Oxygen Transport Measurements Research Articles

The Brain Uses Mostly Dissolved Oxygen During Profoundly Hypothermic Cardiopulmonary Bypass

Background. During profoundly hypothermic cardiopulmonary bypass, cerebral venous oxygen saturation increases (eg, to 98% at 15°C). We reanalyzed results of clinical studies to learn why.Methods. One hundred sixty-eight cerebral oxygen transport measurements were available from 96 infants and children undergoing profoundly hypothermic cardiopulmonary bypass during repair of congenital heart defects.Results. Dissolved oxygen accounted for 2% to 17% of arterial oxygen content, depending on the arterial oxygen partial pressure and hemoglobin concentration. The fraction of the cerebral metabolic rate for oxygen obtained from dissolved oxygen depended on pump flow, temperature, hemoglobin concentration, and arterial oxygen partial pressure (all p < 10−3). For “full-flow” cardiopulmonary bypass, temperatures less than 18°C, and arterial oxygen partial pressure measurements more than 180 mm Hg, the mean ± standard deviation of the fraction of cerebral metabolic rate for oxygen obtained from dissolved oxygen equaled 77% ± 19%.Conclusions. Dissolved oxygen satisfies most of the brain’s oxygen requirements during profound hypothermic cardiopulmonary bypass. This result reflects four properties of profound hypothermic cardiopulmonary bypass: (1) increases in hemoglobin’s oxygen affinity due to profound hypothermia (which impairs oxygen transfer from hemoglobin to cerebral tissue), (2) use of hemodilution, (3) use of high arterial oxygen partial pressure, and (4) low cerebral metabolic rate of oxygen.(Ann Thorac Surg 1997;63:1725–9)

Gastric tonometry and systemic oxygen transport measurements in septic patients

Gastric tonometry and systemic oxygen transport measurements in septic patients

Atomic transport of oxygen in nonstoichiometric oxides

Abstract Atomic transport of oxygen in nonstoichiometric oxides is an extremely important topic that overlaps science and technology. In many cases, diffusion of oxygen controls sintering, grain growth, and creep. High oxygen diffusivity is critical for efficient operation of many fuel cells. Additionally, oxygen diffusivities are an essential ingredient in any point defect model. Secondary ion mass spectrometry (SIMS) is the most accurate modern technique for measuring oxygen tracer diffusion. This paper will briefly review the principles and applications of SIMS for the measurement of oxygen transport. Case studies will be taken from recent work on ZnO and selected high-temperature superconductors.

Beyond the lung: oxygen delivery and tissue oxygenation.

Beyond the lung: oxygen delivery and tissue oxygenation.

Adequacy of tissue oxygenation.

This paper reviews presently available techniques for monitoring the adequacy of tissue oxygenation, emphasizing the practical and theoretical problems that exist with presently used measurements. The data are based on a review of the literature. Most of the presently available techniques focus on global measurements of oxygen transport and utilization that may be insensitive to changes occurring in vital tissues critically important to overall homeostasis. As a result, they are often insensitive, nonspecific, and become abnormal only at a very late stage of disease. In attempting to develop tools to assess adequate tissue oxygenation, emphasis should be placed on the monitoring of individual tissues that are felt to be highly susceptible to reduced oxygen delivery and key to overall survival. Preliminary data involving measurements of the interstitial pH of the gastrointestinal tract suggest that this measurement may be one approach to pursue.

Oxygen transport in cardiogenic and septic shock

To review clinical studies of oxygen transport in cardiogenic and septic shock. Descriptive and prospective studies. University hospital multi disciplinary ICU. Critically ill cardiogenic and septic shock patients greater than 18 and less than 80 yrs of age. The responses to volume loading with colloid or crystalloid and infusion of catecholamines are documented with baseline hemodynamic and oxygen transport measurements before and after administration of catecholamines. Nineteen patients in cardiogenic shock were studied. In three patients, invasive systemic mean arterial pressure was greater than 80 mm Hg and cardiac index was greater than 2.0 L/min.m2. In all patients, there were increases in oxygen extraction ratio that averaged 48 +/- 18 (SD) %. However, in 30 septic shock patients, extraction ratio was 24 +/- 2%. In both groups, the response to therapy was an increase in mixed venous oxygen saturation from 54 +/- 16% to 69 +/- 8% in cardiogenic patients (p less than .001) and from 75 +/- 2% to 80 +/- 1% in septic shock (p less than .01). There are widely differing oxygen transport patterns in cardiogenic and septic shock that may have implications for therapy.

