SERIAL MEASUREMENTS OF THORACIC IMPEDANCE AND CARDIAC OUTPUT IN HEALTHY NEONATES AFTER NORMAL DELIVERY AND CAESAREAN SECTION

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Abstract
Thoracic electrical impedance measurements were performed during the 1st, 2nd, 8th and up to the 32nd h of life in 2 groups of healthy infants. In group V, all 24 infants were delivered vaginally; in group S, all 24 infants were delivered by cesarean section for obstetrical reasons. Basal thoracic impedance (Zo), heart rate (HR), stroke volume (SV) and cardiac output (.ovrhdot.Q) were determined. In group V, Zo increased from 31.9 to 34.0 ohm between 2 h and the last recording between 8-32 h. SV decreased from 4.1 to 3.4 ml between 2-4 h and was accompanied by a decrease of .ovrhdot.Q from 560 to 450 ml/min. Heart rate slowed from 129 to 115 beats/min between 2 h and the last recording at .gtoreq. 8 h. In group S, Zo increased from 32.2 to 35.9 ohm between 2 and 8 h. Mean SV increased from 3.6 to 4.4 ml between 8 and 32 h and heart rate slowed from 131 to 113 beats/min between 1-8 h. No significant differences were observed between the groups. The accuracy of the impedance-SV and .ovrhdot.Q data cannot be validated. For the most part they compare favorably with values previously obtained by soluble gas methods. Serial changes may reflect decreasing shunts and/or increasing aeration and changes in total fluid volume of the lungs, intra- or extravascular. The precision of the measurements is good since reproducibility of single SV and .ovrhdot.Q determinations is higher than with standard dilution techniques. The data may serve as baseline values for comparison with data from infants of the same age with various anomalies.