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PubMed1994

Psychophysically acceptable weights for a combination lifting task using bags with handles.

This paper presents a study on a combination lift and lower manual handling task and was designed to simulate the loading of grocery bags into a car trunk. Twelve male subjects performed an externally paced task of lifting grocery bags loaded with weights from 15 cm above the floor and over a wooden sill. There were two different sill heights of 70 cm and 90 cm, and for each of these heights there were two frequencies of 3 and 6 lifts per cycle. The dependent variables were maximum acceptable weight of lift (MAWOL). A unique lifting sequence and a modified version of the psychophysical methodology were used to determine MAWOL. There was a significant difference in the MAWOL across the two sill heights as well as the MAWOL at the two different frequencies. Plastic bags were determined to increase the average load lifted by 27% as compared to paper bags. At normal grocery bag weights, the increased load carrying capacity represents an increase in the safety factor. Not only can the risk of lower back injuries be decreased by using plastic bags with handles but the risk of developing a cumulative trauma disorder could also be decreased.

Adult↗
PubMed1994

[Cardiorespiratory management of severe injured patients in intensive care units].

Late mortality of severely injured patients could be prevented by the quality of early cardiorespiratory management. Indeed traumatized patients with high risk of multiple organ failure (according to age, ISS, amount of blood transfused, and/or metabolic acidosis) need a pulmonary artery catheterization as soon as possible (postdefinitive phase: during the surgical period or at the admission in the ICU). Such a procedure allows the intensivist to determine therapeutic goals in term of O2 delivery (DO2) and O2 uptake (VO2) in front of a frequent increased peripheral O2 demand, These goals (usually DO2 > or = 600 ml.min-1m-2 and VO2 > or = 150 ml.min-1.m-2) may be reached by the combination of prolonged mechanical ventilation (adapted to the pulmonary status), subnormal O2 carrying capacity (hematocrite between 30 and 35% in the absence of persistent bleeding), and increased cardiac output through an additional volume loading (without an excessive positive cumulated fluid balance on the second posttraumatic day) and the early administration of inotropic drugs (dobutamine). Reaching these goals usually permits a 61% reduction in the posttraumatic incidence of organ failure.

Critical Care↗
PubMed1994

Regulation of erythropoietin production. New insights into molecular mechanisms of oxygen homeostasis.

EPO plays a key role in O2 homeostasis by regulating blood O2-carrying capacity. The EPO gene is expressed in fetal liver, whereas after birth the kidney becomes the predominant site of synthesis. Transgenic studies indicate that EPO expression in postnatal liver is repressed via DNA sequences that are distant from the gene. Expression in postnatal kidney is dependent upon sequences located between 6 kb and 14 kb 5' to the transcription initiation site. Additional sites of low-level EPO synthesis have been identified, but the functional significance of these observations is unknown at the present time. Modulation of transcription by changes in cellular O2 tension has been studied in the hepatic cell lines Hep3B and HepG2. A kidney-derived cell line in which EPO expression is regulated by O2 tension has not been established. A hypoxia-inducible enhancer, identified in the EPO 3'-flanking sequence, contains binding sites for several transcription factors, including HIF-1, a factor whose DNA-binding activity is induced by hypoxia. Binding of HIF-1 is required for EPO transcriptional activation in response to hypoxia. HIF-1 binding sites are also present in the EPO promoter, which may also play a role in hypoxia-inducible transcription. Binding sites for members of the nuclear hormone receptor superfamily are also present in both the promoter and enhancer. The hypoxia signal-transduction pathway leading to EPO transcriptional activation has not been established. Two hypothetical mechanisms of O2 sensing are oxy-deoxy conformational changes of a hemoprotein and the production of reactive O2 species from molecular O2. HIF-1 activity is induced in a variety of cell types, and in all cell types a single signal transduction pathway appears operative, but its nature is undefined. Moreover, genes encoding glycolytic enzymes are transcriptionally activated in hypoxic cells via a similar mechanism, including the binding of HIF-1 to promoter and enhancer elements. Thus, the molecular mechanisms by which EPO transcription is regulated may also be utilized to control the expression of other genes responsible for cellular and systemic O2 homeostasis.

Animals↗
PubMed1994

Transfusion therapy in autoimmune hemolytic anemia.

