Intratympanic gas-pressure in cases of SOM and atelectasis.

Direct manometric measurement of gas pressure in the middle ear, by piercing the tympanic membrane with a hollow needle, has been made leak-free. Even so, the rather small negative pressures (a few mm of H2O2) found in cases of secretory otitis media (SOM) and in atelectatic ears, are in error due to a previously unsuspected, significant correction factor. For the proper application of the correction, the volume of the free gas-space in each ear would have to be known. This volume was unavailable to us for the individual ear, yet in cases like ours it ranges between 0.5 to 2.5 ml and therefore an average of 1.2 ml was assumed. Our results, calculated on this basis, were -34 +/- 86 mmH2O and -9 +/- 86 mmH2O for 24 cases of SOM and 32 cases of atelectasis respectively. Like all previous measurements, there too show a large scatter. This is accounted for by two factors (i) the use of the average instead of the individual ear volume, (ii) actual fluctuation in middle ear aeration and therefore of pressure, pointing to the fact that underaeration is a functional disorder rather than an obstruction of the Eustachian tube.