The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

THE USE OF SINGLE BREATH MEASUREMENTS FOR TOTAL LUNG CAPACITY (TLC) IN THE PRESENCE OF OBSTRUCTIVE LUNG DISEASE

MG SNOW, BD ANDERSON AND RJ FALLAT California Pacific Medical Center, San Francisco, Ca

OBJECTIVE: Dilutional lung volume measurements of TLC become progressively less reliable in the presence of significant maldistribution or trapped gas(Vtrap). This maldistribution is determined by the severity of obstructive lung disease. Body Plethysmography, although less influenced by maldistribution, is not always available. We evaluated the effect of OAD on Single Breath TLC (TLCsb) and the efficacy of correction factors derived from spirometric variables.

Methods: Plethysmographic (TLCp) and spirometry measurements were evaluated for 478 patients with OAD. TLCsb determinations were made as part of the assessment of diffusing capacity. Vtrap was defined as the difference between TLCp and TLCsb. Results were correlated with both the degree and type of OAD. Analysis of variance (ANOVA), discriminant analysis and least squares regression for best fit were determined for several spirometric variables. These regressions were used to evaluate a correction for TLCsb to minimize Vtrap.

Results:

F to cum r^{2} p value Individ r^{2} Eq Match

Enter

FEF2575% 631.1 0.570 < 0.0001 0.575 y=a + b exp(-x/c)

FET/MMF 472.8 0.606 < 0.0001 0.498 y=a + bx

MMF/FVC 470.8 0.615 < 0.0001 0.499 y=a + b exp(-x/c)

FEVI/FVC 529.7 0.620 < 0.0001 0.530 y=a + bx

Conclusions: Previously, a correction factor was evaluated for a specific dilutional lung volume technique compared with radiographic TLC using a small number of mixed type OAD patients. Our data confirms the feasability of correcting for OAD and provides an alternative means of adjusting alveolar volume determinations already available from DLCO measurements. This expanded utility can significantly reduce testing time and equipment expense as well as permit evaluation of patients previously untestable.

Reference: OF-96-157

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