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Home > RNJ > 2011 > July/August > Wheelchair Positioning and Breathing in Children with Cerebral Palsy: Study Methods and Lessons Learned (CE)

Wheelchair Positioning and Breathing in Children with Cerebral Palsy: Study Methods and Lessons Learned (CE)
Lee Barks, PhD ARNP Peggy Shaw, BSOT OTR/L

In children with cerebral palsy (CP), poor trunk control can lead to spinal deformity, pulmonary compromise (Canet, Praud, & Bureau, 1998), and increased health risks and costs of long-term care (Braddock, 2002). Evidence links posture and pulmonary function, but the influence of wheelchair components on pulmonary function is unknown. This article reports on a study evaluating pulmonary measurement in wheelchairs and how it affected children with CP. The objectives of the study were to (a) describe recruitment and retention of school-aged children with CP and (b) discuss participants’ response to the protocol. Using a wheelchair simulator, participants experienced five seating parameters while pulmonary mechanics measures were recorded. A process log captured participant recruitment and retention challenges and response to the protocol. Recruitment was challenging; retention was 50%. The protocol was feasible for 50% of participants, none of whom could participate in conventional pulmonary function testing. Among the study’s participants, facemask and seating simulator acceptability were 75%, improving with participants’ increased verbal communication abilities (verbal children tolerated the procedure best). The facemask was vulnerable to tilt; 75% of participants experienced fatigue.

Background

Frontline staff members are responsible for positioning patients who cannot reposition themselves. The safe patient handling and movement initiative has made substantial contributions to research and practice, and evidence is growing for strategic positioning of patients on ventilators and with traumatic brain injury (Gavin-Dreschnack & Barks, 2008; Yeaw, 1996). There is still little science to guide rehabilitation professionals in positioning immobile patients for health outcomes such as breathing and eating. Literature shows that these are outcomes of posture (Lin et al., 2006; Logemann, Kahrilas, Kobara, & Vakil, 1989; McFarland, Lund, & Gagner, 1994; Nwaobi & Smith, 1986), which is an outcome of repositioning or positioning. Two studies investigated (a) the impact of “adaptive” wheelchairs on pulmonary function (Nwaobi & Smith) and (b) the impact of trunk straightening with a soft orthosis on total airway resistance (Leopando et al., 1999). Investigators have yet to translate applied physiology findings in posture and breathing to rehabilitation nursing and positioning patients in wheelchairs, including how wheelchair features affect posture and breathing. Furthermore, all rehabilitation settings include some individuals who are unable to reposition themselves, either temporarily or for the long term. Providers need more evidence for patient positioning.

Health outcomes of patient positioning relate to rehabilitation because improving pulmonary function for people who use wheelchairs is a crucial goal of treatment. In one study, pulmonary measurement with wheelchair positioning was conducted with prepubertal, nonambulatory children with cerebral palsy (CP; Barks, 2007). The group was chosen because they had flexible spines, had not yet developed fixed deformity, and could serve as their own control group because their posture could be manipulated. The purpose of this article is to report the responses of children with CP in a study using novel methods of pulmonary measurement, with breathing as an outcome of wheelchair components that may straighten the trunk and improve breathing.

The study posed the questions (1) What are the challenges associated with subject recruitment and retention in a sample of prepubertal children (5–10 years) with CP? and (2) What is the response of children with CP to the data collection protocol?

This article is relevant to rehabilitation nurses because rehabilitation patients are generally a vulnerable population. Recruitment issues, particularly of vulnerable participants, can slow research progress and accumulation of evidence for practice. Lessons learned from studies using technology with vulnerable populations may help investigators with similar studies, and rehabilitation clinicians are increasingly important in the research process, referring participants, using the evidence base, implementing new interventions, and voicing the need for new evidence. This paper contributes to nursing science by reporting on the use of novel methods with a vulnerable population.

In an environment in which justification for reimbursement is required, rehabilitation professionals need evidence showing the effects of wheelchair components (e.g., tilt, armrests, lateral trunk supports) and other positioning technology on health outcomes. The phenomena of scoliosis, breathing, wheelchair positioning, and the genesis of deformity in people with CP have been subjects of a prior research synthesis (Barks, 2004). The evidence for patient positioning, or postural management, is limited (Farley et al., 2003). Measurement and description of the effects of postural management on health (e.g., breathing, eating, digestion, physical function) in rehabilitation are needed. Nurses already position patients who cannot position themselves, often in wheelchairs. Positioning patients according to strategies meant to maximize physiological and physical function may not require additional interventions, just different ones.

