Requirements for estimation of doses from contaminants dispersed by a 'dirty bomb' explosion in an urban area.

The ARGOS decision support system is currently being extended to enable estimation of the consequences of terror attacks involving chemical, biological, nuclear and radiological substances. This paper presents elements of the framework that will be applied in ARGOS to calculate the dose contributions from contaminants dispersed in the atmosphere after a 'dirty bomb' explosion. Conceptual methodologies are presented which describe the various dose components on the basis of knowledge of time-integrated contaminant air concentrations. Also the aerosolisation and atmospheric dispersion in a city of different types of conceivable contaminants from a 'dirty bomb' are discussed.

Estimation of health hazards resulting from a radiological terrorist attack in a city.

In recent years, the concern for protection of urban populations against terror attacks involving radiological, biological or chemical substances has attracted increasing attention. It sets new demands to decision support and consequence assessment tools, where the focus has traditionally been on accidental exposure. The aim of the present study was to illustrate issues that need to be considered in evaluating the radiological consequences of a 'dirty bomb' explosion. This is done through a worked example of simplified calculations of relative dose contributions for a specific 'dirty bomb' scenario leading to atmospheric dispersion of 90Sr contamination over a city area. Also, the requirements of atmospheric dispersion models for such scenarios are discussed.

Data assimilation in the decision support system rodos.

Model predictions for a rapid assessment and prognosis of possible radiological consequences after an accidental release of radionuclides play an important role in nuclear emergency management. Radiological observations, e.g. dose rate measurements, can be used to improve such model predictions. The process of combining model predictions and observations, usually referred to as data assimilation, is described in this article within the framework of the real time on-line decision support system (RODOS) for off-site nuclear emergency management in Europe. Data assimilation capabilities, based on Kalman filters, are under development for several modules of the RODOS system, including the atmospheric dispersion, deposition, food chain and hydrological models. The use of such a generic data assimilation methodology enables the propagation of uncertainties throughout the various modules of the system. This would in turn provide decision makers with uncertainty estimates taking into account both model and observation errors. This paper describes the methodology employed as well as results of some preliminary studies based on simulated data.

History of blood gas analysis. VI. Oximetry.

Oximetry, the measurement of hemoglobin oxygen saturation in either blood or tissue, depends on the Lambert-Beer relationship between light transmission and optical density. Shortly after Bunsen and Kirchhoff invented the spectrometer in 1860, the oxygen transport function of hemoglobin was demonstrated by Stokes and Hoppe-Seyler, who showed color changes produced by aeration of hemoglobin solutions. In 1932 in Göttingen, Germany, Nicolai optically recorded the in vivo oxygen consumption of a hand after circulatory occlusion. Kramer showed that the Lambert-Beer law applied to hemoglobin solutions and approximately to whole blood, and measured saturation by the transmission of red light through unopened arteries. Matthes in Leipzig, Germany, built the first apparatus to measure ear oxygen saturation and introduced a second wavelength (green or infrared) insensitive to saturation to compensate for blood volume and tissue pigments. Millikan built a light-weight ear "oximeter" during World War II to train pilots for military aviation. Wood added a pneumatic cuff to obtain a bloodless zero. Brinkman and Zijlstra in Groningen, The Netherlands, showed that red light reflected from the forehead could be used to measure oxygen saturation. Zijlstra initiated cuvette and catheter reflection oximetry. Instrumentation Laboratory used multiple wavelengths to measure blood carboxyhemoglobin and methemoglobin is cuvette oximeters. Shaw devised an eight-wavelength ear oximeter. Nakajima and co-workers invented the pulse oximeter, which avoids the need for calibration with only two wavelengths by responding only to the pulsatile changes in transmitted red and infrared light. Lübbers developed catheter tip and cuvette fiberoptic sensors for oxygen tension, carbon dioxide tension, and pH.

History of blood gas analysis. V. Oxygen measurement.

