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The inverse problem for cardiac arrhythmias. CHAOS (WOODBURY, N.Y.) 2023; 33:123130. [PMID: 38149994 DOI: 10.1063/5.0161210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Accepted: 11/20/2023] [Indexed: 12/28/2023]
Abstract
A cardiac arrhythmia is an abnormality in the rate or rhythm of the heart beat. We study a type of arrhythmia called a premature ventricular complex (PVC), which is typically benign, but in rare cases can lead to more serious arrhythmias or heart failure. There are three known mechanisms for PVCs: reentry, an ectopic focus, and triggered activity. We develop minimal models for each mechanism and attempt the inverse problem of determining which model (and therefore which mechanism) best describes the beat dynamics observed in an ambulatory electrocardiogram. We demonstrate our approach on a patient who exhibits frequent PVCs and find that their PVC dynamics are best described by a model of triggered activity. Better identification of the PVC mechanism from wearable device data could improve risk stratification for the development of more serious arrhythmias.
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mTOR Inhibitor-Induced Transient Acantholytic Dermatitis. J Drugs Dermatol 2022; 21:315-316. [PMID: 35254759 DOI: 10.36849/jdd.5956] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
A 61-year-old Caucasian male with a medical history of metastatic carcinoid presented to dermatology with a new onset severely pruritic “breakouts” on the arms, neck, and chest. Approximately ten years prior, he was diagnosed with a small bowel carcinoid tumor and liver metastases treated with a combination of resection and ablation.
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2021 Canadian Surgery Forum01. Design and validation of a unique endoscopy simulator using a commercial video game03. Is ethnicity an appropriate measure of health care marginalization?: A systematic review and meta-analysis of the outcomes of diabetic foot ulceration in the Aboriginal population04. Racial disparities in surgery — a cross-specialty matched comparison between black and white patients05. Starting late does not increase the risk of postoperative complications in patients undergoing common general surgical procedures06. Ethical decision-making during a health care crisis: a resource allocation framework and tool07. Ensuring stability in surgical training program leadership: a survey of program directors08. Introducing oncoplastic breast surgery in a community hospital09. Leadership development programs for surgical residents: a review of the literature10. Superiority of non-opioid postoperative pain management after thyroid and parathyroid operations: a systematic review and meta-analysis11. Timing of ERCP relative to cholecystectomy in patients with ductal gallstone disease12. A systematic review and meta-analysis of randomized controlled trials comparing intraoperative red blood cell transfusion strategies13. Postoperative outcomes after frail elderly preoperative assessment clinic: a single-institution Canadian perspective14. Selective opioid antagonists following bowel resection for prevention of postoperative ileus: a systematic review and meta-analysis15. Peer-to-peer coaching after bile duct injury16. Laparoscopic median arcuate ligament release: a video abstract17. Retroperitoneoscopic approach to adrenalectomy19. Endoscopic Zenker diverticulotomy: a video abstract20. Variability in surgeons’ perioperative management of pheochromocytomas in Canada21. The contribution of surgeon and hospital variation in transfusion practice to outcomes for patients undergoing elective gastrointestinal cancer surgery: a population-based analysis22. Perioperative transfusions for gastroesophageal cancers: risk factors and short- and long-term outcomes23. The association between frailty and time alive and at home after cancer surgery among older adults: a population-based analysis24. Psychological and workplace-related effects of providing surgical care during the COVID-19 pandemic in British Columbia, Canada25. Safety of venous thromboembolism prophylaxis in endoscopic retrograde cholangiopancreatography: a systematic review26. Complications and reintervention following laparoscopic subtotal cholecystectomy: a systematic review and meta-analysis27. Synchronization of pupil dilations correlates with team performance in a simulated laparoscopic team coordination task28. Receptivity to and desired design features of a surgical peer coaching program: an international survey9. Impact of the COVID-19 pandemic on rates of emergency department utilization due to general surgery conditions30. The impact of the current COVID-19 pandemic on the exposure of general surgery trainees to operative procedures31. Association between academic degrees and research productivity: an assessment of academic general surgeons in Canada32. Laparoscopic endoscopic cooperative surgery (LECS) for subepithelial gastric lesion: a video presentation33. Effect of the COVID-19 pandemic on acute care general surgery at an academic Canadian centre34. Opioid-free analgesia after outpatient general surgery: a pilot randomized controlled trial35. Impact of neoadjuvant immunotherapy or targeted therapies on surgical resection in patients with solid tumours: a systematic review and meta-analysis37. Surgical data recording in the operating room: a systematic review of modalities and metrics38. Association between nonaccidental trauma and neighbourhood socioeconomic status during the COVID-19 pandemic: a retrospective analysis39. Laparoscopic repair of a transdiaphragmatic gastropleural fistula40. Video-based interviewing in medicine: a scoping review41. Indocyanine green fluorescence angiography for prevention of anastomotic leakage in colorectal surgery: a cost analysis from the hospital payer’s perspective43. Perception or reality: surgical resident and faculty assessments of resident workload compared with objective data45. When illness and loss hit close to home: Do health care providers learn how to cope?46. Remote video-based suturing education with smartphones (REVISE): a randomized controlled trial47. The evolving use of robotic surgery: a population-based analysis48. Prophylactic retromuscular mesh placement for parastomal hernia prevention: a retrospective cohort study of permanent colostomies and ileostomies49. Intracorporeal versus extracorporeal anastomosis in laparoscopic right hemicolectomy: a retrospective cohort study on anastomotic complications50. A lay of the land — a description of Canadian academic acute care surgery models51. Emergency general surgery in Ontario: interhospital variability in structures, processes and models of care52. Trauma 101: a virtual case-based trauma conference as an adjunct to medical education53. Assessment of the National Surgical Quality Improvement Program Surgical Risk Calculator for predicting patient-centred outcomes of emergency general surgery patients in a Canadian health care system54. Sustainability of a narcotic reduction initiative: 1 year following the Standardization of Outpatient Procedure (STOP) Narcotics Study55. Barriers to transanal endoscopic microsurgery referral56. Geospatial analysis of severely injured rural patients in a geographically complex landscape57. Implementation of an incentive spirometry protocol in a trauma ward: a single-centre pilot study58. Impostor phenomenon is a significant risk factor for burnout and anxiety in Canadian resident physicians: a cross-sectional survey59. Understanding the influence of perioperative education on performance among surgical trainees: a single-centre experience60. The effect of COVID-19 pandemic on current and future endoscopic personal protective equipment practices: a national survey of 77 endoscopists61. Case report: delayed presentation of perforated sigmoid diverticulitis as necrotizing infection of the lower limb62. Investigating disparities in surgical outcomes in Canadian Indigenous populations63. Fundoplication is superior to medical therapy for Barrett esophagus disease regression and progression: a systematic review and meta-analysis64. Development of a novel online general surgery learning platform and a qualitative preimplementation analysis65. Hagfish slime exudate as a potential novel hemostatic agent: developing a standardized assessment protocol66. The effect of the first wave of the COVID-19 pandemic on surgical oncology case volumes and wait times67. Safety of same-day discharge in high-risk patients undergoing ambulatory general surgery68. External validation of the Codman score in colorectal surgery: a pragmatic tool to drive quality improvement69. Improved morbidity and gastrointestinal restoration rates without compromising survival rates for diverting loop ileostomy with colonic lavage versus total abdominal colectomy for fulminant Clostridioides difficile colitis: a multicentre retrospective cohort study70. Potential access to emergency general surgical care in Ontario71. Immersive virtual reality (iVR) improves procedural duration, task completion and accuracy in surgical trainees: a systematic review01. Clinical validation of the Canada Lymph Node Score for endobronchial ultrasound02. Venous thromboembolism in surgically treated esophageal cancer patients: a provincial population-based study03. Venous thromboembolism in surgically treated lung cancer patients: a population-based study04. Is frailty associated with failure to rescue after esophagectomy? A multi-institutional comparative analysis