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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↗
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↗
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↗
PubMed1988

Experimental evaluation of the antibiotic carrying capacity of a muscle flap into a fibrotic cavity.

A study was undertaken to determine the antibiotic carrying capacity of a transferred muscle flap into a fibrotic cavity using a tissue cage model in rabbits. Blood and chamber fluid antibiotic levels were determined after intramuscular hindlimb gentamicin injection up to 56 days following muscle transfer. This study suggests that muscle flaps increase the concentration of antibiotics that can be achieved within a fibrotic cavity. The measurable peak level decreases with time, probably due to increased scarring around the muscle. This model should enable the study of many different classes of antibiotics with different protein binding and other administration schedules using multiple timed doses or a combination of agents.

Animals↗
PubMed1994

Subsistence ecology and carrying capacity in two Papua New Guinea populations.

This article examines the mechanisms of subsistence adaptation of two Papua New Guinea populations, the Metroxylon sago-depending lowland Gidra and the taro-monoculture Mountain Ok, surviving in low population densities of 0.5 and 1.4 persons per km2. Observation of the groups' land use systems strongly suggests that their population densities have not been far below the carrying capacity, although the territory of each population is markedly heterogeneous. Both groups have maintained their sustainable food production not only for resource management but also for survival at a population level, either expanding their territory or changing the sustainable level in tandem with changes of subsistence system.

Adult↗
PubMed1978

[The load carrying capacity of the teeth of the human jaw].

Three different methods of measurement are used to objectify the maximum load-carrying capacity of individual pairs of teeth. For these, use is made of a mechanical, electric, and elastooptic measuring instrument. The measurement results obtained using the mechanical and electric instruments are largely identical. They are in the neighborhood of 20 kgf and 50 kgf for incisors and molars, respectively, of male subjects. The results obtained for female test subjects were lower by an average of 10 kgf. The mechanical and electric measuring instruments may be used for the examination of a larger number of test subjects as well as under pathological conditions.

Dental Stress Analysis↗
PubMed1982

[Experimental investigations of the axial load carrying capacity of the long bones using Steinmann-pins (author's transl)].

This paper reports the results of experimental investigations of the axial load carrying capacity of the long human bones. These investigations were conducted using a commercial high precision materials testing machine. Force-transmission was effected by Steinmann-pins or screws drilled transversely into the various long bones. The measured loading capacities are reported for various sections of the long bones. Their importance in regard to biomechanics, application and dimensioning of compression osteosyntheses by external fixation is discussed in length.

Bone Nails↗
PubMed1993

[Oxygen carrying capacity of totally artificial red cell substitute--liposome embedded heme--in hemorrhagic beagle dogs].

Liposome embedded heme (L/H) was produced by embedding synthesized lipid-heme in liposomes. The oxygen carrying capacity of this totally artificial oxygen carrier was evaluated in dogs. Under controlled ventilation, 30ml/kg of blood was drawn. Thirty minutes after bleeding, 30mg/kg of the L/H solution was intravenously injected in group I (n = 6) and the same volume of normal saline solution was injected in group II (n = 7). No transfusion was performed in group III (n = 7). In group I, mixed venous O2 tension (PvO2), O2 transport (TO2) and O2 consumption (VO2) increased significantly compared with those observed before injection of the L/H (p < 0.05). PvO2 kept higher level compared with group II until 90 minutes after injection of the L/H (p < 0.05). Following the L/H injection, TO2 by the dogs' Hb was 187ml/min and that by the L/H was 43ml/min. VO2 from the dogs' Hb was 51ml/min and that from the L/H was 16ml/min. Thus TO2 by the L/H provided 19% of the total TO2 and VO2 from the L/H provided 24% of the total VO2. Thus, this exchange transfusion experiment show that the L/H has ability as an oxygen carrier to bind and to transport oxygen to the tissues.

