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 1,009 records · Page 56Linked to original sources
PubMed1995

[Basic evaluation of nitric oxide inhalation therapy].

We studied the site of action of nitric oxide (NO) and the dose-response relationship between inhaled NO and PaO2. We also measured nitrosyl-hemoglobin (Hb-NO) levels in arterial and mixed venous blood and NO2 levels in our NO inhalation system to confirm the safety of NO inhalation. In an ovine model of ARDS induced by lung lavage, pressure-flow plots indicated that the site of action of inhaled NO was close to the alveoli. During hypoxia, pulmonary artery pressure decreased as the concentration of inhaled NO increased; PaO2 peaked at 10-20 ppm NO. The levels of Hb-NO in arterial and mixed venous blood during inhalation of 40-60 ppm NO under hypoxic conditions were greater than the levels under normoxic conditions, but Hb-NO still accounted for less than 0.1% of the total Hb. Less than 0.1 ppm on NO2 was generated during inhalation of 5 ppm NO. In conclusion, inhaled NO can dilate pulmonary vessels near alveoli without lowering the O2 carrying capacity of blood. In the present system, only a negligible amount of NO2 was produced.

Administration, Inhalation↗
PubMed1996

Microvascular and tissue oxygen distribution.

Understanding of oxygen delivery by the microcirculation has been dominated by the unitary component analysis of Krogh and Erlangen focussed on oxygen transport mediated by single capillaries, oxygenation of tissue as a whole being extrapolated from findings on oxygen exchange in these vessels. This analysis is under revision since capillaries are not sole sources of oxygen. It is increasingly apparent that arterioles are a significant equivalent source, while venules may serve as sinks for capillary and arteriolar oxygen. As a consequence detailed descriptions of the architecture of the microcirculation based on the tissue cylinder conceptualization does not yield new information given the non-exclusive role of capillaries as purveyors of oxygen to tissue. In the present study we investigate how tissue is oxygenated directly from the arteriolar supply on the basis of current results with newly developed optical techniques for the measurement of local intra- and extravascular pO2 by phosphorescence decay. This methodology shows that tissue regions between arterioles and venules have essentially uniform tissue pO2. The only experimentally detectable gradients in pO2 are those present in the immediate vicinity of arterioles. Findings on vascular longitudinal gradients are used to devise a model that links convective and diffusive processes, showing how blood viscosity, blood oxygen-carrying capacity and the slope of the oxygen dissociation curve are linked in determining intravascular and tissue pO2. The integrated approach provides a numerical basis for interpreting consequences of alterations in transport properties of blood applicable to the field of blood substitutes.

Humans↗
PubMedDate not supplied

Leg ulcers in patients with sickle cell disease.

Chronic leg ulcers may result from vasoocclusive complications associated with the decreased oxygen-carrying capacity of hemoglobin in patients with sickle cell disease or its variants. Nonsurgical management includes the use of anti-sickling drugs and chemical manipulation of the hemoglobin composition. It has been suggested that the use of recombinant human erythropoietin (r-HuEPO) may help by stimulating proliferation of red blood cell precursors; it also has been proposed that r-HuEPO may act as a growth factor to non-hematologic tissues. Surgical management is a choice of last resort, often requiring microsurgical techniques, such as free-flap transfer.

Anemia, Sickle Cell↗
PubMed1996

[Quantitative parameters of the arterial bed of the heart].

Structural organization of intraorganic bed was studied in hearts of 5 people who died from extracardiac reasons. Coronary bed was exposed by method of corrosive preparation. Daughter vessels were found to differ significantly and to be smaller in diameter than maternal vessels. Vessel diameter correlates with its length and shape. Regularities of the cardiac arterial bed structural organization mentioned may be used in working out the mathematical model of cardiac arterial system total graph and assessment of its carrying capacity.

Coronary Vessels↗
PubMed1996

Respiratory and circulatory parameters of African elephants (Loxodonta africana) anaesthetised with etorphine and azaperone.