of outcomes05. Routine systematic sampling versus targeted sampling of lymph nodes during endobronchial ultrasound: a feasibility randomized controlled trial06. Gastric ischemic conditioning reduces anastomotic complications in patients undergoing esophagectomy: a systematic review and meta-analysis07. Move For Surgery, a novel preconditioning program to optimize health before thoracic surgery: a randomized controlled trial08. In case of emergency, go to your nearest emergency department — Or maybe not?09. Does preoperative SABR increase the risk of complications from lung cancer resection? A secondary analysis of the MISSILE trial10. Segmental resection for lung cancer: the added value of near-infrared fluorescence mapping diminishes with surgeon experience11. Toward competency-based continuing professional development for practising surgeons12. Stereotactic body radiotherapy versus surgery in older adults with NSCLC — a population-based, matched analysis of long-term dependency outcomes13. Role of adjuvant therapy in esophageal cancer patients after neoadjuvant therapy and curative esophagectomy: a systematic review and meta-analysis14. Evaluation of population characteristics on the incidence of thoracic empyema: an ecological study15. Determining the optimal stiffness colour threshold and stiffness area ratio cut-off for mediastinal lymph node staging using EBUS elastography and AI: a pilot study16. Quality assurance on the use of sequential compression stockings in thoracic surgery (QUESTs)17. The relationship between fissureless technique and prolonged air leak for patients undergoing video-assisted thoracoscopic lobectomy18. CXCR2 inhibition as a candidate for immunomodulation in the treatment of K-RAS-driven lung adenocarcinoma19. Assessment tools for evaluating competency in video-assisted thoracoscopic lobectomy: a systematic review20. Understanding the current practice on chest tube management following lung resection among thoracic surgeons across Canada21. Effect of routine jejunostomy tube insertion in esophagectomy: a systematic review and meta-analysis22. Recurrence of primary spontaneous pneumothorax following bullectomy with pleurodesis or pleurectomy: a retrospective analysis23. Surgical outcomes following chest wall resection and reconstruction24. Outcomes following surgical management of primary mediastinal nonseminomatous germ cell tumours25. Does robotic approach offer better nodal staging than thoracoscopic approach in anatomical resection for non–small cell lung cancer? A single-centre propensity matching analysis26. Competency assessment for mediastinal mass resection and thymectomy: design and Delphi process27. The contemporary significance of venous thromboembolism (deep venous thrombosis [DVT] and pulmonary embolus [PE]) in patients undergoing esophagectomy: a prospective, multicentre cohort study to evaluate the incidence and clinical outcomes of VTE after major esophageal resections28. Esophageal cancer: symptom severity at the end of life29. The impact of pulmonary artery reconstruction on postoperative and oncologic outcomes: a systematic review30. Association with surgical technique and recurrence after laparoscopic repair of paraesophageal hernia: a single-centre experience31. Enhanced recovery after surgery (ERAS) in esophagectomy32. Surgical treatment of esophageal cancer: trends in surgical approach and early mortality at a single institution over the past 18 years34. Adverse events and length of stay following minimally invasive surgery in paraesophageal hernia repair35. Long-term symptom control comparison of Dor and Nissen fundoplication following laparoscopic para-esophageal hernia repair: a retrospective analysis36. Willingness to pay: a survey of Canadian patients’ willingness to contribute to the cost of robotic thoracic surgery37. Radiomics in early-stage lung adenocarcinoma: a prediction tool for tumour immune microenvironments38. Effectiveness of intraoperative pyloric botox injection during esophagectomy: how often is endoscopic intervention required?39. An artificial intelligence algorithm for predicting lymph node malignancy during endobronchial ultrasound40. The effect of major and minor complications after lung surgery on length of stay and readmission41. Measuring cost of adverse events following thoracic surgery: a scoping review42. Laparoscopic paraesophageal hernia repair: characterization by hospital and surgeon volume and impact on outcomes43. NSQIP 5-Factor Modified Frailty Index predicts morbidity but not mortality after esophagectomy44. Trajectory of perioperative HRQOL and association with postoperative complications in thoracic surgery patients45. Variation in treatment patterns and outcomes for resected esophageal cancer at designated thoracic surgery centres46. Patient-reported pretreatment health-related quality of life (HRQOL) predicts short-term survival in esophageal cancer patients47. Analgesic efficacy of surgeon-placed paravertebral catheters compared with thoracic epidural analgesia after Ivor Lewis esophagectomy: a retrospective noninferiority study48. Rapid return to normal oxygenation after lung surgery49. Examination of local and systemic inflammatory changes during lung surgery01. Implications of near-infrared imaging and indocyanine green on anastomotic leaks following colorectal surgery: a systematic review and meta-analysis02. Repeat preoperative endoscopy after regional implementation of electronic synoptic endoscopy reporting: a retrospective comparative study03. Consensus-derived quality indicators for operative reporting in transanal endoscopic surgery (TES)04. Colorectal lesion localization practices at endoscopy to facilitate surgical and endoscopic planning: recommendations from a national consensus Delphi process05. Black race is associated with increased mortality in colon cancer — a population-based and propensity-score matched analysis06. Improved survival in a cohort of patients 75 years and over with FIT-detected colorectal neoplasms07. Laparoscopic versus open loop ileostomy reversal: a systematic review and meta-analysis08. Posterior mesorectal thickness as a predictor of increased operative time in rectal cancer surgery: a retrospective cohort study09. Improvement of colonic anastomotic healing in mice with oral supplementation of oligosaccharides10. How can we better identify patients with rectal bleeding who are at high risk of colorectal cancer?11. Assessment of long-term bowel dysfunction in rectal cancer survivors: a population-based cohort study12. Observational versus antibiotic therapy for acute uncomplicated diverticulitis: a noninferiority meta-analysis based on a Delphi consensus13. Radiotherapy alone versus chemoradiotherapy for stage I anal squamous cell carcinoma: a systematic review and meta-analysis14. Is the Hartmann procedure for diverticulitis obsolete? National trends in colectomy for diverticulitis in the emergency setting from 1993 to 201515. Sugammadex in colorectal surgery: a systematic review and meta-analysis16. Sexuality and rectal cancer treatment: a qualitative study exploring patients’ information needs and expectations on sexual dysfunction after rectal cancer treatment17. Video-based interviews in selection process18. Impact of delaying colonoscopies during the COVID-19 pandemic on colorectal cancer detection and prevention19. Opioid use disorder associated with increased anastomotic leak and major complications after colorectal surgery20. Effectiveness of a rectal cancer education video on patient expectations21. Robotic-assisted rectosigmoid and rectal cancer resection: implementation and early experience at a Canadian tertiary centre22. An online educational app for rectal cancer survivors with low anterior resection syndrome: a pilot study23. The effects of surgeon specialization on the outcome of emergency colorectal surgery24. Outcomes after colorectal cancer resections in octogenarians and older in a regional New Zealand setting — What are the predictors of mortality?25. Long-term outcomes after seton placement for perianal fistulae with and without Crohn disease26. A survey of patient and surgeon preference for early ileostomy closure following restorative proctectomy for rectal cancer — Why aren’t we doing it?27. Crohn disease independently associated with longer hospital admission after surgery28. Short-stay (≤ 1 d) diverting loop ileostomy closure can be selectively implemented without an increase in readmission and complication rates: an ACS-NSQIP analysis29. A comparison of perineal stapled rectal prolapse resection and the Altemeier procedure at 2 Canadian academic hospitals30. Mental health and substance use disorders predict 90-day readmission and postoperative complications following rectal cancer surgery31. Early discharge after colorectal cancer resection: trends and impact on patient outcomes32. Oral antibiotics without mechanical bowel preparation prior to emergency colectomy reduces the risk of organ space surgical site infections: a NSQIP propensity score matched study33. The impact of robotic surgery on a tertiary care colorectal surgery program, an assessment of costs and short-term outcomes — a Canadian perspective34. Should we scope beyond the age limit of guidelines? Adenoma detection rates and outcomes of screening and surveillance colonoscopies in patients aged 75–79 years35. Emergency department admissions for uncomplicated diverticulitis: a nationwide study36. Obesity is associated with a complicated episode of acute diverticulitis: a nationwide study37. Green indocyanine