A USEFUL TYMPANOMETRIC TEST FOR DOCUMENTING SUCCESSFUL AUTO-INFLATION MANEUVRE

 

Christos Kassionis MD

ENT Dept., Kefallonia General Hospital – Island  of Kefallonia, Greece.

 

 

 

 

Introduction

During recent years amateur SCUBA diving and spear – fishing became very popular in several parts of the world. As a result, we see an increasing number of patients with barotraumas of the middle ear and, less frequently, of the inner ear. In our practice we also see a considerable number of people referred by their diving school for preventive ENT evaluation. In all of these cases we want to be sure that the individual is able to consistently perform the auto – inflation (Valsava) maneuvre to equalize pressures across the tympanic membrane, when diving. The tympanometric test described below was devised to help us counsel these individuals on pursuing their favorite sport. 

 

Material and Method

We use the commercial electroacoustic impedance bridge and x – y – t plotter of Amlaid, model 720.

A tympanogram is first obtained the usual way, to make sure that the tympanic membrane is mobile and to determine the point of maximum admittance. The subject is then instructed to perform the auto – inflation maneuvre or a yawn – like movement of the lower jaw, whenever asked by the examiner.

The impedance bridge is turned to controlateral reflex mode, the plotter to y – t function, and the pressure in the external canal is set at about 50 dekaPa less than the middle ear pressure. The knob for sound level is set at its minimum (10 dBHL). When the subject and the examiner are ready, the y – t plotter is started and the touch – button for stimulus presentation is constantly activated. The examiner indicates when the subject should pop his/her ears or yawn to release pressure back.

 

Results

Two patterns of deflection have been recorded with our technique. In type I, the deflection is in the same direction as the normal middle ear reflex, as admittance decreases (Fig. Ia, b and Fig. II). The width of the recording corresponds to the time for which the auto – inflation was sustained. In type II, an almost flat recording is obtained (Fig. Ic). In Fig. Ia and b, arrows correspond to a yawn – like movement.

 

Discussion

With our technique, real time recordings of admittance of the middle ear are obtained, as admittance is varied with changes in middle ear pressure, caused by voluntary auto – inflation. It is obvious that sound stimulation can by no means play a role in the recording, because the level of stimulation is too low to elicit a reflex, even in case of cochlear pathology. Nevertheless, activation of the stimulus presenting mechanism is essential with our equipment, because changes in admittance can only be observed during and within one sec after cessation of sound stimulus. This is a built–in provision for rejection of artifacts during regular examination of the reflexes.

Type I recording is found in association with successful auto–inflation maneuvre. In most cases admittance returns to its reference value (baseline or close to it) upon cessation of the maneuvre. Occasionally, an appreciable amount of air is retained within the middle ear cleft, keeping admittance from readily assuming its base-line value. Observing the base line of the recording can assess passive equalization of pressures. The effect of yawning on equalization of pressures after auto-inflation can also be assessed (Fig. Ia, b). Type II recording corresponds to an unsuccessful attempt to auto-inflation. Fig. Ic represents a forceful, sustained, unsophisticated attempt. If the pressure within the external ear canal is set at a greater value than that of the middle ear, it is obvious that with auto-inflation, the admittance of the tympanic membrane will first increase, then decrease to its minimum value. The ensuing recording will be a type I variety resembling that of the on-off reflex phenomenon (Fig. II). From a practical point of view, this variety of type I is equivalent to regular type I, but it has a few drawbacks: greater excursions, more artifacts and does not show adequately residual pressure in the middle ear.

Before this test was available we used to monitor the auto-inflation maneuvre with an auscultation tube. This was also acceptable, but objective proof could not be obtained. Apart from being useful in the documentation of successful auto-inflation maneuvers, our technique has helped a number of difficult – to – teach individuals to learn the procedure of auto-inflation through self-monitoring (visual feedback).

 

 

 

Fig. I :  Successful auto-inflation maneuvers (a, b). Unsuccessful attempt ( c ). The pressure in the external canal is –50 dekaPa (a, c) and –100 dekaPa (b). Arrows correspond to a yawn-like movement.

 

Fig. II : Successful auto-inflation maneuvre. The pressure in the external canal is +20 dekaPa. Note “on-off” spikes, magnitude of excursions and “uncertainty” of  base-line.