Large Impedance Changes Research Articles

Humidity Sensing Properties of (In+Nb) Doped HfO2 Ceramics

(In+Nb) co-doped HfO2 ceramics, Hf1-x(In0.5Nb0.5)xO2 (x = 0, 0.005, 0.05, and 0.1), were prepared via a solid-state reaction method. Dielectric measurements reveal that the environmental moisture has an obvious influence on the dielectric properties of the samples. The best humidity response was found in a sample with the doping level of x = 0.005. This sample was therefore selected as a model sample to further investigate its humidity properties. In doing so, nanosized particles of Hf0.995(In0.5Nb0.5)0.005O2 were fabricated via a hydrothermal method and the humidity sensing properties of this material were studied in the relative humidity range of 11-94% based on impedance sensor. Our results show that the material exhibits a large impedance change of nearly four orders of magnitude over the tested humidity range. It was argued that the humidity-sensing properties were related to the defects created by doping, which improves the adsorption capacity for water molecules.

Controlling the Magnetoimpedance Property of Thin-Film Elements Using Joule Heating

Optimizing the performance of magnetoimpedance (MI) requires controlling the anisotropy of material which is often done with field annealing. However, field annealing needs large-scale equipment with a vacuum environment and consumes a large amount of electricity for heating and generating a large magnetic field. Conversely, Joule heating has advantages of simple, compact, and possible-to-use small current. Thus, we attempted controlling the magnetic anisotropy on thin-film MI elements using Joule heating and the applied field by magnets. Before annealing, the element has an easy axis with a direction parallel to the longitudinal direction of the element owing to shape anisotropy. After Joule heating, the MI behavior showed a double peak profile, which is a typical impedance profile when large impedance changes are obtained. The peak height in the impedance and inductance increases with the heating current up to 100 mA and then becomes constant or slightly increases. The field at which the impedance and inductance have a peak increases monotonically with increasing heat current. We confirm that the magnetic anisotropy direction changes with Joule heating and with a field applied by magnets based on observing the magnetic domain structure using a Kerr effect microscope.

Electrochemical antigenic sensor for the diagnosis of chronic Q fever

• Differential diagnosis of chronic Q fever occurs through antigen- antibody interactions. • GroEl is a higly sensitive antigen which interacts specifically with antibodies against chronic Q fever. • The developed imedimetric biosensor, based on the immobilization of GroEl antigenic protein can be easily used for the rapid diagnosis of chronic Q fever in humans. • The developed system can be modified for the detection of other biomarkers, such as antibodies against acute Q fever. In this work, we report the development of an impedimetric biosensor for the direct, quick, and easy diagnosis of chronic Q fever. The biosensor is based on highly sensitive antigens that can selectively recognize antibodies against Coxiella burnetii . The biosensor is based on the immobilization of antigens onto a gold electrode using the EDC/NHS immobilization methodology. The detection is performed by impedance spectroscopy that monitors specific frequencies which provide the maximum sensitivity for the biosensor. Q fever antibodies that are present in the sera of patients interact selectively with the biosensor antigens, thereby altering the impedance of the biosensor surfaceand generating a large impedance change within a few seconds. The biosensor allows for the specific serological detection of chronic Q fever, while the developed system can also be modified for the detection of other biomarkers, such as the ones against acute Q fever.

Enhanced Humidity Sensing Performance of the La2Ti2O7/La(OH)3 Nanocomposite

A La2Ti2O7/La(OH)3 nanocomposite was prepared by the one-step hydrothermal method. Humidity sensing properties of this material were investigated based on the impedance-type sensor in the relative humidity range of 11–94%. This material in the tested humidity range shows a large impedance change of more than four orders of magnitude. This impedance change is one order larger than that of the sensors based on La2Ti2O7 and La(OH)3. Excitingly, the impedance has an excellent linear relationship with humidity with a figure of merit R2 = 0.995. The enhanced humidity properties of the La2Ti2O7/La(OH)3-based sensor are argued to be due to the existence of a heterojunction between La2Ti2O7 and La(OH)3. The excellent linearity was argued to be due to the synergetic effect of the heterojunction and Grotthuss mechanism.

