Biomedical subjects

Robert P Patterson

Publications and source records attributed to Robert P Patterson.

5 recordsLinked to original sources

PubMed2005

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. The chest expansion introduced artifacts in the center of the EIT images, ranging from -2% to 31% of the image magnitude. With the increase of simulated chest expansion, the percentage contribution of chest expansion relative to lung resistivity change in the EIT image remained relatively constant. The averaged resistivity changes in the lung regions caused by chest expansion ranged from 0.65% to 18.31%. 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.

Artifacts↗

PubMed2004

Improved lung edema monitoring with coronary vein pacing leads: a simulation study.

This computer simulation study compared the ability of left ventricular coronary vein (LV) pacemaker leads against right ventricular (RV) and right atrial (RA) leads to monitor lung edema using electrical impedance measurements. MRI images were used to construct electrical models of the thorax. Four lead configurations were tested with increases of pulmonary edema, intravascular fluids and heart dilation. The impedance changes observed at end systole with severe lung edema were 8.5%, 11.2%, 12.3% and 26.8% for the RA, RV, RV coil and LV configurations, respectively. Sensitivities in ohms per litre of lung fluid were 19.15, 19.15, 25.07 and 52.11 for the same configurations. The impedance changes for intravascular fluid overload with constant lung status were 1%, 1.3%, 9.2% and 6.4% while the sensitivities were 2, 2, 17 and 11 ohms per litre of intravascular fluid, respectively. Regional analysis of the thoracic sources of impedance revealed a high sensitivity near pacing electrodes and generator, and a low sensitivity to the right lung and all pulmonary vessels. Simulations showed that LV leads have a threefold advantage in sensitivity when monitoring lung edema in comparison to conventional RV leads. To monitor vascular and lung fluids independently, combined impedance configurations may be used. Regional sensitivities must be taken into account for proper clinical interpretation of impedance changes.

Cardiac Pacing, Artificial↗

PubMed2003

Evaluation of an EIT reconstruction algorithm using finite difference human thorax models as phantoms.

A finite difference model of the human thorax with 113,400 control volumes (nodes) based on ECG gated MRI images was used to evaluate the Sheffield DAS-01P EIT system. Sixteen simulated electrode positions equally spaced around the thorax model at approximately the fourth intercostals space level were selected. Pairs of adjacent positions were excited sequentially by injecting current in a manner similar to that used by the Sheffield DAS-01P EIT system. The resulting voltages on the non-excited electrode positions were calculated and used to reconstruct the image using the Sheffield filtered back projection algorithm. By changing the resistivities of the lungs, the ventricles and the atria over a range of 1% to 40%, the resulting changes in the images were quantified by measuring the average resistivity change over a region defined automatically by two thresholds, 40% or 80% of the average of the first four pixels with the largest change. The results show that the changes observed in the images are consistently less than the changes in the model, but changed in a nearly linear manner as a function of resistivity in the model. For 40% resistivity changes in the model for right lung, right ventricle and right atrium, the observed resistivity changes in the region of interest (ROI, defined by the 80% threshold) of the images are 32% for the right lung, 11% for the right ventricle and 5.5% for the right atrium, which suggests strong volume dependence of EIT imaging. The effect of structural (size) change between end diastole and end systole was also studied, which showed large resistivity changes caused in the heart region of the constructed image. The study demonstrates that the Sheffield DAS-01P EIT reconstruction algorithm tracks the change occurring in the lungs most closely and with proper scaling may be used to observe physiological changes.

Algorithms↗

PubMed2003

Determining the relationship of heart rate and blood pressure using voluntary cardio-respiratory synchronization (VCRS).

Voluntary cardio-respiratory synchronization (VCRS) was used to investigate heart rate and blood pressure changes in the supine position in 21 subjects. VCRS involves a breathing pattern that is synchronized with the cardiac cycle. The signals to inhale and exhale are derived from the ECG. In this study, the subjects inspired for four heart beats and expired for four heart beats for 35 cycles. This technique is designed to have the heart beat occur at exactly the same phase in the respiratory cycle and lends itself to the study of the influence of the respiration cycle on heart rate and blood pressure changes. The heart rate and blood pressure changed simultaneously in the same direction, with the largest significant positive change occurring on the second heart beat during inspiration. The authors discuss the potential of VCRS for research, and clinical applications as a respiration modulator for hypertension therapy or increased heart rate variability.

Adult↗

PubMed2003

Comparison of R-wave detection errors of four wireless heart rate belts in the presence of noise.

Four commercial wireless chest belts (Vetta, Nashbar, Polar and new Polar) were assessed for their susceptibility to noises in R-wave detection. A normal ECG signal was generated using a LionHeart simulator (Bio-tek Instruments, Inc.) with a fixed RR interval (750 ms) and R-wave amplitude (1 mV). Different levels of EMG and baseline wanderings (sinusoidal waves) were recorded from a healthy subject and a Quartec Model MFG-1 generator, respectively. They were added to the ECG signal in a BioPac system (BioPac systems Inc., Santa Barbara, CA) to simulate an ECG in physiological noise. The BioPac system applied the 'contaminated' ECG to the belts via a voltage divider. A PC-based Polar Precision Performance system was used to receive the detected R-wave pulses transmitted from the wireless belts and to calculate the RR intervals. Two types of detection errors were observed in the RR intervals: small time shifts, the potentially non-fixable small variance, and missed/false beats, the abnormally large and potentially fixable intervals. Results showed that small time shifts exist in all tests ranging from -10 ms to 10 ms and increase with the level of EMG before missed/false beats occur. Missed/false beats occur only when EMG level is beyond the threshold of 0.4 mV, 1.6 mV, 1.2 mV and 1.2 mV for Vetta, Nashbar, Polar and new Polar, respectively. The potential to detect and fix EMG introduced missed/false beats showed that this type of error could only be improved when the added EMG was below a certain value. Results also showed that no missed/false beats occur when the frequency and amplitude of sinusoidal waves were below 1 Hz and 5 mV.

Artifacts↗