angiography for low anterior resection in patients with rectal cancer: a prospective before-and-after study38. The impact of age on surgical recurrence of fibrostenotic ileocolic Crohn disease39. A qualitative study to explore the optimal timing and approach for the LARS discussion01. Racial, ethnic and socioeconomic disparities in diagnosis, treatment and survival of patients with breast cancer: a SEER-based population analysis02. First-line palliative chemotherapy for esophageal and gastric cancer: practice patterns and outcomes in the general population03. Frailty as a predictor for postoperative outcomes following pancreaticoduodenectomy04. Synoptic electronic operative reports identify practice variation in cancer surgery allowing for directed interventions to decrease variation05. The role of Hedgehog signalling in basal-like breast cancer07. Clinical and patient-reported outcomes in oncoplastic breast conservation surgery from a single surgeon’s practice in a busy community hospital in Canada08. Upgrade rate of atypical ductal hyperplasia: 10 years of experience and predictive factors09. Time to first adjuvant treatment after oncoplastic breast reduction10. Preparing to survive: improving outcomes for young women with breast cancer11. Opioid prescription and consumption in patients undergoing outpatient breast surgery — baseline data for a quality improvement initiative12. Rectal anastomosis and hyperthermic intraperitoneal chemotherapy: Should we avoid diverting loop ileostomy?13. Delays in operative management of early-stage, estrogen-receptor positive breast cancer during the COVID-19 pandemic — a multi-institutional matched historical cohort study14. Opioid prescribing practices in breast oncologic surgery15. Oncoplastic breast reduction (OBR) complications and patient-reported outcomes16. De-escalating breast cancer surgery: Should we apply quality indicators from other jurisdictions in Canada?17. The breast cancer patient experience of telemedicine during COVID-1918. A novel ex vivo human peritoneal model to investigate mechanisms of peritoneal metastasis in gastric adenocarcinoma (GCa)19. Preliminary uptake and outcomes utilizing the BREAST-Q patient-reported outcomes questionnaire in patients following breast cancer surgery20. Routine elastin staining improves detection of venous invasion and enhances prognostication in resected colorectal cancer21. Analysis of exhaled volatile organic compounds: a new frontier in colon cancer screening and surveillance22. A clinical pathway for radical cystectomy leads to a shorter hospital stay and decreases 30-day postoperative complications: a NSQIP analysis23. Fertility preservation in young breast cancer patients: a population-based study24. Investigating factors associated with postmastectomy unplanned emergency department visits: a population-based analysis25. Impact of patient, tumour and treatment factors on psychosocial outcomes after treatment in women with invasive breast cancer26. The relationship between breast and axillary pathologic complete response in women receiving neoadjuvant chemotherapy for breast cancer01. The association between bacterobilia and the risk of postoperative complications following pancreaticoduodenectomy02. Surgical outcome and quality of life following exercise-based prehabilitation for hepatobiliary surgery: a systematic review and meta-analysis03. Does intraoperative frozen section and revision of margins lead to improved survival in patients undergoing resection of perihilar cholangiocarcinoma? A systematic review and meta-analysis04. Prolonged kidney procurement time is associated with worse graft survival after transplantation05. Venous thromboembolism following hepatectomy for colorectal metastases: a population-based retrospective cohort study06. Association between resection approach and transfusion exposure in liver resection for gastrointestinal cancer07. The association between surgeon volume and use of laparoscopic liver resection for gastrointestinal cancer08. Immune suppression through TIGIT in colorectal cancer liver metastases09. “The whole is greater than the sum of its parts” — a combined strategy to reduce postoperative pancreatic fistula after pancreaticoduodenectomy10. Laparoscopic versus open synchronous colorectal and hepatic resection for metastatic colorectal cancer11. Identifying prognostic factors for overall survival in patients with recurrent disease following liver resection for colorectal cancer metastasis12. Modified Blumgart pancreatojejunostomy with external stenting in laparoscopic Whipple reconstruction13. Laparoscopic versus open pancreaticoduodenectomy: a single centre’s initial experience with introduction of a novel surgical approach14. Neoadjuvant chemotherapy versus upfront surgery for borderline resectable pancreatic cancer: a single-centre cohort analysis15. Thermal ablation and telemedicine to reduce resource utilization during the COVID-19 pandemic16. Cost-utility analysis of normothermic machine perfusion compared with static cold storage in liver transplantation in the Canadian setting17. Impact of adjuvant therapy on overall survival in early-stage ampullary cancers: a single-centre retrospective review18. Presence of biliary anaerobes enhances response to neoadjuvant chemotherapy in pancreatic ductal adenocarcinoma19. How does tumour viability influence the predictive capability of the Metroticket model? Comparing predicted-to-observed 5-year survival after liver transplant for hepatocellular carcinoma20. Does caudate resection improve outcomes in patients undergoing curative resection for perihilar cholangiocarcinoma? A systematic review and meta-analysis21. Appraisal of multivariable prognostic models for postoperative liver decompensation following partial hepatectomy: a systematic review22. Predictors of postoperative liver decompensation events following resection in patients with cirrhosis and hepatocellular carcinoma: a population-based study23. Characteristics of bacteriobilia and impact on outcomes after Whipple procedure01. Inverting the y-axis: the future of MIS abdominal wall reconstruction is upside down02. Progressive preoperative pneumoperitoneum: a single-centre retrospective study03. The role of radiologic classification of parastomal hernia as a predictor of the need for surgical hernia repair: a retrospective cohort study04. Comparison of 2 fascial defect closure methods for laparoscopic incisional hernia repair01. Hypoalbuminemia predicts serious complications following elective bariatric surgery02. Laparoscopic adjustable gastric band migration inducing jejunal obstruction associated with acute pancreatitis: aurgical approach of band removal03. Can visceral adipose tissue gene expression determine metabolic outcomes after bariatric surgery?04. Improvement of kidney function in patients with chronic kidney disease and severe obesity after bariatric surgery: a systematic review and meta-analysis05. A prediction model for delayed discharge following gastric bypass surgery06. Experiences and outcomes of Indigenous patients undergoing bariatric surgery: a mixed-methods scoping review07. What is the optimal common channel length in revisional bariatric surgery?08. Laparoscopic management of internal hernia in a 34-week pregnant woman09. Characterizing timing of postoperative complications following elective Roux-en-Y gastric bypass and sleeve gastrectomy10. Canadian trends in bariatric surgery11. Common surgical stapler problems and how to correct them12. Management of choledocholithiasis following Roux-en-Y gastric bypass: a systematic review and meta-analysis. Can J Surg 2021; 64:S80-S159. [PMID: 35483046 PMCID: PMC8677574 DOI: 10.1503/cjs.021321] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Cardiac Allograft Vasculopathy in Pediatric Heart Transplant Recipients: Does Early Onset Portend a Worse Prognosis? J Heart Lung Transplant 2021. [DOI: 10.1016/j.healun.2021.01.1818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
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An Analysis of Learning Curve Effect on the Speed and Quality of High Dose Rate Prostate Brachytherapy Procedures. Int J Radiat Oncol Biol Phys 2020. [DOI: 10.1016/j.ijrobp.2020.07.482] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Long ECGs reveal rich and robust dynamical regimes in patients with frequent ectopy. CHAOS (WOODBURY, N.Y.) 2020; 30:113127. [PMID: 33261339 DOI: 10.1063/5.0023987] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Accepted: 10/26/2020] [Indexed: 06/12/2023]
Abstract
We have analyzed the electrocardiographic data collected during continuous 7-day ambulatory recordings in patients with frequent premature ventricular complexes (PVCs). We analyze the dependence of the frequency and patterns of PVCs on the heart rate and the time of the day. Patients display rhythms of a complex yet consistent structure. In a given patient, the pattern remains robust over different days and particular repetitive patterns appear at specific heart rates, suggesting the appearance of bifurcations in the dynamics. Over the course of 24 h, we find that in some patients, patterns appear to depend only on the heart rate, whereas in others, both the time of the day and the heart rate play a role in controlling the dynamics. Identifying parameter values at which bifurcations occur facilitates the development of dynamical models for arrhythmia. The use of powerful recording and analysis techniques will enable improved analysis of data and better understanding of mechanisms of arrhythmia in individual patients.
