The functional ambivalence of adaptive processes--considerations based on the example of the hemodynamically overloaded heart.
Cardiac hypertrophy and neuro-humoral reactions in hemodynamic overload are employed as examples to show that adaptive processes, while in principle enabling the whole organ to cope with increased load, as a rule also include unfavorable components. This is primarily due to competition between different demands with respect to, for instance, mechanical or energetic parameters. An impressive demonstration of the ambivalence of adaptive processes can be seen in the functional consequences of myocardial mass increase, eccentric configurational changes, and the alteration of the myocardium towards a "slower muscle". It can be demonstrated that, due to structural modifications in the heart, unfavorable effects occur at the level of the whole organ as well as in macromolecular dimensions from the very beginning, and not only as a consequence of qualitatively and quantitatively inappropriate adaptation. Thus, a clear-cut distinction between "physiological" and "pathological" processes is almost impossible. In the clinic, the unfavorable effects of the process of hypertrophy are often emphasized and the reduction of hypertrophy is declared the principal therapeutic aim. However, in the individual case the extent to which vascular alterations participate in, or are even mainly responsible for the unfavorable effects occurring in pressure hypertrophy should be clarified. In any case, reduction of hemodynamic overload should be the focus of therapeutic concern.
Jacob
R
R
Physiologisches Institut II, Universität Tübingen, FRG.
D000222:Adaptation, Physiological; D000818:Animals; D006332:Cardiomegaly / Q000209:etiology* / Q000628:therapy; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans