THE COMMON MANUAL wheelchair is an effective, but

Transcription

1 702 PROSTHETICS/ORTHOTICS/DEVICES Evaluation of a Pushrim-Activated, Power-Assisted Wheelchair Rory A. Cooper, PhD, Shirley G. Fitzgerald, PhD, Michael L. Boninger, MD, Karin Prins, BS, Andrew J. Rentschler, BS, Julianna Arva, BS, Thomas J. O Connor, MS ABSTRACT. Cooper RA, Fitzgerald SG, Boninger ML, Prins K, Rentschler AJ, Arva J, O Connor TJ. Evaluation of a pushrim-activated, power-assisted wheelchair. Arch Phys Med Rehabil 2001;82: From the Human Engineering Research Laboratories, VA Rehabilitation Research & Development Center, VA Pittsburgh Healthcare System (Cooper, Fitzgerald, Boninger, Prins, Rentschler, Arva, O Connor), and Departments of Rehabilitation Science & Technology (Cooper, Rentschler, Arva, O Connor), Physical Medicine & Rehabilitation (Cooper, Fitzgerald, Boninger), and Bioengineering (Cooper, Boninger, Rentschler), University of Pittsburgh, Pittsburgh, PA. Accepted in revised form June 5, Supported in part by Yamaha Motor Corporation, Paralyzed Veterans of America, and VA Affairs Rehabilitation Research & Development Service, US Department of Veterans. An organization with which one or more of the authors is associated has received or will receive financial benefits from a commercial party having a direct financial interest in the results of the research supporting this article. Reprint requests to Rory A. Cooper, PhD, Human Engineering Research Laboratories (151-R1), VA Pittsburgh Healthcare System, 7180 Highland Dr, Pittsburgh, PA 15206, /01/ $35.00/0 doi: /apmr Objective: To evaluate a novel pushrim-activated, powerassisted wheelchair (PAPAW) for compliance with wheelchair standards, metabolic energy cost during propulsion, and ergonomics during selected activities of daily living (ADLs). Design: A 3-phase study, the second and third of which were repeated-measures designs. Setting: A rehabilitation engineering center within a Veterans Affairs medical center. Patients: Eleven full-time, community-dwelling, manual wheelchair users (4 women, 6 men) with spinal cord injuries or multiple sclerosis. Interventions: Phase 1: Compliance testing, with a test dummy, in accordance with the wheelchair standards of the American National Standards Institute and the Rehabilitation Engineering and Assistive Technology Society of North America. Phase 2: Metabolic energy consumption testing at 2 speeds and 3 resistance levels in subjects manual wheelchair and the PAPAW. Phase 3: Evaluation of ability to perform ADLs and ergonomics of the PAPAW compared with the subjects personal wheelchair. Main Outcome Measures: Phase 1: The PAPAW s static stability, static strength, impact strength, fatigue strength, environmental response, obstacle climbing ability, range, maximum speed, and braking distance. Phase 2: Subjects oxygen consumption per minute, minute ventilation, and heart rate during different speeds and workloads with a PAPAW and their own wheelchairs. Phase 3: Subject ratings of perceived comfort and basic ergonomics while performing selected ADLs. Completion time, stroke frequency, and heart rate during each ADL. Results: Phase 1: The PAPAW was found to be in compliance with wheelchair standards. Phase 2: With the PAPAW, the user had a significantly lower oxygen consumption (V O2 ml/min: p.0001; V O2 ml/kg min: p.0001) and heart rate (p.0001) when compared with a manual wheelchair at different speeds. Phase 3: The PAPAW had a significantly higher mean ergonomic evaluation (p.01) than the subjects personal wheelchairs. The results of comparing the ratings of the car transfer between the PAPAW and the subjects personal wheelchair showed a significant difference in the task of taking the wheels off (p.001) and putting the wheels back on (p.001), with the PAPAW receiving lower ratings. Conclusion: This study indicated that the PAPAW is compliant with wheelchair standards, reduces the energy demand placed on the user during propulsion, and that subjects rated its ergonomics favorably when compared with their personal wheelchair. PAPAWs may provide manual wheelchairs with a less physiologically stressful means of mobility with few adaptations to the vehicle or home environment. Key Words: Activities of daily living; Ergonomics; Rehabilitation; Wheelchairs by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation THE COMMON MANUAL wheelchair is an effective, but at times inefficient, means of conveyance. 1 Moreover, there are many people who have difficulty effectively propelling a manual wheelchair because of pain, low cardiopulmonary reserves, insufficient arm strength, or the inability to maintain a posture effective for propulsion. 