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Author: search.filters.author.Cao, HongSubject: search.filters.subject.Resistivity

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    In vitro measurement of myocardial impedivity anisotropy with a miniature rectangular tube
    (2003-04-01)
    Tsai, Jang Zern
    ;
    Will, James A.
    ;
    Vorperian, Vicken R.
    ;
    Hubbard-Van Stelle, Scott
    ;
    Cao, Hong
    Due to rapid change of fiber orientation, it is difficult to measure myocardial impedivity separately in a longitudinal or transverse fiber direction without mutual influence in the two directions. Previously published values of the longitudinal and the transverse myocardial impedivity were derived indirectly from measurements that mixed the impedivity in all directions. Those values are questionable because the derivations were based on a simplified uniform myocardial fiber model. In this paper, a miniature rectangular tube was devised to facilitate direct measurement of myocardial impedivity in a uniform fiber direction. The average transverse-to-longitudinal ratio of the measured in vitro swine myocardial impedivity was about 1.66 from 1 Hz to 1 kHz and dropped to 1.25 at 1 MHz. The result is important for accurate modeling of the electrical property of myocardium in biomedical research of radio-frequency cardiac catheter ablation.
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    In-vivo measurement of swine myocardial resistivity
    (2002-04-30)
    Tsai, Jang Zern
    ;
    Will, James A.
    ;
    Stelle, Scott Hubbard Van
    ;
    Cao, Hong
    ;
    Tungjitkusolmun, Supan
    We used a four-terminal plunge probe to measure myocardial resistivity in two directions at three sites from the epicardial surface of eight open-chest pigs in-vivo at eight frequencies ranging from 1Hz to 1 MHz. We calibrated the plunge probe to minimize the error due to stray capacitance between the measured subject and ground. We calibrated the probe in saline solutions contained in a metal cup situated near the heart that had an electrical connection to the pig's heart. The mean of the measured myocardial resistivity was 319 Ω cm at 1 Hz down to 166 Ωcm at 1 MHz. Statistical analysis showed the measured myocardial resistivity of two out of eight pigs was significantly different from that of other pigs. The myocardial resistivity measured with the resistivity probe oriented along and across the epicardial fiber direction was significantly different at only one out of the eight frequencies. There was no significant difference in the myocardial resistivity measured at different sites.