The effects of adaptation to intermittent and continuous hypoxia on the electrical stability of the heart were compared in middle altitude conditions and in altitude chamber in Wistar rats with ...postinfarction cardiosclerosis. It has been shown that both forms of adaptation could restore the heart fibrillation threshold and restrict the ectopic activity in postinfarction cardiosclerosis. Beneficial effects of adaptation to intermittent hypoxia in conditions of the altitude chamber appeared to be more radical.
Preliminary adaptation to short-term stress was shown to prevent the fall of the heart fibrillation threshold and its increased ectopic activity which is usually observed in experimental myocardial ...infarction. This protective effect involves an enhanced activity of the organism's antioxidant systems. On this basis, synthetic antioxidant ionol was applied to prevent disturbances of heart electric stability in infarction. Ionol completely prevented the decrease in the electric threshold and the increase in ectopic activity of the heart in experimental infarction, demonstrating thereby an anti-arrhythmic effect.
In the initial phase of its action on the contracting myocardium the inductor of lipid peroxidation (LPO) H2O2 displays marked positive ino- and chronotropic as well as relaxant effects which are, ...therefore, close to catecholamine effects. Since catecholamines activate LPO it suggests that such activation may be involved in the mechanism of their physiologic action. The prolongation of H2O2 action inevitably leads to the development of bradycardia and bradyarrhythmic arrhythmia which may ultimately end in cardiac arrest. The atrial resistance to H2O2 in animals exposed to stress is considerably diminished: in response to this inductor of LPO such animals develop more pronounced bradyarrythmic arrhythmia and cardiac arrest without the stage of the initially positive inotropic effect. The preincubation of the contracting atrium by HP-6, a LPO inhibitor of the hydroxypyridine class, checks the development of bradyarrhythmic arrhythmia and in many cases prevents cardiac arrest. Taken as a whole these data suggest that LPO activation may play an important role in the pathogenesis of cardiac rhythm disorders which may serve as substantiation for the use of antioxidants in the treatment and prevention of arrhythmias.
The influence of adaptation to altitude hypoxia (2100 m) on rat myocardial contractility was examined during transitory ischemia induced by ligation of the descending branch of the left coronary ...artery and subsequent reperfusion. In control animals and those after adaptation, ischemia caused the same depression of heart function, while during reperfusion, the animals after adaptation, unlike the control ones, showed partial recovery of contractile function. Evaluation of heart function after ischemia and reperfusion demonstrated that the hearts of the animals after adaptation preserve the ability to bear the maximal isometric load on the level attained during adaptation to hypoxia, while the control animals experience substantial disorders of heart function because of ischemia and reperfusion. Thus, adaptation to altitude hypoxia increases the heart resistance to the damages that occur during reoxygenation.
IGR - Book Section Vershkovskaya, O. V.; Krasnova, V. S.; Saltykova, V. S. ...
International geology review,
19/1/1/, Letnik:
12, Številka:
1
Journal Article
Basing on the utilization of the benefit-injury concept the authors put forward an approach to the substantiation of permissible errors in the values of the mean doses intended for the patient's ...critical organs in x-ray examination. It was shown that in the elaboration of methods to determine the mean tissue doses one should aim at reaching a mean quadratic error of +/- 30% in their values.
