Engineering and Clinical Evaluation of the VA-PAMAID Robotic Walker

The Veterans Affairs Personal Adaptive Mobility Aid (VA-PAMAID) is a robotic walker that is designed to provide physical support and obstacle avoidance and navigational assistance to frail visually impaired individuals. The goal of this study was to develop and implement testing protocols to determine the performance and safety capabilities of the device and use the results to redesign the walker to make it more reliable and effective.Engineering tests were performed to determine factors such as stability, range, speed, and fatigue strength. Additional tests to characterize the reliability and accuracy of the sensors and avoidance/navigation algorithms were also conducted. The walker traveled 10.9 kilometers on a full charge, and was able to avoid obstacles while traveling at a speed of up to 1.2 m/s. There were no failures during static stability, climatic, or static, impact, and fatigue testing. Some problems were encountered during obstacle climbing and sensor and control testing. Several significant differences were found with respect to the detection distance of the device when varying the obstacle height, material, approach angle, and lighting source. The walker also failed to detect 40-50% of the doorways during the hallway test.Clinical trials were conducted to compare the VA-PAMAID to a low-tech mobility aid (AMD). Subjects were recruited and trained to use both devices efficiently. Each participant was then asked to traverse an obstacle course several times. The time to complete the course, number of wall and obstacle collisions, and number of reorientations were all recorded and averaged. There were no significant differences between the VA-PAMAID and the AMD with respect to collisions or reorientations. The AMD had a significantly lower completion time (p=0.017) than the VA-PAMAID on the obstacle course. The results of the engineering and clinical tests were then used in a house of quality model to determine what factors of the walker needed to be revised. Specific modifications were recommended that would make the device safer, more reliable, and more marketable. Changing the wheel size, mass, component positions, detection algorithm, and other variables would make the VA-PAMAID easier to use and more effective for elderly visually impaired individuals

Analysis of the ANSI/RESNA Wheelchair Standards: A Comparison Study of Five Different Types of Electric Powered Wheelchairs

The number of individuals using electric powered wheelchairs (EPWs) is increasing every year. Advances in technology have led to the design of EPWs that are more complex and can perform multiple functions. The ANSI/RESNA wheelchair standards consist of a battery of tests that are designed to evaluate the safety and performance of both manual and power wheelchairs. However, there is a deficit of information available to the general public on the performance of wheelchairs on these tests. The purpose of this study was to compare the results of standards testing on five different types of EPWs. The value and intentions of each section of the standard were also reviewed and suggestions were made for possible improvements. A total of fifteen EPWs (three of each type) were tested using the following sections: static stability, dynamic stability, effectiveness of brakes, energy consumption, overall dimensions, speed and acceleration, seating dimensions, static, impact, and fatigue testing, climatic testing, obstacle climbing ability, and power and control systems. Statistical analysis was performed on the relevant sections. Significant differences were found between the different types of wheelchairs with respect to static stability, dynamic stability, braking distance, theoretical range, and obstacle climbing ability. The EPWs with the highest velocity and accelerations were found to be the most dynamically unstable and have the longest braking distances. Dynamic stability and braking distance were also found to be directly related to the slope of the test surface. It is apparent from the results that EPWs can differ in both performance characteristics and safety. Evaluation of the wheelchair standards also illustrated the need to continually revise the standards to keep pace with new technology. Stability, fatigue strength, and control system testing are three of the sections that will need to be adapted to help evaluate the next generation of EPWs

A quantitative analysis of the effect of cycle length on arrhythmogenicity in hypokalaemic Langendorff-perfused murine hearts

The clinically established proarrhythmic effect of bradycardia and antiarrhythmic effect of lidocaine (10 μM) were reproduced in hypokalaemic (3.0 mM K+) Langendorff-perfused murine hearts paced over a range (80–180 ms) of baseline cycle lengths (BCLs). Action potential durations (at 90% repolarization, APD90s), transmural conduction times and ventricular effective refractory periods (VERPs) were then determined from monophasic action potential records obtained during a programmed electrical stimulation procedure in which extrasystolic stimuli were interposed following regular stimuli at successively decreasing coupling intervals. A novel graphical analysis of epicardial and endocardial, local and transmural relationships between APD90, corrected for transmural conduction time where appropriate, and VERP yielded predictions in precise agreement with the arrhythmogenic findings obtained over the entire range of BCLs studied. Thus, in normokalaemic (5.2 mM K+) hearts a statistical analysis confirmed that all four relationships were described by straight lines of gradients not significantly (P > 0.05) different from unity that passed through the origin and thus subtended constant critical angles, θ with the abscissa (45.8° ± 0.9°, 46.6° ± 0.5°, 47.6° ± 0.5° and 44.9° ± 0.8°, respectively). Hypokalaemia shifted all points to the left of these reference lines, significantly (P < 0.05) increasing θ at BCLs of 80–120 ms where arrhythmic activity was not observed (∼63°, ∼54°, ∼55° and ∼58°, respectively) and further significantly (P < 0.05) increasing θ at BCLs of 140–180 ms where arrhythmic activity was observed (∼68°, ∼60°, ∼61° and ∼65°, respectively). In contrast, the antiarrhythmic effect of lidocaine treatment was accompanied by a significant (P < 0.05) disruption of this linear relationship and decreases in θ in both normokalaemic (∼40°, ∼33°, ∼39° and ∼41°, respectively) and hypokalaemic (∼40°, ∼44°, ∼50° and ∼48°, respectively) hearts. This extended a previous approach that had correlated alterations in transmural repolarization gradients with arrhythmogenicity in murine models of the congenital long QT syndrome type 3 and hypokalaemia at a single BCL. Thus, the analysis in terms of APD90 and VERP provided a more sensitive indication of the effect of lidocaine than one only considering transmural repolarization gradients and may be particularly applicable in physiological and pharmacological situations in which these parameters diverge

Common variants in 22 loci are associated with QRS duration and cardiac ventricular conduction

The QRS interval, from the beginning of the Q wave to the end of the S wave on an electrocardiogram, reflects ventricular depolarization and conduction time and is a risk factor for mortality, sudden death and heart failure. We performed a genomewide association meta-analysis in 40,407 individuals of European descent from 14 studies, with further genotyping in 7,170 additional Europeans, and we identified 22 loci associated with QRS duration ( P &lt; 5 x 10(-8)). These loci map in or near genes in pathways with established roles in ventricular conduction such as sodium channels, transcription factors and calcium-handling proteins, but also point to previously unidentified biologic processes, such as kinase inhibitors and genes related to tumorigenesis. We demonstrate that SCN10A, a candidate gene at the most significantly associated locus in this study, is expressed in the mouse ventricular conduction system, and treatment with a selective SCN10A blocker prolongs QRS duration. These findings extend our current knowledge of ventricular depolarization and conduction