Table 2—

Definitions and calculations

ParameterDefinition
VT mLMean tidal volume of at least 5 breaths prior to occlusion
RR min−1Mean respiratory rate of at least 5 breaths prior to the occlusion calculated as (60/total breath time)
Pao kPaMean pressure at the airway opening over the plateau obtained during airway occlusion. During the MOT, multiple measures of Pao will be obtained (P1, P2, etc)
VEEL mLMean volume at baseline end expiratory level from previous 5 breaths, after the baseline has been adjusted for any drift
Vocc mLDifference between the mean end expiratory level (VEEL) prior to the occlusion and the volume during the occlusion (calculated as V1-VEEL). The volume during the occlusion is taken as the mean overall samples from 50–200 ms after start of occlusion. Labelled as Vocc,1,2,…n to relate to corresponding P1, P2,…n data when applying the MOT (figs. 2 and 3)
V1 mLVolume in the lung at time of occlusion (Vocc-VEEL); see figure 2. The number represents the volume at serial occlusions. Thus 1=volume at first occlusion and so forth
Vext mLExtrapolated volume, i.e. the volume in the lung at time of occlusion above the elastic equilibrium volume
VicSO mLVolume intercept for the SOT. The volume difference between Vx and mean VEEL prior to the occlusion, calculated as VEEL-Vx. Note: Vic is calculated with respect to the mean EEL prior to airway occlusion and not to the actual EEL from the occluded breath since infants frequently inspire early following release of occlusion (fig. 1). NB. volume intercept must not be negative and is generally <3 mL·kg−1
r2SOCoefficient of determination for linear regression of trs over the selected portion of the descending expiratory flow/volume loop. Regression should encompass at least 40% of expiration, start <65% and extend to within at least 15% of end expiration. The suggested default for regression would be between 55 to 5% of volume remaining in the lung during expiration (fig. 1)
CrsSO mL·kPa−1Respiratory system compliance measured with the single occlusion technique calculated as (Vext/P1)
trsSO sTime constant of the respiratory system calculated by linear regression of the relaxed descending portion of the expiratory flow/volume curve (trs=V′/V=Crs×Rrs)
Rapp kPa·L−1·s−1Resistance of the apparatus calculated as P/V′ at mid-flow point from trs analysis
RrsSO kPa·L−1·s−1Respiratory system resistance derived from the single occlusion technique as Rrs=(trs/Crs)-Rapp
GrsSO L·s−1·kPa−1Respiratory system conductance (the reciprocal of resistance (1/Rrs) derived from the single occlusion technique
Vext mL·s−1Pseudoflow at moment of occlusion, calculated by backward extrapolation of the trs
CrsMO mL·kPa−1Respiratory system compliance measured with the multiple occlusion technique as the regression of volume on pressure from acceptable occlusions
VicMO mLVolume intercept from MOT is the volume where the slope of the resulting volume-pressure plot crosses the volume axis (fig. 3)
r2MOCoefficient of determination for V/P regression during MOT