Variability of body surface impedance measurements in cardiac transplant patients and normal subjects

The aim was to establish the variability of body surface impedance measurements in cardiac transplant patients and healthy subjects. In 11 healthy subjects, impedance measurements were taken: i) daily over 5 days; ii) before and after a meal; iii) in 5 different body positions. In the transplant group of 3 patients, 2 consecutive impedance recordings were taken daily after transplantation. All recordings were of 1 minute duration at excitation frequencies of 1, 3, 10, 30 and 100 kHz. There were large differences in the impedance of different subjects in both the healthy and patient groups which ranged from 15 ohm to 98 ohm at 1 kHz. The maximum difference in daily repeated measurements in the transplant group was a mean of 9 ohm. The maximum difference in recordings taken on the same day was less than 1 ohm. In the control group the largest mean change in impedance due to change in posture was from supine to lying on left side for which the impedance increased by 4 ohm. Eating a meal reduced the impedance by a mean of 2 ohm in the supine position.