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At least 397 records · Page 22Linked to original sources
PubMed2006

Transintestinal systemic oxygenation using perfluorocarbon.

PURPOSE: Perfluorocarbons have an excellent oxygen- and carbon dioxide-carrying capacity. This prompted us to investigate the feasibility of transintestinal systemic oxygenation using perfluorocarbon. METHODS: A rat hypoventilation model (room air, 20 breaths/min and a tidal volume of 10 ml/kg) was thus established, and FC-77 (Sumitomo-3M, Osaka, Japan) was used as a perfusate. Oxygenated FC-77 was perfused through the small intestine for 4 h. The rats were allocated into three groups as follows. Group 1 (n = 6): hypoventilation only; Group 2 (n = 6): saline was perfused instead of FC-77; Group 3 (n = 6): FC-77 was perfused. Arterial blood samples were drawn from the common iliac artery every 30 min until the end of perfusion. A standard blood gas analysis was performed. RESULTS: The PaO2 level in Group 3 was significantly higher than in Groups 1 or 2 (P = 0.006: at the end of perfusion, Group 1 = 58.6 +/- 14.5 mmHg, Group 2 = 65.2 +/- 29.4 mmHg, Group 3 = 84.0 +/- 35.5 mmHg). The PaCO2 level in Group 3 was significantly lower than that in Groups 1 or 2 (P = 0.014: at the end of perfusion, Group 1 = 56.8 +/- 8.5 mmHg, Group 2 = 52.6 +/- 5.7 mmHg, Group 3 = 44.4 +/- 11.1 mmHg). CONCLUSION: Our findings indicate that transintestinal systemic oxygenation is indeed possible and could therefore become a useful new modality for respiratory assist.

Animals↗
PubMed2005

Transintestinal oxygenation with perfluorocarbon: investigation of perfusion rate.

OBJECTIVE: Perfluorocarbons are structurally similar to hydrocarbons but with the hydrogen atoms replaced by fluorine. In general, perfluorocarbons have an excellent oxygen and carbon dioxide carrying capacity. We studied the suitability of oxygenated perfluorocarbon as an agent for transintestinal oxygenation and measured its perfusion rates under different conditions. SUBJECTS AND METHODS: We used FC-77 (Sumitomo 3M, Tokyo, Japan) perfluorocarbon and a rat hypoventilation model (room air, 20 breaths/min, a tidal volume of 10 ml/kg). Oxygenated FC-77 was perfused through the small intestine for 4 hours. Rats were allocated to 3 experimental groups according to the perfusion rate and a control group: Group 1 (n=6), 10 ml/min; Group 2 (n=6), 2.5 ml/min; Group 3 (n=6), 0.75 ml/min; Group 4 (n=6) served as a control (hypoventilation only). Arterial blood samples were drawn every 30 minutes. Standard blood gas analysis was performed. RESULTS: After four hours of perfusion, the PaO2 levels in Groups 1 to 3 were significantly better than Group 4 (p<0.01, Group 1: 141.7 +/- 18.0 mmHg, Group 2: 145.2 +/- 25.1 mmHg, Group 3: 120.5 +/- 21.2 mmHg, Group 4: 67.4 +/- 7.2 mmHg). PaCO2 levels in Groups 1 and 2 were significantly better than Groups 3 and 4 (p<0.01, Group 1: 42.6 +/- 7.2 mmHg, Group 2: 52.1 +/- 7.7 mmHg, Group 3: 78.2 +/- 22.8 mmHg, Group 4: 75.3 +/- 10.3 mmHg). CONCLUSION: In the present settings, 8 ml/kg/min was adequate for oxygenation and CO2 clearance. This approach promises to become another modality for respiratory assistance.

Animals↗
PubMed2005

Cerebral Vasospasm in Subarachnoid Hemorrhage.

