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S E C T I O N I I

Clinical Data Obtained from Laboratory Tests and Special Procedures—Objective Findings

OUTLINE

Chapter 4 Pulmonary Function Testing

Chapter 5 Blood Gas Assessment

Chapter 6 Assessment of Oxygenation

Chapter 7 Assessment of the Cardiovascular System

Chapter 8 Radiologic Examination of the Chest

Chapter 9 Other Important Tests and Procedures

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C H A P T E R 4

Pulmonary Function Testing

CHAPTER OUTLINE

Normal Lung Volumes and Capacities

Restrictive Lung Disorders: Lung Volume and Capacity Findings

Indirect Measurements of the Residual Volume and Lung Capacities Containing the Residual Volume

Forced Expiratory Flow Rate and Volume Measurements

Forced Vital Capacity

Forced Expiratory Volume Timed

Forced Expiratory Volume in 1 Second/Forced Vital Capacity (FEV1/FVC) Ratio

Forced Expiratory Flow 25% to 75%

Forced Expiratory Flow Between 200 and 1200 mL of Forced Vital Capacity Peak Expiratory Flow Rate

Maximum Voluntary Ventilation Flow-Volume Loop

Pulmonary Diffusion Capacity

Assessment of Respiratory Muscle Strength Cardiopulmonary Exercise Testing

Other Diagnostic Tests for Asthma

Impulse Oscillometry

Self-Assessment Questions

CHAPTER OBJECTIVES

After reading this chapter, you will be able to:

•Describe the following lung volumes and capacities:

•List the normal lung volumes and capacities of normal recumbent subjects who are 20 to 30 years of age.

•Describe the residual volume/total lung capacity ratio (RV/TLC ratio).

•Identify lung volumes and lung capacity findings characteristic of restrictive lung disorders.

•List the anatomic alterations of the lungs associated with restrictive lung disorders.

•Identify forced expiratory volume in 1 second/forced vital capacity ratio lung volumes and capacity findings characteristic of obstructive lung disorders.

•List the anatomic alterations of the lungs associated with obstructive lung disorders.

•Describe the indirect measurements of the residual volume and lung capacities contained in the total lung capacity (TLC).

•Describe expiratory flow rate and volume measurements and their respective normal values.

•Describe how the FVC, FEV1, and FEV1/FVC ratio (FEV1%) are used to differentiate restrictive and obstructive lung disorders.

•Identify forced expiratory flow rate findings characteristic of restrictive lung disorders.

•Identify forced expiratory flow rate findings characteristic of obstructive lung disorders.

•Describe the pulmonary diffusion capacity (DLCO).

•Identify DLCO findings characteristic of restrictive lung disorders.

•Identify DLCO findings characteristic of obstructive lung disorders.

•Describe the following tests used to assess the patient's muscle strength at the bedside:

•Maximum inspiratory pressure (MIP)

•Negative inspiratory force

•Maximum expiratory pressure (MEP)

•Forced vital capacity (FVC)

•Maximum volume ventilation

•Describe the role of cardiopulmonary exercise testing (CPET) in the evaluation of pulmonary function.

•Identify other diagnostic tests used to measure airway responsiveness in patients with asthma.

•Define key terms and complete self-assessment questions at the end of the chapter and on Evolve.

KEY TERMS

Air Trapping

Anaerobic Threshold (AT)

Body Plethysmography

Cardiopulmonary Exercise Testing (CPET) Closed-Circuit Helium Dilution Test Exercise or Cold Air Challenge Expiratory Reserve Volume (ERV) Flow-Volume Loop

Forced Expiratory Flow 200 to 1200 mL of FVC (FEF200–1200) Forced Expiratory Flow 25% to 75% (FEF25%–75%)

Forced Expiratory Flow at 50% (FEF50%) Forced Expiratory Volume in 1 Second (FEV1)

