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?

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

1. Emphysema

2. Cystic fibrosis

3. Pneumonia

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?

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

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

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:

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

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

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.

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.

c. VC is decreased in restrictive disease and is normal or decreased in obstructive disease.

d. A normal value is 4800 mL.

Exam Note

A decreased VC may be the result of pneumonia, atelectasis, pulmonary edema, pulmonary fibrosis, kyphoscoliosis or lung cancer.

4. Forced vital capacity (FVC)

a. Is the maximum amount of air that can be exhaled as fast and forcefully as possible after a maximum inspiration.

b. Is measured by simple spirometry.

c. Is used to measure FEVs and flows.

d. FVC is decreased in both obstructive and restrictive disease.

5. Total lung capacity (TLC)

a. Is the amount of air remaining in the lungs at the end of a maximal inspiration.

b. Is calculated by a combination of other measured volumes (i.e., FRC + IC or VC + RV).

c. TLC is decreased in restrictive disease and increased in obstructive disease.

d. A normal value is 6000 mL.

Exam Note

TLC decreases as a result of atelectasis, pulmonary edema, and consolidation; TLC increases as a result of emphysema.

6. RV/TLC (ratio)

a. Is the percentage of the TLC that remains in the lungs after a maximal expiration.

b. Is measured by dividing the RV by TLC and multiplying by 100 to get a percentage.

c. RV/TLC is normal in restrictive disease and increased in obstructive disease.

d. A normal value is 20% to 35%.

II. LUNG STUDIES

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

A. Ventilation Studies

1. VT (discussed previously in the chapter)

2. Respiratory rate

a. Is the number of breaths in 1 min.

b. Is measured by counting chest excursion for 1 min.

c. Is increased in hypoxia and hypercarbia and is decreased with central respiratory center depression or depressing hypoxic drive in a COPD patient.

d. A normal value is 10/min to 20/min.

3. Minute volume (MV,

)

a. Is the total volume of air (in liters) inhaled or exhaled in 1 min. It is calculated by multiplying the respiratory rate times the VT.

b. Is measured by simple spirometry or at bedside with a respirometer.

Exam Note

When measuring at the bedside, use a respirometer with a mouthpiece. Instruct the patient to breathe normally through the mouthpiece as you time the breathing for 1 min. The reading on the respirometer after 1 min is the .

c. Is increased by hypoxia, hypercarbia, acidosis, or decreased lung compliance and decreased by hypocarbia, alkalosis, and increased lung compliance.

d. A normal value is 5 to 10 L/min.

B. Flow Studies

1. Forced expiratory volume (FEV_0.5, FEV₁, FEV₃)

a. Is the volume of air that is exhaled over a specific time interval during the FVC maneuver.

b. Is measured over 0.5, 1, or 3 s (shown as subscript to FEV). The FEV₁ is the most common measurement.

c. The severity of airway obstruction may be determined because it is a measurement at specified time intervals. FEV is usually decreased in both obstructive and restrictive disease.

Exam Note

FEV may be decreased in restrictive disease because the FVC is below normal and the measurement of FEV is from the patient’s predicted FVC, not his or her actual FVC. A better indicator of an obstructive or restrictive disorder is determined from the FEV/FVC ratio, which compares the FEV to the patient’s actual FVC (discussed next).

2. FEV/FVC (ratio)

a. Is a ratio (percentage) of the relationship of FEV to FVC.

b. Normal values are:

• 50% to 60% of the FVC is exhaled in 0.5 s

• 75% to 85% of the FVC is exhaled in 1 s

• 94% of the FVC is exhaled in 2 s

• 97% of the FVC is exhaled in 3 s

c. Obstructive disease is indicated by below normal values of FEV/FVC. Patients with restrictive disease have normal or above normal values.

d. Because the FEV₁ is most commonly measured, look for an FEV₁/FVC of less than 75% to indicate an obstructive disease.

3. FEF_200-1200

a. Is the average flow rate of the exhaled air after the first 200 mL and 1200 mL during an FVC maneuver.

b. Is measured on the spirograph tracing between the 200-mL mark and the 1200-mL mark to determine the average flow rate from the FVC.

c. Is decreased in obstructive disease.

d. A normal value is 6 to 7 L/s (400 L/min).

