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12 Cards in this Set
- Front
- Back
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What are the types of measurements in PFT?
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Lung volumes-measure maximum volume of lungs as well as sub-compartments; spirometer is common tool
Flow rates-measure the maximal flow of gas out of and into the lung Diffusing capacity-measures transfer of gas from alveolar space into capillary bloodstream Maximal inspiratory/expiratory pressures-measure applied strength of respiratory muscles |
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Volume of air inspired and expired during normal quiet breathing
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tidal volume (TV)
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The maximum amount of air that can be inhaled after a normal tidal volume inspiration
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Inspiratory Reserve Volume (IRV)
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Maximum amount of air that can be exhaled from the resting expiratory level
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Expiratory Reserve Volume (ERV)
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Volume of air remaining in the lungs at the end of maximum expiration
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residual volume (RV)
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Volume of air that can be exhaled from the lungs after a maximum inspiration
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vital capacity (VC)
IRV + TV + ERV FVC: when VC exhaled forcefully SVC: when VC is exhaled slowly |
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Maximum amount of air that can be inhaled from the end of a tidal volume
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inspiratory capacity (IC)
IRV + TV |
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Volume of air remaining in the lungs at the end of a TV expiration
The elastic force of the chest wall is exactly balanced by the elastic force of the lungs |
Functional Residual Capacity (FRC)
ERV + RV |
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Volume of air in the lungs after a maximum inspiration
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total lung capacity (TLC)
IRV + TV + ERV + RV |
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Describe other ways to measure functional residual capacity (FRC)
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Helium dilution-Helium is insoluble gas; amount of helium is same before and after equilibrium
Body Plethymograph-At the end of normal expiration, subject is asked to take a deep breath into a body plethymograph box; pressure and volume changes are measured |
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Describe Fick's Law
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Fick's Law: Vgas=(A/T) * D * (P1-P2)
amount of gas transferred is proportional to the area (A), a diffusion constant (D), and the difference in partial pressure (P1-P2); is inversely proportional to the thickness (T) The constant (D) is proportional to the gas solubility (Sol) but inversely proportional to the square root of its molecular weight (MW) |
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Describe diffusing capacity
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diffusing capacity (Dl)=flow (Vgas)/change in pressure (P1-P2)
CO is a good molecule to use to measure diffusing capacity-because CO binds so tightly to hemoglobin, partial pressure in capillaries is considered zero |
