Lesson 3

Pulmonary Function Testing Overview

  • Static Lung Volumes: Measure the amount of air the lungs can hold at a single point in time.

    • Examples: RV (Residual Volume), ERV (Expiratory Reserve Volume), VT (Tidal Volume), IRV (Inspiratory Reserve Volume), FRC (Functional Residual Capacity), IC (Inspiratory Capacity), VC (Vital Capacity), TLC (Total Lung Capacity).

  • Dynamic Lung Volumes: Measure the rate of airflow in and out of the lungs over time.

    • Examples: FEV1 (Forced Expiratory Volume in 1 second), FVC (Forced Vital Capacity), FEV1/FVC ratio, MMEF (Mid Maximal Expiratory Flow).

  • Diffusing Capacity: Assesses how well gas transfers across the alveolocapillary membrane.

    • Example: DLCO (Diffusing Capacity of Carbon Monoxide).

Key Normal Values

  • FEV1: Normal is > 80% of predicted value.
  • FEV1/FVC Ratio: Normal is > 75-80% of predicted value.

Measurements

  • Spirometry: Used for measuring both static lung volumes and dynamic lung capacities.
  • Dynamic Lung Variables: Assessing airflow speed measures airway resistance and lung recoil.
    • FEV1: Volume expired in 1 second after maximal inhalation; declines with age.
    • FVC: Total volume of air exhaled after maximum inhalation; aids in diagnosing obstructive vs restrictive diseases.
    • FEV1/FVC Ratio: Useful for differentiation; < 70% suggests obstructive disease.
    • Forced Expiratory Flow 25-75%: Related to airflow in the middle of FEV; indicates small airway disease sensitivity.

Diffusing Capacity (DLCO)

  • Measures gas exchange efficiency through the alveolocapillary membrane.
    • Determined by Fick's Law of Diffusion.
    • Normal Values: 17-25 mL/min/mmHg.