Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Carrying Capacity”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources
PubMed1981

Experimental study of new cerebral protective substances - functional recovery of severe, incomplete ischaemic brain lesions pretreated with mannitol an fluorocarbon emulsion.

Using the "canine model of complete ischemic brain regulated with a perfusion method" in which it is possible to control the degree of blood flow to a cerebral hemisphere via a perfusion pump, the effects of mannitol (which acts as a free radical scavenger) and fluorocarbon emulsion (FC) (which has 0.1 micron of average particle size and a high oxygen-carrying capacity) on cerebral ischaemia were investigated. After pretreatment with the drugs, blood flow was reduced via the pump to 1/10 the normal state and 1 hour later, return to a normal state allowed. Subsequent changes in electrical activity were observed and the effectors of the drugs evaluated. In the control group, no recovery of electrical activity was seen, but in the animals treated with either mannitol or FC, incomplete, yet distinct recovery was apparent. In the animals administered mannitol together with FC, however, marked recovery was evident. These experimental results indicate that the combined administration of mannitol and FC is effective in protecting the brain from cerebral ischaemia.

Animals↗
PubMed1996

Influence of severe hemodilution on brain function and brain oxidative metabolism in the cat.

OBJECTIVE: It has been established that during constant pressure arterio-venous bypass perfusion, brain metabolism gradually deteriorates in parallel with the declining hematocrit. However, whether this is due to a disturbance of flow regulation or to the decline in the oxygen-carrying capacity of the blood has not been documented. Therefore, intact animals were submitted to severe hemodilution to determine the threshold for the beginning of functional and biochemical impairment of the brain. METHODS: Six anesthetized and paralyzed adult mongrel cats were submitted to gradual isovolemic hemodilution by stepwise exchange of blood with Ringer lactate/dextran (1 : 1) solution. Exchange of 80 ml/kg body weight resulted in a final hematocrit level ranging from 6.1% to 11%. RESULTS: Cerebral blood flow gradually increased during hemodilution, with a sharp rise to eight times the prehemodilution value when the hematocrit fell below 10%. The calculated oxygen delivery to the brain remained relatively unchanged. Hemodilution did not cause suppression of spontaneous ECoG or somatically evoked primary cortical potentials, even at the lowest hematocrit value of 6.1%. Brain tissue ATP and phosphocreatine content were largely maintained, although tissue lactate content was elevated (9.54 +/- 5.99 micromol/g). CONCLUSIONS: The hemodynamically unimpaired healthy mammal is able to support a substantial degree of hemodilution without major functional or biochemical disturbance to the brain. The previously observed disturbances during prolonged bypass perfusion are, therefore, most probably due to the associated abnormalities of flow regulation.

Adenosine Triphosphate↗
PubMed1982

A predator prey model with age structure.

A general predator-prey model is considered in which the predator population is assumed to have an age structure which significantly affects it fecundity. The model equations are derived from the general McKendrick equations for age structured populations. The existence, stability and de-stabilization of equilibria are studied as they depend on the prey's natural carrying capacity and the maturation period m of the predator. The main result of the paper is that for a broad class of maturation functions positive equilibria are either unstable for small m or are destabilized as m decreases to zero. This is in contrast to the usual rule of thumb that increasing (not decreasing) delays in growth rate responses cause instabilities.

Aging↗
PubMed1990

Endothelial cells as part of a vascular oxygen-sensing system: hypoxia-induced release of autacoids.

Higher developed organisms are equipped with many central and local control mechanisms, which enable an adequate blood and oxygen supply to tissues over a wide range of demands. Global adaptive responses include changes in the circulatory and ventilatory system as well as increases in the oxygen carrying capacity of the blood. At the level of the specialized organs there exist additional control systems for the regulation of local blood flow. Most systems make use of highly specialized cells which are able to sense the oxygen partial pressure of the transport medium, blood, and within the tissues. In the past years, it has been shown that the vascular endothelium lining the entire circulatory system can actively modulate the vascular tone and platelet functions by the release of autacoids, among them prostacyclin and endothelium-derived nitric oxide (EDRF). Recent experiments demonstrate that the release of EDRF is PO2-dependent, which suggests that endothelial cells may act as functional local oxygen sensors within the vascular system.

Adenine Nucleotides↗
PubMed1990

Role of erythropoietin in adaptation to hypoxia.

