Tension tissue oxygen

E.M.R. Doppenberg, A. Zauner, R. Bullock, J.D. Ward, P.P. Fatouros, and H.F. Young, Correlations between brain tissue oxygen tension, carbon dioxide tension, pH, and cerebral blood flow - a better way of monitoring the severely injured brain Surg. Neurol. 49, 650-654 (1998). 

B.J. Dardzinski, C.H. Sotak, Rapid tissue oxygen tension mapping using F inversion-recovery echo-planar imaging of Perfluoro-15-crown-5-ether, Magn. Reson. Med. 32 (1994) 88-97. 

R.P. Mason, H.P. Shukla, P.P. Antich, Oxygent A novel probe of tissue oxygen tension. Biomater. Artif. Cells Immobilization. Biotechnol. 20 (1992) 929-935. 

H.P. Shukla, Application of Perfluorocarbon Emulsions as Fluorine-19 Nuclear Magnetic Resonance Molecular Probes of Cardiac Tissue Oxygen Tension, University of Texas Southwestern Graduate School of Biomedical Sciences, 1994Ph.D.. 

Clark LC Jr (1956) Monitor and control of blood and tissue oxygen tensions. Trans Am Soc Artif Intern Organs 2 41 -48... 

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

E6. Evans, N. T. S., and Naylor, P. F. D., The effect of oxygen breathing and radiotherapy upon the tissue oxygen tension of some human tumours. Brit. J. Radiol. 36, 418-425 (1963). 

G18. Gotoh, F., and Meyer, J. S., A combined electrode for recording absolute tensions of oxygen and carbon dioxide from small areas of tissue. Electroencephalog. Clin. Neurophysiol. 13, 119-122 (1961). 

Halothane [CF3 CH Br Cl] the first of the modern halogenated volatile anesthetics was introduced into clinical practice in 1956. It is normally metabolized in an oxidative pathway forming bromide ions and trif-luoroacetic acid, neither of which has tissue toxic potential [36, 37]. Reductive metabolism of halothane takes place during low tissue oxygen tension states [38]. This pathway has been linked to halothane induced liver necrosis through production of free radicals that bind to cellular macromolecules [39,40]. Reductive metabolism is also associated with production of fluoride ions [41]. The quantities found are too small to have nephrotoxic importance. 

Clark L C 1956 Monitor and control of blood tissue oxygen tensions Trans. Am. 

Because of discrepancies between experimental tests and predicted tissue oxygen response by convection-diffusion models, the influence of physiological control mechanisms was considered. It is proposed that a minimum of two autoregulatory actions (at least conceptually) are functional in helping prevent neuron damage when low blood oxygen tensions are encountered. 

The second action that prevents neuron damage and which could be considered, at least conceptually, as feedback control is oxygen consumption rate. Even though the brain normally operates at a constant consumption rate, recent experimental results (8) indicate that the rate decreases when the tissue oxygen tension drops. 

The oxygen consumption rate as a function of tissue tension is considered to have a Michaelis-Menten form. [It has been shown (8) that neuron activity increases to a much higher rate as tissue oxygen tension decreases (injury potential) and then it drops off to essentially zero. This would indicate that a true Michaelis-Menten form would not be followed.] A zero-order reaction is assumed for high tissue tension a first-order reaction is then imposed when the tension drops to a prescribed value, and then the consumption rate is set equal to zero at a second prescribed tissue tension (i.e., PT > 30 mm Hg, zero-order reaction, 20 < PT < 30 mm Hg, first-order reaction, and PT < 20, zero consumption). When the consumption rate goes to zero, the model restricts oxygen transport in the reverse direction (tissue to blood) even if the blood tension drops below the tissue tension. This assumption was included to achieve a flat plateau like the experimental results however, it is still open to speculation. Back diffusion can be considered in the model by simply removing a diode from the computer circuit. (This assumes a barrier to tissue washout.)... 

The experimental curve in Figure 3 demonstrates overshoot in the tissue oxygen response. It was determined previously (22) that a term representing pure delay along with the steady-state blood flow vs. arterial oxygen tension data would cause overshoot. In this investigation it was found that a first-order time constant delay would also produce overshoot. Therefore, since exact controller mechanisms are not being postulated, the flow controlled dynamics used in this study include pure delay and time constant lag. To consider the problem of sensor location, feedback and feedforward control loops were superimposed on the capillary-tissue model. 

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