9/9- Pulmonary Function Testing in Lung Dz Flashcards
Indications for pulmonary function tests?
- Evaluation of patients with respiratory disease
- Assessment of respiratory involvement in patients with cardiovascular disease
- Evaluation of impairment and disability
- Preoperative evaluation
- Screening of high risk patients
- Assessing response to therapy
What are some different pulmonary function tests?
- Spirometry
- Lung volumes
- Diffusing capacity
- Airway resistance
- Respiratory muscle force
- Exercise tests: 6 minute walk, cardiopulmonary exercise tests
- Bronchoprovocation tests: Methacholine, Exercise induced bronchospasm, Specific antigen testing
What is the most important pulmonary function test? What is the basic process/principle?
Spirometry
- Pt inhales and exhales with full effort
- Measures change of volume and airflow over time
In spirometry, what measurement provides the most important clinical information?
Analysis of expiratory maneuver (FVC)
What is the forced FVC maneuver?
Patient inspires maximally to total lung capacity, then exhales into spirometer as forcefully, as rapidly, and completely as possible (nose clipped)
What are some spirometry indices?
- FEV1
- FVC
- FEV1/FVC
- PEF (peak expiratory flow)
Example spirometry curve (picture)
- Note inspiratory loop is relatively symmetrical while expiratory is not
- Can plot volume vs. time or airflow vs. volume
What is FEV1? Normal value?
- Measures volume- amount of air blown out forcefully in first second of FVC maneuver
- Indicates large and small airways function
- Best measure of severity in airflow obstruction
- Normal FEV1 > 80% predicted for age, sex, and height
Example of spirometry curve (picture) with airflow vs. volume
What are determinants of lung function?
- Gender
- Height
- Age
- Race
- Spirometry
What is FVC? Normal values?
- Measures volume
- Indicates degree of lung and chest expansion
- Measures amount of air patient can blow out very rapidly
- Good indicator of pt effort
- Normal FVC > 80% predicted for age, sex, and height
What is the FEV1/FVC ratio (what does it indicate)? Normal values?
- Distinguishes airway obstruction from restriction
- FEV1/FVC ratio under 70% = obstruction
What is FEF(25-75) (what does it reflect)?
- Measures flow
- Indicates patency of small airways
- Measures flow generated in the middle third of an FVC maneuver
- Least effort-dependent
- Also called maximal mid-expiratory flow rate (MMFR)
What are aspects of spirometry/test quality to consider?
- Watch patient and graph for consistency in effort
- Full inhalation before start of test
- Maximal effort with sharp initial peak
- Total time at least 6 seconds
- No evidence of coughing or hesitation at least during the first second
- Three reproducible attempts should be made
- The two largest values of FVC and FEV1 should be within 5% or 0.1 L
What will be seen in spirometry with obstruction?
(Think asthma, bronchectasis, cystic fibrosis…)
- Decrease FEV1, Normal or decreased FVC
- FEV1/FVC under 70% = obstruction
- If FVC is decreased, may have combined restriction
On graph:
- Expiratory loop is skewed down (spooned) and narrow
- Peak flow is also lower
What test can be performed on patients with obstruction to identify asthma or COPD as a possible cause?
What is the process of the test and what is a positive response?
Bronchodilator Responsiveness
- Inhale albuterol and repeat after 15 min
Positive response:
- Either FEV1 or FVC
- Magnitude of change: 200 mL AND 12% difference
What are some obstructive lung diseases?
- Asthma
- Bronchiectasis
- COPD- chronic bronchitis, emphysema
- Cystic fibrosis
- Bronchiolitis
What will be seen on the spirometry curves in upper airway obstruction?
Truncation of expiratory or inspiratory flow loop
What may cause expiratory loop truncation?
Variable intrathoracic (tracheal tumor above carina)
What may cause inspiratory loop truncation?
Variable extrathoracic (vocal cord paralysis)
What may cause both expiratory and inspiratory loop truncation?
Fixed obstruction (e.g. tracheal stenosis)
What will be seen in spirometry with restriction?
