Work of Breathing & Airway Compliance

The latest release of flexiWare (8.2) brings with it the capacity to assess both work of breathing (WOB) and airway compliance, expanding the comprehensive array of pulmonary assessments possible with the flexiVent system.

Work of breathing

WOB is the amount of energy required overcome the elastic and resistive qualities of the respiratory system; thereby producing tidal ventilation. It can be calculated as the product of pressure and volume (a unit of work).

The WOB parameter now incorporated into flexiWare originated from a publication from Dr. Jonathan Phillips (Amgen), where WOB was calculated as the integral of the inspiratory limb of the pressure volume loop (lower branch), plotted against volume (see the below reference for more information). 

SCIREQ worked to incorporate this WOB parameter into flexiWare, where we calculate:

• Minute WOB (mWOB) The work required to breath-in, or inspiratory WOB can be determined from the area under the inflation segment of the SnapShot pressure-volume curve. Note that the SnapShot being a manoeuvre of tidal volume amplitude, this is a novel method of calculation for this parameter, consistent with the approach used in human. During the determination, the area under the inflation segment is first normalized to the volume at maximal pressure, and expressed on a minute basis, giving rise to what is referred to as the minute WOB (mWOB). This new outcome is expressed in Joules/Liter.minute (J/L.min).
• WOB normalized (WOBn): WOBn is a volume-normalized parameter, extracted from the inflation limb of a large amplitude manoeuvre, reflecting the inspiratory work of breathing.

Airway compliance

The additional parameter of airway compliance (Caw) is also now available with flexiWare 8.2. This parameter is calculated from the initial inflation limb of the full-range PV curve (Lung Volume maneuver only), which occurs after lung degassing. Following lung collapse the lungs are inflated, in the portion of the curve before the lungs re-open the slope of the pressure volume relationship represents the airway tree distension (airway compliance Caw) (see fig. 1).

Figure 1: A full range pressure volume loop output from flexiWare showing compliance (C), opening pressure (Pop) and airway compliance (Caw).

For more information on Caw, please refer to the recent publication (below) which assessed airway compliance in mouse models of obstructive and restrictive respiratory diseases along with the work of breathing, a parameter susceptible to move with changes in Caw. 

For more information on the above parameters or how to access flexiWare 8.2 please contact [email protected].