Basic spirometry testing and interpretation for the primary care provider

Abstract

Spirometry testing plays an important role in the diagnosis and management of COPD and asthma in the primary care setting. Verifying the accuracy of the spirometer, using accurate patient demographics and appropriate reference equations, and ensuring the competency of testing personnel are key components of spirometry test interpretation. Spirometry testing plays an important role in the diagnosis and management of lung disease in the primary care setting. Spirometry interpretation should include an assessment of test quality and be based on sound statistical principals.

Keywords: lower limit of normal; primary care; respiratory function tests; spirometry.

FIGURE 1. Normal spirometry, all values fall within the normal range. The flow–volume loop exceeds the expected flows and volumes (dotted line). FVC, forced vital capacity; FEV₁, forced expiratory volume in the first second; FEV₃, forced expiratory volume in the third second; M, median; LLN, lower limit of normal.

FIGURE 2. Common spirometry errors. (A) Obstructed airflow due to a patient obstructing their pharyngeal and laryngeal structures (grunting) causing saw tooth flow patterns. (B) Poor expiratory effort, the red arrow indicates there should be a spiked, not rounded peak expiratory flow graphic. (C) Poor start, the red arrow indicates leaked air prior to the forced expiratory maneuver (excessive back extrapolated volume). (D) Premature termination of expiratory flow, the red arrow indicates a sudden vertical drop in flow. FEV₁, forced expiratory volume in the first second; FEV₃, forced expiratory volume in the third second.

FIGURE 3. Spirometry data displayed on a bell curve. LLN, lower limit of normal; M, median; ULN, upper limit of normal; FVC, forced vital capacity; FEV₁, forced expiratory volume in the first second. (Courtesy of Morgan Scientific Inc., Haverhill, MA, USA)

FIGURE 4. Obstructive spirometry pattern, the FEV₁ and FEV₁/FVC are < LLN. The flow–volume loop shows less than expected expiratory flows (dotted line), which create a concave contour. FVC, forced vital capacity; FEV₁, forced expiratory volume in the first second; FEV₃, forced expiratory volume in the third second; M, median; LLN, lower limit of normal.

FIGURE 5. Restrictive spirometry pattern, the FVC and FEV₁ are <LLN but the FEV₁/FVC is >LLN. The flow–volume loop is narrow indicating low volumes. FVC, forced vital capacity; FEV₁, forced expiratory volume in the first second; FEV₃, forced expiratory volume in the third second; M, median; LLN, lower limit of normal.

FIGURE 6. Significant bronchodilator response, the post-bronchodilator FEV₁ has increased more than 12% and 200 mL and is >LLN. The flow–volume loop overlay shows higher flows and volumes after bronchodilator (red tracing). FVC, forced vital capacity; FEV₁, forced expiratory volume in the first second; FEV₃, forced expiratory volume in the third second; M, median; LLN, lower limit of normal.