Eric J. Guilbeau

The Oxygen Tension Field within a Discrete Volume of Cerebral Cortex

Abstract The purpose of this investigation was to experimentally determine with oxygen microelectrodes the characteristics of the oxygen tension field in a discrete volume of rabbit cortex. Over 20,000 measurements were made in 40 New Zealand white rabbits. These measurements were analyzed: (a) graphically, by plotting oxygen tension versus cortex depth; (b) statistically, by constructing oxygen tension histograms; and (c) mathematically, by calculating the arithmetic mean and standard deviation. The majority of values were between 0 and 40 mm Hg. Often sharp changes occurred within small distances. The measured oxygen tension values ranged from near 0 to 90 mm Hg, but 50% of the values occurred between 5 and 20 mm Hg and 70% of all values were below 35 mm Hg. The arithmetic mean was calculated to be 24.54 mm Hg with a standard deviation of 17.98. The oxygen tension histogram was characterized by a concentration of values between 10 and 20 mm Hg and was skewed toward the higher oxygen tension values.

Oxygen Dynamics in Brain

Abstract Following cardiac arrest, measurements with microelectrodes indicate that extracellular brain P O 2 decreases to approximately 0 mm Hg within a few seconds. Theoretical simulations compared with the experimental measurements indicate that the metabolic demand for oxygen, under these conditions, is constant until a very low extracellular P O 2 is attained.

A theoretical analysis of the dynamics of oxygen transport and exchange in the placental-fetal system

This paper presents a systematic mathematical analysis of the transient response of oxygen in the placental and fetal system when disturbances create changes in normal conditions. Particular emphasis is given to changes resulting from upsets in placental maternal flow such as may occur during the contractions of labor. Response in the placenta was found to be rapid, but when interconnected with the fetal system both the quality and quantity of response was altered. Oxygen response in the fetal system to changes in maternal placental flow was considerably damped at the organ level and relatively slow. Following a total cessation of maternal flow, several minutes were required theoretically to obtain anoxia in brain provided all other factors remained constant.

A Distributed Parameter Mathematical Analysis of Oxygen Exchange from Maternal to Fetal Blood in the Human Placenta

Based on the present state of knowledge concerning the anatomy and physiology of the placenta, a theoretical analysis of the transport of oxygen from maternal to fetal blood is presented in this paper. Distributed parameter mathematical models are derived which describe the convection, diffusion and reaction processes involved in the oxygen exchange. Steady state simulations of placental oxygen transport are obtained by solving the mathematical models for two cases. Case 1 is a simulation of oxygen transport as if it occurred from maternal blood flowing concurrently to fetal blood in a straight capillary. Case 2 simulated the process as if it occurred in a multivillous flow pattern with concurrent flow characteristic of each exchange unit.

Label Free Detection of L-Glutamate Using Microfluidic Based Thermal Biosensor

A thermoelectric biosensor for the detection of L-glutamate concentration was developed. The thermoelectric sensor is integrated into a micro-calorimeter which measures the heat produced by biochemical reactions. The device contains a single flow channel that is 120 µm high and 10 mm wide with two fluid inlets and one fluid outlet. An antimony-bismuth (Sb-Bi) thermopile with high common mode rejection ratio is attached to the lower channel wall and measures the dynamic changes in the temperature when L-glutamate undergoes oxidative deamination in the presence of glutamate oxidase (GLOD). The thermopile has a Seebeck coefficient of ~7 µV·(m·K)−1. The device geometry, together with hydrodynamic focusing, eliminates the need of extensive temperature control. Layer-by-layer assembly is used to immobilize GLOD on the surface of glass coverslips by alternate electrostatic adsorption of polyelectrolyte and GLOD. The impulse injection mode using a 6-port injection valve minimizes sample volume to 5 µL. The sensitivity of the sensor for glutamate is 17.9 nVs·mM−1 in the linear range of 0–54 mM with an R2 value of 0.9873. The lowest detection limit of the sensor for glutamate is 5.3 mM.

