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At least 19 recordsLinked to original sources
PubMed1967

Radiation of hemocyanin: inactivation and reactivation of oxygen-carrying capacity.

Oxygen-carrying capacity of hemocyanin from Limulus and Busycotypus (Busycon) decreases with increasing radiation, giving initial yield values for G(-O(2),) of 1.1 and 1.0, respectively. High radiation doses regenerate this capacity of Busycotypus hemocyanin. These effects are attributed largely to the dual nature of hydrogen peroxide, which, at low concentrations, oxidizes protein-bound copper and at high concentrations, that is, at high doses, reduces oxidized copper. The ability of hemocyanin to decompose hydrogen peroxide is relatively unaffected by irradiation, which suggests that copper atoms at the active sites are not all equivalent. The catalase-like activity of Busycotypus hemocyanin can be simulated by amino acid chelates of copper, including arginine, histidine, and glycine.

Animals↗
PubMed1997

Use of oxygen-15 to measure oxygen-carrying capacity of blood substitutes in vivo.

A method for determining oxygen-carrying capacity of blood substitutes has been developed using the short-lived cyclotron-produced positron-emitting isotope 15O. This method measures the oxygen-carrying capacity of the blood substitutes in vivo in the presence of red blood cells and allows determination of changes in the oxygen-carrying capacity over time after exchange transfusion. This method is applied to the blood substitutes of liposome-encapsulated hemoglobin (LEH) and cell-free hemoglobin (Hb). We have used 15O (half-life of 2 min) to quantitate the lung uptake and tissue delivery of [15O2]LEH. Lung uptake studies were performed in intubated, catheterized rats after a 40% exchange transfusion of bovine LEH (LEBH; 0.68 g Hb/kg body wt), human hemolysate LEH (LEHH; 1.0 g Hb/kg body wt), or free bovine hemoglobin (SFHS; 0.56 g Hb/kg body wt). A bolus inhalation of 15O2 (3-5 mCi) was given at 15 min, 3 h, and 24 h post-transfusion. Arterial blood samples were collected, spun, and separated into LEH, red blood cell, and plasma fractions. 15O activity and hemoglobin content were determined for each fraction. Oxygen-carrying capacity was calculated as a percentage of the original red blood cell fraction removed. For LEBH, the carrying capacity was 15% at 15 min, 13% at 3 h, and 1% at 24 h. For LEHH, the carrying capacity was 30% at 15 min, 26% at 3 h, and 19% at 24 h. The marked decrease in carrying capacity at 24 h for LEBH compared with LEHH was attributable to the increased formation of methemoglobin in the circulating LEBH rather than increased removal from circulation, because total hemoglobin concentrations measured for both LEH samples decreased at a similar rate during the 24 h. The presence of methemoglobin reductase and other naturally occurring antioxidants in the LEHH may be responsible for maintaining the higher levels of oxyhemoglobin. Oxygen-carrying capacity for SFHS also decreased over time but at a much sharper rate compared with both LEH formulations. The carrying capacity for SFHS of 8% measured at 15 min decreased to 0.3% at 3 h and undetectable levels at 24 h. This sharper decrease in carrying capacity for SFHS is attributable to the rapid removal of the hemoglobin from circulation.

Animals↗
PubMed1999

Experimental critical care in ventilated rats: effect of hypercapnia on arterial oxygen-carrying capacity.

