Age Considerations for Children Performing Spirometry

Age considerations are a common concern that cannot be addressed until spirometry is attempted. Children as young as 3 years have the potential to perform the maneuver but with limitations. It has been suggested that at least 50% of children this age can perform pulmonary function tests (PFTs). Published data from several sources suggest that preschool children can perform technically repeatable forced vital capacity (FVC) maneuvers within 10%. Introducing spirometry to children at a young age often yields remarkable results within only a few training sessions. Figure 8-1 is a 5-year-old child performing spirometry for the first time. Note the child is standing, with noseclips in place, and mouthpiece fully in mouth.

Recommendations published from an ATS-ERS focus group on preschool lung function tests more clearly define acceptable and repeatable spirometry in this young age group. The most difficult part of spirometry for a very young child is to continue to exhale once the initial blast of air occurs. Small children do not understand how to sustain applied pressure to their chest and abdomen once they feel their lungs are empty. Additional guidelines from the ATS-ERS include the following:

Although it is desirable to have at least two repeatable maneuvers, even a single satisfactory trial provides important information. However, learning variability and lack of repeatability should be noted. Other testing modalities available in assessing very young children are discussed later in the chapter.

On average, by age 5 years, most children can perform spirometry with adequate technique and repeatability. Published guidelines from the ATS-ERS task force offer more realistic expectations for young children. There is not an age that all children, without exception, can perform technically acceptable spirometry. The ATS-ERS guidelines suggest that certain flow-volume curves may be “usable,” if not technically acceptable. Consider Figure 8-2, A. This is the first experience for this 5-year-old child in the pulmonary lab. On multiple attempts, her FEV₁ was repeatable with the best curve, as shown. Note, however, that exhalation is incomplete and expiratory time is very short (slightly over 1 second). Therefore, the FVC values are underestimated and the FEV₁/FVC is inaccurate. The curves, however, meet criteria for satisfactory start of test and are free of artifact for at least the first second. These classify as usable flow-volume loops, although not technically perfect.

As long as the patient blows for at least 1 second and that first second is free of artifact, the F-V loop and values may be used for interpretation. Caution is suggested in interpreting the FEV₁/FVC or any parameter, based on a full expiratory maneuver. It is certainly understood that this may not represent the child’s maximal effort; however, identifying that this young child’s FEV₁ is repeatable and within the normal range for her age is valuable information for the pulmonologist. The shape of the postbronchodilator flow-volume loop in Figure 8-2, B, is similar to the one in Figure 8-2, A, but larger. There is a proportional increase in both FVC and FEV₁, which suggests the child took a deeper breath before performing the FVC maneuver. Learning effect can be seen even during the first session of working with a young child and should definitely be considered when interpreting this study. Although a bronchodilator response should not be ruled out, it is likely that learning effect was responsible for most of the improvement. It should be emphasized that spirometry is an effort-dependent test that requires cooperation and attention from the child. Equally important is the experience and patience of a well-trained pulmonary function technologist. Children who are mentally delayed or not capable of following directions may not perform adequate spirometry at any age, regardless of the coach or technologist. Patients who are not feeling well or having chest pain, for example, may follow instructions but not perform maximally.

Ensuring Maximal Effort on the Part of the Child

First, gain the child’s confidence and do not rush into testing. Children are fearful that the testing will hurt. When possible, reassure the child by carrying on a conversation that is directed toward the child. As illustrated in Figure 8-3, try some “blowing” games with the very young child before approaching the PFT equipment. Use of a pinwheel is often very successful. It teaches the child the need to take a big breath and blow fast. Additionally, have the child try to continue to blow until the pinwheel stops turning. This important step reinforces a complete exhalation. Demonstrate the test and reassure the child that it is easy and fun. Pinwheels also make an excellent and inexpensive prize for the patient when testing is over. If a pinwheel is unavailable, the use of a tissue will substitute, although it is a bit harder. Demonstrate blowing the tissue as high, and keeping the tissue suspended for as long, as possible.

Once the child has practiced several times, move the child to the PFT machine and prepare for testing. When possible, the child should be standing and the technologist should be at eye level with the child. See Box 8-1 for a list of suggestions that will “break the ice” and get things going in a positive direction. The use of noseclips is recommended, depending on the age and cooperation of the child. The anatomy of the nasopharyngeal structures in younger children is such that the use of noseclips may not be necessary. If the child is willing to wear noseclips, encourage him or her to do so.