Autoimmune hemolytic anemias include warm and cold reactive autoimmune hemolytic anemias (WAIHA and CAD), paroxysmal cold hemoglobinuria (PCH), and drug-induced hemolytic anemias. If autoimmune hemolytic anemia is suspected, the clinical history should be communicated to the transfusion service, because specific tests to confirm these diagnoses are not routinely performed. This includes evaluation of the patient's RBCs for bound IgG and complement (direct antiglobulin test) and evaluation of the patient's serum for antibodies with RBC specificity. For warm or cold autoimmune hemolytic anemia, special procedures including autoabsorption may be necessary to identify underlying RBC alloantibodies prior to transfusion. Transfused RBCs may not have normal survival in patients with RBC autoantibodies. The decision to transfuse should consider the patient's need for oxygen-carrying capacity, the risk of withholding transfusion, and the potential benefit of alternative therapy.

Anemia, Hemolytic, Autoimmune↗
PubMed1995

Recruitment-driven, spatially discontinuous communities: a null model for transferred patterns in target communities of intestinal helminths.

Populations and therefore communities of intestinal helminths of vertebrates are fueled by recruitment of new individuals from outside the host. The source of new individuals is often an intermediate host that harbors several infective propagules of 1 or more species. Hence these source communities are transmitted in packets of infective propagules to target communities in definitive hosts. Packets not only provide recruits to target communities, but, because a packet of propagules possesses its own structure, it may also transmit structure to the target community. We use this system to examine the contribution that structure in the source pool of propagules makes to the structure of recruitment-driven target populations and communities. By treating the dynamics of such target populations and communities as immigration-death processes, we conclude: (1) Unlike a birth-driven population a recruitment-driven target population will grow to an asymptotic limit even in the absence of density-dependent processes or reaching carrying capacity; (2) the frequency distribution of the number of recruits entering target populations will determine the frequency distribution of adults in target populations; (3) interspecific associations among species in the source community will be transmitted to target communities, but the magnitude of the transmitted associations will depend upon the relative survival rates of the species; and (4) for associations of equal magnitude in a source community, the magnitude of a transferred negative association will be less than the magnitude of a positive association in a target community. Two examples of source communities in salt marsh crabs reveal that source infracommunities exist with the hypothesized structure. Further, the source helminth communities display a greater number of positive than negative interspecific associations. The inequity in transfer and the existence of a greater proportion of positive associations in source communities may explain the widespread occurrence of excess positive associations that has been noted in recruitment-driven communities.

Animals↗
PubMed1994

Global environmental change and human health: new challenges to scientist and policy-maker.

Human health may not remain sustainable if damage to the global environment continues. The argument is simple: Earth is essentially a closed system; humans are proliferating and commandeering more surface area, food and energy; the resultant accumulation of waste gases, depletion of soil and water, and loss of biodiversity is starting to overload Earth's carrying capacity. There are limits in any closed system and our species is now pressing against some of them. These are new problems and we cannot be certain of the consequences for human health. A warmer world will probably have more frequent heatwaves, unstable weather, increased spread of mosquito-borne infectious diseases, and disruptions to agriculture. Ozone depletion, if sustained, may cause moderate increases in skin cancer and cataracts, and may damage crop growth and marine stocks. Depletion of agricultural resources, overfishing, and loss of genetic resources from species extinction all entail potentially serious consequences for human health. The manifest uncertainties of these global change processes and the need for prediction, rather than empirical observation, create new challenges to health scientists. Likewise, policy-makers will have to deal with best estimates and long time-frames, informed by understanding of ecological realities.

Environmental Health↗
PubMed1976

Cryobiology overview of red cell preservation: achievements and prospective.

Preserved red cells are transfused to improve the delivery of oxygen to tissue. The preserved red cells must circulate to increase the red cell volume and improve the oxygen carrying capacity. The correlation between oxygen transport function and the red cell 2,3 DPG level has been known since 1967. but it was only recently that the importance of the oxygen delivering capacity of transfused red cells during the immediate posttransfusion period became apparent. Red cells with low 2,3 DPG levels and increased affinity for oxygen will increase cardiac output and/or decrease venous pO2 for at least 4 hours after transfusion. Oxygen transport function is maintained longer in red cells stored in CPD than in ACD-stored red cells. Supplementation of CPD red cells with inosine, ascorbate; dihydroxyacetone and other substances helps to maintain the oxygen transport function during storage at 4 C. Liquid-stored red clls can be biochemically modified before freeze-preservation to increase the 2,3 DPG levels to to 1-1/2 to 2 times normal; these red cells have decreased oxygen affinity. The red cells have acceptable posttransfusion survival and improved oxygen releasing capacity for at least 72 hours after transfusion. The well-being of certain patients may be placed in jeopardy of they are given preserved red cells with increased affinity for oxygen. The patient may not be able to meet the accompanying demand for increased blood flow, and the venous-capillary oxygen tension may fall to a critical level. Clearly, patients in hemorrhagic and septic shock, those subjected to extracorporeal circulation during cardiac surgery, and anemic patients with myocardial or cerebrovascular insufficiency are best treated with red cells that have 150% normal 2,3 DPG levels.

