Application of noninvasive cerebral electrical impedance measurement on brain edema in patient with cerebral infarction

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to investigate the change of brain edema in patients with cerebral infarction (CI) by the measurement of noninvasive cerebral electrical impedance (CEI). an invariable secure current at a frequency 50 kHz and an intensity of 0.1 mA was applied into a person's brain. The CEI of values for both hemispheres of 200 healthy volunteers and 107 CI patients was measured. The results were compared with the volume of edema on CT. (1) in healthy volunteers, the CEI values in the left and right hemisphere were 8.0 ± 1.0 and 8.0 ± 0.7 respectively. And there was no significant difference between either side (P > 0.05). Age, sex and different measuring time points did not obviously affect the CEI values (P > 0.05). (2) In CI patients, the CEI was more sensitive in the volumes of lesion which was more than 20 ml (80.0%), the CEI was75.9% and 83.3% in the volumes of lesion which was 20 - 50 ml and more than 50 ml respectively. The CEI was low when the volume fell under 20 ml; (3) The CEI of the ipsilateral side was higher than contralateral side in the patients at Day 3 after onset. It increased obviously at Days 3 - 5 after onset. The difference of two sides was the most significant. CEI of two sides was 9.2 ± 2.1 and 8.8 ± 1.8 (n = 91, P < 0.01) respectively at Day 3 after onset. CEI of the infarction side increased continuously at Day 5 after onset (9.2 ± 2.3 vs. 8.6 ± 1.9) (n = 84, P < 0.01) respectively. It gradually decreased at Day 7 after onset, but remained higher than that of the contralateral side (8.9 ± 2.2 vs. 8.7 ± 2.3, n = 68, P > 0.05); (4) There was a positive correlation between the ispilateral CEI and the volume of infarction detected within 24 hours (n = 31, r = 0.682, P < 0.05) and at Day 3 (n = 56, r = 0.602, P < 0.05) after onset. CEI may be a sensitive parameter for noninvasive monitoring the change of brain edema in CI patients. The higher the CEI, the more severe edema resulted. The sensitivity of CEI is higher when the volume of infarction exceeds 20 ml. CEI is a new technique for judging the patient condition of brain edema noninvasively.