PH measurements blood

The present state of the art in blood pH measurements allows for rapid (1 minute) determination of pH between 6.4 and 8.0 to within at least 0.005 units for whole blood sample volumes < 100 microliters. The temperature of the electrodes and sample is generally controlled to within 0.1 °C for this level of precision and frequent calibration is carried out (in some cases a one point calibration for each sample). The electrodes require (both the glass and external reference) some maintenance due to protein fouling, however this procedure is largely automated. The useful life of an electrode is one year or less and the cost is well over 100 (U.S.) each. New technologies, both electrochemical and non-electrochemical, must compete with this attractive performance and provide for lower operating costs in order to be successful. 

Grant S.A., Glass S.R., A sol-gel based fiber optic sensor for local blood pH measurements, Sensors andActuat. B 1997 45 35. 

Nl. Natelson, S., and Tietz, N., Blood pH measurement with the glass electrode. Clin. Chem. 2, 320-327 (1956). 

A3. Anker, P., Ammann, D., and Simon, W., Blood pH measurement with a solvent polymeric membrane electrode in comparison with a glass electrode. Mikrochim. Acta 1, 237-242 (1983). 

The KH2P04-Na2HP04 buffer (pH 7.384 at 38°C) is particularly suited for calibration for blood pH measurements. Many blood pH measurements are made... 

Recall from Chapter 7 that, because the equilibrium constants of the blood buffer systems change with temperature, the pH of blood at the body temperature of 37°C is different than at room temperature. Hence, to obtain meaningful blood pH measurements that can be related to actual physiological conditions, the measurements should be made at 37°C and the samples should not be exposed to the atmosphere. (Also recall that the pH of a neutral aqueous solution at 3TC is 6.80, and so the acidity scale is changed by 0.20 pH unit.)... 

Some useful rules in making blood pH measurements are as follows ... 

An evaluation of the pH sensor [52] in sheep, developed by Peterson et al. demonstrated its aptitude for in vivo blood pH measurement. Although not identical with the values obtained with an invasive microelectrode and with data obtained on withdrawn blood, the agreement between numerical data and trends is very good. It was not possible to say which of the measurements was the most correct. This demonstrates that the fiber-optic method is generally applicable for blood pH measurements in vivo, and gives as good an indication of pH levels as electrode methods. The pH of ewe blood as determined by an electrode, a blood gas analyzer, and a fiber-optic device is shown in Figure 18-9. 

Glass electrode for pH measurement A bulb or other form of hydrogen ion-sensitive glass is attached to the end of a glass tube made from high-resistance glass. Commercially it is usually obtained outfitted with internal filling solution and an internal reference electrode. For special applications, e.g., blood pH measurements, other forms, such as capillaries, are more convenient. 

Immersion electrodes are the most common glass electrodes. These are roughly cylindrical and consist of a barrel or stem of inert glass that is sealed at the lower end to a tip, which is often hemispherical, of special pH-responsive glass. The tip is completely immersed in the solution during measurements. Miniature and microelectrodes are also used widely, particularly in physiological studies. Capillary electrodes permit the use of small samples and provide protection from exposure to air during the measurements, eg, for the determination of blood pH. This type of electrode may be provided with a water jacket for temperature control. 

Aperture impedance measurements of cell volume must take into account the osmolaUty and pH of the medium. A hypotonic medium causes cells to swell a hypertonic medium causes them to shrink. Some manufacturers of aperture impedance counters deHberately provide hypertonic electrolytic media for red blood cell measurements. The shmnken red cells not only become more nearly spherical and thus less affected by orientation, but also less deformable than cells in isotonic media and thus less affected by differences in hemoglobin content. 

The Newborn and the Laboratory. The wellbeing of the pre-mature infant can be ascertained by measuring blood pH, electrolytes and other blood components on a routine basis. The maintenance of these infants electrolyte balance and normal pH is shown in Figure 3. An infant placed on a high protein diet milk formula developed an acidosis, and when brought to normal pH... 

Four major areas of electrochemistry related to medical diagnostics have been reviewed. Blood pH and gas measurements as well as ISE s represent relatively mature areas which enjoy widespread commercialization. New approaches should yield devices which have superior performance and which are less expensive to produce. Enzyme electrodes and electrochemical immunoassay arc still largely experimental, but the intense level of current research effort coupled with some interesting recent developments should lead to commercial success over the next decade. 

