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1.  Early Life Growth Trajectories in Cystic Fibrosis are Associated with Pulmonary Function at Age 6 Years 
The Journal of pediatrics  2015;167(5):1081-8.e1.
To determine whether severity of lung disease at age 6 years is associated with changes in nutritional status before age 6 within individual children with cystic fibrosis (CF).
Study Design
Children with CF born between 1994 and 2005 and followed in the CF Foundation Patient Registry from age ≤2 through 7 years were assessed according to changes in annualized weight-for-length (WFL) percentiles between ages 0 and 2 and body mass index (BMI) percentiles between ages 2 and 6. The association between growth trajectories before age 6 and forced expiratory volume in one second (FEV1) % predicted at age 6-7 years was evaluated using multivariable linear regression.
A total of 6,805 subjects met inclusion criteria. Children with annualized WFL-BMI always >50th percentile [N=1,323 (19%)] had the highest adjusted mean [95% Confidence Interval (CI)] FEV1 at 6-7 years [101.8 (100.1, 103.5)]. FEV1 at 6-7 years for children whose WFL-BMI increased >10 percentile points by age 6 years was 98.3 (96.6, 100.0). This was statistically significantly higher than FEV1 for children whose WFL-BMI was stable [94.4 (92.6, 96.2)] or decreased >10 percentile points [92.9 (91.1, 94.8)]. Among children whose WFL-BMI increased >10 percentile points, achieving and maintaining WFL-BMI >50th percentile at younger ages was associated with significantly higher FEV1 at 6-7 years.
Within-patient changes in nutritional status in the first 6 years of life are significantly associated with FEV1 at age 6-7 years, suggesting that interventions that improve nutrition in early life may lead to improvements in later lung function.
PMCID: PMC5017309  PMID: 26340874
CF; FEV1; Forced expiratory volume in 1 second; Weight; BMI; Newborn screening
2.  Treatment satisfaction in cystic fibrosis: early patient experience with tobramycin inhalation powder 
Patient preference and adherence  2016;10:2163-2169.
This study assessed treatment satisfaction of cystic fibrosis (CF) patients in a routine clinical setting for tobramycin inhalation powder (TIP), the first dry powder–inhaled antibiotic for Pseudomonas aeruginosa infection.
CF patients aged 6 years or older treated with at least one cycle of TIP completed a web survey on experience with TIP, including the Treatment Satisfaction Questionnaire for Medication (TSQM). Regression analysis determined the factors associated with TSQM global satisfaction.
Eighty patients (mean age ± standard deviation: 24.4±9.4 years; 57.5% female; mean forced expiratory volume in 1 second ± standard deviation: 67.1%±27.3% predicted) completed the survey. The majority expressed satisfaction with TIP’s administration time (100%), time to clean (97.1%), portability (97.1%), and ease of use (94.3%). Effectiveness was significantly associated with TSQM global satisfaction (regression R-squared: 0.54).
Patient preferences for TIP were based on administration time and ease of use. Global satisfaction was related to greater patient-perceived effectiveness.
PMCID: PMC5087789  PMID: 27822017
cystic fibrosis; patient satisfaction; tobramycin; dry powder inhalers
3.  Strategies to optimize treatment adherence in adolescent patients with cystic fibrosis 
While development of new treatments for cystic fibrosis (CF) has led to a significant improvement in survival age, routine daily treatment for CF is complex, burdensome, and time intensive. Adolescence is a period of decline in pulmonary function in CF, and is also a time when adherence to prescribed treatment plans for CF tends to decrease. Challenges to adherence in adolescents with CF include decreased parental involvement, time management and significant treatment burden, and adolescent perceptions of the necessity and value of the treatments prescribed. Studies of interventions to improve adherence are limited and focus on education, without significant evidence of success. Smaller studies on behavioral techniques do not focus on adolescents. Other challenges for improving adherence in adolescents with CF include infection control practices limiting in-person interactions. This review focuses on the existing evidence base on adherence intervention in adolescents with CF. Future directions for efforts to optimize treatment adherence in adolescents with CF include reducing treatment burden, developing patient-driven technology to improve tracking, communication, and online support, and rethinking the CF health services model to include assessment of individualized adherence barriers.
