Oxygen measurements, tissue

Totaro et al. published a detailed paper on the factors affecting measurement of cerebrovascular reactivity when measured by NIR [49]. Some of the points covered were the relative transparency of the skin, skull, and brain in the 700- to 1100-nm region and the oxygen-dependent tissue absorption changes of hemoglobin. Their study covered all relevant factors, such as age, sex, reproducibility (often neglected in many academic papers), and venous return. The test was based on a 3-min baseline, a 3-min hypercapnia (5% C02 in air), and a 2-min recovery period. 

A very good review paper pertaining to tissue imaging was written by Stephen Joffe [171]. He cites 34 published articles on topics such as oxygen measurements, but the strength of the article is in the detailed comparison of NIR with other methods like X-ray, MRI, ultrasound, positron emission, thermal emission, electrical impedance, and more. He discusses the various types of equipment used, detectors, and light sources. He also gives one of the best short descriptions of time-resolved spectroscopy seen in any review article. 

C22. Connelly, C. M., Methods for measuring tissue oxygen tension theory and evaluation the oxygen electrode. Federation Proc. 16, 681-684 (1957). 

Without doubt vitamin E is the most important lipid-soluble chain-breaking antioxidant in the human body. It is able to interact with lipid peroxyl radicals and is also able to react with singlet oxygen. The role of vitamin E as an antioxidant in vivo has been established several times by measuring tissue lipid peroxidation in vitamin E-deficient or in vitamin E-supplemented animals. 

Tissue transillumination experiments allow multi-spectral determination of tissue optical constants and light fluxes, with application to optical mammography [51], photodynamic tumour therapy [52,53] and brain oxygenation measurements... 

Hill, D. W., Oxygen Measurements in Blood and Tissues and Their Sig-... 

Work with these types of electrodes enables to achieve steady-state current conditions within a short time-period. Primarily proposed for monitoring and control of blood and tissue oxygen tension [10], the electrode systems with selective membranes were manufactured and used in continuous oxygen measurement in a wide variety of aqueous solutions [11]. The sensors of this type, called Clark electrodes, are described in chapter 6 of this volume. Improvements designed for continuous monitoring in industrial bioreactors may be found in section 6 of chapter 3. The most important feature of the membranes used in these sensors is their selectivity which prevents poisoning the electrode system and deteriorating the adherent electrolyte solution. 

OXYGEN TRANSPORT TO TISSUE XXlll Oxygen Measurements in the 21 Century Basic Techniques and Chnical Relevance... 

Randers-Eichorn, L., R. Bartlett et al. 1996. Noninvasive oxygen measurements and mass transfer considerations in tissue culture flasks. Biotechnol Bioeng 51 466-78. 

The quantity P50, a measure of O2 concentration, is the partial pressure of Oj that half-saturates a given hemoglobin. Depending on the organism, P50 can vary widely, but in all instances it will exceed the PO2 of the peripheral tissues. For example, values of P50 for HbA and fetal HbF are 26 and 20 mm Hg, respectively. In the placenta, this difference enables HbF to extract oxygen from the HbA in the mother s blood. However, HbF is suboptimal postpartum since its high affinity for O2 dictates that it can deliver less Oj to the tissues. 

Newer techniques include monitors capable of performing microdialysis, or measuring brain oxygenation and lactate, which may be useful in monitoring penumbral tissue adjacent to a large area of infarction. No randomized studies have been performed to clearly document their impact on patient outcomes to date. 

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