A 9.6-mW/Ch 10-MHz Wide-Bandwidth Electrical Impedance Tomography IC With Accurate Phase Compensation for Early Breast Cancer Detection

An eight-channel 10-MHz wide-bandwidth electrical impedance tomography (EIT) IC is proposed for early breast cancer detection system. To increase the resolution of EIT images, the proposed IC has three key features: 1) wide-bandwidth instrumentation amplifier (WB-IA) to detect large impedance changes in cancer cells at a high frequency; 2) dual-mode driver (DM-driver) to obviate the complex switching network to reduce the noise and the system form factor; and 3) phase compensation loop (PCL) to efficiently correct the phase error for accurate images without artifacts. The proposed EIT IC occupies 16 mm2 in the 65-nm CMOS technology and consumes 9.6 mW for each channel. Thanks to the key features, the proposed breast cancer detection system with the dedicated EIT IC can operate up to 10 MHz with a small phase error of 4.32° and a state-of-the-art impedance resolution of 1.6 $\text{m}\Omega /\surd $ Hz eventually can detect a small-size target object of 0.5 cm and verify with the phantom experiments.

Do Impedance Changes Correlate With a Delayed Hearing Loss After Hybrid L24 Implantation?

Preservation of residual hearing is one of the main goals in present cochlear implantation surgery. Especially for this purpose, smaller and softer electrode carriers were developed that are to be inserted through the round window membrane to minimize trauma. By using these electrodes and insertion technique, residual hearing can be preserved in a large number of patients. Unfortunately, some of these patients with initially preserved residual hearing after cochlear implantation lose it later on. The reason for this is unknown but it is speculated about a correlation with an increase in impedance, since increased impedance values are linked to intracochlear inflammation and tissue reaction. Our hypothesis for this study design was that an increase in impedance predicts changes in residual hearing under clinical conditions. Data of all adult patients (N = 122) receiving a Hybrid-L24 cochlear implant at our center between 2005 and early 2015 were retrospectively evaluated. Impedance values in Common Ground mode as measured during clinical routine and referring audiological test data (audiometric thresholds under headphones) were collected. Changes between consecutive measurements were calculated for impedance values and hearing thresholds for each patient. Correlations between changes in impedances and acoustic hearing thresholds were calculated. Average values were compared as well as patients with largest impedance changes within the observation period were evaluated separately. Group mean values of impedances were between 5 and 7 kΩ and stable over time with higher values on basal electrode contacts compared with apical contacts. Average hearing thresholds at the time of initial fitting were between 40 to 50 dB (250 Hz) and 90 dB (1 kHz) with a loss of about 10 dB compared with preoperative values. Correlation between impedance changes and threshold changes was found, but too inconsistently to imply a true relationship. When evaluating the 20 patients with the largest impedance changes during the observation period (all >1 kΩ from one appointment to the next one), some patients were found where hearing loss is timely connected and highly correlated with an unusual impedance change. But large impedance changes were also observed without affecting hearing thresholds and hearing loss was found without impedance change. Changes in impedance as measured during clinical routine cannot be taken as an indicator for a late acoustic hearing loss.

Impedance testing of porous Si3N4 scaffolds for skeletal implant applications

Si3N4 ceramics show excellent characteristics of mechanical and chemical resistance in combination with good biocompatibility, antibacterial property and radiolucency. Therefore, they are intensively studied as structural materials in skeletal implant applications. Despite their attractive properties, there are limited data in the field about in vitro studies of cellular growth on ceramic implant materials. In this study, the growth of bone cells was investigated on porous silicon nitride (Si3N4) ceramic implant by using electrochemical impedance spectroscopy (EIS). Partial sintering was performed at 1700 °C with limited amount of sintering additive for the production of porous Si3N4 scaffolds. All samples were then sterilized by using ethylene oxide followed by culturing MG-63 osteosarcoma cells on the substrates for in vitro assays. At 20 and 36 h, EIS was performed and results demonstrated that magnitude of the impedance as a result of the changes in the culture medium increased after incubation with osteosarcoma cells. The changes are attributed to the cellular uptake of charged molecules from the medium. Si3N4 samples appear to show large impedance magnitude changes, especially between 100 and 1 Hz. Impedance changes were also correlated with WST-1 measurements (36 h) and DAPI results.

