Referred Sensation Areas in Bilateral Upper Limb Amputee

Phantom limb pain (PLP) following amputation considerably reduces the quality of life, given a difficult to treat pain of highly variate profile. The loss of sensory input induces a complex pattern of neuroplastic changes of the sensory neural pathways and their central projections. Referred sensation areas (RSAs) may occur on the stump as a consequence of amputation, providing a direct path towards the altered central sensory projections. Modulated electrical stimulation of RSAs was investigated in a long-term experiment in the case of a 62 years-old participant with bilateral upper limb amputation due to traumatic injury. RSAs were investigated using mechanical (vibration and pressure) and electrical stimuli over five sessions within a five weeks period. Further test of sensations induced by steady state and modulated electrical stimuli was performed during additional 4 sessions. Location and features of RSAs were highly dependent on the type of stimulus and time of delivery between sessions.Clinical Relevance- The case study presents a variety of types and locations of the sensation induced by electrical and mechanical stimuli that may eventually be used as artificially generated sensory input as individualized alternative form of therapy for PLP alleviation. Furthermore, possible multichannel stimulus delivery on RSAs on both arms and the cross-over effect of the bilateral amputation in perception of the induced sensation in the opposite phantom hand may be considered in dedicated design of an experimental setup that may possibly help investigation of mechanisms for PLP.

Referred Sensation Areas in a Bilateral Toes Amputee

Various mechanisms in generating phantom limb pain (PLP) have been hypothesized in the literature. However, there still is no clear understanding of how PLP develops and why it presents. Amputation leads to permanent anatomical and physiological changes of the neural path previously supplying the brain with sensory input, as well as to formation of referred sensation areas (RSAs) on the stump or its vicinity. Sensations may be evoked in the lost body part upon stimulation of RSAs that may be exploited as artificial sensory input. In this work, we present the analysis of RSA maps from a 45-year-old female with bilateral toes amputation. Maps of the RSAs were identified in eight sessions over 107 days, characterized by dynamics in both location and type of associated evoked sensation. The evoked sensations were reported to be felt like current through and brushing of the phantom toes at low intensities close to the sensation threshold. Sensations evoked by electrical stimuli delivered through electrodes covering one or more RSAs approximated the sensation of summation of sensations evoked by mechanical stimuli (light brushing). No painful evoked sensations were observed.Clinical Relevance- The technique presented may be further improved by using various profiles for stimulation over a longer period of time for possible efficient PLP treatment with artificially generated sensory input.

Referred Sensation Areas in Transpelvic Amputee

Electrical stimulation (ES) of referred sensation areas (RSAs) may provide sensory input attempting to alleviate phantom limb pain (PLP). Characterization of referred sensation areas (RSAs) in a 34 year-old male with transpelvic amputation is presented in this paper. PLP was experienced as cramps of muscles of phantom leg and as piercing sensation of the phantom ankle alternating with unpleasant sensation as that given by crawling spiders in an atypical pattern lasting for e.g. 36 hours, with short episodes experienced approximately every 15 seconds on a 7-10 level on VAS scale. RSAs were determined by light brushing of a 350 x 250 mm area around the scar on the amputation site. Combinations of pulse widths of 200 to 600 μs and frequencies from 20 to 120 Hz were used for test of ES of RSAs. Pleasant massaging effect of muscles of phantom leg and of phantom toes, with lasting effect of minutes, was evoked by ES. However, increase of pain level was reported for stimuli of certain parameters and location of electrodes. Sensation evoked by tactile stimulation of given RSA differed of that evoked by ES of the corresponding RSA and neighbour areas. Following ES, increase in non-painful sensations from extended areas of phantom leg was reported as phantom leg coming to life. Furthermore, the phantom leg was perceived lighter and easier to move imaginary. RSAs may qualify for generating sensory input attempting to alleviate PLP, however, thorough analysis of sensation evoked by ES and of pain profile must be performed.

