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Chapter 12

Lung (Pulmonary) Function Tests

First professional examination SAQs1. Name the lung function tests

2. What is diffusing capacity?

LUNG FUNCTION TESTS

1. To test the efficiency of ventilation-a. Vital capacity (Vc)

Normal. Male: 3.2 to 4.6 liter.Female: 2.9 to 4.2 liter.

b. Forced expiratory volume (FEV). This measures the amount of air aperson can exhale with force in one breath. The amount of air exhaled may

be measured at 1 second (FEV1), 2 seconds (FEV2), or 3 seconds (FEV3).Normal FEV1 (vital capacity in first second) is: 80% in first second.

c. FEV1/FVC ratio (FEV1%): FEV1/FVC (FEV1%) is the ratio of FEV1 to FVC. Inhealthy adults this should be approximately 7580%.

d. Peak expiratory flow rate (PEFR)Normal: 6 to 15 L/sec.

e. Maximum voluntary ventilation (MVV). This measures the greatestamount of air one can breathe in and out during one minute. Normal: 125-

170 L/min

f. Slow vital capacity (SVC). This measures the amount of air a person canslowly exhale after a person inhale as deeply as possible.

g. Total lung capacity (TLC). This measures the amount of air in a personslungs after a person inhale as deeply as possible.

h. Functional residual capacity (FRC). This measures the amount of air in apersons lungs at the end of a normal exhaled breath.

i. Expiratory reserve volume (ERV). This measures the difference betweenthe amount of air in a persons lungs after a normal exhale (FRC) and the

amount after a person exhale with force (RV).

2. To test the efficiency of gaseous exchange at alveolar level: by-Diffusion capacity (Transfer factor)

Normal: about 25ml/mmHg/min.3. To test the efficiency of the regulation of

respiration (Respiratory centre)4. Measurement of lung compliance.

Normal: about 0.22 L/cm of H2O

5. Measurement of maximal O2 uptake.Normal: about 250ml/min.

6. Ventilation-perfusion ratio test.Normal: about 0.84.

7. Arterial blood gas analysis.

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FORCE EXPIRATORY VOLUME IN L SEC. (FEV1):Vital capacity in timed that means the percentage of vital capacity that is expired in

1 sec. is determined. Normally FEV1 is 83% to 84% in 1 sec; volume of air expired atone second is called forced expiratory volume at one second (FEV1).

Figure: FEV1

Importance:

If FEV1 is found less than 80% in first second then there is obstruction some where inthe air passage such as in asthma.

DIFFUSION CAPACITY

Diffusion capacity is a measurement of the lung's ability to transfer gases. The "diffusing capacity" or "diffusion capacity" is part of a comprehensive test

series of lung function called pulmonary function testing. In Europe, this is often

called the "transfer factor".

Transfer of oxygen and carbon dioxide over the alveolocapillary membrane is the

main function of the lungs and can be measured by the diffusing capacity.

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LUNG FUNCTION TESTS RELATING TO DIFFERENT CLINICAL CONDITIONSIN LUNGS

LFT Pulmonary Disorder

Obstructive disease Restrictive disease Neuromuscular

disease

FEV1

Vital capacity (VC) or

Functional residual

capacity (FRC)

Residual volume(RV)

Total lung capacity(TLC)

or

= Decreased, = Increased, = Normal

RESPIRATORY EXCHANGE RATIO

The ratio of carbondioxide output to oxygenuptake is called the respiratory

e.\change ratio (R). That is.Rate of carbon dioxide output

R = Rate of oxygen uptake

The value for R changes under different metabolic conditions. When a person is

using exclusively carbohydrates for body metabolism. R rises to 1.00. Conversely,

when the person is using exclusively fats for metabolic energy, the R level falls to aslow as 0.7.

WHAT DO YOU MEAN BY PHYSIOLOGIC SHUNTThe total quantitative amount of shunted blood per minute is called physiologic

shunt. The greater the amount of physiologic shunt the greater the amount of bloodfails to be oxygenated as it passes through the lungs.

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