Pulmonary function test

Introduction
Pulmonary function tests is a generic term used to indicate a battery of studies or maneuvers
that may be performed using standardized equipment to measure lung function.

 Evaluate one or more aspects of the respiratory system

 Respiratory mechanics
 Lung parenchymal function/ Gas exchange
 Cardiopulmonary interaction

ASPECTS OF PULMONARY FUNCTION:

Perfusion- Blood flow.

Diffusion- Movement of O2 & CO2.
Ventilation- Air exchange between alveolar spaces & the atmosphere.

SIGNIFICANCE
1. Investigation of patients with symptoms/signs/ investigations that suggest pulmonary
disease e.g. • (Cough/Wheeze/Breathlessness/Crackles)
2. Monitoring patients with known pulmonary disease for progression and response to
treatment e.g. • Interstitial fibrosis • COPD • Asthma • Pulmonary vascular disease
3. investigation of patients with disease that may have a respiratory complications e.g.
• Connective tissue disorders
• Neuromuscular diseases
4. Preoperative evaluation prior to e.g.
• Lung resection
• Abdominal surgery
• Cardiothoracic surgery
5. Evaluation patients a risk of lung diseases e.g.
• Exposure to pulmonary toxins such a radiation/ medication/environmental/occupational
exposure
6. Surveillance following lung transplantation to assess for
• Acute rejection
• Infection
• Obliterative bronchiolitis

CONTRAINDICATIONS
 Myocardial infarction within the last month
 Unstable angina
 Recent thoraco-abdominal surgery
 Recent ophthalmic surgery
 Thoracic or abdominal aneurysm
 Current pneumothorax

LUNG VOLUME
Four Lung volumes:
• Tidal volume (500-750ml)
• Inspiratory reserve volume(2500-3000ml)
• Expiratory reserve volume(1000-1500ml)
• Residual volume( 1300-1500ml)

LUNG CAPACITIES
Five capacities:
• Inspiratory capacity ( TV + IRV )
• Expiratory capacity ( TV + ERV )
• Vital capacity ( IRV + TV + ERV )
• Functional residual capacity ( RV + ERV )
• Total lung capacity(IRV+TV+ERV+RV)

TESTS
 Bed side pulmonary function tests
 Spirometry
 N2 Washout Technique
 Helium Dilution technique
 Body Plethysmography
 Cardiopulmonary interaction

BED SIDE PULMONARY FUNCTION TESTS

1. SABRASEZ BREATH HOLDING TEST

>25 SEC.-NORMAL Cardiopulmonary Reserve 15-25 SEC- LIMITED CPR

<15 SEC- VERYPOOR CPR (Contraindication for elective surgery)

25-30 SEC - 3500 ml VC

20 -25 SEC - 3000 ml VC
15 -20 SEC - 2500 ml VC
10 -15 SEC - 2000 ml VC
5-10 SEC - 1500 ml VC

2. SCHNEIDER MATCH BLOWING TEST

MBC < 60 L/min FEV1 < 1.6L Able to blow out a match
MBC > 60 L/min FEV1 > 1.6L
Modified match test: DISTANCE MBC
9” >150 L/MIN.
 6” >60 L/MIN.
3” > 40 L/MIN

3. COUGH TEST
Deep breath followed by cough
Inadequate cough if: FVC<20 ml/kg FEV1 < 15 ml/kg PEFR < 200 l/min.
VC ~ 3 times TV for effective cough.

4. FORCED EXPIRATORY TIME

Normal FET – 3-5 SECS.
Obstructive Lung Disease. - > 6 SEC
Restrictive Lung Disease.- < 3 SEC

5.SINGLE BREATH COUNT

After deep breath, hold it and start counting till the next breath.
N- 30-40 COUNT
Indicates vital capacity

6.WRIGHT PEAK FLOW METER:

Measures PEFR (Peak Expiratory Flow Rate)
N – MALES- 450-700 L/MIN.
FEMALES- 350-500 L/MIN.

7.DE-BONO WHISTLE BLOWING TEST: MEASURES PEFR.

Patient blows down a wide bore tube at the end of which is a whistle, on the side is a hole
with adjustable knob. As subject blows → whistle blows, leak hole is gradually increased till
the intensity of whistle disappears. At the last position at which the whistle can be blown , the
PEFR can be read off the scale.

8.WRIGHT RESPIROMETER:
 measures TV,MV Instrument- compact, light and portable.
 Can be connected to endotracheal tube or face mask MV- instrument record for 1 min.
 And read directly TV-calculated and dividing MV by counting Respiratory Rate.