Forced Expiratory Volume in 1 Second/Forced Vital Capacity Ratio (FEV1/FVC ratio) Forced Expiratory Volume in 1 Second Percentage (FEV1%)

Forced Expiratory Volume Timed (FEVT) Forced Inspiratory Volume (FIV) Forced Vital Capacity (FVC)

Functional Residual Capacity (FRC) Impulse Oscillometry (IOS) Inhaled Mannitol

Inhaled Methacholine or Histamine Inspiratory Capacity (IC) Inspiratory Reserve Volume (IRV) Lung Capacities

Lung Volumes

Maximum Expiratory Pressure (MEP)

Maximum Inspiratory Pressure (MIP)

Maximum Voluntary Ventilation (MVV) Obstructive Lung Disorders Open-Circuit Nitrogen Washout Test Peak Expiratory Flow Rate (PEFR)

Pulmonary Diffusion Capacity of Carbon Monoxide (DLCO) Reactance (Xrs)

Residual Volume (RV)

Residual Volume/Total Lung Capacity Ratio (RV/TLC) Resistance (Rrs)

Respiratory impedance (Zrs) Restrictive Lung Disorders Tidal Volume (VT)

Total Expiratory Time (TET)

Total Lung Capacity (TLC)

Vital Capacity (VC)

Pulmonary function studies play a major role in the assessment of pulmonary disease. The results of pulmonary function studies are used to (1) evaluate pulmonary causes of dyspnea, (2) differentiate between obstructive and restrictive pulmonary disorders, (3) assess severity of the pathophysiologic impairment, (4) follow the course of a particular disease,

(5) evaluate the effectiveness of therapy, and (6) assess the patient's preoperative status. Pulmonary function studies are commonly subdivided into the following categories: (1) lung volumes and lung capacities, (2) forced expiratory flow rate and volume measurements, (3) pulmonary diffusion capacity measurements, (4) test of respiratory muscle strength, and (5) cardiopulmonary exercise testing.

Pulmonary function tests and studies range from the simple and inexpensive to the complex and expensive. The more complex tests are reserved for use in patients with hard-to-diagnose dyspnea when physical examination, chest imaging studies, and simple pulmonary function studies have not been definitive. A general hierarchy of the increasing expense and complexity of pulmonary function tests is given in Table 4.1.

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TABLE 4.1

General Hierarchy of Expense and Complexity of Pulmonary Function Tests

Cost	Pulmonary Function Test
$	Peak expiratory flow rate determinations
$$	Expiratory only (simple) spirometry*
$$$	Conventional spirometry*
$$$$	Flow-volume loop analysis
$$$$	Complete lung volume studies (open-circuit and closed-circuit)
$$$$	Pulmonary diffusion capacity studies
$$$$	Peak inspiratory and expiratory pressure determinations
$$$$$	Pulmonary mechanics (body plethysmography)
$$$$$	Studies of pulmonary compliance (esophageal balloon)
$$$$$$	Cardiopulmonary exercise tests†

*With and without bronchodilator.

†With and without arterial blood gas analysis.

Normal Lung Volumes and Capacities

As shown in Table 4.2, gas in the lungs is divided into four lung volumes and four lung capacities. The lung capacities represent different combinations of lung volumes. The amount of air the lungs can accommodate varies with age, weight, height, gender, and, to a much lesser extent, race. Prediction formulas for normal values exist that take these variables into account. Lung volumes and capacities change as a result of pulmonary disorders. These changes are classified as either restrictive lung disorders or obstructive lung disorders.

