Patient Care,

Departments & Programs,UW Hospital and Clinics,Pulmonary Diagnostic Lab

Spirometry Values

Spirometry Values - Departments & Programs, UW Hospital and Clinics, Pulmonary Diagnostic Lab


Where they come from/basic calculations

Since computerized devices are generally very reliable, persons performing spirometry rarely have a need to hand calculate a spirometry tracing, however a basic understanding of where the data comes from will surely make you a better clinician.

The Flow Volume Curve


Flow volume curve (normal)

FVC liters (Forced vital capacity)
PEF (Peak exp flow) highly effort dependant
FEF 25 (Forced exp flow at 25% of the curve)
FEF 50
FEF 75
FIVC in (Forced inspiratory vital capacity)
PIF 50 (Peak inspiratory flow)
PIFR (Peak inspiratory flow rate)

Great curve provides instantly useful information.

Helps to differentiate normal-obstructive or possible restrictive defect. Also allows assessment of patient effort and inspiratory flow characteristics.

Pulmonary parameters

FEV1 l/s 2.9 L/S
FVC liters 4 L
FEV1/FVC (Ratio) : simple division
FET: Forced expiratory time (how long they exhaled, quality indicator)
FEV6: Forced expiratory volume in 6 seconds
FEF25-75 can be calculated from this curve

The volume / time curve is valuable to assess effort-- using FET, expiratory plateau, and evidence of back extrapolation error.

Persons familiar with this graphic can pick out obstruction.

Spirometry steps:

  1. Maximal inspiration
  2. Blast the air out
  3. Continue exhalation for 6 seconds or ( 3 seconds if < 10 years old) or until expiratory plateau (no change in volume

Adequate test requires

Minimum of 3 acceptable FVC maneuvers
Acceptable repeatability: Largest FVC and next largest FVC is 0.150 L or less and the difference between the largest and next largest FEV1 is 0.150 L or less.
After 8 spirometry attempts-further attempts are not required.

Spirometry: Acceptable Maneuver Criteria

Assuming correct instruction and coaching, the subject should provide a maximal inspiration, with a good start, with a smooth continuous exhalation, with maximal effort and must meet the following conditions:

  1. Without a unsatisfactory start of expiration, no hesitation or false start
  2. Without coughing during the first second of the maneuver.
  3. Without early termination of expiration
  4. Without a Valsalva maneuver
  5. Without a leak
  6. Without an obstructed mouthpiece
  7. Without evidence of an extra breath being taken during the maneuver.

Exhalation time

If 10 or less years old = 3 seconds minimum
Older that 10 years = 6 seconds minimum

Repeatability Criteria

After 3 acceptable spirograms have been obtained, apply the following tests:

  1. The two largest FVCs must be within 0.150 L of each other
  2. The two largest FEV1s must be within 0.150 L of each other

If both of these criteria have been met, the testing session may be concluded.
If both of these criteria are not met, continue testing unitl:

  1. Both of the criteria are met with analysis of additional acceptable spirograms OR
  2. A total of eight tests have been performed (optional)
  3. The patient /subject cannot or should not continue
    Save, as a minimum, the 3 satisfactory maneuvers