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. Author manuscript; available in PMC: 2013 Apr 29.
Published in final edited form as: Lung. 2011 Jun 10;189(4):323–330. doi: 10.1007/s00408-011-9306-3

Table 1.

Selection criteria

  1. Criteria to select flow–volume curves for visual inspectiona
    1. All curves with observed FEV1 values larger than 6 L and values lower than 0.5 L
    2. All curves with observed FVC values larger than 8 L and values lower than 0.5 L
    3. All curves with observed PEF values lower than 100 L/min and values higher than 800 L/min
    4. All curves for twins with only one observed blow
    5. All curves for twins with two or three observed blows and a difference larger than 25% between largest and second largest value
    6. All curves with a calculated maxFEV1/maxFVC ratio larger than 0.98
    7. All curves with a calculated maxFEV1/maxFVC ratio lower than 0.40
  2. Further selection criteria
    1. If no curves were available for inspection and one of the criteria for visual inspection was fulfilled, the values were converted to missing.
    2. FEV1, FVC, and PEF were evaluated separately for each twin so that if, for example, PEF values were approved after evaluation of the flow-volume curves, FEV1 and FVC could be converted to missing values as a result of the evaluation and vice versa.
    3. For calculations of correlations and variance components, the max value of the observed data for each twin was chosen, providing us with maxFEV1, maxFVC, and maxPEF.
a

Visual inspection of the flow–volume curves was done by the first author and a chief respiratory physician together