Gregory S. Sawicki

High treatment burden in adults with cystic fibrosis: challenges to disease self-management.

BACKGROUND 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. METHODS 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. RESULTS 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 min). 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 >or=30 min were significantly associated with increased treatment burden. CONCLUSION 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, are associated with higher perceived treatment burden. Efforts to assess the effects of high treatment burden on outcomes such as quality of life are warranted.

Measuring the Transition Readiness of Youth with Special Healthcare Needs: Validation of the TRAQ—Transition Readiness Assessment Questionnaire

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.

Powered lower limb orthoses for gait rehabilitation

Bodyweight supported treadmill training has become a prominent gait rehabilitation method in leading rehabilitation centers. This type of locomotor training has many functional benefits but the labor costs are considerable. To reduce therapist effort, several groups have developed large robotic devices for assisting treadmill stepping. A complementary approach that has not been adequately explored is to use powered lower limb orthoses for locomotor training. Recent advances in robotic technology have made lightweight powered orthoses feasible and practical. An advantage to using powered orthoses as rehabilitation aids is they allow practice starting, turning, stopping, and avoiding obstacles during overground walking.

Reducing the energy cost of human walking using an unpowered exoskeleton

With efficiencies derived from evolution, growth and learning, humans are very well-tuned for locomotion. Metabolic energy used during walking can be partly replaced by power input from an exoskeleton, but is it possible to reduce metabolic rate without providing an additional energy source? This would require an improvement in the efficiency of the human–machine system as a whole, and would be remarkable given the apparent optimality of human gait. Here we show that the metabolic rate of human walking can be reduced by an unpowered ankle exoskeleton. We built a lightweight elastic device that acts in parallel with the users calf muscles, off-loading muscle force and thereby reducing the metabolic energy consumed in contractions. The device uses a mechanical clutch to hold a spring as it is stretched and relaxed by ankle movements when the foot is on the ground, helping to fulfil one function of the calf muscles and Achilles tendon. Unlike muscles, however, the clutch sustains force passively. The exoskeleton consumes no chemical or electrical energy and delivers no net positive mechanical work, yet reduces the metabolic cost of walking by 7.2 ± 2.6% for healthy human users under natural conditions, comparable to savings with powered devices. Improving upon walking economy in this way is analogous to altering the structure of the body such that it is more energy-effective at walking. While strong natural pressures have already shaped human locomotion, improvements in efficiency are still possible. Much remains to be learned about this seemingly simple behaviour.

Cystic fibrosis and transition to adult medical care.

Transition of young adults with cystic fibrosis (CF) from pediatric to adult medical care is an important priority, because many patients are living well into their fourth decade, and by 2010 more than half of all people living with CF will be older than 18 years. Transition to adulthood, a developmental process of skill-building in self-management supported by the health system, is important for the successful transfer to adult CF care. The US Cystic Fibrosis Foundation has been proactive in preparing for increasing numbers of young adults in need of specialized adult-oriented care by creating specialized clinical fellowships for physician providers and mandating establishment of adult CF programs. Despite these initiatives, how to best facilitate transition and to define and measure successful outcomes after transfer to adult care remains unclear. Many adults with CF continue to receive care in the pediatric setting, whereas others transfer before being developmentally prepared. In this state-of-the-art review we provide context for the scope of the challenges associated with designing and evaluating health care transition for adolescents and young adults with CF and implications for all youth with special health care needs.

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.

A pneumatically powered knee-ankle-foot orthosis (KAFO) with myoelectric activation and inhibition

