Pulmonary Function Testing Flashcards
Spirometry function and criteria for quality test
o Measures volume of air exhaled during forced expiration
o Plot exhaled volume against time
o Criteria for a quality spirometry test
• Minimum of 6 second expiration (3 sec if <10 years)
• No obvious back extrapolation error
• Common in poor effort/coordination, patients with elevated BMI, neuromuscular patients
• Evidence of an expiratory plateau
FEV1/FEV ratio
o FEV1 = Forced expiratory volume in the 1st second
FEV1/FVC ratio important
• Able to determine severity of obstruction
• Normally: >70-75%
• Obstructive disease: FEV1 more decreased than FVC → FEV1/FVC ratio decreased (<70%)
• Restrictive: reduction in both FEV1 and FVC → higher than normal FEV1/FVC ratio
• Confirm by measuring TLC
Also able to determine if fixed or reversible obstruction
• Administer inhaled bronchodilator
• If improved by 12% in FEV1 or FVC with increase of at least 200 ml = significant
• Characteristic of asthma, some patients with COPD
Flow volume loops
o Flow-volume curves have steep rise, sharp peak, and tapering flow
• Peak expiratory flow rate (PEF) = highest point on curve
• Initial part = effort dependent
• Later part = effort independent (instead = determined by positive pleural pressure during expiration that compresses intra-thoracic airway)
• FEF25-75 = flow rate during middle 50% of vital capacity
• Sensitive to increases in small airway resistance
Criteria/ acceptable efforts if: • No hesitation or false start • No coughing in first second (Leads to “saw-toothing," but can also be from secretions, tongue, soft tissue) • No early termination (Common in lung tx patients, adolescents, developmentally disabled, disability seekers) • No Valsalva maneuver • No leak • No obstruction in mouthpiece • No extra breath during maneuver
o FEF25%= from large airways
o FEF25% to FEF50% = from small airways
More severe the obstruction:
• FVC decreases (volume between TLC and RV)
• More pronounced concave shape of expiratory curve
Describe the differences between obstructive and restrictive patterns of disease.
- Airway obstruction = FEV1/FVC < 0.7
- If ≥0.85 = obstruction ruled out
- Fixed obstruction when a proportional decrease in FIF50 and FEF50% (so FIF50/FIF50% = 1)
- Variable extra-thoracic obstruction is when FIF50/FIF50% is reduced
Describe the differences between intra-thoracic and extra-thoracic airway obstruction.
Intra-thoracic obstruction
o Pleural pressure during inspiration becomes more negative → decreases alveoli and airway pressures → air flows from mouth down into airways
o Lumen diameter at site of variable obstruction = larger (Because subject to more negative intrapleural pressure when intrathoracic)
o Result = higher flow rates in inspiration
o During expiration: positive pleural pressure compresses airways → narrows them
• Pressure drop across obstructed area is greater
• Lowers intra-luminal pressures further
o See truncated Pressure-volume loop during expiration
o Possible causes: tracheal or bronchial polyps or tumors; tracheomalacia
Extra-thoracic obstruction
o Inspiration: luminal diameter is narrower
o Since intraluminal pressures are lower than atmospheric pressures = net transmural pressure across the airway → compresses airway
o Exacerbated at level of obstruction = air flow across narrow segment creates a higher than normal pressure drop → increases transmural difference in pressure across airway wall → further narrows luminal diameter
o During expiration: intraluminal pressure in extrathoracic airways > atmospheric pressures → transmural pressure different favors an increase in luminal diameter at level of obstruction
o See truncated Pressure-Volume loop during inspiration
o Causes: vocal cord paralysis, laryngeal edema, upper airway polyps or tumors
Diffusion Capacity test
o Result: measures both diffusion across alveolar-capillary membrane and ability of hemoglobin in alveolar capillaries to take up gas
o CO transfer is limited by alveolar-capillary membrane diffusion rate (smaller extent by the RBC membrane diffusion rate and chemical reaction between CO and hemoglobin)
Variables affecting DLCO
o Alveolar capillary surface area and volume
o Alveolar-capillary membrane thickness
o Lung volume and surface area
o Hemoglobin concentration
o Carboxyhemoglobin concentration
o Distribution of ventilation and perfusion in the lung
Causes of decreased diffusing capacity
Anemia
Decreased area for diffusion • Emphysema • Lung/lobe resection • Bronchial obstruction, as by a tumor • Multiple pulmonary emboli
Increased thickness of alveolar-capillary membrane
• Idiopathic pulmonary fibrosis
• Sarcoidosis, involving parenchyma
• Asbestosis
• Alveolar proteinosis
• Hypersensitivity pneumonitis, including farmer’s lung
• Histiocytosis X (eosinophilic granuloma)
• Congestive heart failure
• Collagen vascular disease: scleroderma, lupus
• Drug-induced alveolitis or fibrosis: bleomycin, nitrofurantoin, amiodarone, methotrexate
Miscellaneous
• High carbon monoxide back pressure from smoking (elevated carboxyhemoglobin)
• Pregnancy
• Ventilation-perfusion mismatch
Describe the differences in pulmonary function test results between different types of lung restriction.
• Restrictive lung disease if TLC < 80% of predicted value for age, height, and gender
Causes: Diseases of lung parenchyma • Idiopathic pulmonary fibrosis • Sarcoidosis • Asbestosis, silicosis • Hypersensitivity pneumonitis • Fibrosis due to drugs, poisons, radiation • Collagen-vascular disease • Lymphangitis carcinomatosa • Replacement or loss of lung units or tissue Pleural diseases • Pneumothorax • Pleural effusion • Pleural thickening or fibrosis Diseases of the chest wall • Scoliosis or kyphoscoliosis • Ankylosing spondylitis • Obesity (also has effects from adominal fat) Neuromuscular disorders • Muscular dystrophies • Amyotrophic lateral sclerosis • Poliomyelitis • Spinal cord injuries • Guillain Barre syndrome • Myasthenia gravis