TABLE 4.2

Lung Volumes and Capacities of Normal Recumbent Subjects 20 to 30 Years of Age

Measurements	Male (mL)	Female (mL)
Lung Volume Measurements
Tidal volume (VT): The volume of gas that normally moves into and out of the lungs in	500	400–500
one quiet breath.
Inspiratory reserve volume (IRV): The volume of air that can be forcefully inspired	3100	1900
after a normal tidal volume.
Expiratory reserve volume (ERV): The volume of air that can be forcefully exhaled	1200	800
after a normal tidal volume exhalation.
Residual volume (RV): The amount of air remaining in the lungs after a forced	1200	1000
exhalation.
Lung Capacity Measurements
Vital capacity (VC): VC = IRV + VT + ERV. The volume of air that can be exhaled after a	4800	3200
maximal inspiration.
Inspiratory capacity (IC): IC = VT + IRV. The volume of air that can be inhaled after a	3600	2400
normal exhalation.
Functional residual capacity (FRC): FRC = ERV + RV. The lung volume at rest after a	2400	1800
normal tidal volume exhalation.
Total lung capacity (TLC): TLC = IC + ERV + RV. The maximal amount of air that the	6000	4200
lungs can accommodate.
Residual volume/total lung capacity ratio (RV/TLC × 100): The percentage of TLC
occupied by the RV.

Restrictive Lung Disorders: Lung Volume and Capacity Findings

Table 4.3 provides some of the more common restrictive anatomic alterations of the lungs and examples of respiratory disorders that cause them. Restrictive lung disorders result in an increased lung rigidity, which in turn decreases lung compliance. When lung compliance decreases, the ventilatory rate increases and the tidal volume (VT) decreases (see

Fig. 3.4). Table 4.4 presents an overview of the lung volume and capacity findings characteristic of restrictive lung disorders. Restrictive lung volumes and capacities are associated with pathologic conditions that alter the anatomic structures of the lungs distal to the terminal bronchioles (i.e., the alveoli or the lung parenchyma).

TABLE 4.3

Anatomic Alterations of the Lungs Associated With Restrictive Lung Disorders: Pathology of the Alveoli or Lung Parenchyma

Pathology (Anatomic Alteration of the	Examples of Respiratory Disorders Associated With Specific
Alveoli)	Pathology
Atelectasis	Pneumothorax, pleural effusion, flail chest, or mucous plugging
Consolidation	Pneumonia, acute respiratory distress syndrome, lung abscess,
	tuberculosis
Increased alveolar-capillary membrane	Pulmonary edema, pneumoconiosis, tuberculosis, fungal disease
thickness

TABLE 4.4

Restrictive Lung Disorders: Lung Volume and Capacity Findings

VT	IRV	ERV	RV
N or ↓	↓	↓	↓
VC	IC	FRC	TLC	RV/TLC
↓	↓	↓	↓	N

ERV, Expiratory reserve volume; FRC, functional residual capacity; IC, inspiratory capacity; IRV, inspiratory reserve volume; N, normal; RV, residual volume; TLC, total lung capacity; VC, vital capacity; VT, tidal volume.

Obstructive Lung Disorders: Lung Volume and Capacity Findings

Table 4.5 provides an overview of the lung volumes and capacity findings characteristic of obstructive lung disorders. These lung volume and capacity findings are associated with pathologic conditions that alter the tracheobronchial tree. Table 4.6 provides some of the more common obstructive anatomic alterations of the lungs and examples of respiratory disorders that cause them.

TABLE 4.5

Obstructive Lung Disorders: Lung Volume and Capacity Findings

VT	IRV	ERV	RV
N or ↑	N or ↓	N or ↓	↑
VC	IC	FRC	TLC	RV/TLC ratio
↓	N or ↓	↑	N or ↑	N or ↑

ERV, Expiratory reserve volume; FRC, functional residual capacity; IC, inspiratory capacity; IRV, inspiratory reserve volume; N, normal; RV, residual volume; TLC, total lung capacity; VC, vital capacity; VT, tidal volume. Note FVC is often reduced (see Fig. 4.5).

