Resistance & Compliance

The Linear First-order Single Compartment Model is the standard model of respiratory mechanics. It produces the widely used dynamic Resistance and Compliance parameters.

Estimation of R&C

• Before computerized data acquisition and analysis, R&C were estimated based on waveforms recorded on oscilloscopes or strip-chart recorders. However, techniques used at the time, such as the Mead and Whittenberger technique, relied on a few singular points in the breathing cycle, making the results susceptible to measurement noise and not necessarily representative of the entire breath.
• Today, R&C are most commonly estimated using mathematical model-fitting techniques such as Multiple Linear Regression that take all data points into account.

Measurements in active subjects

• Fitting the single compartment model always requires measurements of trans-pulmonary pressure.
• In spontaneously breathing subjects (conscious or unconscious), trans-pulmonary pressure can be measured using pleural or oesophageal catheters. This technique yields lung mechanics measurements that do not include chest wall properties.

Measurements in passive subjects

• In passive anaesthetized subjects, the single compartment model is commonly fit to airway opening pressure and flow obtained from a body plethysmograph during mechanical ventilation with passive expiration.
• However, it is advantageous to fit the model to data obtained during a Single-frequency Forced Oscillation manoeuvre where amplitude and frequency content are precisely standardized. This is the technique used by the flexiVent.
• In both cases, measurements represent respiratory system mechanics that include both lung and chest wall components (unless the chest wall is surgically opened).

Parameters