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Heart Transplant Outcomes in Children with Fontan-Associated Plastic Bronchitis: A Pediatric Heart Transplant Society Analysis. J Heart Lung Transplant 2020. [DOI: 10.1016/j.healun.2020.01.1313] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Entrainment and Annihilation of Reentrant Excitation in a Periodically Stimulated Ring of Excitable Media. Methods Inf Med 2018. [DOI: 10.1055/s-0038-1636861] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Abstract:Excitable media, such as nerve, heart and the Belousov-Zhabo- tinsky reaction, exhibit a large excursion from equilibrium in response to a small but finite perturbation. Assuming a one-dimensional ring geometry of sufficient length, excitable media support a periodic wave of circulation. As in the periodic stimulation of oscillations in ordinary differential equations, the effects of periodic stimuli of the periodically circulating wave can be described by a one-dimensional Poincaré map. Depending on the period and intensity of the stimulus as well as its initial phase, either entrainment or termination of the original circulating wave is observed. These phenomena are directly related to clinical observations concerning periodic stimulation of a class of cardiac arrhythmias caused by reentrant wave propagation in the human heart.
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Retracted: Nrf2: a novel therapeutic target in fragile X syndrome is modulated by NNZ2566. GENES BRAIN AND BEHAVIOR 2017; 16:739. [DOI: 10.1111/gbb.12373] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Self-Reported and Directly Measured Physical Activity in Children and Youth with Cardiomyopathies. J Heart Lung Transplant 2017. [DOI: 10.1016/j.healun.2017.01.700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
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Synchronizing the fertile sperm population in the ejaculate by improving collection and selection. Fertil Steril 2013. [DOI: 10.1016/j.fertnstert.2013.07.572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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A prospective, observational study of the effects of implementation strategy on compliance with a surgical safety checklist. BMJ Qual Saf 2013; 22:940-7. [DOI: 10.1136/bmjqs-2012-001749] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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Interaction of tremor and magnification in a motor performance task with visual feedback. J Mot Behav 2012; 30:158-68. [PMID: 20037031 DOI: 10.1080/00222899809601333] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
In this study, the interaction between increased gain in the visual feedback loop and motor control of the periphery was investigated. Participants (N = 15) were asked to maintain a constant finger position while they used magnified visual feedback. The measure of the accuracy of each trial was the standard deviation (trial error) of the finger position. Trials performed under magnification had lower trial errors than trials without magnification. The change in trial error between trials with and without magnification proved greater than the difference between trials at any 2 magnifications. In contrast, the differences between individual subjects were often greater than the differences between performances at individual magnifications. At higher magnifications, performance seemed to be limited by the tremor; the ratio of trial error to tremor intensity was constant. When applied to microsurgery, the present results accord with those found in earlier research, including investigations that have found that the level of magnification used in microsurgery is not the most significant factor in achieving good results and that tremor is the limiting factor in microsurgical tasks.
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The impact of the World Trade Center attack on FDNY firefighter retirement, disabilities, and pension benefits. Am J Ind Med 2011; 54:672-80. [PMID: 21557282 DOI: 10.1002/ajim.20965] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/12/2011] [Indexed: 11/09/2022]
Abstract
BACKGROUND Our goal was to examine the effect of the World Trade Center (WTC) attack and subsequent New York City Fire Department (FDNY) rescue/recovery activities on firefighter retirements. We also analyzed the financial impact associated with the increased number and proportion of service-connected "accidental" disability retirements on the FDNY pension system. METHODS A total of 7,763 firefighters retired between 9/11/1994 and 9/10/2008. We compared the total number of retirements and the number and proportion of accidental disability retirements 7 years before and 7 years after the WTC attack. We categorized WTC-related accidental disability retirements by medical cause and worked with the New York City Office of the Actuary to approximate the financial impact by cause. RESULTS In the 7 years before 9/11 there were 3,261 retirements, 48% (1,571) of which were accidental disability retirements. In the 7 years after 9/11, there were 4,502 retirements, 66% (2,970) were accidental disability retirements, of which 47% (1,402) were associated with WTC-related injuries or illnesses. After 9/11, the increase in accidental disability retirements was, for the most part, due to respiratory-related illnesses. Additional increases were attributed to psychological-related illnesses and musculoskeletal injuries incurred at the WTC site. Pension benefits associated with WTC-related accidental disability retirements have produced an increased financial burden of over $826 million on the FDNY pension system. CONCLUSIONS The WTC attacks affected the health of the FDNY workforce resulting in more post-9/11 retirements than expected, and a larger proportion of these retirees with accidental disability pensions.
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A topological theorem for nonlinear dynamics in chemical and ecological networks. Proc Natl Acad Sci U S A 2010; 72:2856-7. [PMID: 16592264 PMCID: PMC432875 DOI: 10.1073/pnas.72.8.2856] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A topological theorem is given which places restrictions on the numbers and types of critical points in nonlinear chemical and ecological systems, provided certain stringent conditions on the flows on the boundary of the concentration space are satisfied. The sets of critical points that are found for stable and unstable oscillations, and for competitive exclusion, represent the simplest sets of critical points that satisfy the topological theorem. The restrictions that are imposed on bifurcations of the dynamics are discussed.
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Effects of peroxisome proliferator-activated receptor (PPAR)-alpha and PPAR-gamma agonists on glucose and lipid metabolism in patients with type 2 diabetes mellitus. Diabetologia 2007; 50:1723-31. [PMID: 17520238 DOI: 10.1007/s00125-007-0698-9] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/23/2006] [Accepted: 03/05/2007] [Indexed: 12/14/2022]
Abstract
AIMS/HYPOTHESIS The aim of the study was to examine the effects of pioglitazone (PIO), a peroxisome proliferator-activated receptor (PPAR)-gamma agonist, and fenofibrate (FENO), a PPAR-alpha agonist, as monotherapy and in combination on glucose and lipid metabolism. SUBJECTS AND METHODS Fifteen type 2 diabetic patients received FENO (n = 8) or PIO (n = 7) for 3 months, followed by the addition of the other agent for 3 months in an open-label study. Subjects received a 4 h hyperinsulinaemic-euglycaemic clamp and a hepatic fat content measurement at 0, 3 and 6 months. RESULTS Following PIO, fasting plasma glucose (FPG) (p < 0.05) and HbA(1c) (p < 0.01) decreased, while plasma adiponectin (AD) (5.5 +/- 0.9 to 13.8 +/- 3.5 microg/ml [SEM], p < 0.03) and the rate of insulin-stimulated total-body glucose disposal (R (d)) (23.8 +/- 3.8 to 40.5 +/- 4.4 micromol kg(-1) min(-1), p < 0.005) increased. After FENO, FPG, HbA(1c), AD and R (d) did not change. PIO reduced fasting NEFA (784 +/- 53 to 546 +/- 43 micromol/l, p < 0.05), triacylglycerol (2.12 +/- 0.28 to 1.61 +/- 0.22 mmol/l, p < 0.05) and hepatic fat content (20.4 +/- 4.8 to 10.2 +/- 2.5%, p < 0.02). Following FENO, fasting NEFA and hepatic fat content did not change, while triacylglycerol decreased (2.20 +/- 0.14 to 1.59 +/- 0.13 mmol/l, p < 0.01). Addition of FENO to PIO had no effect on R (d), FPG, HbA(1c), NEFA, hepatic fat content or AD, but triacylglycerol decreased (1.61 +/- 0.22 to 1.00 +/- 0.15 mmol/l, p < 0.05). Addition of PIO to FENO increased R (d) (24.9 +/- 4.4 to 36.1 +/- 2.2 micromol kg(-1) min(-1), p < 0.005) and AD (4.1 +/- 0.8 to 13.1 +/- 2.5 microg/ml, p < 0.005) and reduced FPG (p < 0.05), HbA(1c) (p < 0.05), NEFA (p < 0.01), hepatic fat content (18.3 +/- 3.1 to 13.5 +/- 2.1%, p < 0.03) and triacylglycerol (1.59 +/- 0.13 to 0.96 +/- 0.9 mmol/l, p < 0.01). Muscle adenosine 5'-monophosphate-activated protein kinase (AMPK) activity did not change following FENO; following the addition of PIO, muscle AMPK activity increased significantly (phosphorylated AMPK:total AMPK ratio 1.2 +/- 0.2 to 2.2 +/- 0.3, p < 0.01). CONCLUSIONS/INTERPRETATION We conclude that PPAR-alpha therapy has no effect on NEFA or glucose metabolism and that addition of a PPAR-alpha agonist to a PPAR-gamma agent causes a further decrease in plasma triacylglycerol, but has no effect on NEFA or glucose metabolism.
