Spectroscopy study of the dynamics of the transencephalic electrical impedance in the perinatal brain during hypoxia

Abstract

Hypoxia/ischaemia is the most common cause of brain damage in neonates. Thousands of newborn children suffer from perinatal asphyxia every year. The cells go through a response mechanism during hypoxia/ischaemia, to maintain the cellular viability and, as a response to the hypoxic/ischaemic insult, the composition and the structure of the cellular environment are altered. The alterations in the ionic concentration of the intra-and extracellular and the consequent cytotoxic oedema, cell swelling, modify the electrical properties of the constituted tissue. The changes produced can be easily measured using electrical impedance instrumentation. In this paper, we report the results from an impedance spectroscopy study on the effects of the hypoxia on the perinatal brain. The transencephalic impedance, both resistance and reactance, was measured in newborn piglets using the four-electrode method in the frequency range from 20 kHz to 750 kHz and the experimental results were compared with numerical results from a simulation of a suspension of cells during cell swelling. The experimental results make clear the frequency dependence of the bioelectrical impedance, confirm that the variation of resistance is more sensitive at low than at high frequencies and show that the reactance changes substantially during hypoxia. The resemblance between the experimental and numerical results proves the validity of modelling tissue as a suspension of cells and confirms the importance of the cellular oedema process in the alterations of the electrical properties of biological tissue. The study of the effects of hypoxia/ischaemia in the bioelectrical properties of tissue may lead to the development of useful clinical tools based on the application of bioelectrical impedance technology.

Electrical Bioimpedance Cerebral Monitoring

“…The total output impedance for this type of VCCS can be approximated by a general equivalent circuit modeled as three impedances building up a parallel bridge; see Figure 19, where Z in is the input impedance of the VCCS considering the Op-Amp ideal, Z i is the equivalent input impedance of the Op-Amp from the inverting input to ground, Z f is the impedance in the feedback loop, and opz(s) is the OpAmp impedance factor as defined in (10).…”

“…Notice that the notation changes in equation (2.13) from r 1 in equation (10) to r i, and from r in equation (2.10) to z * . Usually the resistivity effect of the plasma membrane is neglected and the membrane is considered as an ideal capacitor.…”

“…Figure 5(A) shows a well-known NIC topology (A. S. , widely used in EIS and EIT (A. S. . Such topology is able to synthesize an inductance between the points a and b with the value given by (10).…”

Electrical Bioimpedance Cerebral Monitoring

“…The Op-Amp impedance factor, opz (10), plays the same role in the currentdriven VCCS as in the pure VCCS. As is seen in (9), opz is a crucial factor that links the value of Z in directly to the output impedance Z out .…”

Simple voltage-controlled current source for wideband electrical bioimpedance spectroscopy: circuit dependences and limitations

“…Examples of this are skin cancer screening (Aberg et al , Beetner et al 2003 and methods for detection of tumours (Skourou et al 2004(Skourou et al , 2007, meningitis (Van Kreel 2001), brain cellular oedema (Lingwood et al 2002, Seoane et al 2005 and breast cancer (Assenheimer et al 2001). All these applications depend on the EBI recorded over a wide frequency range.…”