Critique of a Large-Scale Organ System Model: Guytonian Cardiovascular Model

1975 ◽  
Vol 97 (3) ◽  
pp. 259-265
Author(s):  
K. Sagawa
Keyword(s):  
Renal Function ◽  
Arterial Pressure ◽  
Large Scale ◽  
Renal Hypertension ◽  
Experimental Studies ◽  
Oxygen Demand ◽  
Sensitivity Tests ◽  
Vascular Autoregulation

This paper reviews Guyton’s model which is large not only in the number of its components but also in the time scale that it spans. The evolution of this model is explained in three stages. Guyton started with a drastically simplified model of the entire cardiovascular system as a closed hydraulic loop. It accounted for short-term regulations of cardiac output with a special emphasis on the role of blood volume and the vascular capacity. Guyton’s research objective was then directed toward the analysis of longterm regulation of arterial pressure. Two slowly acting mechanisms were considered as particularly important: (1) the marked increase or decrease of urinary output with only slight increase or decrease in arterial pressure (the renal function curve in the Guytonian model) and (2) long-term vascular autoregulation which includes changes in the extent of vascularization as well as constriction or dilation of existing vessels to match the blood flow with the oxygen demand in tissues. This second-stage model explained the transient dynamics and steady equilibrium of renal hypertension. The current version of Guyton’s model incorporates a variety of additional endocrine and neural mechanisms which parametrically control the renal function curve. With the enormous growth, the identification (or estimation) capability of the model is bound to degrade while its use for multiple parameter sensitivity tests expands. The modeller’s group has attempted to minimize the hazards by frequent checks of model predictions with experimental studies. This interactive effort, plus their concern over these long-term regulatory mechanisms, make the Guytonian model a unique venture in modern cardiovascular physiology.

Recent insights into the interactions between the baroreflex and the kidneys in hypertension

2005 ◽  
Vol 288 (4) ◽  
pp. R828-R836 ◽  
Author(s):  
Thomas E. Lohmeier ◽  
Drew A. Hildebrandt ◽  
Susan Warren ◽  
Paul J. May ◽  
J. Thomas Cunningham
Keyword(s):  
Arterial Pressure ◽  
Experimental Studies ◽  
Secondary Hypertension ◽  
Experimental Models ◽  
Renal Nerves ◽  
Excretory Function ◽  
Clinical Hypertension ◽  
Theoretical Evidence

Recent findings in chronically instrumented animals challenge the classic concept that baroreflexes do not play a role in the chronic regulation of arterial pressure. As alterations in renal excretory function are of paramount importance in the chronic regulation of arterial pressure, several of these recent studies have focused on the long-term interactions between the baroreflex and the kidneys during chronic perturbations in arterial pressure and body fluid volumes. An emerging body of evidence indicates that the baroreflex is chronically activated in several experimental models of hypertension, but in most cases, the duration of these studies has not exceeded 2 wk. Although these studies suggest that the baroreflex may play a compensatory role in attenuating the severity of the hypertension, possibly even in primary hypertension with uncertain causes of sympathetic activation, there has been only limited assessment of the quantitative importance of this interaction in the regulation of arterial pressure. In experimental models of secondary hypertension, baroreflex suppression of renal sympathetic nerve activity is sustained and chronically promotes sodium excretion. This raises the possibility that the renal nerves may be the critical efferent link for baroreceptor-induced suppression of central sympathetic output through which long-term compensatory reductions in arterial pressure are produced. This contention is supported by strong theoretical evidence but must be corroborated by experimental studies. Finally, although it is now clear that pressure-induced increases in baroreflex activity persist for longer periods of time than previously suggested, studies using new tools and novel approaches and extending beyond 2 wk of hypertension are needed to elucidate the true role of the baroreflex in the pathogenesis of clinical hypertension.

Approaches to Supporting Local and Community Development

2018 ◽  
Author(s):  
Liesel Mack Filgueiras ◽  
Andreia Rabetim ◽  
Isabel Aché Pillar
Keyword(s):  
Large Scale ◽  
Mining Company ◽  
The Sustainable Development ◽  
Social Partnership ◽  
The Public ◽  
Mining Investment ◽  
The Social ◽  
Corporate Social

Reflection about the role of community engagement and corporate social investment in Brazil, associated with the presence of a large economic enterprise, is the major stimulus of this chapter. It seeks to present how cross-sector governance can contribute to the social development of a city and how this process can be led by a partnership comprising a corporate foundation, government, and civil society. The concept of the public–private social partnership (PPSP) is explored: a strategy for building a series of inter-sectoral alliances aimed at promoting the sustainable development of territories where the company has large-scale enterprises, through joint efforts towards integrated long-term strategic planning, around a common agenda. To this end, the case of Canaã dos Carajás is introduced, a municipality in the State of Pará, in the Amazon region, where large-scale mining investment is being carried out by the mining company Vale SA.

