PULMONARY FUNCTION TESTING

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CHAPTER 16 PULMONARY FUNCTION TESTING

PRETEST QUESTIONS

Answer the pretest questions before studying the chapter. This will help you determine your strong and weak areas in the material covered.

1. What is the minimum percent increase in inspiratory flow following a before-and-after bronchodilator study that indicates significant improvement?

A. 5%
B. 10%
C. 15%
D. 25%

2. In which of the following lung conditions would the FRC be increased?

1. Emphysema
2. Cystic fibrosis
3. Pneumonia
A. 1 only
B. 1 and 2 only
C. 1 and 3 only
D. 2 and 3 only

3. Which of the following pulmonary function tests would best determine the patient’s ability to cough?

A. VT
B. Alveolar minute ventilation
C. FRC
D. MIP

4. To evaluate the distribution of ventilation to perfusion with a V/Q scan, instruct the patient to inhale which of the following substances?

A. Helium
B. CO
C. Xenon
D. Argon

5. Following are the results of a patient’s spirometry test before and after bronchodilator therapy.

  Before After
FEV1 32% of predicted 53% of predicted
FVC 38% of predicted 66% of predicted
FEV1/FVC 50% 64%

Which of the following is the correct interpretation of these results?

A. Mild restrictive disease with significant bronchodilator response
B. Severe obstructive disease with significant bronchodilator response
C. Severe restrictive disease with no significant bronchodilator response
D. Severe obstructive disease with no significant bronchodilator response

See answers and rationales at the back of the text.

REVIEW

I. LUNG VOLUMES AND CAPACITIES

CRT Exam Content Matrix: IA4, IA7b-c, IB9d-e,m,s, IB10d-e,s, IC5, IIC4, IIIE7a-f

RRT Exam Content Matrix: IA4, IA7b-c, IB9d-e,m,t, IB10d-e,u, IC6, IIC4, IIIE7a-f

image

FIGURE 16-1

A. Lung Volumes
1. Tidal volume (VT)
a. The volume of air (usually in milliliters) that is inhaled or exhaled during a normal breath
b. The exhaled VT is usually measured with a respirometer at the bedside or by spirometry.

image Exam Note

When VT is measured at the bedside, it is most accurately achieved by the patient being instructed to breathe normally through a mouthpiece connected to a respirometer for 1 full min. The volume reading is then divided by the patient’s respiratory rate over that 1 min to obtain the VT. Nose clips may be used to ensure mouth breathing only.

c. VT is decreased or normal in restrictive disease and increased or normal in obstructive disease.
d. A normal value is 500 mL (or 3 mL/lb of body weight)
2. Inspiratory reserve volume (IRV)
a. Is the maximum volume of air that can be inspired after a normal inspiration.
b. Is normally not measured during simple spirometry, but if it is, it should be measured from a slow vital capacity.
c. IRV could be normal in both obstructive and restrictive disease; therefore its measurement is not clinically significant.
d. A normal value is 3000 mL.
3. Expiratory reserve volume (ERV)
a. Is the volume of air exhaled after a normal expiration.
b. ERV is measured directly by spirometry from a slow VC (i.e., VC − inspiratory capacity).
c. ERV may be normal or decreased in obstructive or restrictive disease.
d. A normal value is 1000 mL and 20% to 25% of the VC.
4. Residual volume (RV)
a. Is the volume of air left in the lungs after a maximal expiration.
b. It is derived after FRC is calculated, with the use of either the nitrogen washout test or helium dilution test (see FRC section in this chapter).
c. Once FRC is calculated, subtract the ERV from FRC; this equals the residual volume (i.e., RV = FRC − ERV)
d. RV is increased in obstructive disease and decreased in restrictive disease.
e. A normal value is 1500 mL.

B. Lung Capacities
1. Functional residual capacity (FRC)
a. Is the amount of air left in the lungs after a normal expiration (i.e., ERV + RV).
b. Is measured by the helium dilution or nitrogen washout test or by body plethysmography.
c. Measurement of FRC by helium dilution test
(1) Also called the closed-circuit method
(2) A spirometer is normally filled with about 600 mL of gas with about 10% helium added to the volume. The volume of the gas and the concentration of helium is measured and recorded before the test.
(3) The patient is instructed to breathe normally and, at the end of a normal exhalation, is connected to the system.
(4) The patient rebreathes the gas in the spirometer while carbon dioxide is removed by a CO2 absorbent.
(5) Helium is then diluted until equilibrium is reached. This normally takes about 7 min, but in patients with severe lung disease, it may take as long as 30 min for equilibrium to occur. Equilibrium occurs as the helium analyzer falls to a stable level.
(6) The final concentration of helium is then recorded.
d. Calculations for FRC


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image Exam Note

A helium analyzer reads zero when calibrated to room air.

e. Measurement of FRC with the use of the nitrogen washout test
(1) Also called the open-circuit method
(2) During this test, the patient breathes in 100% oxygen to wash out the nitrogen in the lungs. The nitrogen concentration in the lungs is approximately 79%.
(3) The patient is instructed to breathe normally, and at the end of a normal exhalation, the patient is connected to the 100% oxygen breathing system.
(4) During the procedure, the exhaled volume is monitored and recorded and nitrogen percentages are measured.
(5) Complete nitrogen washout occurs in about 7 min.
f. FRC may now be calculated with the use of the following formula:

image

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g. Measurement of FRC with the use of body plethysmography
(1) The plethysmograph (“body box”) is an airtight chamber in which the patient sits during the procedure.
(2) While being tested, the patient is instructed to seal his or her lips tightly around the mouthpiece and to breathe normally. (The patient may also be tested while being instructed to breathe in shallow, panting breaths.)
(3) As the patient breathes, a pressure transducer measures pressure at the airway as well as inside the chamber.
(4) An electrical shutter is used to periodically close the airway, causing the patient to breathe against a closed airway, at which time volume and pressure values are measured.
(5) The technique of plethysmography is based on Boyle’s law, which states that the volume of gas is inversely proportional to the pressure to which it is subjected.
h. FRC can then be calculated with the use of the following formula

image

i. Body plethysmography also measures thoracic gas volume (VTG), total lung capacity (TLC), and residual volume (RV).

image Because body plethysmography actually measures the total amount of gas in the thorax, FRC measurements may be higher than those measured by the helium dilution or nitrogen washout method.

j. FRC is increased in obstructive disease and decreased in restrictive disease.
k. A normal value is 2500 mL.
2. Inspiratory capacity (IC)
a. Is the maximum amount of air that can be inspired after a normal expiration (i.e., VT + IRV).
b. Is measured by simple spirometry from a VC.
c. Usually is decreased or normal in obstructive or restrictive disease.
d. A normal value is 3500 mL (75% to 85% of the VC).
3. Vital capacity (VC)
a. Is the maximum amount of air that can be exhaled after a maximum inspiration (i.e., VT + IRV + ERV).
b. Is measured by simple spirometry or at the bedside with the use of a respirometer.

image Exam Note

At the bedside, use a mouthpiece connected to a respirometer. Instruct the patient to inhale as deeply as possible and then, slowly, completely exhale through the mouthpiece.

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