AmpliVox Otowave 302+, Инструкция по эксплуатации

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APPENDIX A – 1000 HZ TYPANOMETRY & MEATUS COMPENSATION
59 OTOWAVE 302+ INSTRUCTION FOR USE
𝑌_𝑡𝑚 =
|
𝑌_𝑚𝑒𝑎𝑠
|
−
|
𝑌_𝑒𝑐
|
When considering the general case, including probe tone frequencies at higher frequencies than 226Hz, the above
subtraction of the effect of the ear canal air volume is more complicated. In mathematical terms, a complex subtraction
is required, which involves taking into account the
G and B components separately. In graphical terms, this can be
described as a vector subtraction, and the equation now takes on the form:
𝑌_𝑡𝑚 =
|
𝑌_𝑚𝑒𝑎𝑠 − 𝑌_𝑒𝑐
̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅ |
The baseline value ( Y
ec
) is the measured admittance of the ear when at maximum pressure (no200daPa for the
Otowave 302+). This approximates Y
ec
because the applied pressure reduces Y
tm
towards 0 (but not all the way to 0,
otherwise it would not be possible to hear the probe tone at all; nonetheless the approximation is sufficient for clinical
purposes). This value is subtracted from each of the tympanogram measurements in turn to generate the meatus-
compensated tympanogram normally presented to the clinician.
The above subtractions are represented in terms of vectors in Figure 1 and Figure 2 shown at the end of this section for
probe tone frequencies of 226Hz and 1000Hz respectively. In Figure 1, it can be seen that there is minimal loss of
accuracy by performing a scalar subtraction instead of a vector subtraction. In other words, the phase angles of the
vectors (directions of arrows) are similar.
Figure 1: 226 Hz probe tone: The distance between the n th sample Y
n
(admittance value of the n th sample in the tympanogram) and
the baseline sample Y
ec
is essentially the same as the difference in lengths between the length
|𝑌_𝑒𝑐 |
because conductance is
always small at 226 Hz and reading are always stiffness dominated. Scalar subtraction (
|
𝑌
𝑛
|
− |𝑌_𝑒𝑐 | ) is adequate.