PMCID: PMC5085292  PMID: 27799838
compliance; adolescence; medication; self management; intervention
4.  Tackling the Increasing Complexity of CF Care 
Pediatric pulmonology  2015;50(0 40):S74-S79.
PMCID: PMC4562023  PMID: 26335957
Treatment burden; treatment complexity; adherence; comparative effectiveness research; implementation research
5.  Development and Validation of the Adolescent Assessment of Preparation for Transition (ADAPT): A Novel Patient Experience Measure 
Significant gaps exist in health care transition (HCT) preparation that can impact care and outcomes in young adults with chronic illness. No quality measure exists to directly assess adolescent experiences of HCT preparation. Our objective was to develop an adolescent-reported measure of the quality of HCT preparation received from pediatric health care providers.
The ADolescent Assessment of Preparation for Transition (ADAPT) is a 26-item mailed survey designed for completion by 16- and 17-year-old adolescents with a chronic health condition. Adolescents from 3 samples (2 large Medicaid insurance plans [n=3000 each] and 1 large tertiary care pediatric hospital [n=623]) were mailed the survey. An iterative developmental process included focus groups and cognitive interviews, and validity was assessed using confirmatory factor analysis and ordinal reliability coefficients.
Reliability and validity was evaluated for three pre-specified composite measures: (1) Counseling on Transition Self-Management; (2) Counseling on Prescription Medication; (3) Transfer Planning. Across the 3 samples, all but one measure had good internal consistency (ordinal reliability coefficient ≥ 0.7). Confirmatory factor analysis using tetrachoric correlation coefficients was stable across samples and supported the construct validity of the first 2 composite measures.
ADAPT is a reliable, validated instrument measuring the quality of HCT preparation experiences reported by adolescents with chronic disease. ADAPT will enable clinical programs and health care delivery systems to assess the quality of HCT preparation and provide targets for improvement in adolescent counseling related to transition.
PMCID: PMC4548278  PMID: 26299555
6.  Adding Stiffness to the Foot Modulates Soleus Force-Velocity Behaviour during Human Walking 
Scientific Reports  2016;6:29870.
Previous studies of human locomotion indicate that foot and ankle structures can interact in complex ways. The structure of the foot defines the input and output lever arms that influences the force-generating capacity of the ankle plantar flexors during push-off. At the same time, deformation of the foot may dissipate some of the mechanical energy generated by the plantar flexors during push-off. We investigated this foot-ankle interplay during walking by adding stiffness to the foot through shoes and insoles, and characterized the resulting changes in in vivo soleus muscle-tendon mechanics using ultrasonography. Added stiffness decreased energy dissipation at the foot (p < 0.001) and increased the gear ratio (i.e., ratio of ground reaction force and plantar flexor muscle lever arms) (p < 0.001). Added foot stiffness also altered soleus muscle behaviour, leading to greater peak force (p < 0.001) and reduced fascicle shortening speed (p < 0.001). Despite this shift in force-velocity behaviour, the whole-body metabolic cost during walking increased with added foot stiffness (p < 0.001). This increased metabolic cost is likely due to the added force demand on the plantar flexors, as walking on a more rigid foot/shoe surface compromises the plantar flexors’ mechanical advantage.
PMCID: PMC4945910  PMID: 27417976
7.  Predictors of Timing of Transfer From Pediatric-to Adult-Focused Primary Care 
JAMA pediatrics  2015;169(6):e150951.
A timely, well-coordinated transfer from pediatric- to adult-focused primary care is an important component of high-quality health care, especially for youths with chronic health conditions. Current recommendations suggest that primary-care transfers for youths occur between 18 and 21 years of age. However, the current epidemiology of transfer timing is unknown.
To examine the timing of transfer to adult-focused primary care providers (PCPs), the time between last pediatric-focused and first adult-focused PCP visits, and the predictors of transfer timing.
Retrospective cohort study of patients insured by Harvard Pilgrim Health Care (HPHC), a large not-for-profit health plan. Our sample included 60 233 adolescents who were continuously enrolled in HPHC from 16 to at least 18 years of age between January 2000 and December 2012. Pediatric-focused PCPs were identified by the following provider specialty types, but no others: pediatrics, adolescent medicine, or pediatric nurse practitioner. Adult-focused PCPs were identified by having any provider type that sees adult patients. Providers with any specialty provider designation (eg, gastroenterology or gynecology) were not considered PCPs.
