5 курс / Пульмонология и фтизиатрия / Clinical_Manifestations_and_Assessment_of_Respiratory

FIGURE 4.7 Forced expiratory flow at 25% to 75% (FEF25%–75%). This test measures the average rate of flow between 25% and 75% of a forced vital capacity (FVC) maneuver. The flow rate is measured when 25% of the FVC has been exhaled and again when 75% of the FVC has been exhaled. The average rate of flow is derived by dividing the combined flow rates by 2. Note that expiration (in this figure) starts at 1.0 L on the upward axis.

The FEF25%–75% progressively decreases in obstructive diseases and with age. The FEF25%–75% also may be decreased in moderate or severe restrictive lung disorders. This decrease is believed to be caused primarily by the reduced cross-

sectional area of the small airways associated with restrictive lung problems. Clinically, the FEF25%–75% is often used to further confirm or rule out the presence of an obstructive pulmonary disease in the patient with a borderline FEV1% value.

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

The forced expiratory flow 200–1200 (FEF200–1200) measures the average flow rate between 200 and 1200 mL of an FVC (Fig. 4.8). The first 200 mL of the FVC is usually exhaled more slowly than at the average flow rate because of the normal inertia involved in the respiratory maneuver and the initial slow response time of the pulmonary function equipment.

Because the FEF200–1200 measures expiratory flows at high lung volumes (i.e., the initial part of the FVC), it provides a good assessment of the large upper airways. The FEF200–1200 is relatively effort-dependent.

FIGURE 4.8 Forced expiratory flow between 200 and 1200 mL of forced vital capacity (FVC) (FEF200–1200). This test measures the average rate of flow between 200 mL and 1200 mL of the FVC. The flow rate is measured when 200 mL has been exhaled and again when 1200 mL has been exhaled. The average rate of flow is derived by dividing the combined flow rates by 2. Note that expiration (in this figure) starts at 1.0 L on the upward axis.

The normal FEF200–1200 for the average healthy man 20 to 30 years of age is about 8 L/s (480 L/min). The normal FEF200– 1200 in the average healthy woman 20 to 30 years of age is about 5.5 L/s (330 L/min). The FEF200–1200 decreases in obstructive lung disorders. The FEF200–1200 is a good test to determine the patient's response to bronchodilator therapy. In restrictive lung disorders the FEF200–1200 is usually normal because it measures the early expiratory flow rates during the first part of an FVC maneuver (i.e., when the patient's VC is at its highest level). The FEF200–1200 progressively decreases with age.

Peak Expiratory Flow Rate

The peak expiratory flow rate (PEFR) (also known as the peak flow rate) is the maximum flow rate generated during an FVC maneuver (Fig. 4.9). The PEFR provides a good assessment of the large upper airways. It is very effort-dependent. The normal PEFR in the average healthy man 20 to 30 years of age is about 10 L/s (600 L/min). The normal PEFR in the average healthy woman 20 to 30 years of age is about 7.5 L/s (450 L/min). The PEFR decreases in obstructive lung diseases. In restrictive lung disorders, the PEFR is usually normal because it measures the early expiratory flow rates during the first part of an FVC maneuver (i.e., when the patient's VC is at its highest level). The PEFR progressively decreases with age.

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FIGURE 4.9 Peak expiratory flow rate (PEFR). The steepest slope of the ΔV̇/ΔT line is the PEFR (V̇).

The PEFR also can be measured easily at the patient's bedside with a hand-held peak flowmeter (e.g., Wright peak flowmeter). The hand-held peak flowmeter is used to monitor the degree of airway obstruction on a moment-to-moment basis and is relatively small, inexpensive, accurate, reproducible, and easy for the patient to use. In addition, the mouthpieces are disposable, thus allowing the safe use of the same peak flowmeter from one patient to another. PEFR measurements should routinely be performed at the patient's bedside to assess the degree of bronchospasm, effect of bronchodilators, and day-to-day progress. The PEFR results generated by the patient before and after bronchodilator therapy can serve as excellent objective data by which to assess the effectiveness of therapy.

