In patients with severe alpha-1-protease inhibitor (alpha 1-Pi) deficiency forced expiratory volume in 1 s (FEV1) is an accepted parameter to monitor the progression of emphysema. In a patient with severe alpha 1-Pi deficiency (PiZZ) more than 1,000 FEV1 measurements were performed over a period of 12 years. FEV1 dramatically decreased initially (delta FEV1 > 500 ml/year), but stabilized after augmentation therapy was instituted. Three years later, the FEV1 decreased again abruptly; the deterioration was paralleled by an increasing number of severe bronchopulmonary infections. This nonlinear decline implies a positive influence of augmentation therapy and a deleterious effect of bronchopulmonary infections in the disease (p < 0.0005). Daily variation of FEV1 in infection-free intervals exceeded 30% and were thus higher than the mean decrease in FEV1 per year. In this instance, FEV1 measurements performed once or twice per year may reveal a deterioration, whereas the change of FEV1 is still within the range of spontaneous variation. More frequent measurements of FEV1 can be useful to minimize the influence of high intraindividual variation.
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Wencker et al. (2009) studied this question.