Pulmonary Function


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Table of Contents

Pulmonary Function

Purpose of Pulmonary Function Testing

How much air volume can be moved in and out of the lungs - how large the lungs are for this patient.

How fast the air in the lungs can be moved in and out - a question about how open the lungs are moment to moment.

How stiff are the lungs and chest wall - a question about lung compliance

The diffusion characteristics of the alveolar membrane through which gases must move (determined by special tests).

How the lungs respond to chest physical therapy procedures - it will be important to have an admissions PFT and a discharge PFT performed.

Uses for PFTs

Uses cont’d

Uses cont’d

Uses cont’d

Uses cont’d


Has to be calibrated using a 3-Liter syringe along with temperature and barometric pressure information at the testing site.

Performance of the PFT

When three PFTs are within < 5% variance between the tests, then the testing is over.

What Are Normal Values ?

Factors to take into consideration when developing a nomogram are such things as :

Important Lung Volumes and Capacities

FVC is a major marker for obstructive lung disease.

Forced Expiratory Volume in One Second (FEV1)

FEV1 is a major marker for obstructive disease.

FEV1/FVC - FEV1 Percent (FEV1%)

FEV1% is a very important number in determining the presence of restrictive or obstructive disease. If FEV1% is 88% - 100%, it indicates the presence of restrictive disease. If this number is 69% or lower, then the presence of obstructive disease must be expected.

FEV3 - This is the amount of air that can be blown out of the lungs on exhalation in three seconds. In most people, FEV3 maybe very close to the actual value of FVC.

PEFR - Peak Expiratory Flow Rate This is the maximum flow rate achieved by the patient during the forced vital capacity maneuver. It can either be measured in L/sec or L/min

PEFR is a useful measure to see if a bronchodilatory treatment is improving obstruction as seen in asthma where there is lots of bronchoconstriction.

Forced Expiratory Flow 25% - 75% This measurement describes the amount of air expelled from the lungs during the middle half of the forced vital capacity test.

Many physicians like to look at FEF25%-75% because it is an indicator of obstructive disease.

Restrictive Diseases

Obstructive Diseases

How Do I Determine The Extent Of Lung Disease ?

Normal PFT Outcomes - > 85 % of predicted values

Reversible Lung Disease

What is Acceptible Change ?

How Do I Read A PFT ?

Step 3. If both FVC and FEV1 are normal, then you do not have to go any further - the patient has a normal PFT test.

Step 4. If FVC and/or FEV1 are low, then the presence of disease is highly likely.

Step 5. If Step 4 indicates that there is disease then you need to go to the %predicted for FEV1/FVC.

If the %predicted for FEV1/FVC is 88%-90% or higher, then the patient has a restricted lung disease. If the %predicted for FEV1/FVC is 69% or lower, then the patient has an obstructed lung disease.

Example # 1

Example # 2

Example # 3

Author: Microsoft Corporation

Email: David.Arnall@NAU.EDU , DAArnall@AOL.COM

Home Page: http://jan.ucc.nau.edu/~daa/heartlung/

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