Diffusion coefficients of oxygen and hemoglobin measured by facilitated oxygen diffusion through hemoglobin solutions.

Diffusion coefficients of oxygen (DO2) and hemoglobin (DHb) were obtained from measuring the oxygen flux through thin layers of hemoglobin solutions at 20 degrees C. The liquid layers were supported by a membrane and not soaked in any filter material. Oxygen fluxes were measured from the changes in oxygen partial pressure in the gas phases at both sides of the layer. A mathematical treatment is presented for correct evaluation of the measurements. Measurements were done for bovine and for human hemoglobin. Hemoglobin concentrations (CHb) were between 11 and 42 g/dl, which covers the concentrations in the erythrocyte. Both DO2 and DHb could be fitted to the empirical equation D = D0(1-CHb/C1)10-CHb/C2. The following parameters were obtained: DO = 1.80 x 10(-9) m2/s, C1 = 100 g/dl, C2 = 119 g/dl, for oxygen and D0 = 7.00 x 10(-11) m2/s, C1 = 46 g/dl, C2 = 128 g/dl, for hemoglobin. No difference between the diffusion coefficients of bovine or human hemoglobin was found. The diffusion coefficients of hemoglobin were higher than most values reported in the literature, probably because in this study the mobility of hemoglobin was not hindered by surrounding filter material.

Reaction rates of oxygen with hemoglobin measured by non-equilibrium facilitated oxygen diffusion through hemoglobin solutions.

The purpose of this study was to verify the concept of non-equilibrium facilitated oxygen diffusion. This work succeeds our previous study, where facilitated oxygen diffusion by hemoglobin was measured at conditions of chemical equilibrium, and which yielded diffusion coefficients of hemoglobin and of oxygen. In the present work chemical non-equilibrium was induced using very thin diffusion layers. As a result, facilitation was decreased as predicted by theory. Thus, this work presents the first experimental demonstration of non-equilibrium facilitated oxygen diffusion. In addition, association and dissociation rate parameters of the reaction between oxygen and bovine and human hemoglobin were calculated and the effect of the homotropic and heterotropic interactions on each rate parameter was demonstrated. The results indicate that the homotropic interaction--which leads to increasing oxygen affinity with increasing oxygenation--is predominantly due to an increase in the association rate. The heterotropic interaction--which leads to decreasing oxygen affinity by anionic ligands--appears to be effected in two ways. Cl- increases the dissociation rate. In contrast, 2,3-diphosphoglycerate decreases the association rate.

Reestimation of the effects of inorganic phosphates on the equilibrium between oxygen and hemoglobin.

In a previous paper, published in this journal, we showed that the data obtained in patients with severe ketoacidosis suggest that inorganic phosphates (K2HPO4) can increase their P50 and therefore enhance tissue oxygenation without concomitant alteration of the 2,3 diphosphoglycerate (DPG). In order to test the hypothesis that K2HPO4 could influence the oxyhemoglobin dissociation curve (ODC) by a mecanism which was not DPG mediated we have measured the total ODC on whole blood with and without addition of 13-80 mmol/l of inorganic phosphates. On average, the level of DPG remained unchanged when the P50 with K2HPO4 was significantly higher (p greater than 0.001) (P50 = 29.9 +/- 3.7 mmHg) than when phosphates were not administered (P50 = 25.5 +/- 2.8 mmHg). The relationship between P50 (mmHg) and K2HPO4 (= X mmol/l) was delta P50 = -2.97 10(-3)(X)2 +0.26(X)-0.42 (r = 0.78). Seeing that phosphates have an immediate action on the ODC, we calculated in our ketoacidosis patients, the relationship between the P50, the inorganic phosphates (P(i) in mg%) and the DPG in mumol/gHb. Both factors exert a highly significant effect (p less than 0.001) on the P50, according to the following equation: P50 = 0.35 DPG +0.26 P(i) + 18.92 (r = 0.73). Our data are important in two points. First it is useful to add inorganic phosphates to the treatment of patients with severe ketoacidosis in order to enhance their tissue oxygenation. Second they recall that the ODC is not only determined by the classical effects of temperature, pH and DPG but also by inorganic anions, like phosphates as described by Benesh and Benesh in their pioneering work.