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Reduction in hematocrit and hemoglobin following pioglitazone treatment is not hemodilutional in Type II diabetes mellitus. Clin Pharmacol Ther 2007; 82:275-81. [PMID: 17361126 DOI: 10.1038/sj.clpt.6100146] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Peripheral edema, mild weight gain, and anemia are often observed in type II diabetic patients treated with thiazolidinediones (TZDs). Small decreases in hemoglobin (Hb) and hematocrit (Hct) appear to be a class effect of TZDs and are generally attributed to fluid retention, although experimental data are lacking. We analyzed 50 patients with type II diabetes mellitus undergoing either placebo or pioglitazone (PIO, 45 mg/day) for 16 weeks. Before and after therapy, we measured Hb/Hct and used (3)H(2)O and bioimpedance to quantitate total body water (TBW), extracellular water, and fat-free mass. The majority (89%) of the increment in body weight was accounted for by increased body fat. Hb and Hct fell significantly in the PIO group (-0.9+/-0.2 g/dl, -2.4+/-0.5%, both P<0.0001), without change in TBW. A decline in white blood cell (-0.8+/-0.1 x 10(3)/mm(3), P<0.0001) and platelet (-15+/-6 x 10(3)/mm(3), P<0.02) counts was seen after PIO. In conclusion, the small decreases in Hb/Hct observed after 16 weeks of PIO treatment cannot be explained by an increase in TBW. Other causes, such a mild marrow suppressive effect, should be explored.
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Apparent discontinuities in the phase-resetting response of cardiac pacemakers. J Theor Biol 2004; 230:499-519. [PMID: 15363672 DOI: 10.1016/j.jtbi.2004.03.027] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2003] [Revised: 03/19/2004] [Accepted: 03/22/2004] [Indexed: 11/29/2022]
Abstract
Injection of a brief stimulus pulse resets the spontaneous periodic activity of a sinoatrial node cell: a stimulus delivered early in the cycle generally delays the time of occurrence of the next action potential, while the same stimulus delivered later causes an advance. We investigate resetting in two models, one with a slow upstroke velocity and the other with a fast upstroke velocity, representing central and peripheral nodal cells, respectively. We first formulate each of these models as a classic Hodgkin-Huxley type of model and then as a model representing a population of single channels. In the Hodgkin-Huxley-type model of the slow-upstroke cell the transition from delay to advance is steep but continuous. In the corresponding single-channel model, due to the channel noise then present, repeated resetting runs at a fixed stimulus timing within the transitional range of coupling intervals lead to responses that span a range of advances and delays. In contrast, in the fast-upstroke model the transition from advance to delay is very abrupt in both classes of model, as it is in experiments on some cardiac preparations ("all-or-none" depolarization). We reduce the fast-upstroke model from the original seven-dimensional system to a three-dimensional system. The abrupt transition occurs in this reduced model when a stimulus transports the state point to one side or the other of the stable manifold of the trajectory corresponding to the eigendirection associated with the smaller of two positive eigenvalues. This stable manifold is close to the slow manifold, and so canard trajectories are seen. Our results demonstrate that the resetting response is fundamentally continuous, but extremely delicate, and thus suggest one way in which one can account for experimental discontinuities in the resetting response of a nonlinear oscillator.
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The genome sequence of the filamentous fungus Neurospora crassa. Nature 2003; 422:859-68. [PMID: 12712197 DOI: 10.1038/nature01554] [Citation(s) in RCA: 1129] [Impact Index Per Article: 53.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2002] [Accepted: 03/14/2003] [Indexed: 11/09/2022]
Abstract
Neurospora crassa is a central organism in the history of twentieth-century genetics, biochemistry and molecular biology. Here, we report a high-quality draft sequence of the N. crassa genome. The approximately 40-megabase genome encodes about 10,000 protein-coding genes--more than twice as many as in the fission yeast Schizosaccharomyces pombe and only about 25% fewer than in the fruitfly Drosophila melanogaster. Analysis of the gene set yields insights into unexpected aspects of Neurospora biology including the identification of genes potentially associated with red light photobiology, genes implicated in secondary metabolism, and important differences in Ca2+ signalling as compared with plants and animals. Neurospora possesses the widest array of genome defence mechanisms known for any eukaryotic organism, including a process unique to fungi called repeat-induced point mutation (RIP). Genome analysis suggests that RIP has had a profound impact on genome evolution, greatly slowing the creation of new genes through genomic duplication and resulting in a genome with an unusually low proportion of closely related genes.
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Abstract
In vitro and in vivo studies have demonstrated that prostaglandins of the E series enhance muscle glucose uptake. We examined the effect of acute misoprostol (PGE1) administration on whole body insulin-mediated glucose disposal, as well as the major intracellular pathways of glucose metabolism in type 2 diabetic (n = 10) and non-diabetic (n = 4) subjects. Each subject received two 240-min euglycaemic insulin (40 mU/m2/min) clamp studies with tritiated glucose and indirect calorimetry. During one of the insulin clamp studies, 200 microg of misoprostol was ingested at 90 and 150 min after the start of the insulin infusion. Insulin-mediated total body glucose disposal, glycolysis, glycogenesis and glucose oxidation were similar during the insulin clamp studies performed without and with misoprostol in both the diabetic and non-diabetic groups. These results demonstrate that the acute administration of misoprostol does not enhance insulin-mediated glucose disposal in either type-2-diabetic or non-diabetic subjects.
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Abstract
AIMS/HYPOTHESIS We aimed to examine the mechanisms by which rosiglitazone improves glycaemic control in Type II (non-insulin-dependent) diabetic patients. METHODS Altogether 29 diet-treated diabetic patients were assigned at random to rosiglitazone, 8 mg/day (n = 15), or placebo (n = 14) for 12 weeks. Patients received 75 g OGTT and two-step euglycaemic insulin (40 and 160 mU/m(2)min) clamp with 3-(3)H-glucose, (14)C-palmitate and indirect calorimetry. RESULTS After 12 weeks, rosiglitazone reduced fasting plasma glucose (195 +/- 11 to 150 +/- 7 mg/dl, p < 0.01), mean plasma glucose (PG) during OGTT (293 +/- 12 to 236 +/- 9 mg/dl, p < 0.01), and HbA1 c (8.7 +/- 0.4 to 7.4 +/- 0.3 %, p < 0.01) without changes in plasma insulin concentration. Basal endogenous glucose production (EGP) declined (3.3 +/- 0.1 to 2.9 +/- 0.1 mg/kg FFM. min, p < 0.05) and whole body glucose metabolic clearance rate increased after rosiglitazone (first clamp step: 2.8 +/- 0.2 to 3.5 +/- 0.2 ml/kg FFM. min, p < 0.01; second clamp step: 6.7 +/- 0.6 to 9.2 +/- 0.8, p < 0.05) despite increased body weight (86 +/- 4 to 90 +/- 4 kg, p < 0.01) and fat mass (33 +/- 3 to 37 +/- 3 kg, p < 0.01). Fasting plasma non-esterified fatty acid (NEFA) (735 +/- 52 to 579 +/- 49 microEq/l, p < 0.01), mean plasma NEFA during OGTT (561 +/- 33 to 424 +/- 35, p < 0.01), and basal NEFA turnover (18.3 +/- 1.5 to 15.5 +/- 1.2 microEq/kg FM. min, p < 0.05) decreased after rosiglitazone. Changes in EPG and mean plasma glucose (PG) during OGTT correlated with changes in basal EGP (r = 0.54; r = 0.58), first EGP (r = 0.36; r = 0.41), first MCR (r = -0.66; r = -0.68), second MCR (r = -0.49; r = -0.54), fasting plasma NEFA (r = 0.53; r = 0.49), and NEFA during OGTT (r = 0.66; r = 0.66). CONCLUSION/INTERPRETATION Rosiglitazone increases hepatic and peripheral (muscle) tissue insulin sensitivity and reduces NEFA turnover despite increased total body fat mass. These results suggest that the beneficial effects of rosiglitazone on glycaemic control are mediated, in part, by the drug's effect on NEFA metabolism.