We used multivariable Cox proportional hazards regression to model age at first adult-focused PCP visit and time from the last pediatric-focused to the first adult-focused PCP visit (gap) for any type of office visit and for those that were preventive visits.
Younger age at transfer was observed for female youths (hazard ratio [HR], 1.32 [95% CI, 1.29–1.36]) who had complex (HR, 1.06 [95% CI, 1.01–1.11]) or noncomplex (HR, 1.08 [95% CI, 1.05–1.12]) chronic conditions compared with those who had no chronic conditions. Transfer occurred at older ages for youths who lived in lower-income neighborhoods compared with those who lived in higher-income neighborhoods (HR, 0.89 [95% CI, 0.83–0.95]). The gap between last pediatric-focused to first adult-focused PCP visit was shorter for female youths than male youths (HR, 1.57 [95% CI, 1.53–1.61]) and youths with complex (HR, 1.35 [95% CI, 1.28–1.41]) or noncomplex (HR, 1.24 [95% CI, 1.20–1.28]) chronic conditions. The gap was longer for youths living in lower-income neighborhoods than for those living in higher-income neighborhoods (HR, 0.80 [95% CI, 0.75–0.85]). Multivariable models showed an adjusted median age at transfer of 21.8 years for office visits and 23.1 years for preventive visits and an adjusted median gap length of 20.5 months for office visits and 41.6 months for preventive visits.
Most youths are transferring care later than recommended and with gaps of more than a year. While youths with chronic conditions have shorter gaps, they may need even shorter transfer intervals to ensure continuous access to care. More work is needed to determine whether youths are experiencing clinically important lapses in care or other negative health effects due to the delayed timing of transfer.
PMCID: PMC4862601  PMID: 26030515
8.  Reducing the energy cost of human walking using an unpowered exoskeleton 
Nature  2015;522(7555):212-215.
PMCID: PMC4481882  PMID: 25830889
9.  Ready, Set, Stop: Mismatch Between Self-Care Beliefs, Transition Readiness Skills, and Transition Planning Among Adolescents, Young Adults, and Parents 
Clinical pediatrics  2014;53(11):1062-1068.
Health care transition (HCT) from pediatric to adult-focused systems is a key milestone for youth. Developing self-care skills and HCT planning are key elements. In a survey at 4 pediatric specialty clinics to 79 youth aged 16 to 25 years and 52 parents, skill-based HCT readiness was assessed using the Transition Readiness Assessment Questionnaire (TRAQ). Multivariable logistic regression evaluated the association between TRAQ scores and self-care beliefs. In all, 70% of youth and 67% of parents believed that they/their child could manage their care. Only 38% of youth and 53% of parents reported thinking about HCT; only 18% of youth and 27% of parents reported having a HCT plan. Youth with higher TRAQ scores were more likely to believe they could manage their care, controlling for age and gender (adjusted odds ratio = 4.0, 95% confidence interval = 1.7–9.5). Transition readiness skills are associated with self-care beliefs. However, a mismatch exists between high reported self-care beliefs and low levels of transition planning.
PMCID: PMC4443439  PMID: 25006112
health care transition; adolescent
10.  Revisiting the mechanics and energetics of walking in individuals with chronic hemiparesis following stroke: from individual limbs to lower limb joints 
Previous reports of the mechanics and energetics of post-stroke hemiparetic walking have either not combined estimates of mechanical and metabolic energy or computed external mechanical work based on the limited combined limbs method. Here we present a comparison of the mechanics and energetics of hemiparetic and unimpaired walking at a matched speed.
Mechanical work done on the body centre of mass (COM) was computed by the individual limbs method and work done at individual leg joints was computed with an inverse dynamics analysis. Both estimates were converted to average powers and related to simultaneous estimates of net metabolic power, determined via indirect calorimetry. Efficiency of positive work was calculated as the ratio of average positive mechanical power \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\overline{P}}^{+} $$\end{document}P¯+ to net metabolic power.
