RESUMEN
This study presents an optical assembly and digital reconstruction method that is based on digital holography for characterizing transparent objects. The image-plane optical setup is based on a versatile Mach-Zehnder interferometer for the formation of controlled parallel fringe patterns, of tens micrometers of separations or less. The numerical reconstruction of the propagated wavefront by the hologram is performed by the Fresnel-Kirchhoff transform, and it is used of three ways: (a) interferometric phase reconstruction (as in interferometry) in the phase object position, (b) reconstruction of the wavefront amplitude at a determined distance from the object (shadowgraph technique), and (c) a composed digital reconstruction process of the wavefront amplitude, defined by a digital optical assembly for the selection of angular deflections produced by the phase object (schlieren technique). The resolving power of holographic reconstruction methodology proposed is determined by the sensitivity of hologram for detecting the interferometric phase. The fringe pattern of the hologram defines a minimum phase shift resolution of 0.15π rad. The scope of the technique is experimentally tested for a steady-state phase object.
RESUMEN
'Conventional' (lung volumes, airway conductance, CO transfer factor) and 'small-airway dysfunction' (single-breath N2 washout, maximal expiratory flows with air and a helium-oxygen mixture) tests were performed in a group of asymptomatic male ex-smokers (n = 20) with normal spirometry and compared to those of a similar group of middle-aged nonsmokers (n = 41). The study group had a mean life-long consumption of 13.2 +/- (SD) 8.8 pack-years and had stopped smoking 1-21 years ago, mean 7.3 +/- (SD) 5.8 years. Among the conventional tests, a minimal increase in residual volume and residual volume/total lung capacity ratio was found. Ex-smokers had a steeper phase III slope, a higher closing volume/vital capacity ratio, lower forced flows with air and a higher volume of isoflow, but neither difference between the group means was significant. There was a trend to more abnormal small-airway tests as a function of increased smoking, but only the correlation between percent of predicted closing volume and pack-years reached significance (r = +0.51, p less than 0.05). We conclude that small-airway function normalizes in the long term in most ex-smokers if they become asymptomatic, with less than 10% still having abnormal results years after they stopped smoking.