PURPOSE: We have previously demonstrated an increased arterial O2-carrying capacity in normal ventilated dogs subjected to both acute and prolonged exogenous hypercapnia. In the present study, we tested if arterial hypercapnia, during controlled ventilation, can increase O2-carrying capacity also in rats. MATERIALS AND METHODS: Twenty young male Sprague Dawley rats were anesthetized (60 mg/kg pentobarbital), tracheostomized, intubated, and one femoral vein and artery were cannulated. Anesthesia and paralysis were maintained using 15 mg/kg/h pentobarbital intravenously, and 2 mg/kg/h vecuronium bromide. The fluid balance (5 mL/kg/h saline), normothermia, and minute volume were maintained. The mean arterial blood pressure and heart rate were continuously monitored. Experiments included the following: (1) a control group, ventilated with normoxic air for 150 minutes (n = 5); (2) mild hypercapnia, a group of eight rats ventilated with normoxic air for 30 minutes and then ventilated with a mixture of normoxic air at 60 mm Hg CO2 (8 kPa) for 1 hour; and (3) severe hypercapnia, a group of seven rats were treated exactly as in group II, except a 90 mm Hg (12 kPa) CO2 during hypercapnia. Gas-exchange profile, arterial hemoglobin (Hb) concentration, arterial Hb-oxygen saturation (Hb-O2), and arterial O2 content were periodically determined during normocapnia and 1 hour of hypercapnia. RESULTS: Exposures to mild and severe hypercapnia, in rats with maintained ventilation, significantly reduced the arterial O2 content by 20% and 33%, respectively, without significant changes in the arterial Hb concentration (-2%). Severe hypercapnia generated a significant reduction of -14% in the PaO2, but not in PaO2/ FiO2 ratio. CONCLUSION: Rats subjected to controlled ventilation and permissive hypercapnia, unlike dogs and perhaps humans, show no augmentation of Hb concentration. Hypercapnia in rats also provokes much stronger Bohr effect than in dogs. Hypercapnia-induced Bohr effect in rats is accompanied with extreme desaturations of Hb-O2, and substantial reduction in the O2-carrying capacity. We speculate that the strong hypercapnia-induced Bohr effect in rats may prevent hypoxia at the tissue level. However, to maintain a stable oxygen-carrying capacity in rats used for pulmonary critical care studies with hypercapnia, we suggest to use hyperoxia, with or without a mild hypothermia.

Analysis of Variance↗
PubMed2002

Carrying capacity as "Informed Judgment": the values of science and the science of values.

Contemporary park and wilderness carrying capacity frameworks rely on formulation of standards of quality, which are defined as minimum acceptable resource and social conditions. Formulation of standards of quality involves elements of both science and values, and both of these elements must be integrated into informed judgments on the part of park and wilderness managers. That is, managers must ultimately make value-based judgments about the maximum acceptable level of visitor-caused impacts to the resource base and the quality of the visitor experience. However, such judgments should be as informed as possible by scientific data on the relationships between visitor use and resulting impacts and the degree to which park and wilderness visitors and other interest groups judge such impacts to be acceptable. Such information represents the "values of science" to managing carrying capacity in parks and wilderness. A growing body of literature has begun to address the corresponding "science of values," and how this type of information might be integrated in park and wilderness management. Visitor-based research has employed normative theory and techniques to explore the acceptability of a range of resource and social impacts related to visitor use, and findings from these studies are being integrated into a body of knowledge and applied in management decision-making. Conceptual and methodological extensions of the normative approach are currently being explored in a variety of park and wilderness contexts, and new theoretical and empirical approaches are being adapted to address trade-offs inherent in carrying capacity. In these ways, the science of values is progressing to meet the opportunities and challenges of the values of science to park and wilderness management. The concept of carrying capacity, along with the theoretical and methodological approaches described in this paper, can be extended to a large number of natural resource and environmental issues.

Conservation of Natural Resources↗
PubMed1995

Deviation from the carrying capacity for physicians and growth rate of physician supply: the Taiwan case.

This study applies the theory of carrying capacity to examine the effects of market forces on the location pattern of physicians in Taiwan between 1974 and 1982. The data for the analysis were collected from governmental publications. The township was selected as the geographic unit of analysis. By using a regression model of physician supply, this study developed a proxy for physician carrying capacity and a deviation indicator to classify townships as attractive or unattractive. The results of this study indicate that: (1) within attractive townships, the greater the deviation from physician carrying capacity, the faster the growth rate of the physician-population ratio; (2) the overall pattern of the growth rate is quite similar across different sizes of townships; and (3) due to a loss of population, unattractive townships do not necessarily have the lowest growth rates of the physician-population, unattractive they gain few physicians. This study thus concludes that market forces are powerful in determining the physician distribution.

