Anoxia direct effects

The toxic effect is known as histotoxic hypoxia. Cyanide also directly stimulates chemoreceptors, causing hyperpnea. Lack of ATP will affect all cells, but heart muscle and brain are particularly susceptible. Therefore, cardiac arrythmias and other changes often occur, resulting in circulatory failure and delayed tissue ischemic anoxia. Death is usually due to respiratory arrest resulting from damage to the CNS, as the nerve cells of the respiratory control center are particularly sensitive to hypoxia. The susceptibility of the brain to pathological damage may reflect the lower concentration of cytochrome oxidase in white matter. 

Modification of radiation injury produced by these chemical agents must be mediated by neutralization of either the direct or the indirect effects of radiation or by altering the physiologic state of the cells to a more or less resistant state. These general problems have been considered in detail by Patt (9, 44). It would appear superficially that sulfhydryl compounds and anoxia exert their protective effect through partial neutralization of the indirect effects of radiation and not through neutralization of the effects of direct ionization and excitation of solute molecules. 

The potential obtained with the potential-sensitive barrel is called DC in the figure and the potential recorded with the ion-sensitive barrel is called pK + DC. The difference between these two potentials (called pK in the figure) is obtained with the differential amplifier and represents the potential that arises from the K" -activity. If electrodes were selected so that the tip potential of the reference barrel varied less than 2mV between 150mM KCl and 150 mil NaCl, and if we assume that the tip potential is the same in these solutions and in the brain then the resting level of in the brain corresponds to 3mM. This value was also obtained in the ventricle. The E.E.G. and E.C.G. are also shown. Before the rat was made anoxic at the electrical potential was stable but there are slow variations in pK (frequency of about 0.001 HZ, amplitude 5mV)., These variations disappered after the rat had been dead for a few minutes (heart stopped completely). A potential synchronous with the breathing was picked up equally well with the potential and the K" -sensitive barrel so that it cancelled out in the pK trace. The two small peaks, one at and one 1 minute before, show an electrostatic effect caused by the jet of gas mixture as it passed the head of the rat the first peak was caused by gas not directed at the tracheal cannula the second represents the onrush of gas that caused the anoxia. The immediate effect of the nitrous oxide + 5% carbon dioxide (start at ) is a decrease in pK of about 3mV (corresponding to a decrease in K" -activity of 16%). This decrease lasts for about 40 sec. and is followed by an increase in pK of about 5mV (which... 

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