Compound LY231617 was given at a dose of 10 mg/kg i.v. over a period of 5-7 min beginning 1 h after MCAO. Reperfusion occurred at 2 h after MCAO and at that time the rats received 5.0 mg/kg i.v. for 24 h. Mean arteriai blood pressure (MABP), heart rate, arteriai blood pH, PO2 and pCOi were measured. Body temperature was regulated at 36-37°C for the entire 24 h period. 

Measurement of free t-PA in plasma presents challenges in terms of preventing t-PA from complexing to PAI-1 released from platelets after blood collection. To dissociate any preformed t-PA-PAI-1 complex, the anticoagulant pH has to be close to 3.0. Even if blood is collected with an acidic anticoagulant, the blood pH will rise because of the powerful buffering action of hemoglobin. Thus, the pH of plasma has to be adjusted to 3.0 in order to dissociate the t-PA-PAI-I complex (115). 

Suidan J.S., Young B.K., Hetzel F.W., Seal H.R., pH Measurement with a fiber-optic tissue-pH monitor and a standard blood-pH meter, Clin. Chem. 1983 29 1566. 

Furthermore, pH determination has been used in other clinical research, both alone and in combination with other measurements. This research includes studies into the relationship between extracellular and intracellular pH in an ischemic heart [6, 7], the pH of airway lining fluid in respiratory disease [8], the study of pH as a marker for pyloric stenosis [9], malnutrition in alkalotic peritoneal dialysis patients [10], pH modulation of heterosexual HIV transmission [11, 12], and wound prevention and treatment [13], In addition, pH changes due to blood acidosis have been used to trigger and pace the ventricular rate of an implanted cardiac pacemaker [14], Research using pH measurements... 

Reference electrodes provide a standard for the electrochemical measurements. For potentiometric sensors, an accurate and stable reference electrode that acts as a halfcell in the measurement circuit is critical to providing a stable reference potential and for measuring the change in potential difference across the pH sensitive membrane as the pH concentration changes. This is especially important in clinical applications such as pH measurements in the blood, heart, and brain, where the relevant physiological pH range is restricted to a very small range, usually less than one unit. 

Yoon el al. [112] reported an all-solid-state sensor for blood analysis. The sensor consists of a set of ion-selective membranes for the measurement of H+, K+, Na+, Ca2+, and Cl. The metal electrodes were patterned on a ceramic substrate and covered with a layer of solvent-processible polyurethane (PU) membrane. However, the pH measurement was reported to suffer severe unstable drift due to the permeation of water vapor and carbon dioxide through the membrane to the membrane-electrode interface. For conducting polymer-modified electrodes, the adhesion of conducting polymer to the membrane has been improved by introducing an adhesion layer. For example, polypyrrole (PPy) to membrane adhesion is improved by using an adhesion layer, such as Nafion [60] or a composite of PPy and Nafion [117],... 

Metabolic Effects. In studies where metabolic parameters (blood pH, electrolytes, glucose) were measured, no effects were seen after inhalation exposure to -hexane in Fischer 344 rats at up to... 

Metabolic Effects. Metabolic effects have not been reported in humans after exposure to -hexane. In animal studies where metabolic parameters (blood pH, electrolytes, glucose) were measured, no effects were seen after inhalation exposure to -hexane in rats at up to 10,000 ppm for 6 hours a day, 5 days a week for 13 weeks (Cavender et al. 1984) or in B6C3Fj mice similarly exposed (Dunnick et al. 1989 ... 

Homeostatic mechanisms also allow animals to control their intracellular pH very strictly. In humans for example, blood pH (usually taken as a reliable but indirect measure of cellular pH) is 7.4 0.04. At 37 °C cytosolic pH is actually slightly lower at about 7.0 but different compartments within the eukaryotic cells may have quite different pH, for example, lysosomes have an internal pH of about 5 the inside of a mitochondrion is more alkaline than the outside whilst the inside of a phagosome in a white blood cell is more acidic than its surrounding cytosol, both situations arising due to proton pumping across a membrane. 

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