Many pulmonary function systems offer two mouthpiece techniques for performing spirometry: “closed” and “open” techniques. Each offers advantages and disadvantages. Attempt the technique with which laboratory personnel are most comfortable and consistent. For the closed technique, have the child stand with noseclips in place and the mouthpiece situated securely. Ask the patient to breathe tidally for several breaths. This offers the opportunity to observe the child and ensure that the seal around the mouthpiece is tight. It also gives the child a feeling of security that he or she will get plenty of air through the mouthpiece. The child should be reassured during tidal breathing that he or she is doing very well. If the spirometer permits real-time visualization of flow, the clinician may show the child that he or she is “drawing pictures” with his or her breathing. It is essential to gain the child’s confidence and offer praise whenever possible. It is very important to talk the child through the maneuver. Use simple words and phrases. For example, “Breathe in, breathe out,” “Take easy, little baby breaths,” or “One more little breath. Now take a giant breath in.” The technologist should be vocal and use hands and arms to demonstrate. The intonation of the voice should mimic the action, for example, “easy, gentle breaths” in a soft voice versus “big, fast, and long breath” in a louder tone. Sometimes having the child “race” with another technologist is helpful. Again the use of the pinwheel or tissue can reinforce what is expected of a very young patient while the test is actually going on.

If the child is having particular difficulty, changing the technique may lead to success. At times, tidal breathing may confuse the child. Have the patient get onto the mouthpiece, immediately take a maximal breath in and blast the air out. Alternately, use a different mouthpiece or try the open technique. The child may have a sensitive gag reflex or, for unclear reasons, become anxious with tidal breathing. With the open technique, the child should first be instructed to hold the mouthpiece close to his or her face, perhaps supported on the cheek. Next, open the mouth wide, take in the deepest breath possible, place the mouthpiece in the mouth, and immediately blow. The disadvantage of this technique is that air may be lost as the child tries to get the mouthpiece into his or her mouth and form a seal. To aid in a complete exhalation, the technologist can place his or her hands on the child’s belly. As the patient exhales, gently press on the stomach. This reinforces a smooth and continuous expiratory maneuver. Once the child is more comfortable performing spirometry, transition to a closed mouthpiece technique without any assistance from the technologist.

Importance of Effort

One of the biggest challenges with children is ensuring a maximal breath in before the forced expiration. The concept is simple: The more air in, the more air out. The technologist should strive to get the child to breathe in as deeply as possible and observe the child’s chest excursion. Movement of the shoulders upward without chest excursion is common and can fool the technologist into believing it is a maximal inspiratory capacity. This may also be a pitfall when comparing prebronchodilator and postbronchodilator spirometry. Figure 8-4 is also from a 5-year-old patient performing spirometry for the first time. The prebronchodilator spirometry (see Figure 8-4, A) appears to be normal and was repeatable. Postbronchodilators, both FVC and FEV₁, improve significantly (see Figure 8-4). The increase in FVC and FEV₁ is very symmetric, similar to the last example presented (see Figure 8-2, A). Learning effect cannot be ruled out. However, the shape of the F-V curve is very different with postbronchodilator spirometry. This is an example of a situation where the change in FEV_0.5 might be more helpful in assessing intrathoracic airflow obstruction than the change in FEV₁

The child is at a low lung volume when 1 second is reached (close to FVC) and the FEV₁ is not reflective of airflow changes that are occurring at mid-lung volumes. It is critically important to realize that all of the “action” has already taken place by the time 1 second has elapsed. Parameters such as FEV_0.5 or FEV_0.75 should be assessed in these young children, although standards and guidelines for interpretation are not available. Contrast Figure 8-4 with Figure 8-5, A and B. In this example of a 7-year-old child, both FVC and FEV₁ increase with postbronchodilator spirometry; however, the increase in FEV₁ is proportionately higher, which also increases the FEV₁/FVC ratio. Although learning may have some effect in this example, it is evident that mild intrathoracic airflow obstruction is completely reversed. Once a child has learned the technique and is capable of performing spirometry, the results are remarkably repeatable. The ATS-ERS guidelines now base repeatability of FVC and FEV₁ on lung volume. Because younger children have smaller lung volumes than adults, these revised guidelines pertain to the pediatric population as well as to older patients with severe lung disease.

Older children often are able to perform spirometry with an FVC and FEV₁ within 5%. However, for smaller children with even more reduced lung volume, the 100 mL criterion correlates with repeatability closer to 10%.