The treatment of vasospasm after subarachnoid hemorrhage remains a formidable challenge. The prompt recognition of this complication is essential to prevent ischemic damage. Initial orders should include adequate fluid and sodium supplementation to avoid volume depletion. Prophylactic hypervolemia is not effective in reducing the incidence of vasospasm and may be deleterious. Oral nimodipine (60 mg every 4 hours for 21 days) should be started on admission because it protects against delayed ischemic damage. Increasing blood flow velocities on serial transcranial Doppler studies are reliable indicators of early development of vasospasm. When symptomatic vasospasm occurs, hemodynamic augmentation therapy should be instituted. Crystalloids and colloids may be used to promote hypervolemia. Colloids may provide additional benefit by producing hemodilution. However, the rheological benefits of hemodilution may be offset by reduced oxygen carrying capacity when hematocrit drops below 28%. Hypertension may be induced by administering inotropic drugs and, in certain cases, cardiac output optimization using dobutamine also is necessary. When aggressive medical therapy fails to reverse ischemic deficits, prompt endovascular intervention is indicated. Focal vasospasm of larger vessels may be effectively treated with angioplasty and the benefits of this procedure are durable. Diffuse vasospasm involving smaller arterial branches may be treated with intra-arterial infusion of vasodilators, such as papaverine, verapamil, or nicardipine. Unfortunately, these dilatory effects tend to be short-lasting. In refractory cases, hypothermia may be considered, although value of this strategy remains largely unexplored.

Journal Article↗
PubMed1975

Hemodynamic effects of staged hematocrit reduction in patients with stable cor pulmonale and severely elevated hematocrit levels.

Patients with cor pulmonale and high hematocrit levels are often subjected to phlebotomy in the belief that the adverse effects of high viscosity may outweigh the benefit of increased oxygen carrying capacity. To evaluate this, 12 patients with stable cor pulmonale and hematocrit values greater than 55 per cent were studied before and after a series of venesections. Right heart and aortic pressures, cardiac output and blood gases were measured at three mean hematocrit levels, 61 per cent (stage I), 50 per cent (stage II) and 44 per cent (stage III), with blood volume unchanged. From stages I to II, there were significant decreases in both man pulmonary artery pressure and total pulmonary resistance. Oxygen transport fell but not oxygen consumption. Right ventricular end-diastolic pressure and cardiac output did not change. Right ventricular work either fell or was maintained by increased output. Frank-Starling performance (supine exercise) improved. No significant changes occurred with further reduction in hematocrit to normal levels (stage III). The findings of this study support the concept of overcompensating erythrocytosis in cor pulmonale, and the effects of moderate hematocrit reduction should not be overlooked in these severely ill patients.

Adult↗
PubMed1994

Association of perioperative transfusions with poor outcome in resection of gastric adenocarcinoma.

The clinical records of patients identified by a prospective database as having undergone curative gastric resections for adenocarcinoma not involving the gastroesophageal junction were reviewed in order to examine transfusional practices and to determine if perioperative transfusion had an adverse effect on outcome. Between January 1985 and January 1992, 232 patients received such curative resections. The median follow-up for these patients was 19.0 months, whereas median survival for nonsurvivors was 12.3 months. Fifty-eight percent of the patients received transfusion of blood products. Fifty-four percent of these transfusions amounted to less than 2 units of blood products. By chi 2 analysis, advanced stage of disease (p = .03), advanced T-stage of primary tumor (p = .004), and total gastrectomy (p = .04) were associated with greater likelihood of transfusion. By univariate analysis, male sex (p = .004), total gastrectomy (p = .01), advanced stage of disease (p = .000006), high histologic grade of tumor (p = .03), and blood transfusion (p = .006) were predictors of poor outcome. By multivariate analysis using the proportional hazards model with stage, tumor grade, gender, extent of resection, and transfusion as covariates, blood transfusion was an independent predictor of poor outcome (p = .029, hazard 1.74). These results encourage prospective studies of transfusion on cancer recurrence and studies of alternatives to allogeneic blood transfusions in restoration of oxygen-carrying capacity during surgery in patients with gastric cancer.

Adenocarcinoma↗
PubMed1983

Hemoglobin-inulin conjugate as an oxygen carrying blood substitute.

Pyridoxylated hemoglobin was modified with the activated ester of inulin. From the oxygen equilibrium curve, this conjugate was estimated to have about fivefold oxygen carrying capacity compared with a free hemoglobin. The half disappearance time of this conjugate in the circulation of a rat was 21 hours in contrast to 3 hours of a free hemoglobin. The oncotic pressure and the viscosity can be adjusted nearly equal to those of whole blood. This conjugate can be concluded to have sufficient properties for use as a blood substitute.

