The law relating distending pressure and tension in a blood vessel wall is called:

Law of Laplace states that transluminal pressure varies inversely with vessel radius and is directly propoional to tension that develops in the vessel walls. It means the pressure pushes against the wall causing them to stretch(tension), as the size of the vessels decreases the tension in the wall decreases too. Law of Laplace states that tension in the wall of a cylinder (T) is equal to the product of the transmural pressure (P) and the radius (r) divided by the wall thickness (w). T =Pr/w Einthoven's law The relationships of the bipolar limb leads are such that the sum of the electrical currents recorded in leads I and III equal the sum of the electric current recorded in lead II. This relationship is called Einthoven's law, and is expressed mathematically as: Lead I + Lead III = Lead II It follows that if the values for any two of the leads are known, the value for the third. Frank-Starling law of the hea: which states that the ventricular output is propoional to the ventricular end-diastolic volume. Ref: Principles of medical physiology, By Sabyasachi Sicar,Page 212.