Barks Table 1Methods

Sample and Sampling

Sixteen children were recruited from outpatient clinics at a university pediatric neurology division and a children’s orthopedic hospital. Inclusion criteria included English-speaking, prepubertal, 5–10 years old, CP diagnosis, lacking trunk control, and without a full meal in past 2 hours (gastric volume can interfere with breathing). The sample included an equal number of males and females. Exclusion criteria included children with spinal cord injury; spina bifida/myelomeningocele; degenerative neurologic diseases; existing cardiovascular, hematologic, or respiratory pathology; or history of either respiratory illness in the past 3 weeks or of apnea; children with a history of pain on movement; and those with fixed spinal deformity or history of spinal surgery. Fifty percent of participants did not meet the inclusion criteria. Only two participants were receiving any medication (i.e., oral diazepam, baclofen, and oxcarbazepine, which was far fewer than expected. Extent of spasticity was evenly distributed; all participants had some increased tone. No data were missing. Characteristics of both retained and excused participants are reported in Table 1. After human subjects protection approval was obtained from the appropriate boards, the convenience sample was recruited by clinic staff offering study information to interested families during a 4-month period. The sampling goal was to reflect the ethnic and gender composition of Florida: 51.2% female, 48.8% male; 65.4% non-Hispanic White, 16.8% Hispanic, 14.6% African American, and 3.2% other (U.S. Census Bureau, 2000).

The investigator answered questions from interested families, legal guardians provided informed consent, and participant assent was sought. All but two guardians chose to schedule the study procedure immediately following the medical visit on the clinic day. Participants were screened in clinic.

Barks Table 1

 

Measures

Prairie Reflections Seating SimulatorTM

The Prairie Reflections Seating Simulator (Figure 1; Prairie Seating Corporation, 2007) provides multiple seating surfaces; all measurements were made with a goniometer or metal tape measure. Seat tilt was measured in degrees by a gauge at the right seat-to-back angle vertex, used to measure 30 degrees backward tilt from vertical and zeroed daily. The seat-to-back angle was set at 100 degrees. The investigator was certified to measure and apply the seating parameters uniformly by two experts in the Waugh protocol for wheelchair fitting. They certified correct, consistent placement of seatbelt, lateral trunk supports, upper extremity supports, seat depth, and head rest (Shaw, 2006; Waugh, 2005) within ± 10%.

Respironics NICO®

The disposable sensor and short tubing used in the Respironics NICO® (Figure 2) were considered pediatric for patients 15–45 lbs (Model 9766) and adult for patients more than 45 pounds (Model 9767). CO2 sensor accuracy is ± 2 mm Hg for 0–40 mm Hg, ± 5% of reading for 41–70 mm Hg, and ± 8% of reading for 71–150 mm Hg. Accuracy of the flow sensor is ± 3% of the reading or 0.5 L/min (Philips Respironics, 2009). The recommended locus for sampling is immediately proximal to the airway; a facemask is acceptable. At a 30-degree tilt in space, data were easily collected because the tubing and sensor did not need to be presented solely in the frontal plane and were quite mobile. All data were obtained according to factory guidelines, and the investigator was trained by the factory representative. Values were recorded as soon as displayed after 30 seconds or 8 breaths.

Barks Figure 2The Viasys Jaeger Impulse Oscillometry System™

The Viasys Jaeger Impulse Oscillometry System™ (IOS; Figure 3) uses a “forced oscillation technique” with digital signal analysis. An attached computer uses Fast Fourier Transforms to fit the forced oscillation technique data to algorithms. The IOS allows determination of total airway resistance in kiloPascals per liter per second (kPa/L/s) without active patient participation (Horan et al., 2001). R5, or resistance at 5 Hz, was the measure of total airway resistance. Accuracy of the IOS pneumotach is 0.2–12 L/s, ± 2%, with accuracy of the mouth pressure transducer of ± 2%. Disposable Viasys Microgard microbial filters (#769344G) were used. An expert skilled in use of the IOS certified the investigator in IOS use at the Shands/University of Florida pulmonary neurophysiology laboratory (P. Davenport, personal communication, January 26, 2006). An IOS volume calibration check was completed monthly (Viasys Jaeger, 2009).

