Table 9– Important areas of interest for future studies
Area of interestQuestions and needs
Equipment validationFeasible validation methods for end-tidal inert gas concentration and phase III slope measurement
Synchronisation of gas and flow signalsOptimal synchronisation method, protocol for measurement, and the thresholds for acceptable synchronisation error remain unclear
BTPS correctionOptimal BTPS correction. Is dynamic BTPS correction required during testing? How are changes in temperature and relative humidity most accurately measured during inspiration and expiration?
Equipment VD estimationAccurate estimation of effective external VD. Streaming may occur with equipment-related VD. Therefore water displacement measurement of VD may overestimate influence of VD,ext on breathing pattern. This includes facemasks and in-line bacterial filters
Gas analyser propertiesAcceptable maximum response time for different age groups and breathing patterns?
Sample flow (Sidestream gas analysers)Degree of error introduced by sample flow: What is an acceptable sample flow? Given its age-dependence, should it be considered as a % of VT? What is the most appropriate method to correct flow and marker gas volume for sample flow?
Tissue N2Effective correction for effect of tissue nitrogen diffusing into alveoli during washout. What is the error introduced into subsequent indices (FRC, LCI and SnIII analysis)?
N2-based MBWAt what age does 100% O2 no longer have a detrimental effect on breathing pattern?
Use of sedation in infantsEffect of sedation on ability of infants to actively maintain FRC or effect on breathing pattern? This has been speculated upon but remains unproven [110, 111]
Measures of global ventilation inhomogeneity Can test duration be shortened whilst preserving acceptable sensitivity?
Flexibility of current MBW end-test thresholds (e.g. evaluation of 1/20 for LCI and 6 TO for moment ratios)
How many tests are needed to give an accurate estimate? [108]
Can wash-in data also be utilised to calculate indices?
Utility of interpolation or curve fitting methods to determine exact end-of-test for LCI
Validation of pre- and post-gas sampling point VD corrections
MBW SnIII analysisValidity of paediatric correction of SnIII by VT to account for differences in tidal VT and breathing pattern
Most appropriate inert gas reference concentration for normalisation of SIII
Formal objective criteria for exclusion of outlying SnIII values
Can accurate estimates be obtained from two tests?
Considerations for FRC, CEV and TOInfluence of geometric choice within the airstream and the time point chosen for FRC determination during the washout on FRC, CEV and TO on subsequently reported ventilation inhomogeneity indices
Importance of FRC repeatabilityFRC repeatability recommendations here are based on consensus and further research is needed to define these in future studies; the impact of FRC variability on SnIII indices is unclear
SBW SIII analysisValidity of paediatric correction of SIII by expiratory VC to account for differences in lung size
Normative dataNormative data needs to be collected for indices across different age, sex and ethnic groups. Standardisation of procedures is essential if results are to be comparable across centres and between devices. Differences in results obtained among gases with different molecular masses are expected; formal comparisons are lacking
Commercial devicesDevelopment of robust accurate commercial devices which can be used across wide age ranges
  • BTPS: body temperature, ambient pressure, saturated with water; VD: deadspace volume; N2: nitrogen gas; MBW: multiple-breath washout; SnIII: normalised phase III slope; FRC: functional residual capacity; CEV: cumulative expired volume; TO: lung turnovers, calculated as CEV/FRC; SBW: single-breath washout; SIII: phase III slope; VD,ext: external equipment deadspace volume; VT: tidal volume; LCI: lung clearance index; VC: vital capacity.