Introduction to Pulmonary Function Tests (PFTs)

Overview

• Series by Eric Strong from Stanford University
• First in a five-part series on pulmonary function tests (PFTs)
• Topics covered in the series:
  • Introduction to PFTs
  • Spirometry and flow volume loops
  • Lung volumes and measurement techniques
  • Diffusing capacity of carbon monoxide (DLCO)
  • Summary with practice cases integrating clinical history and chest x-rays

Learning Objectives

• Understand the general purpose of PFTs
• Know different types of PFTs
• Identify three major categories of chronic and diffuse lung disease
• Comprehend the subdivisions of lung volume

Purpose of PFTs

• Diagnose symptomatic disease
  • Common reasons: chronic dyspnea, cough, unexplained hypercapnia, or hypoxemia
  • High-risk patients: smokers, occupational exposures
• Screening for asymptomatic disease
  • Example: Long-term amiodarone use patients
• Prognostication of known disease
• Estimate surgical risks
  • E.g., lung resection in COPD patients
• Monitor response to treatment

Categories of Lung Disease

• Obstructive Lung Disease
  • COPD (chronic bronchitis to emphysema), asthma, bronchiectasis, cystic fibrosis
• Restrictive Lung Disease
  • Interstitial lung disease, chest wall pathology, obesity, neuromuscular disease
• Pulmonary Vascular Disease
  • Primary pulmonary hypertension, chronic thromboembolic disease

Functions Tested by PFTs

• Airways patency
• Parenchyma (alveoli and interstitium)
• Pulmonary vasculature
• Bellows and pump mechanism (diaphragm and chest wall)
• Neural control of ventilation

Types of PFTs

• Standard PFTs
  • Spirometry (airflow measure)
  • Lung volumes
  • DLCO (alveolar capillary membrane integrity)
• Specialized PFTs
  • Arterial blood gases (ABGs)
  • Exercise oximetry: measures pulse oximetry at rest and with activity
  • Six-minute walk test: prognosis and treatment response monitoring
  • Bedside peak flow: measures maximum expiratory airflow
  • Maximum inspiratory and expiratory pressure: diaphragmatic strength estimate

Lung Volume Subdivisions

• Tidal Volume: Air exchanged in resting breath
• Inspiratory Reserve Volume: Volume inhaled above tidal volume
• Expiratory Reserve Volume: Volume exhaled beyond normal exhalation
• Residual Volume: Air left after maximal exhalation

Lung Capacities

• Inspiratory Capacity: Tidal volume + inspiratory reserve volume
• Functional Reserve Capacity: Expiratory reserve volume + residual volume
• Vital Capacity: Tidal volume + inspiratory and expiratory reserve volumes
• Total Lung Capacity: Sum of all volumes

PFT Report Components

• Values reported as a percentage of predicted values based on age, gender, and height
• Normal range: 80-120% of predicted or 5th-95th percentile

Report Sections

• Spirometry
  • Key measurements: FVC, FEV1, FEV1/FVC ratio
  • Response to bronchodilators
  • Flow volume loop
• Lung Volumes
  • Key measurement: Total Lung Capacity (TLC)
• Diffusing Capacity
  • DLCO

Conclusion

• Introduction to PFTs covered
• Next video: Spirometry and flow volume loop