The first biologic use of a platinum cathode for oxygen monitoring was reported in 1938 by Blinks and Skow, who was studying photosynthesis. Their report led to the tissue oxygen studies of Davies, Brink, and Bronk. Clark, by covering cathode and anode with a polyethylene membrane, changed the polarographic cathode from a sensor of oxygen availability by diffusion to a measure of oxygen tension (PO2) in the solution and thereby facilitated an enormous expansion of the study of the respiratory physiology of blood oxygen after 1956. Clark's electrode led to the development of the present commercial blood gas systems that measure pH, carbon dioxide tension (PCO2), and PO2 and calculate many derived variables. Variations on Clark's electrode were designed for in vivo catheter-tip recording; gas phase oxygen monitoring; determining oxygen content of blood by releasing hemoglobin-bound oxygen and measuring PO2; and determining oxygen consumption in cell cultures (thus replacing Warburg manometry). By reducing the cathode diameter, Staub and others eliminated the need for stirring the blood samples. Concurrent research with amperometric or polarographic oxygen measurement led Hersch to develop the means of determining oxygen content by coulometry in large cells that consumed all the injected oxygen. Methods of applying noninsulating, but protein impermeable, membranes to cathodes and of recessing cathodes into glass permitted measurement of PO2 in tissues and fluids with microelectrodes.

History of blood gas analysis. IV. Leland Clark's oxygen electrode.

The electrochemical reduction of oxygen was discovered by Heinrich Danneel and Walter Nernst in 1897. Polarography using dropping mercury was discovered accidentally by Jaroslav Heyrovsky in Prague in 1922. This method produced the first measured oxygen tension values in plasma and blood in the 1940s. Brink, Davies, and Bronk implanted platinum electrodes in tissue to study oxygen supply, or availability, from about 1940, but these bare electrodes became poisoned when immersed in blood. Leland Clark sealed a platinum cathode in glass and covered it first with cellophane; he then tested silastic and polyethylene membranes. In 1954 Clark conceived and constructed the first membrane-covered oxygen electrode having both the anode and cathode behind a nonconductive polyethylene membrane. The limited permeability of polyethylene to oxygen reduced depletion of oxygen from the sample, making possible quantitative measurements of oxygen tension in blood, solutions, or gases. This invention led to the introduction of modern blood gas apparatus.

History of blood gas analysis. III. Carbon dioxide tension.

The measurement of carbon dioxide tension (Pco2) owes its development to the 1952 polio epidemics in Copenhagen and the United States, during which artificial ventilation was first widely and effectively used and it was necessary to assess its effectiveness. Pco2 had been determined by various "bubble methods" in which carbon dioxide (CO2) was measured in gas equilibrated with blood at body temperature, or by one of two methods using the manometric apparatus of Van Slyke: interpolation on a plot of CO2 content versus equilibration gas Pco2 or use of the Henderson-Hasselbalch equation to calculate Pco2 from pH and plasma CO2 content. In 1954 Richard Stow described a CO2 electrode--a new concept--using a rubber membrane permeable to CO2 to separate a wet pH and reference electrode from the blood sample. This was the first membrane electrode, a device now used in hundreds of different ways. Severinghaus developed Stow's electrode, stabilizing it with a bicarbonate-salt solution and a spacer. The CO2 electrode concept had occurred to Gesell in 1925, but for measurement of gas only, and to Gertz and Loeschcke, who were unaware of the Stow-Severinghaus electrode, in 1958. The development of the CO2 electrode terminated the use of bubble methods, the Van Slyke methods, and the Astrup technique and at the same time reinforced the Astrup-Siggaard-Andersen acid-base analytic theory.

History of blood gas analysis. II. pH and acid-base balance measurements.