Natural Resources and Problems of Development

1974 ◽  
Vol 9 (2-3) ◽  
pp. 179-184
Author(s):  
Per Antonsen
Keyword(s):  
Developing Countries ◽  
Third World ◽  
Large Scale ◽  
Mineral Resources ◽  
World Market ◽  
Economic Security ◽  
Industrial Enterprises ◽  
The Third World

The author focuses on problems in the economy of the developing countries likely to arise as a consequence of mineral exploitation in the new territories. A general shortage of mineral resources, although predicted, should not uncritically be adopted as a sufficient explanation of the demonstrated interest of industrial enterprises in undertaking heavy investments in the new territories. The economic security claimed by institutions financing large-scale investments, may just as likely force the companies to seek options for long-term supplies from these areas, unhampered by the politically caused instabilities perceived in the Third World. This development may tend to push the developing countries into the role of subsidiary suppliers in the world market. The committees preparing the UN Conference on the Law of the Sea have so far taken no realistic measures to counteract this possibility, which may prove detrimental to the economies of several developing countries. The Conference will, in the opinion of the author, provide little but a settlement of disputed interests among the coastal states.

Intraseasonal to decadal variability of Rossby wave packet properties

2021 ◽  
Author(s):  
Georgios Fragkoulidis ◽  
Volkmar Wirth
Keyword(s):  
Rossby Wave ◽  
Large Scale ◽  
Decadal Variability ◽  
Phase Speed ◽  
Diagnostic Methods ◽  
Temperature And Precipitation ◽  
Ongoing Work ◽  
Large Scale Flow

<p>The large-scale extratropical upper-tropospheric flow tends to organize itself into eastward-propagating Rossby wave packets (RWPs). Investigating the spatiotemporal evolution of RWPs and the underlying physical processes has been beneficial in showcasing the role of the upper-tropospheric flow in temperature and precipitation extremes. The use of recently developed diagnostics of local in space and time wave properties has provided further insight in this regard. Motivated by the above, these diagnostic methods are now being employed to investigate the intraseasonal to decadal variability of key RWP properties such as their amplitude, phase speed, and group velocity in reanalysis datasets. It is shown that these properties exhibit a distinct seasonal and interregional variability, while interesting patterns thereof emerge. Moreover, the interannual and long-term variability in these RWP properties is explored and significant decadal trends for specific regions and seasons are highlighted. Ongoing work aims at further utilizing the presented diagnostics and analyses toward an improved understanding of the extratropical large-scale flow variability from weather to climate time scales.</p>

Planning or Improvisation

2020 ◽  
pp. 116-120
Author(s):  
Alasdair Roberts
Keyword(s):  
United States ◽  
Twentieth Century ◽  
Large Scale ◽  
The United States ◽  
Unintended Consequences ◽  
Governance Strategies ◽  
The Face ◽  
Imperfect Knowledge

This chapter assesses the role of planning in the design of governance strategies. Enthusiasm for large-scale planning—also known as overall, comprehensive, long-term, economic, or social planning—boomed and collapsed in twentieth century. At the start of that century, progressive reformers seized on planning as the remedy for the United States' social and economic woes. By the end of the twentieth century, enthusiasm for large-scale planning had collapsed. Plans could be made, but they were unlikely to be obeyed, and even if they were obeyed, they were unlikely to work as predicted. The chapter then explains that leaders should make plans while being realistic about the limits of planning. It is necessary to exercise foresight, set priorities, and design policies that seem likely to accomplish those priorities. Simply by doing this, leaders encourage coordination among individuals and businesses, through conversation about goals and tactics. Neither is imperfect knowledge a total barrier to planning. There is no “law” of unintended consequences: it is not inevitable that government actions will produce entirely unexpected results. The more appropriate stance is modesty about what is known and what can be achieved. Plans that launch big schemes on brittle assumptions are more likely to fail. Plans that proceed more tentatively, that allow room for testing, learning, and adjustment, are less likely to collapse in the face of unexpected results.