4. FEF_25%–75%

a. Is the average flow rate during the middle portion of the FEV.

b. The 25% and 75% points are marked on the spirographic curve from the FVC.

c. Values are decreased in obstructive disease.

d. A normal value is 4 to 5 L/s.

5. Peak flow

a. Is the maximum flow rate achieved during an FVC.

b. Is measured from an FVC or by a peak flowmeter.

Exam Note

When measuring with a peak flowmeter at the bedside, instruct the patient to take as deep a breath as possible and exhale quickly as hard and fast as possible through the mouthpiece. This test is often done before a bronchodilating agent is administered and again afterward to determine the agent’s effectiveness.

c. Is decreased in obstructive diseases

d. A normal value is 400 to 600 L/min (6.5 to 10 L/s).

6. Maximum voluntary ventilation (MVV)

a. Is the maximum volume of air moved into and out of the lungs voluntarily in 12 to 15 s.

b. This measurement tests for overall lung function, ventilatory reserve capacity, and air-trapping.

c. Is decreased in obstructive disease and decreased or normal in restrictive disease.

d. Normal value is 170 L/min.

7. Flow volume loop (curve)

a. A flow volume loop is displayed on a graph and represents the flow generated during an FEV maneuver followed by a forced inspiratory volume maneuver; both are plotted against volume change.

b. With the use of a flow volume loop, the following values may be measured

(1) Peak inspiratory flow (PIF)

(2) Peak expiratory flow (PEF)

(3) FVC

(4) FEV_0.5, FEV₁, FEV₃

(5) FEF_25%–75%

c. The three diagrams (Figure 16-2) show a comparison of flow volume loops representing normal, obstructive, and restrictive disorders.

FIGURE 16-2 Comparison of flow volume loops.

From Scanlan C, Spearman C, Sheldon R, Egan’s fundamentals of respiratory care, ed 5, St Louis, 1990, Mosby, and Wilkins RL, Stoller JK, Kacmarek R, Egan’s fundamentals of respiratory care, ed 9, St Louis, 2009, Mosby.

(1) The restriction pattern shows a decreased VC and normal expiratory flow rates.

(2) The obstructive pattern shows a decreased peak expiratory flow rate and a normal exhaled volume.

8. Diffusion capacity of the lung (DL)

a. Represents the gas exchange capabilities of the lungs.

b. This measurement evaluates how well gas diffuses across the alveolar–capillary membrane into the pulmonary capillaries.

c. The most common method for measuring DL is the single-breath method.

d. The patient is connected to a system in which the inspired gas contains a mixture of 10% helium and 0.3% CO. CO is used because of its increased affinity for Hb, which keeps the partial pressure of CO in the capillaries low, and because it diffuses rapidly across the alveolar–capillary membrane.

e. The patient is instructed to exhale completely to the RV level, place the mouthpiece in the mouth, inhale as deeply as possible, hold the breath for 10 s, and then exhale.

f. The DLCO (carbon monoxide diffusion capacity), or the measurement of the amount of CO diffusing from the alveoli to the pulmonary blood flow, is calculated with the use of the following formula

g. Normal diffusion capacity is approximately 25 to 30 mL/min/mm Hg.

h. Diffusion capacity is typically decreased because of either a decreased surface area available for diffusion or thickening of the membrane itself.

i. DLCO is decreased as a result of

9. V/Q scanning

a. This radiograph evaluates the relationship of the distribution of ventilation to pulmonary perfusion in the lungs.

b. For the determination of gas distribution, the patient inhales the radioactive isotope xenon and holds the breath for 10 to 20 s. Radiographs (photoscintigrams) are obtained to observe how the xenon was distributed in the lung.

c. For the determination of pulmonary perfusion, the patient is injected with a radioactive iodine preparation and photoscintigrams are taken as the blood perfuses the lungs.

III. OBSTRUCTIVE VERSUS RESTRICTIVE LUNG DISEASES

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

A. Obstructive Diseases: These diseases result in decreased flow studies (FEV₁, FEV/FVC, FEF_25%–75%, FEF_200-1200) and increased FRC, TLC, and RV values.

