The Science Journal of the American Association for Respiratory Care

2010 OPEN FORUM Abstracts

VITAL CAPACITY ABOVE THE LOWER LIMIT OF NORMALITY DOES NOT EXCLUDE A RESTRICTIVE LUNG DEFECT.

Alan J. Moore, Laura A. Liddiard; Respiratory Physiology Service, Sandwell and West Birmingham Hospitals NHS Trust, Birmingham, United Kingdom

BACKGROUND: The ATS/ERS Task Force Paper 5: “Interpretative Strategies for lung function tests” provides a simplified algorithm showing a pathway where if FEV1/VC ≥ LLN, then if Vital Capacity is also ≥ LLN, a restrictive lung defect is excluded. The algorithm statement is “Total lung capacity (TLC) is necessary to confirm or exclude the presence of a restrictive defect when VC is below the LLN”. The study purpose was to test the validity of the algorithm pathway and statement. METHOD: A search of our lung function test database with age range 18 – 65 years was conducted. The reference equation set used was the ERS 1993 update. The specific age range selected was that used in the ERS reference set studies. Measured parameters were compared to reference values using Standardised Residuals (SR). Search criteria were ‘FEV1/VC ≥ LLN and VC ≥ LLN and TLC < LLN’. Output parameters were FEV1, VC, FEV1/VC, TLC, TLCO, VA. For each parameter, reference value was output with the standardised residual. Demographic parameters output were Age, Ethnic Origin, BMI and Provisional Diagnosis. RESULTS: 120 males (mean age 47.1 years, range 18 – 65) and 58 females (mean age 54.5 years, range 30 – 65) were identified. In the male group, the ethnic origin was Caucasian n=40, Afro-Caribbean n=28, Asian n=51 and Oriental n=1. In the female group, the ethnic origin was Caucasian n=12, Afro-Caribbean n=18, Asian n=20. Of the males identified, the range of SR for TLC was -1.757 to -3.300 and, for females, was -1.650 to -3.000 where a SR value of less than -1.645 is below the LLN. In the male group, TLCO was < LLN in 54 patients (mean SR -2.754, range -1.702 to -4.965) and for the female group in 38 subjects (mean SR -2.715, range -1.709 to -5.128). BMI was >30 in 32 males (28 had ÉTLCO/VA) and 28 females (10 had É TLCO/VA). Provisional diagnosis was documented for 95 males and 48 females. Analysis of the provisional diagnoses revealed no clear pattern but suggests that pulmonary sarcoidosis (n=31) may feature more prominently. CONCLUSIONS: There are a number of patients with normal FEV1/VC ratio and normal VC where a restrictive defect is identifiable only by measuring TLC. Neither reduced TLCO nor raised BMI (>30) are reliable indicators of restriction in these patients. Asian patients in this study group were more likely to have a restrictive defect. The authors recommend that the ATS/ERS task force review the interpretative algorithm and accompanying statements. Sponsored Research - None