scholarly journals Increasing the gradient of energetic cost does not initiate adaptation in human walking

Author(s):  
Surabhi N Simha ◽  
Jeremy D. Wong ◽  
Jessica C Selinger ◽  
Sabrina J Abram ◽  
J. Maxwell Donelan

When in a new situation, the nervous system may benefit from adapting its control policy. In determining whether or not to initiate this adaptation, the nervous system may rely on some features of the new situation. Here we tested whether one such feature is salient cost savings. We changed cost saliency by manipulating the gradient of participants' energetic cost landscape during walking. We hypothesized that steeper gradients would cause participants to spontaneously adapt their step frequency to lower costs. To manipulate the gradient, a mechatronic system applied controlled fore-aft forces to the waist of participants as a function of their step frequency as they walked on a treadmill. These forces increased the energetic cost of walking at high step frequencies and reduced it at low step frequencies. We successfully created three cost landscapes of increasing gradients, where the natural variability in participants' step frequency provided cost changes of 3.6% (shallow), 7.2% (intermediate) and 10.2% (steep). Participants did not spontaneously initiate adaptation in response to any of the gradients. Using metronome-guided walking-a previously established protocol for eliciting initiation of adaptation-participants next experienced a step frequency with a lower cost. Participants then adapted by -1.41±0.81 (p=0.007) normalized units away from their originally preferred step frequency obtaining cost savings of 4.80±3.12% That participants would adapt under some conditions, but not in response to steeper cost gradients, suggests that the nervous system does not solely rely on the gradient of energetic cost to initiate adaptation in novel situations.

2020 ◽  
Author(s):  
Surabhi N. Simha ◽  
Jeremy D. Wong ◽  
Jessica C. Selinger ◽  
Sabrina J. Abram ◽  
J. Maxwell Donelan

AbstractWhen in a new situation, the nervous system may benefit from adapting its control policy. In determining whether or not to initiate this adaptation, the nervous system may rely on some features of the new situation. Here we tested whether one such feature is salient cost savings. We changed cost saliency by manipulating the gradient of participants’ energetic cost landscape during walking. We hypothesized that steeper gradients would cause participants to spontaneously adapt their step frequency to lower costs. To manipulate the gradient, a mechatronic system applied controlled fore-aft forces to the waist of participants as a function of their step frequency as they walked on a treadmill. These forces increased the energetic cost of walking at high step frequencies and reduced it at low step frequencies. We successfully created three cost landscapes of increasing gradients, where the natural variability in participants’ step frequency provided cost changes of 3.6% (shallow), 7.2% (intermediate) and 10.2% (steep). Participants did not spontaneously initiate adaptation in response to any of the gradients. Using metronome-guided walking— a previously established protocol for eliciting initiation of adaptation—participants next experienced a step frequency with a lower cost. Participants then adapted by −1.41±0.81 (p=0.007) normalized units away from their originally preferred step frequency obtaining cost savings of 4.80±3.12%. That participants would adapt under some conditions, but not in response to steeper cost gradients, suggests that the nervous system does not solely rely on the gradient of energetic cost to initiate adaptation in novel situations.


2018 ◽  
Author(s):  
Surabhi N Simha ◽  
J. Maxwell Donelan

A general principle of human movement is that our nervous system is able to learn optimal coordination strategies. However, how our nervous system performs this optimization is not well understood. Here we design, build, and test a mechatronic system to probe the algorithms underlying optimization of energetic cost in walking. The system applies controlled fore-aft forces to a hip-belt worn by a user, decreasing their energetic cost by pulling forward or increasing it by pulling backward. The system controls the forces, and thus energetic cost, as a function of how the user is moving. In testing, we found that the system can quickly, accurately, and precisely apply target forces within a walking step. We next controlled the forces as a function of the user's step frequency and found that we could predictably reshape their energetic cost landscape. Finally, we tested whether users adapted their walking in response to the new cost landscapes created by our system, and found that users shifted their step frequency towards the new energetic minima. Our system design appears to be effective for reshaping energetic cost landscapes in human walking to study how the nervous system optimizes movement.


