Major components of pulmonary function testing
- lung volumes
- expiratory airflow
- gas exchange
Technique of lung volume measurement in pulmonary function testing
- measured by spirometer, helium dilution method or body plethysmography
- LV should = 80-120% of predicted total lung capacity
- If residual volume is elevated ==> air trapping
Technique of expiratory airflow measurement
- measured by spirometer
- expiration for at least 6 seconds w/curve plateau of at least 1 sec
Technique of gas exchange measurement
- measured by DLCO
- determined by surface area, membrane thickness, diffusion gradient, presence of hemoglobin
Characterisctics of volumes
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Volumes: can be measured or estimated
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On spirogram (right) upward deflection are inspiratory and downward deflections are expiratory
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Tidal volume (VT): volume of normal, even respirations at rest
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Expiratory reserve volume (ERV): Volume of gas remaining in the lung after a normal, tidal expiration that can be exhaled
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Inspiratory Reserve volume (IRV): Volume of gas that can be inhaled above that inhaled with a normal tidal inspiration
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Residual Volume (RV): Volume of gas remaining in the lung at the end of a maximum expiration
Volumes: can be measured or estimated
On spirogram (right) upward deflection are inspiratory and downward deflections are expiratory
Tidal volume (VT): volume of normal, even respirations at rest
Expiratory reserve volume (ERV): Volume of gas remaining in the lung after a normal, tidal expiration that can be exhaled
Inspiratory Reserve volume (IRV): Volume of gas that can be inhaled above that inhaled with a normal tidal inspiration
Residual Volume (RV): Volume of gas remaining in the lung at the end of a maximum expiration
Characteristics of capacities
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Capacities: sums of at least 2 volumes
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Functional residual capacity (FRV): Where the tendency for the chest to expand and the lungs to contract are at equilibrium. Volume of gas remaining in the lung at the end of a tidal expiration". Sum of ERV and RV.
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Inspiratory capacity (IC): Volume of gas that can be maximally inspired from FRC. Sum of VT and IRV
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Vital Capacity (VC): Volume of gas that can be maximally inspired from RV. Sum of ERV, VT, and IRV
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Total Lung Capacity (TLC): Total volume of gas in the lung. Sum of RV, ERV, TV, and IRV
Capacities: sums of at least 2 volumes
Functional residual capacity (FRV): Where the tendency for the chest to expand and the lungs to contract are at equilibrium. Volume of gas remaining in the lung at the end of a tidal expiration". Sum of ERV and RV.
Inspiratory capacity (IC): Volume of gas that can be maximally inspired from FRC. Sum of VT and IRV
Vital Capacity (VC): Volume of gas that can be maximally inspired from RV. Sum of ERV, VT, and IRV
Total Lung Capacity (TLC): Total volume of gas in the lung. Sum of RV, ERV, TV, and IRV
Determinants of FRC (aka TGV)
- "functional residual capacity" (aka "thoracic gas volume")
- Expiratory Reserve Volume + Residual Volume
Obstructive vs. Restrictive Pulmonary Function Test Results
- Obstructive: FEV1/FVC ratio tells if you have this or not, should be 0.7 - 0.8; < 0.7 is obstructive.
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Asthma
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COPD (emphysema, bronchitis)
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Bronchiolitis
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Restrictive: Can’t diagnose with spirometry - ratio can be preserved or elevated. Trouble with the chest wall expansion or elastic recoil
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Pulmonary edema
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ILD
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Neuromuscular weakness
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Pleural disease
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Obesity
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Asthma -
COPD (emphysema, bronchitis) -
Bronchiolitis
Restrictive: Can’t diagnose with spirometry - ratio can be preserved or elevated. Trouble with the chest wall expansion or elastic recoil
- Pulmonary edema
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ILD -
Neuromuscular weakness -
Pleural disease -
Obesity
Major factors contributing to DLCO
- 1. amount of hemoglobin
- 2. surface area
- 3. membrane thickness
DLCO definition
- diffusion capacity of carbon monoxide
- gas used to quantify gas exchange
- anything that alters the ability of gases to diffuse will alter this measurement
Factors that increase/decrease DLCO
- Increased DLCO:
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Polycythemia
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Interstitial edema
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asthma
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Alveolar hemorrhage
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Decreased DLCO:
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Emphysema
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Pulmonary vascular disease
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Interstitial lung disease
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anemia
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pulmonary edema
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pneumonia
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Polycythemia -
Interstitial edema -
asthma -
Alveolar hemorrhage
Decreased DLCO:
- Emphysema
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Pulmonary vascular disease -
Interstitial lung disease -
anemia -
pulmonary edema -
pneumonia
P-V curves in abnormal pulmonary function tests
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Relative to the normal curve:Recall that the emphysemic curve is on the left and up (more compliance).
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Asthma is slightly up and to the left, much less dramatic
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f
ibrotic lung disease curve is on the right and down (less compliance)
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decreased chest wall compliance curve (obesity) is slightly down and to the right.
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slopes of chest wall compliance and asthma curves is more or less the same as that of the normal curve, while the slopes of emphysema and fibrosis are steeper and flatter respectively.
Relative to the normal curve:Recall that the emphysemic curve is on the left and up (more compliance).
Asthma is slightly up and to the left, much less dramatic
f
ibrotic lung disease curve is on the right and down (less compliance)
decreased chest wall compliance curve (obesity) is slightly down and to the right.
slopes of chest wall compliance and asthma curves is more or less the same as that of the normal curve, while the slopes of emphysema and fibrosis are steeper and flatter respectively.
Major disease process PFT patterns
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Interstitial lung disease or fibrosis decreases diffusion capacity
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Water in lung increases diffusion distance and decreases surface area
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Pulmonary vascular disease decreases blood flow to lungs
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Intra or extra thoracic obstructions limit airflow
Interstitial lung disease or fibrosis decreases diffusion capacity
Water in lung increases diffusion distance and decreases surface area
Pulmonary vascular disease decreases blood flow to lungs
Intra or extra thoracic obstructions limit airflow
Bronchoprovocation characteristics
- used as a test in asthma <==usually diagnosed on spirometry ==> obstructive pattern w/relief w/bronchodilator
- sometimes require impetus for bronchoconstriction to help dx asthma
- example: metacholine challenge
Metacholine challenge characteristics
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metacholine challenge: pt inhales progressively higher concentrations of nebulized methacholine (or histamine), which stimulates bronchoconstriction
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In asthmatics, the concentration required to reduce airflow by 20% (PC20) is several orders of magnitude lower than in healthy subjects.
measurement of the PC20 can help diagnose asthma in patients with normal spirometry and no response to bronchodilator
metacholine challenge: pt inhales progressively higher concentrations of nebulized methacholine (or histamine), which stimulates bronchoconstriction
In asthmatics, the concentration required to reduce airflow by 20% (PC20) is several orders of magnitude lower than in healthy subjects.
measurement of the PC20 can help diagnose asthma in patients with normal spirometry and no response to bronchodilator