The glycoprotein hormone erythropoietin (EPO) counteracts tissue hypoxia by increasing the systemic oxygen-carrying capacity. It induces augmentation of red blood cell mass by stimulating the formation and differentiation of erythroid precursor cells in the bone marrow. EPO production is increased under various forms of diminished oxygen supply such as anemic or hypoxic hypoxia. In the adult organism, the kidneys are the major source of EPO. The precise nature of the cells responsible for renal EPO production, however, has not yet been elucidated. Most likely, peritubular cortical cells, e.g. interstitial or endothelial cells, are involved in the elaboration of the hormone. From the observation that isolated perfused rat kidneys produce EPO in an oxygen-dependent fashion we conclude that the 'oxygen sensor' that controls hypoxia-induced EPO synthesis is located in the kidney itself. Within the kidneys, the local venous oxygen tension which reflects the ratio of oxygen supply to oxygen consumption is measured and transformed into a signal that regulates the formation of EPO. However, the mechanism by which a decrease of oxygen delivery to the kidneys is linked to an enhanced EPO gene expression is not yet known. Two possible mechanisms of regulation are discussed: First, renal hypoxia could lead to enhanced formation of metabolic mediators, for example prostaglandins or adenosine, which might stimulate EPO gene transcription by increasing cellular levels of second messenger molecules. Second, some kind of molecular 'oxygen receptor' such as a heme protein, that controls EPO formation by an oxygen-dependent conformational change, could mediate signal transduction.

Animals↗
PubMed1978

Utilisation by sheep of herbage under tree crops in Ghana.

A study conducted into the utilisation by sheep of herbage under a mango/cashew plantation at Kade (Ghana) showed the native herb, Asystasia gangetica to be the most preferred herbage. Centrosema pubescens was preferred to Pueraria phaseoloides. The physical condition of the herbage affected their preference but the crude protein content did not have any influence. The mean daily digestible dry matter intake of yearling rams (g/kg W0.75) was 34, 31 and 39 for animals on Brachiaria lata/Pueraria phaseoloides, Pueraria phaseoloides and Centrosema pubescens/Aystasia gangetica stands respectively. Intake was not correlated with crude protein levels of the herbage. The mean carrying capacity of the associations was found to be between 11 and 18 sheep/ha/annum.

Animal Feed↗
PubMed1991

Autocrine and paracrine growth factors in tumor growth: a mathematical model.

A mathematical model of tumor growth including autocrine and paracrine control has been developed. The model starts with the logistic equation of Verhulst: dV/dt = rV (1-V/K). Autocrine controls are described as modifiers of the Malthusian growth rate (r), while paracrine controls modify the carrying capacity (K) of the system. The control mechanisms are expressed in terms of "candidate" functions, which are based upon the dynamic distribution of TGF-alpha TGF-beta in the local tumor environment. Three paradigms of tissue growth have been modeled: normal tissue wound repair, unrestricted, unperturbed tumor growth, and tumor growth in a (radiation) damaged environment (the Tumor Bed Effect, TBE). These scenarios were used to test the dynamics of the system against known phenomena. Computer simulations are presented for each case. The mode is being extended to include the description of heterogeneous tumors, within which subpopulations can express differential degrees of growth activity. Heterogeneous tumor models, with and without emergent subpopulations, and models of terminal differentiation are also discussed.

Animals↗
PubMed1993

Growth factors and growth control of heterogeneous cell populations.

In an earlier work a model of the autocrine and paracrine pathways of tumor growth control was developed (Michelson and Leith. 1991. Autocrine and paracrine growth factors in tumor growth. Bull. math. Biol. 53, 639-656). The target population, a generic tumor, was modeled as a single, homogeneous population using the standard Verhulst equation of logistic growth. Mitogenic signals were represented by modifications to the Malthusian growth parameter and adaptational signals were represented by modifications to the carrying capacity. Three growth scenarios were described: (1) normal tissue wound healing, (2) unperturbed tumor growth, and (3) tumor growth in a radiation damaged environment, a phenomenon termed the Tumor Bed Effect (TBE). In this paper, we extend those results to include a "triad" of growth factor controls (autocrine, paracrine and endocrine) and heterogeneity of the target population. The heterogeneous factors in the model represent either intrinsic, epigenetic or environmental differences in both normally differentiating tissues and tumors. Three types of growth are modeled: (1) normal tissue differentiation or wound healing, assuming no communication between differentiated and undifferentiated cell compartments; (2) normal wound healing with feedback inhibition, due to signalling from the differentiated compartment; and (3) the development of hypoxia in a spherical tumor. The signal processing within the triad is discussed for each model and biologically reasonable constraints are defined for limits on growth control.

