Intra-breath arterial oxygen oscillations detected by a fast oxygen sensor in an animal model of acute respiratory distress syndrome

Background There is considerable interest in oxygen partial pressure (Po2) monitoring in physiology, and in tracking PO2 changes dynamically when it varies rapidly. For example, arterial PO2 (PaO2) can vary within the respiratory cycle in cyclical atelectasis (CA), where PaO2 is thought to increase and decrease during inspiration and expiration, respectively. A sensor that detects these PaO2 oscillations could become a useful diagnostic tool of CA during acute respiratory distress syndrome (ARDS). Methods We developed a fibreoptic PO2 sensor (<200 µm diameter), suitable for human use, that has a fast response time, and can measure PO2 continuously in blood. By altering the inspired fraction of oxygen (FIO2) from 21 to 100% in four healthy animal models, we determined the linearity of the sensor's signal over a wide range of PaO2 values in vivo. We also hypothesized that the sensor could measure rapid intra-breath PaO2 oscillations in a large animal model of ARDS. Results In the healthy animal models, PaO2 responses to changes in FIO2 were in agreement with conventional intermittent blood-gas analysis (n=39) for a wide range of PaO2 values, from 10 to 73 kPa. In the animal lavage model of CA, the sensor detected PaO2 oscillations, also at clinically relevant PaO2 levels close to 9 kPa. Conclusions We conclude that these fibreoptic PaO2 sensors have the potential to become a diagnostic tool for CA in ARDS

A mathematical model for breath gas analysis of volatile organic compounds with special emphasis on acetone

Recommended standardized procedures for determining exhaled lower respiratory nitric oxide and nasal nitric oxide have been developed by task forces of the European Respiratory Society and the American Thoracic Society. These recommendations have paved the way for the measurement of nitric oxide to become a diagnostic tool for specific clinical applications. It would be desirable to develop similar guidelines for the sampling of other trace gases in exhaled breath, especially volatile organic compounds (VOCs) which reflect ongoing metabolism. The concentrations of water-soluble, blood-borne substances in exhaled breath are influenced by: (i) breathing patterns affecting gas exchange in the conducting airways; (ii) the concentrations in the tracheo-bronchial lining fluid; (iii) the alveolar and systemic concentrations of the compound. The classical Farhi equation takes only the alveolar concentrations into account. Real-time measurements of acetone in end-tidal breath under an ergometer challenge show characteristics which cannot be explained within the Farhi setting. Here we develop a compartment model that reliably captures these profiles and is capable of relating breath to the systemic concentrations of acetone. By comparison with experimental data it is inferred that the major part of variability in breath acetone concentrations (e.g., in response to moderate exercise or altered breathing patterns) can be attributed to airway gas exchange, with minimal changes of the underlying blood and tissue concentrations. Moreover, it is deduced that measured end-tidal breath concentrations of acetone determined during resting conditions and free breathing will be rather poor indicators for endogenous levels. Particularly, the current formulation includes the classical Farhi and the Scheid series inhomogeneity model as special limiting cases.Comment: 38 page

Oxygen reduction reaction features in neutral media on glassy carbon electrode functionalized by chemically prepared gold nanoparticles

Gold nanoparticles (AuNPs) were prepared by chemical route using 4 different protocols by varying reducer, stabilizing agent and solvent mixture. The obtained AuNPs were characterized by transmission electronic microscopy (TEM), UV-Visible and zeta potential measurements. From these latter surface charge densities were calculated to evidence the effect of the solvent mixture on AuNPs stability. The AuNPs were then deposited onto glassy carbon (GC) electrodes by drop-casting and the resulting deposits were characterized by cyclic voltammetry (CV) in H2SO4 and field emission gun scanning electron microscopy (FEG-SEM). The electrochemical kinetic parameters of the 4 different modified electrodes towards oxygen reduction reaction (ORR) in neutral NaCl-NaHCO3 media (0.15 M / 0.028 M, pH 7.4) were evaluated by rotating disk electrode voltammetry and subsequent Koutecky-Levich treatment. Contrary to what we previously obtained with electrodeposited AuNPs [Gotti et al., Electrochim. Acta 2014], the highest cathodic transfer coefficients were not obtained on the smallest particles, highlighting the influence of the stabilizing ligand together with the deposits morphology on the ORR kinetics

tidal breathing model of the forced inspired inert gas sinewave technique

We have shown previously that it is possible to assess the cardio-respiratory function using sinusoidally oscillating inert gas forcing signals of nitrous oxide and argon (Hahn et al., 1993). This method uses an extension of a mathematical model of respiratory gas exchange introduced by Zwart et al. (1976), which assumed continuous ventilation. We investigate the effects of this assumption by developing a mathematical model using a single alveolar compartment and incorporating tidal ventilation, which must be solved using numerical methods. We compare simulated results from the tidal model with those from th

tidal breathing model of the forced inspired inert gas sinewave technique

We have shown previously that it is possible to assess the cardio-respiratory function using sinusoidally oscillating inert gas forcing signals of nitrous oxide and argon (Hahn et al., 1993). This method uses an extension of a mathematical model of respiratory gas exchange introduced by Zwart et al. (1976), which assumed continuous ventilation. We investigate the effects of this assumption by developing a mathematical model using a single alveolar compartment and incorporating tidal ventilation, which must be solved using numerical methods. We compare simulated results from the tidal model with those from th

