Physiological measurement
-
Physiological measurement · May 2006
Clinical TrialParametric EIT for monitoring cardiac stroke volume.
The bio-impedance technique appears appropriate for non-invasive cardiac stroke volume (SV) measurement, as the thoracic conductivity distribution is altered during the cardiac cycle due to the heart contraction and blood perfusion. In the present work, the feasibility of a parametric electrical impedance tomography (EIT) for assessing the cardiac SV was studied. An impedance model of the thorax was constructed from segmented axial MRI images along 19 phases of the cardiac cycle. ⋯ The simulation results were compared to physical data, collected with a portable EIT system (PulmoTrace, CardioInspect). The validation study was employed for a group of N = 28 healthy patients, and a comparison with impedance cardiography measurements (BioZ, Cardiodynamics) was made, showing a correlation of r = 0.86 (p = 4 x10(-9)). The preliminary results demonstrate that parametric EIT has the potential to measure SV, and may be applicable for both clinical and home environment usage.
-
Physiological measurement · May 2006
Clinical TrialStudy of the optimum level of electrode placement for the evaluation of absolute lung resistivity with the Mk3.5 EIT system.
Inter-subject variability has caused the majority of previous electrical impedance tomography (EIT) techniques to focus on the derivation of relative or difference measures of in vivo tissue resistivity. Implicit in these techniques is the requirement for a reference or previously defined data set. This study assesses the accuracy and optimum electrode placement strategy for a recently developed method which estimates an absolute value of organ resistivity without recourse to a reference data set. ⋯ However, the differences in absolute lung resistivity between normal and deep tidal breathing at the same electrode level are significant. No significant difference was found in the coefficient of variation between the electrode levels of 4 and 5 cm (9.5 +/- 3.6%, 8.5 +/- 3.2% at 4 and 5 cm, respectively: mean +/- standard deviation in individual subjects). Therefore, the electrode levels of 4 and 5 cm above the xiphoid process showed reasonable reliability in the measurement of absolute lung resistivity both among individuals and over time.
-
Physiological measurement · May 2006
Comparative Study Clinical TrialComparison of different methods to define regions of interest for evaluation of regional lung ventilation by EIT.
The measurement of regional lung ventilation by electrical impedance tomography (EIT) has been evaluated in many experimental studies. However, EIT is not routinely used in a clinical setting, which is attributable to the fact that a convenient concept for how to quantify the EIT data is missing. The definition of region of interest (ROI) is an essential point in the data analysis. ⋯ Our results indicate that both approaches to ROI definition using statistical parameters are suitable when impedance signals with high sensitivity to ventilation-related phenomena are to be analyzed. The definition of the ROI contour as 20-35% of the maximum standard deviation or regression coefficient is recommended. Simple segmental ROIs are less convenient because of the low ventilation-related signal component in the dorsal region.
-
Physiological measurement · May 2006
Controlled Clinical TrialImaging pathologic pulmonary air and fluid accumulation by functional and absolute EIT.
The increasing use of EIT in clinical research on severely ill lung patients requires a clarification of the influence of pathologic impedance distributions on the validity of the resulting tomograms. Significant accumulation of low-conducting air (e.g. pneumothorax or emphysema) or well-conducting liquid (e.g. haematothorax or atelectases) may conflict with treating the imaging problem as purely linear. First, we investigated the influence of stepwise inflation and deflation by up to 300 ml of air and 300 ml of Ringer solution into the pleural space of five pigs on the resulting tomograms during ventilation at constant tidal volume. ⋯ The results of the animal model show that f-EIT based on back projection is not disturbed by the artificial pneumo- or haematothorax. Application of SIRT allows reliable discrimination and detection of the location and amplitude of pneumo- or haematothorax. These results were supported by the good agreement between the electrical impedance tomograms and CT scans on patients and by the significant differences of regional resistivity data between patients and healthy volunteers.
-
Physiological measurement · May 2006
Factors limiting the application of electrical impedance tomography for identification of regional conductivity changes using scalp electrodes during epileptic seizures in humans.
Electrical impedance tomography (EIT) has the potential to produce images during epileptic seizures. This might improve the accuracy of the localization of epileptic foci in patients undergoing presurgical assessment for curative neurosurgery. It has already been shown that impedance increases by up to 22% during induced epileptic seizures in animal models, using cortical or implanted electrodes in controlled experiments. ⋯ No reproducible changes with the expected time course of some tens of seconds and magnitude of about 0.1% could be reliably measured. This demonstrates that it is feasible to acquire EIT images in parallel with standard EEG during presurgical assessment but, unfortunately, expected EIT changes on the scalp of about 0.1% are swamped by much larger movement and systematic artefact. Nevertheless, EIT has the unique potential to provide invaluable neuroimaging data for this purpose and may still become possible with improvements in electrode design and instrumentation.