What does a flow volume loop tell you?
) displays airflow (in L/second) as it relates to lung volume (in L) during maximal inspiration from complete exhalation (residual volume [RV]) and during maximum expiration from complete inhalation (TLC).
What is expiratory flow volume curve?
The maximal expiratory flow-volume (MEFV) curve depicts the inter-relationship between flow and volume during a maximal expiration. In young healthy subjects, the MEFV curve is highly reproducible within an individual, but shows between-subject variability (Green et al., 1974).
What determines maximum expiratory flow?
Because maximal airflow depends on elastic recoil and the resistance of the airways peripheral (“upstream”) to the equal pressure point, the resistance of the small airways is a larger component of the upstream resistance at small lung volumes and therefore is a greater determinant of maximal expiratory flow at lower …
What is intrathoracic and extrathoracic?
Intrathoracic obstruction is most severe during expiration and is relieved during inspiration. Extrathoracic obstruction is increased during inspiration because of the effect of atmospheric pressure to compress the trachea below the site of obstruction.
Is flow volume loop part of spirometry?
Typically, a flow-volume loop needs to be requested specifically, as an order for “spirometry” frequently yields just the expiratory portion. (See “Overview of pulmonary function testing in adults”, section on ‘Flow-volume loop’.)
How are flow curves used to diagnose obstruction?
Flow-volume curves may be especially helpful in identifying tracheal or other upper airway lesions as a cause of obstruction. 31 Central airway obstruction (i.e., proximal to the tracheal carina) that is located within the thorax produces a plateau during forced exhalation instead of the usual rise to and descent from peak flow ( Fig. 25-8 ).
What causes decreased airflow in the thorax?
Lesions located in the trachea within the thorax cause decreased airflow particularly during exhalation; during inhalation, the posterior tracheal membrane is pulled out by negative intrathoracic pressure, so increased effort increases airflow rates and the inspiratory limb of the flow-volume curve can appear normal.
How to estimate the diameter of a stenotic lesion?
It is possible to estimate the diameter of a stenotic lesion by analysis of the flow-volume curve with an accuracy of ±1 mm ( eFig. 25-1 ), but the length of the flow-limiting segment must be confirmed by computed tomography (CT) scan to plan surgical correction, if required.
Which is the peak expiratory flow volume curve?
E-FIGURE 85-3. Flow-volume curve. A, The maximal expired flow-volume curve in a normal subject. The peak expiratory flow (PEF) and forced expiratory flows at 50% and 75% of the exhaled vital capacity (FEF 50 and FEF 75) are indicated.