Disadvantage: It under- reads at low flow rates and over- reads at high flow rates.

PREREQUESITE

 Do not smoke for at least 1 hour before the test.

 Do not drink alcohol for at least 4 hours before the test.
 Do not exercise heavily for at least 30 minutes before the test.
 Do not wear tight clothing that makes it difficult for you to take a deep breath.
 Do not eat a large meal within 2 hours before the test.

DISADVANTAGE

Only for single use due to CO2 accumulation & O2 cannot be supplied.

• Residual Volume, Functional Residual Capacity and Total Lung Capacity cannot be
measured.

N2 WASHOUT TECHNIQUE

 The patient breathes 100% oxygen, and all the nitrogen in the lungs is washed out.
 The exhaled volume and the nitrogen concentration in that volume are measured.
 The difference in nitrogen volume at the initial concentration and at the final exhaled
concentration allows a calculation of intrathoracic volume, usually FRC.

HELIUM DILUTION TECHNIQUE

Pt breathes in and out from a reservoir with known volume of gas containing trace of helium.
Helium gets diluted by gas previously present in lungs. eg: if 50 ml Helium introduced and
the helium concentration is 1% , then volume of the lung is 5L.

BODY PLETHYSMOGRAPHY
Plethysmography (derived from greek word meaning enlargement). Based on principle of
BOYLE’S LAW(P*V=k) A patient is placed in a sitting position in a closed body box with a
known volume The patient pants with an open glottis against a closed shutter to produce
changes in the box pressure proportionate to the volume of air in the chest. As measurements
done at end of expiration, it yields FRC

CARDIOPULMONARY INTERACTION
 Star climbing test
 Shuttle walk test
 6min walk test
 Cardiopulmonary exercise test
Shuttle walk test:-
 Walk test is based on 20m shuttle walk test
 Measures maximum distance walked by the patient at a pace set by audio signals
 Requires patients to walk at increasing speads up and down a 10m course 
 Speed walking is increased every minute by 0.17m/s

6 min walk test:-

 The tester will measure your blood pressure, pulse and oxygen level usually with a pulse
oximeter before you start to walk.
 You should be given the following instructions: The object of the test is to walk as far as
possible for six minutes. You will walk at your normal pace to a chair or cone, and turn
around. And you continue to walk back and forth for six minutes.
 Let the staff know if you are having chest pain or breathing difficulty.
 It is acceptable to slow down, rest or stop. After every minute interval, you will be given
an update.

Nursing Responsibilities

Before the Procedure

 Your physician will explain the procedure to you and offer you the opportunity to ask any
questions that you might have about the procedure.

 Generally, no prior preparation, such as fasting, fluid restriction, or sedation is required.

However, you may be asked to avoid eating a heavy meal before the test.

 If you are pregnant or suspect that you may be pregnant, you should notify your
physician.

 Notify your physician of all medications (prescription and over-the-counter) and herbal
supplements that you are taking.

 If you are a smoker, you will usually be asked to refrain from smoking for a period
of time before the test.

 Your height and weight will be recorded so that your results can be accurately calculated.
 Based upon your medical condition, your physician may request other specific
preparation.

During the Procedure

Pulmonary Function test may be done on an outpatient basis or as part of your stay in the hospital. Procedures
may be vary depending on your condition and your physicians practices

Generally, PFTs follow this process:

1.You will be asked to loosen tight clothing, jewelry, or other objects that may interfere with the
procedure
2. If you wear dentures, you will be asked to wear them during the procedure.
3.You will be asked to empty your bladder before the procedure to optimize comfort.
4. You will sit in a chair or stand for the procedure
5. You will be given a soft nose clip to wear during the procedure so that all of your breaths will go through
your mouth, rather than your nose.
6. You will be given a sterile mouthpiece that will be attached to the spirometer.
7. With your mouth forming a tight seal around the mouthpiece, you will be instructed to perform various
breathing maneuvers. The maneuvers will be done by inhaling and exhaling. Depending on what
measurements are ordered, you may be asked to repeat the maneuvers several times before the test is
completed
8. You may be given a bronchodilator after certain tests have been performed. These tests will be repeated
several minutes later after the bronchodilator has taken effect
9. You will be monitored carefully during the procedure for faintness, dizziness, difficulty breathing, or any
other problems.

After the Procedure

1. Generally, there is no special type of care following PFTs. You may resume your usual diet
medications, and activities unless your physician advises you otherwise.

2. If you have a history of respiratory problems, you may be tired after the procedure. You
will begiven the opportunity to rest afterwards.

3. Your physician may give you additional or alternate instructions after the procedure depending
upon your particular situation.