Adenosine Triphosphate↗
PubMed1994

The red blood cell transfusion trigger. Physiology and clinical studies.

The need for red blood cell transfusion is determined by the etiology, chronicity, and severity of anemia, the patient's ability to compensate for decreased oxygen carrying capacity, and tissue oxygen requirements. The compensatory mechanisms invoked by acute blood loss differ from the physiologic adaptations to chronic anemia. Factors such as myocardial depression and inadequate ventilation can also decrease oxygen delivery, but their occurrence cannot be reliably predicted, particularly in surgical patients. A margin of safety is therefore necessary to prevent inadequate oxygen delivery and potential morbidity and mortality in anemic patients. Appropriate use of pharmacologic agents can obviate the need for red blood cell administration in some chronically anemic patients. There is no single red blood cell transfusion trigger. The entire clinical picture not just the hemoglobin, must be considered in each patient.

Anemia↗
PubMed1993

Immunoecological succession in host-parasite communities.

From the unique perspective of the parasite, each potential host exists as an ecosystem in its own right, comprised of biotic and abiotic components. If the parasite's limits of tolerance are not exceeded by the host environment, parasitism may occur. The organs of the host can be viewed as integrated communities comprised of distinct cell populations. Each population of cells occupies a unique ecological niche and contributes to the community in an essential way. The coordinated interactions among cells within each community and among the communities themselves are essential for the host to maintain itself in a homeostatic state. As with free-living systems in equilibrium, introduction of an exotic population into the community disrupts the balance, and ecological succession resumes until a new equilibrium is established. Such is the case when parasites invade the host. The successful invader must not exceed the carrying capacity of the environment nor modify the habitat so drastically that its own survival is compromised. The specific interactions that occur between invading parasites and the populations of cells that comprise the host's immune system can also be viewed in ecological terms. The successful parasite must "compete" with cells in the host community for available niches and avoid "predation" by cells of the host immune system. As is true for interactions among organisms in a free-living ecosystem, the outcome of the host-parasite interaction is not readily predicted from knowledge of the component parts in isolation.

Animals↗
PubMed1993

Re-aiming the canon.

Although it is unlikely that the national goals for educational reform--such as that, by the year 2000, U.S. students will be first in the world in science and mathematics achievement--can be achieved, a vigorous effort must be made to reach those goals as rapidly as possible. Reform will come not from a massive expansion of what we now do but from a basic shift in the manner in which we educate students in grades K-16 in the sciences and mathematics. Important elements in that basic shift must include an increase in teaching of science, mathematics, and technology (SMT), to about 20%-25% of the curriculum; SMT must include rich hands-on experiences, with an emphasis on concepts and understanding, rather than on facts and memorization, and on how science as a way of knowing differs from other ways of knowing; SMT must consider human problems; and SMT must deal with the basic problem facing humanity--how we must adjust our behavior so as not to exceed, on a worldwide basis, the carrying capacity of the environment.

Curriculum↗
PubMed1977

Blood volume changes in patients with cystic fibrosis.

Simultaneous red blood cell (RBC) and plasma volume determinations were obtained in 16 patients with cystic fibrosis (CF) and moderately severe pulmonary involvement. Hypervolemia with an increase in both RBC and plasma volumes was observed. Changes in blood volume were marked when values were indexed by weight but less significant when indexed by height. Decreasing systemic arterial oxygen saturation was associated with a progressive increase in RBC mass, hematocrit value, and hemoglobin level and a decrease in mean corpuscular hemoglobin concentration. RBC and total blood volumes were highest in patients with cor pulmonale and congestive heart failure. However, the compensatory polycythemic response in patients with CF was inadequate when compared with the response to hypoxemia in patients with cyanotic congenital heart disease. The insufficient oxygen-carrying capacity may compromise tissue oxygen delivery and necessitate treatment.