Economic Competition↗
PubMed1985

Hemodynamic and metabolic responses of the working heart in relation to the oxygen carrying capacity of the perfusion medium.

Hemodynamic and metabolic adaptations of isolated working heart perfused alternatively with normal or low oxygen carrying capacity medium were studied in an experimental model. A step change in arterial oxygen content (1.75 to 15.3 ml O2/100 ml) was followed by a decrease in coronary flow, an increase in aortic flow, external work, myocardial oxygen consumption and efficiency, respectively. Metabolic investigations (steady state values) showed the activities of both glycolysis and the Krebs cycle to increase with the oxygen carrying capacity of the perfusion medium. Within the limits of these aerobic conditions, most of the cardiac changes were reversible. The use of reconstituted blood provides physiological conditions of oxygenation, allows a dynamic equilibrium between oxygen supply and oxygen requirements and maintains a near physiological regulation between cardiac dynamic and metabolic functions. These conclusions stress the importance of optimal O2 carrying capacity of perfusion medium in metabolic studies on isolated working heart.

Aerobiosis↗
PubMed1994

Ventilatory responses to hypoxia in the toad Bufo paracnemis before and after a decrease in haemoglobin oxygen-carrying capacity.

The ventilatory and cardiovascular effects of a decreased O2-carrying capacity of the blood were evaluated in the toad Bufo paracnemis. Pulmonary ventilation was monitored using a pneumotachographic technique. Chronic arterial catheters served to record both cardiac frequency and blood pressure and enabled the withdrawal of blood samples for analysis of pH and partial pressure of O2 (PO2). Haemoglobin concentrations were determined by the cyanmethaemoglobin method. The ventilatory response to hypoxia was not affected by the reduction in blood O2-carrying capacity, which suggests that PO2 rather than O2 content is the regulated variable. The reduction in capacity is accompanied by an increased normoxic heart rate and by a reversal of the hypoxic tachycardia normally observed.

Animals↗
PubMed1994

On the carrying capacity for large ungulates of African savanna ecosystems.

The effect of pastoral management on the standing crop biomass of large ungulates, an index of carrying capacity, is analysed at a regional level by using data compiled from published sources covering east and south Africa. The effect of primary production is controlled for by using two environmental factors, rainfall and soil nutrient availability, and the effect of species richness of the ungulate community is evaluated. The results confirm the dominant effect of rainfall, and demonstrate that soil nutrient levels also strongly affect the biomass of large ungulate communities. For a given level of rainfall, on rich soils (high nutrient availability) the biomass of large ungulates is about 20 times as great as on poor soils with low nutrient availability. The model based on rainfall and soil nutrient classes accounts for 87% of the variance in large ungulate biomass. Pastoral and natural ecosystems do not differ significantly in large ungulate biomass; there is therefore currently no evidence that extensive pastoral management increases carrying capacity for large ungulates above the levels observed in natural communities. Species richness, a measure of biodiversity, had a significant but very small effect on the biomass-rainfall relation in the complete data set. When analysed by pastoral management, the effect of this factor was significant for the set of natural ecosystems only. Pastoral management and species richness may therefore have compensatory effects. These results suggest that the carrying capacity is limited at the community, rather than the species, level.

Africa↗
PubMed1995

Population growth and earth's human carrying capacity.

Earth's capacity to support people is determined both by natural constraints and by human choices concerning economics, environment, culture (including values and politics), and demography. Human carrying capacity is therefore dynamic and uncertain. Human choice is not captured by ecological notions of carrying capacity that are appropriate for nonhuman populations. Simple mathematical models of the relation between human population growth and human carrying capacity can account for faster-than-exponential population growth followed by a slowing population growth rate, as observed in recent human history.

Culture↗
PubMed2002

Estimating carrying capacity in a newly colonized sand fly Lutzomyia serrana (Diptera: Psychodidae).