A facemask/airway is recommended for use with children by the manufacturers for both NICO and IOS. The IOS facemask/mouthpiece was unacceptable to some participants because it stimulated gagging. Participants were also unable to close their lips around it, so a noninvasive facemask by Hans Rudolph, Inc. (HRI; 2007; Figure 4), which provided an adequate seal, was used instead. The facemask design produced measures that were different from the software-predicted values, but it was consistently applied to all participants, who served as their own controls, and it was not used for clinical testing. To reduce shunt impedance of the cheeks, patients are required to hold their hands against their cheeks (Viasys Jaeger, 2009); however, the study participants were unable to do this, so the HRI facemasks passively applied this pressure. A seal was carefully secured before measurement occurred. If the seal is broken, the red pressure tracing and green overlay of tidal breathing are not visible in the lower half of the screen display. When this occurred, the seal was restored and a clear tracing visualized; 30 seconds of clear data (displayed onscreen) were kept.

Modified Ashworth Scale

Presence of spasticity was measured with the Modified Ashworth Scale (MAS; Haley & Inacio, 1990), a single scale with six possible choices (i.e., 0, 1, 1+, 2, 3, 4) for grading the extent of muscle tone. Scores for tone in the hip and shoulder joints were averaged to obtain an overall score for each participant. Gregson and colleagues (1999) found kappa = 0.84 for interrater and 0.83 for intrarater comparisons. The investigator’s scoring was certified by an occupational therapist skilled in its use (Shaw, 2006).

Barks Figure 3Process Log

Descriptive data were captured in a narrative log after each child’s session, including date, subject ID, age, weight, spasticity (MAS), facemask response, strengths or difficulties/solutions, and miscellaneous observations.

Data Collection Procedures

During a single session in a therapy room in the wheelchair seating department of a children’s hospital, participants experienced five seating parameters conducted in a Prairie wheelchair simulator (four experimental wheelchair components and one condition with all four components present, plus one control condition with none). Each condition was introduced independently, according to the Waugh protocol (Waugh, 2005). All other seating components were held constant. Order of introduction of experimental components—left and right upper extremity supports (armrests); left and right lateral trunk supports; level, de-rotated pelvis secured with seatbelt; seat tilt 30 degrees from vertical, and all four parameters together—was randomized by drawing combinations from a hat. The simulator was decorated with a large spangled hat and ladybug, flower, and bird hand puppets to appear child-friendly (Figure 1). Seating conditions served as predictors of change in the dependent variable, pulmonary function, measured in four components, total airway resistance, tidal volume, minute ventilation, and deadspace to tidal volume ratio.

In the “unsupported” condition, the child received no extrinsic trunk support except from the seating surface and leg support, in addition to the guardian holding the child’s thighs on the seat surface to prevent falling. Observational monitoring for discomfort and capillary/pulse oximetry desaturation (92% or less) occurred throughout. The facemask seal was validated by the IOS tracing display observed by the investigator. Angles of seating conditions (seat-to-back angle, tilt) were measured by goniometer or simulator gauge, as trained by Waugh; participant ankle, knee, and hip flexion/extension range of ¨motion were ascertained at the start of the session, and joint angles were held constant across all conditions, for all participants (90 degrees ankle and knee flexion and 100 degrees hip flexion). Backrest height, headrest height, and seat depth and width were measured by tape measure in inches and matched to body dimensions. The hips were positioned against the backrest at a slight anterior pelvic tilt to ensure a secured, level pelvis. Participants whose condition did not permit measurement were excused. No desaturation occurred with any of the participants. To allay anxiety that could influence breathing and compliance, the Disney channel played within view of participants.

Barks Figure 4The IOS pneumotach and elbow piece are designed to be presented in the frontal plane, with the participant sitting upright. In 30-degrees tilt, the facemask of some of the participants lost its seal at the nasal bridge. In these cases, the guardian lightly held the mask down with one finger over the bony prominence of the nasal bridge. The IOS tracing was immediately restored, and additional pressure was not placed on the cheeks or the airway, so no increase in airway resistance was expected.

Spasticity (by MAS), medications, and other patient characteristics, all potential influencers of wheelchair posture, were recorded in a process log that also captured participant recruitment and retention challenges and response to protocol.

Analysis

The process log data were coded and summarized according to emerging themes. These themes were categorized as challenges associated with participant recruitment and retention, or response to the protocol.

