Pulmonary Function Tests (PFTs) are a group of diagnostic investigations used to evaluate lung function, ventilation, and gas exchange. These tests help diagnose respiratory disorders, assess disease severity, monitor treatment response, and guide therapeutic decisions. Understanding PFTs is essential for clinical pharmacists, respiratory therapists, and healthcare professionals involved in pulmonary care.
Objectives of Pulmonary Function Tests
- Diagnose obstructive and restrictive lung diseases.
- Assess severity of respiratory impairment.
- Monitor response to bronchodilators and long-term therapy.
- Evaluate pre-operative lung function.
- Detect early airway disease before symptoms appear.
Spirometry
Spirometry is the most commonly performed PFT. It measures the volume and flow of air during inhalation and exhalation.
Key Spirometric Parameters
1. Forced Vital Capacity (FVC)
The maximum amount of air exhaled forcefully after a full inspiration.
2. Forced Expiratory Volume in 1 Second (FEV1)
The volume of air exhaled during the first second of forced expiration.
3. FEV1/FVC Ratio
Important in distinguishing between obstructive and restrictive diseases.
4. Peak Expiratory Flow Rate (PEFR)
Maximum speed of exhalation; useful in monitoring asthma control.
Interpretation of Spirometry
Obstructive Lung Disease
Characterized by difficulty in exhaling air.
- Common diseases: COPD, asthma, bronchitis.
- Findings: Low FEV1, low FEV1/FVC ratio.
- FVC may be normal or reduced.
Restrictive Lung Disease
Characterized by reduced lung expansion.
- Common diseases: pulmonary fibrosis, scoliosis, obesity.
- Findings: Reduced FVC, normal/near-normal FEV1/FVC ratio.
Mixed Disorders
Features of both obstructive and restrictive patterns.
Lung Volumes and Capacities
Measured using body plethysmography or gas dilution techniques.
1. Tidal Volume (TV)
Amount of air inhaled or exhaled during normal breathing.
2. Inspiratory Reserve Volume (IRV)
Additional air inhaled after normal inspiration.
3. Expiratory Reserve Volume (ERV)
Extra air exhaled after normal expiration.
4. Residual Volume (RV)
Air remaining in the lungs after forceful expiration.
5. Total Lung Capacity (TLC)
Total volume of air the lungs can hold.
- Low TLC indicates restrictive disease.
- High TLC indicates hyperinflation (e.g., emphysema).
Diffusion Capacity Test (DLCO)
Measures the ability of gases (like oxygen) to transfer from the lungs into the blood.
Clinical Significance of DLCO
- Low DLCO: pulmonary fibrosis, emphysema, anemia.
- High DLCO: asthma, polycythemia.
Peak Flow Meter Test
Peak flow monitoring is widely used for asthma management.
- Measures PEFR.
- Helps detect early bronchoconstriction.
- Used in home monitoring plans.
Asthma Zone System (Using PEFR)
- Green Zone: 80–100% of predicted value (well-controlled).
- Yellow Zone: 50–79% (caution, step-up therapy required).
- Red Zone: <50% (medical emergency).
Arterial Blood Gas (ABG) Analysis
Although not a PFT itself, ABG provides important information about oxygenation and acid–base balance.
- PaO₂
- PaCO₂
- HCO₃⁻
- pH
Chest Imaging in Respiratory Assessment
Often used alongside PFTs.
- Chest X-ray: Detects structural abnormalities.
- CT scan: Identifies fibrosis, tumors, emphysema.
Indications for Pulmonary Function Testing
- Chronic cough, dyspnea, wheezing.
- Evaluation of known lung diseases (COPD, asthma).
- Pre-operative risk assessment.
- Monitoring occupational exposures.
- Assessing disability or fitness levels.
Contraindications
- Recent myocardial infarction.
- Uncontrolled hypertension.
- Thoracic/abdominal surgery.
- Severe respiratory distress.
Role of Clinical Pharmacists in PFT Interpretation
- Evaluate medication effectiveness (bronchodilators, corticosteroids).
- Counsel patients on inhaler techniques.
- Identify adverse drug effects influencing respiratory function.
- Participate in asthma and COPD management programs.
Detailed Notes:
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