Numerical simulation of the time−dependent current to membrane−covered oxygen sensors .4. Experimental verification that the switch−on transient is non−Cottrellian for microdisc electrodes

We have undertaken an experimental investigation to determine the transient current characteristics of membrane-covered Clark-type microdisc electrode oxygen sensors and have compared the results with those obtained using the two-dimensional numerical simulation methods described previously (D.J. Gavaghan, J.S. Rollett and C.E.W. Hahn, J. Electroanal. Chem., 325 (1992) 23), We obtain improved agreement between experiment and theory, and, in particular, are able to verify the non-Cottrellian behaviour of the switch-on transient for membrane-covered microdisc electrodes that

NUMERICAL−SIMULATION OF THE TIME−DEPENDENT CURRENT TO MEMBRANE−COVERED OXYGEN SENSORS .1. THE SWITCH−ON TRANSIENT

We have examined the nature of the diffusion processes and determined the transient current characteristics of membrane-covered Clark-type oxygen sensors by solving the axially symmetric two-dimensional diffusion equation. Correction for a singularity at the edge of the cathode allows us to achieve a numerical solution which we demonstrate to be accurate to 1%. Earlier one-dimensional theories based on linear or hemispherical diffusion are shown to be grossly inadequate for predicting the variation in behaviour with cathode radius and electrolyte layer thickness. The calculated depletion patterns give insight into the ways in which

Microelectrode studies of isoflurane and oxygen vapour mixtures in dimethyl sulfoxide

The electrochemical reduction of the inhalation anaesthetic agent isoflurane was investigated at a commercially available Au microelectrode (5 μm) in DMSO solvent, individually, and also as a component of a simple vapour mixture with oxygen using both traditional voltammetric and potential step chronoamperometric techniques. In a binary gas mixture with oxygen, isoflurane is shown to react with the superoxide anion radical, formed from the electro-reduction of oxygen complicating their simultaneous detection. The observed cross-interference reaction is shown to be dependent of the electrode size and the concentration of the anaesthetic agent, isoflurane. Under steady-state conditions, and using small diameter microelectrodes (5 μm) and low isoflurane concentration ([ISO] &lt;0.2% v/v), the superoxide/isoflurane reaction is shown to approach a one-electron process, where the coupled homogeneous reaction kinetics are almost "out-run". The use of potential step chronoamperometric techniques however, is shown to significantly reduce the deleterious cross-interference reaction between superoxide and isoflurane. In essence, this work provides scope for the development of a rapid, accurate and inexpensive electrochemical gas sensor for measuring anaesthetic vapour mixture under clinically relevant conditions. © 2004 Elsevier B.V. All rights reserved

Mathematical modelling of pulmonary gas transport

Equations governing the transport of the gases oxygen and carbon dioxide inside the pulmonary capillaries are written down. By analysing these equations it is predicted that there will be negligible limitation to the transport of oxygen when oxygen concentration takes a normal physiological or higher value. For low values of oxygen concentration, there may be limitation to oxygen transport. It is predicted further that the quantity of carbon dioxide excreted from blood into alveolar gas is dependent on oxygen concentration, with low oxygen concentrations inhibiting the carbon dioxide transport process. The relatively slow reaction involving carbon dioxi

A modification of the Bohr method to determine airways deadspace for non-uniform inspired gas tensions

The Bohr method is a technique to determine airways deadspace using a tracer gas such as carbon dioxide or nitrogen. It is based on the assumption that the inspired concentration of the tracer gas is constant throughout inspiration. However, in some lung function measurement techniques where inspired concentration of the tracer gas may be required to vary, or where rapid injection of the tracer gas is made in real time, uniform inspired concentration is difficult or impossible to achieve, which leads to inaccurate estimation of deadspace using the Bohr equation. One such lung function measurement technique is the inspired sinewave technique.In this paper, we proposed a modification of the Bohr method, relaxing the requirement of absolute uniformity of tracer concentration in the inspired breath.The new method used integration of flow and concentration. A computer algorithm sought an appropriate value of deadspace to satisfy the mass balance equation for each breath. A modern gas mixing apparatus with rapid mass flow controllers was used to verify the procedure.Experiments on a tidally ventilated bench lung showed that the new method estimated dead space within 10% of the actual values whereas the traditional Bohr deadspace gave more than 50% error.The new method improved the accuracy of deadspace estimation when the inspired concentration is not uniform. This improvement would lead to more accurate diagnosis and more accurate estimations of other lung parameters such as functional residual capacity and pulmonary blood flow