2 Until recently, there were only 3 viable options for people with significant lower extremity impairments who were unable to propel a manual wheelchair effectively: electric-powered wheelchair usage; driving a scooter; or being pushed by an assistant. All 3 of these options have advantages and disadvantages for an individual s independence. Previous studies have shown manual wheelchair propulsion efficiency to be between 5% and 18%. 3-5 The low efficiency of manual wheelchairs makes them difficult or impossible for some individuals to use effectively. To address this problem, several alternatives have been explored, including lever-drive units, 6 crank drives, 7 and geared hubs. 8 However, none of these solutions have proven themselves practical or widely commercially accepted. Manual wheelchair users also experience a high degree of upper extremity joint degeneration and pain. The incidence of injuries to the wrist, elbow, and shoulder among manual wheelchair users is between 25% and 80%. 9,10 There is also some indication that the incidence of pain increases with the length of wheelchair use, 11 and that cardiopulmonary fitness tends to decrease with age. 12 These issues are compelling reasons to investigate alternatives to pushrim propulsion. A new concept is the pushrim-activated, power-assisted wheelchair (PAPAW) (fig 1). There are several PAPAWs currently under development. The particular PAPAW tested during this study was the JWII. a Applying a torque to the pushrims activates the wheelchair. The pushrim force is regulated by sets of linear compression springs and recorded by a simple potentiometer that senses the relative motion between the pushrim and hub. The potentiometer signals from both wheels are interfaced to a microcontroller contained in a housing under the

2 POWER-ASSISTED WHEELCHAIRS, Cooper 703 METHODS Fig 1. The PAPAW used in this study. battery. The microcontroller algorithm coordinates control of each wheel s direct current (DC) motor, which are attached to a transmission within the hub. The software stimulates inertia (ie, allows for a coast), compensates for discrepancies between the 2 wheels (eg, differences in friction), and provides an automatic braking system activated when applying a reverse torque to the pushrims. The system is supplied power by either a single custom-designed nickel-cadmium (NiCd) or a nickelmetal (NiMH) hydride battery. The wheels have quick-release axles, and can be retrofitted to some types of manual wheelchairs with some customized hardware. This technology represents an entirely new type of wheelchair and user interface. When developing a new mobility device for people with disabilities, the US Food and Drug Administration requires that the device be both safe and effective. 13 A means of showing safety and efficacy is to use the American National Standards Institute (ANSI) and Rehabilitation Engineering and Assistive Technology Society of North America (RESNA) wheelchair standards. 14 Several studies have presented the results of ANSI RESNA standards testing and shown that there are differences in the results among wheelchairs and that not all wheelchairs meet the standards It is important for new products to be tested in accordance with recognized standards and to compare the results with similar products. This study sought to determine the performance of the PA- PAW with appropriate ANSI RESNA standards, to compare metabolic energy demands for the PAPAW with subjects manual wheelchairs, and to compare performance of selected activities of daily living (ADLs) with the PAPAW with subjects personal wheelchairs. It was hypothesized that the PAPAW would comply with ANSI RESNA standards and perform similarly to other wheelchairs. There would be significantly lower economy (ie, steadystate rate of oxygen consumption), ventilation rate, and heart rate (HR) among the 2 conditions (manual wheelchair, PA- PAW). There would be no significant difference in wheelchair user ratings for ADLs or general wheelchair ergonomics for their personal wheelchair and the PAPAW. Phase 1: Wheelchair Standards Testing Two Quickie GP wheelchairs b equipped with a JWII were tested by using the ANSI RESNA standards. 14 Because of the unique characteristics of PAPAWs, we determined that sections 1 (static stability), 2 (dynamic stability), 3 (effectiveness of brakes), 4 (energy consumption), 5 (overall mass, dimensions), 6 (speed, acceleration), 7 (seating and wheel dimensions), 8 (static, impact, fatigue strength), 9 (obstacle climbing ability), and 10 (environmental testing) of the ANSI RESNA standards were most relevant. Both chairs were tested with a 100-kg wheelchair test dummy. 