[Reproducibility of the measurement of thoracic electric impedance].

Recordings of thoracic electrical impedance were consecutively taken in 10 normal subjects (age 18-48 years, mean 38.6) two times during the same day, during the following day and after 1 month. The following parameters were evaluated: heart rate, systolic blood pressure, diastolic blood pressure, left ventricular ejection time, pre-ejection time, baseline electrical impedance, DZ positive peak, Q-dZ/dt interval and Heather Index. Data were processed in order to quantify the different source of variability: subjects or biological variability, days, beats. Total variability was expressed in absolute units as coefficient of variation. Results were as follows: Q-dZ/dt interval had the lowest coefficient of variation (7.7%). Inter subject was the largest source of variability for all the indices showed, ranging from 70.5% to 89.3%. On the contrary intraindividual variability was moderate racing from 1% to 2.6% for various impedance measurements. In conclusion, thoracic electrical impedance measurements showed good reproducibility, especially when successive measurements were compared in a same subject.