The nonspecific pulmonary function test: longitudinal follow-up and outcomes.
BACKGROUND
The nonspecific (NS) pulmonary function (PF) pattern refers to a PF test with a normal total lung capacity (TLC), normal FEV₁/FVC ratio, and a low FEV₁, a low FVC, or both. Currently, no information is available regarding the long-term stability of the NS pattern or variables that predict changes in subjects with an initial NS PF pattern.


METHODS
From 1990 to 2005 we identified 1,284 subjects with an NS pattern on initial PF testing with one or more follow-up PF tests 6 months or more after the initial NS test result. Lung volumes, diffusing capacity, and spirometry data were analyzed. A multivariate, multinomial logistic regression model was used to study the association between different variables and the final PF pattern.


RESULTS
Overall, 3,674 PF tests were performed in 1,284 subjects over a median follow-up period of 3 years. At last follow-up, 818/1,284 (64%) subjects continued to show the NS pattern, whereas 208/1,284 (16%) showed a restrictive pattern, 191/1,284 (15%) an obstructive pattern, 42/1,284 (3%) a normal pattern, and 25/1,284 (2%) a mixed pattern. The multinomial logistic regression analysis showed that increasing values for specific airway resistance and the difference between TLC and alveolar volume were predictors of a change to an obstructive pattern on follow-up.


CONCLUSIONS
The NS pattern is a distinct and stable PF test pattern with roughly two-thirds of patients continuing to show this pattern on follow-up testing. Current interpretation guidelines erroneously label the NS pattern as representing obstruction and need to be changed to reflect these data.
Iyer
Vivek N
VN
Division of Pulmonology and Critical Care Medicine, Rochester, MN. Electronic address: iyer.vivek@mayo.edu.
Schroeder
Darrell R
DR
Department of Biostatistics, Mayo Clinic College of Medicine, Rochester, MN.
Parker
Kenneth O
KO
Division of Pulmonology and Critical Care Medicine, Rochester, MN.
Hyatt
Robert E
RE
Division of Pulmonology and Critical Care Medicine, Rochester, MN.
Scanlon
Paul D
PD
Division of Pulmonology and Critical Care Medicine, Rochester, MN.
D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D005540:Forced Expiratory Flow Rates / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D011658:Pulmonary Fibrosis / Q000175:diagnosis / Q000503:physiopathology*; D012129:Respiratory Function Tests / Q000379:methods*; D012189:Retrospective Studies; D012720:Severity of Illness Index; D013997:Time Factors; D014109:Total Lung Capacity / Q000502:physiology*