18 The wheelchairs were selected with the features described in table 1 to increase the likelihood of detecting a potential problem via the standards testing. Table 1 also lists the technical specifications for the JWII unit. The JWII automatically supplements the users manual pushrim input with additional rear-wheel torque for speeds up to 6km/hr. The supplemental torque is proportional to the user input to the pushrims. Power assistance is provided for both forward and reverse travel. The ANSI RESNA tests were conducted in the order prescribed by the standards. 14 Double-drum and curb-drop testing were the last tests to which the wheelchairs were subjected. 19 A double-drum tester is simply 25.4-cm diameter rollers with 12-mm high slats attached to each wheel. The front roller turns 7% faster than the rear roller to avoid exciting harmonics. The rear rollers turn at an equivalent speed of 1m/s. The wheelchair is balanced over the rollers with a swing-arm attached to the wheelchair s rear axles to provide stability. A double-drum cycle is defined as 1 revolution of the rear roller. The curb-drop tester is a device that lifts the wheelchair 5cm and allows it to free-fall to a hard surface (ie, cement floor). Each wheelchair was to be tested for at least 200,000 cycles on the double-drum tester, as prescribed in the standards. If the wheelchair completed 200,000 cycles without a Class III failure, it was transferred to the curb-drop tester for 6666 drops. A Class III failure is defined as permanent damage, deformation, Table 1: Technical Specifications for the PAPAW JWII a Motor: DC with brushes, 60W each Battery: NiCd or NiMH: 24V DC, 2.5A-hr, 1.8kg, charge time 1hr Control interface: Bilateral pushrim moment Gears: Ring gear, assist ratio 1.5 3, depending on settings Maximum speed: 60km/hr with assistance Range: Greater than 7km at 5km/hr on a single battery charge Total mass: Mass added to wheelchair is 13.8kg Quickie GP Wheelchairs b Seat Width: 460mm (18 ) Depth: 460mm (18 ) Backrest height: 460mm (18 ) Rear wheels: 610mm (24 ) Radial stainless steel spokes, aluminum rings Rear tires: Pneumatic, inflated to rated tire pressure of 5.25kg/cm 2 Front casters: 12mm (5 ) in diameter Polyurethane tires

3 704 POWER-ASSISTED WHEELCHAIRS, Cooper or failure that significantly affects the ability to operate the wheelchair. Our test machines are calibrated to detect failures and to power-down to avoid further damage to the wheelchair. In addition, all wheelchairs were inspected at least every 10,000 double-drum cycles and 300 curb-drops. All of the test equipment was calibrated before testing of these wheelchairs. All tests were performed by thoroughly trained and experienced wheelchair testing engineers within our laboratories. Phase 2: Metabolic Energy Consumption Subjects. Ten full-time manual wheelchair users (4 women, 6 men) were recruited from the laboratories database. Sample size was based on a pilot study examining the differences between a standard wheelchair and the PAPAW on an able-bodied population. The predominantly white (90%) sample had a mean age standard deviation (SD) of years. Mean length of time post spinal cord injury (SCI) was years. Nine of the subjects had a T2 12 injury and 1 had multiple sclerosis (MS). All subjects gave written informed consent before participating. Protocol. In random order, subjects were asked to propel their own chair and a PAPAW on a computer-controlled wheelchair dynamometer. 20 Subjects were allowed 5 minutes to acclimate to the experimental set-up. Subjects were also given a 5-minute break between each trial. Speed and torque were sampled from the dynamometer at 240Hz. The target propulsion speeds were 0.9 and 1.8m/s, with the dynamometer set on normal (0.9m/s, 10W; 1.8m/s, 25W), slight (0.9m/s, 12W; 1.8m/s, 30W), and moderate (0.9m/s, 14W) resistances. The order of chairs, speeds, and resistances was randomized. Oxygen consumption (V O2 ml/kg min, V O2 ml/min) and ventilation (V E L/min) were measured with a metabolic measurement cart, c HR was measured with a HR monitor. d A pretrial calibration was completed with the metabolic cart before each subject s testing session. Three minutes of physiologic data were collected for each trial (speed and resistance combination), recording the data every 20 seconds. HR was also recorded every 20 seconds. Only the last minute of data, after the subjects achieved steady state (defined when values reached a plateau), were analyzed to ensure that the subjects were in steady state. Statistical analysis. The last minute of physiologic data were averaged for each