The Relationship Between FEV1 and Peak Expiratory Flow in Patients With Airways Obstruction Is Poor

Abstract

Study objectives To evaluate the correlation between FEV1 and peak expiratory flow (PEF) values expressed as a percentage of their predicted value, and to assess factors influencing differences between the two measurements. Design Cross-sectional. Setting Pulmonary function laboratory at a tertiary-level teaching hospital in northern India. Participants A total of 6,167 adult patients showing obstructive pattern on spirometry over a 6-year period. Interventions None. Measurements and results There was considerable variability between percentage of predicted FEV1 (FEV1%) and percentage of predicted PEF (PEF%). Locally weighted least-square modeling revealed that PEF% overestimated FEV1% in patients with less severe obstruction and underestimated it in those with more severe obstruction. Using Bland-Altman analysis, PEF% underestimated FEV1% by a mean of only 0.7%; however, limits of agreement were wide (− 27.4 to + 28.8%), indicating that these two measurements cannot be used interchangeably. PEF% and FEV1% were > 5% apart in approximately three fourths and differed by > 10% in approximately one half of the patients. On multivariate analysis, discordance > 5% was significantly influenced by female gender (odds ratio, 1.26; 95% confidence interval [CI], 1.01 to 1.58) and increasing FEV1% (odds ratio, 1.09 for every 10% increase; 95% CI, 1.04 to 1.14) but not by height or age. Conclusions FEV1% and PEF% are not equivalent in many patients, especially women and those with less severe airflow limitation. Assumptions of parity between PEF% and FEV1% must be avoided. To evaluate the correlation between FEV1 and peak expiratory flow (PEF) values expressed as a percentage of their predicted value, and to assess factors influencing differences between the two measurements. Cross-sectional. Pulmonary function laboratory at a tertiary-level teaching hospital in northern India. A total of 6,167 adult patients showing obstructive pattern on spirometry over a 6-year period. None. There was considerable variability between percentage of predicted FEV1 (FEV1%) and percentage of predicted PEF (PEF%). Locally weighted least-square modeling revealed that PEF% overestimated FEV1% in patients with less severe obstruction and underestimated it in those with more severe obstruction. Using Bland-Altman analysis, PEF% underestimated FEV1% by a mean of only 0.7%; however, limits of agreement were wide (− 27.4 to + 28.8%), indicating that these two measurements cannot be used interchangeably. PEF% and FEV1% were > 5% apart in approximately three fourths and differed by > 10% in approximately one half of the patients. On multivariate analysis, discordance > 5% was significantly influenced by female gender (odds ratio, 1.26; 95% confidence interval [CI], 1.01 to 1.58) and increasing FEV1% (odds ratio, 1.09 for every 10% increase; 95% CI, 1.04 to 1.14) but not by height or age. FEV1% and PEF% are not equivalent in many patients, especially women and those with less severe airflow limitation. Assumptions of parity between PEF% and FEV1% must be avoided.