Maximum Voluntary Ventilation

The maximum voluntary ventilation (MVV) is the largest volume of gas that can be breathed voluntarily in and out of the lungs in 1 minute (Fig. 4.10). The normal MVV in the average healthy man 20 to 30 years of age is about 170 L/min. The normal MVV in the average healthy woman 20 to 30 years of age is about 110 L/min. The MVV progressively decreases in obstructive pulmonary disorders. In restrictive pulmonary disorders, the MVV may be normal or decreased. It is very effort-dependent.

FIGURE 4.10 Volume-time tracing for a maximum voluntary ventilation (MVV) maneuver. Note that the patient actually performs the MVV maneuver for only 12 seconds, not 60 seconds.

Flow-Volume Loop

The flow-volume loop is a graphic illustration of both a forced vital capacity (FVC) maneuver and a forced inspiratory volume (FIV) maneuver. The FVC and FIV are plotted together as two curves that form what is called a flow-volume loop. As shown in Fig. 4.11, the upper half of the flow-volume loop (above the zero-flow axis) represents the maximum expiratory flow generated at various lung volumes during an FVC maneuver plotted against volume. This portion of the curve shows the flow generated between the TLC and RV. An excellent example of this portion of the flow-volume loop is shown in Fig. 4.12, where “chatter” caused by a large pedunculated endobronchial tumor in the trachea was identified using this technology. Poor patient effort also can be identified on the “flow portion” of the flow-volume loop—for example, the upper half of the flow-volume loop (above the zero-flow axis) will show flow decrease, hesitation, or flow stoppage altogether, and there will be variability between successive patient efforts.

FIGURE 4.11 Normal flow-volume loop.

FIGURE 4.12 Flow-volume loop “chatter” seen in a patient with a pedunculated (vibrating) endobronchial tumor.

The lower half of the flow-volume loop (below the zero-flow axis) illustrates the maximum inspiratory flow generated at various lung volumes during a forced inspiration (called a forced inspiratory volume [FIV]) plotted against the volume inhaled. This portion of the curve shows the flow generated between the RV and TLC. Depending on the sophistication of the equipment, several important pulmonary function study values can be obtained, including the following:

•FVC

•FEVT

•FEF25%–75%

•FEF200–1200

•PEFR

•Peak inspiratory flow rate (PIFR)

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•Forced expiratory flow at 50% (FEF50%)

•Instantaneous flow at any given lung volume during forced inhalation and exhalation

In the normal subject the expiratory flow rate decreases linearly during an FVC maneuver, immediately after the PEFR has been achieved. In the patient with an obstructive lung disease, however, the flow rate decreases in a nonlinear fashion after the PEFR has been reached. This nonlinear flow rate causes a cuplike or scooped-out appearance in the expiratory

flow curve when 50% of the FVC has been exhaled. This portion of the flow curve is the FEF50%, or Vmax 50 (Fig. 4.13). Table 4.7 summarizes the forced expiratory flow rate and volume measurements and the normal values found in healthy men and

women ages 20 to 30 years.

FIGURE 4.13 Flow-volume loop demonstrating the shape change that results from an obstructive lung disorder. The curve on the right represents intrathoracic airway obstruction.

TABLE 4.7

Normal Forced Expiratory Flow Rate Measurements in Healthy Men and Women 20 to 30 Years of Age

Forced Expiratory Flow Rate Measurement	Men	Women
	Usually equals vital	Usually equals
	capacity (VC)	VC (FVC and
	(FVC and VC	VC should be
	should be within	within 200 mL
	200 mL of each	of each other)
	other)
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 caused by dynamic compression of the
airways.
	FEV0.5: 60%	FEV0.5: 60%
	FEV1.0: 83%	FEV1.0: 83%
	FEV2.0: 94%	FEV2.0: 94%
	FEV3.0: 97%	FEV3.0: 97%
Forced expiratory volume timed (FEVT): FEV0.5, FEV1.0, FEV2.0, FEV3.0. In
obstructive disorders, more time is needed to exhale a specified volume.
Forced expiratory volume in 1 second/forced vital capacity ratio (FEV1/FVC):	Derived by	Derived by
Commonly called forced expiratory volume in 1 second percentage (FEV1%).	dividing the	dividing
	predicted	the
	FEV1 by the	predicted
	predicted	FEV1 by
	FVC	the
	Should be >83%	predicted
	<70% = airway	FVC
	obstruction	Should be

