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. Al1 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.
Langley P, Dark JH, Murray A. Variability of body surface impedance measurements in cardiac transplant patients and normal subjects. Computers in Cardiology 2002; 29: 721-4.
Dr. Philip Langley, Freeman Unit, Newcastle upon Tyne. Tel: +44 (0)191-223-6161.
Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, NE7 7DN, UK.
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