SESSION TITLE: Physiology/PFTs/Rehabilitation
SESSION TYPE: Original Investigation Slide
PRESENTED ON: Tuesday, October 28, 2014 at 08:45 AM - 10:00 AM
PURPOSE: Spirometry is used to diagnose COPD and requires subjects to exhale for at least six seconds to meet end of test criteria. However, patients with COPD may have a shorter expiratory time; we intended to evaluate the role of Forced Expiratory Volume in 1 second (FEV1)/Forced Expiratory Volume in 3 seconds (FEV3) to recognize obstruction and reliably diagnose obstructive lung disease in patients who are unable to meet current end of test criteria.
METHODS: Data was collected from all PFTs done in our hospital within the last 10 years. Out of 3172 PFTs patients having Forced Expiratory Time (FET) ≥ 6 seconds were included (n= 2207) in our study. FEV1/Forced Vital Capacity (FVC), FEV1/ FEV3 and FEV1/ Forced Expiratory Volume in 6 seconds (FEV6) ratios were calculated and correlations between these ratios were analyzed. The subjects were divided into two groups based on the presence or absence of obstruction on their PFTs. Mean FEV1/FEV3 ratio of these two groups were compared using an independent sample t-test. Statistical analysis was done using SPSS 17.0.
RESULTS: Among the 2207 study subjects 56% were male, 87% were African-American and 38% were non-smokers. The mean age was 57 with a mean BMI of 30.8. 914 patients showed features of obstruction post-bronchodilator (FEV1/FVC ratio <70%) on PFT. FEV1/FEV3 ratio had a strong positive correlation with FEV1/FVC (r=0.84, p<0.001) and with FEV1/FEV6 (r=0.91, p<0.001). There was a statistically significant difference in mean FEV1/FEV3 ratios between the obstructive and non-obstructive group (85% vs. 69%, p<0.001). A cutoff value of 80% for FEV1/FEV3 ratio had a sensitivity of 94% and specificity of 88% with positive and negative predictive values of 84% and 96% respectively for obstructive lung disease.
CONCLUSIONS: We believe shorter expiratory time may result in under diagnosis of airflow obstruction (based on underestimation of FVC and an overestimation of FEV1/FVC). Therefore use of FEV1/FEV3 may offer both a diagnostic and a practical advantage in this patient population.
CLINICAL IMPLICATIONS: FEV1/FEV3 <0.8 can reliably diagnose COPD in patients who do not meet the end of test criteria of 6 seconds.
DISCLOSURE: The following authors have nothing to disclose: Bikash Bhattarai, Meenakshi Ghosh, Abhisekh Sinha Ray, Mohammed Raihan Azad, Bhradeev Sivasambu, Sai Kwan Wan, Santu Saha, Saurav Pokharel, Rakesh Vadde, Vikram Oke, Marie Frances Schmidt, Danilo Enriquez, Joseph Quist, Anita Pandey, Saveena Manhas
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