Results

Participants unable to complete the protocol were excused. As seen in Tables 1 and 2, excused participants were similar in gender, age, and ethnicity, although fewer Hispanic participants were excused. Notably, excused participants differed from retained participants (n = 8) on medications, spasticity, and verbal ability, with six participants receiving medication on a regular basis; five participants having high levels of spasticity; and seven participants being nonverbal, one being verbal. Body weight did not appear related to airway resistance in the sample; only one participant was overweight for height and age. In retained participants, total airway resistance (RAW) varied with wheelchair seating parameters, but sample size did not allow detection of significant differences by parameter.

Barks Table 2Challenges Associated with Participant Recruitment and Retention

Twenty guardians received study information; two guardians declined to participate. Two participants did not meet study criteria; 16 enrolled; 8 were retained. Recruitment was 90%. Postural instability was an emerging theme in retention; when the first two participants became agitated when their posture was destabilized by removing support at the start of the protocol, they were excused. Therefore, the “unsupported” condition was moved to the end of the sequence. This eliminated the opportunity to randomize order of presentation of totally supported and unsupported conditions. The second theme was verbal ability; participants with greater verbal ability tolerated the protocol more often than others and were retained. Third, four participants demonstrated primitive reflex activity: startle, persistent gagging, repeated sneezing, and persistent tongue thrusting. This reflex activity disrupted the protocol for half (n = 2) of these participants; they were ultimately excused from the study. Clinic recruitment emerged as the fourth theme; participants were not available until the end of clinic, which averaged 3.5 hours. It is not known whether length of time in clinic also influenced staff members’ decision to approach potential participants or whether decrease of one staff surgeon decreased the number of potential participants seen in clinic. In addition, fewer outpatients’ disabilities were as severe as staff had projected, so the number of recruited participants was markedly fewer than anticipated. The fifth challenge to participant recruitment and retention found by reviewing the process log was airway obstruction, which occurred for only one participant. This participant experienced repeated gagging, which interfered with IOS measurement. He may have retracted his tongue and involuntarily and briefly obstructed his upper airway. He was excused from the protocol. Finally, intolerance of instruments was an emerging theme among those participants who were excused. Of the 16 participants who began the study, four did not tolerate the facemask; two did not tolerate the seating simulator, and two did not accept the IOS. These eight were excused.

Response of Children with CP to the Protocol

Emerging themes were essentially the same for response to protocol as challenges associated with participant recruitment and retention. The chief barrier to retention was intolerance of the protocol.

Verbal Ability and Motor Control. Verbal ability emerged as a theme from sampling (Table 2). Although cognitive testing data were unavailable, 75% (6) participants who completed the study were verbal communicators. Two participants were nonverbal but completed the procedure; one nonverbal child’s guardian showed remarkable rapport and ability to communicate with her. Nearly the opposite was true for excused participants. Of the excused participants, 88% (8) were nonverbal. Only 12.5% (2) of the excused participants had some receptive language and ability to cooperate with the procedure but very little motor control to allow stable positioning or pulmonary measurement. Verbal ability did not necessarily correspond to age; 2 younger participants were quite verbal and enthusiastic, and two 10-year-old children had very limited communication skills.

Seating Simulator and Facemask Acceptability. Seventy-five percent enrolled tolerated the facemask, and 87% tolerated the seating simulator. Nonacceptance, along with miscellaneous other factors related to disability, accounted for the high attrition. In all, study methods were usable in 50% of our sample. Due to small sample size of our study population, significance of differences in effects of the various wheelchair parameters on total airway resistance cannot be determined. Implications for nursing practice, therefore, would be premature. That being said, slumping in a seated posture is known to compromise breathing, so seated posture should be aligned to prevent this. In order for the study to detect statistically significant differences, we would have needed 2.5 years to recruit participants, recruiting in all three clinics 3 days per week, to obtain 64 participants.