Total \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\overline{P}}^{+} $$\end{document}P¯+ was 20% greater for the hemiparetic group (H) than for the unimpaired control group (C) (0.49 vs. 0.41 W · kg−1). The greater \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\overline{P}}^{+} $$\end{document}P¯+ was partly attributed to the paretic limb of hemiparetic walkers not providing appropriately timed push-off \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\overline{P}}^{+} $$\end{document}P¯+ in the step-to-step transition. This led to compensatory non-paretic limb hip and knee \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\overline{P}}^{+} $$\end{document}P¯+ which resulted in greater total mechanical work. Efficiency of positive work was not different between H and C.
Increased work, not decreased efficiency, explains the greater metabolic cost of hemiparetic walking post-stroke. Our results highlighted the need to target improving paretic ankle push-off via therapy or assistive technology in order to reduce the metabolic cost of hemiparetic walking.
PMCID: PMC4357211  PMID: 25889030
Locomotion; Individual limbs method; Mechanical power; Metabolic power; Joint power; Inverse dynamics; Stroke
11.  A neuromechanics-based powered ankle exoskeleton to assist walking post-stroke: a feasibility study 
In persons post-stroke, diminished ankle joint function can contribute to inadequate gait propulsion. To target paretic ankle impairments, we developed a neuromechanics-based powered ankle exoskeleton. Specifically, this exoskeleton supplies plantarflexion assistance that is proportional to the user’s paretic soleus electromyography (EMG) amplitude only during a phase of gait when the stance limb is subjected to an anteriorly directed ground reaction force (GRF). The purpose of this feasibility study was to examine the short-term effects of the powered ankle exoskeleton on the mechanics and energetics of gait.
Five subjects with stroke walked with a powered ankle exoskeleton on the paretic limb for three 5 minute sessions. We analyzed the peak paretic ankle plantarflexion moment, paretic ankle positive work, symmetry of GRF propulsion impulse, and net metabolic power.
The exoskeleton increased the paretic plantarflexion moment by 16% during the powered walking trials relative to unassisted walking condition (p < .05). Despite this enhanced paretic ankle moment, there was no significant increase in paretic ankle positive work, or changes in any other mechanical variables with the powered assistance. The exoskeleton assistance appeared to reduce the net metabolic power gradually with each 5 minute repetition, though no statistical significance was found. In three of the subjects, the paretic soleus activation during the propulsion phase of stance was reduced during the powered assistance compared to unassisted walking (35% reduction in the integrated EMG amplitude during the third powered session).
This feasibility study demonstrated that the exoskeleton can enhance paretic ankle moment. Future studies with greater sample size and prolonged sessions are warranted to evaluate the effects of the powered ankle exoskeleton on overall gait outcomes in persons post-stroke.
Electronic supplementary material
The online version of this article (doi:10.1186/s12984-015-0015-7) contains supplementary material, which is available to authorized users.
PMCID: PMC4367918  PMID: 25889283
Stroke; Exoskeleton; Gait; Rehabilitation; Ankle
12.  Asthma Care Quality for Children with Minority-Serving Providers 
To compare asthma care quality for children with and without minority-serving providers.
Cross-sectional telephone survey of parents, linked with a mailed survey of their children’s providers.
A Medicaid-predominant health plan and multispecialty provider group in Massachusetts.
Children with persistent asthma identified from claims and encounter data.
Main Exposure
Whether the child’s provider was minority-serving (>25% of patients black or Latino).
Parent report of whether the child had: 1) ever received inhaled steroids; 2) received influenza vaccination during the past season and 3) received an asthma action plan in the past year.
The study included 563 children. In unadjusted analyses, Latino children and those with minority-serving providers were more likely to have never received inhaled steroids. In adjusted models, the odds of never receiving inhaled steroids were not significantly different for children with minority-serving providers (OR 1.29, 95% CI 0.63–2.64), or for Latino vs. white children (OR 1.76, 95% CI 0.74–4.18); odds were increased for children receiving care in community health centers (OR 4.88, 95% CI 1.70–14.02) or hospital clinics (OR 4.53, 95% CI 1.09–18.92) vs. multi-specialty practices. Such differences were not seen for influenza vaccinations or action plans.
Children with persistent asthma were less likely to receive inhaled steroids if they received care in community health centers or hospital clinics. Practice setting mediated initially-observed disparities in inhaled steroid use by Latino children and those with minority-serving providers. No differences by race/ethnicity or minority-serving provider were observed for influenza vaccinations and asthma action plans.
