at time intervals of 15 s over a period of 120 s in a group of 20 normal adults. The middle ear pressure was found to increase 22 daPa (mean; S.D. = 12.1), whereas a stable middle ear pressure was reached after 30 s, indicating a steady state concerning the increase in volume of the middle ear mucosa. Thus, it is recommended that experiments with subjects in the supine position should be carried out only after assuming the position for 30 s. The increase in pressure did not correlate to the prevailing middle ear pressure or to the body height.