Respiratory mechanics:
P = V/C + R·Q̇ (pressure = elastic + resistive)
Compliance C = ΔV/ΔP — stiffness of lung tissue.
Low C → stiff lungs (ARDS). High R → obstruction (COPD, asthma).
Work of breathing ∝ area of P–V loop.
About the Lung Mechanics Simulator
This simulation models a single-compartment lung during cyclic ventilation, animating the lungs and diaphragm while plotting real-time volume, airway-pressure and flow waveforms plus a pressure-volume loop. It is built on the equation of motion of the respiratory system, P = V/C + R·Q̇, where airway pressure equals an elastic term (volume divided by compliance) plus a resistive term (resistance times flow). Expiration follows a passive exponential decay governed by the time constant τ = R·C.
The sliders set compliance C (5–100 mL/cmH₂O), airway resistance R (0.5–20 cmH₂O·s/L), functional residual capacity, respiratory rate (4–40 breaths/min), driving pressure ΔP and the I:E inspiratory fraction. Tidal volume is derived as C × ΔP. Preset buttons load characteristic Normal, COPD, ARDS and asthma profiles. The model illustrates how clinicians reason about ventilator settings and obstructive or restrictive lung disease.
Frequently Asked Questions
What does this lung mechanics simulator show?
It depicts one breathing cycle of a simplified single-compartment lung. You see an animated lung and diaphragm alongside live traces of volume, airway pressure (Paw) and flow, plus a pressure-volume loop. Summary statistics report tidal volume, minute volume, peak pressure and work of breathing.
What is the key equation behind the model?
It uses the respiratory equation of motion, P = V/C + R·Q̇. Airway pressure is the sum of an elastic component, the volume above FRC divided by compliance, and a resistive component, the airway resistance multiplied by flow. This single relationship drives every waveform in the simulation.
What is compliance and what does the slider do?
Compliance C is the change in lung volume per unit change in pressure, in mL/cmH₂O, and reflects how easily the lungs distend. The slider spans 5 to 100 mL/cmH₂O. A low value means stiff, hard-to-inflate lungs, while a high value means floppy, over-compliant lungs.
How is tidal volume calculated here?
Tidal volume is computed simply as compliance times driving pressure, Vt = C × ΔP. So with a compliance of 60 mL/cmH₂O and a driving pressure of 8 cmH₂O the model delivers about 480 mL per breath. Minute volume is then tidal volume multiplied by the respiratory rate.
What does airway resistance change?
Resistance R (0.5–20 cmH₂O·s/L) opposes gas flow through the airways. Raising it increases the resistive pressure term during flow and lengthens the expiratory time constant τ = R·C, so the lungs empty more slowly. High resistance characterises obstructive conditions such as COPD and asthma.
Why does expiration follow an exponential curve?
Expiration in this model is passive: stored elastic energy drives gas out through the airway resistance, producing an exponential decay of volume back towards FRC. The rate is set by the time constant τ = R·C. A longer time constant, from high resistance or high compliance, leaves less time to exhale fully at fast rates.
What do the disease presets represent?
Normal uses a moderate compliance and low resistance. COPD raises resistance and FRC (air trapping) with high compliance. ARDS sets a very low compliance with raised driving pressure, modelling stiff, restricted lungs. Asthma uses very high resistance with near-normal compliance to model bronchoconstriction.
What is the pressure-volume loop?
The P-V loop plots airway pressure on the horizontal axis against volume on the vertical axis over one breath. Its slope reflects compliance and its enclosed area is proportional to the work of breathing. Stiff lungs produce a flatter, wider loop; high resistance widens the loop through hysteresis.
Is this simulation clinically accurate?
It is an educational, qualitative model. It captures the correct relationships between compliance, resistance, pressure and volume, but it is a single-compartment linear approximation. Real lungs have regional heterogeneity, non-linear compliance, surfactant effects and active expiratory muscles, none of which are included here.
How is work of breathing represented?
Work of breathing is approximated from the driving pressure and tidal volume and shown in the statistics panel in joules per litre. Conceptually it equals the area enclosed by the pressure-volume loop. Stiff lungs or high resistance enlarge this area, meaning more energy is needed for each breath.
How is this relevant to real-world ventilation?
Intensive-care clinicians adjust ventilator settings such as rate, driving pressure and I:E ratio against a patient's measured compliance and resistance. This simulator lets learners see how those choices change tidal volume, peak pressure and air trapping, which underpins lung-protective ventilation strategies for ARDS and obstructive disease.