PMCID: PMC4319182  PMID: 20048240
13.  Motivating Adherence Among Adolescents With Cystic Fibrosis: Youth and Parent Perspectives 
Pediatric pulmonology  2014;50(2):127-136.
As advances in the care of individuals with cystic fibrosis (CF) have resulted in improved survival, therapeutic regimens for treatment of CF have become increasingly complex. This high treatment burden poses challenges to chronic disease self-management, particularly amongst adolescents. The aim of this qualitative study was to understand the barriers and facilitators of adherence to chronic CF therapies as perceived by adolescents with CF and their parents. In a series of structured interviews with 18 youth and their parents, we explored issues related to daily routines, youth and parental roles regarding chronic therapy, and motivators for adherence. All interviews were audio-recorded and coded for themes and patterns. Reported barriers to adherence included time pressures, competing priorities, heightened awareness of disease trajectory, privacy concerns, and lack of perceived consequences from non-adherence. Identified facilitators for adherence included recognizing the importance of therapies, developing strong relationships with care teams, establishing structured routines, and focusing on shifting responsibilities from a parent to their adolescent child. The themes uncovered by these interviews identify areas for intervention and support by clinical programs seeking to improve adherence and self-management strategies for adolescents with CF Pediatr Pulmonol.
PMCID: PMC4160425  PMID: 24616259
cystic fibrosis; adolescents; adherence
14.  Treatment Complexity in Cystic Fibrosis: Trends over Time and Associations with Site-Specific Outcomes 
Patients with cystic fibrosis (CF) have increasing treatment complexity and high treatment burden. We describe trends in treatment complexity and evaluate its relationship with health outcomes.
Using Epidemiologic Study of Cystic Fibrosis (ESCF) data, we developed a treatment complexity score (TCS) from 37 chronic therapies and assessed change by age group (6–13, 14–17, and 18+ years) over a three year period. Differences in average site TCS were evaluated by quartiles based on FEV1, BMI, or Treatment Burden score on the Cystic Fibrosis Questionnaire-Revised (CFQ-R).
TCS scores were calculated for 7252 individual patients (42% child, 16% adolescent, 43% adult) across 153 sites. In 2003, mean TCS was 11.1 for children, 11.8 for adolescents, and 12.1 for adults. In all 3 age groups, TCS increased over 3 years; the increase in TCS from 2003–2005 for children was 1.25 (95% CI 1.16–1.34), for adolescents 0.77 (0.62–0.93), and for adults 1.20 (1.08–1.31) (all p<0.001 for trend over time). At the site level, there were no significant differences in mean TCS based on FEV1 quartile. Mean TCS was higher in the highest BMI z-score quartile. Across all 3 versions of the CFQ-R, mean TCS was lower at sites in the highest quartiles (lowest burden) for CFQ-R Treatment Burden scores.
Treatment complexity was highest among adults with CF, although over 3 years, we observed a significant increase in treatment complexity in all age groups. Such increases in treatment complexity pose a challenge to patient self-management and adherence. Future research is needed to understand the associations between treatment complexity and subsequent health outcomes to reduce treatment burden and improve disease management.
PMCID: PMC4073628  PMID: 23352205
15.  Transition Care: Future Directions in Education, Health Policy, and Outcomes Research 
Academic pediatrics  2014;14(2):120-127.
All youth must transition from pediatric to adult-centered medical care. This process is especially difficult for youth with special health care needs. Many youth do not receive the age-appropriate medical care they need and are at risk during this vulnerable time. Previous research has identified barriers that may prevent effective transition, and protocols have been developed to improve the process. Health outcomes related to successful transition have yet to be fully defined.
Health care transition can also be influenced by education of providers, but there are gaps in medical education at the undergraduate, graduate, and postgraduate levels. Current changes in federal health policy allow improved health care coverage, provide some new financial incentives, and test new structures for transitional care, including the evolution of accountable care organizations (ACO). Future work must test how these systems changes will affect quality of care. Finally, transition protocols exist in various medical subspecialties; however, national survey results show no improvement in transition readiness, and there are no consistent measures of what constitutes transition success.