Error-Free Text Typing Performance of an Inductive Intra-Oral Tongue Computer Interface for Severely Disabled Individuals

For severely paralyzed individuals, alternative computer interfaces are becoming increasingly essential for everyday life as social and vocational activities are facilitated by information technology and as the environment becomes more automatic and remotely controllable. Tongue computer interfaces have proven to be desirable by the users partly due to their high degree of aesthetic acceptability, but so far the mature systems have shown a relatively low error-free text typing efficiency. This paper evaluated the intra-oral inductive tongue computer interface (ITCI) in its intended use: Error-free text typing in a generally available text editing system, Word. Individuals with tetraplegia and able bodied individuals used the ITCI for typing using a MATLAB interface and for Word typing for 4 to 5 experimental days, and the results showed an average error-free text typing rate in Word of 11.6 correct characters/min across all participants and of 15.5 correct characters/min for participants familiar with tongue piercings. Improvements in typing rates between the sessions suggest that typing ratescan be improved further through long-term use of the ITCI.

Development and functional demonstration of a wireless intraoral inductive tongue computer interface for severely disabled persons

PURPOSE

Individuals with tetraplegia depend on alternative interfaces in order to control computers and other electronic equipment. Current interfaces are often limited in the number of available control commands, and may compromise the social identity of an individual due to their undesirable appearance. The purpose of this study was to implement an alternative computer interface, which was fully embedded into the oral cavity and which provided multiple control commands.

METHODS

The development of a wireless, intraoral, inductive tongue computer was described. The interface encompassed a 10-key keypad area and a mouse pad area. This system was embedded wirelessly into the oral cavity of the user. The functionality of the system was demonstrated in two tetraplegic individuals and two able-bodied individuals Results: The system was invisible during use and allowed the user to type on a computer using either the keypad area or the mouse pad. The maximal typing rate was 1.8 s for repetitively typing a correct character with the keypad area and 1.4 s for repetitively typing a correct character with the mouse pad area.

CONCLUSION

The results suggest that this inductive tongue computer interface provides an esthetically acceptable and functionally efficient environmental control for a severely disabled user. Implications for Rehabilitation New Design, Implementation and detection methods for intra oral assistive devices. Demonstration of wireless, powering and encapsulation techniques suitable for intra oral embedment of assistive devices. Demonstration of the functionality of a rechargeable and fully embedded intra oral tongue controlled computer input device.

Alternative design of inductive pointing device for oral interface for computers and wheelchairs

An inductive pointing device was designed and implemented successfully in a tongue controlled oral interface. Sensors were manufactured as an assembly of multilayer coils in the printed circuit board technology on two pads. The sensor pads were encapsulated together with electronics and battery in a mouthpiece, placed in the upper palate of the oral cavity. The PCB technology allowed surface activation of one or more sensors by gliding over the surface of the coils assembly of a small cylindrical unit attached to the tongue. The model consisted of 8 sensors and allowed real time proportional control of both speed and direction similar to a joystick. However, the size of the oral cavity, the number and geometry of the coil loops and characteristics of the activation unit impose limits in designing the sensors and call for an alternative layout design. Two alternative sensor designs are proposed in this paper, aiming to reduce the size of the sensor pad by one third, extending the target group, including children, and increasing the easiness of wear of the oral interface.

Mapping sensor activation time for typing tasks performed with a tongue controlled oral interface

Two tetraplegic subjects performed typing tasks on a computer in an experiment using a tongue controlled oral interface. This paper reports mapping of the sensor activation time for a full alphabet text input using 10 inductive sensors. A small cylindrical piece of soft ferromagnetic material activated the sensors when placed at or glided along the surface of the sensor. The activation unit was attached to the tongue as the upper ball of a piercing. The tasks consisted of typing characters according to ordered (rows and columns) or random test strings during 30 seconds, with and without deleting characters typed by mistake. Visual feedback assisted the subjects to perform the typing tasks. Average activation times were of 0.82+/-0.38 and 1.06 +/-0.27 seconds respectively for the two subjects. Analysis of activation times may be useful in characterization of the tongue ability to activate the interface as well as in design optimization of the layout of the sensors.