of the variables of interest and for each trial. Distributions of the averaged variables were examined. Data were normally distributed for only some of the variables. To compare the PAPAW with the participant s own wheelchair, appropriate statistics were used depending on the distribution of the data (paired t test for normal distribution, a Wilcoxon rank-sum test for not normally distributed data). Significance level was set at p less than.05. The physiologic variables compared between the 2 types of chairs (manual vs PAPAW) were HR, ventilation, V O2 ml/kg min, and V O2 ml/min. A mixed analysis of variance (ANOVA) model was used to determine if differences existed between the 2 types of chairs and 5 trials (2 speeds, 3 resistance levels). Traditional ANOVA designs have a assumption of independence between groups, therefore, not allowing the same subject to be in the 2 different groups. A mixed ANOVA model allowed for a comparison between the 2 types of chairs even though the individuals in the chairs were the same. Phase 3: ADL Evaluation Subjects. Ten manual wheelchair users (6 men, 4 women) volunteered for phase 3 of the study and provided written informed consent. Subjects were recruited from the laboratories database. The average age of the subjects was years. All subjects were manual wheelchair users because of an SCI (8 subjects with thoracic SCI, 1 subject with lumbar SCI) or MS (1 subject). The subjects had been using manual wheelchairs for an average of years. All subjects used the same type of PAPAW as described in phase 1. Protocol. Measurements were made of subjects wheelchairs, and a PAPAW (in this case, a Quickie 2 wheelchair equipped with JWII) was selected for seat depth, seat width, and adjusted for legrest length and backrest height based on subjects personal wheelchairs. All subjects began by propelling over a standardized ADLs course 3 times. The ADL driving course and survey have been previously described and validated. 21 Subjects completed a portion of the survey after completing the first trial and the remainder after having finished the third trial. Subjects were asked to open and close a 91.4-cm wide door as they passed through it; the door required 25N of force to open and close. Subjects maneuvered into a simulated public bus wheelchair docking space. In addition, subjects were asked to traverse down and up a 4.1-meter long ramp with a grade of 4.8 at their freely chosen speed. While each subject propelled through a 62-meter long hallway, an investigator drove a powered wheelchair alongside each subject, acting as a pace vehicle, at a constant speed of 1m/s. Subjects were instructed to keep pace with the investigator while using as few strokes as possible. The number of propulsion strokes were recorded. Subjects were also asked to transfer to a simulated car after which they had to take the wheelchair apart and put the wheels and the chair in the car. Then the subjects were asked to remove the wheelchair and reassemble it. Subjects completed a brief survey after performing each exercise. Ratings were on a Likert-type scale from 0 to 10cm, with 0 indicating extremely difficult to complete and 10 indicating extremely easy to complete. Subjects were also asked to rate the ergonomics of each wheelchair. Time to complete each task was measured for all activities with a stopwatch. HR was recorded continuously during all of the testing, and event markers were used to match HRs with specific tasks. Janssen et al 22 described physical strain during ADLs. Physical strain was estimated by HR response after finishing a task (HR task ), expressed as a percentage of the HR reserve (%HRR), determined by the equation %HRR HR task HR rest HR peak HR rest 100% The HR measurement used for tasks of short duration was the HR just after completing the task. HR rest was that measured at rest while seated before testing. Subjects were at rest for about 10 minutes before recording. The physical strain was expressed relative to the HRR, to compare among subjects. The HR peak is the subjects predicted maximum HR for arm work, 19 determined by HR peak 220 age.80 The effectiveness of the PAPAW was partially evaluated by using the subjects ratings, HR, completion time, and stroke frequency in the hallway. The learnability of the PAPAW was examined by comparing the results of trail 1 with the results of trial 3. All subjects performed each exercise with their own wheelchairs and a PAPAW. The order in which the wheelchairs were presented was randomized. Subjects were given at least 30 minutes to rest between switching wheelchairs. Statistical analysis. A single investigator measured the distance from the left edge of the rating scale questions to the nearest millimeter by using a ruler. A second investigator