Animals↗
PubMed1989

An investigation into the role of porcelain thickness in determining the load-carrying capacity of porcelain laminates.

The effect of specimen thickness on the strength of dental porcelain has been investigated. It has been shown that for core, dentine and combinations of these porcelains, the shell strength decreases with increasing thickness. Consequently, the load carrying capacity does not increase as much as might be expected with thicker sections. Possible reasons for this phenomenon and methods of limiting this effect are discussed.

Dental Porcelain↗
PubMed1992

The role of oxygen-carrying capacity in myocardial ischemia.

Myocardial ischemia results when myocardial oxygen demand exceeds oxygen supply. The oxygen content of blood is only one of several interdependent variables influencing myocardial oxygen supply. The impetus for assessing the contribution of the oxygen content of blood to myocardial ischemia, and thus the need to treat anemia, stems from current concern about the risks associated with blood transfusion and the recognition that hemodilution has protean effects on the oxygen-carrying capacity of blood. The rheological changes that accompany hemodilution favorably influence the delivery of oxygen to the tissues and have the capacity to at least partially compensate for the decrease in blood oxygen content during hemodilution. However, nonrheological compensatory mechanisms (e.g., cardiac effects) also influence oxygen delivery and may profoundly influence the adequacy of tissue oxygenation. Furthermore, occlusive vascular lesions that restrict blood flow to the tissues also profoundly influence tissue oxygenation. The evidence in the myocardium and in systemic tissues indicates that considerable degrees of normovolemic hemodilution are well tolerated in physiological settings. In contrast, coexisting disease such as coronary artery stenosis may limit the patient population that benefits from normovolemic hemodilution. Unfortunately, well-controlled prospective studies of normovolemic hemodilution in patients with severe vascular or cardiac disease have not yet been conducted. As we progress to that point, it will be especially important to critically examine studies that use anesthetized or revascularized preparations. Results obtained under controlled conditions of hemodilution may not apply to postoperative anemia in awake patients with coronary artery disease who are experiencing the stress of surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1981

[Oxygen tension in skeletal muscle in patients with reduced O2-carrying capacity (author's transl)].

In 10 patients (age: 31--72 years) oxygen supply of skeletal muscle was measured by pO2-multiwire technique. All patients suffered from chronic renal failure of differing etiologies and from chronic renal anemia. In muscle tissue 1,128 different O2-tensions were registered and the results were expressed as pO2-histograms. Seven of these pO2-histograms show a normal distribution, three are shifted to the left to lower O2-tensions. Therefore the microcirculation in the skeletal muscle of patients with chronic reduced O2-carrying capacity is largely undisturbed. The microcirculation is able to increase with exercise as shown by a shift to the right in the PO2-histogram. The use of the pO2-multiwire electrode is largely devoid of risk to the patient. Important pathological features may be demonstrated.

Carbon Dioxide↗
PubMed1982

The effect of changes in blood oxygen-carrying capacity on ventilation volume in the rainbow trout (Salmo gairdneri).

1. Changes in ventilation volume (Vg) of rainbow trout caused by hypercapnia, hypoxia and anaemia were measured directly by collection of expired water. 2. Exposure to hypercapnic water (PCO2 range 0.5-2 kPa) increased Vg (by up to four times) by augmenting ventilatory stroke volume; breathing frequency remained constant. O2 added to the inspired water in maintained hypercapnia reduced Vg at all but the highest level of PCO2. 3. Vg increased when blood oxygen content was decreased by exposure to normoxic hypercapnia, but addition of O2 to the water increased blood oxygen content and Vg decreased. 4. When blood oxygen-carrying capacity was depressed by hypoxia or anaemia, Vg increased as it did during normoxic hypercapnia. 5. We suggest that ventilatory responses to low levels of hypercapnia, to hyperoxic hypercapnia, to hypoxia, and to anaemia in trout are related to changes in levels of blood oxygen content under these conditions.

Anemia↗