Software transparency for |
All correction algorithms and factors applied to data (e.g. BTPS and temperature modelling) |
All algorithms used for subsequently calculated indices |
Method used to synchronise flow and inert marker gas concentration signals |
Normative data or upper limit of normal incorporated, including details of source and population characteristics (number of subjects, sex distribution, age range, ethnic group, etc.) |
General recommendations |
Full availability of raw data, calibrated data and BTPS-converted data which should be saved and readily exportable in widely acceptable formats, e.g. ASCII (.txt) or .xls Ability to assess accuracy of flow and inert gas concentration synchronisation, re-measure and manually adjust as necessary |
Ability to review tidal volume tracing to ensure correct identification of breath detection (start and end-points), and manually adjust as necessary |
Ability to review inert gas expirogram for each breath, and manual adjustment if necessary, to ensure correct estimation of |
End-tidal inert marker gas concentration |
SIII if SBW or if MBW SnIII analysis is being performed |
Ability to examine for and correct any gas-analyser drift occurring during the test. The zero calibration point may be useful as a reference for many of the gases used (N2, CO2, He and SF6) whilst 100% can be used for O2. Any correction applied should be clearly stated |
If available, monitor end-tidal CO2 values during MBW to screen for hyperventilation |
FRC |
FRC is measured over all breaths of the washout, and updated after each breath, until a defined end-point in time. The end-point used for FRC determination should correspond to the end-test threshold used for ventilation inhomogeneity indices (e.g. LCI threshold) |
Exhaled inert gas volume must be corrected for re-inspired gas from the post-gas VD for each breath |
Reported FRC is that measured at the FRCgs. If other FRC values are reported, e.g. FRCao (i.e. FRCgs – pre-gas sampling point VD) these values should be described appropriately |
Report mean, sd and CoV of three technically acceptable measurements |
If only two technically acceptable measurements are available, report mean only, and state e.g. “based on two measurements alone” |
If FRC values are not within 10% of the highest FRC value, then alert the operator. Exclude FRC values which differ by >25% from the median FRC value across the three tests. Excluded tests should not be used for calculation of other MBW indices |
Indices of global ventilation distribution inhomogeneity (e.g. LCI and moment ratios) |
Correct VT for external VD (see section E6.2 in the online supplementary material) |
Use appropriate corresponding FRC for calculation |
Report mean, sd and CoV of three technically acceptable measurements |
If only two technically acceptable measurements are available, report mean and % difference, and state “based on two measurements alone” |
If LCI values are more than 1.0 TO apart (highest versus lowest), then alert the operator to perform further tests |
SnIII analysis (if performed) |
Calculation of SIII and SnIII |
SIII limits set to maximise the phase III used for linear regression, excluding phase II and phase IV contributions, and be manually adjustable, typically 50–95% of the expired volume in adults and 65–95% of the expired volume in children |
Manual adjustment of the SIII for breaths, where marked low frequency noise (or cardiogenic oscillations) or phase IV phenomena occur if automated estimations of SIII |
Expired inert gas concentration used for SIII normalisation (e.g. mean expired concentration or mean SIII concentration) should be clearly stated |
Acceptance criteria for breaths – identify and discard SnIII values of breaths that do not fulfil the following criteria |
Specific to tidal breathing protocols (e.g. paediatrics) |
Adequate expired volume for SnIII calculation: volume corresponding to SIII should be>50% of expiratory VT |
The expired volume should not be excessive: volume corresponding to SIII should not be>75% of expiratory VT |
Note: to try and achieve suitable breaths, an initial tidal breathing range of 10–15 mL·kg−1 can be used but may need to be adjusted for the individual patient depending on the expirogram seen |
Specific to adult protocols using VT of 1 L |
Expired volume should be >0.950 L |
Expired volume should not be >1.4 L |
A clear SIII should be identifiable. Failure to identify SIII due to the presence of artefact (e.g. breath hold, cardiogenic oscillations, cough) should prompt exclusion of that SnIII value |
When SnIII values are excluded do not discard the contribution of that breath to other indices (e.g. FRC and TO), only the SnIII value |
Tests should only contribute to overall SnIII analysis if at least two out of three of the breaths remain after SnIII breath exclusion. If >1/3 of SnIII values have been excluded due to above criteria then that entire test should be discarded |
Number of excluded SnIII values and reasons for exclusion should be reported |
Presentation of SnIII data |
Data collated from all acceptable breaths of the three technically acceptable MBW tests |
Acceptable first breath quality on all three tests for subsequent Sacin calculation |
In TO calculation, FRC and VT are calculated from the same airstream reference point used in ventilation inhomogeneity indices (see the online supplementary material section E6.2) |
Data displayed graphically as SnIII (y-axis) versus TO for each breath (x-axis) |
SnIII and SnIII × VT (i.e. VT-corrected SnIII) displayed for each breath on two separate graphs. |
These indices rely on the fact that DCDI generates a horizontal asymptote and CDI does not and are therefore only valid in cases where SnIII progression does not show a horizontal asymptote |
Clinical indices calculation |
Sacin calculation |
Requires three technically acceptable first breath SnIII values |
Sacin calculated as the mean SnIII of the three first breaths minus the Scond contribution (based on the mean TO value of the three first breaths) |
Scond calculation |
Scond calculated as the linear regression of SnIII values between approximately 1.5 and 6.0 TO |
Calculate 95% CI of the Scond regression, reject outlying values and repeat linear regression; data should be pooled from all three runs |
If SnIII analysis is performed with only two or less technically acceptable MBW tests, this should be clearly stated on the report and results interpreted with caution |
SBW SIII |
Report as mean, sd and CoV of three technically acceptable measurements |
If only two technically acceptable measurements are available, report mean and actual difference, and state “based on two measurements” |
VC measurements not within 10% of highest VC value across the SBW tests, then alert the operator |
Report both SIII (%·L−1) and SIII × expiratory VC (%) separately. |
BTPS: body temperature, ambient pressure, saturated with water; ASCII: American Standard Code for Information Interchange; SIII: phase III slope; SBW: single-breath washout; MBW: multiple-breath washout; SnIII: normalised SIII; N2, nitrogen; CO2: carbon dioxide; He: helium; and SF6: sulfur hexafluoride; O2: oxygen; FRC: functional residual capacity; LCI: lung clearance index; VD: deadspace volume; FRCao: FRC at the airway opening; FRCgs: FRC measured at the gas sampling point; CoV: coefficient of variation; VT: tidal volume; TO: lung turnovers, calculated as cumulative expired volume/FRC; DCDI: diffusion convection-interaction-dependent inhomogeneity; Sacin: DCDI contribution to first breath SnIII. CDI: convection-dependent inhomogeneity; Scond: rate of increase of SnIII from 1.5–6 TOs, also CDI contribution to SnIII; VC: vital capacity.