Pathophysiology of variable and late decelerations.

The classification of the fetal heart rate patterns developed around 1960 lack still a clear and definitive pathophysiological base. The names given to the several decelerations suggest however that the pathophysiological pathways along which they arise are completely clarified. Therefore we directed our research the last years to this subject. This paper is restricted to the presentation of some data concerning the Simulation of variable and late decelerations in chronically instrumented sheep preparations. Acute changes in the fetal heart rate pattern can in general and theoretically be caused by 1. direct hemodynamic changes 2. activitation of the fetal autonomic System by chemoreceptor mediated hypoxaemia and or direct fetal adrenal release of catecholamines. 3. direct myocardial depression. Correct Interpretation of changes in the fetal heart rate pattern and estimation of the fetal condition requires knowledge about the activity of each of the three factors mentioned.