# Focus

**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**

(normal)

**Parameters:**

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.

**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:

- Maximal inspiration
- Blast the air out
- 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:

- Without a unsatisfactory start of expiration, no hesitation or false start
- Without coughing during the first second of the maneuver.
- Without early termination of expiration
- Without a Valsalva maneuver
- Without a leak
- Without an obstructed mouthpiece
- 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:

- The two largest FVCs must be within 0.150 L of each other
- 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:

- Both of the criteria are met with analysis of additional acceptable spirograms OR
- A total of eight tests have been performed (optional)

OR - The patient /subject cannot or should not continue

Save, as a minimum, the 3 satisfactory maneuvers