Kopp - 9/19/25Pulmonary Function and Obstructive Lung Diseases

Obstructive Lung Diseases and Pulmonary Function Testing

Chronic Obstructive Pulmonary Disease (COPD)

• Core Problem: The primary issue in COPD is difficulty getting air out of the lungs, not necessarily getting air in.

• Examples of Obstructive Lung Diseases: Asthma, chronic bronchitis, and cystic fibrosis are all classified as obstructive lung diseases.

• Diagnosis: Specific spirometry numbers can indicate an obstructive disease pattern.

• Lung Function Deterioration: Even individuals with perfect lifestyles (exercise, non-smokers) experience some deterioration in lung function with age.

Spirometry

• Purpose: Spirometry measures lung function, specifically how much air an individual can inhale and exhale, and how quickly they can exhale.

• Types of Spirometers:

  • Full Pulmonary Function Testing (PFT) Lab: Equipped with large, sophisticated machinery for comprehensive testing.

  • Bedside Spirometry: Utilizes small, portable handheld devices for quick patient screenings. This is commonly performed pre-surgery to establish a baseline or check for deterioration, allowing for medication adjustments (e.g., starting steroids) before the patient experiences full-blown symptoms.

• Testing Procedure:

  • Patients are instructed to take a deep breath and then exhale forcefully and completely.

  • Effort Dependence: The accuracy of spirometry heavily relies on the patient's maximal effort. Technicians often provide vocal encouragement to ensure this.

  • Repeatability: Ideally, tests should be performed three times to ensure consistent and reliable results. However, in acute critical situations (e.g., severe asthma in an emergency room), repeated testing might worsen the patient's condition.

• Bronchodilator Response:

  • In a full PFT lab, a complete test often involves administering a bronchodilator treatment and then repeating the test to assess if there is an improvement in lung function, indicating a bronchodilator response.

  • Respiratory Therapist Role: Respiratory clinicians evaluate the effectiveness of bronchodilator treatments. If there's no improvement after a day of scheduled treatments, it suggests the bronchodilator isn't reaching the alveoli or isn't effective, prompting a re-evaluation of the treatment plan.

• Physiological Basis of Obstruction:

  • The conducting zone of the airways (bronchi, bronchioles) contains smooth muscle. When activated (e.g., during an asthma attack), this smooth muscle contracts, leading to narrowing of the airways and an increase in airflow resistance.

  • Alveoli, in contrast, are not designed to contract and expand; their primary role is gas exchange.

  • Bronchodilator treatments aim to relax this smooth muscle, reducing airway resistance and improving airflow.

• Flow Measuring Devices: Devices that measure airflow are called pneumotachometers.

  • Calibration: All spirometry devices must be calibrated and tested daily to ensure accuracy.

Key Spirometry Measurements

• Forced Expiratory Volume in 1 Second (FEV$_{1}$):

  • Measures the volume of air exhaled during the first second of a forced exhalation.

  • Normal Value: In healthy individuals, approximately $80\%$ of the total forced vital capacity should be exhaled in the first second.

  • Clinical Significance: A key screening tool; a value below $70\%$ often indicates an obstructive defect.

• Peak Expiratory Flow (PEF or Peak Flow):

  • A simple, handheld device measures the maximum flow rate achieved during a forced exhalation.

  • Useful for quick assessment of airway narrowing and monitoring asthma control.

• Forced Expiratory Flow between $200$ and $1200$ mL (FEF$<em>{200-1200}$) and Forced Expiratory Flow between $25\%$ and $75\%$ (FEF$</em>{25-75\%}$):

  • These are more detailed flow measurements that can help pinpoint the location of obstruction, particularly in the small airways.

  • Interpretation: While FEV$<em>{1}$ below $70\%$ is a general indicator of obstruction, values like FEF$</em>{25-75\%}$ can specifically suggest small airway issues.

Lung Volumes

• Tidal Volume (TV): The amount of air inhaled or exhaled during a normal, quiet breath.

  • Typical Range: Approximately $300-500$ mL ($0.3-0.5$ liters) per breath.

• Inspiratory Reserve Volume (IRV): The maximum amount of air that can be inspired over and above a normal tidal inspiration (i.e., a deep breath).

• Expiratory Reserve Volume (ERV): The maximum amount of air that can be exhaled forcibly after a normal tidal exhalation.

• Residual Volume (RV): The volume of air remaining in the lungs after a maximal forced exhalation. (Not explicitly defined, but conceptually important for capacities).

Lung Capacities (Combinations of Volumes)

• All capacities are combinations of two or more lung volumes.

• Inspiratory Capacity (IC): The maximum amount of air that can be inspired after a normal tidal expiration. ($IC = TV + IRV$).

• Functional Residual Capacity (FRC): The volume of air remaining in the lungs after a normal tidal expiration. ($FRC = ERV + RV$).

• Vital Capacity (VC): The maximum amount of air that can be exhaled after a maximal inspiration. ($VC = TV + IRV + ERV$). This is represented by the