Hydrostatic pressure measurements of endolymph and perilymph in a guinea pig model of endolymphatic hydrops.

The primary histologic correlate of Menière's disease is endolymphatic hydrops. From this, many investigators have postulated the existence of endolymphatic hypertension, although there have been no measurements published to substantiate this concept. Seventy guinea pigs, surgically treated with right endolymphatic duct obstruction, were later assessed by use of a micro-electrode technique that measured their endolabyrinthine hydrostatic pressures. For 21 of these animals, the pressures of both scala tympani (Pst) and scala media (Psm) of both ears of each animal were successfully measured. Similar measurements were made in a control group of 25 guinea pigs that had not undergone any previous surgery. For normal ears--as well as those with hydrops-pressure differences between perilymph and endolymph (Psm - Pst) varied around 0 +/- 2.0 mm Hg. When only the right (obstructed) ears were considered, there appeared to be a slight, relative pressure elevation (p less than 0.05) in scala media during the first 7 days after endolymphatic duct obstruction-and in those ears with EP, less than 70 mV. The magnitude of this pressure difference that can be attributed to the state of endolymphatic hydrops-and not to natural variability-is calculated (within 95% confidence limits) to be less than 0.5 mm Hg.