1.1 Simple Invariant - Closed System

1. Find a system that is closed

• A closed system has a simple invariant in the form of an equality

\[ OUT = IN \tag{invariant}\] \[ \text{Pulmonary Circulation}=\text{Systemic Circulation}\]

1.2 State the assumptions

• Blood is mostly water so we can assume it is incompressible
• Pressure is like Voltage; it is always relative wrt to something, we assume pressure is relative to atmospheric pressure in this system.

1.3 Break model to small components

• First we will model a very simple blood vessel like a rigid pipe
• Find what stays constant
  • Volume(t)_IN = Volume(t)_OUT therefore Volume stays constant over time
• Find what changes