4 POWER-ASSISTED WHEELCHAIRS, Cooper 705 Table 2: Results of Wheelchair Testing* of the PAPAW Static Stability Stability Direction Tip Angle Downhill 27.9 Uphill Rear wheels locked 14.8 Rear wheels unlocked 7.0 Antitippers 21.0 Lateral Left 23.2 Right 19.3 Dynamic Stability Stability Direction 0 Slope 3 Slope 6 Slope Scoring System Start uphill No tip Fwd brake uphill Release Transient tip Reverse Hits antitippers Power off stuck on antitippers Bwd brake downhill Release Full tip Reverse PAPAW s were equipped with rear antitip devices. Power off Turning on downhill slope Effectiveness of Brakes Condition 0 Slope 3 Slope 6 Slope Braking distance (mm) Maximum speed (m/s) Energy Consumption Terrain Driver Mass Total Time Range Average Velocity Tennis court 75kg 1:41: km 7.08km/hr Hallway 75kg 1:29: km 7.25km/hr Hallway 100kg 1:29: km 7.41km/hr Overall Dimensions Dimension Results Length (mm) 940 Length (no footrest) (mm) 880 Width (mm) 690 Height (mm) 910 Mass (kg) 24 Minimum turning radius (mm) 610 Turn-around width (mm) 1220 Maximum Speed, Acceleration, and Retardation Condition 0 Slope 3 Slope 6 Slope Maximum speed (m/s) Overall retardation (m/s 2 ) 1.37 Maximum retardation (m/s 2 ) 2.06 Overall acceleration (m/s 2 ).78 Maximum acceleration (m/s 2 ) 2.32 Abbreviations: Fwd, forward; Bwd, backward. * ANSI RESNA wheelchair testing. Scoring system for dynamic stability: 4 no tip, 3 transient tip, 2 hits antitippers, 1 stuck on antitippers, 0 full tip. PAPAWs were equipped with rear antitip devices. Maximum speed is defined as the top speed at which assistance is provided by the device. Above this speed, the device begins to use regenerative braking, hence, slowing the wheelchair. independently verified the readings of the first investigator. One-way ANOVA was used to identify differences in ratings for ease and comfort of tasks, as well as to identify differences in physical strain. A significance level of p less than.05 was used. When appropriate, a multiple comparison least significant difference post hoc test was applied to identify significant differences among the groups (.05). A paired 1-tailed t test was used to identify differences for all variables for the car transfer. Paired t tests were also used to identify differences in ratings, time period, and physical strain among ADL tasks performed during trial 1 and 3 with the PAPAW (p.05). Repeated-measures ANOVA was used to identify task completion time differences at the subject level among the groups (p.05). Differences in the amount of strokes used for

5 706 POWER-ASSISTED WHEELCHAIRS, Cooper significantly lower (p.05) last minute mean in all 5 trials for V O2 ml/kg min and V O2 ml/min when compared with each subject s manual wheelchair. For HR, the PAPAW was significantly lower (p.05) than the subject s manual wheelchair for 2 of the 5 conditions. For ventilation, only 2 of the 5 trials were significantly different between the 2 chairs. Interestingly, for those 2 trials, the ventilation was higher with the PAPAW. Results from the mixed model indicated that for V O2 ml/kg min, V O2 ml/min and HR were significantly different (p.001) between the chairs and speed, but not the resistance level. For ventilation, there was no difference (p.05) between the chairs (as indicated in the univariate analysis) or between the speeds and resistances. Fig 2. Fatigue fracture of PAPAW hub. propelling through the hallway with each wheelchair were analyzed with a Kruskal-Wallis test (p.05). RESULTS Phase 1: Wheelchair Standards Testing Table 2 provides the results from the static stability, dynamic stability, brake effectiveness, energy consumption, overall dimensions, and speed and acceleration tests. Product redesign was required for the curb-drop fatigue test and the cold-storage environmental tests. After completing 200,000 cycles on the double-drum tester, the shell of the hub on the first JWII experienced a fatigue fracture during the curb-drop test after 4000 of the 6666 required drops (fig 2). The shell wall thickness was increased and tested on the second JWII without incident. In addition, the first JWII exhibited erratic behavior after the initial cold storage test (ie, storage in an environmental chamber at 40 C). In the second JWII, the electronics enclosure was redesigned and the environmental testing indicated that the problem had been resolved. After modifications were made by the manufacturer, the PAPAW completed all of the ANSI RESNA standards without notable deviation from expected performance. Phase 2: Metabolic Energy Consumption Table 3 shows the mean values of the PAPAW and manual wheelchair for each of the 5 conditions. The PAPAW had a Phase 3: ADL Evaluation The mean ratings and SDs for each of the tasks are provided in table 4. All subjects were able to perform all tasks with their personal wheelchairs and a PAPAW. The personal wheelchairs had the highest mean ratings for all performed tasks during trials 1 and 3. The results for the completion times and the HRR values are shown in table 5. A significant difference was identified for the completion time (p.01) of the ADL course and the rating for the large speed bump (p.02) (table 4) between trials 1 and 3. No other significant differences were found at a task level. There also were not any significant differences (p.05) identified for the physical strain and completion time values of each trial among wheelchairs. The PAPAW had the highest mean ergonomic ratings (table 4). The PAPAW also had the highest mean rating for appearance. There were no significant differences (p.05) between the PAPAW and the subjects personal wheelchairs for the hallway and the ramp (table 5). There also was not a significant difference (p.05) in the number of strokes among the wheelchairs. Subjects pushed a mean of 51 strokes with the personal wheelchairs, and a mean of 47 strokes with the PAPAW. Five subjects were not able to do 1 or more of the car transfer tasks with the PAPAW. Comparing the ratings of the car transfer between the PAPAW and the regular wheelchairs showed a significant difference in the exercises of taking the wheels off (p.004) and putting the wheels back on (p.001), with the PAPAW receiving lower ratings (table 4). There were no significant differences (p.05) in physical strain for all car transfer tasks among the wheelchairs. DISCUSSION PAPAWs offer an alternative between manual wheelchair mobility and electric-powered wheelchair driving. A PAPAW Table 3: Results of Metabolic Testing With the PAPAW and Subjects Personal Wheelchair Trial V O2 (ml/min) Ventilation (L/min) V O2 (ml/kg min) Heart Rate (bpm) Personal PAPAW Personal PAPAW Personal PAPAW Personal PAPAW 1.8m/s, 25W p.001 p m/s, 30W p.001 p.001 p m/s, 10W p.009 p.05 p.01 p m/s, 12W p.006 p.04 p m/s, 14W p.003 p.01

6 POWER-ASSISTED WHEELCHAIRS, Cooper 707 Table 4: Subject Ratings on a Scale From 0 to 10 of Their Personal Wheelchairs and a PAPAW for Selected Tasks Task First Trial Third Trial Personal PAPAW Personal PAPAW Truncated domes Carpet Door threshold Slope Guidance strip Small bump Medium bump Large bump Doorway Bus docking space Hallway ADA ramp Car Transfers Remove wheels * Load wheelchair Remove wheelchair Replace wheels Ergonoomics Stability Maneuverability Appearance Remove battery N/A Replace battery N/A Power switch N/A Audio signals N/A Visual signals N/A Comfort Pushrim Wheelchair NOTE. Values presented as mean SD. Abbreviations: ADA, Americans with Disabilities Act; N/A, not available. * p.004. p.001. p.013. operates much like a manual wheelchair but with less effort. This may make a PAPAW suitable for people with or at risk for upper extremity joint degeneration, with reduced exercise capacity, and low upper-extremity strength or endurance. We were unable to find any published data on the testing of PAPAWs for compliance with ANSI RESNA standards. Although the ANSI RESNA standards do not directly address PAPAWs, there are several standards tests that are appropriate for evaluating them. The first model of the JWII that we tested did not comply with the fatigue tests. This was likely because of the goal of minimizing the weight of the device and the reduction in strength of the shell of the hub when changing from a machined part to a casting. The hub wall was increased, with a nominal change in weight, for the second JWII, and it passed the fatigue tests. In addition, the weather seals of the first model of the JWII did not pass the cold storage tests. A new enclosure for the electronics with better seals was implemented and no further problems were observed. Compared with the performance of manual wheelchairs on ANSI RESNA tests, the PAPAW compared favorably, performing similarly to published values for ultralight (Medicare Class KO5) manual wheelchairs and electric-powered wheelchairs on static, impact, fatigue strength tests, and static stability tests. 16,23 The PAPAW performed better on ANSI RESNA tests than lightweight (Medicare Class KO4) manual wheelchairs. 