Respiratory rate, heart rate, blood-gas tensions (PO2 and PCO2) and pH of arterial (a) and peripheral venous (v) blood, concentration of haemoglobin in arterial blood (Hb), saturation of arterial haemoglobin with oxygen and the end-expiratory concentration of oxygen were measured in 22 juvenile African elephants (Loxodonta africana) anaesthetised with etorphine and azaperone during a period of 35-65 minutes after they had assumed lateral recumbency. Based on these parameters the alveolar-arterial and arterial-peripheral venous differences of PO2 [P(A-a)O2 and P(a-v)O2 respectively] and oxygen content of arterial blood (CaO2) were calculated. Elephants with body mass of < or = 600 kg showed statistically significant changes in the following parameters, compared with elephants with a body mass of more than 600 kg (x +/- SD): PaO2 (64 +/- 11 versus 82 +/- 8 mmHg), P(a-v)O2 (9 +/- 5 versus 22 +/- 9 mmHg), P(A-a)O2(37 +/- 16 versus 15 +/- 8 mmHg) and Hb (148 +/- 20 versus 130 +/- 10 g/l) (p < 0.05). These findings suggested a tendency towards impaired oxygen exchange in the lungs, reduced peripheral extraction of oxygen and elevated oxygen-carrying capacity of arterial blood in smaller elephants. These changes were theoretically attributed to the respiratory-depressant and sympathomimetic effects of higher dosages of etorphine used in the smaller elephants to maintain a clinically acceptable anaesthetic plane. Individual elephants spent 35-150 minutes under anaesthesia and all recovered uneventfully after reversal of etorphine with diprenorphine.

Anesthesia, General↗
PubMed1997

In vitro effects of a novel hemoglobin-based oxygen carrier on routine chemistry, therapeutic drug, coagulation, hematology, and blood bank assays.

Red blood cell (RBC) replacement solutions are being developed as alternatives to allogeneic RBC use in blood transfusions in the treatment of massive trauma, to achieve hemodynamic stability during elective surgery, and to increase oxygen-carrying capacity in anemia. Hemoglobin-based oxygen carrier (HBOC)-201 (Biopure Corp.) is a purified, sterile, isosmotic glutaraldehyde-polymerized bovine hemoglobin. Because this product is acellular, blood components containing this substance appear hemolyzed. This study reports on the interferences produced by the presence of HBOC-201 in a variety of clinical assays. This product was added in vitro at concentrations up to 60 g/L (6.0 g/dL) to normal human serum, plasma, or whole blood before testing for serum chemistries, coagulation profiles, and hematology and blood bank assays. In addition, a set of normal human sera containing HBOC-201 was supplemented with various therapeutic drugs and assayed for these agents. The results of these studies demonstrate that the presence of HBOC-201 in blood components does not result in significant analytical interference that would be of concern with many clinical assays at HBOC-201 concentrations encountered during routine clinical use of this RBC replacement solution in patients.

Animals↗
PubMed1996

Host response in tumor growth and progression.

Tumor growth and progression result from complex controls that appear to be facilitated by the growth factors (GFs) which emerge from the tumor and find responsive targets both within the tumor and in the surrounding host. For example, basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) are both angiogenic signals which appear to emerge from upregulated genetic messages in the proliferating rim of a solid tumor in response to tumor-wide hypoxia. If these signals are generated in response to unfavorable environmental conditions, i.e. a tumor-wide decrease in oxygen tension, then the tumor may be playing a role in manipulating its own environment. Two questions are raised in this paper: (1) How does the host respond to such signals? (2) Is there a linkage between the host's response and the ultimate growth of the tumor? To answer these questions, we have idealized these adaptive signals within a mathematical model of tumor growth. The host response is characterized by a function which represents the host's carrying capacity for the tumor. If the function is constant, then environmental control is strictly limited to tumor shape and mitogenic signal processing. However, if we assume that the response of the local stroma to these signals is an increase in the host's ability to support an ever larger tumor, then the model describes a positive feedback controller. In this paper, we summarize our previous results and ask the question: What form of host response is reasonable, and how will it affect ultimate tumor growth? We examine some specific candidate response functions, and analyze them for system stability. In this model, unstable states correspond to 'infinite' tumor growth. We will also discuss countervailing negative feedback signals and their roles in maintaining tumor stability.

