Estimating Va/Q distributions from inert gas data with an enforced smoothing algorithm.

The accuracy of a noniterative smoothing algorithm without a nonnegativity constraint for estimating continuous Va/Q distributions from inert gas retentions was evaluated. Simulated retention measurements computed from three assumed distributions were processed by the algorithm. Original and recovered distributions were compared with the root-mean-square (rms) difference. With noise-free retentions, the rms differences were minimum with zeta = 0 (no smoothing). With simulated 3% noise, the minima occurred when 0.01 less than zeta less than 0.10. Seven trials with independent simulated errors showed a large variation in the recovered distribution and the rms difference. All recovered distributions were qualitatively different from the originals especially at low and high Va/Q values. Negative fractional flows existed in all distributions that were not grossly different from the originals. We believe that this method which did not include a nonnegativity constraint, is inappropriate for processing inert gas retentions.