Impact of Peritoneal Membrane Function on Long Term Clinical Outcome in Peritoneal Dialysis Patients

1999 ◽  
Vol 19 (2_suppl) ◽  
pp. 91-94 ◽  
Author(s):  
Simon J. Davies ◽  
Louise Phillips ◽  
Anne M. Griffiths ◽  
Lesley H. Russell ◽  
Patrick F. Naish ◽  
...  
Keyword(s):  
Renal Function ◽  
Solute Transport ◽  
Residual Renal Function ◽  
Clinical Implications ◽  
Water Removal ◽  
Peritoneal Membrane ◽  
Dialysis Patients ◽  
Membrane Function

It is increasingly clear that peritoneal membrane transport status has clinical implications. The role of the peritoneum in dialysis delivery becomes para mount once residual renal function is lost, particularly as the membrane characteristics may change for the worse with time on treatment. These findings have several important implications: Clinicians need to take solute transport character istics into account as they assess their patients. Adverse effects of high solute transport include reduced ultrafiltration, solute removal (in particular, sodium), and increased peritoneal protein losses. A need exists to replace lost residual renal function, not just with enhanced solute removal, but also with adequate salt and water removal. The interpretation of urea and creatinine clear ances in anuric PD patients needs further consideration and validation. Hypoalbuminemia in PD patients will result from the combined effects of high protein losses, over hydration, comorbidity, and malnutrition.

Hyperosmotic NaCl and severe hemorrhagic shock: role of the innervated lung

1981 ◽  
Vol 241 (6) ◽  
pp. H883-H890 ◽  
Author(s):  
O. U. Lopes ◽  
V. Pontieri ◽  
M. Rocha e Silva ◽  
I. T. Velasco
Keyword(s):  
Cardiac Output ◽  
Arterial Pressure ◽  
Metabolic Response ◽  
Term Survival ◽  
Long Term Survival ◽  
Vagal Blockade ◽  
Intravenous Infusions ◽  
Acid Base Equilibrium

Infusions of hyperosmotic NaCl (2,400 mosmol/l; 4 ml/kg) were given to dogs in severe hemorrhagic hypotension by intravenous injection (72 expts) or intra-aortic injection (25 expts). In 46 experiments intravenous infusions were given during bilateral blockage of the cervical vagal trunks (local anesthesia or cooling). Intravenous infusions (without vagal blockade) restore arterial pressure, cardiac output, and acid-base equilibrium to normal and cause mesenteric flow to overshoot prehemorrhage levels by 50%. These effects are stable, and indefinite survival was observed in every case. Intra-aortic infusions of hyperosmotic NaCl produce only a transient recovery of arterial pressure and cardiac output but no long-term survival. Intravenous infusions with vagal blockage produce only a transient recovery of cardiac output, with non long-term survival. Measurement of pulmonary artery blood osmolarity during and after the infusions shows that a different pattern is observed in each of these three groups and strongly indicates that the first passage of hyperosmotic blood through the pulmonary circulation at a time when vagal conduction is unimpaired is essential for the production of the full hemodynamic-metabolic response, which is needed for indefinite survival.

scholarly journals Trophic Features, Benthic Recovery, and Dominance of the Invasive Mytilopsis Sallei in the Yundang Lagoon (Xiamen, China) Following Long-Term Restoration

Water ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1692 ◽  
Author(s):  
Paolo Magni ◽  
Serena Como ◽  
Maria Flavia Gravina ◽  
Donghui Guo ◽  
Chao Li ◽  
...  
Keyword(s):  
Land Reclamation ◽  
Environmental Gradients ◽  
Oxygen Demand ◽  
Current Status ◽  
Pest Species ◽  
Future Evolution ◽  
Mytilopsis Sallei ◽  
Biological Tool