Animals↗
PubMed1980

Safe limit of hemodilution in cardiopulmonary bypass -comparative analysis between cyanotic and acyanotic congenital heart disease.

A safe limit of hemodilution in cardiopulmonary bypass (CPB) for open heart surgery was investigated by analyzing of the perfusion results of 100 patients with tetralogy of Fallot (TOF) and ventricular septal defect (VSD). The higher perfusion flow was necessary to compensate for the reduced oxygen carrying capacity and to maintain adequate arterial pressure in proportion to the increase in hemodilution. Once the dilution ratio reached over 40% in TOF and 50% in VSD, however, adequate oxygen transfer and stable hemodynamic conditions could not be maintained. The former was due to inadequate oxygen delivery and the latter to an impaired venous return. In these cases, various complications caused by residual diluent in the body space despite of extensive diuretic therapy occurred immediately postop. The safe limit of hemodilution is 50%. However, that of cyanotic disease, even in the presence of remarkable polycythemia, must be limited to less than 40%.

Cardiopulmonary Bypass↗
PubMed1977

High-flow total body perfusion with severe hemodilution and normothermia in infants weighing less than 10 kg--safe limits of hemodilution in cardiopulmonary bypass in infants.

Cardiopulmonary bypass with 17 to 57 per cent dilution of hemoglobin for repair of ventricular septal defect (VSD) was applied to 26 infants weighing less than 10 kg at normal temperature. The higher flow rate was required to compensate the reduced oxygen carrying capacity and to maintain an adequate arterial pressure in proportion to a decrease of hemoglobin value. Perfusion index resulted in 3.0 to 6.5 L/m2/min in this series. When the dilution ratio of hemoglobin became more than 50 per cent and high flow rate was required, however, oxygen transfer ratio decreased remarkably on account of inadequate oxygen delivery and imparied venous return. In these cases, it was difficult to remove the diluent immediately after the operation in spite of powerful diuretic therapy. The results of the present study indicate that the safe limits of hemodilution is 50 per cent in cardiopulmonary bypass at normal temperature in infants.

Age Factors↗
PubMedDate not supplied

Whitaker Lecture 1996: microcirculation, biomedical engineering, and artificial blood.

The development of artificial blood requires the understanding of how blood behaves at the level of the microcirculation. A number of measuring systems have recently become available that allow analysis of the transport properties of blood and the microvessels in terms of pressure, flow, the dynamics of their diameter changes, and the rate and manner of oxygen delivery. Findings from this technology have led to the development of an analytical framework with which to assess the consequences of altering the physical properties of blood and to verify quantitatively theoretical predictions. Results show that blood viscosity and oxygen-carrying capacity are directly related, and must be jointly modified in a prescribed manner to maintain tissue oxygen delivery. The use of optical techniques to assess flow and oxygen delivery in experimental animal models show that the consumption of oxygen by the microvessel wall is an important determinant of tissue oxygenation. Furthermore, the viscosity of blood and/or the mixture of blood and an artificial substitute must achieve a viscosity that is close to normal. Low blood viscosity is not necessarily beneficial, unless blood flow velocity rises to maintain the shear stress at the wall needed for the generation of local vasodilators. Manipulating physical properties of currently available modified hemoglobins by mixing them with conventional plasma expanders yield fluids that may provide optimal blood replacements.

Biomedical Engineering↗
PubMed2005

Nutrients and toxin producing phytoplankton control algal blooms - a spatio-temporal study in a noisy environment.

A phytoplankton-zooplankton prey-predator model has been investigated for temporal, spatial and spatio-temporal dissipative pattern formation in a deterministic and noisy environment, respectively. The overall carrying capacity for the phytoplankton population depends on the nutrient level. The role of nutrient concentrations and toxin producing phytoplankton for controlling the algal blooms has been discussed. The local analysis yields a number of stationary and/or oscillatory regimes and their combinations. Correspondingly interesting is the spatio-temporal behaviour, modelled by stochastic reaction-diffusion equations. The present study also reveals the fact that the rate of toxin production by toxin producing phytoplankton (TPP) plays an important role for controlling oscillations in the plankton system. We also observe that different mortality functions of zooplankton due to TPP have significant influence in controlling oscillations, coexistence, survival or extinction of the zoo-plankton population. External noise can enhance the survival and spread of zooplankton that would go extinct in the deterministic system due to a high rate of toxin production.

