Physiological measurement
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Physiological measurement · Jun 2009
Comparative StudyDifferences in regional pulmonary pressure-impedance curves before and after lung injury assessed with a novel algorithm.
Global pressure-volume (PV) curves are an adjunct measure to describe lung characteristics in patients with acute respiratory distress syndrome (ARDS). There is convincing evidence that high peak inspiratory pressures (PIP) cause barotrauma, while optimized positive end-expiratory pressure (PEEP) helps avoid mechanical injury to the lungs by preventing repeated alveolar opening and closing. The optimal values of PIP and PEEP are deduced from the shape of the PV curve by the identification of so-called lower and upper inflection points. ⋯ The results demonstrate a clear increase in lower inflection point (LIP) along the gravitational axis both before and after lung injury. Moreover, it is clear from comparison of the local EIT-derived LIPs with those derived from global PV curves that a ventilation strategy based on the PV curve alone may leave dependent areas of the lung collapsed. EIT-based PI curve analysis may help choosing an optimal ventilation strategy.
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Physiological measurement · Jun 2009
Comparative StudyA comparison study of electrodes for neonate electrical impedance tomography.
Electrical impedance tomography (EIT) is an imaging technique that has the potential to be used for studying neonate lung function. The properties of the electrodes are very important in multi-frequency EIT (MFEIT) systems, particularly for neonates, as the skin cannot be abraded to reduce contact impedance. In this work, the impedance of various clinical electrodes as a function of frequency is investigated to identify the optimum electrode type for this application. ⋯ For the electrode-interface impedance, the average magnitude decreased with frequency, with an average value of 5 kOmega at 10 kHz and 337 Omega at 1 MHz; for the tissue impedance, the respective values were 987 Omega and 29 Omega. Overall, the Ambu BRS, Kendall ARBO and Textronics textile electrodes gave the lowest electrode contact impedance at 1 MHz. Based on the results of the two-electrode measurements, simple RC models for the Ambu BRS and Kendall-ARBO and Textronics textile electrodes have been derived for MFEIT applications.