The phlebotomine sand fly Lutzomyia serrana (Damasceno & Arouck) was mass-reared tinder conditions of varying densities in an effort to improve colony production efficiency. To do this, the experimental carrying capacity of a standard rearing chamber was determined, i.e., the optimum population size in relation to density (individuals per unit of space). Rearing chambers of 100 cm3 were populated with 1-50 L. serrana engorged females and an equal number of males. Laboratory conditions were maintained at 23-26 degrees C and 85-95% RH. The following parameters were recorded for each experimental chamber (three replicates): (1) female mortality without oviposition, (2) number of eggs oviposited and (3) number of adults emerging from the egg cohort. Female mortality began to increase substantially in the 26-female chamber, from 5.7% to 15% and finally reaching 60.2% in the 46-50 female chambers. In the chambers containing 1-20 females, egg number and realized adult progeny increased linearly to reach an asymptote. In the 20-50 female chambers, the number of eggs ranged from 420 to 699, and adult production from 306 to 432. The optimum carrying capacity for the 100-cm3 chambers was 22 +/- 2 females. Beyond this number, auto-regulation was initiated, i.e., female mortality without oviposition increased as the number of females per chamber increased. Total number of eggs and adult production was similar in all chambers containing 20-50 females. In conclusion, for optimizing production of mass reared sand flies, determination of the carrying capacity is essential to optimize use of insectary resources, to avoid loss of valuable potentially ovipositing females, and to increase overall production efficiency.

Animals↗
PubMed2001

Shear-load carrying capacity of cancellous bone after implantation of self-reinforced polyglycolic acid and poly-L-lactic acid pins: experimental study on rats.

Both distal femora of 40 rats were implanted with a self-reinforced polyglycolic acid (SR-PGA) pin in the right femur and with a self-reinforced poly-L-lactic acid (SR-PLLA) pin in the left femur. The intact femora of 20 rats served as controls. The follow-up times were 1, 3, 6, 12, 24, 36, 48, and 52 weeks. After killing all operated and control femora were examined macroscopically and radiographically. The shear-load carrying capacities of all the femurs were investigated, and the SR-PGA and SR-PLLA fixed specimens were compared with each other and with the control specimens. The shear-load carrying capacities reached their highest values at 36 weeks in the SR-PGA and SR-PLLA fixed and control specimens. Thereafter they gradually decreased. At 52 weeks both the SR-PGA fixed specimens and the control specimens had statistically significantly (p < 0.001) higher values than the SR-PLLA fixed specimens, when the influence of the pins had ceased. Otherwise, the shear-load capacities showed higher values in the SR-PLLA fixed specimens, as the pins carried the load. During the whole follow-up period the mean shear-load carrying capacity of the SR-PGA fixed specimens was 171.2 N and that of the SR-PLLA fixed specimens 180.9 N, the corresponding value of the control specimens was 148.2 N.

Animals↗
PubMed1986

The promotion of catecholamine release in rainbow trout, Salmo gairdneri, by acute acidosis: interactions between red cell pH and haemoglobin oxygen-carrying capacity.

A fall in blood pH was generated either by infusion of HCl or by reducing gill ventilation and raising blood PCO2 in rainbow trout, Salmo gairdneri Richardson. The acute acidosis resulting from HCl infusion caused an increase in plasma adrenaline and noradrenaline concentrations, the adrenaline increase being proportional to the decrease in blood pH. Fish subjected to a prolonged respiratory acidosis, caused by a reduction in gill ventilation, showed no increase in catecholamines 24 h after the change in gill ventilation. We suggest that catecholamine levels increase in response to a pH decrease, but if acidotic conditions are maintained, circulating catecholamines return to low levels. There was a much smaller decrease in erythrocytic pH with a fall in plasma pH when catecholamine levels were high. This ameliorating effect of catecholamines on erythrocytic pH during a plasma acidosis maintains the oxygen-carrying capacity of the haemoglobin. If erythrocytic pH was decreased by increasing blood PCO2 in vitro, then there was a fall in haemoglobin oxygen-carrying capacity which was proportional to the reduction in pH. We conclude that catecholamines are released into the blood in proportion to the fall in blood pH but if the pH is maintained the circulating catecholamines return to their initial low levels. The elevated catecholamine concentrations in blood safeguard against any impairment of haemoglobin oxygen-carrying capacity by maintaining erythrocytic pH in the face of a plasma acidosis.

