Impedance imaging in the newborn
Murphy D., Burton P., Coombs R., Tarassenko L., Rolfe P.
The authors have been investigating the use of electrical impedance methods for the study of cerebral haemodynamic in the newborn for many years. Of particular interest has been the early detection of intraventricular haemorrhage, which is a major cause of death or handicap in low birthweight infants. Several problems exist in obtaining representative impedance measurements from the newborn, most notably movement artefact, respiratory-based modulation and a blood-flow related pulsatile component. Movement artefact is by far the most significant problem; in order to perform long-term monitoring the authors have developed an effective algorithm for rejection of corrupted data. To remove the respiratory component, which can be 1-2% of the impedance measurement, the authors link to the output of a respiratory monitor (standard in intensive care units) as a means of synchronizing measurements to a fixed point in the respiratory cycle. Similarly, to remove the blood-flow pulsatile component, measurements are gated from the R-wave of the recorded ECG. The authors' total system consists of a front-end measurement system that passes image data over a serial link to a host computer. Data storage, image reconstruction and display are performed on the host, which can be any of a wide range of performance computers. The front-end contains the impedance measurement circuit, electrode switching electronics and a microprocessor for control, and is of a sufficiently small size to fit into the incubator next to the baby.