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Flow-Volume loop showing successful FVC maneuver. Positive values represent expiration, negative values represent inspiration. At the start of the test both flow and volume are equal to zero (representing the volume in the spirometer rather than the lung). The trace moves clockwise for expiration followed by inspiration.
Forced expiratory volume (time): a generic term indicating the volume of air exhaled under forced conditions in the first t seconds: FEV 1: Volume that has been exhaled at the end of the first second of forced expiration: FEF x: Forced expiratory flow related to some portion of the FVC curve; modifiers refer to amount of FVC already exhaled ...
The minimum and maximum volumes (V max and V min) from each loop in the series of loops are plotted on a graph. V max and V min lines are extrapolated and at their point of intersection, where V max is equal to V min, must be zero—conductance is parallel conductance only. The volume at this point is the correction volume.
A pressure–volume diagram (or PV diagram, or volume–pressure loop) [1] is used to describe corresponding changes in volume and pressure in a system. They are commonly used in thermodynamics , cardiovascular physiology , and respiratory physiology .
Pulmonary compliance is calculated using the following equation, where ΔV is the change in volume, and ΔP is the change in pleural pressure: = For example, if a patient inhales 500 mL of air from a spirometer with an intrapleural pressure before inspiration of −5 cm H 2 O and −10 cm H 2 O at the end of inspiration.
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There is a flaw in the first image explaining the flow-volume loop: it appears as if FEV1 (the yellow zone) is atteined in the first 10% of the FV loop. Clearly this is not the case (if it were, the FEV1/FVC ratio would be only 10%...). The yellow zone should comprise around 80% of the expiratory FVC loop.
The amount of He in the spirometer is known at the beginning of the test (concentration × volume = amount). The patient is then asked to breathe (normal breaths) in the mixture starting from FRC (functional residual capacity), which is the gas volume in the lung after a normal breath out. The spirometer measures helium concentration.
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