Adolescent↗
PubMed1995

[Transgenicular amputation with special reference to partial secondary femoral condyle resection].

During the last five years 54 patients (mean age 69 years) have undergone a unilateral, transgenicular (through-knee) amputation, instead of an impending amputation through the thigh. The indication for surgery was a chronic, or an acute critical ischemia of the leg. In 32 and 22 cases respectively, amputations have been preceded by a multitude of reconstructive measures. Uncomplicated stump healing was observed in 25 of 51 survivors (49%). Disturbances in the wound healing process necessitated further amputation in 26 cases (51%). In 13 of these cases the advantage of the transgenicular amputation could be retained by a partial femoral condylectomy, whereas in the other 13 cases a thigh amputation was inavoidable. Thus, in three out of four of the survivors, a long, strong stump with a good terminal load-carrying capacity could be retained which, when supplied by a prosthesis, led to the recovery of the original walking ability in 90% of these cases.

Aged↗
PubMedDate not supplied

Oxygen delivery with a single cannula tidal flow venovenous system for extracorporeal membrane oxygenation.

Venovenous tidal flow perfusion for extracorporeal membrane oxygenation via a single lumen cannula in the right atrium avoids the sacrifice of a carotid artery inherent in venoarterial systems, and eliminates the problems of two cannula venovenous perfusion. Oxygen delivery and hemodynamic effects of a single cannula, single lumen system with tidal flows directed by alternating tubing occluders were studied in six newborn lambs to define optimal system performance and possible adverse hemodynamic effects. The ratio of drainage to infusion time was fixed at 2:1 to avoid excessive reinfusion pressures. Total length of the in/out cycle was varied from 2-6 sec, resulting in a cycling frequency of 30 to 10 cycles/min and a tidal volume of 17-50 ml. Systemic arterial, mixed venous, and pre and post oxygenator partial pressure of oxygen and oxygen saturation were measured. Recirculation, oxygen delivery, and effective bypass flow (total flow--recirculated flow) were calculated. With slower cycling frequency, recirculation progressively fell, and effective flow and oxygen delivery increased (p < 0.001 for each parameter across the cycle length). In these animals, oxygen delivery was limited by low oxygen carrying capacity (mean hemoglobin, 8.1 g/dl). The authors concluded that with longer cycles, the system minimizes recirculation without apparent adverse hemodynamic consequences, achieving sufficient effective bypass flow to assure adequate oxygen delivery when hemoglobin levels are normal.

Animals↗
PubMed1995

[Clinical chemical and hematological blood values and adaptation reactions in suckling calves in the first weeks of life].

Suckler calves of the mother cow herd were used for this investigation. Body weight, growth rate and venous blood acid base status, gas content, creatinine, urea, lactate, total protein, albumin, Ca, Mg, Na, K and Cl were measured at 20, 60 and 90 days of postnatal life. Body weight and growth rate showed strong correlations with some blood values especially at 60 and 90 days of age meaning that adaptation is performed successful in some calves and incomplete in others. Disproportionate growth of body parts and the limited oxygen-carrying capacity below the oxygen needs of the tissues may cause the great lactate values in some calves of all age groups.

Acclimatization↗
PubMedDate not supplied

Depression of stimulated erythropoietin production in mice with enhanced erythropoiesis.