In order to advance the field of transition, research must be done to integrate transition curricula at the undergraduate, graduate, and postgraduate levels; to provide advance financial incentives and pilot the ACO model in centers providing care to youth during transition; to define outcome measures of importance to transition; and to study the effectiveness of current transition tools on improving these outcomes.
PMCID: PMC4098714  PMID: 24602574
health care financing; health policy; medical education; outcomes research; transition; youth with special health care needs
16.  Estimation of Quasi-Stiffness of the Human Hip in the Stance Phase of Walking 
PLoS ONE  2013;8(12):e81841.
This work presents a framework for selection of subject-specific quasi-stiffness of hip orthoses and exoskeletons, and other devices that are intended to emulate the biological performance of this joint during walking. The hip joint exhibits linear moment-angular excursion behavior in both the extension and flexion stages of the resilient loading-unloading phase that consists of terminal stance and initial swing phases. Here, we establish statistical models that can closely estimate the slope of linear fits to the moment-angle graph of the hip in this phase, termed as the quasi-stiffness of the hip. Employing an inverse dynamics analysis, we identify a series of parameters that can capture the nearly linear hip quasi-stiffnesses in the resilient loading phase. We then employ regression analysis on experimental moment-angle data of 216 gait trials across 26 human adults walking over a wide range of gait speeds (0.75–2.63 m/s) to obtain a set of general-form statistical models that estimate the hip quasi-stiffnesses using body weight and height, gait speed, and hip excursion. We show that the general-form models can closely estimate the hip quasi-stiffness in the extension (R2 = 92%) and flexion portions (R2 = 89%) of the resilient loading phase of the gait. We further simplify the general-form models and present a set of stature-based models that can estimate the hip quasi-stiffness for the preferred gait speed using only body weight and height with an average error of 27% for the extension stage and 37% for the flexion stage.
PMCID: PMC3857237  PMID: 24349136
17.  Estimation of Quasi-Stiffness of the Human Knee in the Stance Phase of Walking 
PLoS ONE  2013;8(3):e59993.
Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as prostheses and orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75–2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R2 > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking.
PMCID: PMC3606171  PMID: 23533662
18.  Estimation of Quasi-Stiffness and Propulsive Work of the Human Ankle in the Stance Phase of Walking 
PLoS ONE  2013;8(3):e59935.
Characterizing the quasi-stiffness and work of lower extremity joints is critical for evaluating human locomotion and designing assistive devices such as prostheses and orthoses intended to emulate the biological behavior of human legs. This work aims to establish statistical models that allow us to predict the ankle quasi-stiffness and net mechanical work for adults walking on level ground. During the stance phase of walking, the ankle joint propels the body through three distinctive phases of nearly constant stiffness known as the quasi-stiffness of each phase. Using a generic equation for the ankle moment obtained through an inverse dynamics analysis, we identify key independent parameters needed to predict ankle quasi-stiffness and propulsive work and also the functional form of each correlation. These parameters include gait speed, ankle excursion, and subject height and weight. Based on the identified form of the correlation and key variables, we applied linear regression on experimental walking data for 216 gait trials across 26 subjects (speeds from 0.75–2.63 m/s) to obtain statistical models of varying complexity. The most general forms of the statistical models include all the key parameters and have an R2 of 75% to 81% in the prediction of the ankle quasi-stiffnesses and propulsive work. The most specific models include only subject height and weight and could predict the ankle quasi-stiffnesses and work for optimal walking speed with average error of 13% to 30%. We discuss how these models provide a useful framework and foundation for designing subject- and gait-specific prosthetic and exoskeletal devices designed to emulate biological ankle function during level ground walking.
PMCID: PMC3605342  PMID: 23555839
19.  The mechanics and energetics of human walking and running: a joint level perspective 
Humans walk and run at a range of speeds. While steady locomotion at a given speed requires no net mechanical work, moving faster does demand both more positive and negative mechanical work per stride. Is this increased demand met by increasing power output at all lower limb joints or just some of them? Does running rely on different joints for power output than walking? How does this contribute to the metabolic cost of locomotion? This study examined the effects of walking and running speed on lower limb joint mechanics and metabolic cost of transport in humans. Kinematic and kinetic data for 10 participants were collected for a range of walking (0.75, 1.25, 1.75, 2.0 m s−1) and running (2.0, 2.25, 2.75, 3.25 m s−1) speeds. Net metabolic power was measured by indirect calorimetry. Within each gait, there was no difference in the proportion of power contributed by each joint (hip, knee, ankle) to total power across speeds. Changing from walking to running resulted in a significant (p = 0.02) shift in power production from the hip to the ankle which may explain the higher efficiency of running at speeds above 2.0 m s−1 and shed light on a potential mechanism behind the walk–run transition.