		>83%
		<70% =
		airway
		obstruction
	4.5 L/s (270 L/min)	3.5 L/s
		(210 L/min)
Forced expiratory flow 25%–75% (FEF25%–75%). This test measures the
average rate of flow between 25% and 75% of an FVC maneuver. The flow
rate is measured when 25% of the FVC has been exhaled and again when
75% of the FVC has been exhaled. The average rate of flow is derived by
dividing the combined flow rates by 2.
	8 L/s (480 L/min)	5.5 L/s
		(330 L/min)
Forced expiratory flow 200–1200 (FEF200–1200). This test measures the
average rate of flow between 200 mL and 1200 mL of an FVC maneuver.
The flow rate is measured when 200 mL has been exhaled and again when
1200 mL has been exhaled. The average rate of flow is derived by dividing
the combined flow rates by 2.
	8–10 L/s (500–	7.5 L/s
	600 L/min)	(450 L/min)
Peak expiratory flow rate (PEFR). The maximum flow rate (steepest slope of
the volume-time trace) generated during an FVC maneuver.
	170 L/min	110 L/min

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Maximum voluntary ventilation (MVV). The largest volume of gas that can be breathed voluntarily in and out of the lungs in 1 minute.

Table 4.8 provides an overview of the expiratory flow rate measurements characteristic of restrictive lung disorders. In these disorders, flow and volume are, in general, reduced equally. Clinically, this phenomenon is referred to as symmetric reduction in flows and volumes. The flow-volume loop is therefore a small version of normal in restrictive pulmonary disease (Fig. 4.14).

TABLE 4.8

Restrictive Lung Disease

Forced Expiratory Flow Rate and Volume Findings

FVC	FEVT	FEV1/FVC	FEF25%–75%
↓	N or ↓	N or ↑	N or ↓
FEF50%	FEF200–1200	PEFR	MVV
N or ↓	N or ↓	N or ↓	N or ↓

FEF25%–75%, Forced expiratory flow 25%–75%; FEF50%, forced expiratory flow at 50%; FEF200–1200, forced expiratory flow 200–1200 mL of FVC; FEV1/FVC, forced expiratory volume in 1 second/forced vital capacity ratio; FEVT, forced expiratory volume timed; FVC, forced vital capacity; MVV, maximum voluntary ventilation; N,

normal; PEFR, peak expiratory flow rate.

FIGURE 4.14 Flow-volume loop demonstrating the shape change that results from a restrictive lung disorder. Note the symmetric loss of flow and volume.

Table 4.9 provides an overview of the expiratory flow rate measurements characteristic of obstructive lung disorders. Obstructive lung disorders cause increased airway resistance (Raw) and airway closure during expiration. When Raw

becomes high, the patient's ventilatory rate decreases and the tidal volume increases. This ventilatory pattern is thought to be an adaptation to reduce the work of breathing (see Fig. 3.4).

TABLE 4.9

Obstructive Lung Disease

Forced Expiratory Flow Rate and Volume Findings

FVC	FEVT	FEV1/FVC	FEF25%–75%
↓	↓	↓	↓
FEF50%	FEF200–1200	PEFR	MVV
↓	↓	↓	↓

FEF25%–75%, Forced expiratory flow 25%–75%; FEF50%, forced expiratory flow at 50%; FEF200–1200, forced expiratory flow 200–1200 mL of FVC; FEV1/FVC, forced expiratory volume in 1 second/forced vital capacity ratio; FEVT, forced expiratory volume timed; FVC, forced vital capacity; MVV, maximum voluntary ventilation; N,

normal; PEFR, peak expiratory flow rate.

