title: Inspiratory conductance: an alternative index of the relationship between inspiratory effort and airflow with potential for clinical use.
abstract: OBJECTIVE
  There is a need for a measure of airway status that is easier for patients to use. If airflow is briefly occluded at the onset of inspiration, the maximum rate of pressure fall, dP/dtmax can be measured. After the occlusion is released, the maximum rate of change of inspiratory airflow (dF/dtmax) can be measured and expressed as a ratio of dP/dtmax to generate an index of inspiratory conductance (IC). We explored the characteristics of IC as a preliminary step towards developing it as an easy-to-use alternative.
  
  
  METHODS
  To measure IC, we constructed an apparatus consisting of a pneumotachograph, a low-resistance spring-loaded valve and a pressure transducer to measure airflow and pressure drop at the start of inspiration. We studied 30 healthy adults to define the values of the index, its stability and its response to external inspiratory resistive loads.
  
  
  RESULTS
  Mean IC was 2.49 (SD 0.96) Ls(-1) kPa(-1) , with no significant difference between men and women. The index was stable with a mean long-term variation of 11.25% around the normalised mean, compared with 2.1% for forced expiratory volume in 1 s (FEV1) and within-test variation < 5%. In response to external resistive loading, IC fell in a non-linear but consistent manner from 3.96 (0.32) to 0.96 (0.10) Ls(-1) kPa(-1) across an added resistance range of 0-70 kPasL(-1) .
  
  
  CONCLUSIONS
  We showed that IC was measurable with a minimal need for subject participation. It was stable and reproducible in normal individuals and responded to added inspiratory resistive loads in a way that suggested it could be of clinical utility.
authors.affiliation: Department of Medicine, The Royal Bournemouth Hospital, Dorset, UK. stephen.allen@rbch.nhs.uk
authors.forename: Stephen
authors.initials: S
authors.lastname: Allen
authors.forename: Ian
authors.initials: I
authors.lastname: Brown
authors.forename: Ahmed
authors.initials: A
authors.lastname: Khattab
authors.forename: Jeff
authors.initials: J
authors.lastname: Bagust
mesh_terms: D000328:Adult; D000403:Airway Resistance / Q000502:physiology*; D000704:Analysis of Variance; D005260:Female; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008297:Male; D012129:Respiratory Function Tests