Acidosis↗
PubMed1998

Oxygen carrying capacity and oxygen supply rate of artificial oxygen carrier, Neo Red Cell (NRC).

Neo Red Cell (NRC), which is the liposome encapsulated hemolysate, has been developed as an artificial oxygen carrier. Oxygen carrying capacity and oxygen supply rate of NRC were estimated by continuous measurement of dissolved oxygen concentration in a spinner vessel. Oxygen carrying capacity of the medium was risen by adding NRC. The oxygen supply rate of the NRC medium containing hepatocytes was determined by the oxygen consumption rate of hepatocytes. The addition of NRC gave no effect on the oxygen transfer rate from gas phase to liquid phase (or kL a value) of the solution in the spinner vessel. The rate of oxygen absorption to NRC was limited by the oxygen transfer rate from gas phase to liquid phase in the spinner vessel. These results indicate that the oxygen supply from NRC may sustain the high-density culture of mammalian cells.

Air↗
PubMed2000

Oxygen-carrying capacity during 10 hours of hypercapnia in ventilated dogs.

OBJECTIVE: To test if a relatively long-term exogenous hypercapnia, equivalent to those maintained during permissive hypercapnia, can persistently increase oxygen-carrying capacity in ventilated dogs. DESIGN: Prospective study. SETTING: Research laboratory in a hospital. SUBJECTS: Six mongrel dogs (3 males; 3 females). INTERVENTIONS: The dogs were anesthetized (30 mg/kg pentobarbital, i.v.), intubated, and cannulated in one femoral artery, one femoral vein, and the right jugular vein. The mean arterial blood pressure, heart rate, and mean pulmonary artery pressure were continuously recorded. Anesthesia, fluid balance, and normothermia were maintained. Arterial hypercapnia was generated by the addition of 60 torr dry CO2 (8 kPa) to the inspired air for 10 hrs, continuously. All subjects were paralyzed (vecuronium bromide) and ventilated with room air, while the ventilator settings were kept constant. MEASUREMENTS AND MAIN RESULTS: Arterial and venous gas exchange profiles, hemoglobin concentration, oxygen saturation, oxygen content, cardiac output, and oxygen consumption were determined, before, during, and after 10 hrs of hypercapnia, periodically. Both hemoglobin concentration and oxygen content were gradually increased during hypercapnia and reached significant levels at 8 and 10 hrs of hypercapnia, respectively. These increases continued up to 2 hrs after termination of hypercapnia. The PaO2/FIO2, as an index of arterial oxygenation, was significantly increased during the first 3 hrs of hypercapnia and then remained at the normoxic level up to 10 hrs of hypercapnia. No significant changes occurred in the mean arterial blood pressure and oxygen consumption. The heart rate and cardiac output were significantly reduced at 4 and 8 hrs of hypercapnia, respectively. The mean pulmonary artery pressure was increased throughout the hypercapnic trial. CONCLUSIONS: A relatively long-term exogenous hypercapnia can significantly increase oxygen-carrying capacity in normal ventilated dogs. Whether this effect can occur during permissive hypercapnia because of controlled ventilation in patients warrants investigation.

Animals↗
PubMed2000

Predicting the time to quasi-extinction for populations far below their carrying capacity.

Populations threatened by extinction are often far below their carrying capacity. A population collapse or quasi-extinction is defined to occur when the population size reaches some given lower density. If this density is chosen to be large enough for the demographic stochasticity to be ignored compared to environmental stochasticity, then the logarithm of the population size may be modelled by a Brownian motion until quasi-extinction occurs. The normal-gamma mixture of inverse Gaussian distributions can then be applied to define prediction intervals for the time to quasi-extinction in such processes. A similar mixture is used to predict the population size at a finite time for the same process provided that quasi-extinction has not occurred before that time. Stochastic simulations indicate that the coverage of the prediction interval is very close to the probability calculated theoretically. As an illustration, the method is applied to predict the time to extinction of a declining population of white stork in southwestern Germany.

