Continuous limb blood flow estimation in the newborn using electrical impedance plethysmography.

This study aims to define a method for acquiring limb flood flow data from newborn babies on a continuous basis which would be suitable for automatic processing. Pulsatile electrical impedance and strain gauge signals were analyzed in 3 different ways. The results were compared with estimates of flow derived from venous occlusion plethysmography with a mercury-in-rubber strain gauge. Measurements were made from 33 babies. The impedance technique was easier to perform than the strain gauge technique. The reproducibility of the various estimates of flow is shown in Table 3. The beat-to-beat reproducibility of simultaneous pulsatile mesurements and of repeated measurements on different subjects was greater from the impedance recordings than from the strain gauge recordings. The results of linear regression analyses between the different flow estimates are shown in Table 4. The best correlation with flow measured using venous occlusion plethysmography was with flow calculated from the impedance pulse height, F(Zmax) (r = 0.76; n = 30; P < 0.001). The regression line between these 2 variables was not statistically significantly different from the line of identity, (P < 0.98), and the intercept is close to zero. The measurement of the impedance pulse height, delta Zmax, and the subsequent calculation of F(Zmax) could be automated and provide continuous beat-to-beat blood flow estimations.