Animals↗
PubMed2006

Development of alternative support system for viable count of cyanobacteria by most probable number method.

A technique was developed to evaluate alternative support systems to test tubes used in the standard most probable number technique, for simultaneous isolation and enumeration of cyanobacteria. Five different support systems were tested for their suitability in terms of accuracy, sensitivity, economics and ease of handling. PCR plates with 96 wells and carrying capacity of 300 microL per well were found to be most sensitive, besides being cost- and time-effective. This technique can also be useful for isolation of cyanobacteria, due to immobilization of colonies in the gel matrix and storage of samples at room temperature, without loss of viability for 5-6 weeks. This technique can help to process large sample size with ease--both for enumeration and isolation and can be extended for enumeration of other microorganisms from diverse sources.

Colony Count, Microbial↗
PubMed1992

Perioperative haemotherapy: I. Indications for blood component transfusion.

The practice of transfusion medicine has undergone substantial change over the last decade. Much of the impetus for the change has come from the isolation of human immunodeficiency virus (HIV) and the linkage of HIV transmission to blood transfusion. The purpose of this paper is to collate and review the literature relating to the indications for blood transfusion and provide recommendations for the appropriate utilization of blood products. Peer-reviewed and published studies and reviews relating to aspects of clinical blood transfusion were identified through computer searches and searching of the bibliographies of identified articles. Emphasis was placed on the literature published within the last decade and particularly in the years 1985-91. Material was chosen which was of proved clinical importance and in which findings were consistent among different investigators or different centres. Less emphasis was placed on material reporting new findings of uncertain clinical relevance or findings that were not consistent with majority reports. It is concluded that the only indication for red cell transfusion is to increase the oxygen carrying capacity of the blood and that an adjustment downwards in the haemoglobin concentration at which blood is transfused (transfusion trigger) from the traditional level of 100 g.L-1 is supported by the physiological and clinical data. Perioperative haemoglobin concentrations of 80 g.L-1 are acceptable in otherwise healthy young patients. The transfusion trigger should be adjusted upwards from this in medically compromised patients and in the elderly (greater than 60 yr). Fresh frozen plasma (FFP) is only indicated when there are documented deficiencies of coagulation factors. Platelet concentrates (PC) are indicated for the treatment of clinical coagulopathy resulting from thrombocytopaenia or platelet dysfunction. Routine or prophylactic administration of either FFP or PC after cardiopulmonary bypass or during resuscitation from haemorrhage is not indicated.

Blood Component Transfusion↗
PubMed1999

The prevention and treatment of cerebral ischemia.

Although the major focus of recent cerebral protection research has been aimed at developing receptor-specific drugs, this effort has currently resulted in few improvements in patient outcome. Until advances in pharmacology translate to improvements in humans, the clinician and his patients will be well served by using more traditional techniques to prevent and treat cerebral ischemic events. This approach will involve interventions to a) identify patients who are experiencing or are at risk for developing cerebral ischemia, and b) alter systemic physiology in an attempt to lessen the duration and severity of any ischemic insults. Initial therapy should include interventions to improve cerebral perfusion and the oxygen carrying capacity of the blood. Once this is accomplished, measures should be taken to control blood glucose concentrations and treat fever. In otherwise stable surgical patients, mild reductions in patient temperature also may be of benefit, provided the temperature reductions do not introduce problems in systemic physiology and the patient is rewarmed prior to awakening from general anesthesia. General anesthetic choice may be of importance in controlling intracranial pressure and seizure activity; however, if direct cerebral protection is desired, the anesthetic of choice should be a barbiturate. Finally, in the patient at risk for cerebral vasospasm, nimodipine treatment should be considered. Collectively, these interventions should increase the patient's chance for optimal neurologic recovery following ischemia.

Anesthesia↗
PubMed2005

Arthrodesis of the first tarsometatarsal joint for correction of the advanced splayfoot accompanied by a hallux valgus.

