A continuum model for the dynamics of the phase transition from slow-wave sleep to REM sleep

Previous studies have shown that activated cortical states (awake and rapid eye-movement (REM) sleep), are associated with increased cholinergic input into the cerebral cortex. However, the mechanisms that underlie the detailed dynamics of the cortical transition from slow-wave to REM sleep have not been quantitatively modeled. How does the sequence of abrupt changes in the cortical dynamics (as detected in the electrocorticogram) result from the more gradual change in subcortical cholinergic input? We compare the output from a continuum model of cortical neuronal dynamics with experimentally-derived rat electrocorticogram data. The output from the computer model was consistent with experimental observations. In slow-wave sleep, 0.5–2-Hz oscillations arise from the cortex jumping between “up” and “down” states on the stationary-state manifold. As cholinergic input increases, the upper state undergoes a bifurcation to an 8-Hz oscillation. The coexistence of both oscillations is similar to that found in the intermediate stage of sleep of the rat. Further cholinergic input moves the trajectory to a point where the lower part of the manifold in not available, and thus the slow oscillation abruptly ceases (REM sleep). The model provides a natural basis to explain neuromodulator-induced changes in cortical activity, and indicates that a cortical phase change, rather than a brainstem “flip-flop”, may describe the transition from slow-wave sleep to REM

What can a mean-field model tell us about the dynamics of the cortex?

In this chapter we examine the dynamical behavior of a spatially homogeneous two-dimensional model of the cortex that incorporates membrane potential, synaptic flux rates and long- and short-range synaptic input, in two spatial dimensions, using parameter sets broadly realistic of humans and rats. When synaptic dynamics are included, the steady states may not be stable. The bifurcation structure for the spatially symmetric case is explored, identifying the positions of saddle–node and sub- and supercritical Hopf instabilities. We go beyond consideration of small-amplitude perturbations to look at nonlinear dynamics. Spatially-symmetric (breathing mode) limit cycles are described, as well as the response to spatially-localized impulses. When close to Hopf and saddle–node bifurcations, such impulses can cause traveling waves with similarities to the slow oscillation of slow-wave sleep. Spiral waves can also be induced. We compare model dynamics with the known behavior of the cortex during natural and anesthetic-induced sleep, commenting on the physiological significance of the limit cycles and impulse responses

Management of premature rupture of the membranes after 34 weeks' gestation - early versus delayed induction of labour

Objective. To determine the optimal way to manage patients with premature rupture of the membranes after 34 weeks' gestation.Design. A prospective, randomised controlled trial comparing immediate induction and delayed induction after 24 • 48 hours.Setting. Tygerberg Hospital, Gape Town.Participants. Seventy consecutive patients with premature rupture of the membranes who presented at Tygert>erg Hospital between July and October 1991.Main outcome measures. The two groups were compared with regard to infectious morbidity and antibiotic requirements in the mothers and babies, days spent in hospital, caesarean section rates, duration of labour and analgesic requirements.Results. There was no difference between the two groups in terms of infectious morbidity in either the mothers or the babies, the duration of labour or the caesarean section rates. Nine patients (26%) in the delayed induction group required analgesic treatment during labour versus 18 patients (52%) in the group that was induced immediately (P = 0.049; odds ratio = 0.327; 95% confidence limits = 0.014 - 0.0998). In the delayed induction group, 74% of the patients went into spontaneous labour during the conservative management period. Patients in the active group (immediate induction) had a statistically significant better chance of being discharged within 48 hours of admission (P = 0.028; odds ratio = 3.34; 95% confidence limits = 1.12 -10.73).Conclusions. The management of patients with premature rupture of the membranes after 34 weeks should be decided upon according to the level of antepartum and neonatal care which is available at the particular unit. Where there is adequate neonatal support and pressure on bed occupancy, immediate induction of labour should be considered, while peripheral units should consider conservative management before referral of patients

Connexin36 knockout mice display increased sensitivity to pentylenetetrazol-induced seizure-like behaviors

Large-scale synchronous firing of neurons during seizures is modulated by electrotonic coupling between neurons via gap junctions. To explore roles for connexin36 (Cx36) gap junctions in seizures, we examined the seizure threshold of connexin36 knockout (Cx36KO) mice using a pentylenetetrazol (PTZ) model