B. Restrictive Diseases or Disorders: These diseases result in decreased volumes (FRC, FVC, IC, IRV) and a normal FEV/FVC value.

1. Pulmonary fibrosis

2. Chest wall disease

3. Pneumonia

4. Neuromuscular disease

5. Pleural disease

6. Postsurgical situations

C. Severity of disease (by interpretation of pulmonary function tests)

1. Normal pulmonary function test results: 80% to 100% of predicted value

2. Mild disorder: 60% to 79% of predicted value

3. Moderate disorder: 40% to 59% of predicted value

4. Severe disorder: less than 40% of predicted value

D. Predicted values are determined from

IV. MISCELLANEOUS PULMONARY FUNCTION STUDIES

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

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

A. Before-and-After Bronchodilator Studies

1. Used to determine the reversibility of lung dysfunction and the effectiveness of the bronchodilator.

2. Patients, most commonly those with asthma, are instructed to perform a peak flow test before administration of a bronchodilating agent. The value is recorded. The administration of the agent is followed by another peak flow study.

3. Reversibility of obstructed airways and improved flow rates are considered significant if increases in flow studies are at least 12%.

B. Methacholine Challenge Test

1. Determines the degree of airway reactivity to methacholine, a drug that stimulates bronchoconstriction.

2. May be performed in a before-and-after bronchodilator study or before exercise-induced asthma studies.

3. The objective of the test is to determine the minimum level of methacholine that elicits a 20% decrease in FEV₁.

4. A physician should be present during testing, and bronchodilators and resuscitation equipment should be readily available.

C. Measurement of Maximal Inspiratory Pressure (MIP)

1. This measurement is also referred to as negative inspiratory force (NIF).

2. This value represents the maximum amount of negative pressure a patient can generate during inspiration.

3. This is measured with an aneroid manometer, which connects to an ET tube via an adapter. The patient is then instructed to inhale as deeply as possible. The manometer records the negative pressure.

4. An adapter attached to the manometer, with a one-way valve that allows for exhalation but not for inspiration, is also an effective method for obtaining an MIP value.

These two methods for determining MIP may cause agitation and anxiety in alert patients. The respiratory therapist should always explain the procedure to the patient before beginning it.

5. Obtain an MIP value in patients who are not intubated by connecting the manometer to a mouthpiece and placing nose clips on the patient.

6. A normal MIP is approximately −50 to −100 cm H₂O.

7. A patient who cannot generate at least −20 cm H₂O of pressure has inadequate respiratory muscle strength. The patient is not capable of generating the necessary negative inspiratory pressures required to cough and maintain a patent airway or to maintain spontaneous ventilation; therefore, mechanical ventilation is most likely indicated.

D. Maximal expiratory pressure (MEP)

1. An aneroid manometer is attached to the patient’s ET tube, and the patient is instructed to inhale as deeply as possible and exhale forcefully and completely.

2. The maximum pressure is observed and recorded.

3. Obtain an MEP value in patients who are not intubated by attaching the manometer to a mouthpiece and placing nose clips on the patient.

4. A normal MEP is 90 to 100 cm H₂O.

5. Patients unable to generate an MEP of at least 40 cm H₂O of pressure are not able to maintain adequate spontaneous ventilation or secretion clearance, which makes mechanical ventilation necessary.

V. INTERPRETATION OF CHART SUMMARY

CRT Exam Content Matrix: IA4, IB9s, IB10s, IIIE7a-c

RRT Exam Content Matrix: IA4, IB9t, IB10u, IIIE7a-c

	Disease
Function	Obstructive	Restrictive
FVC	Decreased	Decreased
IC	Decreased or normal	Decreased
ERV	Decreased or normal	Decreased
VT	Increased	Decreased or normal
FRC	Increased	Decreased
RV	Increased	Decreased
RV/TLC	Increased	Normal
FEV₁	Decreased	Normal or decreased
FEF₂₀₀_–₁₂₀₀	Decreased	Normal
FEF_25%_–_75%	Decreased	Normal
FEV/FVC	Decreased	Normal
MVV	Decreased	Decreased