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Abstract: Slide Presentations |

A LOGARITHMIC MODEL OF PREDICTING FVC BASED ON FEV1, FEV2, AND FEV3 FREE TO VIEW

Octavian C. Ioachimescu, MD*; Kevin McCarthy, RRT; Mani Kavuru, MD; James Stoller, MD
Author and Funding Information

Cleveland Clinic Foundation, Cleveland, OH


Chest


Chest. 2005;128(4_MeetingAbstracts):173S. doi:10.1378/chest.128.4_MeetingAbstracts.173S
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Abstract

PURPOSE:  Accurate measurement of forced vital capacity (FVC) is important in pulmonary function testing. Since the rate of achieving spirometric end-of-test criteria is usually less than optimal, with resultant under-recording of the FVC, the current analysis proposes a logarithmic model of predicting FVC based on FEV1, FEV2, and FEV3, especially when end of test criteria are not met (i.e., no expiratory plateau or short exhalation time).

METHODS:  Estimated logFVC and exp(Estimated logFVC) were derived after multivariate analysis and construction of a logarithmic regression model from volume measurements within the first 3 seconds of exhalation (based on FEV1, FEV2, and FEV3). We developed the model on a large derivation cohort and subsequently evaluated it on a distinct validation cohort of patients.

RESULTS:  The derivation group consisted of 35,885 consecutive spirometric tests performed in the Cleveland Clinic Foundation Pulmonary Function Laboratory. The equation derived was as follows: Estimated logFVC = –0.04 –0.416×logFEV1 –1.612×logFEV2 + 2.991×logFEV3 (R2 = 0.95, p < 0.0001, RMSE = 0.087). The equation was applied to an independent validation set of 61,290 spirometric measurements on as many consecutive, different patients. Based on the above equation, Exp (Estimated logFVC) = 0.10 + 0.963×FVC (R2 = 0.97, p < 0.0001, RMSE = 0.241). In the validation cohort, the prevalence of obstruction was 66% (based on values of the measured FEV1/FVC compared to NHANES III values). In the same cohort, the mean residual, i.e. the difference between estimated and measured FVC (± standard deviation) was 6.9 (± 238) mL.

CONCLUSION:  Our predictive model based on logarithmic values of the spirometric measurements had a good diagnostic performance and behaved reasonably accurate in situations of short exhalation time and/or when no expiratory plateau is achieved.

CLINICAL IMPLICATIONS:  Since FVC is frequently under-recorded with resultant over-estimation of FEV1/FVC and under-diagnosis of airflow obstruction, we showed that estimating FVC from FEV1, FEV2 and FEV3 using a logarithmic model can improve the precision of the estimation and offer practical diagnostic advantages.

DISCLOSURE:  Octavian Ioachimescu, None.

Tuesday, November 1, 2005

10:30 AM - 12:00 PM


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