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Automatic detection of atrial fibrillation using the coefficient of variation and density histograms of RR and deltaRR intervals. Med Biol Eng Comput 2001; 39:664-71. [PMID: 11804173 DOI: 10.1007/bf02345439] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The paper describes a method for the automatic detection of atrial fibrillation, an abnormal heart rhythm, based on the sequence of intervals between heartbeats. The RR interval is the interbeat interval, and deltaRR is the difference between two successive RR intervals. Standard density histograms of the RR and deltaRR intervals were prepared as templates for atrial fibrillation detection. As the coefficients of variation of the RR and deltaRR intervals were approximately constant during atrial fibrillation, the coefficients of variation in the test data could be compared with the standard coefficients of variation (CV test). Further, the similarities between the density histograms of the test data and the standard density histograms were estimated using the Kolmogorov-Smirnov test. The CV test based on the RR intervals showed a sensitivity of 86.6% and a specificity of 84.3%. The CV test based on the deltaRR intervals showed that the sensitivity and the specificity are both approximately 84%. The Kolmogorov-Smirnov test based on the RR intervals did not improve on the result of the CV test. In contrast, the Kolmogorov-Smirnov test based on the ARR intervals showed a sensitivity of 94.4% and a specificity of 97.2%.
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Noise effects on the complex patterns of abnormal heartbeats. PHYSICAL REVIEW LETTERS 2001; 87:068104. [PMID: 11497867 DOI: 10.1103/physrevlett.87.068104] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2000] [Indexed: 05/23/2023]
Abstract
Patients at high risk for sudden death often exhibit complex heart rhythms in which abnormal heartbeats are interspersed with normal heartbeats. We analyze such a complex rhythm in a single patient over a 12-h period and show that the rhythm can be described by a theoretical model consisting of two interacting oscillators with stochastic elements. By varying the magnitude of the noise, we show that for an intermediate level of noise, the model gives best agreement with key statistical features of the dynamics.
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Abstract
The sedentary lifestyle of many people with spinal cord injury (SCI) has lead to cardiovascular diseases being a major health concern. A suitable exercise program may help improve the SCI individual's cardiovascular fitness level. GAMEWheels is an interface between a custom wheelchair roller system and a computer that enables an individual to control computer video games by driving his or her wheelchair. The purpose of Phase 1 was to evaluate the design of the GAMEWheels system and to determine the type of computer video game that is likely to motivate wheelchair users to exercise. Phase 2 included physiologic testing of wheelchair users and the GAMEWheels system to investigate whether the system elicits an exercise training response. Thirty-five subjects were recruited to evaluate the GAMEWheels by playing three commercial computer games (Phase 1) and to identify the computer game that they would prefer to use when exercising. The feedback from Phase 1 was used with test subjects to verify that the GAMEWheels system elicits an exercise training effect (Phase 2). Phase 2 included 10 subjects using the GAMEWheels system to play Need for Speed II. During game play, physiologic data were collected and the subjects' oxygen consumption and heart rate were analyzed. Analysis showed that the GAMEWheels system induced nine subjects to reach their training zone, defined as 50% and 60% of their maximum oxygen consumption and heart rate, respectively. This study demonstrates that the GAMEWheels system elicits an exercise training response.
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Abstract
OBJECTIVE To elucidate the effects of pioglitazone treatment on glucose and lipid metabolism in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS A total of 23 diabetic patients (age 30-70 years BMI < 36 kg/m2) who being treated with a stable dose of sulfonylurea were randomly assigned to receive either placebo (n = 11) or pioglitazone (45 mg/day) (n = 12) for 16 weeks. Before and after 16 weeks of treatment, all subjects received a 75-g oral glucose tolerance test (OGTT) and hepatic peripheral insulin sensitivity was measured with a two-step euglycemic insulin (40 and 160 mU x min(-1) x m(-2) clamp performed with 3-[3H]glucose and indirect calorimetry HbA1c measured monthly throughout the study period. RESULTS After 16 weeks of pioglitazone treatment, the fasting plasma glucose (FPG; 184 +/- 15 to 135 +/- 11 mg/dl, P < 0.01), mean plasma glucose during OGTT(293 +/- 12 to 225 +/- 14 mg/dl, P < 0.01), and HbA1c (8.9 +/- 0.3 to 7.2 +/- 0.5%, P < 0.01 ) decreased significantly without change in fasting or glucose-stimulated insulin/C-peptide concentrations. Fasting plasma free fatty acid (FFA; 647 +/- 39 to 478 +/- 49) microEq/l, P < 0.01) and mean plasma FFA during OGTT (485 +/- 30 to 347 +/- 33 microEq/l, P < 0.01) decreased significantly after pioglitazone treatment. Before and after pioglitazone treatment, basal endogenous glucose prodution (EGP) and FPG were strongly correlated (r = 0.67, P < 0.01). EGP during the first insulin clamp step was significantly decreased after pioglitazone treatment (P < 0.05) whereas insulin-stimulated total and nonoxidative glucose disposal during the second insulin clamp was increased (P < 0.01). The change in FPG was related to the change in basal EGP, EGP during the first insulin clamp step, and total glucose disposal during the second insulin clamp step. The change in mean plasma glucose concentration during the OGGTT was strongly related to the change in total body glucose disposl during the second insulin clamp step. CONCLUSIONS These results suggest that pioglitazone therapy in type 2 diabetic patients decreases lasting and postprandial plasma glucose levels by improving hepatic and peripheral (muscle) tissue sensitivity to insulin.
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Abstract
Complex bodily rhythms are ubiquitous in living organisms. These rhythms arise from stochastic, nonlinear biological mechanisms interacting with a fluctuating environment. Disease often leads to alterations from normal to pathological rhythm. Fundamental questions concerning the dynamics of these rhythmic processes abound. For example, what is the origin of physiological rhythms? How do the rhythms interact with each other and the external environment? Can we decode the fluctuations in physiological rhythms to better diagnose human disease? And can we develop better methods to control pathological rhythms? Mathematical and physical techniques combined with physiological and medical studies are addressing these questions and are transforming our understanding of the rhythms of life.
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Symbolic dynamics and computation in model gene networks. CHAOS (WOODBURY, N.Y.) 2001; 11:160-169. [PMID: 12779450 DOI: 10.1063/1.1336498] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We analyze a class of ordinary differential equations representing a simplified model of a genetic network. In this network, the model genes control the production rates of other genes by a logical function. The dynamics in these equations are represented by a directed graph on an n-dimensional hypercube (n-cube) in which each edge is directed in a unique orientation. The vertices of the n-cube correspond to orthants of state space, and the edges correspond to boundaries between adjacent orthants. The dynamics in these equations can be represented symbolically. Starting from a point on the boundary between neighboring orthants, the equation is integrated until the boundary is crossed for a second time. Each different cycle, corresponding to a different sequence of orthants that are traversed during the integration of the equation always starting on a boundary and ending the first time that same boundary is reached, generates a different letter of the alphabet. A word consists of a sequence of letters corresponding to a possible sequence of orthants that arise from integration of the equation starting and ending on the same boundary. The union of the words defines the language. Letters and words correspond to analytically computable Poincare maps of the equation. This formalism allows us to define bifurcations of chaotic dynamics of the differential equation that correspond to changes in the associated language. Qualitative knowledge about the dynamics found by integrating the equation can be used to help solve the inverse problem of determining the underlying network generating the dynamics. This work places the study of dynamics in genetic networks in a context comprising both nonlinear dynamics and the theory of computation. (c) 2001 American Institute of Physics.
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Abstract
The explosive growth in knowledge of the genome of humans and other organisms leaves open the question of how the functioning of genes in interacting networks is coordinated for orderly activity. One approach to this problem is to study mathematical properties of abstract network models that capture the logical structures of gene networks. The principal issue is to understand how particular patterns of activity can result from particular network structures, and what types of behavior are possible. We study idealized models in which the logical structure of the network is explicitly represented by Boolean functions that can be represented by directed graphs on n-cubes, but which are continuous in time and described by differential equations, rather than being updated synchronously via a discrete clock. The equations are piecewise linear, which allows significant analysis and facilitates rapid integration along trajectories. We first give a combinatorial solution to the question of how many distinct logical structures exist for n-dimensional networks, showing that the number increases very rapidly with n. We then outline analytic methods that can be used to establish the existence, stability and periods of periodic orbits corresponding to particular cycles on the n-cube. We use these methods to confirm the existence of limit cycles discovered in a sample of a million randomly generated structures of networks of 4 genes. Even with only 4 genes, at least several hundred different patterns of stable periodic behavior are possible, many of them surprisingly complex. We discuss ways of further classifying these periodic behaviors, showing that small mutations (reversal of one or a few edges on the n-cube) need not destroy the stability of a limit cycle. Although these networks are very simple as models of gene networks, their mathematical transparency reveals relationships between structure and behavior, they suggest that the possibilities for orderly dynamics in such networks are extremely rich and they offer novel ways to think about how mutations can alter dynamics. (c) 2000 American Institute of Physics.