Once a maximal inspiration is accomplished, most young children do not have difficulty blowing out forcefully. As for adult spirometry, the technologist should minimize hesitation before the forced maneuver that may create a “time zero” or back-extrapolated volume error. Do not encourage a breath hold. Delayed exhalation can result in a poor peak flow measurement and falsely raise the FEV₁. Figure 8-6 demonstrates this volume extrapolation or time zero error.

Figure 8-6, A, is an acceptable FVC maneuver. Note how the delayed exhalation in Figure 8-6, B, can skew the curve to the right and falsely elevate timed parameters. Young children have a desire to please and, unless they are feeling unwell, will usually respond to the direction to “blast or burst the air out.”

Obtaining a maximal peak flow can actually be more difficult in an adolescent. Teenage children often can be reluctant to perform maximally unless strongly encouraged to do so. This may be due to chest pain, embarrassment, or fear that something is wrong with them. Occasionally, this poor effort may be related to typical teenage angst or attention-seeking motivation. A sensitive and perceptive technologist can often combine the right amount of compassion with the necessary verbal encouragement to obtain optimal results. Variability caused by effort alone may be especially important if the patient is performing serial measurements, as in a methacholine challenge. A change in treatment regimen or admission to the hospital is often based on spirometric changes; therefore, repeatability is critical.

Length of Exhalation for a Child During an FVC Maneuver

Long-established criteria from the ATS suggested that an FVC maneuver should last for at least 6 seconds or until there was a plateau in the volume-time curve. Young children often cannot meet these criteria. The 2005 ATS-ERS guidelines have added an age stipulation to the recommendations.

Because children have lung volumes that are significantly smaller than adult lung volumes, their lungs may completely empty in only 2 or 3 seconds. When a child feels empty, the natural instinct is take a breath back in. With instruction, practice, and maturing, the child can learn to continue the expiration; however, this may not be possible on the first several visits to the lab. This does not invalidate the FVC maneuvers but requires that the testing be evaluated carefully. Figure 8-7, A, represents three prebronchodilator flow-volume (F-V) loops superimposed over each other. Although this young child does not meet the end-of-test criteria, the FEV₁ and shape of the F-V loop are remarkably repeatable. Postbronchodilator (see Figure 8-7, B) F-V loops are significantly improved and repeatable. The current ATS-ERS guidelines more realistically represent what can be expected of a younger child.

Children who are severely obstructed, like their adult counterparts, may have the ability to exhale for an extended time. Figure 8-8 shows the F-V loop and volume-time tracing of a 10-year-old girl with cystic fibrosis. This child is able to sustain expiration for 15 seconds. However, the additional volume measured in this prolonged expiration is small and may exhaust the child performing the test. She approaches a flow plateau at approximately 7–8 seconds, and the maneuver can be terminated at this point. The spirometry is certainly still valid for interpretation if terminated before zero flow occurs. Many decisions regarding acceptability of PFT results require good judgment from the technologist and careful interpretation from the physician.

Reliability of FEF_25%–75% in Children

Historically, FEF_25%–75% has been used to evaluate flow from the “small airways”. More precisely, the FEF_25%–75% should be considered a measurement of flow at lower lung volumes, not merely flow from medium-sized and smaller airways. As in adults, the variability of the FEF_25%–75% is greater than that of the FVC and FEV₁. Because children may be even less repeatable at baseline, the reliability of this measurement in pediatric testing may be questionable. In addition, if the child does not fully exhale to RV, FEF_25%–75% may be artificially elevated because of reduced vital capacity. If it is reported, the FEF_25%–75% in a pediatric subject should be interpreted with caution, especially in a very young child. A substantially greater change postbronchodilator is needed before a change can be considered significant. Refer back to Figure 8-4, A and B. Although the exhalation times do not meet the revised 3-second guideline for a child younger than age 10 years, it does appear that this patient exhaled to a volume plateau. The change in shape of the F-V loop, as well as the change in FEF_25%–75% of 65%, is certainly suggestive of a reversal of intrathoracic airflow obstruction. An FEF_25%–75% that improves by more than 35%–45% after a bronchodilator may be indicative of airway reactivity, but again caution is advised when considering this parameter. Repeatability of the FEF_25%–75% is more reliable in older children and teenagers. As previously noted, FEF_25%–75% can be reduced for several reasons that are not always related to peripheral airway disease. Refer to Figure 8-9. This F-V loop is from a 17-year-old patient who had tracheal stenosis after a prolonged intubation as a young child. The FEF_25%–75% of this curve is severely reduced, as is the FEV₁. The reduction is not caused by peripheral airway obstruction but by a large central (tracheal) airway obstruction.

