Variability in measurements of pressure-volume curves in normal subjects.

Changes in lung elasticity as measured by the pressure-volume curve are used in clinical investigative studies to diagnose abnormalities in lung function and to evaluate changes in a patient either over time or with an acute intervention. To assess the intrinsic variability of parameters derived from this technique, 4 static deflation curves per day on 5 separate days during a 2-month period were constructed for 10 healthy adults. The pressure-volume data were fitted to the exponential equation: V = A-Be-KP. The coefficients of variation for maximal elastic recoil pressure, transpulmonary pressures at 90, 80, 70, and 60% total lung capacity, static expiratory compliance, and the constants A, B, and k were determined. No significant correlation was found between the variability of daily curves and that of curves performed on separate occasions. The natural log of the exponential constant showed the lowest coefficient of variation, indicating that this parameter is the most reproducible.