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Re: Multifrequency Tympanometry
Delta B is based on Funasaka e& Kumakawa (1988)approach to estimate the resonant frequency. It has implemented on the GSI machines. Basically the resonant frequency is the frequency at which the total effect of mass and stiffness becomes equal and the only component that contributes to the impedance is the resistive element. Therefore, it would be easy for the energy to transfer into the system at that frequency (impedance would be very low and admittance would be very high). Susceptance (B) is representing the total effect of mass and stiffness in the system. The GSI measures the B at the positive tail across frequencies (250-2000 Hz) in 50 Hz interval and then measures B again at pressure corresponding to the peak across the same frequencies. Then it subtracts the two at corresponding frequencies and plots the value as a function of frequency. The zero crossing of B corresponds to resonant frequency. If the total B value is zero it means that the effect of mass and stiffnes
s are equal and they have cancelled each other. The resonant frequency varies depending on the pathology of the middle ear. Resonant frequency is directly proportional to the square of stiffness and indirectly proportional to the effect of mass. Therefore, say for example if we have an otosclerotic condition, it increases the stiffness of the middle ear and as a result the resonant frequency of the middle ear will be increased. A word of caution: we have estimated the resonant frequency through Delta B plot (automatic calculation) and then measured it manually by looking at the B tympanogram at different frequencies and have noticed that the Delta B is not always corresponding to the value estimated manually especially in the diseased condition. Part of these results will be presented in CAA (Canadian Academy of Audiology) at then end of October.
Navid Shahnaz, Ph.D
School of Audiology & Speech Sciences
Faculty of Medicine
5804 Fairview Ave.
Vancouver, B.C. V6t 1Z3
---------- Original Message ----------------------------------
From: megha jp <meghajp11@xxxxxxxxxxx>
Reply-To: megha jp <meghajp11@xxxxxxxxxxx>
Date: Sat, 14 Oct 2006 15:24:07 +0100
> I would like to know details about Delta B, parameter extracted on a sweep frequency mode in multifrequency tympanometry using GSI tymstar middle ear analyser.
> I wanted to know is this an independent entity? If so does it have any clinincal relevance?
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