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Abstract
The newly inaugurated Research Resource for Complex Physiologic Signals, which was created under the auspices of the National Center for Research Resources of the National Institutes of Health, is intended to stimulate current research and new investigations in the study of cardiovascular and other complex biomedical signals. The resource has 3 interdependent components. PhysioBank is a large and growing archive of well-characterized digital recordings of physiological signals and related data for use by the biomedical research community. It currently includes databases of multiparameter cardiopulmonary, neural, and other biomedical signals from healthy subjects and from patients with a variety of conditions with major public health implications, including life-threatening arrhythmias, congestive heart failure, sleep apnea, neurological disorders, and aging. PhysioToolkit is a library of open-source software for physiological signal processing and analysis, the detection of physiologically significant events using both classic techniques and novel methods based on statistical physics and nonlinear dynamics, the interactive display and characterization of signals, the creation of new databases, the simulation of physiological and other signals, the quantitative evaluation and comparison of analysis methods, and the analysis of nonstationary processes. PhysioNet is an on-line forum for the dissemination and exchange of recorded biomedical signals and open-source software for analyzing them. It provides facilities for the cooperative analysis of data and the evaluation of proposed new algorithms. In addition to providing free electronic access to PhysioBank data and PhysioToolkit software via the World Wide Web (http://www.physionet. org), PhysioNet offers services and training via on-line tutorials to assist users with varying levels of expertise.
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Paroxysmal starting and stopping of circulating waves in excitable media. PHYSICAL REVIEW LETTERS 2000; 84:4248-4251. [PMID: 10990657 DOI: 10.1103/physrevlett.84.4248] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/1999] [Indexed: 05/23/2023]
Abstract
Levels of intracellular Ca2+ were monitored using fluorescence from Ca2+-sensitive dyes in chick embryonic heart cells cultured in an annular geometry. There was spontaneous starting and stopping of reentrant waves of activity. The results are modeled using modified FitzHugh-Nagumo equations representing pacemakers embedded in a conducting medium. These results provide a potential mechanism for spontaneous abnormal cardiac rhythms in which there are rapid heart beats (tachycardias) that repetitively start and stop.
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Abstract
INTRODUCTION Successful radiofrequency ablation of an ectopic focus requires accurate localization of the region of enhanced automaticity. Present localization techniques require detailed electrical mapping that is time-consuming and involves much trial and error. Here, we propose two new localization techniques which were used to locate a pacemaker in a computer simulation. METHODS AND RESULTS We suggest that an ectopic focus can be located by measuring the activation sequence of three or more intracardiac electrodes subsequent to an ectopic depolarization. Furthermore, the resetting response of an ectopic pacemaker can be used to estimate the distance from the stimulation electrode to the ectopic focus. We derive simple geometric localization strategies based on these ideas and examine the sensitivity of the strategies with respect to measurement uncertainties and electrode arrangements. Our localization strategies were tested using a numerical simulation of a pacemaker in a sheet of excitable media described by modified FitzHugh-Nagumo equations. The strategy based on electrode activation sequences located the pacemaker region in a homogeneous isotropic sheet after an average of 2.2 +/- 0.8 iterates in 10 out of 10 trials starting from random initial catheter positions. In the case of an inhomogeneous anisotropic sheet, the pacemaker was located after an average of 4 +/- 3 iterates in 9 out of 10 trials. The localization strategy based on resetting successfully found the pacemaker in a homogeneous isotropic sheet after an average of 1.2 +/- 0.4 iterates in 5 out of 5 trials and localized the pacemaker in an inhomogeneous anisotropic sheet after an average of 1.4 +/- 0.5 iterates in 5 out of 5 trials. CONCLUSIONS Simple geometric strategies can be used to locate an ectopic focus. Although our basic localization strategies are sensitive to the electrode arrangement and measurement uncertainties, we show that iteration of our techniques quickly locates the pacemaker.
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Abstract
We explore the behavior of richly connected inhibitory neural networks under parameter changes that correspond to weakening of synaptic efficacies between network units, and show that transitions from irregular to periodic dynamics are common in such systems. The weakening of these connections leads to a reduction in the number of units that effectively drive the dynamics and thus to simpler behavior. We hypothesize that the multiple interconnecting loops of the brain's motor circuitry, which involve many inhibitory connections, exhibit such transitions. Normal physiological tremor is irregular while other forms of tremor show more regular oscillations. Tremor in Parkinson's disease, for example, stems from weakened synaptic efficacies of dopaminergic neurons in the nigro-striatal pathway, as in our general model. The multiplicity of structures involved in the production of symptoms in Parkinson's disease and the reversibility of symptoms by pharmacological and surgical manipulation of connection parameters suggest that such a neural network model is appropriate. Furthermore, fixed points that can occur in the network models are suggestive of akinesia in Parkinson's disease. This model is consistent with the view that normal physiological systems can be regulated by robust and richly connected feedback networks with complex dynamics, and that loss of complexity in the feedback structure due to disease leads to more orderly behavior.
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Abstract
Rotating waves (rotors) of cellular activity were observed in nonconfluent cultures of embryonic chick heart cells by using a macroscopic imaging system that detected fluorescence from intracellular Ca2+. Unlike previous observations of rotors or spiral waves in other systems, the rotors did not persist but exhibited a repetitive pattern of spontaneous onset and offset leading to a bursting rhythm. Similar dynamics were observed in a cellular automaton model of excitable media that incorporates spontaneous initiation of activity, and a decrease of excitability as a consequence of rapid activity (fatigue). These results provide a mechanism for bursting dynamics in normal and pathological biological processes.
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Entrainment and annihilation of reentrant excitation in a periodically stimulated ring of excitable media. Methods Inf Med 1997; 36:290-3. [PMID: 9470381] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Excitable media, such as nerve, heart and the Belousov-Zhabotinsky reaction, exhibit a large excursion from equilibrium in response to a small but finite perturbation. Assuming a one-dimensional ring geometry of sufficient length, excitable media support a periodic wave of circulation. As in the periodic stimulation of oscillations in ordinary differential equations, the effects of periodic stimuli of the periodically circulating wave can be described by a one-dimensional Poincaré map. Depending on the period and intensity of the stimulus as well as its initial phase, either entrainment or termination of the original circulating wave is observed. These phenomena are directly related to clinical observations concerning periodic stimulation of a class of cardiac arrhythmias caused by reentrant wave propagation in the human heart.
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Bursting behavior during fixed-delay stimulation of spontaneously beating chick heart cell aggregates. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C331-46. [PMID: 9252472 DOI: 10.1152/ajpcell.1997.273.1.c331] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Spontaneously beating embryonic chick atrial heart cell aggregates were stimulated with depolarizing current pulses delivered at a fixed delay after each action potential. This preparation is an experimental model of a reentrant tachycardia. During fixed-delay stimulation, bursting behavior was typically observed for a wide range of delays. Episodes of bursting at a rate faster (slower) than control were followed by overdrive suppression (underdrive acceleration). We use a simple nonlinear model, based on the interaction between excitability and overdrive suppression, to describe these dynamics. A modified version of the Shrier-Clay ionic model of electrical activity of the embryonic chick heart cell aggregates that includes a simplified Na+ pump term is also presented. We show that the complex patterns during fixed-delay stimulation arise as a result of delicate interactions between overdrive suppression and phase resetting, which can be described in terms of the underlying ionic mechanisms. This study may provide a basis for understanding incessant tachycardias in the intact heart, as well as an alternative mechanism for the emergence of bursting activity in other biologic tissue.
