The interpretation of the spirogram. How accurate is it for 'obstruction'?

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology

Background:

• Airway obstruction diagnosis relies on airflow limitation assessment.
• Spirometry is a key tool, but its accuracy requires evaluation.

Purpose of the Study:

• To prospectively assess the accuracy of spirogram in detecting or excluding airway obstruction.
• To compare different methods for interpreting spirometry results.

Main Methods:

• Prospective study of 200 subjects (74 with obstruction, 126 without).
• Diagnosis of airway obstruction based on clinical and body plethysmography.
• Analysis of forced expiratory volume in 1 second to forced vital capacity (FEV1/FVC %) ratio.
• Evaluation of fixed versus predicted lower limits for FEV1/FVC %.
• Assessment of combining FEV1/FVC % with forced expiratory flow (FEF) at 50% FVC.

Main Results:

• FEV1/FVC % showed high specificity (0.98) and good sensitivity (0.82).
• A fixed lower limit for FEV1/FVC % performed better than prediction formulas.
• Combining FEV1/FVC % with FEF at 50% FVC improved sensitivity with comparable specificity.
• Normal FEF (25-75% FVC) effectively ruled out obstruction, but low values lacked specificity.

Conclusions:

• Spirometry, particularly the FEV1/FVC % ratio, is accurate for diagnosing airway obstruction.
• A fixed lower limit for FEV1/FVC % is recommended for clinical use.
• Combining spirometry parameters can enhance diagnostic accuracy for airway obstruction.