Effects of sensory feedback in intra-oral target selection tasks with the tongue

PURPOSE

To investigate the effects of visual and tactile intra-oral sensor-position feedback for target selection tasks with the tip of the tongue.

METHOD

Target selection tasks were performed using an inductive tongue-computer interface (ITCI). Visual feedback was established by highlighting the area on a visual display corresponding to the activated intra-oral target. Tactile feedback was established using a sensor-border matrix over the sensor plates of the ITCI, which provided sensor-position tactile queues via the user's tongue. Target selection tasks using an on-screen keyboard by controlling the mouse pointer with the ITCI's was also evaluated.

RESULTS

Mean target selection rates of 23, 5 and 15 activations per minute were obtained using visual, tactile and "none" feedback techniques in the 3rd training session. On-screen keyboard target selection tasks averaged 10 activations per minute in the 3rd training session. Involuntary activations while speaking or drinking were significantly reduced either through a sensor-matrix or dwell time for sensor activation.

CONCLUSIONS

These results provide key design considerations to further increase the typing efficiency of tongue-computer interfaces for individuals with upper-limb mobility impairments.

Tip of the tongue selectivity and motor learning in the palatal area

This study assessed the ability of the tongue tip to accurately select intraoral targets embedded in an upper palatal tongue-computer interface, using 18 able-bodied volunteers. Four performance measures, based on modifications to Fitts's Law, were determined for three different tongue-computer interface layouts. The layouts differed with respect to number and location of the targets in the palatal interface. Assessment of intraoral target selection speed and accuracy revealed that performance was indeed dependent on the location and distance between the targets. Performances were faster and more accurate for targets located farther away from the base of the tongue in comparison to posterior and medial targets. A regression model was built, which predicted intraoral target selection time based on target location and movement amplitude better than the predicted by using a standard Fitts's Law model. A 30% improvement in the speed and accuracy over three daily practice sessions of 30 min emphasizes the remarkable motor learning abilities of the tongue musculature and provides further evidence that the tongue is useful for operating computer-interface technologies.

Clinical evaluation of wireless inductive tongue computer interface for control of computers and assistive devices

Typing performance of a full alphabet keyboard and a joystick type of mouse (with on-screen keyboard) provided by a wireless integrated tongue control system (TCS) has been investigated. The speed and accuracy have been measured in a form of a throughput defining the true correct words per minute [cwpm]. Training character sequences were typed in a dedicated interface that provided visual feedback of activated sensors, a map of the alphabet associated, and the task character. Testing sentences were typed in Word, with limited visual feedback, using non-predictive typing (map of characters in alphabetic order associated to sensors) and predictive typing (LetterWise) for TCS keyboard, and non-predictive typing for TCS mouse. Two subjects participated for four and three consecutive days, respectively, two sessions per day. Maximal throughput of 2.94, 2.46, and 2.06, 1.68 [cwpm] were obtained with TCS keyboard by subject 1 and 2 with predictive and non-predictive typing respectively. Maximal throughput of 2.09 and 1.71 [cwpm] was obtained with TCS mouse by subject 1 and 2, respectively. Same experimental protocol has been planned for a larger number of subjects.

Character activation time prediction model for tongue-typing: adaptation of Fitts's law

This paper presents the development of a character activation time prediction model for tongue-typing. This model is based on a modification of Fitts's law that is more suitable for tip-of-tongue selectivity tasks around the palatal area. The model was trained and evaluated with data from tongue-selectivity experiments using an inductive tongue-computer interface. It takes into account the movement amplitude, target position, interactions between them, character disambiguation time and error correction time.

Focality assessment in transcranial magnetic stimulation with double and cone coils

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.

Novel method for measurement of medium size arterial lumen area with an impedance catheter: in vivo validation

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.

Measurement of Coronary Lumen Area Using an Impedance Catheter: Finite Element Model and in Vitro Validation

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.