Ultrasensitive label-free detection of circulating tumor cells using conductivity matching of two-dimensional semiconductor with cancer cell

The excellent conductivity matching of two-dimensional (2D) semiconductor nanomaterials (e.g. MoS2) with cancer cell plays an important role in ultrasensitive label-free impedimetric detection of circulating tumor cells (CTC) (<1 cell/mL). Firstly, 2D semiconductor materials (e.g. 2D MoS2) exfoliated by folic acid (FA) is used to construct MoS2/FA-modified gold electrode (AuE/MoS2/FA). Then, the fabricated electrode is applied for HeLa cell detection in a linear range from 1 to 105 cell/mL with a detection limit of 0.43 cell/mL (S/N = 3). The detection mechanism of high sensitivity might be owing to the electric conductivity matching of MoS2 (0.14 S/m) to cancer cell (0.13–0.23 S/m). A negligible conductivity change induced by cancer cell will produce a large impedance change of semiconductor electrode. Furthermore, HeLa cells dispersed in healthy blood samples are detected by suggested cytosensor in a linear range from 50 to 105 cell/mL with a detection limit of 52.24 cell/mL (S/N = 2). Finally, we demonstrate that the cytosensor is capable of differentiating patients of cervical and liver cancers by the real CTC analysis from healthy control.

Impedance Change Ratio and Sensitivity of Micromachined Single-Layer Thin Film Magneto-Impedance Sensor

Thin-film techniques are important in the miniaturization of electronic devices. We studied a thin-film magneto-impedance element made with Co-based amorphous soft magnetic material and developed a highly sensitive magnetic field sensor with high spatial resolution. Thin films are several micrometers thick, and show significant impedance changes as frequencies change from the megahertz to the gigahertz region. Multilayer systems are often used to achieve a large impedance change, but they typically require a complex thin-film structure and a length of several millimeters. Our thin-film sensors have lengths between 30 µm and 1 mm in a simple monolayer configuration and successfully overcome the demagnetizing field. The impedance change ratio was 300% for a 1 mm long element at 1 GHz and between 20–30% at 1 GHz for a miniaturized element of 30 µm. The sensors had a maximum sensitivity of 33.4%/Oe.

Drive and measurement electrode patterns for electrode impedance tomography (EIT) imaging of neural activity in peripheral nerve

Objective; To establish the performance of several drive and measurement patterns in EIT imaging of neural activity in peripheral nerve, which involves large impedance changes in the nerve’s anisotropic length axis. Approach; Twelve drive and measurement electrode patterns are compared using a finite element (FE) four-cylindrical shell model of a peripheral nerve and a 32 channel dual-ring nerve cuff. The central layer of the FE model contains impedance changes representative of neural activity of −0.30 in length axis and −8.8 × 10−4 in the radial axis. Six of the electrode patterns generate longitudinal drive current, which runs parallel to the anisotropic axis, while the remaining six patterns generate transverse drive current, which runs perpendicular to the anisotropic axis. Main results; Of the twelve patterns evaluated, transverse current patterns produce higher resolution than longitudinal current patterns but are also more susceptible to noise and errors, and exhibit poorer sensitivity to impedance changes in central sample locations. Three of the six longitudinal current patterns considered can reconstruct fascicle level impedance changes with up to 0.2 mV noise and error, which corresponds to between −5.5 and +0.18 dB of the normalised signal standard deviation. Reducing the spacing between the two electrode rings in all longitudinal current patterns reduced the signal to error ratio across all depth locations of the sample. Significance; Electrode patterns which target the large impedance change in the anisotropic length axis can provide improved robustness against noise and errors, which is a critical step towards real time EIT imaging of neural activity in peripheral nerve.

Distinguishment of populated metastatic cancer cells from primary ones based on their invasion to endothelial barrier by biosensor arrays fabricated on nanoroughened poly(methyl methacrylate)

Determining the migratory and invasive capacity of cancer cells as well as clarifying the underlying mechanisms are most relevant for developing biosensors in cancer diagnosis, prognosis, drug development and treatment. Intravasation of metastatic cells into blood stream initiated by their invasion to vascular layer would be a significant characteristic of metastasis. Many types of biochemical and bioelectrical sensors were developed for early detection of metastasis. The simplicity of the setup, the ease of the readout, detection of the trace of rare metastatic cells and the feasibility to perform the assay with standard laboratory equipment are some of the challenges limiting the usability of the sensors in tracing the metastasis. Here we describe a biosensor based on recently reported metastatic diagnosis assay; Metas-Chip, with the assistance of nanoroughened Poly-methyl methacrylate (PMMA) layer to diagnose populated metastatic breast cells from primary cancerous ones. Retraction and detachment of Human Umbilical Vein Endothelial Cells (HUVECs) invaded by metastatic cells as a recently found phenomena is the mechanism of the action. A population of HUVECs would be detached from the gold microelectrodes, patterned on nanoroughened surface, which would lead to large changes in impedance. Here, applying biocompatible and patternable nanoroughened surface instead of using adhesive layers which might produce electrical noises resulted in great sensitivity and detectivity of the sensor. Apart from the tight interaction between endothelial cells and nanocontacts of the electrodes, using low concentration (10%) of tumor cells in this invasion assay, might enhance its application in clinical trials.

