Robert Patterson

GREIT: A unified approach to 2D linear EIT reconstruction of lung images

Electrical impedance tomography (EIT) is an attractive method for clinically monitoring patients during mechanical ventilation, because it can provide a non-invasive continuous image of pulmonary impedance which indicates the distribution of ventilation. However, most clinical and physiological research in lung EIT is done using older and proprietary algorithms; this is an obstacle to interpretation of EIT images because the reconstructed images are not well characterized. To address this issue, we develop a consensus linear reconstruction algorithm for lung EIT, called GREIT (Graz consensus Reconstruction algorithm for EIT). This paper describes the unified approach to linear image reconstruction developed for GREIT. The framework for the linear reconstruction algorithm consists of (1) detailed finite element models of a representative adult and neonatal thorax, (2) consensus on the performance figures of merit for EIT image reconstruction and (3) a systematic approach to optimize a linear reconstruction matrix to desired performance measures. Consensus figures of merit, in order of importance, are (a) uniform amplitude response, (b) small and uniform position error, (c) small ringing artefacts, (d) uniform resolution, (e) limited shape deformation and (f) high resolution. Such figures of merit must be attained while maintaining small noise amplification and small sensitivity to electrode and boundary movement. This approach represents the consensus of a large and representative group of experts in EIT algorithm design and clinical applications for pulmonary monitoring. All software and data to implement and test the algorithm have been made available under an open source license which allows free research and commercial use.

Bicycle pedalling forces as a function of pedalling rate and power output

Eleven men with recreational bicycling experience rode a bicycle ergometer with instrumented force pedals to determine the effects of pedalling rate and power output on the total resultant pedal force, Fr, and the component of the force perpendicular to the crank arm. The force patterns were obtained at power outputs of 100 W and 200 W for pedalling rates of 40-120 rpm in intervals of 10 rpm. Data were not obtained at 40 rpm at the 200 W power output. The Fr averaged over a crank cycle (Far) was lowest at 90 rpm and 100 W, a value statically different (P less than 0.05) from those at 40, 50, and 120 rpm. At 200 W, the Fr was lowest at 100 rpm, a value statistically different (P less than 0.05) from those at 50, 60, and 70 rpm. The Far varied widely (range of 30% of mean for all subjects) for individuals at a given power output. The results suggest that pedalling at 90-100 rpm may minimize peripheral forces and therefore peripheral muscle fatigue even though this rate may result in higher oxygen uptake.

Mindfulness-Based Stress Reduction Versus Pharmacotherapy for Chronic Primary Insomnia: A Randomized Controlled Clinical Trial

OBJECTIVE The aim of this study was to investigate the potential of mindfulness-based stress reduction (MBSR) as a treatment for chronic primary insomnia. DESIGN A randomized controlled trial was conducted. SETTING The study was conducted at a university health center. PATIENTS Thirty adults with primary chronic insomnia based on criteria of the Diagnostic and Statistical Manual of Mental Disorders, Text Revision, 4th Edition were randomized 2:1 to MBSR or pharmacotherapy (PCT). INTERVENTIONS Mindfulness-based stress reduction, a program of mindfulness meditation training consisting of eight weekly 2.5 hour classes and a daylong retreat, was provided, with ongoing home meditation practice expectations during three-month follow-up; PCT, consisting of three milligrams of eszopiclone (LUNESTA) nightly for eight weeks, followed by three months of use as needed. A 10-minute sleep hygiene presentation was included in both interventions. MAIN OUTCOMES The Insomnia Severity Index (ISI), Pittsburgh Sleep Quality Index (PSQI), sleep diaries, and wrist actigraphy were collected pretreatment, posttreatment (eight weeks), and at five months (self-reports only). RESULTS Between baseline and eight weeks, sleep onset latency (SOL) measured by actigraphy decreased 8.9 minutes in the MBSR arm (P < .05). Large, significant improvements were found on the ISI, PSQI, and diary-measured total sleep time, SOL, and sleep efficiency (P < .01, all) from baseline to five-month follow-up in the MBSR arm. Changes of comparable magnitude were found in the PCT arm. Twenty-seven of 30 patients completed their assigned treatment. This study provides initial evidence for the efficacy of MBSR as a viable treatment for chronic insomnia as measured by sleep diary, actigraphy, well-validated sleep scales, and measures of remission and clinical recovery.