Discussion

This study adds to earlier research and is the first clinical study to use novel methods to passively measure pulmonary function (i.e., total airway resistance) in people in wheelchairs. These patients have the greatest risk of pulmonary compromise as an outcome of wheelchair characteristics and require positioning by nurses. Although this study lacked sufficient statistical power to draw conclusions for clinical practice in wheelchair positioning, it does report methods that rehabilitation investigators can replicate with a larger sample. Although an attempt was made to design the protocol for the population with CP, some characteristics interfered with retention and reliable measurement (e.g., reflex activity, low verbal ability, associated lack of cooperation with the protocol, postural instability when presented with the unsupported position, fatigue). Excused participants accounted for 50% of attrition, contributing, in part, to the small sample size. The characteristics that resulted in attrition are the very characteristics that make postural intervention so essential for this group. In future work, data could be collected either by appointment or at the beginning of clinic rather than at the end to minimize fatigue. Other study limitations included a lack of information about participants’ types of CP, cognitive function, and Gross Motor Function Classification System levels, although one admission criterion was the demonstrated inability to sit unsupported.

Participants with less disability handled the challenge of the protocol more easily, but the intent was to study a population with multiple disabilities who could benefit most from future intervention. It may be possible to conduct a similar study with participants lacking full trunk control, but having greater verbal ability; however, this would contribute to even more stringent inclusion criteria and probably lower enrollment.

Conclusion

The Jaeger IOS performed quite well in measuring airway resistance without the voluntary control of participants. The greatest challenge was to obtain airway resistance measurement using a facemask rather than the recommended mouthpiece. For participants who were able to tolerate it, the facemask was quite useful, providing valid measurements. Future research should compare facemask to mouthpiece airway resistance values in children without disabilities.

Differences in RAW were found for the six wheelchair seating conditions; however, due to the small sample size, statistical test power was insufficient to determine whether differences were significant. The challenges associated with participant recruitment and retention were verbal ability of the participants; the data collection protocol, particularly the seating simulator, IOS, and facemasks used for nonverbal children and those with primitive reflex activity; and presentation of the unsupported position first, the small number of eligible participants, and the logistics of travel and time in clinic. Approximately half of the school-aged children with CP lacking trunk control who participated in our study had successful measurement of total airway resistance with HRI facemasks and headsets in conjunction with the Viasys Jaeger IOS and Respironics NICO. Although the IOS is marketed as a device that can be used for individuals who cannot comply with conventional pulmonary testing, the recommended mouthpiece was not usable with our sample. For this sample, optimal measurement intervals began immediately upon presentation of each seating parameter and ended when the pulmonary function measure was obtained. Seating simulator and facemask acceptability increased in the presence of greater verbal ability. Wearing an HRI facemask for 1 hour posed a small risk of skin breakdown at the nasal bridge. These methods may contribute to fatigue, although fatigue may have been related to scheduling of data collection at the end of clinic. Other methods of measuring wheelchair configuration parameters and pulmonary function need to be explored, including the establishment of RAW reference values using the Jaeger IOS in normally abled children for HRI facemasks.

In the future, practicing nurses should partner with researchers to expand recruitment for research in this area, assist in securing adequate samples, and produce evidence for practice. This will be necessary if people with multiple disabilities are to be studied by rehabilitation nurse investigators using new technology.

Acknowledgments

This study was funded by a Rehabilitation Nurses Foundation (RNF) New Investigator Award. Thanks to RNF, the study participants, the first author’s dissertation committee at the University of South Florida (Audrey Nelson, PhD RN FAAN, Chair; William Lee, PhD; Jason Beckstead, PhD; and Mary Evans, PhD RN FAAN), Shriners Hospitals for Children-Tampa; Shriners Medical Director Dennis Grogan, MD; and the pediatric neurology outpatient clinics at the University of Florida in Gainesville, FL.

About the Authors

Lee Barks, PhD ARNP, is a nurse investigator at the Tampa, FL, VA HSR&D/RR&D Center of Excellence. Address correspondence to Lelia.Barks@va.gov.

 

Peggy Shaw, BSOT OTR/L, is an occupational therapist with extensive experience in wheelchair assessment and fitting and oral motor therapy with individuals with severe physicial disabilities.

References

Barks, L. (2004). Therapeutic positioning, wheelchair seating, and pulmonary function of children with cerebral palsy: A research synthesis. Rehabilitation Nursing, 29(5), 146–153.

Barks, L. (2007). Wheelchair positioning and pulmonary function in children with cerebral palsy. Doctoral dissertation, University of South Florida, Tampa, FL. Retrieved December 9, 2009, from http://purl.fcla.edu/usf/dc/et/SFE0002107.

Braddock, D. L. (2002). Public financial support for disability at the dawn of the 21st century. American Journal of Mental Retardation, 107(6), 478–489.

