Electrode invasive

The partial oxygen pressure, p02, is particularly significant in metabolic processes of cells, and its variation from normal values often indicates pathologies (ischemic diseases, strokes, tumors). Accurate and localized measurements of the oxygen concentration are also desirable for differentiation between venous and arterial blood, or for cerebral mapping of task activation. In the past, invasive methods were used involving oxygen-sensitive electrodes which had to be placed directly in the blood or tissue and could only offer p02 from a few body points. 

In contractile experiments the time from the stimulation of the nerve to the CMAP recorded in muscle provides an estimate of NCV. The length of the nerve from the stimulating electrode to the muscle can simply be measured and divided by the time. However, the time recorded in this way includes the delay for synaptic transmission, which may be increased in models with synaptic defects. If this is a concern or if the only parameter desired is NCV, then the measurement can be obtained non-invasively with a relatively simple setup (e.g., (3)). Using the sciatic nerve, NCV can be calculated by measuring the latency of compound motor action potentials recorded in the muscle of a rear paw. Action potentials are produced by subcutaneous stimulation at two separate sites proximal stimulation at the sciatic notch and distally at the ankle. NCV is then calculated by using the two latencies and conduction distance. Decreases in nerve conduction velocity most often reflect defects in myelination, but may also be the result of changes in internodal distance, decreased axon diameters, or altered excitability. 

Q4 An electroencephalogram (EEG) is a recording of electrical activity arising from the cortical surface of the brain. It is recorded from scalp electrodes on 16 channels simultaneously. The technique is non-invasive and is not painful. The main uses of electroencephalography are to investigate sleep and its disorders and to diagnose epilepsy. The wave/spike patterns produced can be analysed to reveal alterations in or to localize areas of the specific electrical activity associated with seizures. The EEG can also be used medico-legally to determine whether a person is actually brain dead . 

Chemical sensors (i) Gases (e.g. blood oxygen electrode, carbon monoxide detector) (ii) pH and ions (e.g. pH meter, potassium-selective elecbode) and (iii) optical oximetry (e.g. pulse oximeby for non-invasive monitoring of blood oxygenation). 

Khan, A.S. and Michael, A.C. (2003) Invasive consequences of using micro-electrodes and microdialysis probes in the brain. Trends in Analytical Chemistry TRAC, 22 (9), 503-508. 

C. G., Garbay, J.R., Billard, V. et al. (2006) Standard operating procedures of the electrochemotherapy instructions for the use of bleomycin or cisplatin administered either systemically or locally and electric pulses delivered by the Cliniporator by means of invasive or non-invasive electrodes. European Journal of Cancer Supplement, 4, 14-25. 

Critical care as well as process control and food industry require enzyme electrodes for invasive and in situ analysis. However, direct application in bioreactors is associated with significant difficulties ... 

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. 

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