17 There was some asymmetry in the lateral stability of the PAPAW, which may be because the battery is mounted to 1 side. It is also interesting to note that when braking while going backward, the PAPAW tipped fully over when the pushrims were released; this did not occur with the other 2 braking methods. This may be caused by the loss of interaction between the user interface (pushrim) and the device with the power on. In the other modes of braking, the PAPAW either implemented controlled braking or was essentially a manual wheelchair (ie, the case of power off). The range of the PAPAW was less than has been reported for common electric-powered wheelchairs (typically 30km), 24 but the PAPAW can be propelled like a manual wheelchair once the battery is discharged. The standards testing indicated that the PAPAW operates safely and to accepted norms. The metabolic energy cost and HR for propelling a PAPAW was lower than when propelling the subject s personal wheelchairs. This indicates that the PAPAW reduced the cardiovascular demand over manual wheelchair propulsion for different speeds. Our metabolic results for manual wheelchair propulsion were similar to those reported in the literature. 7,8 The results with the PAPAW showed a reduction in metabolic demand that is greater than geared hubs 8 and lever-drive 7 systems, and comparable to arm-crank 6 systems. However, arm-crank devices are typically too large for indoor use and interfere with the performance of ADLs. The PAPAW may provide a viable mobility option that is more desirable than either current manual or electric-powered mobility. It is likely that the retail price for a PAPAW will be comparable to an average electric-powered wheelchair. Metabolic cost and mechanical work are related by the device efficiency, therefore, the reduced metabolic cost of the PAPAW likely relates to less stress on the upper extremities. Stress on the upper extremities has been related to injury secondary to wheelchair use. 25 Significant differences (p.05) were identified for both taking the JWII wheels off and putting them back on again, with the JWII being rated lower than subjects own wheelchairs. Five of the 10 subjects were not able to do 1 or more of the car transfer tasks with the PAPAW. There are several probable reasons for this result: the JWII wheels are heavier than those of the subjects personal wheelchairs; the 2-pin assembly of the JWII made alignment of the axles more difficult than the single-pin design of manual wheelchair quickrelease axles; the battery-holder of the JWII tended to rotate the wheel, making it hard to position the wheel; and unfamiliarity Table 5: HR Reserve and Completion Times for Selected Tasks Task HR Reserve (%) Completion Tie (s) Personal PAPAW Personal PAPAW ADL driving course ADA Ramp up Ramp down Hallway Transfer into car Load wheelchair into car N/A Remove wheelchair from car NOTE. There were no statistically significant differences. Abbreviation: N/A, not available because of problems with HR instrumentation.

7 708 POWER-ASSISTED WHEELCHAIRS, Cooper with the JWII versus their personal wheelchairs. None of the subjects who had quick disconnect wheels on their personal wheelchairs reported any trouble with disassembling their wheelchair, even if they had rarely disassembled them. The PAPAW could be improved by developing a better mechanism for attaching the wheels, and a different location for the battery. No significant differences (p.05) were identified for putting the chair frames in or taking them out of the car. There were no significant differences (p.05) in physical strain for all car transfer tasks between wheelchairs. However, all subjects completed the car transfer faster with their personal wheelchairs than with the PAPAW. No significant differences were identified for the ratings for any of the performed tasks on the ADL course. This may be because the subjects were familiar with their personal wheelchairs. The ratings for the PAPAW on the third trial were significantly higher than the rating for the first trial. The completion time of the third trial was significantly less than the completion time of the first trial with the PAPAW. None of the variables defining the efficiency (physical strain, completion time) were significantly different among the 2 types of chairs (manual vs PAPAW). This could be because of the quality of the subjects manual wheelchairs and the fitness levels of the subjects. Greater practice with a PAPAW and more difficult tasks may have elicited differences with the PAPAW. The PAPAW had a higher mean ergonomic and comfort ratings than the subjects personal wheelchairs. Subjects reported that the PAPAW behaved very much like their personal wheelchairs. This may account for the few differences in the ratings on ADLs. Future studies should include subjects who are older