A proposed curvilinearity index for quantifying airflow obstruction

Area of Science:

• Pulmonary Medicine
• Biomedical Engineering
• Respiratory Physiology

Background:

• Forced expiratory volume in the first second (FEV(1)) is key for airway obstruction assessment.
• Expiratory flow-volume curve (FVC) curvilinearity supports FEV(1) obstruction assessment.
• A quantitative index for pathological FVC curvilinearity is currently lacking.

Purpose of the Study:

• Introduce a novel "curvature" index (k(max)) to quantify expiratory flow-volume curve abnormalities.
• Compare the new k(max) index with forced expiratory volume in the first second (FEV(1)) values.
• Analyze spirometry data from a sequential patient cohort.

Main Methods:

• Fit a hyperbolic function to the descending phase of the expiratory flow-volume curve.
• Defined a global curvature index k(max) = b(1)/2(b(0)b(2)+b(1)) based on estimated coefficients.
• Utilized statistical software to calculate k(max) from 67 patient spirometry datasets.

Main Results:

• Individual k(max) estimates correlated well with observed curvilinearity.
• A significant exponential relationship was found between k(max) and FEV(1) values.
• The k(max) index effectively quantifies the curvilinear phenomenon in the FVC loop.

Conclusions:

• A new curvature index (k(max)) was defined to quantify expiratory flow-volume loop curvilinearity.
• The index utilizes data from a substantial portion of the flow-volume curve.
• Preliminary findings suggest an exponential relationship between k(max) and FEV(1), enabling quantitative study of obstruction.