Welch Allyn TM 262 Auto Tymp - User Manual - Manual (Page 62)

TM 262
4-4 Revised 4/11/08
NOTE: If a compliance value is measured to be greater than 1.5 cm, the instrument changes
the range assigned to the graph automatically and the tympanogram is traced to 3.0 cm.
The validity of tympanometry and acoustic reflex testing is dependent upon a healthy tympanic
membrane. A pathological condition at this membrane can mask the true condition of the
middle ear.
Pressure Peak
Normal
Strict rules for middle-ear pressure indicate a normal range of ±50 daPa. However, for most
applications, a normal range of -150 daPa to +100 daPa is used.
Abnormal
Very rarely will you obtain an extreme positive pressure condition. Some researchers have
reported high positive pressures at the onset of acute otitis media.
Pressure values more negative than -150 daPa are indicative of a poorly functioning eustachian
tube. The severity of this condition is determined by how negative the pressure is and its impact
on the compliance peak.
If no pressure peak is measured over the pressure range of +200 daPa to -400 daPa, then the
letters NP will appear on the screen and the printout. This indicates that no pressure peak was
detected over this pressure range.
Gradient
Normal
When testing a child, the normal range for the gradient is between 60 and 150 daPa. (Infants
may show higher gradient values due to the mobility of their ear canals.) The range of normal is
somewhat narrower for adults i.e., 50 to 110 daPa.
Abnormal
A high gradient value (greater than the high end of the normal range per age group) is
indicative of middle-ear effusion. The reduced compliance values and negative middle-ear
pressure characteristic of developing or resolving otitis media with effusion (OME) will be
manifested in a broad tympanogram with a large gradient value. However, abnormal gradient
values may also be found in the absence of abnormal parameters. This could indicate a transient
OME, so a retest after several weeks may be recommended.
When the middle ear’s mobility is reduced to near 0 cm 3 , due to viscous effusion or a “glue-ear”
condition, no gradient value can be measured. In this case, dashes (—) will be displayed next to
the letters GR.
Very low gradient values are associated with a flaccid middle ear system. These low values
should be taken into consideration with the ear canal volume and compliance peak values to
determine the probable use of the flaccid condition.