OBJECTIVE: Arthrodesis of the first tarsometatarsal joint for the treatment of a painful splayfoot with the aim to restore a normal weight bearing on the first ray. Correction of hallux valgus deformity. INDICATIONS: Advanced splayfoot deformity with a first intermetatarsal angle > 18 degrees. Hypermobility of the first tarsometatarsal joint with reduced weight bearing on the first ray and development of a transfer metatarsalgia. Painful, primary or secondary osteoarthritis of the first tarsometatarsal joint. Recurrence of splayfoot deformity after previous attempt at surgical correction. Elevation of the first ray such as after developmental clubfoot. Metatarsus primus varus deformity accompanied by hallux valgus in the presence of a hypermobile flatfoot. CONTRAINDICATIONS: Minimal or moderate splayfoot deformity with a first intermetatarsal angle < 17 degrees and a clinically stable first tarsometatarsal joint. Untreated hindfoot deformities such as flatfoot combined with heel valgus. Inability to use walking aids for postoperative partial weight bearing. Insufficient circulation of forefoot. SURGICAL TECHNIQUE: Dorsomedial incision overlying the first tarsometatarsal joint. Splitting of the extensor aponeurosis medial to the tendon of the extensor hallucis longus. Subperiosteal exposure of the first tarsometatarsal joint. Opening of the joint. Judicious removal of articular cartilage and resection of a laterally based bony wedge from the medial cuneiform for correction of the increased first intermetatarsal angle. Manual correction of the splayfoot with concomitant plantar displacement of the base of the first metatarsal. Selection of properly fitting fixed-angle plate and internal fixation. Soft-tissue correction at the first metatarsophalangeal joint or metatarsal neck osteotomy to realign the articular surface of the first metatarsal head. RESULTS: Clinical and radiologic results based on 56 patients (64 feet) followed up for an average of 8.2 months. COMPLICATIONS: one reflex sympathetic dystrophy, four nonunions of the first tarsometatarsal joint (6.2%). Radiologic evidence of consolidation at a mean of 9 weeks. Improvement of the first intermetatarsal angle from 20.4 degrees to 11.2 degrees. Pressure measurement showed a significantly improved load-carrying capacity of the first ray. The score of the American Orthopaedic Foot and Ankle Society improved significantly (p < 0.01) from 51 to 92 points.

Arthrodesis↗
PubMed1999

[Cerebral effects of perfluorocarbons].

For the usage as blood substitutes perfluorocarbons (PFC) have been developed as artificial oxygen carriers. In addition they may have potency for protective use in ischemic tissue. Formulation improvement achieved higher oxygen carrying capacity and better compatibility than the first generation of PFC. Preclinical studies have been performed in animal heart and brain. Former and progressed emulsification for intravascular use have been investigated for infarction and reperfusion injury. This investigations are reviewed and the potencies for the use of PFC in neurology, neurosurgery, diagnostics today and in the future are emphasized.

Animals↗
PubMed1997

Effects of nitrite exposure on acid-base balance, respiratory protein, and ion concentrations of giant freshwater prawn Macrobrachium rosenbergii at low pH.

Macrobrachium rosenbergii that had been exposed individually for 24 h to 0 (control), 2, 5, 10 mg/L nitrite-N (nitrite as nitrogen) at 4. 3 and 7.7 pH levels were examined for hemolymph nitrite-N, oxyhemocyanin, protein, acid-base balance, ion concentrations, and ammonia-N (ammonia as nitrogen) excretion. Hemolymph oxyhemocyanin, protein, pH, HCO3- , TCO2, osmolality, and ion concentrations were inversely related to ambient nitrite-N concentration and were lower at pH 4.3. However, hemolymph nitrite-N, PO2 and PCO2 levels, and ammonia-N excretion were directly related to ambient nitrite-N, and were higher at pH 4.3. Ambient nitrite-N and pH level interacted to cause changes in hemolymph nitrite-N, oxyhemocyanin, protein, PO2, and pH levels. It is concluded that for M. rosenbergii following nitrite exposure, the incorporated nitrite causes a decrease of pH and an increase of PO2 in the hemolymph where it reduces oxyhemocyanin level; disturbs nitrogen excretion, ion regulation, and respiratory gas exchange; and may lead to a decrease of oxygen-carrying capacity, which are affected more at low pH.

Acid-Base Equilibrium↗