A comprehensive set of physicochemical variables in near-bottom water and surface sediments, as well as the soft-bottom macrozoobenthic assemblages were investigated at six sites across the Yundang Lagoon (Southeast China) in November 2012. This lagoon was severely damaged in the 1970s due to domestic and industrial pollution and land reclamation and underwent a massive restoration effort over the past 30 years. Our objectives were to: (1) assess the current trophic and environmental condition of the lagoon; (2) investigate the pattern of spatial variation in the macrozoobenthic assemblages; and (3) assess the benthic recovery in relation to the main environmental gradients and the presence of invasive alien species. Nutrient, chlorophyll-a, biological oxygen demand (BOD5), chemical oxygen demand (CODMn), and total organic carbon (TOC) concentrations were lower than those reported in previous decades, yet organically-enriched conditions occurred at an inner site. From azoic conditions in the 1980s and a few benthic species reported prior to this study, we found a significant increase in benthic diversity with 43 species heterogeneously distributed across the lagoon. The invasive bivalve Mytilopsis sallei was the dominant species, which was associated with the richest benthic assemblage. However, M. sallei is a pest species, and its spatiotemporal distribution should be carefully monitored. These results highlight the central role of the macrozoobenthos in providing important ecological information on the current status of the Yundang Lagoon and as an effective biological tool to follow the recovery’s progress and the future evolution of this highly valued ecosystem.

scholarly journals The Role of mTOR Inhibitors in Liver Transplantation: Reviewing the Evidence

2014 ◽  
Vol 2014 ◽  
pp. 1-45 ◽  
Author(s):  
Goran B. Klintmalm ◽  
Björn Nashan
Keyword(s):  
Metabolic Syndrome ◽  
Liver Transplantation ◽  
Renal Function ◽  
De Novo ◽  
Immunosuppressive Agents ◽  
Mammalian Target Of Rapamycin ◽  
Calcineurin Inhibitors ◽  
Mtor Inhibitors

Despite the success of liver transplantation, long-term complications remain, includingde novomalignancies, metabolic syndrome, and the recurrence of hepatitis C virus (HCV) and hepatocellular carcinoma (HCC). The current mainstay of treatment, calcineurin inhibitors (CNIs), can also worsen posttransplant renal dysfunction, neurotoxicity, and diabetes. Clearly there is a need for better immunosuppressive agents that maintain similar rates of efficacy and renal function whilst minimizing adverse effects. The mammalian target of rapamycin (mTOR) inhibitors with a mechanism of action that is different from other immunosuppressive agents has the potential to address some of these issues. In this review we surveyed the literature for reports of the use of mTOR inhibitors in adult liver transplantation with respect to renal function, efficacy, safety, neurological symptoms,de novotumors, and the recurrence of HCC and HCV. The results of our review indicate that mTOR inhibitors are associated with efficacy comparable to CNIs while having benefits on renal function in liver transplantation. We also consider newer dosing schedules that may limit side effects. Finally, we discuss evidence that mTOR inhibitors may have benefits in the oncology setting and in relation to HCV-related allograft fibrosis, metabolic syndrome, and neurotoxicity.

The role of connectivity in Australian conservation

2004 ◽  
Vol 10 (4) ◽  
pp. 266 ◽  
Author(s):  
M. E. Soulé ◽  
B. G. Mackey ◽  
H. F. Recher ◽  
J. E. Williams ◽  
J. C. Z. Woinarski ◽  
...  
Keyword(s):  
Large Scale ◽  
Biological Diversity ◽  
Ecological Resilience ◽  
Landscape Permeability ◽  
Conservation Assessment ◽  
Ecological Processes ◽  
Trophic Relations ◽  
Scientific Framework

The existing system of nature reserves in Australia is inadequate for the long-term conservation and restoration of native biological diversity because it fails to accommodate, among other elements, large scale and long-term ecological processes and change, including physical and biotic transport in the landscape. This paper is an overview of the connectivity elements that inform a scientific framework for significantly improving the prospects for the long-term conservation of Australia's biodiversity. The framework forms the basis for the WildCountry programme. This programme has identified connectivity at landscape, regional and continental scales as a critical component of an effective conservation system. Seven categories of ecological phenomena are reviewed that require landscape permeability and that must be considered when planning for the maintenance of biological diversity and ecological resilience in Australia: (1) trophic relations at regional scales; (2) animal migration, dispersal, and other large scale movements of individuals and propagules; (3) fire and other forms of disturbance at regional scales; (4) climate variability in space and time and human forced rapid climate change; (5) hydroecological relations and flows at all scales; (6) coastal zone fluxes of organisms, matter, and energy; and, (7) spatially-dependent evolutionary processes at all scales. Finally, we mention eight cross-cutting themes that further illuminate the interactions and implications of the seven connectivity-related phenomena for conservation assessment, planning, research, and management, and we suggest how the results might be applied by analysts, planners, scientists, and community conservationists.

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