TABLE 4.6

Anatomic Alterations of the Lungs Associated With Obstructive Lung Disorders: Pathology of the Tracheobronchial Tree

Pathology (Anatomic Alteration of the Bronchial	Examples of Respiratory Disorders Associated With Specific
Airways)	Pathology
Excessive mucous production and accumulation	Chronic bronchitis, asthma, respiratory syncytial virus
Bronchospasm	Asthma
Distal airway weakening	Emphysema

In obstructive lung disorders, the gas that enters the alveoli during inspiration (when the bronchial airways are naturally wider) is prevented from leaving the alveoli during expiration (when the bronchial airways narrow). As a result, the alveoli become overdistended with gas, a condition known as air trapping. Fig. 4.1 provides a visual comparison of obstructive and restrictive lung disorders.

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FIGURE 4.1 Visual comparison of lung volumes and capacities in obstructive and restrictive lung disorders. (From Kacmarek, R. M., Stoller, J. K., & Albert, H. J. [2017]. Egan's fundamentals of respiratory care [11th ed.]. St. Louis, MO: Elsevier.)

Indirect Measurements of the Residual Volume and Lung Capacities Containing the Residual Volume

Because the residual volume (RV) cannot be exhaled, the RV and the lung capacities that contain the RV—the functional residual capacity (FRC) and total lung capacity (TLC)—can be measured indirectly by one of the following methods: the closed-circuit helium dilution test, the open-circuit nitrogen washout test, or body plethysmography. A brief explanation of each of these tests follows.

For the closed-circuit helium dilution test, the patient rebreathes both a known volume of gas (V1) and a known concentration (C1) of helium (He) for about 7 minutes (Fig. 4.2). The concentration of He is normally 10%. During the test,

the patient is “switched in” to a closed-circuit system at the end of a normal tidal volume breath or at the top of the FRC (see Fig. 4.1). A helium analyzer continuously monitors the helium concentration, and the exhaled carbon dioxide is chemically removed from the system. The gas in the patient's FRC, which at the beginning of the test contained no helium, mixes with the gas in the closed-circuit system. This causes the helium to spread throughout the entire closed-circuit system—the patient's lungs, spirometer, and circuit. When the helium concentration changes by 0.2%, or less, over a 1- second period, the test is completed. The helium concentration at this point is C2. The final volume of the entire system—

the helium circuit and lungs (V2)—now can be calculated by using the following equation:

FIGURE 4.2 Helium dilution method for measuring functional residual capacity, residual volume, and total lung capacity. (From Kacmarek, R. M., Stoller, J. K., & Albert, H. J. [2017]. Egan's fundamentals of respiratory care [11th ed.]. St. Louis, MO: Elsevier.)

which can be rearranged to solve for V2 as follows:

The FRC can be calculated by subtracting the initial spirometer volume (V1) from the equilibrium volume (V2) as follows: FRC = V2 − V1. The RV can be calculated by subtracting the ERV from the FRC: FRC − ERV. The TLC can be determined by

adding the VC to the RV—RV + VC.

For the open-circuit nitrogen washout test, the patient inhales and exhales 100% oxygen through a one-way valve for about 7 minutes (Fig. 4.3). At the start of the test, the concentration of nitrogen (N2) in the alveoli is 79% (C1). After a few

moments into the test, the patient is switched in to the system at the end of a normal tidal volume—or, at the top of the FRC (see Fig. 4.1). At this point, the patient inhales 100% oxygen and exhales nitrogen-rich gas from the FRC. Over the next several minutes, the nitrogen in the patient's FRC progressively washes out. During the washout period, the exhaled gas volume is measured and the average nitrogen concentration is measured with a nitrogen analyzer. The test is terminated when the nitrogen concentration drops to 1.5% or less, at which time a forced expiration is performed and the FAN2 alveolar 2 is recorded. Based on the initial nitrogen concentration and the final nitrogen concentration, the volume of

air in the patient's lungs at the start of the test—that is, the FRC—can be calculated as follows:

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FIGURE 4.3 Open-circuit equipment used for N2 washout determination of functional residual capacity (FRC). The patient inspires O2 from a regulated source and exhales past a rapidly responding N2 analyzer into a pneumotachometer. FRC is calculated from the total volume of N2 exhaled and the change in alveolar N2 from the beginning to the end of the test. (From Mottram, C. D. [2018]. Ruppel's manual of pulmonary function testing [11th ed.]. St. Louis, MO: Elsevier.)

where:

FEN2 final = Fraction of N2 in volume expired.