Pulmonary Diffusion Capacity

The pulmonary diffusion capacity of carbon monoxide (DLCO) measures the amount of carbon monoxide (CO) that moves across the alveolar-capillary membrane. When the patient has a normal hemoglobin concentration, pulmonary capillary blood volume, and ventilatory status, the only limiting factor to the diffusion of carbon monoxide is the alveolar-

capillary membrane. Under normal conditions, the average DLCO value for the resting man is 25 mL/min/mm Hg (STPD, A volume of gas, at the standard (S) temperature (T) of 0°C and a barometric pressure (P) of 760 mmHg, and in a dry state (D)). This value is slightly lower in women, presumably because of their smaller normal lung volumes. Table 4.10 provides a general guide to conditions that alter the patient's DLCO.

TABLE 4.10

Pulmonary Diffusion Capacity of Carbon Monoxide

Obstructive lung disorders*	Restrictive lung disorders†
N or ↓	N or ↓

*A decreased DLCO is a hallmark clinical manifestation in emphysema (because of the destruction of the alveolar pulmonary capillaries and decreased surface area for gas diffusion associated with the disease). The DLCO, especially when corrected for alveolar volume (VA), is usually normal in all other obstructive lung disorders.

†This is usually decreased when moderate to severe alveolar atelectasis, alveolar consolidation, or increased alveolar-capillary membrane thickness is present in the restrictive lung disorder.

N, Normal.

Assessment of Respiratory Muscle Strength

The most commonly used tests to evaluate the patient's respiratory muscle strength at the bedside are maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP), forced vital capacity (FVC), and maximum voluntary ventilation (MVV). (See page 61 for discussion of FVC and page 58 for discussion of MVV.)

Maximum inspiratory pressure (MIP), also called the negative inspiratory force (NIF), is the maximum inspiratory pressure the patient is able to generate against a closed airway and is recorded as a negative number in either centimeters of water or millimeters of mercury. The MIP can be measured through an endotracheal tube or by using a mask or mouthpiece and an external pressure gauge. The MIP primarily measures inspiratory muscle strength—that is, the power of the diaphragm and external intercostal muscles.

In the normal healthy adult, the MIP is about –80 to –100 cm H2O. Ideally, the MIP should be measured at the patient's residual volume. An MIP of –25 cm H2O or less (more negative) usually indicates adequate muscle strength to maintain spontaneous breathing. An MIP of –20 cm H2O or greater (less negative) is a strong indicator for the need for ventilatory

support (see Protocols 11.1 and 11.2). Reduced MIP values are also commonly seen in patients with neuromuscular disease (e.g., amyotrophic lateral sclerosis [ALS], Guillain-Barré syndrome, or myasthenia gravis), chronic obstructive pulmonary disease (COPD), and chest wall deformities (e.g., kyphoscoliosis).

Maximum expiratory pressure (MEP) is the highest pressure that can be generated during a forceful expiratory effort against an occluded airway and is recorded as a positive number in either centimeters of water or millimeters of mercury. The MEP primarily measures the strength of the abdominal muscles—that is, the rectus abdominis muscles, external abdominis obliquus muscles, internal abdominis obliquus muscles, transversus abdominis muscles, and internal intercostal muscles. Ideally, the MEP is measured at maximal inspiration (near the total lung capacity). The adult normal MEP is greater than 100 cm H2O in males and greater than 80 cm H2O in females. Unsatisfactory MEP values are commonly seen

in patients with neuromuscular disease (e.g., ALS, Guillain-Barré syndrome, or myasthenia gravis), COPD, and high cervical spine fractures. Finally, it should be noted that a low MEP is associated with a poor or inadequate cough effort. Thus in patients with excessive airway secretions (e.g., chronic bronchitis or cystic fibrosis) a low MEP, accompanied by the inability to effectively mobilize airway secretions, can further complicate the patient's respiratory condition.

Cardiopulmonary Exercise Testing

When one considers the fact that dyspnea on exertion is the most common sign of pulmonary disease (see Chapter 3, Dyspnea), it should be noted that the pulmonary function tests, as described in the foregoing text, are all done at rest. Tests done during exercise range from simple and inexpensive (e.g., the 6-minute walk used in pulmonary rehabilitation) to the more complex cardiopulmonary exercise test (CPET) with or without blood gas analyses. CPET involves treadmill or bicycle ergometer testing while a variety of physiologic parameters are measured and/or calculated (Box 4.1). Contraindications to CPET are listed in Box 4.2.