The megaproject sponsor as leader

CITATION: Louw, W., et al. 2018. The megaproject sponsor as leader. South African Journal of Industrial Engineering, 29(3):173-187, doi:10.7166/29-3-2058.The original publication is available at http://sajie.journals.ac.zaENGLISH ABSTRACT: The importance of the sponsor role, including its contribution to the success or failure of a project, is widely recognised in the project management literature. References to the sponsor’s leadership, and the substantial component it represents in the profile of the sponsor, are equally prevalent in the literature reviewed. A megaproject is a large-scale, complex venture that typically costs US$1 billion or more, takes many years to develop and build, involves multiple public and private stakeholders, is transformational, and influences millions of people. Executive sponsors are primarily allocated to projects of strategic importance that are complex, carry a considerable degree of risk, and are very visible. A megaproject is thus entitled to a sponsor from the executive (most senior) ranks within an organisation. Rather than joining the debates on complexity and leadership in the project management literature, this paper explains how leadership theories are used to identify instruments that can assist in the assessment of the leadership style and traits/attributes of a sponsor. A framework is then proposed to identify assessment instruments to evaluate the leadership style and leader traits/attributes of a project sponsor.AFRIKAANSE OPSOMMING: Die belangrikheid van die rol van die bestuursborg, insluitend die bydrae wat hy/sy maak tot die sukses of faling van ’n projek word wyd erken in die projekbestuur literatuur. Verwysings na die leierskapsrol van die bestuursborg asook die wesenlike komponent wat dit uitmaak van die profiel van die bestuursborg word bykans net soveel aangetref in die literatuur. ’n Megaprojek word gedefinieer as ’n grootskaalse, komplekse onderneming wat tipies 1 miljard Amerikaanse dollar of meer kos, etlike jare neem om te ontwikkel en te bou, veelvuldige publieke en privaat belanghebbendes betrek, transformasioneel van aard is, en miljoene mense beïnvloed. Uitvoerende bestuursborge word hoofsaaklik aangewys vir projekte van strategiese aard wat kompleks is, ’n beduidende hoeveelheid risiko dra, en uitsonderlik sigbaar is. Dit is dus duidelik dat ’n megaprojek geregtig is op ’n bestuursborg vanuit die uitvoerende en mees senior bestuursvlakke van ’n organisasie. Eerder as om aan te sluit by die debatte oor kompleksiteit en leierskap in die projekbestuur literatuur, dui hierdie artikel aan tot welke mate leierskapsteorieë benut kan word om instrumente te identifiseer wat kan meehelp in die evaluering van leierskapstyle asook die leierskap eienskappe/ attribute van ’n bestuursborg. Ter afsluiting word ’n raamwerk voorgestel om assesseringsinstrumente te identifiseer vir die evaluering van leierskapstyle en leier eienskappe/ attribute.http://sajie.journals.ac.za/pub/article/view/2058Publisher's versio

Entropies of the EEG: The effects of general anaesthesia

The aim of this paper was to compare the performance of different entropy estimators when applied to EEG data taken from patients during routine induction of general anesthesia. The question then arose as to how and why different EEG patterns could affect the different estimators. Therefore we also compared how the different entropy estimators responded to artificially generated signals with predetermined, known, characteristics. This was done by applying the entropy algorithms to pseudoEEG data: (1) computer-generated using a second-order autoregressive (AR2) model, (2) computer-generated white noise added to step signals simulating blink and eyemovement artifacts and, (3) seeing the effect of exogenous (computer-generated) sine-wave oscillations added to the actual clinically-derived EEG data set from patients undergoing induction of anesthesia

Postnatal β2 adrenergic treatment improves insulin sensitivity in lambs with IUGR but not persistent defects in pancreatic islets or skeletal muscle

Placental insufficiency causes intrauterine growth restriction (IUGR) and disturbances in glucose homeostasis with associated β adrenergic receptor (ADRβ) desensitization. Our objectives were to measure insulin-sensitive glucose metabolism in neonatal lambs with IUGR and to determine whether daily treatment with ADRβ2 agonist and ADRβ1/β3 antagonists for 1 month normalizes their glucose metabolism. Growth, glucose-stimulated insulin secretion (GSIS) and glucose utilization rates (GURs) were measured in control lambs, IUGR lambs and IUGR lambs treated with adrenergic receptor modifiers: clenbuterol atenolol and SR59230A (IUGR-AR). In IUGR lambs, islet insulin content and GSIS were less than in controls; however, insulin sensitivity and whole-bodyGUR were not different from controls.Of importance, ADRβ2 stimulation with β1/β3 inhibition increases both insulin sensitivity and whole-body glucose utilization in IUGR lambs. In IUGR and IUGR-AR lambs, hindlimb GURs were greater but fractional glucose oxidation rates and ex vivo skeletal muscle glucose oxidation rates were lower than controls. Glucose transporter 4 (GLUT4) was lower in IUGR and IUGR-AR skeletal muscle than in controls but GLUT1 was greater in IUGR-AR. ADRβ2, insulin receptor, glycogen content and citrate synthase activity were similar among groups. In IUGR and IUGR-AR lambs heart rates were greater, which was independent of cardiac ADRβ1 activation. We conclude that targeted ADRβ2 stimulation improved whole-body insulin sensitivity but minimally affected defects in GSIS and skeletal muscle glucose oxidation. We show that risk factors for developing diabetes are independent of postnatal catch-up growth in IUGR lambs as early as 1 month of age and are inherent to the islets and myocytes

