🫁 Respiratory Time Constant (τ)
UseWhen to use: obstructive ventilation / auto-PEEP teaching when Raw and Crs (or VT/PEF) are known.
StrataProlonged τ needs longer expiratory time to limit gas trapping.
LimitsWhen not to use: active exhalation. · Pitfall: mixing Cdyn with Cstat carelessly. · VT/PEF is approximate.
SourceStandard respiratory time-constant teaching definition
This-shift next steps
After scoring: open the scene pack, peer scores, and the matching pathway. Local reference — no HIS write.
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Methodology · worked example, guidelines & full notes
Raw×Crs.
When to use
When to use: obstructive ventilation / auto-PEEP teaching when Raw and Crs (or VT/PEF) are known.
How it works
τ = Raw × Crs (Crs in L/cmH₂O); approx τ ≈ VT/PEF.
Key points
- Raw×Crs.
- ≈3τ for near-emptying.
- Next: I:E / auto-PEEP.
References
- Standard respiratory time-constant teaching definition
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Input mode | Raw + Crs |
|---|---|
| Airway resistance (Raw) | 10 cmH₂O·s/L |
| Compliance (Crs) | 40 mL/cmH₂O |
| Exhaled VT | 400 mL |
| Peak expiratory flow | 0.5 L/s |
→τ0.40s
- From：Raw × Crs
- Cue：≤0.5 s — shorter τ teaching band
| Input mode | VT / peak expiratory flow (approx) |
|---|---|
| Airway resistance (Raw) | 10 cmH₂O·s/L |
| Compliance (Crs) | 40 mL/cmH₂O |
| Exhaled VT | 400 mL |
| Peak expiratory flow | 0.5 L/s |
→τ0.80s
- From：VT/PEF approximation
- Cue：0.5–0.8 s — intermediate τ band
Verification & sources · governance
FAQ
Frequently asked questions
- Does Respiratory Time Constant (τ) upload patient data? Where is it calculated?
- Calculation runs locally in the browser; inputs and results are not uploaded. For licensed clinicians only; interpret with history, investigations and local protocols — not a diagnosis or prescription.
- How is Respiratory Time Constant (τ) calculated in practice? Can you show a worked example?
- Inputs: Input mode Raw + Crs, Airway resistance (Raw) 10 cmH₂O·s/L, Compliance (Crs) 40 mL/cmH₂O, Exhaled VT 400 mL, Peak expiratory flow 0.5 L/s → Result: τ 0.40 s（From: Raw × Crs, Cue: ≤0.5 s — shorter τ teaching band） Inputs: Input mode VT / peak expiratory flow (approx), Airway resistance (Raw) 10 cmH₂O·s/L, Compliance (Crs) 40 mL/cmH₂O, Exhaled VT 400 mL, Peak expiratory flow 0.5 L/s → Result: τ 0.80 s（From: VT/PEF approximation, Cue: 0.5–0.8 s — intermediate τ band）