Development of a minimally invasive microvascular ischemia monitor: analysis of noise and artifact components

Long-term postoperative pH monitoring of transplanted tissue for ischemia produces signals contaminated with noise and artifacts of various origins. The objective of our research is to analyze these artifacts. Four noise components/artifacts were identified: motion and position artifacts, a 24-hour biorhythm component, and drift. They were extracted by fourth-order Butterworth filtering, and their frequency and amplitude characteristics were determined. Through the analysis, the nature and source of the artifacts were better understood. It was concluded that, to achieve clinical usefulness, only motion and position artifacts need to be rejected from the signal, while the influences of the "24 hour component" and drift are not significant.