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Figure 2 Correlation of resting lung function measurements in 79 primary pulmonary hypertension (PPH) patients. Each symbol indicates an individual PPH patient. Upper left: Values are percent predicted (%pred) for FVC and FEV₁; upper right: absolute values for FEV₁ and MVV; lower left: absolute values for alveolar volume determined from single breath dilution of inert gas (VA') and TLC determined by body plethysmography or N₂ washout method; and lower right: %pred values for DL_CO and FVC. The mean ± SD of their sample ratio values are: FEV₁/FVC = 0.99 ± 0.09, MVV/FEV₁ = 39 ± 7, and VA'/TLC = 0.96 ± 0.03. Solid lines are the regressions lines for the data; dotted lines are the lines of identity. DL_CO = gas transfer index; FEV₁ = forced expiratory volume in 1 s; FVC = forced vital capacity; MVV = maximum voluntary ventilation; TLC = total lung capacity; VA' = effective alveolar volume.