Thermoelectric lab-on-a-chip ELISA

We report a new, thermoelectric method for performing enzyme-linked immunosorbent assay (ELISA) in a microfluidic device. The concentration of the analyte is determined by measuring the heat of an enzymatic reaction between glucose and glucose oxidase using thin-film antimony/bismuth thermopile. The feasibility of lab-on-a-chip thermoelectric ELISA is demonstrated by measuring the concentration of 8-hydroxy-2-deoxyguanosine (8OHdG) in urine samples from amyloid precursor protein transgenic mice. The detection method is based on formation of a complex between 8OHdG, anti-8OHdG capture antibody and glucose oxidase linked IgG antibody. The complex is immobilized at the lower channel wall of the microfluidic device, over the measuring junctions of the thermopile. The amount of heat detected by the thermoelectric sensor is inversely proportional to the concentration of 8OHdG. Standard calibration curve was created using synthetic 8OHdG. The regression line equation of the standard calibration curve was used to estimate the concentration of 8OHdG in mouse urine.

Mathematical Analysis of Combined Placental-Fetal Oxygen Transport

During contractions of labor, uterine blood flow varies directly with the strength and duration of the contraction (3,5,6). in addition to observations in sheep and dogs, radioangiographic studies have shown that in both monkeys and humans, placental intervillous blood flow is reianded in bySynchrony Will the atenine contractions of labor (2,13). Prolonged partial asphyxia resulting from strong oxytoxin induced contractions have been shown to produce varying degrees of brain damage in term monkey fetuses (11,12).

Fetal brain PO2 transient response during hypoxia and hyperoxia

Abstract The purpose of this investigation was to experimentally determine the response of fetal brain PO2 to dynamic changes in the oxygen tension of maternal arterial blood using oxygen microelectrodes. Both hyperoxia and hypoxia were investigated. Recordings of the variation in fetal cortical oxygen tension during the transition from maternal hyperoxia to maternal normoxia and the return to maternal hyperoxia were obtained. Also recordings showing the variations in fetal cortical oxygen tension during the transition from maternal hyperoxia to maternal hypoxia and the subsequent return to hyperoxia were obtained. It was observed that fetal brain oxygen tensions are considerably lower than those measured in the adult. In many instances administration of 100% oxygen to the mother improved fetal brain oxygenation. The response of fetal brain PO2 to changes in the oxygen tension of maternal arterial blood was delayed by a finite quantity of time. The average value obtained for this delay was 38 sec. An overshoot phenomena was observed during hypoxia recovery, which indicates a fetal control mechanism which acts to compensate for brief periods of hypoxia in the microenvironment.

Experimental and Theoretical Analysis of Oxygen Transport in Fetal Brain

Based on the results obtained in this study and the results of others it seems safe to conclude the following: 1) Fetal brain PO2 values are considerably lower than those found in adult brain. 2) Administration of 100% oxygen to the mother can (but not always) significantly raise the PO2 at a specific point in the fetal cortex. 3) The response of fetal brain PO2 to changes in maternal arterial PO2 is delayed by a finite quantity of time of the order of magnitude of 38 seconds. 4) The time required for the fetal brain PO2 to reach a minimum following a decrease in the PO2 of maternal arterial blood coincides closely with the time required for the maternal arterial PO2 to reach its minimum plus the pure transport delay time (38 seconds). 5) The fetus has available a control mechanism which acts to compensate for periods of reduced PO2 in the microenvironment of the fetal cortex.

Highly Sensitive Microfluidic Chip Sensor for Biochemical Detection

Chip calorimetry offers a power tool for fast and high throughput analysis of biochemical process. However, it is challenging to realize an inexpensive, easy to fabricate microfluidic chip-based calorimeter with high sensitivity. This paper describes the design of a novel, highly sensitive, and continuous flow microfluidic chip sensor with an integrated antimony (Sb)–bismuth (Bi) thin-film thermopile heat detection element. The geometry and the design of the microfluidic device facilitate hydrodynamic flow focusing, and the integration and design of the thermopile sensor into the microfluidic device eliminates the need for reference temperature control. The device contains a single flow channel that is