Oxygen transport measurements to evaluate tissue perfusion and titrate therapy

Increased cardiac index, oxygen delivery (DO2), and oxygen consumption (VO2) patterns were shown to characterize the physiologic status of surviving high-risk surgical patients, and indicate increased metabolic needs; relatively normal DO2 and VO2 values were found to characterize the sequential pattern of nonsurvivors who developed an early oxygen debt followed by lethal organ failure. The cardiac index, DO2, and VO2 values empirically determined from survivors' patterns were shown to improve outcome in prospective randomized trials. The present study considers these criteria to evaluate the tissue perfusion status as well as the effects of therapy on tissue perfusion and oxygenation. To summarize new information on the temporal patterns of DO2, VO2, and oxygen debt on outcome and the effects of fluids and inotropes on these patterns in a wide range of clinical, temporal, and physiologic conditions. Descriptive analysis based on data gathered prospectively using a specified protocol. High-risk patients with accidental or elective surgical trauma, and patients with or without sepsis or septic shock and organ failure. University-run county hospital with a large trauma service. Fluids, dobutamine, and dopamine at various times and at various doses throughout critical illness of postoperative, posttraumatic, septic, and hypovolemic patients with and without lethal and nonlethal organ failure. The pattern of DO2 plotted against the corresponding VO2 values in 437 consecutive critically ill surgical patients showed a wide variability and poor correlation probably because complex clinical conditions may obscure the supply-dependent and supply-independent VO2 relationships observed in normal dogs bled or given bacterial infusions. However, the use of specific therapy by well-defined protocols was shown to provide objective evidence of efficacy. Significant increases in DO2 and VO2 were previously shown after whole blood, packed red cells, and colloid administration, but not after crystalloid administration. Dobutamine administration in 715 circumstances in postoperative, traumatic, septic patients and patients with adult respiratory distress syndrome, renal failure, and multiple organ failure significantly improved DO2 and VO2. Dopamine under comparable conditions produced less improvement in DO2 and VO2 than that of dobutamine; most of the VO2 changes were not significant. The monitored patterns of cardiac index, DO2, and VO2 may be used to evaluate the adequacy of tissue perfusion as well as the relative effectiveness of alternative therapies. Second, these physiologic criteria may be used to titrate therapy in order to achieve optimal outcome. Third, after colloids optimally expand the plasma volume, dobutamine may be used to enhance flow and the distribution of flow in order to improve tissue oxygenation. Vasodilators may be used when hypertensive episodes occur or there is an inadequate response to inotropic agents. Vasopressors are used as a last resort, usually in the terminal or preterminal state.

Measurement of Oxygen Transport

Measurement of Oxygen Transport

Effect of blood transfusion on oxygen consumption in pediatric septic shock

Treatment plans for pediatric septic shock advocate increasing oxygen consumption (VO2). Recent studies in septic shock indicate that improving oxygen delivery (DO2) by increasing blood flow will increase VO2. We prospectively examined the effect on VO2 of improving DO2 by increasing oxygen content (CO2) with blood transfusion in eight hemodynamically stable septic shock patients. Transfusion consisted of 8 to 10 ml/kg of packed RBC over 1 to 2 h. Hemodynamic and oxygen transport measurements were obtained before and after blood transfusion. Transfusion significantly (p less than .05) increased Hgb and Hct from 10.2 +/- 0.8 g/dl and 30 +/- 2% to 13.2 +/- 1.4 g/dl and 39 +/- 4%, respectively (mean +/- SD). DO2 significantly (p less than .05) increased after transfusion (599 +/- 65 to 818 +/- 189 ml/min.m2), but VO2 did not change (166 +/- 68 to 176 +/- 74 ml/min.m2; NS). In pediatric septic shock patients, increasing CO2 by blood transfusion may not increase VO2.

Oxygen Delivery and Consumption and Ventricular Preload Are Greater in Survivors than in Nonsurvivors of the Adult Respiratory Distress Syndrome

In patients with adult respiratory distress syndrome (ARDS), oxygen consumption (VO2) is pathologically dependent on oxygen delivery (DO2). Because of alterations in ventricular function, DO2 may be inadequate to satisfy oxygen demand and may contribute to multiple-system organ failure (MSOF). To determine whether there are differences in DO2, VO2, ventricular function, and MSOF, between survivors and nonsurvivors of ARDS, we studied 29 patients without cardiac disease early in the course of ARDS (hypoxemia, diffuse bilateral pulmonary infiltrates, and pulmonary artery occlusion pressure less than 18 mm Hg). Simultaneous hemodynamic, radionuclide cineangiographic, and oxygen transport measurements were made within 24 h of onset of ARDS. Thirteen survivors had greater DO2 and VO2 than did 16 nonsurvivors (p = 0.004 and 0.001, respectively). MSOF developed in no survivors and in 63% of nonsurvivors. In four survivors and in six nonsurvivors in whom DO2 was changed acutely, VO2 was dependent on DO2 (p = 0.014). Survivors had greater stroke volume index and right and left ventricular end-diastolic volume indices than did nonsurvivors despite similar right atrial and pulmonary artery occlusion pressures. There were no differences between survivors and nonsurvivors in biventricular ejection fractions. We conclude that survivors of ARDS have greater DO2 and VO2 than do nonsurvivors. Survival may be explained by the strong inverse relation between DO2 and development of MSOF.(ABSTRACT TRUNCATED AT 250 WORDS)

