Pulmonary Function Tests

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Alternative Names: PFTs; Spirometry; Spirogram; Lung function tests
Definition:Pulmonary function tests are a group of tests that measure how well the lungs take in and release air and how well they move oxygen into the blood. These tests can tell your doctor what quantity of air you breathe with each breath, how efficiently you move air in and out of your lungs.
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Pulmonary Function Testing has been a major step forward in assessing the functional status of the lungs as it relates to :

1.How much air volume can be moved in and out of the lungs
2.How fast the air in the lungs can be moved in and out
3.How stiff are the lungs and chest wall – a question about compliance
4.The diffusion characteristics of the membrane through which the gas moves (determined by special tests)
5.How the lungs respond to chest physical therapy procedures

Pulmonary Function Tests are used for the following reasons :

1.Screening for the presence of obstructive and restrictive diseases

2.Evaluating the patient prior to surgery – this is especially true of patients who :
a. are older than 60-65 years of age
b. are known to have pulmonary disease
c. are obese (as in pathologically obese)
d. have a history of smoking, cough or wheezing
e. will be under anesthesia for a lengthy period of time
f. are undergoing an abdominal or a thoracic operation

Note
: A vital capacity is an important preoperative assessment tool. Significant reductions in vital capacity (less than 20 cc/Kg of ideal body weight) indicates that the patient is at a higher risk for postoperative respiratory complications. This is because vital capacity reflects the patient’s ability to take a deep breath, to cough, and to clear the airways of excess secretions.

3.Evaluating the patient’s condition for weaning from a ventilator. If the patient on a ventilator can demonstrate a vital capacity (VC) of 10 – 15 ml/Kg of body weight, it is generally thought that there is enough ventilatory reserve to permit (try) weaning and extubation.

4.Documenting the progression of pulmonary disease – restrictive or obstructive

5.Documenting the effectiveness of therapeutic intervention

How do you prepare for the test?
Do not eat a heavy meal before the test. Do not smoke for 4 – 6 hours before the test. You’ll get specific instructions if you need to stop using bronchodilators or inhaler medications. You may have to breathe in medication before the test.

No other preparation is necessary.

How the Test Will Feel ?
Since the test involves some forced breathing and rapid breathing, you may have some temporary shortness of breath or light-headedness. You breathe through a tight-fitting mouthpiece, and you’ll have nose clips.

What happens when the test is performed?
This testing is done in a special laboratory. During the test, you are instructed to breathe in and out through a tube that is connected to various machines.

A test called spirometry measures how forcefully you are able to inhale and exhale when you are trying to take as large a breath as possible. The lab technicians encourage you to give this test your best effort, because you can make the test result abnormal just by not trying hard.

A separate test to measure your lung volume (size) is done in one of two ways. One way is to have you inhale a small carefully measured amount of a specific gas (such as helium) that is not absorbed into your bloodstream. This gas mixes with the air in your lungs before you breathe it out again. The air and helium that you breathe out is tested to see how much the helium was diluted by the air in your lungs, and a calculation can reveal how much air your lungs were holding in the first place.

The other way to measure lung volume is with a test called plethysmography. In this test, you sit inside an airtight cubicle that looks like a phone booth, and you breathe in and out through a pipe in the wall. The air pressure inside the box changes with your breathing because your chest expands and contracts while you breathe. This pressure change can be measured and used to calculate the amount of air you are breathing.

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Your lungs’ efficiency at delivering oxygen and other gases to your bloodstream is known as your diffusion capacity. To measure this, you breathe in a small quantity of carbon monoxide (too small a quantity to do you any harm), and the amount you breathe out is measured. Your ability to absorb carbon monoxide into the blood is representative of your ability to absorb other gases, such as oxygen.

Some patients have variations of these tests-for example, with inhaler medicines given partway through a test to see if the results improve, or with a test being done during exercise. Some patients also have their oxygen level measured in the pulmonary function lab (see “Oxygen saturation test,” page 29).

Why the Test is Performed  ?

Pulmonary function tests are done to:
*Diagnose certain types of lung disease (especially asthma, bronchitis, and emphysema)
*Find the cause of shortness of breath
*Measure whether exposure to contaminants at work affects lung function
It also can be done to:

*Assess the effect of medication
*Measure progress in disease treatment
*Spirometry measures airflow. By measuring how much air you exhale, and how quickly, spirometry can evaluate a broad range of lung diseases.

Lung volume measures the amount of air in the lungs without forcibly blowing out. Some lung diseases (such as emphysema and chronic bronchitis) can make the lungs contain too much air. Other lung diseases (such as fibrosis of the lungs and asbestosis) make the lungs scarred and smaller so that they contain too little air.

Testing the diffusion capacity (also called the DLCO) allows the doctor to estimate how well the lungs move oxygen from the air into the bloodstream.

Risk Factors:
The risk is minimal for most people. There is a small risk of collapsed lung in people with a certain type of lung disease. The test should not be given to a person who has experienced a recent heart attack, or who has certain other types of heart disease.

Must you do anything special after the test is over?
Nothing.

Normal Results:
Normal values are based upon your age, height, ethnicity, and sex. Normal results are expressed as a percentage. A value is usually considered abnormal if it is less than 80% of your predicted value.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What Abnormal Results Mean:
Abnormal results usually mean that you may have some chest or lung disease.

Considerations:
Your cooperation while performing the test is crucial in order to get accurate results. A poor seal around the mouthpiece of the spirometer can give poor results that can’t be interpreted. Do not smoke before the test.

How long is it before the result of the test is known?
Your doctor will receive a copy of your test results within a few days and can review them with you then.

Resources:
https://www.health.harvard.edu/diagnostic-tests/pulmonary-function-testing.htm
http://www2.nau.edu/~daa/lecture/pft.htm
http://www.nlm.nih.gov/medlineplus/ency/article/003853.htm

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