Controlling sensation intensity for electrotactile stimulation in human-machine interfaces.

A barrier to practical use of electrotactile stimulation for haptic feedback has been large variability in perceived sensation intensity due to changes in the impedance of the electrode-skin interface, such as when electrodes peel or users sweat. Here, we show how to significantly reduce this variability by modulating stimulation parameters in response to measurements of impedance. Our method derives from three contributions. First, we created a model between stimulation parameters and impedance at constant perceived sensation intensity by looking at the peak pulse energy and phase charge. Our model fits experimental data better than previous models (mean R2 > 0.9) and holds over a larger set of conditions (subjects, sessions, magnitudes of sensation, stimulation locations, electrode sizes). Second, we implemented a controller that regulates perceived sensation intensity by using our model to derive a new current amplitude and pulse duration in response to changes in impedance. Our controller accurately predicts subject-chosen stimulation parameters at constant sensation intensity (mean R2 > 0.9). Third, we demonstrated as a proof-of-concept on two subjects with below-elbow amputations-using a prosthesis with electrotactile touch feedback-that our controller can regulate sensation intensity in response to large impedance changes that occur in activities of daily living. These results make electrotactile stimulation for human-machine interfaces more reliable during activities of daily living.

Using Impedance Spectroscopy to Detect the Selective Sorption of Iodine By MOF ZIF-8

Detection of iodine species is important for the safety of the population in cases of nuclear accidents or advanced nuclear fuel reprocessing. Here we leverage the selective sorption of I2 by metal organic framework (MOF) ZIF-8 to create an impedance spectroscopy-based sensor for the real-time detection of gaseous I2. Methanolic ZIF-8 suspensions were cast onto interdigitated electrodes, dried, and exposed to gaseous I2 at 25, 40, or 70 °C. Equivalent circuit models were developed to separate the response of the extremely resistive ZIF-8 from that of the underlying glass substrate. While high fidelity measurements enable electrical characterization of pure ZIF-8, such precision is woefully unnecessary to detect I2; a >105× decrease in ZIF-8 resistance was observed upon sorption of 116 wt% I2 by ZIF-8 at 70 °C. Such large changes in impedance open the door for I2 detection schemes using inexpensive electronics. Tests for interfering gases such as air, argon, methanol, and water revealed minimal changes in impedance and equivalent circuit response. Using an unoptimized sensor geometry, I2 was readily detected at 25 °C in air. Further optimization of sensor geometry, decreasing MOF film thicknesses and maximizing sensor capacitance, will enable faster detection of trace I2, providing a rapid, robust, and reliable iodine sensor for the safety of the populace. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Halfdan 4D workflow and results leading to increased recovery

In 2012, a repeat time-lapse seismic survey was acquired over the Halfdan oil field located in the Danish North Sea. The main oil reservoir is the Cretaceous chalk Tor Formation, and the field is developed with a line-drive water flood. The reservoir saturation changes due to water injection and gas breakout lead to large changes in acoustic impedance, which can be imaged with 4D seismic. The 4D acoustic-impedance changes, in conjunction with production and geologic data, were analyzed on a well-by-well basis and resulted in several interesting correlations between the geology and the 4D response. The 4D was used to update the seismic interpretation of some important layers within the static and dynamic model. In some areas, the impact of local porosity variations on the lateral sweep could be seen. The 4D also provided evidence that some faults serve as potential pathways for formation-water entry into the oil-producing layers. In addition, numerous well-intervention opportunities were identified through integrating the 4D with the production, geologic, and dynamic data. Examples from the two-vintage and three-vintage 4D acoustic-impedance data illustrating these key 3D and 4D learnings and a successful well intervention are shown.