- Reduced FVC and FEV1
(- Reduced lung volumes: TLC or VC)
- Normal or increased FEV1/FVC
Severity:
- Mild =/> 70%
- Moderate: 60-70%
- Moderately severe: under 60%
Curve is shaped normally, but miniature
What are some restrictive diseases? (don’t memorize verbatim)
- Lung resection
- Pleural Effusion
- Pleural fibrosis
- Neuromuscular weakness
- Interstitial lung diseases
- Pulmonary fibrosis
- Atelectasis
- Obesity
Also: parenchymal (pulmonary fibrosis), chest wall and neuromuscular disorders
Overview of spirometry curves
Overview of obstructive vs restrictive disease via spirometry/other tests
Obstructive
- Lower PEF
- More concave as disease worsens
- Improves with beta agonist
Restrictive
- Normal shape but less wide
- PEF normal or decreased
- FEF 25-75 reduced
Summary: lung volumes
More on lung capacities:
What are the equations for:
- VC
- IC
- FRC
- TLC
- VC = IRV + TV + ERV
- IC = TV + IRV
- FRC = ERV + RV
- TLC = IRV + TV + ERV + RV
What is normal TLC?
6 L
What is plethysmography? Advantages and disadvantages?
Aka Body Box
- Best method for lung volume determination
- Uses Boyle’s gas law: volume of gas in closed system varies inversely with the pressure applied to it (P1V1 = P2V2)
Disadvantages:
- Measures all gas in the lungs, including trapped gas (falsely high in emphysema)
What constitutes small lung volumes?
In what cases may this occur?
- Decreased FRC, TLC; under 80%
Caused by:
- Decreased compliance of lung ( increase stiffness of lung and elastic recoil). eg; parenchymal lung disease
- Decrease in chest wall compliance. eg; neuromuscular disorders and chest wall disorders
What constitutes large lung volumes?
In what cases may this occur?
- Increased TLC, FRC; > 120%
Caused by: increased in compliance of lung (decrease stiffness and elastic recoil)
- Ex: emphysema
How do FRC and TLC change with hyperinflation?
- FRC increases
- TLC increase
How does RV change with air trapping?
RV increases
What is diffusion capacity (DLCO)?
Transfer of gas across the membranes
- Measures the facility with which oxygen diffuses across the alveolar-capillary membrane
On what does DLCO depend?
- Total lung surface
- Integrity and thickness of alveolar-capillary membrane
- Amount of blood in the lung
Indications for DLCO?
- Differential diagnosis of obstructive lung diseases
- Screening for early ILD
- Differential diagnosis of pulmonary restriction
- Detection of pulmonary vascular diseases
- Follow up for ILD
What are factors that increase DLCO?
- Decrease in alveolar PO2 (altitude)
- Male sex
- Supine position
- Exercise
- Increasing age to 20 yo
Increases in:
- Body size
- Lung volume
- Alveolar PCO2
What are factors that decrease DLCO?
- Increase in alveolar PO2
- Most lung diseases (discussed later)
- Increasing age after 20 years (2%/yr)
- Smoking (High COHb)
- Lung resection
In what instances can you have normal spirometry but low DLCO?
- Pulmonary vascular disease
- Anemia
In what instances can you have abnormal spirometry and low DLCO?
- Restrictive pattern: interstitial lung disease (pulmonary fibrosis)
- Obstructive pattern: emphysema
What are bronchoprovocation test indications? When is it contraindicated?
- Identify the presence of airway hyperresponsiveness when clinically suspected but spirometry is normal
- Support the diagnosis of asthma in the evaluation of unexplained dyspnea and chronic cough when spirometry normal
- Contraindicated in patients with severe airway obstruction
Summary flow chart
Ex)
- 39 yo Hispanic woman
- FEV1/FVC = 56%
- FEV1 = 1.59 (54%)
- FVC = 2.87 (81%)
- FEV1 increases by 200 mL and > 12%
What does this patient have (broadly)?
Moderate-severe airway obstruction with significant airway response to albuterol
Ex)
- 30 yo African woman
- FEV1/FVC = 95%
- FEV1 = 2.27 (77%)
- FVC = 2.38 (69%)
- TLC = 58%
- Decreased diffusion capacity
What does this patient have (broadly)?
Restrictive disease with low lung volume and decreased diffusion
- Suggests problem with alveolar-cap membrane (interstitial lung disease or…)