Animals↗
PubMed1976

A simple method of intraoperative autotransfusion.

A new method of intraoperative blood collection and autotransfusion can be incorporated into an available suction system. It combines systemic heparinization with immediate extracorporeal citrate phosphate dextrose anticoagulation. Analysis of the autologous blood collected and its recipients indicates that it is safe. The preservation of platelets, coagulation factors and erythrocyte oxygen carrying capacity is better in this autologous blood than in homologous banked units. Potential problems of autotransfusion exist, but they are minimized when this system is used.

Blood Preservation↗
PubMed1994

Advances in erythrocyte preservation and hemoglobin substitutes.

The desirability of extending the therapeutic benefits of erythrocyte transfusions beyond the currently available options is well established. Extended frozen storage of rare blood types, hemoglobin-based or artificial blood substitutes for treatment of short-term deficits in oxygen-carrying capacity, novel approaches to tissue oxygenation for cancer therapy, and efficient storage and availability of erythrocytes in military field installations are all potential applications of ongoing research and development efforts. This review explains the need for improvement in erythrocyte storage and development of blood substitutes, the current problems in the field, and the progress made toward solving these problems in the past year.

Animals↗
PubMed1996

Demersal fish assemblages along the Pacific coast of Costa Rica: a quantitative and multivariate assessment based on the Victor Hensen Costa Rica expedition (1993/1994).

During two cruise legs with the RV Victor Hensen (December 1993, February 1994), the demersal fish assemblages of the Golfo de Nicoya (GN), Bahía Coronado-Sierpe Terraba (ST) and Golfo Dulce (GD) areas were assessed from nearshore (approximately 20 m) to shelf edge (approximately 200 m) waters. 44 Beam- and 29 otter trawl collections were made on an area of 2,119,405 m2, yielding a total of 242 species of fish. Despite the lower number of samples taken, more species were collected by the otter trawl (189 compared to 160), due to a wider area swept. As revealed by the species-area curve and a longnormal-curve constructed from the pooled (log) abundance data, the fish assemblage appeared as well sampled and a theoretical species richness (SR) of-306 was estimated for the whole area. Mean species number per collection and mean biomass per area were much lower in the GD-area (9.3 species, 0.36 g/m2) compared to the ST (15.4, 0.81 g/m2) and GN (17.3, 0.74 g/m2) areas, indicating a depauperate fish assemblage in the former. Lowest species numbers and biomass were found in the central deep part of GD with increasing values towards the sill area at the opening of the gulf and towards the shallow stations above the thermocline. Average biomass was an order of magnitude higher in the interior part of GN compared to the other areas with values up to 18.1 g/m2. Based on results of a multivariate analysis of the collections, the GN area can be divided into (1) an interior shallow area above the thermocline (< 50 m) characterized by scianids, sea carfishes, stingrays, flatfishes, sea robins, (2) an outer part (> 100 m) characterized by cods, scorpionfishes, gobies, cutlassfishes, serranids, anglerfishes and flatfishes and (3) a transition zone of the central and lateral parts with a mixed species assemblage with carangids, pufferfish, snappers, several flatfish species and the lizardfish as common elements. Characteristic for the deep basin of GD were small species of the genera Cynoscion and Porichthys. These occurred in low densities, suggesting a reduced carrying capacity of this deep basin for fish biomass in terms of food and oxygen. Species occurring at the shallow stations of GD are also found at a similar depth in the other areas, but many species are missing, namely ariids and many scianids found in the GN area. The species assemblage of the ST area resembles that of GN. Ariids, however, are missing here too. Biotic station parameters like species richness, biomass, abundance and production were not significantly correlated with abiotic parameters (temperature, oxygen, nutrients) suggesting that other habitat factors not evaluated in this study like habitat heterogeneity, distance to the open ocean, current regime and food availability probably are important factors for the structure of the fish assemblage.

Animals↗
PubMed1997

Implant diameter and bone density: effect on initial stability and pull-out resistance.

