Life Sciences · Human Body · Homeostasis / Principles and Exploration
Lung model and breathing — principles and investigation
The balloon in the lung model does not suck in air on its own, but inflates in response to changes in pressure in the surrounding space. Pull or raise the rubber membrane, open or close the airway, and observe the balloon's volume. This is an experiment that explains inhalation and exhalation in the order of thoracic volume, pressure difference, and air movement.
How does it work?
When the rubber membrane is pulled, the volume of the chest cavity increases and the pressure decreases, allowing air to enter the balloon. When the curtain rises, the air comes out. When the airway is closed, there is no air movement.
P/P₀ = V₀/V · Chest cavity volume 1.1V₀ → Pressure P₀/1.1
Try this investigation
- Pull the rubber membrane down to increase chest cavity volume. You can do the same with the pull slider. When you run it, the balloon volume and air flow change. Automatic breathing shows one cycle of inhalation and exhalation.
- Execute and record the 10% increase condition and the airway-only closed condition. Distinguish between chest cavity volume and balloon volume.
- Under conditions of a 10% reduction in volume, the pressure increases and air escapes. Observe whether the direction of flow changes during automatic breathing.
Interpreting your results
When the airway is closed and the rubber membrane is pulled, what happens to the air movement in this model?
Chest cavity pressure decreases to PV = constant. When the airway is open, the balloon grows larger and allows air to flow in, but when it closes, the air movement is zero. In this simple model, the closed balloon volume is also fixed.
Assumptions and limitations
It is a virtual relative value obtained by applying Boyle's law by considering the thoracic space as a sealed gas at a certain temperature. The balloon approaches the target volume 1+0.8×(V/V₀−1) exponentially. Actual pleural pressure, lung elasticity, thoracic movement, and gas exchange are omitted. A closed balloon is an approximation that also fixes the volume. It does not predict the actual pressure or breathing volume of the human body.