Schrader PC, Quanjer PH. van Zomeren BC, de Groodt EG, Wever AMJ, Wise ME. Selection of variables from maximum expiratory flow-volume curves. Bull Europ Physiopath Resp 1983; 19: 43-49  

ln a longitudinal study, we aim to assess the normal development of lung function in teenagers and to study the influence of past or present lung disease and smoking habits on this development [18]. The population comprises pupils at two schools in The Hague; their ages ranged between 12 and 16 years when they were studied. 191 boys and 142 girls were first measured when they were in the lowest class of a secondary school in September 1978 or 1979. A further 188 boys and 2 girls had started in a vocational (technical) school in September 1980. Measurements are being performed at school every six months until the pupils leave. Informed consent was obtained from the parents, who also filled in a mailed questionnaire on respiratory symptoms, and past or present respiratory or other illnesses in their children and also on their own smoking habits.
The pupils are asked to fill in a confidential form on their smoking habits. The standing height, body weight, thoracic width, mid-clavicular thoracic height and sternal height are measured. The pupils then perform maximum expiratory flow-volume curves and a single and multiple breath nitrogen test [20, 21]; the latter test will not be considered here. All MEFV curves are obtained with the same equipment by one operalor (BCvZ). Each individual produces a set of MEFV curves seated and without a nose-clip. They are recorded and displayed on an oscilloscope and the operator judges straight away by eye whether the blows are technically satisfactorily performed and give reproducible curves with respect to the forced expiratory vital capacity (FVC) and the overall shape and course of the curve. Each subject repeats the blowing until five acceptable curves are obtained. Curves were discarded e.g. if: a) tbe forced expiratory manoeuvre was obviously not started from the level of TLC, or terminated prematurely, b) the subject coughed during the blow, c) the tongue obstructed airflow, d) not all the air was blown through the mouth piece, and e) the subject hesitated at the start of the manoeuvre. Figure 1 shows MEFV curves from one subject.
After a maximal inspiration, the subject blows as hard as possible through a 52 cm long, stiff and heated tube (internal diameter 2.6 cm) connected to a Fleisch 3 pneumotachometer. The assembly of tube, flowmeter and pressure transducer (Gaeltec type LPT) had a constant gain and negligible phase shift well above 45 Hz when tested with a sinusoidal pump (volume deflection 50 mL) [11]. The back pressure at the mouth at a flow rate of 10 l·s^-1 was approximately 0.14 kPa. The flow signal was sampled at 100 cps, filtered (50 Hz, fourth order filter) and processed by a digital computer to give FVC, forced expiratory volume in one second (FEV₁), peak expiratory flow (PEF), maximum mid-expiratory flow (MMEF) and maximum expiratory flows when 75, 50 and 25 per cent of lhe FVC remain in the lung (MEF₇₅, MEF₅₀ and MEF₂₅) [25]. Forced expiration was considered to have commenced when the expiratory flow was more than 0.2 l·s^-1 and to have ended when the expiratory flow had been less than 0.05 l·s^-1 for more than 0.25 s. The gain of the pneumotachometer assembly varied over a wide range of flows when assessed during steady flow (Godart calibration set type 17346); linearization was performed by the computer, so that when tested at various flows with a calibrated 2 L syringe volume readings agreed within 1.0 per cent from the mean.
In the present study, we have used MEFV curves from three groups of teenagers who differed with respect to previous experience with the test. Group A comprises 11 boys and 10 girls with no past or present respiratory symptoms, such as coughing, wheezing, dyspnoea, etc. None of them smoked. They had already performed the test previously one to three limes. Each produced a set of 5 MEFV-curves on 5 consecutive days. Due to sickness absence and poor performance, we obtained only 95 sets of 5 technically satisfactory forced vital capacity manoeuvres. Data from these were used to assess the variability within individuals. Each day, all 21 boys and girls of group A were questioned for current respiratory symptoms. Nine reported minor symptoms confined to upper airways, usually common colds. As LEEDER at al. [12] showed that such minor complaints of upper airways did not affect the reproducibility, the data derived from these pupils were not discarded. In group B, we used 333 sets of technically satisfactory curves from the secondary school pupils who were measured in March 1980. For 219 of them, this was the second time they produced MEFV curves; for the others, it was the fourth time. Group C comprises the teenagers at the technical school. They were studied in October 1980, when they had no previous experience of the test. In this group, 190 sets of technically satisfactory MEFV curves were available.

References

12. LEEDER (S.R.), SWAN (A.V.), PEAT (J.K.), WOOLCOCK (AJf.), BLACKBURN (C.R.B.). - Maximum expiratory fIow-volume curves in children: changes with growth and individual variability. Bull. europ. Physiopathol. resp. 1977, 13, 249-260.
18. SCHRADER (P.C.), VAN ZOMEREN (B.C.), WISE (M.E.), VAN LEEUWEN (P.), QUANJER (P.H.), WEVER (A.M.J.). - Selection of variables trom MEFV-curves in adolescents. Europ. J. Resp. Dis., 1981, 62 (suppl. 113), 117·118.
25. VAN HARTEVELT (J.H.), KRUVT (E.W.), VAN ZOMEREN (B.C.). - On-line bepaling van flow-volume curve. Proceedings Medisch Informatica Congres 79. J.L. Willems, Antwerpen, 1979, pp. 229-232.