2017 ◽  
Vol 118 (2) ◽  
pp. 1425-1433 ◽  
Author(s):  
Jeremy D. Wong ◽  
Shawn M. O’Connor ◽  
Jessica C. Selinger ◽  
J. Maxwell Donelan

Human gait adaptation implies that the nervous system senses energetic cost, yet this signal is unknown. We tested the hypothesis that the blood gas receptors sense cost for gait optimization by controlling blood O2 and CO2 with step frequency as people walked. At the simulated energetic minimum, ventilation and perceived exertion were lowest, yet subjects preferred walking at their original frequency. This suggests that blood gas receptors are not critical for sensing cost during gait.


2018 ◽  
Author(s):  
Sabrina J. Abram ◽  
Jessica C. Selinger ◽  
J. Maxwell Donelan

People prefer to move in energetically optimal ways during walking. We have recently found that this preference arises not just through evolution and development, but that the nervous system will continuously optimize step frequency in response to new energetic cost landscapes. Here we test whether energy optimization is also a major objective in the nervous system's real-time control of step width. To accomplish this, we use a device that can reshape the relationship between step width and energetic cost, shifting the energy optimal width wider than that initially preferred. We find that the nervous system doesn't spontaneously initiate energy optimization, but instead requires experience with a lower energetic cost step width. After initiating optimization, people converge towards their new energy optimal width within hundreds of steps and update this as their new preferred width, rapidly returning to it when perturbed away. However, energy optimization was incomplete as this new preferred width was slightly narrower than the energetically optimal width. This suggests that the nervous system may determine its preferred width by optimizing energy simultaneously with other objectives such as stability or maneuverability. Collectively, these findings indicate that the nervous systems of able-bodied people continuously optimize energetic cost to determine preferred step width.


2019 ◽  
Vol 121 (5) ◽  
pp. 1848-1855 ◽  
Author(s):  
Jeremy D. Wong ◽  
Jessica C. Selinger ◽  
J. Maxwell Donelan

In new walking contexts, the nervous system can adapt preferred gaits to minimize energetic cost. During treadmill walking, this optimization is not usually spontaneous but instead requires experience with the new energetic cost landscape. Experimenters can provide subjects with the needed experience by prescribing new gaits or instructing them to explore new gaits. Yet in familiar walking contexts, people naturally prefer energetically optimal gaits: the nervous system can optimize cost without an experimenter’s guidance. Here we test the hypothesis that the natural gait variability of overground walking provides the nervous system with sufficient experience with new cost landscapes to initiate spontaneous minimization of energetic cost. We had subjects walk over paths of varying terrain while wearing knee exoskeletons that penalized walking as a function of step frequency. The exoskeletons created cost landscapes with minima that were, on average, 8% lower than the energetic cost at the initially preferred gaits and achieved at walking speeds and step frequencies that were 4% lower than the initially preferred values. We found that our overground walking trials amplified gait variability by 3.7-fold compared with treadmill walking, resulting in subjects gaining greater experience with new cost landscapes, including frequent experience with gaits at the new energetic minima. However, after 20 min and 2.0 km of walking in the new cost landscapes, we observed no consistent optimization of gait, suggesting that natural gait variability during overground walking is not always sufficient to initiate energetic optimization over the time periods and distances tested in this study. NEW & NOTEWORTHY While the nervous system can continuously optimize gait to minimize energetic cost, what initiates this optimization process during every day walking is unknown. Here we tested the hypothesis that the nervous system leverages the natural variability in gait experienced during overground walking to converge on new energetically optimal gaits created using exoskeletons. Contrary to our hypothesis, we found that participants did not adapt toward optimal gaits: natural variability is not always sufficient to initiate spontaneous energy optimization.


2021 ◽  
Author(s):  
Mohammad Al-Kadem ◽  
Mohammad Gomaa ◽  
Karam Al Yateem ◽  
Abdulmonam Al Maghlouth