EP 37. Impedance changes occur during threshold measurements in subthalamic nucleus (STN) deep brain stimulation patients

Background In previous work (Carcieri et al.), we observed impedance changes during the measurement of efficacy and side effect thresholds in seven DBS patients. This study investigates a larger group of subjects with more frequent impedance measurements to better characterize the time course of the effect and tests whether electrode impedance varies during the measurement of efficacy and side effect thresholds in DBS patients. Methods Twenty-four patients, implanted in the STN with a current-controlled DBS system (Boston Scientific Corporation) for at least 3 months, were stimulated on 4 different electrode combinations using one or two active electrodes and amplitude was adjusted to measure thresholds. At the beginning and end of threshold measurements, impedance was measured. Average stimulation duration was under 20 min, and amplitude was increased to 5 mA on average. Results Analysis reveals that turning stimulation ON resulted in an immediate reduction in impedance for 41/48 active electrodes, with a maximum decrease of 27%. The inactive electrodes showed a mean impedance decrease of 1%. For the active electrodes, the minimum impedance decrease was 2.8%, and the overall average decrease was 13.1%. Conclusions Deep brain stimulation in the normal range for measurement of thresholds may result in large and rapid impedance changes on the active electrodes. Impedance changes of this magnitude and time scale may have clinical relevance for some patients.

Electrode impedance analysis of chronic tungsten microwire neural implants: understanding abiotic vs. biotic contributions.

Changes in biotic and abiotic factors can be reflected in the complex impedance spectrum of the microelectrodes chronically implanted into the neural tissue. The recording surface of the tungsten electrode in vivo undergoes abiotic changes due to recording site corrosion and insulation delamination as well as biotic changes due to tissue encapsulation as a result of the foreign body immune response. We reported earlier that large changes in electrode impedance measured at 1 kHz were correlated with poor electrode functional performance, quantified through electrophysiological recordings during the chronic lifetime of the electrode. There is a need to identity the factors that contribute to the chronic impedance variation. In this work, we use numerical simulation and regression to equivalent circuit models to evaluate both the abiotic and biotic contributions to the impedance response over chronic implant duration. COMSOL® simulation of abiotic electrode morphology changes provide a possible explanation for the decrease in the electrode impedance at long implant duration while biotic changes play an important role in the large increase in impedance observed initially.

Insights into sweep efficiency using 4D seismic at Halfdan field in the North Sea

A repeat 4D seismic survey was acquired in 2012 over the Halfdan oil field in the Danish North Sea Central Graben. The main objectives were to understand the lateral and vertical waterflood sweep in the reservoir, to identify unswept areas, to guide future well interventions, and to improve the reservoir model. The main oil reservoir is the Cretaceous chalk Tor Formation, and the field is developed via a line-drive waterflood. The reservoir saturation changes caused by water injection lead to large changes in acoustic impedance which can be imaged with 4D seismic. There were two main 4D processing projects for the Halfdan field. The 2012–2005 4D data were processed as a stand-alone project because of the high repeatability of the surveys, and a separate three-vintage processing project for all time steps also was carried out. When the three-vintage processing was not available, the original 4D processing was used for the 2005–1993 time step. Seismic inversion was performed because production effects have a large impact on the acoustic impedance in the chalk reservoir. The rock-physics model was also used to model 4D acoustic-impedance changes based on pressure and saturation changes in the reservoir. The 4D acoustic-impedance changes from the seismic and reservoir model were analyzed in conjunction with the production and geologic data on a well-by-well basis to better understand sweep efficiency.

A Real-time Electrical Impedance Based Technique to Measure Invasion of Endothelial Cell Monolayer by Cancer Cells

