The measurement of coronary lumen cross-sectional area (CSA) is important for coronary physiology and cardiology. The general objective of this study is to develop an accurate and reproducible method to measure the lumen CSA of left anterior descending (LAD) artery using an impedance or conductance catheter. The conductance catheter technique is based on a cylindrical model of the chamber of interest. The first aim of this study was to validate the assumptions of the cylindrical model using a finite-element analysis (FEA) of the conductance catheter in the lumen of the vessel that takes into account the conductance of current through the vessel wall and surrounding tissue (parallel conductance, Gp). The FEA was used to determine the heterogeneity of potential and electrical fields and to optimize the design of the catheter relative to the diameter of the vessel. An optimum relationship between vessel and catheter diameter was obtained based on FEA. The second aim was to validate the in vitro CSA of LAD artery obtained from the conductance catheter method using A-mode ultrasound (US). The present study offers a novel approach to correct for the Gp that involves the injection of two solutions of NaCl (0.5% and 1.5%) with known conductivities directly into the lumen of the coronary artery in a porcine heart. In six hearts obtained from a slaughterhouse, we showed that the CSA and Gp can be determined analytically from two Ohm's law-type algebraic equations (cylindrical model) that account for the parallel conductance. The mean difference in diameter between the conductance catheter using the proposed two-injection method and U.S. was -0.02. The root mean square error for the impedance measurements was 2.8% of the mean US diameter. The future application of this technique to the in vivo condition is discussed.

Gregersen. Novel method for measurement of medium size arterial lumen area with an impedance catheter: in vivo validation. Am J Physiol Heart Circ Physiol 288: H2014 -H2020, 2005; doi:10.1152/ ajpheart.00508.2004.-There is no doubt that the transformation of a cardiac catheter into a conductance catheter that allows reliable and accurate assessment of lumen cross-sectional area (CSA) will provide a powerful diagnostic and treatment tool for the invasive cardiologist. The objective of this study was to develop a method based on the impedance catheter that allows accurate and reproducible measurements of CSA for medium size vessels (e.g., coronary, femoral, and carotid arteries). Two solutions of NaCl (0.5% and 1.5%) with known conductivities were injected directly into the lumen of the artery in eight swine. We showed that the CSA can be determined analytically from two Ohm's law-type algebraic equations that account for the parallel conductance of the current into the surrounding tissue. Excellent agreement was found between the conductance catheter with the proposed two-injection method and B-mode ultrasound (US). The root mean square error for the impedance measurements was 4.8% of the mean US diameter. The repeatability of the technique was assessed with duplicate measurements. The mean of the difference between the two measurements was nearly zero, and the repeatability coefficient was within 2.4% of the mean of the two measurements. The validated method was used to assess the degree of acute vasodilatation of the vessel in response to flow overload. carotid artery; femoral artery; coronary artery; conductance catheter; cylindrical model THE CONDUCTANCE CATHETER METHOD, which has been used previously to measure ventricular volume (4 -5, 7, 14 -16, 29, 30, 33), has recently been adapted to determine the crosssectional area (CSA) of the aorta (11-13). The conductance catheter technique is based on a cylindrical model by measuring the electrical impedance of the blood with two outer electrodes for excitation and two inner electrodes for detection to yield the CSA of the chamber of interest. Two major difficulties have hampered the routine use of the conductance catheter for measurement of absolute CSA or volume of the aorta or ventricle, respectively: 1) nonhomogeneity of the electric field and 2) leakage of current into the organ wall and surrounding tissue (parallel conductance). These two factors violate the assumptions that underlie the cylindrical model for the conductance method. The current approach to the problem is to include a slope correction term in the cylindrical model to account for the nonhomogeneity of the electric field and an offset error term to correct for the current "leakage" through the vessel wall and surrounding tissue.The nonuniformity in electric field is known to be very significant in the aorta under in vivo conditions (13), primarily because of the complex electrical properties of blood cells under dynamic flow conditions (6, 21-28, 31-32). The error due to parallel conductance i...

BackgroundFor an individual with tetraplegia assistive robotic arms provide a potentially invaluable opportunity for rehabilitation. However, there is a lack of available control methods to allow these individuals to fully control the assistive arms.MethodsHere we show that it is possible for an individual with tetraplegia to use the tongue to fully control all 14 movements of an assistive robotic arm in a three dimensional space using a wireless intraoral control system, thus allowing for numerous activities of daily living. We developed a tongue-based robotic control method incorporating a multi-sensor inductive tongue interface. One abled-bodied individual and one individual with tetraplegia performed a proof of concept study by controlling the robot with their tongue using direct actuator control and endpoint control, respectively.ResultsAfter 30 min of training, the able-bodied experimental participant tongue controlled the assistive robot to pick up a roll of tape in 80% of the attempts. Further, the individual with tetraplegia succeeded in fully tongue controlling the assistive robot to reach for and touch a roll of tape in 100% of the attempts and to pick up the roll in 50% of the attempts. Furthermore, she controlled the robot to grasp a bottle of water and pour its contents into a cup; her first functional action in 19 years.ConclusionTo our knowledge, this is the first time that an individual with tetraplegia has been able to fully control an assistive robotic arm using a wireless intraoral tongue interface. The tongue interface used to control the robot is currently available for control of computers and of powered wheelchairs, and the robot employed in this study is also commercially available. Therefore, the presented results may translate into available solutions within reasonable time.

