Can peak expiratory flow be measured accurately during a forced vital capacity manoeuvre?

Spirometry and peak flow measurements traditionally depend on different forced expiratory manoeuvres and have usually been performed on separate, dedicated equipment. As spirometry becomes more widely used in primary care settings, the authors wished to determine whether there was a systematic difference between peak expiratory flow (PEF) derived from a short sharp exhalation (PEF manoeuvre) and from a full forced vital capacity (FVC) manoeuvre, using the same turbine spirometer (Microloop, Micro Medical, Kent, UK). Eighty children (38 with current asthma) aged 7-16 yrs were asked to perform 2 blocks of PEF and FVC manoeuvres, the order being randomly assigned. PEF obtained from a peak flow manoeuvre (PEFPF) was significantly greater than that from a forced vital capacity manoeuvre (PEFVC) in both healthy (group mean difference 20 L x min(-1); p<0.001) and asthmatic children (group mean difference 9 L.min(-1); p<0.004). For clinical purposes, a mean difference of about 3% for children with asthma is of no practical significance, and peak expiratory flow data can usefully be obtained during spirometric recordings.