Teaching the distribution of pulmonary blood flow using a Starling resistor model and turbine flowmeters.

The distribution of pulmonary blood flow is uneven and can be described as a three-zone model, the West zones: zone 1 occurs whenever alveolar pressure exceeds arterial pressure; zone 2 when the arterial pressure is greater than alveolar but the alveolar pressure exceeds the venous pressure; and finally zone 3 when both arterial and venous pressures exceed alveolar pressure. Consequently, the blood flow is almost determined by the difference between the arterial and venous pressures in zone 3 and between arterial and alveolar pressures in zone 2 and ceases in zone 1. The understanding of this subject may be difficult to some medical students. Therefore, to improve the learning of this topic in our physiology course, we used a didactic model to demonstrate the core concept of flow down gradients and its application to pulmonary blood flow. We modeled a Starling resistor by placing a collapsible tube inside a hermetic chamber of variable pressure. Transparent turbine flowmeters were connected to the upstream and downstream extremities of the Starling resistor, and we generated a constant airflow with a brushless motor. By maintaining the input (arterial) pressure constant and varying the chamber (alveolar) pressure, we could simulate the three zones and demonstrate the resulting flow through the turbines. In conclusion, our demonstration using a Starling resistor model combined with visible turbine flowmeters can be used to facilitate comprehension of important concepts in physiology involving flow down gradients, such as pulmonary blood flow. The understanding of respiratory physiology is a challenge to medical students. To improve the learning of pulmonary blood flow distribution through lung vessels in our physiology course, we modeled a Starling resistor model combined with visible turbine flowmeters. Our model can significantly improve the core concept of flow down gradients teaching and its application to West zones.