Animals↗
PubMed1991

A porous implant model for a knee joint.

A study of the lubrication mechanism occurring in knee joint replacement is presented. The idealized model has been shown to produce results consistent with those in normal situations. In the present problem viscoelastic fluid has been considered to represent the synovial fluid in the fluid-film region and purely viscous Newtonian fluid in the porous layer due to filtration. Because of exact solution not being possible for the governing non-linear partial differential equations, the perturbation method has been used to obtain approximate solutions. The effect of an increase in the viscoelastic parameter of the lubricant is similar to that of an increase in concentration of hyaluronic acid molecules in synovial fluid. Important deductions are made for load carrying capacity and coefficient of friction and it has been shown that the slip velocity plays an important role in maintaining the self-adjusting nature of human joints.

Biomechanical Phenomena↗
PubMed1993

Variability in cholesterol content and physical properties of lipoproteins containing apolipoprotein B-100.

The primary objective of this study was to determine the variability in cholesterol carrying capacity of low density lipoproteins (LDLs) and other apolipoprotein B (apo B)-containing lipoproteins in normolipidemic men. One hundred and fifty-nine normolipidemic men, ages 21 to 73 years, were enrolled. In addition to determining plasma lipids and lipoproteins, three primary measurements were made: ratios of cholesterol to apo B in LDL; the electrophoretic pattern of LDL, i.e. pattern A, AB, or B; and levels of cholesterol in all lipoproteins other than high density lipoproteins (nonHDL-cholesterol) along with total apo B. First, the data revealed that about 85% of the variability of LDL-cholesterol levels can be accounted for by LDL-apo B levels, whereas the remaining 15% can be explained by differences in LDL-cholesterol/apo B ratios. Second, LDL electrophoretic pattern A was the predominant pattern in young adult men, but in older men the pattern shifted increasingly to AB and B. And third, there was a high correlation between nonHDL-cholesterol levels and total apo B levels, which suggests that nonHDL-cholesterol can be used as a relatively accurate surrogate for total apo B levels in normolipidemic individuals.

Adult↗
PubMed1989

Stiffness and strain energy criteria to evaluate the threshold of injury to an intervertebral joint.

This study is focused to evaluate the threshold of injury to an intervertebral joint based on its mechanical response. The load-deflection behavior of the intervertebral joint indicated non-linear and sigmoidal characteristics with continuously changing stiffness (a measure of the ability to withstand external force). The load corresponding to the point of zero stiffness was identified, according to the classical theories of mechanics, as the maximum load carrying capacity. Further, the initiation of trauma was defined to occur at the point on the load-deflection curve at which the stiffness begins to decrease for the first time. The load, stiffness and energy absorbing capabilities of normal and degenerated intervertebral joints at the initiation of trauma was determined. Axial compressive load experiments were conducted on nine intervertebral joints of fresh human male cadavers and the resulting load-deflection responses were transformed into stiffness-deflection responses using the derivative principle. Energy characteristics were also derived. Load, stiffness and energy at the initiation of trauma were found to be 9.0 kN, 2850 N mm-1, and 10.2 J for normal and 4.4 kN, 1642 N mm-1, and 5.8 J for degenerated segments, respectively. The load and energy values at failure were 11.0 kN, and 18.0 J for normal and 5.3 kN and 5.7 J for degenerated intervertebral joints, respectively.

Biomechanical Phenomena↗
PubMed1993

Hand position affects elbow joint load during push-up exercise.

Electromagnetic motion sensors and a piezoelectric force plate were used to record simultaneously upper-extremity motion and forces in nine healthy male subjects during push-ups in six different hand positions. The intersegmental loading pattern on the elbow joint during a push-up exercise was investigated. The importance of hand position on these loads was examined. Peak forces exerted on the elbow joint along the forearm axis averaged 45% of the body weight for the 'normal' hand position and were significantly decreased if hands were positioned either 'apart' or 'superior' from 'normal'. The peak torque in the 'normal' position tended to produce elbow flexion and was 2305.9 N cm, or 56% of the maximal isometric extensor torque, which was significantly different from hands 'apart' and hand 'together' at 29 and 71% of the maximal isometric torque, respectively. The maximum torque about the forearm axis tended to produce forearm pronation with a mean value of 315.4 N cm (35% of the maximal isometric supinator torque). The maximum valgus torque at the elbow opposed by the medial ligamentous structure was 1241 N cm and was significantly increased if the hand was positioned superiorly. The valgus torque increased by 42% for the one-handed push-up under simulated fall condition. The results of this analysis give an insight into the biomechanics of a normal elbow and to its load-carrying capacity. The data may be extrapolated to the design of rehabilitation programs and possibly to the mechanisms of forearm injury during a fall.

