Poiseuille's Law: Graph Exploration of Pressure 

A graph geometrically represents a function, and here we show the graph of the linear pressure relation.

With all of the parameters but the pressure fixed, choose the pressure that you want. You can determine the value of the flow geometrically by finding your pressure along the horizontal axis (independent variable), finding the point on the graph directly above this number, and then reading the value of the number directly to the left of this point (dependent variable). 

Because the function is linear, the graph of the function is a straight line. As you can see, the graph is increasing. This means that the flow increases when the pressure rises, and it decreases when the pressure drops. This corresponds to the slope of the line being positive. When the pressure completely disappears (the heart stops beating), what happens to the flow? It goes to zero, which corresponds to the y-intercept of the graph.