Electrometric measurement of the hydrogen ion concentration was discovered by Wilhelm Ostwald in Leipzig about 1890 and described thermodynamically by his student Walther Nernst, using the van't Hoff concept of osmotic pressure as a kind of gas pressure, and the Arrhenius concept of ionization of acids, both of which had been formalized in 1887. Hasselbalch, after adapting the pH nomenclature of Sørensen to the carbonic-acid mass equation of Henderson, made the first actual blood pH measurements (with a hydrogen electrode) and proposed that metabolic acid-base imbalance be quantified as the "reduced" pH of blood after equilibration to a carbon dioxide tension (PCO2) of 40 mm Hg. This good idea, coming 40 years before simple blood pH measurements at 37 degrees C became widely available, was never adopted. Instead, Van Slyke developed a concept of acid-base chemistry that depended on measuring plasma CO2 content with his manometric apparatus, a standard method until the 1960s, when it was displaced by the three-electrode method of blood gas analysis. The 1952 polio epidemic in Copenhagen stimulated Astrup to develop a glass electrode in which pH could be measured in blood at 37 degrees C before and after equilibration with known PCO2. He introduced the interpolative measurement of PCO2 and bicarbonate level (later base excess) using only pH measurements and, with Siggaard-Andersen, developed clinical acid-base chemistry. Controversy arose when blood base excess was noted to be altered by acute changes in PCO2 and when abnormalities of base excess were called metabolic acidosis or alkalosis, even when they represented compensation for respiratory abnormalities in PCO2. In the 1970s it became clear that "in-vivo" or "extracellular fluid" base excess (measured at an average extracellular fluid hemoglobin concentration of 5 g) eliminated the error caused by acute changes in PCO2. Base excess is now almost universally used as the index of nonrespiratory acid-base imbalance.

History of blood gas analysis. I. The development of electrochemistry.

In 1982 Poul Astrup, in writing a history of acid base balance and blood gases, invited me to contribute a chapter about the modern period, from 1950 to the present. Astrup's book is scheduled for publication at the end of 1985 by Radiometer Company of Copenhagen; it will be distributed by Munksgaard (Blackwell). The story of blood gas analysis since 1950 is vast: there are some 420 references to methodology and closely related physiology. This "modern" history will appear in the Journal of Clinical Monitoring as a series of essays. This first essay centers on electrochemistry, the basis of modern blood gas analysis, and accordingly examines its roots in more detail. The 17th and 18th century exploration of electricity and gas laws led to the development of thermodynamic electrochemistry in 1887 through the collaborative efforts of van't Hoff, Arrhenius, Ostwald, and Nernst. The importance of the hydrogen ion in biology and in the body's buffering mechanisms was worked out by Henderson, Van Slyke, Barcroft, and many others in the first quarter of this century. The glass electrode became available after 1925, but practical blood pH measurement was introduced in the 1950s by Astrup and Siggaard Andersen. Succeeding essays will concern micro pH methods and base excess analysis, the discoveries of Stow's CO2 electrode and Clark's O2 electrode, the development of oximetry, and related physiology.

Exposure of rabbits to carbon monoxide and other gas phase constituents of tobacco smoke.

Non cholesterol-fed rabbits were exposed to carbon monoxide at concentrations in air of either 200, 2000, or 4000 ppm (= 0.02, 0.2, or 0.4% vol/vol). Further, exposure was performed to 0.5 ppm hydrogen cyanide alone or in combination with 200 ppm carbon monoxide or with 200 ppm carbon monoxide and 5 ppm nitric oxide and eventually to 50 ppm carbonyl sulphide. Duration of the continuous exposures were between 1/2 week and 12 weeks. Using the same criteria for intimal damage as in earlier morphological studies, no histotoxic effect on intimal/subintimal morphology of coronary arteries or the aorta could be demonstrated, when light-microscopic evaluation was performed blindly.

Moderate hypoxia exposure and fetal development.

Exposure of rabbits to 15.5% oxygen during pregnancy resulted in a 17% decrease of birth weight and a neonatal mortality of 19% as opposed to 1% in the control groups, just corresponding to the effects obtained previously by moderate exposure of pregnant rabbits to carbon monoxide. Since additive effects of hypoxia exposure and carbon monoxide exposure are supposed to occur, it is concluded that women living at a high altitude should be warned particularly about the risk of delivering small babies if they have been smoking during their pregnancy.