Kontraktivt

Kontraktivt is an adjective used in physiology and medicine to describe properties related to muscle contraction. The term is derived from Latin contractilis and is used in Scandinavian languages to denote the contractile nature of muscle tissue.

In cardiology and muscle physiology, contractility refers to the intrinsic ability of muscle fibers to develop force at a given muscle length, independent of external loading. In the heart, kontraktivitet describes the myocardium’s capacity to generate pressure and shorten during systole, while actual force is influenced by preload and afterload. In skeletal muscle, contractility similarly denotes the intrinsic strength of contraction, modulated by neural input and cellular machinery.

Assessment of contractility in clinical practice often relies on indirect indicators. In cardiac settings, measures such as the rate of pressure rise in the ventricle (dP/dt max), changes in ejection fraction with altered loading, and pressure-volume relationships help gauge contractile function, though these are affected by loading conditions and other factors. Pharmacological and physiological interventions that modify contractility are described as inotropic or negative inotropic effects.

Regulation of contractility involves calcium handling and signaling pathways within muscle cells. Positive inotropic agents (for example, certain catecholamines and drugs like dobutamine) increase contractility, while negative inotropes decrease it. In skeletal and smooth muscle, contractility depends on cross-bridge cycling, calcium sensitivity, and energy supply, with tissue-specific regulatory mechanisms such as the calcium-calmodulin-MLCK pathway in smooth muscle.

See also: contractility, inotropy, preload, afterload.