PMCID: PMC3223624  PMID: 21613286
locomotion; speed; mechanical power; efficiency; cost of transport
20.  Measuring the Transition Readiness of Youth with Special Healthcare Needs: Validation of the TRAQ—Transition Readiness Assessment Questionnaire 
Journal of Pediatric Psychology  2009;36(2):160-171.
Objective The aim of this study was to develop the Transition Readiness Assessment Questionnaire (TRAQ), a measure of readiness for transition from pediatric to adult healthcare for youth with special health care needs (YSHCN). Methods We administered TRAQ to 192 YSHCN aged 16–26 years in three primary diagnostic categories, conducted factor analysis, and assessed differences in TRAQ scores by age, gender, race, and primary diagnosis type. Results Factor analysis identified two TRAQ domains with high internal consistency: Skills for Self-Management and Skills for Self-Advocacy. Each domain had high internal consistency. In multivariate regression models, older age and a primary diagnosis of an activity limiting physical condition were associated with higher scores in Self-Management, and female gender and a primary diagnosis of an activity limiting physical condition were associated with higher scores in Self-Advocacy. Conclusions Our initial validation study suggests the TRAQ is a useful tool to assess transition readiness in YSHCN and to guide educational interventions by providers to support transition.
PMCID: PMC3415980  PMID: 20040605
adolescents; chronic illness; health care services
21.  Associations Between Illness Perceptions and Health-Related Quality of Life in Adults with Cystic Fibrosis 
Journal of psychosomatic research  2010;70(2):161-167.
To examine the relationship between illness perception, health status, and health-related quality of life (HRQOL) in a cohort of adults with cystic fibrosis (CF).
In the Project on Adult Care in Cystic Fibrosis (PAC-CF), we administered five subscales (Illness Consequences, Illness Coherence, Illness Timeline-Cyclical, Personal Control, Treatment Control) of the Illness Perception Questionnaire-Revised (IPQ-R). Multivariable linear regression analyses explored the associations between illness perception, health status, symptom burden, and physical and psychosocial HRQOL as measured by various domains of the CF Questionnaire-Revised (CFQ-R).
Among the 199 respondents (63% female, mean age 36.8±10.2 years), IPQ-R scores did not differ based on age, gender, or lung function. In multivariable regression models neither clinical characteristics nor physical or psychological symptom burden scores were associated with CFQ-R physical domains. In contrast, higher scores on Illness Consequences were associated with lower psychosocial CFQ-R scores. Higher scores on lllness Coherence and Personal Control scales were associated with higher psychosocial CFQ-R scores.
Adults with CF report a high understanding of their disease, feel that CF has significant consequences, and endorse both personal and treatment control over their outcomes. Illness perceptions did not vary with increased age or worsening disease severity, suggesting that illness perceptions may develop during adolescence. Illness perceptions were associated with psychosocial but not physical aspects of HRQOL. Efforts to modify illness perceptions as part of routine clinical care and counseling may lead to improved quality of life for adults with CF.
PMCID: PMC3052880  PMID: 21262419
Cystic fibrosis; quality of life; illness perceptions
22.  Tree Nut Allergy, Egg Allergy, and Asthma in Children 
Clinical pediatrics  2010;50(2):133-139.
Children with food allergies often have concurrent asthma.
The authors aimed to determine the prevalence of asthma in children with food allergies and the association of specific food allergies with asthma.
Parental questionnaire data regarding food allergy, corroborated by allergic sensitization were completed for a cohort of 799 children with food allergies. Multivariate regression analysis tested the association between food allergy and reported asthma.
In this cohort, the prevalence of asthma was 45.6%. After adjusting for each food allergy, environmental allergies, and family history of asthma, children with egg allergy (odds ratio [OR] = 2.0; 95% confidence interval [CI] = 1.3–3.2; P < .01) or tree nut allergy (OR = 2.0; 95% CI = 1.1–3.6; P = .02) had significantly greater odds of report of asthma.
There is a high prevalence of asthma in the food-allergic pediatric population. Egg and tree nut allergy are significantly associated with asthma, independent of other risk factors.
PMCID: PMC3070157  PMID: 21098525
asthma; food allergy; food hypersensitivity; nut allergy; nut hypersensitivity; egg allergy; egg hypersensitivity; pediatrics; allergy; asthma epidemiology
23.  Patterns of inhaled corticosteroid use and asthma control in the Childhood Asthma Management Program Continuation Study 
Daily controller medication use is recommended for children with persistent asthma to achieve asthma control.
To examine patterns of inhaled corticosteroid (ICS) use and asthma control in an observational study of children and adolescents with mild-to-moderate asthma (the Childhood Asthma Management Program Continuation Study).
We assessed patterns of ICS use during a 12-month period (consistent, intermittent, and none) and asthma control (well controlled vs poorly controlled). Multivariate logistic regression examined the association between pattern of ICS use and asthma control.
Of 914 patients enrolled, 425 were recommended to continue receiving ICS therapy in the Childhood Asthma Management Program Continuation Study. Of these patients, 46% reported consistent ICS use and 20% reported no ICS use during year 1. By year 4, consistent ICS use decreased to 20%, whereas no ICS use increased to 57%; poorly controlled asthma was reported in 18% of encounters. In multivariate models controlling for age, sex, forced expiratory volume in 1 second, and asthma severity assessment, patients reporting consistent ICS use during a 12-month period were more likely to report poor asthma control (odds ratio, 1.6; 95% confidence interval, 1.2–2.1) compared with those reporting no ICS use.
In this observational study of children and adolescents with mild-to-moderate asthma, most did not report continued use of ICS. Patients recommended to continue receiving ICS therapy and reporting consistent ICS use were less likely to report well-controlled asthma even after controlling for markers of asthma severity. Although residual confounding by severity cannot be ruled out, many children and adolescents may not achieve well-controlled asthma despite consistent use of ICS.
PMCID: PMC3040975  PMID: 20143642
24.  It pays to have a spring in your step 
A large portion of the mechanical work required for walking comes from muscles and tendons crossing the ankle joint. By storing and releasing elastic energy in the Achilles tendon during each step, humans greatly enhance the efficiency of ankle joint work far beyond what is possible for work performed at the knee and hip joints.
Humans produce mechanical work at the ankle joint during walking with an efficiency two to six times greater than isolated muscle efficiency.
PMCID: PMC2821187  PMID: 19550204
gait; locomotion; walking; energetics; exoskeleton; efficiency
25.  High Treatment Burden in Adults with Cystic Fibrosis: Challenges to Disease Self-Management 
More aggressive management of cystic fibrosis (CF), along with the use of new therapies, has led to increasing survival. Thus, the recommended daily treatment regimens for most CF adults are complex and time consuming.
In the Project on Adult Care in CF (PAC-CF), an ongoing longitudinal study of CF adults, we assessed self-reported daily treatment activities and perceived treatment burden as measured by the CF Questionnaire-Revised (CFQ-R), a disease-specific quality of life measure.
Among the 204 respondents, the median number of daily therapies reported was 7 (IQR 5-9) and the mean reported time spent on treatment activities was 108 minutes per day (SD 58 minutes). Respondents reported a median of 3 inhaled and 3 oral therapies on the day prior to the survey. Only 49% reported performing airway clearance (ACT) on that day. There were no differences in the number of medications or the time to complete therapies based on gender, age or FEV1. The mean CFQ-R treatment burden domain score was 52.3 (SD 22.1), with no significant differences in the treatment burden based on age or FEV1. In a multivariable model controlling for age, gender, and FEV1, using 2 or more nebulized medications and performing ACT for ≥30 minutes were significantly associated with increased treatment burden.
The level of daily treatment activity is high for CF adults regardless of age or disease severity. Increasing number of nebulized therapies and increased ACT time, but not gender, age, or pulmonary function, is associated with higher perceived treatment burden. Efforts to assess the effects of high treatment burden on outcomes such as quality of life are warranted.
PMCID: PMC2680350  PMID: 18952504
Cystic fibrosis; treatment burden; quality of life

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