Pulmonary function test (PFT) - PowerPoint Presentation

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Pulmonary function test (PFT)

PFTs

are tests for physiological assessment of pulmonary gas exchange through processes of ventilation, diffusion, and lung perfusion.

1-Ventilation

tests through measuring lung volume (VC), airways patency (FEV1), and alveolar

ventilation.

2-Diffusion test through measuring lung efficacy for gas

exchange by quantifying respiratory and blood gases.

3-Perfusion

test through measuring pulmonary blood flow.

Benefits of PFTs:

1. Diagnose causes and severity of dyspnea (breathlessness). 2. Follow up disease progression and effectiveness

of

treatment

.

3

. Assess respiratory status before and during

anesthesia

and surgery

.

4

. Assess physical fitness and effects of training.

5

. Determine the incidence of respiratory dysfunction

.

6. Medico-legal information in occupational hazard.

Types of Pulmonary Function Tests (PFTs)

I. Clinical (bedside) tests: 1. Chest expansion measured with a tape placed around the chest just below the nipples. Normally chest expands by 5–10 cm after deep inspiration preceded by forceful expiration.

2. Breath holding time: maximum time one can hold his breathing after inhalation.

3. Respiratory endurance test (40 mmHg test): disconnect the rubber tube from the mercury reservoir to the sphygmomanometer cuff. Ask the subject to take a deep breath, pinch his nostrils, and exhale into the tube to raise the mercury to 40 mm Hg and to hold it there for as long as possible.

Normal duration > 40 – 70 seconds.

4

. Expiratory blast test: ask the subject to take deep breath to raise the mercury column as high level as possible. Normally one can raise the mercury > 55–100 mm during single forceful exhalation. 5. Snider’s test: hold burning match stick 12 inches in front of subject’s face and ask him to blow it out with single forceful expiration.

II. Tests of ventilation:

1. VC and FEV1. 2. Peak expiratory flow rate (PEFR). 3. Minute ventilation (MV). 4. Functional residual capacity (FRC) measured by nitrogen washout Method. 5. Ventilation Scan.

III. Tests of gas diffusion:

A- Arterial blood gases and pH.B-Respiratory gases. IV. Tests for lung perfusion: Lung scan and catheterization.

V. Special Techniques

1. Plain chest X-ray.

2. Computerized tomography (CT scan). 3. Magnetic resonance imaging (MRI).

4.

Bronchoscopy

.

5. Computerized

spirometer

.

Peak expiratory flow rate (PEFR)

It measures maximum expiration speed to monitor airflow obstruction in large airways. It is used to follow up asthmatic response to therapy and control of the disease.

Spirometry

It measures airflow and functional lung volumes through assessing how much one inhale and exhale and how quick exhalation occurs. Ask the subject to blow as fast and as long as possible until no more breath can be exhaled into mouthpiece attached to spirometer to record the rate and volume of airflow. Values obtained:

1. FEV

1

: forced expiratory volume in the first second.

2. FVC (forced vital capacity): the total lung volume from maximum inspiration to maximum expiration.

Results are plotted in graph called

vitalograph

or

spirogram

.

Tidal volume (VT):

breathing involves inspiration and expiration = 500 mLInspiratory reserve volume (IRV): Maximal inspiration followed by maximal expiration = 3000 mL

Expiratory reserve volume (ERV):

volume exhaled with maximal expiration = 1200

mL

Residual volume (RV):

volume remains in the lungs after a maximal forced expiration = 1200

mL

Lung volumes and capacities can be made by

spirometry

except residual volume which can’t be measured by

spirometry

.