Adult↗
PubMed1994

A method for the fatigue testing of pedicle screw fixation devices.

Spinal devices/instrumentation are used to augment the stability of a decompressed spinal segment during surgery. Like any other mechanical component, the device can fail. A standard in vitro test protocol, was developed to determine load vs number of cycles to failure curve for a pedicle screw-plate/rod type spinal device. The protocol based on the use of an 'artificial spine' model, is clinically relevant. The protocol was used to characterize the load-carrying capacities and failure modes of a specific pedicle screw-rod type fixation device to demonstrate its appropriateness. The devices (Kaneda) were tested in the quasi-static as well as fatigue bending modes. In the bending fatigue mode, the devices failed at loads significantly smaller than the corresponding quasi-static failure load magnitude (806 N). The device exhibited an endurance limit in the fatigue bending mode. The device is not likely to exhibit failure if subjected to cyclic loads which cause less than 380 N axial compression (and an accompanying bending moment relative to the device of less than 13.57 Nm). The failures observed in specimens subjected to the fatigue tests ranged from complete to partial breakage of the paraspinal rods as opposed to failure due to permanent deformation (yielding) of the rods in the quasi-static bending test specimens. The protocol developed can be used for any other screw-plate/rod type spinal instrumentation. The use of a standard protocol by researchers would enable a comparison of various devices currently available in the market. Such comparative data would be useful for the scientific community, and agencies such as the FDA and ASTM.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Plates↗
PubMed1990

Nested allostery of arthropodan hemocyanin (Eurypelma californicum and Homarus americanus). The role of protons.

Continuous oxygen binding curves for two arthropodan hemocyanins were performed at different pH values ranging from 7.0 to 8.7 and in the presence of physiological concentrations of the bivalent ions Ca2+ and Mg2+. The arthropods Eurypelma californicum and Homarus americanus are classified as chelicerata and crustaceans, respectively. Their structurally well-characterized hemocyanins are composed of, in the case of E. californicum 24 subunits, and in the case of H. americanus 12 subunits. The role of protons as allosteric effectors of the oxygen binding was analysed in terms of the nesting model, which assumes hierarchies of allosteric equilibria that are based on obvious structural hierarchies. For each hemocyanin, the smallest structural repeating unit, the 12-mer or the 6-mer, respectively, was regarded as the "allosteric unit". Two allosteric units are allosterically coupled within the native molecules. The analysis revealed that in accordance with the postulations of the classical Monod-Wyman-Changeux model protons as allosteric effectors do not change the oxygen affinities of the four postulated conformations, but influence the allosteric equilibria between them at two different hierarchical levels. Model-independent determination of the affinity constants for the binding of the first and the last oxygen molecule to the native hemocyanins and to the isolated half-molecules confirmed the affinities calculated according to the nesting model. The stepwise establishment of new conformations during the assembly process from monomers to the structurally identical repeating unit and further on to the native molecule is shown. Possible physiological advantages of allosterically coupled allosteric units in contrast to allosterically uncoupled ones are thought to be (1) the option to regulate oxygen binding on different levels of structural hierarchy and (2) the increase of the oxygen-carrying capacity.

Allosteric Site↗
PubMed1994

Effects of viscosity and oxygen content on cerebral blood flow in ischemic and normal rat brain.

