Totalresistansen

Totalresistansen, or total resistance, is a term used to describe the overall resistance to flow in a system. It is applied in electronics to denote the equivalent resistance of a network of resistors, and in physiology as total peripheral resistance (TPR), the resistance offered by the systemic vasculature to blood flow. The concept is governed by Ohm’s law, adapted to the respective domain: voltage, current, and resistance in electronics; pressure, flow, and resistance in physiology.

In electronics, R_total simplifies complex circuits. For resistors in series, resistances add: R_total = R1 + R2 + ... + Rn. For resistors in parallel, the reciprocals add: 1/R_total = 1/R1 + 1/R2 + ... + 1/Rn. Mixed networks are solved by progressively combining components. The current through the network follows I = V / R_total.

In physiology, total peripheral resistance is the resistance to blood flow offered by the systemic circulation. It is commonly expressed as TPR = (MAP − RAP) / CO, where MAP is mean arterial pressure, RAP is right atrial pressure, and CO is cardiac output. Normal MAP and CO values yield a typical SVR/TPR on the order of tens of Wood units (roughly 9–20 Wood units) depending on measurement. Vascular tone, vessel radius (which affects flow roughly to the fourth power), blood viscosity, and blood vessel length determine TPR. Arterioles are the primary resistance vessels, and autonomic or local mediators can increase or decrease TPR through vasoconstriction or vasodilation.

Clinically, TPR influences blood pressure and tissue perfusion and responds to drugs such as vasodilators or vasoconstrictors. In electronics, accurate R_total calculations are essential for circuit design and power budgeting.