Derivation of flow-volume and time domain spirometric indices by digitisation of volume-time spirograms

All the information regarding the forced expiratory manoeuvre are contained in the simple volume-time spirogram. Flow-volume and time-domain indices could be derived by digitising the volume-time spirogram. This paper describes an electronic means of digitising the spirogram and demonstrates its capability in deriving flow-volume and time-domain spirometric indices. The spirograms of 118 granite quarry workers were digitised using an electronic digitising pen. The volume and time data are stored in a micro-computer and a programme written in dBASEIII Plus is used to smoothen and derive the standard volume-time, flow-volume and time domain indices. There was good agreement between digitised and hand-read values (intraclass correlation coefficients, rI, greater than 0.9) for the forced expiratory flow in one second (FEV1) and forced vital capacity (FVC) irrespective of the pulmonary status. There was a small but statistically significant difference between digitised and hand-read FEV1 for those with normal and restrictive pulmonary function groups (-115 ml/sec and 19 ml/sec respectively). There was however, no evidence of systematic bias between the two methods. The technique described herein provides a rapid and accurate means for deriving flow-volume and time domain indices from a volume-time spirogram. It also provides the opportunity to reanalyse previously collected volume-time spirograms and allow for the assessment of small airways function of these subjects using newer flow-volume and time domain indices.