Time constant is used to describe the change in filling time and emptying time of a lung unit. One time constant
is the time it takes to fill 63% of maximal inflation or deflation of the lung unit. 96% of the lung unit is filled after three time constants. The time constant of the lung is a product of the resistance and the compliance.
is the time it takes to fill 63% of maximal inflation or deflation of the lung unit. 96% of the lung unit is filled after three time constants. The time constant of the lung is a product of the resistance and the compliance.
The resistance for normal lung tissue is 2 cmH2O/L and the total compliance is 100 cmH2O/ml, therefore the time constant for the whole lung is 0.2s
- A long Time Constant results in alveoli that fill slowly on inspiration.
- A short Time Constant results in alveoli that fill and empty quickly.
Time Constant Respiratory Calculation
| Static Lung Compliance: cmH2O/L | |
| Airway Resistance: cmH2O/mL/s | |
| Respiratory Time Constant: Seconds |