Abstract The Cement Packer approach has been successfully implemented to pursue and monetize minor gas reservoirs of poorer quality. Due to its critical role in power supply to meet the nation's needs, license to operate gas fields oftentimes come with contractual obligations to deliver a certain threshold of gas capacity. The cement packer method is a cheaper alternative to workovers that enables operators to build gas capacity by monetizing minor gas reservoirs at lower cost. Group 1 reservoirs are the shallowest hydrocarbon bearing sand with poorer reservoir quality and relatively thin reservoirs. The behind-casing-opportunities in Minor Group-1 reservoirs previously required a relatively costly pull-tubing rig workover to monetize the reservoir. Opportunities in two wells were optimized from pull –tubing rig workovers to a non-rig program by implementing Cement Packer applications. The tubing was punched to create tubing-casing communication and cement was subsequently pumped through the tubing and into the casing. The hardened cement then acted as a barrier to satisfy operating guidelines. The reservoir was then additionally perforated, flow tested and successfully monetized at a lower cost. Tubing and casing integrity tests prior to well entry demonstrated good tubing and casing integrity. This is critical to ensure that cement will only flow into the casing where the tubing was punched. Once the cement hardened, pressure test from the tubing and from the casing indicated that the cement has effectively isolated both tubulars. Subsequent Cement Bond Log and Ultrasonic Imaging Tool showed fair to good cement above the target perforation depth. These data supported the fact that the cement packer was solid and the reservoir was ready for additional perforation. Taking into account the reservoir quality, it was decided to perforate the reservoir twice with the biggest gun available to ensure the lowest skin possible. Post perforation, there was a sharp increase in the tubing pressure indicating pressure influx from the reservoir. Despite that, casing pressure remained low, confirming no communication and thus the success of the cement packer.The well was later able to unload naturally due to its high reservoir pressure, confirming the producibility of the reservoirs and unlocking similar opportunities in other wells. Additionally, the cement packer approach delivered tremendous cost savings between $6 – 8 mil per well. Besides confirming the reservoirs' producibility,the success also unlocked additional shallow gas behind casing opportunities in the area.This method will now be the first-choice option to monetize any hydrocarbon resources in reservoirs located above the top packer.


2011 ◽  
Vol 505 (3) ◽  
pp. 291-293 ◽  
Author(s):  
Azusa Uematsu ◽  
Koh Inoue ◽  
Hiroaki Hobara ◽  
Hirofumi Kobayashi ◽  
Yuki Iwamoto ◽  
...  
Keyword(s):  

2000 ◽  
Vol 85 (5) ◽  
pp. 1810-1814 ◽  
Author(s):  
Giuseppe Paolisso ◽  
Daniela Manzella ◽  
Nicola Montano ◽  
Antonio Gambardella ◽  
Michele Varricchio

Abstract Previous studies have shown that leptin stimulates sympathetic nervous system; heart rate variability (HRV) is a widely used technique for assessing the sympathovagal balance at the cardiac level. The aim of our study was to investigate a possible relationship between plasma leptin levels and the autonomic regulation using spectral analysis of HRV. In 120 healthy nonobese subjects the plasma leptin concentration was determined, and HRV was recorded at baseline and during tilt. All subjects were categorized in quartiles of plasma leptin concentration. Analysis of data showed a significant increase in body mass index, body fat, fasting plasma insulin, triglyceride concentration, and homeostatic model assessment values throughout the different quartiles of plasma leptin concentration. Concerning cardiovascular parameters, heart rate, arterial blood pressures, and RR intervals were not significantly different among the quartiles. Total power and high frequency (HF) in normalized units were significantly decreased, whereas low frequency (LF) normalized units was progressively increased from the first to the fourth quartile. Thus, the LF/HF ratio rose gradually and significantly from the lowest to the highest quartile. Such results were independent of the body fat estimate (P < 0.03 for the trend). The change in the LF/HF ratio was significantly enhanced during tilt (P < 0.001 vs. rest values for all quartiles); the effect was stronger in subjects in the fourth quartile of plasma leptin concentration (P < 0.005 for the trend). The latter parameter was also independent of body fat content and distribution (P < 0.01). Our study shows that increasing fasting plasma leptin concentrations are associated with a shift of the sympathovagal balance toward a progressive increase in sympathetic activation and an increased response to orthostatic stimulus in nonobese subjects with different body fat contents.


1994 ◽  
Vol 30 (5) ◽  
pp. 69-78 ◽  
Author(s):  
L. Somlyódy ◽  
M. Kularathna ◽  
I. Masliev

The Nitra is one of the most polluted rivers in Slovakia due to numerous municipal and industrial discharges, as well as the low level of wastewater treatment. The ongoing economic transition and lack of financial resources for water quality management calls for the development of short-run least-cost policies on the basis of ambient standards or a combination of ambient and effluent ones. A water quality control policy model was developed which incorporates dissolved oxygen simulation models, alternative municipal treatment plans and dynamic programming. Least-cost policies to achieve various water quality goals were developed and compared to effluent standard based strategies (including that deriving from the application of the “best available technology”). The role of industrial emissions was demonstrated in a sensitivity fashion, while the influence of parameter uncertainty on the developed policies was analyzed in a multiobjective framework. The analyses show that significant cost savings are possible in comparison to uniform, effluent standard policies. They also suggest that a long-term strategy should be realized on the basis of a sequence of properly phased least-cost policies corresponding to ambient standards to be tightened gradually.


Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 2407-2407
Author(s):  
Holly Trautman ◽  
Erika Szabo ◽  
Francesco Lo-Coco ◽  
Elizabeth James ◽  
Susan Gabriel ◽  
...  

Abstract Introduction: Granulocyte colony-stimulating factors (G-CSFs) are often administered to reduce the incidence, severity, and duration of febrile neutropenia in chemotherapy patients. Tbo-filgrastim and filgrastim-sndz are short-acting G-CSFs with comparable efficacy and safety to that of filgrastim. The present analysis estimated the budget impact of increasing utilization of health care provider (HCP)-administered tbo-filgrastim and filgrastim-sndz on patients with nonmyeloid malignancies treated with myelosuppressive chemotherapy from a US payer perspective. Methods: An interactive budget impact model was developed to estimate the changes in drug and administration costs for a 1 million member health plan. Administration by an HCP (within a clinic or other outpatient setting) was assumed for 80% of patients receiving short-acting G-CSF treatment, with the majority (85%) of products adjudicated through the patient's medical benefit/provided by the HCP and the remaining 15% purchased through the patient's pharmacy benefit. For medical benefit adjudication, the model projected increases in the market share of tbo-filgrastim from 37% to 42% and filgrastim-sndz from 2% to 4% (with a decrease in filgrastim market share from 61% to 54%). For pharmacy benefit adjudication, the model projected increases in the market share of tbo-filgrastim from <1% to 2% and filgrastim-sndz from 5% to 7% (with a decrease in filgrastim market share from 95% to 91%). Base case data were derived from publicly available resources. The overall plan budget impact was calculated using a 1-year time horizon, along with the difference in per-member per-year (PMPY) cost between the current and future scenarios; one-way sensitivity analyses were conducted. Results: The effective annual plan per-patient drug cost totaled between $11,904 and $27,199, depending on dose, presentation, and benefit adjudication, for tbo-filgrastim, between $15,418 and $26,015 for filgrastim-sndz, and between $15,573 and $30,663 for filgrastim. The estimated overall annual plan cost associated with HCP-administered short-acting G-CSFs was $177,151,918 (PMPY = $177.15) in the current scenario and $175,230,445 (PMPY = $175.23) in the future scenario. Cost savings totaled $1,921,473 (PMPY = $1.92). The model was most sensitive to changes in the overall proportion of patients with HCP-administered G-CSFs and to HCP filgrastim acquisition cost. Conclusions: Budget impact analyses examine the financial impact associated with the introduction of new treatments or shifting existing treatment patterns in order to help decision makers determine how best to allocate resources. The majority of HCP-administered G-CSF is adjudicated through the medical benefit, where the effective annual plan per-patient drug cost was lowest for tbo-filgrastim (24% lower cost than filgrastim). For the remainder of HCP-administered G-CSF adjudicated through the pharmacy benefit, the effective annual plan per-patient drug cost was lowest for filgrastim-sndz (15% lower cost than filgrastim). The present analysis estimated an annual US health plan cost savings approaching $2 million overall or almost $2.00 PMPY following an increase of market share by approximately 5% for tbo-filgrastim and 2% for filgrastim-sndz. Disclosures Trautman: Teva Pharmaceuticals, Inc.: Consultancy. Szabo:Patient Centered Outcomes Research (PCORI): Consultancy; Teva Pharmaceuticals, Inc.: Employment; Eli Lilly & Company; Zoetis: Equity Ownership. Lo-Coco:Teva, Novartis, Baxalta, Pfizer: Consultancy; Teva, Lundbeck: Honoraria, Speakers Bureau. James:Teva Pharmaceuticals, Inc.: Consultancy. Gabriel:Teva Pharmaceuticals, Inc.: Employment. Pathak:Teva Pharmaceuticals: Employment, Equity Ownership. Tang:Teva Pharmaceuticals, Inc.: Employment.


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