and people with impaired upper extremities. CONCLUSION This study indicated that the JWII is compliant with wheelchair standards, reduced the energy demand placed on the user during propulsion, and that subjects rated its ergonomics favorably when compared with their personal wheelchairs. PA- PAWs may provide manual wheelchairs with a less stressful means of mobility with few adaptations to the vehicle or home environment. The PAPAW could be a new tool in the arsenal of rehabilitation professionals to help people with physical impairments. References 1. Veeger HE, van der Woude LH, Rozendal RH. Effect of handrim velocity on mechanical efficiency in wheelchair propulsion. Med Sci Sports Exerc 1992;24: Cooper RA, Quatrano LA, Axelson PW, Harlan W, Stineman M, Franklin B, et al. Physical activity and health among people with disabilities. J Rehabil Res Dev 1999;36: Lakomy HA. Treadmill performance and selected physiological characteristics of wheelchair athletes. Br J Sports Med 1987;21: Glaser RM, Sawka MN, Laubach LL, Suryaprasad AG. Metabolic and cardiopulmonary responses to wheelchair and bicycle ergometry. J Appl Physiol 1979;46: Sawka MN, Glaser RM, Wilde SW, von Luhrte TC. Metabolic and circulatory responses to wheelchair and arm crank exercise. J Appl Physiol 1980;49: van der Woude LH, Botden E, Vriend I, Veeger D. Mechanical advantage in wheelchair lever propulsion: effect on physical strain and efficiency. J Rehabil Res Dev 1997;34: Arabi H, Vandewalle H, Pitor P, de Lattre LJ, Monod H. Relationship between maximal oxygen uptake on different ergometers, lean arm volume and strength in paraplegic subjects. Eur J Appl Physiol 1997;76: O Connor TJ, DiGiovine MM, Cooper RA, DiGiovine CP, Boninger ML. Comparing a prototype geared pushrim and standard manual wheelchair pushrim using physiological data. Saudi J Disabil Rehabil 1998;4: Gellman H, Chandler DR, Petrasek J, Sie I, Adkins R, Waters RL. Carpal tunnel syndrome in paraplegic patients. J Bone Joint Surg Am 1988;70: Nichols PJ, Norman PA, Ennis JR. Wheelchair user s shoulder? Shoulder pain in patients with spinal cord lesions. Scand J Rehabil Med 1979;11: Sie IH, Waters RL, Adkins RH, Gellman H. Upper extremity pain in the postrehabilitation spinal cord injured patient. Arch Phys Med Rehabil 1992;73: Cooper RA, Baldini FD, Langbein WE, Robertson RN, Bennett P, Monical S. Prediction of pulmonary function in wheelchair users. Paraplegia 1993;31: Cooper RA. Rehabilitation engineering: applied to mobility and manipulation. Bristol (UK): Institute of Physics Publishing; American National Standards Institute. American national standards for wheelchairs. New York: ANSI; Cooper RA, Robertson RN, Lawrence B, Heil T, Albright SJ, VanSickle DP, et al. Life-cycle analysis of depot versus rehabilitation manual wheelchairs. J Rehabil Res Dev 1996;33: Cooper RA, Boninger ML, Rentschler A. Evaluation of selected ultralight manual wheelchairs using ANSI/RESNA standards. Arch Phys Med Rehabil 1999;80: Cooper RA, Gonzalez J, Lawrence B, Rentschler A, Boninger ML, VanSickle DP. Performance of selected lightweight wheelchairs on ANSI/RESNA tests. Arch Phys Med Rehabil 1997;78: Cooper RA, O Connor TJ, Gonzalez JP, Boninger ML, Rentschler A. Augmentation of the 100kg ISO wheelchair test dummy to accommodate higher mass. J Rehabil Res Dev 1999;36: Cooper RA. Wheelchair selection and configuration. New York: Demos Medical; Cooper RA. A force/energy optimization model for wheelchair athletics. IEEE Trans Syst Man Cybern 1990;20: DiGiovine MM, Cooper RA, Boninger ML, Lawrence BL, Van- Sickle DP, Rentschler AJ. User assessment of manual wheelchair ride comfort and ergonomics. Arch Phys Med Rehabil 2000;81: Janssen TW, van Oers CA, Veeger HE, Hollander AP, van der Woude LH, Rozendal RH. Relationship between physical strain during standardised ADL tasks and physical capacity in men with spinal cord injuries. Paraplegia 1994;32: Barnicle K. Evaluating powered wheelchairs, request evaluating assistive technology. Washington (DC): Rehabilitation Engineering Center, National Rehabilitation Hospital; Cooper RA, VanSickle DP, Albright SJ, Stewart KJ, Flannery M, Robertson RN. Power wheelchair range testing and energy consumption during fatigue testing. J Rehabil Res Dev 1995;32: Boninger ML, Cooper RA, Baldwin MA, Shimada SD, Koontz A. Wheelchair pushrim kinetics: weight and median nerve function. Arch Phys Med Rehabil 1999;80: Suppliers a. Yamaha Motor Co, 2500 Shingai, Iwata, Shizuoka, , Japan. b. Sunrise Medical Corp, Quickie Div, 2842 Business Pk Ave, Fresno, CA c. Sensormedics Corp, Savi Ranch Pkwy, Yorba Linda, CA d. Polar USA, Inc, 470 West Ave, Stamford, CT