Compliance and Resistance

Human Physiology • Respiratory Physiology

Written by STEM Calculators Team Published April 15, 2026 Updated April 15, 2026

Compliance and Resistance

This teaching calculator compares how easily lungs expand and how strongly the airways oppose airflow. It computes compliance from a volume-pressure change and airway resistance from a pressure-flow pair.

Use separate tabs for compliance and resistance, compare two states, or paste/upload CSV rows with label,dV,dPcomp,dPres,flow,volUnit,pressUnit,flowUnit for extra comparison states.

State A

Preset

Volume unit

Pressure unit

Flow unit

Change in volume

Change in pressure for compliance

Pressure difference for resistance

Airflow

Preset values can still be edited manually after they are applied.

Compliance \(C = \dfrac{\Delta V}{\Delta P}\)

Resistance \(R = \dfrac{\Delta P}{\dot V}\)

State B / comparison

Enable comparison mode

Compare a second preset or a second manual state against State A.

Preset

Volume unit

Pressure unit

Flow unit

Change in volume

Change in pressure for compliance

Pressure difference for resistance

Airflow

State B stays inactive until comparison mode is enabled.

Optional extra states from pasted or uploaded CSV

Paste CSV data

Accepted columns: label, dV, dPcomp, dPres, flow, volUnit, pressUnit, flowUnit. Use mL or L, cmH2O or kPa, and L/s or L/min.

Upload CSV file

Uploaded CSV content is copied into the textarea automatically so it can be reviewed before calculation.

Extra CSV states appear in the comparison bar chart and as additional markers on the mechanics graphs.

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Compliance and resistance

A compliance and resistance calculator summarizes two different parts of respiratory mechanics. Compliance describes how easily the lungs expand for a given pressure change, while airway resistance describes how much pressure difference is needed to maintain airflow through the airways.

These quantities should be interpreted separately because a stiff lung and a narrowed airway are not the same problem. The calculator computes both values, compares states, and helps connect pressure, volume, and flow to mechanical behavior.

Core definitions and formulas

The essential relationships are:

\[ \begin{aligned} C &= \frac{\Delta V}{\Delta P} \end{aligned} \] \[ \begin{aligned} R &= \frac{\Delta P}{\dot V} \end{aligned} \]

Here, \(C\) is compliance, \(\Delta V\) is the change in lung volume, \(\Delta P\) is the pressure change used for the compliance calculation, \(R\) is airway resistance, and \(\dot V\) is airflow. Compliance is commonly expressed in L/cmH₂O or mL/cmH₂O, while resistance is often expressed in cmH₂O·s/L.

How to interpret results

A higher compliance means a larger volume change is produced by each unit of pressure, so the lungs expand more easily. A lower compliance means the lungs are stiffer and require more pressure to produce the same expansion.

A higher airway resistance means airflow meets greater opposition, usually because the airways are narrower or more obstructed. A lower resistance means the same airflow can be maintained with a smaller pressure difference.

The calculator reports compliance, airway resistance, interpretation of low versus high values, and comparison between selected states. The pressure-volume curve emphasizes compliance, while the flow-pressure graph emphasizes resistance.

Using the same pressure change for compliance and resistance without checking the intended input.
Mixing mL and L or L/s and L/min without conversion.
Assuming low compliance automatically means high resistance.
Comparing values without noting the measurement units.

Micro example: if the lung volume change is 0.800 L and the pressure change is 4.00 cmH₂O, then compliance is:

\[ \begin{aligned} C &= \frac{0.800}{4.00} \\ &= 0.200\ \text{L/cmH}_2\text{O} \end{aligned} \]

This means each 1 cmH₂O of pressure change produces 0.200 L of volume change in that example.

This tool is best used for teaching respiratory mechanics and comparing normal lungs with stiff-lung or high-resistance patterns. It is not a full pulmonary function interpretation system; the next step is to connect these mechanics to lung volumes, gas exchange, and clinical spirometry patterns.

Frequently Asked Questions

What is lung compliance?

Lung compliance describes how easily the lungs expand when pressure changes. It is calculated as change in volume divided by change in pressure.

How do you calculate airway resistance?

Airway resistance is calculated by dividing the pressure difference by airflow. In plain form, resistance = pressure difference x 1 over flow, or more simply pressure difference divided by flow.

Why are compliance and resistance different respiratory mechanics measures?

Compliance describes elastic expansion of the lungs, while resistance describes opposition to airflow within the airways. A lung can be stiff with near-normal resistance, or it can have high resistance while compliance remains fairly preserved.

What does low compliance mean?

Low compliance means the lungs require more pressure to produce a given volume change. In teaching terms, that usually represents a stiffer lung expansion pattern.

When should this calculator be used?

This calculator is useful for teaching pressure-volume and flow-pressure mechanics and for comparing normal, stiff-lung, and high-resistance states. It is not a full pulmonary function diagnosis tool by itself.

Compliance and Resistance

Compliance and Resistance

State A

State B / comparison

Optional extra states from pasted or uploaded CSV

Calculation steps

Pressure-volume curve

Flow-pressure graph

Comparison bar chart

Lung-and-airway schematic

Rate this calculator

Frequently Asked Questions

Compliance and Resistance

State A

State B / comparison

Optional extra states from pasted or uploaded CSV

Calculation steps

Pressure-volume curve

Flow-pressure graph

Comparison bar chart

Lung-and-airway schematic

Rate this calculator

Frequently Asked Questions

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