Pulmonary function tests Flashcards
What pulmonary aspects are measured in pulmonary function tests
- Airflow (also called Spirometry) 2. Lung Volumes 3. Gas Exchange (Diffusing Capacity) 4. Respiratory System Compliance 5. Airway Responsiveness 6. Respiratory Muscle Strength
- Airflow (also called Spirometry) 2. Lung Volumes 3. Gas Exchange (Diffusing Capacity) 4. Respiratory System Compliance 5. Airway Responsiveness 6. Respiratory Muscle Strength
- Identify the three major components of routine pulmonary function tests and how they are measured
Lung volumes (spirogram), airflow (spirometry) and gas exchange.
Obstructive diseases
asthma, COPD, bronchiolitis
restrictive diseases
pulmonary edema, interstitial lung disease, neuromuscular weakness, pleural disease, obesity
- Identify components of and distinguish between volumes and capacities
volumes are single entities while capacities are composed of two or more volumes.
- Define the determinants of FRC (aka TGV)
functional residual capacity = residual volume + expiratory reserve volume
tidal volume
This is the amount of gas volume moved during a normal inspiration
Inspiratory reserve volume
This is the volume of gas that a subject can inhale above what they would normally inhale during a tidal breath. This requires maximum effort of the respiratory muscles.
Expiratory reserve volume
This is the volume of gas from the end of a tidal breath that can be expelled by the subject. Requires active work of respiratory muscles
Residual volume
This is the volume of gas retained in the lung even after a maximal exhalation
Functional residual capcity
This capacity represents the sum of the RV and ERV and represents the amount of gas in the lung at the end of a normal exhalation. It is also the point at which the respiratory system is in equilibrium
Inspiratory capacity
Inspiratory capacity. This is the sum of the tidal volume and Inspiratory reserve volume and represents the amount of gas that can be inhaled from Functional residual capcity. This requires maximum effort of the respiratory muscles to perform.
vital capacity
Sum of expiratory reserve volume + tidal volume + inspiratory reserve volume. is the amount of gas that can be inhaled from the end of a maximum expiration (starting at RV) to the maximum inflation.
Total lung capacity
. This represents the total of all 4 volumes of the lung. It is VC plus RV
what does spirometry measure
pulmonary function
Forced vital capacity
The FVC represents the total volume of gas (in liters) exhaled from total lung capacity down as far as possible. Should be the same as vital capacity.
Forced expiratory volume
The FEV1 denotes the volume of gas (in liters) exhaled in the first second from total lung capacity. Most people exhale 70-80% of the VC in the first second
FEV/FVC
This ratio compares the volume of gas expelled in the first second in relation to the total amount of gas exhaled. It normalizes lung mechanics for people with different lung volumes. Most people exhale 70 to 80% of air in the first second, making a normal ratio 0.7-0.8.
- Identify effort dependent and independent components to pulmonary function testing
effort dependent: expiratory reserve volume, inspiratory reserve volume, inspiratory capacity, vital capacity, total lung capcity. Effort independent: tidal volume (exhalation)
- Distinguish between obstructive and restrictive patterns on pulmonary function tests
Obstructive: reduced FEV/FVC ratio b/c it takes longer to expire. Restrictive: may have FEV1/FVC’s greater than 0.8 but airflows are not diagnostic of restrictive lung disease
flow volume loops in obstructiv and restrictive diseases
Obstructive: increased lung volumes (curve shifts to left), airflow is decreased with coving of expiratory flow loop. Restrictive: curve is shifted to right (lower total lung capacity), max airflow is decreased b/c total volume of gas in lungs Is decreased.
intrathoracic resistance
Within the thorax, the airway is held open during inspiration by negative pleural pressure. During forced expiration, however, positive pleural pressure surrounding the airway compresses it, reducing airway diameter. Consequently, intra-thoracic airway resistance is increased during expiration.
extrathoracic resistance
extra-thoracic airways (namely the trachea above the clavicles) are subjected to atmospheric pressure that is transduced through the tissues of the neck to the exterior walls of the trachea. Thus, negative intraluminal pressure is generated in extra-thoracic airways during inspiration resulting in airway narrowing. During expiration, the intraluminal pressure becomes positive, making the airway diameter larger.
