Physiological measurement
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Physiological measurement · Apr 2005
Comparative StudyDetection of emboli in vessels using electrical impedance measurements--phantom and electrodes.
A phantom was constructed to simulate the electrical properties of the neck. A range of possible electrode configurations was then examined in order to improve the sensitivity of the impedance measurement method for the in vivo detection of air emboli. The neck phantom consisted of simulated skin, fat and muscle layers made of agar and a conductive rubber tube mimicking the common carotid artery. The ring-shaped electrodes with a guard electrode showed the highest sensitivity to emboli at short distances.
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Physiological measurement · Apr 2005
Comparative StudyMonitoring lung edema using the pacemaker pulse and skin electrodes.
Previous clinical studies have shown that impedance measurements using right ventricular (RV) leads can monitor congestion due to heart failure. We previously reported on a three-fold advantage of bipolar left ventricular (LV) leads, which are near the lung, over RV leads in detecting pulmonary edema with impedance. A combined system of internal and external electrodes is now investigated using computer models, for use with conventional cardiac resynchronization (CRT) systems with unipolar LV leads. ⋯ The computer models suggest that combined internal-external systems can be as sensitive as the totally implanted ones. Lung edema may be monitored at follow up or home for LV paced patients with only two external electrodes. Using very low impedance configurations optimized by computer can greatly maximize the response, with a cost of poor stability.
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Physiological measurement · Apr 2005
EIT images of ventilation: what contributes to the resistivity changes?
One promising application of electrical impedance tomography (EIT) is the monitoring of pulmonary ventilation and edema. Using three-dimensional (3D) finite difference human models as virtual phantoms, the factors that contribute to the observed lung resistivity changes in the EIT images were investigated. The results showed that the factors included not only tissue resistivity or vessel volume changes, but also chest expansion and tissue/organ movement. ⋯ Tissue/organ movement resulted in an increased resistivity in the lung region and in the center anterior region of EIT images. The increased resistivity with inspiration observed in the heart region was caused mainly by a drop in the heart position, which reduced the heart area at the electrode level and was replaced by the lung tissue with higher resistivity. This study indicates that for the analysis of EIT, data errors caused by chest expansion and tissue/organ movement need to be considered.
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Physiological measurement · Apr 2005
Comparative StudyChanges in the intracranial rheoencephalogram at lower limit of cerebral blood flow autoregulation.
Cerebral blood flow (CBF) reactivity monitoring is an appropriate primary parameter to evaluate cerebral resuscitation due to a systemic or regional cerebral injury leading to possible irreversible brain injury. Use of the electrical impedance method to estimate CBF is rare, as the method's anatomical background is not well understood. Use of intracranial rheoencephalography (iREG) during hemorrhage and comparison of iREG to other CBF measurements have not been previously reported. ⋯ The studies indicate that iREG might reflect cerebrovascular responses more accurately than changes in local CBF measured by LDF and carotid flow. REG may indicate promise as a continuous, non-invasive life-sign monitoring tool with potential advantages over ultrasound, the CBF measurement technique normally applied in clinical practice. REG has particular advantages in non-hospital settings such as military and emergency medicine.