It is well known that the standard diameter dental implant so often utilized is often inadequate in patients with poor bone quality or quantity, and larger diameter implants have been utilized to overcome this deficiency. The objective of this study was to compare the pull-out resistance of small and large diameter (3.25- and 4.5-mm) dental implants and the relationship of these implants to bone density. Two groups of implants, consisting of 18 implants of each diameter, were placed in the mandibles of five embalmed humans. The bone mineral density of the area surrounding the implant site in the coronal cross section was measured by quantitative computed tomography (QCT). Initial implant stability was tested with a periodontium diagnostic device and pull-out resistance was tested with a mechanical testing system. Results showed the same initial stability for the two implants. The maximum pull-out force required for the large diameter implants was 15% greater than that required for the small diameter implants, although given the small number of samples, this difference was not statistically significant. There were significant positive correlations between the pull-out resistance and the bone density for both the large and small diameter implants (p < 0.05, p < 0.01). We conclude that larger diameter implants appear to have advantages over smaller ones; however, more extensive testing is needed to determine quantitatively the increased load-carrying capacity.

Aged↗
PubMed1998

Accuracy of noninvasive oxyhemoglobin saturation, end-tidal carbon dioxide concentration, and blood pressure monitoring during experimentally induced hypoxemia, hypotension, or hypertension in anesthetized dogs.

OBJECTIVE: To determine reliability of noninvasive methods of arterial oxyhemoglobin saturation (SpO2), end-tidal CO2 concentration (PEtCO2), and blood pressure (BP) determination during periods of hypoxemia and systemic arterial BP perturbations. ANIMALS: 7 healthy, conditioned dogs weighing 19 to 22 kg. PROCEDURE: 3 pulse oximeters, 2 capnometers, and 2 oscillometric BP monitors were used to measure oxygen-carrying capacity of the blood, heart rate, ventilatory status and arterial BP changes during hypoxemia, and altered arterial BP. Pulse oximeter-derived SpO2 and PEtCO2 were determined during rapidly induced plateaus of hypoxia (decreased fractional in-spired oxygen concentration [FiO2]) and altered systemic arterial BP. A lead-II ECG was used to monitor heart rate. RESULTS: Pulse oximetry provided an accurate assessment of fractional oxyhemoglobin saturation (SaO2) at SpO2 > 70%. As SaO2 decreased from 70%, the magnitude of the SpO2 error increased (20% error at SpO2 < 30%). The PEtCO2, was accurate at PaCO2, ranging from 30 to 55 +/- 5 mm of Hg under all experimental conditions. When PaCO2 was > 55 mm of Hg, both capnometers produced values that were as much as 20 mm of Hg less than the corresponding PaCO2. Mean BP was least dependent on pulse wave quality, consistently underestimating mean arterial BP by approximately 10 mm of Hg. CONCLUSIONS AND CLINICAL RELEVANCE: The pulse oximeters tested provided an accurate estimation of SaO2 at SpO2 > 70%. A PEtCO2 value > 55 mm of Hg may represent hypercapnia that is more profound than indicated. Systolic BP determinations were most accurate during hypotensive states and least accurate during hypertension. Diastolic BP measurements were generally more accurate during hypertension than normotension. Accuracy is not appreciably affected by hypotension resulting from vasodilation or blood loss. The tendency to underestimate systemic arterial BP should not interfere with trend detection during unstable clinical conditions.

Anesthesia, General↗
PubMedDate not supplied

Mechanism of the toxic action of carbon monoxide.

Our studies indicate that a high concentration of carboxyhemoglobin (COHb) does not interfere with the O2--carrying capacity of the blood. In dogs, both the transfusion of erythrocytes containing 80 percent COHb and the i.p. injection of carbon monoxide (CO) gas do not produce CO toxicity even though the COHb is above 50 percent. Dogs inhaling CO (13 percent in air) for 15 minutes died within 15 minutes to 65 minutes with an average COHb level of 65 percent. The probable toxic action of CO is on the cellular respiration taking place in the mitochondria when CO competes with O2 for cytochrome a3. The presence of dissolved CO in plasma, which is necessary for CO to enter the tissue, probably occurs when the exchange takes place between alveolar air and the blood in the lungs. When air containing CO is inhaled, there will be a significant CO tension in the blood when it leaves the lungs and when it reaches the organs especially the heart and brain. While COHb level is useful as a clinical measure of CO exposure, the most important mechanism by which CO causes toxicity is its combination with cytochrome oxidase.

