Flow Volume Loops

What is a flow-volume loop?

An FVC maneuver followed by a forceful, rapid inhalation

What is the sequence of a flow-volume loop?

Maximal inhalation, forceful exhalation, then forceful inhalation

How does a flow-volume loop compare with a typical FVC volume-time graph?

It provides a more complete representation

What is measured on the vertical axis of a flow-volume loop?

Flow

What is measured on the horizontal axis?

Volume

Can previously discussed spirometry parameters be measured from a flow-volume loop?

Yes

What does the diagram on page 2 show at the top of the expiratory limb?

PEF

What expiratory flow measurements are shown on the loop diagram?

FEF25%, FEF50%, and FEF75%

What inspiratory flow measurements are shown on the loop diagram?

FIF25%, FIF75%, and FIF50%

What does the patient do first when performing a flow-volume loop?

Inspire maximally

How should the patient exhale after maximal inspiration?

Rapidly and forcefully to residual volume

What does the patient do after reaching residual volume?

Inspire forcefully to total lung capacity

Is the flow-volume loop effort dependent?

Yes

What can the shape of a flow-volume loop indicate?

The type of disease process

Where is the expiratory limb shown on the flow-volume loop?

As positive flow above the baseline

Where is the inspiratory limb shown?

As negative flow below the baseline

What portion of the expiratory limb is largely independent of patient effort?

From approximately 75% of FVC down to RV

What mainly controls flow beyond the FEF75% point?

Elastic recoil of the lung and resistance to flow

What happens to peak flow in an obstructive flow-volume loop?

It is reduced

What happens to the middle portion of the expiratory curve in obstruction?

It becomes scooped out

What classic expiratory-loop pattern is associated with COPD?

A scooped-out pattern

Which part of the COPD loop is especially described as scooped out?

The final portion of the expiratory limb

Why can chronic bronchitis produce a similar loop?

Because of mucus production

What happens to flows at different lung volumes in severe obstruction?

Expiratory flows are severely reduced at all lung volumes, and inspiratory flows are also markedly reduced

What does the severe-obstruction example show about expiration time?

There may be no obvious plateau even after 12 seconds of exhalation

What airway phenomenon is associated with higher tidal-breathing flows than maximal forced expiratory flows in severe obstruction?

Dynamic airway compression during forced exhalation

What shape is described for severe obstruction?

A steeple pattern

What happens to peak flow in severe obstruction?

It is reduced

What happens to the curve after peak flow in severe obstruction?

There is a rapid fall-off

What happens to vital capacity in restrictive disorders?

It decrease

What happens to PEFR in restrictive disease?

It may be normal or increased

Why may PEFR be normal or increased in restriction?

Because of enhanced elastic recoil

How does a restrictive flow-volume loop compare with a normal loop?

It is smaller and narrower

What happens to the general shape of the loop in restriction?

The shape remains normal

What happens to peak flow in the restrictive pattern shown?

It remains normal

What major change is seen in restrictive loops?

Reduced volume

According to the comparison on page 22, what happens to FVC in lung or chest-wall restriction?

FVC decreases

What happens to TLC and RV on the restrictive example?

They are displaced toward lower lung volumes

What does an obstructive volume-time pattern look like?

Slow rise, reduced expired volume, and prolonged time to full expiration

What does a restrictive volume-time pattern look like?

Fast rise to a plateau at a reduced maximum volume

How does the restrictive tracing compare with normal?

It mimics the normal shape, but the volume is reduced

What does a mixed pattern look like on the volume-time graph?

A slow rise to a reduced maximum volume

What testing is suggested to confirm a mixed pattern?

Static lung volumes and full PFTs

What type of tumors can flow-volume loops help diagnose?

Tumors of the larger airways

What determines how an obstruction affects the flow-volume loop?

The location of the obstruction

How can large-airway obstruction location be classified?

Intrathoracic or extrathoracic

How else can an airway obstruction be classified?

Variable or fixed

Which phases of breathing can help identify the obstruction location?

Inspiration and expiration

What happens to inspiratory flow in variable intrathoracic obstruction?

Inspiratory flow remains normal

What happens to expiratory flow in variable intrathoracic obstruction?

Expiratory flow is reduced

During which phase is an intrathoracic obstruction most apparent?

Expiration

What happens to the airway during inspiration in an intrathoracic obstruction?

Inspiration tends to pull the airway open

What happens to expiratory flow in variable extrathoracic obstruction?

Expiratory flow remains relatively normal

What happens to inspiratory flow?

Inspiratory flow is reduced

Why does the extrathoracic airway narrow during inspiration?

It is exposed to sub-ambient pressure, which can cause airway collapse

During which phase is variable extrathoracic obstruction most apparent?

Inspiration

What happens to both inspiratory and expiratory flow in a fixed obstruction?

Both are reduced

Why is a fixed obstruction called fixed?

It affects both breathing cycles and does not vary

What example of a fixed obstruction is given?

A large tracheal tumor blocking both inspiratory and expiratory flow

What characteristic shape is shown for fixed airway obstruction?

Flattening of both the inspiratory and expiratory portions of the loop

Which large-airway obstruction reduces expiratory flow but leaves inspiration near normal?

Variable intrathoracic obstruction

Which obstruction reduces inspiratory flow but leaves expiration relatively normal?

Variable extrathoracic obstruction

Which obstruction reduces both inspiration and expiration?

Fixed large-airway obstruction

What general expiratory shape is shown with asthma and emphysema?

A concave expiratory curve

What volume changes are associated with asthma and emphysema in the page 22 diagram?

TLC and RV are consistent with hyperinflation and/or air trapping

What should happen from maximal inspiration to PEF?

There should be a rapid rise

How long should maximal expiratory effort continue?

Until flow returns to the zero baseline

Is glottic closure acceptable during the maneuver?

No

Is an abrupt end of flow acceptable?

No

What must happen during the inspiratory portion for the loop to close?

The patient must make a maximal inspiratory effort and return to the point of maximal inspiration

What happens if the patient does not return to the original maximal inspiratory volume?

The loop will not close

How many acceptable loops must be recorded?

At least three

Which flow-volume loop should ultimately be reported?

The loop from the single best maneuver

How is the single best maneuver selected?

By the highest sum of FEV1 and FVC

What three common technical problems are listed for flow-volume loop testing?

Coughing, variable effort, and glottic closure

What does the variable-effort example show about FVC and FEV1?

The values vary markedly between efforts