Parameters of Inspiratory Forced Flow Helpful in Pediatrics

Spirometry yields a variety of expiratory and inspiratory flows, including FEF_25%, FEF_50%, FEF_75%, FEF_85%, FIF_50%, and the FEF_50%/FIF_50% ratio. Each of these parameters relates to flow at a particular lung volume and may have some benefit for particular instances. These flows, like the FEF_25%–75%, are less repeatable than the FEV₁ and FVC and do not have any reference values. The FEF_50%/FIF_50% ratio may be helpful in identifying intrathoracic versus extrathoracic airflow obstruction (see Chapter 2). Unlike the expiratory limb of the F-V loop, the inspiratory limb has not been well characterized in pediatric subjects. There are several reasons for this; however, the most important are energy expenditure and effort dependence. Expiration from TLC is far more repeatable because of the elastic recoil of the lung. The FEF_50% occurs in the portion of the expiratory limb that is considered effort independent. The inspiratory limb, conversely, is effort dependent and energy dependent for the entire maneuver. Therefore, optimal patient effort is vital for analyzing the inspiratory loop. A great deal of important information can be obtained from an appropriately performed maneuver. Too often, the inspiratory limb is ignored. When teaching children how to perform spirometry, certainly the emphasis is on expiration. Once it is mastered, attention should be paid to the inspiratory maneuver as well.

The aperture, or opening, through the vocal cords is approximately the same at both 50% of expiratory vital capacity and 50% of inspiratory vital capacity. Therefore, the FEF_50%/FIF_50% ratio should not be greater than 1.0. A ratio greater than 1.0 suggests an extrathoracic obstruction; however, this relationship has not been closely studied or reported in pediatric patients. Conversely, an FEF_50%/FIF_50% ratio of less than 1.0 may be normal or may represent significant intrathoracic obstruction. In addition, a ratio close to normal is possible if significant obstruction is seen on both inspiration and expiration (fixed obstruction), yielding a ratio of 1.0. Figure 8-9 demonstrates the effect of tracheal stenosis in a 17-year-old patient on the shape of the flow-volume loop, and the resulting FEF_50%/FIF_50% ratio. This underlies the importance of correlating the F-V loop with the child’s clinical picture and symptoms.

Figure 8-10 shows examples of F-V loops with differing FEF_50%/FIF_50% ratios and the shape of the loops represented by those ratios. Although FEF_50%/FIF_50% may not always discriminate between intrathoracic and extrathoracic airflow obstruction, the importance of extrathoracic obstruction should not be underestimated. Laryngeal webs, subglottic stenosis, tracheal malacia, and other lesions of the laryngeal-tracheal airway are important causes of upper airway obstruction in the pediatric population. In addition, the vocal cords represent a major “choke point” to airflow. The cords may have a structural abnormality, such as nodules or granulomas, or may become edematous, as in croup. The recurrent laryngeal nerve may be damaged, resulting in inappropriate movement or paralyzed cords. These conditions are generally easy to diagnose with direct visualization of the vocal cords. Vocal cord dysfunction (VCD) may also be responsible for poor abduction (opening) of the vocal cords during inspiration.

Role of Vocal Cord Dysfunction

Vocal cord dysfunction has become increasingly recognized as a reason for shortness of breath, in addition to throat and sternal chest pain, often mimicking asthma. Adolescents who are competitive athletes or are exceptionally goal oriented and children who have stress-related disorders are at highest risk. Unfortunately, vocal cord dysfunction is highly variable and may be detectable only when the patient is stressed in a manner that provokes the condition. The term vocal cord dysfunction (VCD) has sparked controversy among pediatric pulmonologists. Perhaps the term is not the most important consideration, but rather understanding that the vocal cords and larynx are very complex structures. There are likely many scenarios, some consciously controlled and others unconsciously controlled, that lead to the malfunction or inappropriate movement of the vocal cords. In very severe forms, “clipping,” or truncation, of the inspiratory loop with a completely normal expiratory loop is the classic presentation (see Figure 8-10, E). The child may or may not sound very stridorous during inspiration. The patient may try to speak while inspiring in short, gasping sentences. More common is a completely normal-appearing child with normal expiratory loops but highly variable inspiratory loops. Some inspiratory loops may be normal (FEF_50%/FIF_50%<1.0); however, many are often abnormal with an FEF_50%/FIF_50% greater than 1.0.