Animals↗
PubMed1998

Hypertonic saline resuscitation.

Treatment of severe hemorrhage offers few theoretical problems, but in practice, severe blood loss usually occurs out of hospital, often in more or less inaccessible scenarios. Controversy rages over ideal fluid, ideal volume, and minimum O2 carrying capacity, but all agree that pre-hospital, isotonic resuscitation is unfeasible. The effects of highly hypertonic 7.5% NaCl (HS) was first described in 1980, when we showed that it induced immediate and long lasting hemodynamic restoration. The addition of 6% dextran-70 to (HSD) significantly enhances the duration and intensity of volume expansion, with no loss of hemodynamic effects. HS/HSD restores cardiac output, arterial pressure, base excess and oxygen availability, induce pre-capillary vasodialtion, moderate hyperosmolarity and hypernatremia, reversal of high glucose and lactate. It interferes with endocrine secretions when administered to animals in hemorrhagic hypotension. HS acts through transient plasma volume expansion, positive inotropic effect on cardiac contractility, precapillary vasodilation through a direct action on vascular smooth muscle. Expansion of circulating volume is part of the mechanism, the extra volume coming from the intracellular compartment fluid, especially from endothelial and red blood cells, which facilitate microcirculatory flow. The new field of interactions of hypertonicity with the immune mechanisms may provide insight into the long lasting effects of hypertonic solutions. Randomized double blind prospective studies on the effects of HS, or HSD, used as first treatment of shock show that both are safe and free from collateral, toxic effects. These studies show an early significant rise in arterial blood pressure and a non-significant trend towards higher levels of survival. HSD administration to patients about to undergo cardiopulmonary bypass for cardiac surgery results in higher cardiac output before, and immediately following cardiopulmonary bypass, as well as zero fluid balance.

Animals↗
PubMed1998

Vasoactive properties of synthetic blood substitutes.

There is a great need for the development of a safe and efficient blood substitute, to overcome the important limitations of homologous blood transfusion. Currently available cell-free hemoglobin-based oxygen-carrying solutions present oxygen transport and exchange properties similar to blood and potential benefits over conventional transfusion, including large supply, absence of transfusion reactions, no need for cross-matching, no risk for transmission of disease and long shelf life. Several experimental studies have suggested that cell-free hemoglobin is a vasoactive agent. In animal models of hemorrhagic shock, small doses of cell-free modified hemoglobin restore arterial pressure, promote adequate tissue oxygenation, and improve survival, when compared with fluids with no oxygen-carrying capacity. On the other hand, it has been demonstrated that hemoglobin-induced vasoconstriction may result in decreased cardiac output, reduced blood flow to vital organs and severe pulmonary hypertension. Cell-free hemoglobin solutions cause their pressor effects by binding and scavenging nitric oxide. Although hemoglobin within the red blood cells is the natural scavenger of NO, when the hemoglobin is free in solution, NO is inactivated to a greater extend. Cell-free hemoglobins are on advanced clinical trials, despite the fact that several concerns raised by experimental studies have not been adequately addressed in early clinical trials. The development of a safe and efficient blood substitute depends on the availability of these products for critical evaluation by the scientific community before the widespread clinical use of these blood substitutes.

Animals↗
PubMed1998

Oxygenation of human tumors: the Mainz experience.

