Pulmonary Function Tests in Children
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Introduction to Pediatric Pulmonary Function Testing
Overview
Pulmonary Function Tests (PFTs) are essential diagnostic tools for assessing respiratory function in children. These tests provide objective measurements of lung volumes, airflow, and gas exchange capabilities.
Key Concepts
- Age Considerations: Reliable spirometry can typically be performed in children aged 5-6 years and older who can follow instructions and perform coordinated respiratory maneuvers.
- Reference Values: Pediatric PFT interpretation requires age, sex, height, and ethnicity-specific reference equations. The Global Lung Function Initiative (GLI) equations are currently recommended.
- Quality Control: Special attention to technique and reproducibility is crucial in pediatric testing. Multiple attempts may be necessary to obtain reliable results.
Indications & Clinical Applications
Primary Indications
- Diagnostic Evaluation:
- Chronic cough or wheeze
- Exercise-induced respiratory symptoms
- Suspected asthma or cystic fibrosis
- Evaluation of restrictive lung disease
- Monitoring:
- Disease progression in chronic respiratory conditions
- Response to therapeutic interventions
- Post-transplant lung function
- Effects of chemotherapy on lung function
Clinical Applications
- Pre-operative Assessment: Evaluation of surgical risks and post-operative complications
- Research: Clinical trials and longitudinal studies
- School/Sports Participation: Fitness evaluation and exercise-induced bronchospasm assessment
Types of Pulmonary Function Tests
Basic Tests
- Spirometry: Measures dynamic lung volumes and flow rates
- Peak Flow Measurement: Quick assessment of airway obstruction
- Bronchodilator Response Testing: Evaluates reversibility of airway obstruction
Advanced Tests
- Body Plethysmography: Measures static lung volumes and airway resistance
- Diffusion Capacity (DLCO): Assesses gas exchange
- Respiratory Muscle Testing: Evaluates respiratory muscle strength
- Exercise Testing: Cardiopulmonary exercise testing (CPET)
Specialized Tests
- Infant Pulmonary Function Testing: Specialized techniques for infants
- Multiple Breath Washout: Assessment of ventilation inhomogeneity
- Forced Oscillation Technique: Measures respiratory impedance
Spirometry in Children
Key Parameters
- FEV1 (Forced Expiratory Volume in 1 second): Volume of air exhaled in the first second
- FVC (Forced Vital Capacity): Total volume of air that can be forcefully exhaled
- FEV1/FVC ratio: Key indicator of airway obstruction
- FEF25-75: Flow rate during the middle portion of expiration
Technical Considerations
- Quality Criteria:
- Back-extrapolated volume < 5% of FVC or 0.15 L
- Expiration time ≥ 3 seconds (≥ 6 years old)
- Plateau in volume-time curve
- Absence of artifacts (cough, glottic closure)
- Reproducibility:
- Three acceptable maneuvers
- FEV1 and FVC within 0.15 L or 10%
Body Plethysmography
Measured Parameters
- Static Lung Volumes:
- Total Lung Capacity (TLC)
- Residual Volume (RV)
- Functional Residual Capacity (FRC)
- Airway Resistance Measurements:
- Raw (Airway Resistance)
- sRaw (Specific Airway Resistance)
- Gaw (Airway Conductance)
Clinical Applications
- Air Trapping Assessment: Elevated RV/TLC ratio
- Restrictive Disease: Reduced TLC
- Small Airway Disease: Increased Raw and sRaw
Diffusion Capacity Testing
Procedure Components
- Gas Mixture: Carbon monoxide (CO) and tracer gas
- Breath-hold Time: 10 seconds standard
- Volume Requirements: Inspiration to TLC level
Clinical Applications
- Reduced DLCO:
- Interstitial lung disease
- Emphysema
- Pulmonary vascular disease
- Increased DLCO:
- Pulmonary hemorrhage
- Polycythemia
- Left-to-right cardiac shunt
Result Interpretation
Pattern Recognition
- Obstructive Pattern:
- Reduced FEV1/FVC ratio
- Normal or reduced FVC
- Possible air trapping (increased RV)
- Restrictive Pattern:
- Reduced TLC
- Normal or increased FEV1/FVC ratio
- Proportionally reduced FVC and FEV1
- Mixed Pattern:
- Features of both obstruction and restriction
- Reduced TLC with reduced FEV1/FVC ratio
Severity Classification
- Mild: FEV1 > 70% predicted
- Moderate: FEV1 60-69% predicted
- Moderately Severe: FEV1 50-59% predicted
- Severe: FEV1 35-49% predicted
- Very Severe: FEV1 < 35% predicted
Special Considerations in Pediatric PFT
Age-Specific Challenges
- Preschool Children (3-6 years):
- Limited attention span and cooperation
- Modified acceptance criteria
- Need for animated incentive displays
- Infants:
- Specialized equipment required
- Sedation may be necessary
- Different testing techniques
Quality Assurance
- Environmental Factors:
- Child-friendly testing environment
- Proper equipment calibration
- Temperature and humidity control
- Personnel Requirements:
- Specialized training in pediatric testing
- Patience and good communication skills
- Experience with behavioral techniques
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