Animals↗
PubMed2002

PEG and DBBF modified porcine hemoglobin and their oxygen-carrying capacity.

Modifications of proteins with polyethylene glycol (PEG) have been proven to enlarge molecule size of proteins, to prolong their retention time in the circulation as well as blunt immune or allergic reactions. Hemoglobin cross-linked with small molecular modifiers turns out to be more stable and to have better oxygen carrying capacity. In the present study, four derivatives of PEG with different activation groups, and several PEGs with different molecular weights were covalently bound to porcine hemoglobin (pHb). PEG-pHbs exhibited a variety of differences in their properties depending on the molecular weights of the used PEGs, the amounts of bound PEGs and the presence or absence of allosteric cofactors. The optimal modification conditions for bis (3, 5-dibromosalicyl) fumarate (DBBF) as well as the physical features and oxygen carrying capacity of DBBF-modified pHb were evaluated. Furthermore, both PEG and DBBF were used simultaneously to modify pHb. The results indicate that the pHbs modified with PEG and DBBF have more stable tetrameric conformations with a molecular weight of 107 kD. Their oxygen half-saturation pressure (P(50)) is around 3.33 kPa which approximates the physiological P(50) of human red blood cells.

Animals↗
PubMed2000

Load-carrying capacity of the human cervical spine in compression is increased under a follower load.

STUDY DESIGN: An experimental approach was used to test human cadaveric cervical spine specimens. OBJECTIVE: To assess the response of the cervical spine to a compressive follower load applied along a path that approximates the tangent to the curve of the cervical spine. SUMMARY OF BACKGROUND DATA: The compressive load on the human cervical spine is estimated to range from 120 to 1200 N during activities of daily living. Ex vivo experiments show it buckles at approximately 10 N. Differences between the estimated in vivo loads and the ex vivo load-carrying capacity have not been satisfactorily explained. METHODS: A new experimental technique was developed for applying a compressive follower load of physiologic magnitudes up to 250 N. The experimental technique applied loads that minimized the internal shear forces and bending moments, loading the specimen in nearly pure compression. RESULTS: A compressive vertical load applied in the neutral and forward-flexed postures caused large changes in cervical lordosis at small load magnitudes. The specimen collapsed in extension or flexion at a load of less than 40 N. In sharp contrast, the cervical spine supported a load of up to 250 N without damage or instability in both the sagittal and frontal planes when the load path was tangential to the spinal curve. The cervical spine was significantly less flexible under a compressive follower load compared with the hypermobility demonstrated under a compressive vertical load (P < 0.05). CONCLUSION: The load-carrying capacity of the ligamentous cervical spine sharply increased under a compressive follower load. This experiment explains how a whole cervical spine can be lordotic and yet withstand the large compressive loads estimated in vivo without damage or instability.

Cadaver↗
PubMed2001

Assessment of newly developed perfluorocarbon emulsion: oxygen carrying capacity as the blood substitute in vivo.

This study provides the evaluation of oxygen carrying capacity of the novel perfluorocarbon emulsion (Neo-PFC) produced by the new emulsifying technology named High Pressure Process. For the performance comparison of oxygen carrying abilities of Neo-PFC and a representative PFC emulsion, the oxidation states of cerebral tissues in substituted animals were measured by near-infrared spectrometry. After the 70% exchange transfusion of whole blood of rats by Neo-PFC and Fluosol-DA, fractional inspired oxygen (FiO2) was gradually decreased from 100% to 0%. As the control experiments, the blood was substituted by Krebs Ringer bicarbonate buffer containing 3% BSA. When the blood of rats was substituted by Neo-PFC, Cyt. ox., a terminal enzyme in mitochondrial respiratory chain maintained fully oxidized state with FiO2 values between 100 to 40%. By contrast, in the models substituted by Fluosol-DA and BSA-buffer. Cyt. ox. was gradually reduced with FiO2 values below 60% and 80%, respectively. This specific advantage of Neo-PFC was explained by its higher oxygen solubility in arterial blood. The novel PFC emulsion prepared by the new emulsifying technology is a potential basis for blood substitutes.

Animals↗