06 Oct - PFT

Office Spirometry

Recommended for anyone over 45

Indication:

Cough, SOB, Cyanosis, Crackles, abnormal chest x-ray, wheezing, smokers, screening, pre-op risk, monitory lung function and medication

·  Total lung capacity (TLC), about six liters, is all the air the lungs can hold.

·  Vital capacity (VC) is the amount of air that can be inhaled after a full breath out.

·  Tidal volume (TV) is the amount of air breathed in or out during normal respiration. It is normally about 500 ml.

·  Residual volume (RV) is the amount of air left in the lungs after a maximal breath out. This averages about 1.5 L.

·  Expiratory reserve volume (ERV) is the amount of additional air that can be breathed out after normal expiration. This is about 1.5 L.

·  Inspiratory reserve volume similarly, is the additional air that can be inhaled after a normal tidal breath in. About 2.5 more liters can be inhaled.

·  Functional residual capacity is the amount of air left in the lungs after a tidal breath out.

·  Inspiratory capacity (IC) is the volume that can be inhaled after a tidal breath out.

FVC - Forced Vital Capacity - after the patient has taken in the deepest possible breath, this is the volume of air which can be forcibly and maximally exhaled out of the lungs until no more can be expired.

FEV1 - Forced Expiratory Volume in One Second - this is the volume of air which can be forcibly exhaled from the lungs in the first second of a forced expiratory maneuver

Indices (Units) / Obstruction / Restriction / Normal
FVC (lts) / ↓ / ↓ / 100 ± 20%
FEV1(lts) / ↓ / ↓ / 100 ± 20%
FEV1/FVC%(Ratio) / ↓ / Normal / > 80%
FEF 25-75% ml/Sec / ↓ / ↓ / 100 ± 35%

Acceptable test –

No cough or problems

No hesitation

At least 6 seconds of exhalation

(Do at least twice)

Restrictive Dx (make lungs stiff)–

Asbestosis

Cystic Fibrosis

Spirometry

Spirometry is the most commonly performed lung function test and is regarded as an essential component in the medical evaluation of patients with respiratory symptoms and signs. Although spirometry is widely performed, there have been some obstacles in its interpretation and hence it’s perceived lack of usefulness. Part of the difficulty and confusion has been contributed by the:

1. Wide variety of spirometers

2. Poor standardization and quality of tests

3. Poor understanding of the interpretation of tests results

Procedure

a. Patient preparation:

i. No bronchodilator within 6 hrs

ii. No recent viral infection within 2 weeks

iii. No acute illness

iv. No heavy meal within I hr.

b. Patient’s weight, height (or arm span) measured to derive reference values.

Quality of test (see Figure 1)

a. No coughing

b. Good start of test (no hesitancy) [Extrapolated volume < 5% FVC or 0.1 L

c. No early termination (>6 sec exhalation or >2 see plateau)

d. No variable flows

e. Consistency (Two largest FVC and FEV1 within 5% or 100ml whichever greater)

Note:

i. Repeated max effort may induce bronchospasm resulting in progressive decrease readings. This could be an indicator of poor health.

ii. Not more than 8 attempts recommended.

iii. All volumes to be expressed at BTPS (body temperature, pressure and saturation)

Interpretation

In the report, only the largest FEV1 and FVC from three best attempts are selected even if they are from different curves. (see Figure 2 and 3)

Flow volumes are obtained from the curve with highest sum of FEV1 and FVC.

FEV1 and FVC > 80% predicted is normal (> 5th percentile) [acceptable range 75 125% predicted]

FEV1 /FVC ratio ³ 80% [acceptable range >75%]

FEF2575%, FEF25%, FEF50%, FEF75% >50% predicted is acceptable.

Figure 1. Examples of Poor Spirometric Performance /
Figure 2
Graphical Data Display in Spirometry /
Figure 3
Graphical Data Interpretation Spirometry /

Spirometry results are expressed as a percentage, and are considered abnormal if less than 80 percent of the normal predicted value

FVC

Indicative of reduced lung size, restrictive lung disease (e.g. interstitial lung disease, neuromuscular disease, chest wall disorder) or severe airflow limitation where the patient cannot continue to exhale long enough to complete emptying or airways collapse.

Restrictive disease characterized by reduction in TLC. This can be inferred when VC reduced and FEVI /FVC ratio is normal or increased.

If there is any contradiction between VC and TLC, restriction should be based on TLC.

FEV1

Indicative of airflow limitation or a severe restrictive process.

The earliest change associated with flow limitation is in small airways (slowing in the terminal portion of spirogram, FEF75% or FEF2575%).

In moderate obstruction there is involvement of larger airways FEF25% and FVC.

In severe obstruction all flows <3040%, FEVI /FVC ratio <50%.

FEV1 65 percent to 79 percent predicted = Mild obstruction

FEV1 40 percent to 59 percent predicted = Moderate obstruction

FEV1 less than 40 percent predicted = Severe obstruction

FEV1 /FVC ratio

Decreased in obstructive disease.

Normal or increased in restrictive disease.

Ratio not useful in assessment of bronchodilator response because FVC will also increase with improved flows.

Mixed obstructive and restrictive disease cannot be confirmed on spirometry alone. Lung volumes assessment is needed.

Long exhale increase (over 6 seconds) – airflow obstruction