FAN2 alveolar 1 = Fraction of N2 in alveolar gas initially (0.79).

FAN2 alveolar 2 = Fraction of N2 in alveolar gas at end of the test (from the final alveolar–end expiratory) sample. N2 tissue = Volume of N2 washed out of blood and tissues. A correction must be made for the N2 washed out of the blood and tissue. It is estimated that for each minute of oxygen breathing, about 30 to 40 mL of N2 is removed

from the blood and tissue. This value is subtracted from the total volume of N2 washed out.

Body plethysmography measures the volume of gas in the lungs (thoracic gas volume [VTG]) indirectly by applying a modification of Boyle's law. The patient sits in an airtight chamber called a plethysmograph (body box; Fig. 4.4). During the first part of the test, the patient breathes quietly in and out through an open valve (shutter). Once the patient is relaxed, the patient is switched in to the system at the end of a normal tidal volume—that is, at the level at which only the FRC remains in the lungs. At this point, the shutter valve is closed and the patient is instructed to pant against the closed shutter. Pressure and volume changes are monitored during this time. The alveolar pressure changes created by the compression and decompression of the lungs are estimated at the patient's mouth. Because there is no air flow during this period, and because the temperature is kept constant, the pressure and volume changes can be used to calculate the trapped volume—the FRC—by applying Boyle's law. Body plethysmography is generally considered to be the most precise of the three methods for measuring the RV and FRC.

FIGURE 4.4 Body plethysmography method for measuring lung volumes. V is the change in gas volume in the lungs, as sensed by the chamber pressure manometer. P is the change in pressure produced by the respiratory effort of breathing against the shutter, as sensed by the airway pressure manometer. (From Kacmarek, R. M., Stoller, J. K., & Albert, H. J. [2017]. Egan's fundamentals of

respiratory care [11th ed.]. St. Louis, MO: Elsevier.)

Body plethysmography also can measure airway resistance (Raw) and airway conductance (1/Raw). Patient claustrophobia in the plethysmograph sometimes limits the application of this valuable test.

Forced Expiratory Flow Rate and Volume Measurements

In addition to the volumes and capacities that can be measured by pulmonary function testing, the flow rate and volume at which gas flows out of the lungs also can be measured. Such measurements provide data on the patency of the airways and the severity of the airway impairment.

Forced Vital Capacity

The forced vital capacity (FVC) is the total volume of gas that can be exhaled as forcefully and rapidly as possible after a maximal inspiration. In the healthy individual, the total expiratory time (TET) necessary to perform an FVC is 4 to 6 seconds. In obstructive lung disease (e.g., chronic bronchitis or emphysema), the TET increases because of the increased airway resistance and air trapping associated with the disorder. TETs of more than 10 seconds have been reported in these patients. In the normal individual the FVC equals the vital capacity (VC). Clinically, the lungs are considered normal if the FVC and the VC are within 200 mL of each other. In the patient with obstructive lung disease, the FVC is lower than the VC because of increased airway resistance and air trapping associated with maximal effort (Fig. 4.5).

FIGURE 4.5 Forced vital capacity (FVC). A is the point of maximal inspiration and the starting point of an FVC maneuver. Note the reduction in FVC in obstructive pulmonary disease.

A decreased FVC is also a common clinical manifestation in the patient with a restrictive lung disorder (e.g., pneumonia, acute respiratory distress syndrome, atelectasis). This decrease is mainly a result of the fact that restrictive lung disorders reduce the patient's ability to fully expand the lungs, thus reducing the VC necessary to generate a good FVC exhalation. However, the TET required to perform an FVC exhalation is usually normal or even less than normal because of the high lung elasticity (low lung compliance) associated with restrictive disorders.