Early detection of hemorrhagic hypovolemia by muscle oxygen pressure assessment: preliminary report.

Skeletal muscle PO2 was studied during graded hemorrhagic shock in Labrador dogs by means of a polarographic needle PO2 electrode. Compared to hemodynamic, blood gas, biochemical, and hematologic variables, a shift to the left of the cumulative histogram of skeletal muscle PO2 was the earliest and most sensitive indicator of impaired skeletal muscle oxygenation. The mean arterial blood pressure and the mean of the medians of the skeletal muscle PO2, respectively, were as follows: during the control period 125 and 38.1 mm Hg, during the imminent shock period 143 and 24.5 mm Hg, and during the shock period 89 and 5.1 mm Hg. This electrode is suitable for clinical use.

Effect of lung volume and positional changes on pulmonary diffusing capacity and its components.

Normal subjects have a larger diffusing capacity normalized per liter alveolar volume (DL/VA) in the supine than in the sitting position. Body position changes total lung diffusing capacity (DL), DL/VA, membrane conductance (Dm), and effective pulmonary capillary blood volume (Qc) as a function of alveolar volume (VA). These functions were studied in 37 healthy volunteers. DL/VA vs. VA yields a linear relationship in sitting as well as in supine position. Both have a negative slope but usually do not run parallel. In normal subjects up to 50 yr old DL/VA and DL increased significantly when subjects moved from a sitting to a supine posture at volumes between 50 and 100% of total lung capacity (TLC). In subjects greater than 50 yr old the responses of DL/VA and DL to change in body position were not significant at TLC. Functional residual capacity (FRC) decreases and DL/VA increases in all normal subjects when they change position from sitting to supine. When DL/VA increases more than predicted from the DL/VA vs. VA relationship in a sitting position, we may infer an increase in effective Qc in the supine position. In 56% of the volunteers, supine DL was smaller than sitting DL despite a higher DL/VA at FRC in the supine position because of the relatively larger decrease in FRC. When the positional response at TLC is studied, an estimation obtained accidentally at a volume lower than TLC may influence results. Above 80% of TLC, Dm decreased significantly from sitting to supine. Below this lung volume the decrease was not significant. The relationship between Qc and VA was best described by a second-order polynomial characterized by a maximum Qc at a VA greater than 60% of TLC. Qc was significantly higher in the supine position than in the sitting position, but the difference became smaller with increasing age. In observing the sitting and supine positions, we saw a decrease in maximum Qc normalized per square meter of body surface area with age.

Effect of metabolic acidosis on pulmonary gas exchange of artificially ventilated dogs.

It is well established that metabolic acidosis induces a reduction in alveolar-arterial O2 difference [(A-a)Do2] in artificially ventilated dogs by shifting the oxyhemoglobin dissociation curve (ODC) and/or by improving the distribution of the ventilation-to-perfusion ratio (VA/Q) throughout the lung. To assess the influence of these two factors we examined eight artificially ventilated dogs before and after induction of metabolic acidosis by a perfusion of 0.3 mol HCl. We measured classic indexes of cardiopulmonary function. VA/Q distribution was estimated using the multiple inert gas elimination technique (MIGET). ODC and Bohr effect of each dog were obtained by a dynamic method. Acidosis increased CO2 excretion, respiratory quotient, blood PO2 at 50% saturation, and arterial PCO2 and PO2 with a simultaneous decrease in (A-a)DO2. In seven dogs, the distribution of VA and Q, as assessed by MIGET, was not substantially modified by HCl perfusion. In the eighth dog the distribution of Q and VA became more homogeneous after acidosis. This led us to conclude that the Bohr effect is the most important and most consistently observed factor responsible for the decrease in (A-a)DO2 found in metabolic acidosis. In rare cases the increase in pulmonary arterial pressure may complement this action by improving the distribution of the VA/Q ratio.

Computed myocardial PO2 histograms: effects of various geometrical and functional conditions.

A model of myocardial oxygenation was developed that allows calculation of Po2 histograms under varying conditions. The model consists of parallel tissue cylinders with varying radii, simulating the heterogeneity of capillary spacing, in agreement with our previous experimental results. The facilitated diffusion of O2 by myoglobin, an additional resistance to diffusion at the capillary level, and the Michaelis-Menten type of O2 consumption were also incorporated. The shape of the histograms depends on input data. When no additional barrier to O2 transport is included, the histograms resemble those obtained with Po2 surface electrodes, and they are strongly dependent on heterogeneity in capillary spacing and capillary blood flow. On the other hand, an inclusion of an additional capillary barrier combined with the Michaelis-Menten type of O2 consumption can generate Po2 histograms similar to those derived from myoglobin cryospectroscopy. In this case, the Po2 histograms are relatively independent of heterogeneity of capillary spacing and blood flow. The facilitation of O2 diffusion by myoglobin has only a modest effect on the form of the histograms in all situations considered.

Early detection of shock in critically ill patients by skeletal muscle PO2 assessment.

The usefulness of skeletal muscle PO2 assessment in monitoring patients at risk of shock was evaluated in 20 critically ill patients. A shock score, inotropic score, and combined inotropic-shock score were calculated. If the median skeletal muscle PO2 assessment was more than 31.5 mm Hg, no shock occurred in the period from 4 hours before to 6 hours after the measurement. The risk of shock occurring during the first 2 hours after the skeletal muscle PO2 assessment was 2.2 times higher if median skeletal muscle PO2 assessment was below 22.5 mm Hg. If inotropes were administered, no significant difference was found in the incidence of shock if skeletal muscle PO2 was below or above 22.5 mm Hg. Skeletal muscle PO2 assessment enables the determination of the severity of shock and determination of risk of shock in critically ill patients, provided no treatment with inotropes has been instituted.

Apical suspension test.

In stress incontinence, urinary leakage can be controlled by support of the anterior vaginal wall by applying pressure directly at the bladder neck (the Marshall test) or applying pressure remotely. In the latter maneuver, a cotton ball, gripped in the jaws of a sponge stick, engages the vaginal vault near the apex and rotates it posteriorly and horizontally. This tenses the anterior vaginal wall thereby controlling stress-induced leakage. The mechanism of action and some surgical implications are discussed.

Regulation of the peripheral vasculature and tissue oxygenation in health and disease.

The evidence has become convincing that in certain critical illnesses such as ARDS, there is pathologic disturbance in O2 delivery to the tissues. This disturbance is marked by an abnormal dependency of O2 uptake upon total O2 delivery. Although this has been attributed to mitochondrial dysfunction in the past, current belief is that such apparent dysfunction is secondary to derangement of the microcirculation that causes an impairment in tissue oxygenation. Microembolization and other disturbances in the local regulation of perfusion have been postulated to be responsible for this derangement. The net effect is to increase the diffusion pathway for oxygen from the tissue capillary. Our ability to deal conceptually with this kind of alteration in tissue oxygenation is dependent upon the mathematical model that is applied. We have discussed two generic models for tissue oxygenation to show the constraints imposed upon quantifying the effects of alteration in any single factor upon tissue PO2. The salient factor that has emerged is that creation of greater than normal heterogeneity in flow or its distribution in the peripheral microcirculation has the inevitable consequence of making tissue hypoxic.

The effect of blood O2 affinity on the efficiency of O2 transport in blood at hypoxic hypoxia.

An index of the efficiency of O2 transport in blood and delivery to tissues, the capacitance coefficient beta, was theoretically analyzed as a function of the position of the blood O2 dissociation curve (ODC). The P50 at which beta reaches its maximum is high at normoxia and decreases with lowering the ambient PO2. At very deep hypoxia this value becomes lower than the normal P50 of human blood. An increase of blood O2 capacity enlarges beta, particularly at deep hypoxia, and also increases the P50 at which maximal beta is reached. Changes of (a-v)O2 have ambivalent effects, depending on both P50 and PaO2. The capacitance coefficient beta was further calculated as a function of PaO2 at three values of P50, simulating the effect of a shift of the ODC. The capacitance coefficient is several times higher at deep hypoxia than at normoxia at all values of P50 used. A shift of the ODC to the left results in a moderate decrease of beta at mild hypoxia but in a large increase at severe hypoxia; a shift to the right has a reverse effect.