Muscle tissue ischemia monitoring using impedance spectroscopy: analysis of R/sub 0/ and /spl tau/ variations with ischemia

Impedance spectroscopy is a promising method for tissue ischemia monitoring. Ischemia causes changes in tissue impedance that can be detected by impedance spectroscopic measurements. This technique has numerous advantages over existing ischemia monitoring methods: it is non-invasive and suitable for long term and continuous use. To fully develop this method, we experimentally investigated the relationships between ischemia and tissue impedance. For this purpose, in-vivo animal experiments were conducted, Results show complex, nonlinear relationships between tissue impedance and ischemia. Previous studies identified R/sub 0/ (DC impedance) as the parameter most sensitive to ischemia. However, R/sub 0/ variations are quite non-specific, therefore R/sub 0/ cannot be quantitatively correlated to ischemia. In this paper, we present an analysis which indicates that ischemia induced variations of the tissue time constant /spl tau/ are well correlated to R/sub 0/ and pH variations. /spl tau/ has a better sensitivity and a higher level of specificity to ischemia variations, compared to R/sub 0/. This is evidence that /spl tau/ is a powerful indicator of tissue ischemia.