Variable intrathoracic vs extrathoracic obstruction
Extrathoracic obstruction will be evident during inspiration (inspiration curve will be smaller), and intrathoracic obstruction will be evident during expiration (expiration curve will be smaller)
Fixed obstruction pressure volume loop
Curve is flattened in both inspiration and expiration due to circumferential lesions such as tracheal stenosis from prior intubation or a circumferential airway neoplasm.
Increased lung volumes are seen in what diseases? Decreased lung volumes are seen in what diseases?
increased lung volumes: obstructive diseases (air trapping b/c decreased ability to exhale). Decreased lung volumes: restrictive processes
How are lung volumes measured? Which one is more accurate
Helium dilution (C1V1=C2(V1+V2)) and Body Plethysmography (P1V1= P2V2). Helium dilution requires uniform diffusion of gas in lungs, so if obstructive disease it may be innacurate and underestimate FRC.
What is air trapping
residual volume is >140% but TLC and FRC are normal.
- Identify the 3 major factors contributing to DLCO
Diffusing capacity depends on surface area, membrane thickness, diffusion gradient of gas/presence of hemoglobin
Diffusing capacity depends on surface area, membrane thickness, diffusion gradient of gas/presence of hemoglobin
How is DLCO measured
single breath of CO, held for 10 seconds, then exhaled. The amount of CO absorbed into blood depends solely on diffusing capcity.
Causes of increased DLCO and decreased DLCO
increased (>120%):Things that increase blood in lung such as Polycythemia, Interstitial edema, Asthma and Alveolar hemorrhage. Decreased (120%):Things that increase blood in lung such as Polycythemia, Interstitial edema, Asthma and Alveolar hemorrhage. Decreased (<80%): emphysema, pulm vascular disease, interstitial lung disease, anemia, pulm edema or pneurmonia.
How do you measure respiratory muscle strength
Pimax measures maximum inspiratory pressure (inspiration against closed valve) and Pemax measures max expiratory pressure (expiration against occluded airway)
Causes of respiratory muscle weakness
neuropathies and myopathies (durgs, collagen vascular diseases, paraneoplastic syndromes)
compliance and elastance
compliance is a measure of how easily the lung inflates (∆V/ ∆P). A more compliant lung means that it takes less pressure to increase the volume in the lung. Elastance is the reciprocal of compliance. Increased elastance means that it takes more pressure to get the same change in lung volume.
- Understand how pressure – volume curves are performed and assist in the interpretation of abnormal pulmonary function tests (specifically in emphysema, asthma, obesity and fibrotic lung disease).
. Patient exhales slowly from TLC (at left) and flow is interrupted at several points and pressure at the mouth (equivalent to alveolar pressure) is measured with no flow (i.e. static pressure).
Pulmonary fibrosis pressure volume curve
Flat curve that is down shifted
emphysema pressure volume curve
Steep curve, left and up shifted
asthma pressure volume curve
Curve is similar in shape to normal, but slightly up shifted
obesity pressure volume curve
curve is similar in shape ot normal, but slightly down shifted
What is bronchoprovocation. What is a positive bronchodilator response
Bronchoprovocation tests stimulate bronchoconstriction. A significant response to bronchodilator is defined as >12% improvement in FEV1 or FVC and > 200cc increase in volume of FEV1 or FVC.
Methacholine challenge
The patient inhales progressively higher concentrations of nebulized methacholine (or histamine), which stimulates bronchoconstriction in both healthy and asthmatic subjects. In asthmatics, the concentration required to reduce airflow by 20% (PC20) is several orders of magnitude lower than in healthy subjects. No bronchodilator is used
Exercise induced bronchoprovocation
For people with exercise induced asthma, The patient performs spirometry before the test, and then exercises on a treadmill breathing cold air. Spirometry is performed at intervals post exercise to see if there is >20% decrease in FEV1.