Tumor oxygenation is dependent on the cellular O2 consumption rate and on the O2 supply to the respiring cells. The latter is mainly determined by the convective transport via the blood and by the diffusional flux from the microvessels to the O2 consuming sites. Peculiarities of tumor tissue oxygenation can therefore mainly be attributed to characteristic structural and functional abnormalities of the tumor microcirculation (perfusion-limited O2 delivery), to a deterioration of the diffusion geometry (diffusion-limited O2 delivery), and--in some cases--to a reduced O2-carrying capacity of the blood due to tumor-associated anemia. As a result of a compromised and anisotropic microcirculation, the O2 availability to the cancer cells shows great variability, and many human malignancies reveal hypoxic tissue areas which are heterogeneously distributed within the tumor mass and which may be located next to well-perfused tumor areas (intra-tumor heterogeneity). As a rule, in most solid malignancies the tissue O2 status is poorer than in normal tissue at the site of tumor growth. Hypoxia in human tumors per se has been shown to contribute to resistance to standard radiotherapy, chemotherapy and photodynamic therapy with photosensitizing hematoporphyrins. In addition to conferring a direct resistance, hypoxia-induced inhibition of proliferation may also contribute to resistance since both modalities are primarily effective against rapidly dividing cells. Hypoxia in solid tumors, however, has further implications in the clinical setting: Recent data provide strong evidence suggesting that O2 deprived tumor cells are predisposed to a more malignant phenotype, i.e., tumor cells are more likely to be more metastatic and/or invasive. In addition, clonal heterogeneity is more pronounced in hypoxic tumors.

Breast Neoplasms↗
PubMed1999

Computer Simulation Modeling for Recreation Management: A Study on Carriage Road Use in Acadia National Park, Maine, USA.

/ The number of visits to outdoor recreation areas has increased dramatically in the last three decades, leading managers and researchers to wonder if there is a limit to the amount of use a resource such as a park can accommodate. One of the difficulties in addressing this carrying capacity-related question has been the complex nature of visitor travel patterns on often extensive networks of roads and trails. Systematic direct observation is often impractical and anecdotal information is usually inadequate. This study explores the utility of computer simulation as a tool for describing visitor travel by building a dynamic model of visitor travel on the carriage roads of Acadia National Park, Maine, USA. The simulation model uses empirical inputs such as travel routes and travel speeds to generate simulated recreation days on the carriage roads. Data on persons-per-viewscape (PPV) conditions were then gathered from multiple model runs and incorporated into the National Park Service's visitor experience and resource protection (VERP) planning process. Results show that PPV conditions under present-day use levels do not violate proposed standards of quality. Results also show likely PPV conditions under scenarios of increasing use and in different areas within the carriage road system. Goodness-of-fit validity tests indicate the model is an accurate representation of the actual system. The findings of this study suggest that computer simulation is useful for estimating current carrying capacity conditions, predicting future conditions, and guiding related research. KEY WORDS: Computer simulation modeling; Carrying capacity; Recreation management; Acadia National Park

Journal Article↗
PubMed1986

Limitation of Photosynthesis by Carbon Metabolism : I. Evidence for Excess Electron Transport Capacity in Leaves Carrying Out Photosynthesis in Saturating Light and CO(2).

It has been investigated how far electron transport or carbon metabolism limit the maximal rates of photosynthesis achieved by spinach leaves in saturating light and CO(2). Leaf discs were illuminated with high light until a steady state rate of O(2) evolution was attained, and then subjected to a 30 second interruption in low light, to generate an increased demand for the products of electron transport. Upon returning to high light there is a temporary enhancement of photosynthesis which lasts 15 to 30 seconds, and can be up to 50% above the steady state rate of O(2) evolution. This temporary enhancement is only found when saturating light intensities are used for the steady state illumination, is increased when low light rather than darkness is used during the interruption, and is maximal following a 30 to 60 seconds interruption in low light. Decreasing the temperature over the 10 to 30 degrees C range led to the transient enhancement becoming larger. The temporary enhancement is associated with an increased ATP/ADP ratio, a decreased level of 3-phosphoglycerate, and increased levels of triose phosphate and ribulose 1,5-bisphosphate. Since electron transport can occur at higher rates than in steady state conditions, and generate a higher energy status, it is concluded that leaves have a surplus electron transport capacity in saturating light and CO(2). From the alterations of metabolites, it can be calculated that the enhanced O(2) evolution must be accompanied by an increased rate of ribulose 1,5-bisphosphate regeneration and carboxylation. It is suggested that the capacity for sucrose synthesis ultimately limits the maximal rates of photosynthesis, by restricting the rate at which inorganic phosphate can be recycled to support electron transport and carbon fixation in the chloroplast.

Journal Article↗