Medical Device Simulators · Interactive Lab
Spirometer Simulator
Flow-measuring spirometers compute volume by integrating flow over time. Shape a synthetic, decaying expiratory flow and watch how volume, FEV₁ and FVC are derived — and how a small sensor offset accumulates into a volume error.
Parameters
Why these controls?
The sliders shape the synthetic expiratory flow: starting flow Q₀ and decay rate k determine the curve, and the volume is its integral. Change them to see how the flow curve becomes FEV₁ and FVC, and use the offset to watch a sensor bias turn into a growing volume error.
Calculated result
Spirometric indices
- FEV₁
- 3.46
- L
- FVC
- 4.00
- L
- FEV₁/FVC
- 86.5%
- ratio
Expiration complete: end flow < 0.025 L/s, so the final volume is reported as FVC.
Numerical vs. analytic check
Analytic V(T) = (Q₀/k)(1 − e^(−kT)) = 4.0000 L
Trapezoid (true flow, Δt = 10 ms) = 4.0001 L · error 0.133 mL
Formulas & units
Q(t) = Q₀ · e^(−k·t)
V(t) = ∫₀ᵗ Q(τ) dτ ≈ Σ ½(Qᵢ₋₁ + Qᵢ)·Δt
FEV₁ = V(1 s), FVC = V(end), ratio = FEV₁/FVC
- Flow Q in L/s · volume V in L · time in s · k in 1/s
- Offset error: ΔV(t) = Q_offset · t (L)
Assumptions & scope
- Synthetic mono-exponential expiratory flow starting at peak at t = 0 (no rise time, no back-extrapolation).
- Flow already at BTPS; uniform 10 ms sampling; trapezoidal integration.
- Expiration is considered complete when flow falls below 0.025 L/s; otherwise no FVC is reported.
- For teaching measurement principles only — this module does NOT produce any diagnosis or interpretation.