BACKGROUND: The reports of lower plasma erythropoietin (EPO) in anemic patients with active erythropoiesis (hyperplastic) than in comparably anemic subjects with erythroid hypoplasia have generally been interpreted as the result of EPO utilization by the target cells of the hormone. An alternative explanation could be that there is a feedback mechanism through which EPO formation by EPO-producing cells is modulated by the erythroid activity of the erythropoietic organs. The present study was thus designed to investigate EPO production during acute hypoxemia in a mouse model in which the oxygen-carrying capacity of blood, the plasma EPO level, the blood viscosity and the plasma EPO half-life are within normal values in spite of an intense stimulation of erythropoiesis. MATERIALS AND METHODS: Adult female mice of the CF1 strain with either normal or increased rates of erythropoiesis were used in this study. Erythropoiesis was stimulated by two injections of 10 units of rhEPO given 24 h apart. All experimental determinations were performed 24 h after the second EPO injection. Erythropoiesis was measured by the percent of a tracer dose of 59Fe incorporated into the spleen. Hypobaric hypoxemia was induced by exposing mice to atmospheric air maintained at 50% atmospheric pressure for 6 h. Plasma EPO concentration was determined by RIA. Plasma disappearance of radiolabeled rhEPO was determined by i.v. injection of the hormone and sampling by cardiac puncture every hour for 6 h. RESULTS: Administration of rhEPO to mice increased splenic 59Fe uptake significantly without affecting the hematocrit, the plasma EPO level or the plasma disappearance of radiolabeled EPO. Plasma EPO titer after 6 h of exposure to hypobaric air was about 70% lower in mice with EPO-induced stimulation of erythropoiesis than in mice with normal erythropoiesis. CONCLUSIONS: The results of this study suggest that there is an inverse relationship between the rate of stimulated EPO production and erythropoietic marrow activity. They also suggest that the variations in plasma EPO levels during periods of rapidly increasing erythropoiesis are the reflection of a decrease in the rate of production rather than an increase in the rate of utilization by a proliferating pool of erythroid cells.

Animals↗
PubMed1995

Perfluorochemical liquid ventilation: from the animal laboratory to the intensive care unit.

Perfluorochemical or perfluorocarbon liquids have an enormous gas-carrying capacity. During tidal liquid ventilation the respiratory medium of both functional residual capacity and tidal volume is replaced by neat perfluorocarbon liquid. Tidal liquid ventilation is characterized by convective and diffusive limitations, but offers the advantage of preserved functional residual capacity, high compliance and improved ventilation-perfusion matching. During partial liquid ventilation only the functional residual capacity is replaced by perfluorocarbon liquid. Both tidal and partial liquid ventilation improve gas exchange and lung mechanics in hyaline membrane disease, adult respiratory distress models and meconium aspiration. Compared to gas ventilation, there is less histologic evidence of barotrauma after liquid ventilation. Cardio-pulmonary interaction, inherent to the high density of liquid, and long term safety need further study. However, extrapolating from animal data, and taking into account promising human pilot studies, liquid ventilation has the desired properties to occupy an important place in the therapy of restrictive lung disease in man.

Animals↗
PubMed1977

Effects of three kinds of hypoxias on vigilance performance.

The consequences for vigilance performance of inhaling carbon monoxide at altitude were examined. In addition, the effects of altitude and CO at an equivalent reduction in O2-carrying capacity were compared. Ten subjects performed a visual vigilance task under four atmospheric conditions. Physiological measures included heart rate, blood pressure, and ventilation. Blood hemoglobin and CO levels were measured directly from blood samples drawn after 0,50 and 120 min of exposure. The physiological variables measured and subjective responses of subjects showed no changes attributable to the atmospheric conditions. A statistically significant change in vigilance performance as measured by precentage of signals detected, was found between control and low oxygen; however, performance under CO and the combination of CO and low oxygen was not different from control. The lack of deterioration in performance under the combination of CO and low oxygen suggested that the increased severity of the stress resulted in activation of compensatory mechanisms which counterbalanced the decreased O2 available to the tissues.

Adult↗
PubMedDate not supplied

Blood acidification in the swimbladder: mechanisms and metabolic pathways.

The metabolism of gas gland cells of the swimbladder epithelium is specialized for the production of acidic metabolites that are released into the blood stream and provoke an increase in gas partial pressure by reducing the effective gas-carrying capacity of the blood. In a subsequent step this initial increase in gas partial pressure is multiplied by back-diffusion of gas molecules from the venous to the arterial side in the countercurrent system, the rete mirabile. Thus, gas partial pressures of up to several hundred atmospheres can be generated in the swimbladder. Measurements of metabolic end products and analysis of the formation of 14CO2 from [1-14C]glucose and [6-14C]glucose revealed that the acidic metabolites are lactic acid, produced in the glycolytic pathway, and also CO2, formed in the pentose phosphate shunt. CO2 easily enters the blood stream by diffusion. The release of protons from isolated gas gland cells, however, is highly dependent on the extracellular sodium concentration. This sodium dependence can in part be blocked by addition of amiloride, indicating that a Na+/H+ exchanger is involved in the release of protons. A significant decrease in the rate of proton secretion in the presence of the carbonic anhydrase inhibitor ethoxzolamide indicates that the second major route for the release of protons includes carbonic anhydrase activity and the diffusion of CO2.

Air Sacs↗