BackgroundThe goal of this study was to test the mechanical performance of a prototype knee-ankle-foot orthosis (KAFO) powered by artificial pneumatic muscles during human walking. We had previously built a powered ankle-foot orthosis (AFO) and used it effectively in studies on human motor adaptation, locomotion energetics, and gait rehabilitation. Extending the previous AFO to a KAFO presented additional challenges related to the force-length properties of the artificial pneumatic muscles and the presence of multiple antagonistic artificial pneumatic muscle pairs.MethodsThree healthy males were fitted with custom KAFOs equipped with artificial pneumatic muscles to power ankle plantar flexion/dorsiflexion and knee extension/flexion. Subjects walked over ground at 1.25 m/s under four conditions without extensive practice: 1) without wearing the orthosis, 2) wearing the orthosis with artificial muscles turned off, 3) wearing the orthosis activated under direct proportional myoelectric control, and 4) wearing the orthosis activated under proportional myoelectric control with flexor inhibition produced by leg extensor muscle activation. We collected joint kinematics, ground reaction forces, electromyography, and orthosis kinetics.ResultsThe KAFO produced ~22%–33% of the peak knee flexor moment, ~15%–33% of the peak extensor moment, ~42%–46% of the peak plantar flexor moment, and ~83%–129% of the peak dorsiflexor moment during normal walking. With flexor inhibition produced by leg extensor muscle activation, ankle (Pearson r-value = 0.74 ± 0.04) and knee ( r = 0.95 ± 0.04) joint kinematic profiles were more similar to the without orthosis condition compared to when there was no flexor inhibition (r = 0.49 ± 0.13 for ankle, p = 0.05, and r = 0.90 ± 0.03 for knee, p = 0.17).ConclusionThe proportional myoelectric control with flexor inhibition allowed for a more normal gait than direct proportional myoelectric control. The current orthosis design provided knee torques smaller than the ankle torques due to the trade-off in torque and range of motion that occurs with artificial pneumatic muscles. Future KAFO designs could incorporate cams, gears, or different actuators to transmit greater torque to the knee.

Human medial gastrocnemius force–velocity behavior shifts with locomotion speed and gait

Humans walk and run over a wide range of speeds with remarkable efficiency. For steady locomotion, moving at different speeds requires the muscle–tendon units of the leg to modulate the amount of mechanical power the limb absorbs and outputs in each step. How individual muscles adapt their behavior to modulate limb power output has been examined using computer simulation and animal models, but has not been studied in vivo in humans. In this study, we used a combination of ultrasound imaging and motion analysis to examine how medial gastrocnemius (MG) muscle–tendon unit behavior is adjusted to meet the varying mechanical demands of different locomotor speeds during walking and running in humans. The results highlighted key differences in MG fascicle-shortening velocity with both locomotor speed and gait. Fascicle-shortening velocity at the time of peak muscle force production increased with walking speed, impairing the ability of the muscle to produce high peak forces. Switching to a running gait at 2.0 m⋅s−1 caused fascicle shortening at the time of peak force production to shift to much slower velocities. This velocity shift facilitated a large increase in peak muscle force and an increase in MG power output. MG fascicle velocity may be a key factor that limits the speeds humans choose to walk at, and may explain the transition from walking to running. This finding is consistent with previous modeling studies.

A PHYSIOLOGIST'S PERSPECTIVE ON ROBOTIC EXOSKELETONS FOR HUMAN LOCOMOTION.

Technological advances in robotic hardware and software have enabled powered exoskeletons to move from science fiction to the real world. The objective of this article is to emphasize two main points for future research. First, the design of future devices could be improved by exploiting biomechanical principles of animal locomotion. Two goals in exoskeleton research could particularly benefit from additional physiological perspective: 1) reduction in the metabolic energy expenditure of the user while wearing the device, and 2) minimization of the power requirements for actuating the exoskeleton. Second, a reciprocal potential exists for robotic exoskeletons to advance our understanding of human locomotor physiology. Experimental data from humans walking and running with robotic exoskeletons could provide important insight into the metabolic cost of locomotion that is impossible to gain with other methods. Given the mutual benefits of collaboration, it is imperative that engineers and physiologists work together in future studies on robotic exoskeletons for human locomotion.

It Pays to Have a Spring in Your Step

In humans, a large portion of the mechanical work required for walking comes from muscle-tendons crossing the ankle joint. Elastic energy storage and return in the Achilles tendon during each step enhance the efficiency of ankle muscle-tendon mechanical work far beyond what is possible for work performed by knee and hip joint muscle-tendons.