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Abstract
To determine the energy savings caused by sucrose taste, we measured heat loss through direct calorimetry for 23 premature and normal term infants who were studied a total of 31 times. Following stabilization in the calorimeter, crying was induced by applying 1 ml cold water to the infant's foot. After 4 min, 0.1 or 0.2 ml sucrose were delivered intraorally through a remote syringe to arrest crying. Crying was accompanied by a 13.2% increase in metabolic rate that was quickly and completely reversed during crying cessation caused by sucrose taste. Heat loss was inversely and linearly related to infant body weight. The implications of these findings for minimizing crying and energy expenditure in normal newborns and especially in ill or small newborns are discussed.
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Abstract
Randomly connected Boolean networks have been used as mathematical models of neural, genetic, and immune systems. A key quantity of such networks is the number of basins of attraction in the state space. The number of basins of attraction changes as a function of the size of the network, its connectivity and its transition rules. In discrete networks, a simple count of the number of attractors does not reveal the combinatorial structure of the attractors. These points are illustrated in a reexamination of dynamics in a class of random Boolean networks considered previously by Kauffman. We also consider comparisons between dynamics in discrete networks and continuous analogues. A continuous analogue of a discrete network may have a different number of attractors for many different reasons. Some attractors in discrete networks may be associated with unstable dynamics, and several different attractors in a discrete network may be associated with a single attractor in the continuous case. Special problems in determining attractors in continuous systems arise when there is aperiodic dynamics associated with quasiperiodicity of deterministic chaos.
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Alternation of atrioventricular nodal conduction time during atrioventricular reentrant tachycardia: are dual pathways necessary? J Cardiovasc Electrophysiol 1996; 7:943-51. [PMID: 8894936 DOI: 10.1111/j.1540-8167.1996.tb00468.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
INTRODUCTION Alternation of atrial cycle length and AV nodal conduction time (NCT) is often observed during AV reentrant tachycardia. Both AV nodal dual pathway and rate-dependent function have been postulated to be involved in this phenomenon. This study was designed to determine the respective role of these two mechanisms in the alternation observed in an in vitro model of orthodromic AV reentrant tachycardia. METHODS AND RESULTS The tachycardia was produced by detecting each His-bundle activation and stimulating the atrium after a retrograde delay, thereby simulating retrograde pathway conduction, in six isolated rabbit heart preparations. After a 5-minute stabilization period at a fast rate, the retrograde delay was decremented by 2 msec every minute until nodal blocks occurred. We observed a sequential alternation of the cycle length and NCT in four preparations in the short retrograde delay range. The magnitude of the alternation gradually increased as the retrograde delay was decreased and reached 4.6 +/- 0.5 msec during 1:1 conduction. The alternation increased further just prior to termination of the tachycardia by an AV nodal block. None of the preparations showed discontinuous AV nodal recovery curves. Moreover, an electrode positioned over the endocardial surface of the node showed that the alternation developed distally to the nodal inputs, which are believed to constitute a major component of dual pathways. A mathematical model predicted the alternation from known characteristics of rate-dependent nodal functional properties. CONCLUSIONS NCT and cycle length alternation can arise during orthodromic AV reentrant tachycardia when the retrograde delay is sufficiently short. The characteristics of the alternation, presence of continuous recovery curves, intranodal location of the alternation, and mathematical modeling suggest that the alternation is predictable from the known functional properties of the AV node without postulating dual pathway physiology.
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Statistical properties of heartbeat intervals during atrial fibrillation. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 54:1779-1784. [PMID: 9965257 DOI: 10.1103/physreve.54.1779] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Entrainment and termination of reentrant wave propagation in a periodically stimulated ring of excitable media. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 53:6353-6360. [PMID: 9964994 DOI: 10.1103/physreve.53.6353] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Subthreshold dynamics in periodically stimulated squid giant axons. PHYSICAL REVIEW LETTERS 1996; 76:4074-4077. [PMID: 10061185 DOI: 10.1103/physrevlett.76.4074] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
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Abstract
Thirteen healthy subjects were asked to maintain a constant index finger position in Experiment 1 or a constant eye position in Experiment 2 using visual feedback. The finger or eye position along with a stationary baseline target was displayed on an oscilloscope placed in front of the subject. Experiments 1 and 2 were carried out under sixteen combinations of delay and amplification of displacement on the screen (i.e., gain). In Experiment 1, increasing the gain in the visual feedback decreased the Root Mean Square (RMS) errors while increasing the delay increased these errors. An interaction between gains and delays was also observed in Experiment 1. In Experiment 2, the RMS errors were systematically higher than those recorded in Experiment 1 for the finger. No systematic pattern was recognized across all conditions of gains and delays for eye movements in Experiment 2. This study clearly illustrates differences in dynamics of motor control systems regulating eye and finger positions, respectively.
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Resetting and Annihilation of Reentrant Abnormally Rapid Heartbeat. PHYSICAL REVIEW LETTERS 1995; 75:2059-2062. [PMID: 10059198 DOI: 10.1103/physrevlett.75.2059] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Direct calorimetry for the measurement of heat release in preterm infants: methods and applications. J Perinatol 1995; 15:375-81. [PMID: 8576750] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Direct calorimetry is a sensitive and accurate method for the measurement of biologic heat release in humans. At the Children's Medical Center of Brooklyn, State University of New York, we have established direct calorimetry for the measurement of heat release by low birth weight premature infants. We have tested the method and find it to be simple, safe, and accurate. We studied heat release in 10 low birth weight infants on 22 occasions. The smallest infant in the study group weighed 1.43 kg. All the infant underwent direct calorimetry between 1 week and 18 weeks of age. Heat release in the infants ranged from 1.31 kcal/kg/hr. This method of direct calorimetry offers a tool for measuring total metabolic heat release from the first weeks of life in very low birth weight infants to estimate the insensible water losses and to examine the effect of various feeding regimens and disease states on total heat release.
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Overdrive suppression of spontaneously beating chick heart cell aggregates: experiment and theory. THE AMERICAN JOURNAL OF PHYSIOLOGY 1995; 269:H1153-64. [PMID: 7573512 DOI: 10.1152/ajpheart.1995.269.3.h1153] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
In spontaneously beating chick heart cell aggregates, sustained periodic stimulation at a rate faster than the intrinsic frequency is generally followed by a transient slowing of the automatic rhythm called "overdrive suppression." We characterize the qualitative aspects of overdrive suppression using three sets of experimental protocols: 1) stimulation at a fixed frequency with various numbers of stimuli, 2) stimulation at different frequencies, 3) stimulation with different intensities. We develop a mathematical model based on a system of nonlinear ordinary differential equations to account for the experimental observations. The main idea of the model is that overdrive suppression arises as a result of a hyperpolarizing current that is induced by action potentials. This work shows that the frequency of action potentials is the major determinant of overdrive suppression. Consequently, during periodic pacing of spontaneous oscillators at different rates, the fastest frequency where 1:1 entrainment can be maintained is associated with maximal overdrive suppression. This type of model is complementary to the development of a rigorous ionic model and can help provide insight into the physiological mechanisms of overdrive suppression.
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Laryngeal papillomatosis in a very low birth weight baby. J Perinatol 1995; 15:240-1. [PMID: 7666276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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Abstract
A theoretical model, formulated as a finite difference equation is proposed for rate-dependent conduction properties of the atrioventricular (AV) node. The AV nodal conduction time, which is defined as the time interval from the atrial activation to the activation of the bundle of His, depends on the history of activation of the node. The theoretical model, which incorporates physiological concepts of recovery, facilitation and fatigue, accurately predicts a variety of experimentally observed complex rhythms of nodal conduction. In particular, alternans rhythms, in which there is an alternation in conduction time from beat to beat, are associated with period-doubling bifurcations in the theoretical model.
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Hard-of-hearing or deaf: issues of ears, language, culture, and identity. SOCIAL WORK 1995; 40:177-182. [PMID: 7732425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Most social work caseloads include some people who are deaf or hard-of-hearing, yet few social workers are attuned to the different and subtle ways in which hearing impairment can affect identity and relationships. People with hearing impairment make many self-defining choices--of communication method; language; and social, cultural, and political allegiance. Using information collected during a three-year research study of people with acquired hearing loss, this article defines and describes the complex and interrelated dimensions involved in assessing and serving people who are deaf or hearing impaired.
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