A number of pulmonary function values can be calculated from a single FVC maneuver. The most common measurements obtained are as follows:

•Forced expiratory volume timed (FEVT)

•Forced expiratory volume in 1 second/forced vital capacity ratio (FEV1/FVC ratio)

•Forced expiratory flow between 200 and 1200 mL of FVC (FEF200–1200)

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•Forced expiratory flow at 25% to 75% (FEF25%–75%)

•Peak expiratory flow rate (PEFR)

Forced Expiratory Volume Timed

The maximum volume of gas that can be exhaled over a specific period is the forced expiratory volume timed (FEVT).

This measurement is obtained from an FVC measurement. Commonly used time periods are 0.5, 1.0, 2.0, 3.0, and 6.0 seconds. The most commonly used time period is 1 second (forced expiratory volume in 1 second [FEV1]). In the

normal adult, the percentages of the total volume exhaled during these periods are FEV0.5, 60%; FEV1, 83%; FEV2, 94%; and FEV3, 97%. In obstructive disease, the FEVT is decreased because the time necessary to exhale a certain volume forcefully is increased (Fig. 4.6). Although the FEVT may be normal in restrictive lung disorders (e.g., pneumonia, acute

respiratory distress syndrome, atelectasis), it is commonly decreased because of the decreased VC associated with restrictive disorders (similar to the FVC in restrictive disorders). The FEVT progressively decreases with age (about 23 mL

per year after age 18).

FIGURE 4.6 Forced expiratory volume timed (FEVT). In obstructive pulmonary disease, more time is needed to exhale a specified volume.

Forced Expiratory Volume in 1 Second/Forced Vital Capacity (FEV1/FVC) Ratio

The FEV1/FVC ratio compares the amount of air exhaled in 1 second with the total amount exhaled during an FVC maneuver. Because the FEV1/FVC ratio is expressed as a percentage, it is commonly referred to as the forced expiratory volume in 1 second percentage (FEV1%). Simply stated, the FEV1/FVC ratio provides the percentage of the patient's total volume of air forcefully exhaled (FVC) in 1 second. As discussed earlier in the section on FEVT, the normal adult exhales 83% or more of the FVC in 1 second (FEV1). Therefore the FEV1/FVC ratio also should be 83% or greater under normal circumstances. The FEV1% and the FEV1/FVC ratio progressively decrease with age. According to the Global

Initiative for Chronic Obstructive Lung Disease (GOLD), the American Thoracic Society (ATS), and European Respiratory Society (ERS), airway obstruction is considered to be present when the FEV1/FVC ratio is less than 70%.

Clinically, the FVC, FEV1, and FEV1% are commonly used to assess the severity of a patient's pulmonary disorder and

determine whether the patient has an obstructive or a restrictive lung disorder. The primary pulmonary function study differences between an obstructive and a restrictive lung disorder are as follows:

•In an obstructive disorder, the FEV1 and FEV1% are both decreased. The FVC is often normal.

•In a classic restrictive disorder, the FVC and FEV1 are decreased and the FEV1% is normal or increased.

Forced Expiratory Flow 25% to 75%

The forced expiratory flow 25%–75% (FEF25%–75%) is the average flow rate generated by the patient during the middle 50% of an FVC measurement (Fig. 4.7). This expiratory maneuver is used to evaluate the status of medium to small airways

in obstructive lung disorders. The normal FEF25%–75% in a healthy man 20 to 30 years of age is about 4.5 L/s (270 L/min). The normal FEF25%–75% in a healthy woman 20 to 30 years of age is about 3.5 L/s (210 L/min). The FEF25%–75% is somewhat effort-dependent because it depends on the FVC exhaled.