The mechanism of hemodilution-induced increases in cerebral blood flow (CBF) was investigated. Hemodilution was achieved with a molecular hemoglobin solution (DCLHb) and albumin which have similar viscosities but different oxygen carrying capacities. Part A: CBF was assessed in rats after one of the following regimens: (1) control-hematocrit not manipulated, (2) 30/Alb-hematocrit decreased to 30% with albumin, (3) 30/DCLHb-hematocrit decreased to 30% with DCLHb, or (4) 16/Alb/DCLHb-hematocrit decreased to 30% with albumin and then 16% with DCLHb. For viscosity matched groups (30/Alb and 30/DCLHb), CBF was greater in animals with decreased oxygen content (30/Alb); while in oxygen content matched groups (30/Alb and 16/Alb/DCLHb), CBF was greater in animals with decreased viscosity (16/Alb/DCLHb) (p < 0.05). Part B: Middle cerebral artery occlusion was performed, hemodilution achieved as in Part A, and CBF determined. For viscosity matched groups (30/Alb and 30/DCLHb), CBF was less in rats with decreased oxygen content (30/Alb); while in oxygen content matched groups (30/Alb and 16/Alb/DCLHb), CBF was greater in animals with decreased viscosity (16/Alb/DCLHb) (p < 0.05). This data supports the premise, that in normal brain, both viscosity and oxygen content effect CBF; while in ischemic brain, a decrease in viscosity but not oxygen content increases CBF.

Animals↗
PubMed1989

Population diffusion in a two-patch environment.

A model of a single-species population diffusing in a two-patch environment is proposed. It is shown that there exists a positive, monotonic, continuous steady-state solution with continuous flux, in the cases of both reservoir and no-flux boundary conditions, that is asymptotically stable. In the case of patches with equal carrying capacities, it is shown that the uniform steady state is globally asymptotically stable.

Ecology↗
PubMed1992

The subcritical collapse of predator populations in discrete-time predator-prey models.

Many discrete-time predator-prey models possess three equilibria, corresponding to (1) extinction of both species, (2) extinction of the predator and survival of the prey at its carrying capacity, or (3) coexistence of both species. For a variety of such models, the equilibrium corresponding to coexistence may lose stability via a Hopf bifurcation, in which case trajectories approach an invariant circle. Alternatively, the equilibrium may undergo a subcritical flip bifurcation with a concomitant crash in the predator's population. We review a technique for distinguishing between subcritical and supercritical flip bifurcations and provide examples of predator-prey systems with a subcritical flip bifurcation.

Animals↗
PubMed1992

Hopf bifurcation in three-species food chain models with group defense.

Three-species food-chain models, in which the prey population exhibits group defense, are considered. Using the carrying capacity of the environment as the bifurcation parameter, it is shown that the model without delay undergoes a sequence of Hopf bifurcations. In the model with delay it is shown that using a delay as a bifurcation parameter, a Hopf bifurcation can also occur in this case. These occurrences may be interpreted as showing that a region of local stability (survival) may exist even though the positive steady states are unstable. A computer code BIFDD is used to determine the stability of the bifurcation solutions of a delay model.

Animals↗
PubMedDate not supplied

Models for diseases with vertical transmission and nonlinear population dynamics.

Vertical transmission, the direct transfer of a disease from an infective parent to a new born offspring, is an important aspect of many diseases. Most of what is known for vertical transmission models assumes birth rates proportional to population size. We consider models with nonlinear population dynamics and finite carrying capacity and analyze the stability of equilibria in the special case in which the overall birth rate does not depend on infective population size.

Female↗
PubMed1996

Environmentally driven epizootics.

Environmental conditions can be the driving force behind an epizootic. Environmental changes may favor growth of a particular species, which results in increased contact rates and spread of a disease. We examine this particular phenomenon in SI and SIS models and use it to explain the possible disease outbreaks in nature. Either infected individuals recover from the disease (SIS model) or suffer disease fatalities (SI model). Epizootic models for a single population are examined where contact rate depends on population size. A reproductive number R is defined that depends on environmental carrying capacity. The single-population models are coupled to form three different two-species models with intra- and interspecies contact rates that depend on the population sizes of both populations. The stability results show that it is possible for the disease to drive one of the populations to extinction, the one with disease fatalities. The surviving species serves as a reservoir for the disease. Single- and two-species epizootic models are examined in a particular case where the contact rates are assumed to be constant. This leads to a new definition for the contact rate. A complete global analysis is possible in these latter cases. The results are compared and contrasted with the models with variable contact rates. The prototype for the models is the spread of disease in wildlife populations, which includes such diseases as plague or Lyme disease.

Animals↗