40
NOTE
If the measured compliance value is less than 0.1 cm
3
, the TM 262
TM
Auto
Tymp
TM
will print the letters NP next to the heading cm
3
on the screen and
printout. The letters “NP” indicate a poorly defined or flat tympanogram.
The tympanogram may depict a very shallow peak.
A compliance value greater than 1.4 cm
3
(or 1.8 cm
3
) indicates a
hyperflaccid tympanic membrane or a possible disarticulation de-
pending upon how far above the normal range the value is. Generally
speaking, a compliance value of greater than 3.0 cm
3
is indicative
of a disarticulated ossicular chain. Further testing is necessary to
confirm this suspicion.
NOTE
If a compliance value is measured to be greater than 1.5 cm
3
, the TM 262
automatically changes the range assigned to the graph and the tympanogram
is traced to 3.0 cm
3
.
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.
4.3 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
An extreme positive pressure condition is rare. 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 the degree of negative pressure and its impact on the
compliance peak.
If no pressure peak is measured over the pressure range of +200 daPa
to –400 daPa, the letters NP will appear on the screen and the printout.
This indicates that no pressure peak was detected over this pressure
range.
4.4 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 mo-
bility of their ear canals). The range of normal is somewhat narrower for
adults, i.e. 50 to 110 daPa.