Metastatic dissemination of malignant cells requires degradation of basement membrane, attachment of tumor cells to vascular endothelium, retraction of endothelial junctions and finally invasion and migration of tumor cells through the endothelial layer to enter the bloodstream as a means of transport to distant sites in the host1-3. Once in the circulatory system, cancer cells adhere to capillary walls and extravasate to the surrounding tissue to form metastatic tumors4,5. The various components of tumor cell-endothelial cell interaction can be replicated in vitro by challenging a monolayer of human umbilical vein endothelial cells (HUVEC) with cancer cells. Studies performed with electron and phase-contrast microscopy suggest that the in vitro sequence of events fairly represent the in vivo metastatic process6. Here, we describe an electrical-impedance based technique that monitors and quantifies in real-time the invasion of endothelial cells by malignant tumor cells. Giaever and Keese first described a technique for measuring fluctuations in impedance when a population of cells grow on the surface of electrodes7,8. The xCELLigence instrument, manufactured by Roche, utilizes a similar technique to measure changes in electrical impedance as cells attach and spread in a culture dish covered with a gold microelectrode array that covers approximately 80% of the area on the bottom of a well. As cells attach and spread on the electrode surface, it leads to an increase in electrical impedance9-12. The impedance is displayed as a dimensionless parameter termed cell-index, which is directly proportional to the total area of tissue-culture well that is covered by cells. Hence, the cell-index can be used to monitor cell adhesion, spreading, morphology and cell density. The invasion assay described in this article is based on changes in electrical impedance at the electrode/cell interphase, as a population of malignant cells invade through a HUVEC monolayer (Figure 1). The disruption of endothelial junctions, retraction of endothelial monolayer and replacement by tumor cells lead to large changes in impedance. These changes directly correlate with the invasive capacity of tumor cells, i.e., invasion by highly aggressive cells lead to large changes in cell impedance and vice versa. This technique provides a two-fold advantage over existing methods of measuring invasion, such as boyden chamber and matrigel assays: 1) the endothelial cell-tumor cell interaction more closely mimics the in vivo process, and 2) the data is obtained in real-time and is more easily quantifiable, as opposed to end-point analysis for other methods.

A Real-time Electrical Impedance Based Technique to Measure Invasion of Endothelial Cell Monolayer by Cancer Cells

Metastatic dissemination of malignant cells requires degradation of basement membrane, attachment of tumor cells to vascular endothelium, retraction of endothelial junctions and finally invasion and migration of tumor cells through the endothelial layer to enter the bloodstream as a means of transport to distant sites in the host(1-3). Once in the circulatory system, cancer cells adhere to capillary walls and extravasate to the surrounding tissue to form metastatic tumors(4,5). The various components of tumor cell-endothelial cell interaction can be replicated in vitro by challenging a monolayer of human umbilical vein endothelial cells (HUVEC) with cancer cells. Studies performed with electron and phase-contrast microscopy suggest that the in vitro sequence of events fairly represent the in vivo metastatic process(6). Here, we describe an electrical-impedance based technique that monitors and quantifies in real-time the invasion of endothelial cells by malignant tumor cells. Giaever and Keese first described a technique for measuring fluctuations in impedance when a population of cells grow on the surface of electrodes(7,8). The xCELLigence instrument, manufactured by Roche, utilizes a similar technique to measure changes in electrical impedance as cells attach and spread in a culture dish covered with a gold microelectrode array that covers approximately 80% of the area on the bottom of a well. As cells attach and spread on the electrode surface, it leads to an increase in electrical impedance(9-12). The impedance is displayed as a dimensionless parameter termed cell-index, which is directly proportional to the total area of tissue-culture well that is covered by cells. Hence, the cell-index can be used to monitor cell adhesion, spreading, morphology and cell density. The invasion assay described in this article is based on changes in electrical impedance at the electrode/cell interphase, as a population of malignant cells invade through a HUVEC monolayer (Figure 1). The disruption of endothelial junctions, retraction of endothelial monolayer and replacement by tumor cells lead to large changes in impedance. These changes directly correlate with the invasive capacity of tumor cells, i.e., invasion by highly aggressive cells lead to large changes in cell impedance and vice versa. This technique provides a two-fold advantage over existing methods of measuring invasion, such as boyden chamber and matrigel assays: 1) the endothelial cell-tumor cell interaction more closely mimics the in vivo process, and 2) the data is obtained in real-time and is more easily quantifiable, as opposed to end-point analysis for other methods.

Ivabradine: An hypothesis generating study – An important link between bench and bedside

Coronary artery disease (CAD) remains a major cause of mortality and morbidity. Flow in coronary circulation occurs predominantly in diastole, matching large input impedance changes imposed by ventricular contraction and relaxation on intra-myocardial vessels. Thus myocardial perfusion time decreases and myocardial oxygen consumption in turn increases with heart rate. Auto-regulation of coronary vessels maintains a marginal balance of oxygen supply and demand in physiologic conditions. A lower vascular resistance causes a nearly five-fold increase in instantaneous diastolic coronary flow [1].