Alternative and effective methods for controlling powered wheelchairs are important to individuals with tetraplegia and similar impairments whom are unable to use the standard joystick. This paper describes a system where tongue movements are used to control a powered wheelchair thus providing users, with high level spinal cord injuries, full control of their wheelchair. The system is based on an inductive tongue control system developed at Center for Sensory-Motor Interaction (SMI), Aalborg University. The system emulates a standard analog joystick in order to interface the wheelchair, thus ensuring that the system works with almost any wheelchair. The total embedment of the tongue interface into the mouth makes the control practically invisible. A fuzzy system combining 8 sensors for directional control allows for multidirectional control of the wheelchair. Preliminary test results show navigation abilities, which are highly competitive when compared to other tongue control system.

The induced electric field transverse to peripheral nerve trunks has been shown to lead to stimulation, contrary to predictions of the cable equation. Two possible mechanisms of activation have been documented in literature: the change in the transmembrane voltage due to an electric field transverse to the membrane of a cylindrical fiber and the transverse field projection on the undulating fiber path within the fascicle. To distinguish between these alternatives, an analysis of the stimulation site was performed in vitro along 15 phrenic nerves from pigs, with a 5-cm-diameter round coil. Stimulation with induced electric field having longitudinal and attenuated transverse components resulted in stimulation sites in the vicinity of the negative peak of the spatial derivative of the longitudinal electric field and threshold variations with coil positions along the nerve trunk. Stimulation with a transverse field yielded patterns of one, two, or three stimulation sites, scattered or uniformly distributed around the location of the two field maxima. A nerve structure analysis outlined the fiber undulation within the fascicle and a network of wavy fascicles. The presence of this network and the variations of the stimulation site, and of the threshold suggest that the path of the fiber has a major undulation due to the undulation of the fascicles within the nerve trunk, which may be responsible for the stimulation with an electric field transverse to the nerve trunk.

To evaluate the performance with respect to selectivity of the effect of the wings bending in the cone coil relative to the double coil in transcranial magnetic stimulation. The focal area and the width vector of the central lobe of the induced electrical field distributed along an elliptic surface approximating the cortex were computed for four coil models. The models represented the real coils, the double B70 and the cone B80 Medtronic, and their corresponding simulated flat coils (B70flat and B80flat). A response function was evaluated in 10 subjects for distal and proximal muscles of the upper limb by stimulation of the motor cortex along a line approximating the central sulcus. The width of the response function, at the level of the center of gravity, provided a quantitative measure for coil focality. The focal area for B70, B70flat, B80, and B80flat calculated from the model was 31.4, 32.2, 94.4, and 50.6 cm2, respectively. The width of the central lobe along the stimulation line was: 36.2, 37, 46, and 48.6 mm, respectively. Mean values of focality measure obtained experimentally were in distal muscles, 5.06 RPU (relative position units) for B70 and 5.99 RPU for B80; in proximal muscles, 4.11 RPU for B70 and 5.13 RPU for B80, with a mean RPU value of 11.13 mm. The difference, a 19% focality measure increase in B80 relative to B70 in distal muscles, was statistically significant (P < 0.001). The focality was demonstrated to be highest for the double coil. The width of the central lobe of the induced electrical field distribution is well reflected in the width of the response function. The increase in B80 is mainly due to wing geometry and relative placement of wings and is not due to the wing bending. The width of the central lobe characterizes the spread of the induced current below the wing junction, and it is a better focality estimator than the focal area for cone coils.

Given the evidence that the primary motor cortex (MI) consists of subpopulations of upper motor neurons tuned to different directional parameters of a motor movement, this study hypothesized that novel motor skill training involving either a bidirectional or more complex multidirectional tongue-typing movement should produce distinct training-related features of tongue MI neuroplasticity in humans. Novel motor skill training consisted of tongue typing using custom-made intra-oral keypads for 30-min over two consecutive days. The bidirectional keypad consisted of three sensors positioned along the upper palatal midline as a 3 × 1 array, whereas the multidirectional keypad consisted of nine sensors arranged as a 3 × 3 array that was centred along the upper palatal midline. Each sensor corresponded to one letter and participants were asked to type sequences of letters by accurately placing the tongue over the correct sensor. Before and after each training session, excitability of the tongue MI was assessed with transcranial magnetic stimulation (TMS)-motor evoked potentials (MEPs) over 13 motor map sites and TMS-MEP stimulus-response curves were constructed for the first dorsal interosseous (FDI, as an internal control). Tongue-typing performance improved within and across training days for both groups; although bidirectional training displayed greater success. Bidirectional and multidirectional training were associated with increases and decreases in a number of cortical motor map sites from where tongue activity could be evoked, however; multidirectional training was associated with a greater number of cortical motor map sites with increased excitability and a shift in the centre of gravity of the motor map. No effects of training were found on the FDI TMS-MEP stimulus-response curves. This study revealed distinct training-related features of tongue MI neuroplasticity and proposes that a greater amount of functionally related neuronal populations may be 'trained' by the inclusion of different and more complex directional parameters within a novel motor task.

Transcutaneous electrical nerve stimulation (TENS) has been reported to alleviate pain in chronic pain patients. Currently, there is limited knowledge how TENS affects can cause cortical neuromodulation and lead to modulation of non-painful and painful sensations. Our aim was therefore to investigate the effect of conventional, high-frequency TENS on cortical activation and perceived sensations in healthy subjects. We recorded somatosensory evoked potentials (SEPs) and perceived sensations following high-frequency TENS (100 Hz) in 40 healthy subjects (sham and intervention group). The effect of TENS was examined up to an hour after the intervention phase, and results revealed significant cortical inhibition. We found that the magnitude of N100, P200 waves, and theta and alpha band power was significantly suppressed following the TENS intervention. These changes were associated with a simultaneous reduction in the perceived intensity and the size of the area where the sensation was felt. Although phantom limb pain relief previously has been associated with an inhibition of cortical activity, the efficacy of the present TENS intervention to induce such cortical inhibition and cause pain relief should be verified in a future clinical trial.