Improving cost-effectiveness of hypertension management at a community health centre

Objectives. To describe the pattern of prescribing for hypertension at a community health centre (CHC) and to evaluate the impact of introducing treatment guidelines and restricting availability of less cost-effective antihypertensive drugs on prescribing patterns, costs of drug treatment and blood pressure (BP) control.Design. Before/after intervention study.Setting. Medium-sized CHC in the Cape Flats area of Cape Town.Subjects. 1 084 hypertensive patients attending the CHC, who had at least two prescriptions for antihypertensive drugs during a 1-year period starting on 1 January 1992. Interventions. 1. Implementation of stepped-care guidelines for hypertension, specifying treatment with more cost-effective drugs and minimising drug treatment. 2. Reducing availability for routine prescribing by CHC doctors of 10 less cost-effective antihypertensive drugs or drug combinations.Outcome measures. 1. Mean number of drugs prescribed per patient. 2. Proportion of prescriptions for: each major class of antihypertensive drug; restricted availability and freely prescribable drugs; and more and less cost-effective drugs. 3. Mean monthly cost of drugs prescribed per patient. 4. Mean blood pressure and proportion of BP readings controlled (<160/95 mmHg) or uncontrolled (≥160/95 mmHg).Results. A mean of 1.7 active drugs was prescribed per patient per visit. The most frequently prescribed drugs were thiazide-like diuretics (44.8%), centrally acting agents (28.4%) and b-blockers (13.2%). Mean monthly drug costs per patient decreased significantly by R1.99 (24.2%) from R8.24 to R6.25 between the first and last prescription for each patient (exclusive of any reduction due to withdrawal of treatment). This was attributable to reduced prescribing of more expensive drugs withdrawn from routine use and a 51.1% increase in prescribing of the most cost-effective drugs. The overall annual cost-saving of the changes in prescribing for this CHC are estimated at R75 150. Blood pressure control did not change significantly.Conclusion. The pattern of changes in prescribing and drug costs was consistent with a causal effect of the interventions. The study demonstrates the potential forimproving cost-effectiveness of hypertension care in primary care in South Africa and the potential for research in this setting

Hypertension care at a Cape Town community health centre

Objectives. To describe the demographic profile of hypertensive patients and the quality of care for hypertension at a Cape Town community health centre (CHC).Design. Prospective, descriptive study.Setting and subjects. Medium-sized CHC, attended by 1098 hypertensive patients during a 1-year period from 1 January 1992.Outcome measures. Default rate - proportion of due visits not attended. Loss to follow-up - proportion of patients persistently defaulting or not responding to recall. Frequency of blood pressure measurement - per 12 due visits. Compliance - proportion of patients collecting ≥ 75% of antihypertensive drugs. Blood pressure control - mean blood pressure of aggregated readings; and proportion controlled (<160/95 mmHg) on the basis of all blood pressure readings and mean blood pressures of individual patients with two or more readings during the study period.Results. More than half (51.6%) of the hypertensive patients were aged ≥ 65 years; 81.7% were female. The default rate was between 11.9% and 19.4%. Compliance was high (76.9%). Loss to follow-up was 8.1 %. Blood pressure was recorded a mean of 4.0 times per 12 due visits. There were no significant gender differences with regard to these measures. Mean blood pressure was 158.3/89.6 mmHg. Over half (56.7%) of all individual readings over the year were uncontrolled and 51.4% of patients were found to be uncontrolled when categorised by their mean blood pressure. Control was significantly poorer among women ≥ 65 years.Conclusion. We found better compliance, more frequent blood pressure measurement, and lower defaulting and loss to follow-up compared with previous South African studies in similar settings. Despite this, blood pressure control was mediocre. Possible explanations for this are discussed. The low proportion of male hypertensives attending the CHC suggests that the accessibility or acceptability of care is poor for this group. The study illustrates the potential for research in this setting and for the use of computers to monitor the quality of primary care.

Second T = 3/2 state in 9^9B and the isobaric multiplet mass equation

Recent high-precision mass measurements and shell model calculations~[Phys. Rev. Lett. {\bf 108}, 212501 (2012)] have challenged a longstanding explanation for the requirement of a cubic isobaric multiplet mass equation for the lowest $A = 9$ isospin quartet. The conclusions relied upon the choice of the excitation energy for the second $T = 3/2$ state in $^9$B, which had two conflicting measurements prior to this work. We remeasured the energy of the state using the $^9{\rm Be}(^3{\rm He},t)$ reaction and significantly disagree with the most recent measurement. Our result supports the contention that continuum coupling in the most proton-rich member of the quartet is not the predominant reason for the large cubic term required for $A = 9$ nuclei