Spin-Label Saturation-Recovery Electron Spin Resonance Measurements of Oxygen Transport in Membranes*

Article Spin-Label Saturation-Recovery Electron Spin Resonance Measurements of Oxygen Transport in Membranes* was published on January 1, 1987 in the journal Zeitschrift für Physikalische Chemie (volume 153, issue 1-2).

Airway pressure gradient during high-frequency ventilation

Six mongrel dogs, each serving as its own control, underwent ventilatory trials on high-frequency positive-pressure ventilation (HFPPV) and high-frequency oscillation (HFO), before and after oleic acid-induced lung injury. Central and distal airway pressures were compared to simultaneous measurements of oxygen transport and shunt fraction. Airway pressure differences were more pronounced with HFO. Mean proximal pressure with HFO was 4.91 +/- 1.9 mm Hg, rising to 11.6 +/- 3.6 mm Hg distally. HFPPV produced somewhat higher proximal and distal pressures of 9.5 +/- 5.2 and 14.2 +/- 6.9 mm Hg, respectively. After induction of lung injury with a subsequent decrease in compliance, central (proximal) airway pressures remained relatively unchanged, while distal pressures showed a further rise, thus increasing the pressure gradient to 9.2 +/- 3.8 mm Hg for HFO and 6.6 +/- 4.6 mm Hg for HFPPV. Shunt fraction increased with decreased oxygen transport after lung injury in both models; however, the increase was less pronounced with HFO, which maintained a greater pressure gradient. The distal increase in airway pressures may be important in maintaining critical closing volumes in the diseased lung. By creating a pressure gradient, high-frequency ventilation by either jet or oscillator may improve functional residual capacity and oxygenation.

Measurements of oxygen transport in single capillaries.

Most oxygen is tranported to tissue cells across the walls of capillaries. The thin barrier between blood and the interstitial space and the relatively long contact time of blood within the capillary make diffusional oxygen exchange an effective process. Since most oxygen is carried in reversible combination with. hemoglobin inside the red cells (RBC), erythrocytes play a dominant role in any description of oxygen transport at the capillary level. The rate at which oxygen is delivered to a capillary is equal to the number of red cells entering the capillary per unit time (RBC flux) times the oxygen content per red cell. The amount of oxygen removed from an RBC as it traverses a capillary depends upon the radial gradient in oxygen partial pressure (PO2), the RBC flux and length of the capillary. The radial gradient in PO2 at the capillary wall is determined by tissue oxygen consumption, diffusion coefficient and solubility. In addition, the neighboring capillaries can influence the PO2 distribution in tissue.

Anodization and backscattering measurements of superimposed metal film-GaAs structures

This paper reports the growth of composite anodic Nb or V oxide and GaAs oxide films on GaAs and studies of the resulting films using Rutherford scattering. The deposited metal films had thicknesses ranging from 6 to 100 nm. These films and a portion of the underlying GaAs where anodized galvanostatically in an acid-glycol-water electrolyte. The resulting voltage time graphs of the composite anodic metal/GaAs system are compared with those measured on the virgin GaAs crystal. Measurements of oxide thickness versus oxide voltage show that the anodization constant is 1.85 nm/V. Rutherford backscattering measurements using 1.6 MeV He + ions are used to measure the composition and the fraction of the composite oxide formed by oxygen ion transport. The latter quantity is measured by implanting a 136Xe layer into the GaAs substrate. The position of the 136Xe layer and its distribution is measured using Rutherford scattering prior and subsequent to anodic oxidation. The results of these measurements are that 82±2% of oxide thickening is due to oxygen transport and the remaining 18% is due to Ga and As transport. This is comparable with measurements of oxygen transport in pure V and Nb systems where it is found to be 72% and 76% respectively. Oxide composition measurements show that both Ga and As are present at the surface of the composite vanadium oxide whereas the niobium oxide is superimposed on the native GaAs oxide in a layered structure.