Box 4.1

Cardiopulmonary Exercise Testing Parameters

Measured and/or Observed Values

•Heart rate (HR)

•Cardiac rhythm

•Electrocardiogram (ECG)

•Blood pressure

•O2 saturation (SpO2)

•Breath sounds (e.g., wheezing, crackles)

•Arterial blood gas (ABG)

•Minute ventilation

Derived (Calculated) Values

•Oxygen consumption (VO2)

•Maximum oxygen consumption (VO2max)

•Heart rate reserve

•CO2 production (VCO2)

•Respiratory quotient (RQ)

•Dead space/tidal volume ratio (VD/VT)

•Anaerobic threshold (VO2 AT)

•Impairment classification for prolonged physical work

•Oxygen pulse (VO2 ÷ HR)

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•Breathing reserve

•Ventilatory equivalent for CO2 (VE/VCO2)

Box 4.2

Contraindications to Cardiopulmonary Stress Testing

•Acute myocardial infarction (3–5 days)

•Unstable angina pectoris

•Uncontrolled cardiac arrhythmias, hypertension, or seizure history

•Lightheadedness or syncope

•Uncontrolled congestive heart failure/pulmonary edema

•Uncontrolled asthma

•Pulmonary embolism

•Room air SpO2 ≤85%

•Respiratory failure

•Mental impairment limiting cooperation

•Orthopedic/neurologic impairment

Although the performance and interpretation of CPET variables are beyond the scope of this volume, evaluation of the physiologic data seen with increasing exercise, at or near the anaerobic threshold (AT), at which minute ventilation as a function of oxygen consumption increases sharply in response to the onset of metabolic acidosis, can assist in the clinical diagnosis of malingering and deconditioning, obesity, hyperventilation/anxiety, coronary artery disease, neuromuscular disease, congestive heart failure/valvular heart disease, interstitial lung disease, obstructive pulmonary disease, pulmonary vascular disease, and for the purpose of disability determinations.

Other Diagnostic Tests for Asthma

Because some patients have clinical manifestations associated with asthma, but otherwise normal lung function between asthma episodes, measurements of airway responsiveness to inhaled methacholine or histamine, or an indirect challenge test to inhaled mannitol, or to an exercise or cold air challenge may be useful in confirming a diagnosis of asthma (see Chapter 14, Asthma). These inhalation challenge tests can be performed only when the patient has an FEV1 of

80% or greater, to avoid electively inducing significant asthma symptoms in an already compromised patient.

Impulse Oscillometry1

Impulse oscillometry (IOS) is a simple, noninvasive, effort-independent test that applies oscillating pressure impulses to the lungs during normal passive breathing. It is used to assess both large and small airway obstructions. A small loudspeaker placed close to the patient's mouthpiece generates the pressure impulses. The pressure impulses are superimposed on the normal tidal volume as the patient inhales and exhales. Pressure-flow transducers measure the impulse changes and, subsequently, separated from the breathing pattern by “signal filtering.” The following two types of pressure oscillations are measured during this test:

•Resistance (Rrs) pressure oscillations: Oscillations that are in phase with air flow. Resistance represents the energy required to move a pressure wave through the bronchi and bronchioles and to distend the lung parenchyma. Resistance pressure oscillations are determined when the pressure waves are unopposed by airway recoil and are in phase with air flow.

•Reactance (Xrs) pressure oscillations: Oscillations that are out of phase with air flow. Reactance represents the energy generated by the elastic recoil of the lungs after distention and inertia.

Respiratory impedance (Zrs) is the sum of all the forces (i.e., Zrs = Rrs + Xrs) and is calculated from the ratio of pressure and flow at each frequency during the test.