Canet, E., Praud, J., & Bureau, M. (1998). Chest wall diseases and dysfunction in children. In T. Boat and V. Chernick (Eds.), Kendig’s disorders of the respiratory tract in children (pp. 794–799). Philadelphia, PA: Saunders.

Gavin-Dreschnack, D., & Barks, L. (2008). Positioning; Positioning: Wheelchair. In B. Ackley, G. Ladwig, B. Swan, & S. Tucker (Eds.), Evidence-based nursing care guidelines: Medical-surgical interventions (pp. 622–630). St. Louis, MO: Mosby-Elsevier.

Farley, R. C., Davidson, J. C., Evans, G., Maclennan, K., Michael, S., Morrow, M., et al. (2003). What is the evidence for the effectiveness of postural management? International Journal of Therapy and Rehabilitation, 10(10), 449–455.

Gregson, J. M., Leathley, M., Moore, A. P., Sharma, A. K., Smith, T. L., & Watkins, C. L. (1999). Reliability of the Tone Assessment Scale and the modified Ashworth scale as clinical tools for assessing poststroke spasticity. Archives of Physical Medicine and Rehabilitation, 80(9), 1013–1016.

Haley, S., & Inacio, C. (1990). Evaluation of spasticity and its effect on motor function. In M. Glenn & J. Whyte (Eds.), The practical management of spasticity in children and adults (pp. 70–96). Philadelphia, PA: Lea & Febiger.

Hans Rudolph, Inc. (2007). Oro-Nasal NIV Face Masks and Headgear. [Product manual]. Kansas City, MO: Author.

Horan, T., Mateus, S., Beraldo, P., Araujo, L., Urschel, J., Urmenyi, E., et al. (2001). Forced oscillation technique to evaluate tracheostenosis in patients with neurologic injury. Chest, 120(1), 69–73.

Leopando, M. T., Moussavi, Z., Holbrow, J., Chernick, V., Pasterkamp, H., & Rempel, G. (1999). Effect of a Soft Boston Orthosis on pulmonary mechanics in severe cerebral palsy. Pediatric Pulmonology, 28(1), 53–58.

Lin, F., Parthasarathy, S., Taylor, S. J., Pucci, D., Hendrix, R. W., & Makhsous, M. (2006). Effect of different sitting postures on lung capacity, expiratory flow, and lumbar lordosis. Archives of Physical Medicine and Rehabilitation, 87, 504–509.

Logemann, J. A., Kahrilas, P. J., Kobara, M., & Vakil, N. (1989). The benefit of head rotation on pharyngoesophageal dysphagia. Archives of Physical Medicine and Rehabilitation, 70, 767–771.

McFarland, D. H., Lund, J. P., & Gagner, M. (1994). Effects of posture on the coordination of respiration and swallowing. Journal of Neurophysiology, 72(5), 2431–2437.

Nwaobi, O. M., & Smith, P. D. (1986). Effect of adaptive seating on pulmonary function of children with cerebral palsy. Developmental Medicine and Child Neurology, 28(3), 351–354.

Philips Respironics. (2009). Products: Non-Invasive Cardiac Output Monitor. Retrieved April 18, 2011, from http://nico.respironics.com.

Prairie Seating Corporation. (2007). Simulators. Retrieved April 29, 2011, from www.prairieseating.com/PSsimulators.htm.

Shaw, P. (2006, February). Wheelchair seating and Modified Ashworth Scale. Training presented at Milestones Therapy Center, St. Petersburg, FL.

Viasys Jaeger MasterScreen IOS. (2009). Products and Services: MasterScreen IOS. Retrieved April 18, 2011, from www.viasyshealthcare.com/prod_serv/prodDetail.aspx?config=ps_prodDtl&prodID=14.

Waugh, K. (2005, April). Wheelchair seating for postural control and function. Training presented at Shriners Hospital for Children, Tampa, FL. [This training is often presented at the Rehabilitation Engineering and Assistive Technology Society of North America (RESNA) annual meetings.]

Yeaw, E. M. (1996). The effect of body positioning upon maximal oxygenation of patients with unilateral lung pathology. Journal of Advanced Nursing, 23(1), 55–61.

U.S. Census Bureau. (2000). U.S. Census Bureau state and county quick facts. Retrieved September 15, 2002, from http://quickfacts.census.gov/qfd/states/12000.html.