Fundamentals of impedance cardiography

The most widely used impedance method for cardiac stroke volume and cardiac output measurements is described. It uses band electrodes around the ends of the thorax and forward extrapolation of the systolic portion of the impedance waveform. Studies performed to determine the physiological origin of the impedance change and the apparently conflicting results are summarized. Comparative studies with other methods are briefly discussed. It is concluded that for the present technique to be placed on a sound scientific base, it is necessary to determine what regions or organs contribute to the impedance change recorded from the thoracic surface, but that it shows remarkably good correlation with other cardiac output measurement systems if applied to a select relatively healthy population, given all the assumptions involved.<<ETX>>

Multiple sources of the impedance cardiogram based on 3-D finite difference human thorax models

Two 3D electrical models of the human thorax, each consisting of 216,000 control volumes, were constructed based upon MR images taken at end diastole and end systole. Using the finite difference method, the contributions of various sources to the impedance cardiogram were studied for the traditional band electrode configuration. The contributions were categorized into three areas: 1) the structural changes between end diastole and end systole, 2) the flow-induced blood resistivity changes in major arteries and veins, and 3) the lung resistivity variation due to the lung blood volume change. Based on the models, Z/sub 0/ and /spl Delta/Z between end diastole and end systole were 24.4 /spl Omega/ and -0.132 /spl Omega/, as compared with the measurements of 21.8 /spl Omega/ and -0.123 /spl Omega/ made on the same subject from whom the images were taken. Arterial and venous blood resistivity changes caused approximately 57% of the total impedance change. The lung resistivity change and the structural changes contributed 39% and 4%, respectively. The structural changes inside the thorax included the dimensional changes of blood vessels, the blood volume changes of the heart chambers, and heart movement. Although the net impedance change due to the structural changes was relatively small, the individual variation of various factors was large, with significant cancellation occurring. The results suggest that the thoracic impedance cardiographic signal is a mixed representation of many inseparable factors and may not be reliable for the stroke volume calculation. Also, the O-wave, which is clinically observed in various cardiac conditions, may be linked to the diastolic blood flow in the central veins.<<ETX>>

Sources of the thoracic cardiogenic electrical impedance signal as determined by a model.

A three-dimensional electrical model was developed to study the origin of ΔZ due to cardiac activity recorded from band electrodes around the neck and lower thorax. Volume changes were simulated with resistivity changes in the lungs, large arteries, large veins and atria, ventricles, small arteries and veins and the skeletal muscle for a typical 80 ml ventricular stroke volume. The results showed the contributions to ΔZ to be 61 per cent from the lungs, 23 per cent from the large arteries and 13 per cent from the skeletal muscle. The ΔZ signal was most sensitive to skeletal muscle volume change The results indicate that the ΔZ signal has many origins which could cause significant error in calculated cardiac function it all the regions do not change in the normal related pattern.

Body fluid determinations using multiple impedance measurements

It is shown that a significant potential for error exists when a single measurement from wrist to ankle is used to determine body water volume and percentage of body fat, and that by making measurements of multiple regions of the body (arms, legs, and trunk) a more accurate determination can be obtained. This concept is suggested by the results of multiple impedance measurements made on a group of 11 patients undergoing haemodialysis.<<ETX>>

Sitting forces and wheelchair mechanics

The effects of back angle and leg height on sitting forces in a wheelchair were studied, using a force plate mounted on a wheelchair seat. Readings of both normal force (perpendicular to the seat) and shear force were measured while the chairs back angle and footrest height were changed. Pressure under the ischial tuberosities was also measured during the footrest height adjustments. Five normal subjects sat directly on the plate as well as upon ROHO and Jay cushions placed on the force plate. Returning the back to the upright position after a recline caused the normal force (+/- SD) to increase 5.4 +/- 2.5, 9.5 +/- 4.0, and 10.0 +/- 2.3 kg for the hard surface, Jay cushion, and ROHO cushion respectively, while shear at the plate increased to 5.1 +/- 2.2, 11.6 +/- 2.6, and 12.3 +/- 2.7 kg for the hard surface, Jay cushion, and ROHO cushion respectively. Leaning forward (away from the back) caused all the forces to return to measurements close to the starting values. The results suggest that the wheelchair user should momentarily lean forward after a recline to reduce undesired forces. If a cushion with firm thigh support is used, ischial tuberosity pressure can be reduced by lowering the leg height as much as possible, which causes a levering action by lifting the pelvis.

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.

Thirty-minute continuous sitting force measurements with different support surfaces in the spinal cord injured and able-bodied.

Able-bodied, paraplegic, and quadriplegic subjects sat for 30-minute intervals on various surfaces in a wheelchair with a forceplate mounted on the seat in order to determine factors that could contribute to the formation of decubitus ulcers. All three groups of subjects sat on ROHO and Jay cushions; in addition to sitting on the two cushions, the able-bodied subjects sat on a hard surface. Factors studied were: normal and shear seat forces, the location of the center of mass, and armrest force. The forceplate was under the cushions; therefore, the values reflect average forces over the buttocks and posterior thighs. These factors were compared between disability levels as well as between surface types. Larger, normal, and forward shear forces and a more anterior position of the center of mass were observed with the ROHO cushion. More frequent and larger lateral weight shifts occurred with the Jay cushion. The armrests tended to support from 5 percent of the body weight for quadriplegics to 9 percent for paraplegics. The results suggest that armrests reduce seat forces by carrying some of the body weight.