The pressure oscillations are applied at a fixed (square wave) frequency of 5 Hz, from which all other frequencies of interest are derived. Low-frequency oscillations (5 Hz) penetrate throughout the small airways of the lung periphery, where high-frequency impulses (20 Hz) only reach the proximal airways. When analyzed, these pressure changes separately quantify the degree of obstruction in the central and peripheral airways.

Because the test is easy to administer, it is commonly used with preschool and school-aged children and adults with physical and cognitive limitations (Fig. 4.15). IOS is also used to measure bronchodilator response and bronchoprovocation testing. IOS can also be performed in patients on ventilators and during sleep. Fig. 4.16 shows graphs of IOS and spirometry in patients with normal, obstructive, and restrictive lung disease.

FIGURE 4.15 Impulse oscillometry (IOS) test performed on a 5-year-old child. During the test, the sitting position is preferred. Nose clips should be worn, and the mouthpiece should be positioned so that the neck is slightly extended. Ensure a tight seal between the mouthpiece and lips, and the patient's cheeks should be held firmly by the patient or examiner from behind. The patient is instructed to perform relaxed, normal tidal breathing between 30 and 45 seconds. During this time, about 120 to 150 oscillations are transmitted throughout the lungs while, at the same time, the pressure-flow sensors determine the mean resistance, reactance, and respiratory impedance values between frequencies of 5 and 20 Hz. A minimum of three tests should be performed. If there are breathing segments that contain artifacts (e.g., caused by coughing, gagging, swallowing, air leaks, or tongue obstructions), they should be discarded. (Courtesy Dayton Children's Hospital, Dayton, Ohio.)

FIGURE 4.16 Representative graphs of impulse oscillometry (IOS) and spirometry in patients with normal, obstructive, and restrictive lung disease. Tracings of lung resistance and reactance in comparison with spirometric flow-volume loop for prototypical patients with normal lung function, distal obstruction, proximal obstruction, and restrictive lung disease. Dotted lines indicate the normal tracing, and solid lines show pathologic tracings.

Self-Assessment Questions

1.What is the PEFR in the normal healthy woman 20 to 30 years of age?

a.250 L/min

b.350 L/min

c.450 L/min

d.550 L/min

2.A restrictive lung disorder is confirmed when the:

1.FEV1 is decreased

2.FVC is increased

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3.FEV1/FVC ratio is normal or increased

4.FEV1 is increased

a.1 only

b.4 only

c.1 and 3 only

d.2 and 4 only

3.Which of the following expiratory maneuver findings are characteristic of restrictive lung disease? 1. Normal FVC

2. Decreased FEF25%–75%

3.Increased PEFR

4.Decreased FEVT

a.1 and 3 only

b.2 and 4 only

c.3 and 4 only

d.2 and 3 only

4.In an obstructive lung disorder, which of the following occurs? 1. FRC is decreased

2. RV is increased

3.VC is decreased

4.IRV is increased

a.1 and 3 only

b.2 and 3 only

c.2 and 4 only

d.2, 3, and 4 only

5.Under normal conditions, the average DLCO value for the resting man is which of the following?

a.10 mL/min/mm Hg

b.15 mL/min/mm Hg

c.20 mL/min/mm Hg

d.25 mL/min/mm Hg

6.What is the vital capacity of the normal recumbent man 20 to 30 years of age?

a.2700 mL

b.3200 mL

c.4000 mL

d.4800 mL

7.What is the normal percentage of the total volume exhaled during an FEV1?

a.60%

b.83%

c.94%

d.97%

8.Which of the following can be obtained from a flow-volume loop study?

1.FVC

2.PEFR

3.FEVT

4.FEF25%–75%

a. 4 only

b. 1 and 2 only

c.1, 3, and 4 only

d.1, 2, 3, and 4

9.An obstructive lung disorder is confirmed when the:

1.FEV1 is decreased

2.FVC is increased

3.FEV1 is increased

4.FEV1/FVC ratio is decreased

a.3 only

b.4 only

c.1 and 3 only

d.1 and 4 only

10.Which of the following anatomic alterations of the lungs is or are associated with a restrictive lung disorder? 1. Bronchospasm

2.Atelectasis

3.Distal airway weakening

4.Consolidation

a.1 only

b.3 only