Vocal cord dysfunction is an example of a disorder in which the variability in the patient’s inspiratory loop is the hallmark of the dysfunction (Figure 8-11, A). These are the baseline loops from one patient, a 15-year-old teenager. Note how different all of the inspiratory loops look. Some have a triangular-shape appearance, some with the more classic flat, truncated appearance, and others have multiple inflection points. The inspiratory volume may be limited, giving a short, gasping type of inspiratory loop. A more normal inspiratory loop may appear among many abnormal loops (Figure 8-11, A, Trial 4). This is very important to capture when possible. It indicates that the child is capable of performing normal inspiratory loops, and the problem is likely more dynamic in nature, that is, a vocal cord malfunction. If there is a structural upper airway abnormality, the inspiratory loops should all look abnormal and very similar in shape. Structural obstructions are usually more fixed in nature with expiratory clipping also present. Refer again to an example of fixed airflow obstruction, as seen in Figure 8-10.

Bronchoprovocation testing can sometimes provoke vocal cord dysfunction; however, conclusive evidence of inappropriate movement of the vocal cords should be visualized through a laryngoscope, ideally during an episode. Because laryngoscopy may not be practical or available, a series of well-performed F-V loops may be helpful in making this presumptive diagnosis. It should be noted that VCD, on the milder side of the spectrum, is primarily a diagnosis of exclusion, and the absence of inspiratory clipping on F-V loops does not rule out the diagnosis. It is important to emphasize that effort, technique, and learning play a major role in the shape of inspiratory loops. In young children, it may require several sessions, on different days, with abnormal inspiratory loops consistently obtained before the diagnosis of vocal cord dysfunction can be suggested.

Under certain circumstances, very unusual inspiratory loops can be seen in multiple trials that are not effort- or technique-related. Consider Figure 8-11, B. These loops were obtained in a patient with excessive secretions and laryngospasm. Flow-volume loops are rarely diagnostic as a single test but certainly can suggest and support other diagnoses that are being considered.

VCD Combined with Intrathoracic Airflow Obstruction

To further complicate matters, vocal cord dysfunction is often seen in children with asthma. The relationship between these two disorders is not fully understood. There is certainly some similarity in symptoms, primarily shortness of breath, chest pain, and/or throat pain. However, some children who experience both asthma and vocal cord dysfunction can actually distinguish between the two disorders. Refer to Figure 8-12, A. These loops are from a known asthmatic child experiencing symptoms of shortness of breath and chest pain. The expiratory loops show very mild (if any) airflow obstruction. However, the inspiratory flow loops are variable and abnormal, as described in the earlier section. Vice versa, in Figure 8-12, B, note the characteristic “scoopy” appearance of severe expiratory airflow obstruction. This is accompanied by a normal appearing inspiratory loop. Note that the relationship of FEF₅₀/FIF₅₀ is skewed when the expiratory loop is not normal. The FEF₅₀/FIF₅₀ ratio discussed earlier is no longer valid in the face of intrathoracic obstruction. This ratio also does not hold true when the inspiratory loops are not complete, full loops or very irregular in shape.

Non-Repeatability in the Expiratory Maneuver

The ATS-ERS recommendations emphasize the importance of repeatability of the FVC and FEV₁. In some instances, patients cannot reproduce these parameters, and effort is not the reason. Figure 8-13 shows an example of such an instance. If only a single (best) F-V loop (Trial 1) were reported to the physician, the interpretation would state that this patient has mild to moderate intrathoracic airflow obstruction. However, the next two successive maneuvers performed by this 15-year-old asthmatic are also illustrated (Figure 8-11, A, Trials 2 and 3). These successive trials reveal progressively significant drops in FEV₁ and FEV₁/FVC, which are not repeatable with Trial 1. This pattern is an extremely important clue to the hyperreactivity of the patient’s airway. Simply performing repeated forced maneuvers may cause an asthmatic to become suddenly more obstructed and vulnerable to further bronchospasm. In such an instance, the technologist should stop testing the patient and administer a bronchodilator. If the patient’s report included only his or her best prebronchodilator and postbronchodilator spirometry, it would completely omit this important information and might prevent necessary changes in his or her asthma medication regimen.

An interesting but opposite phenomenon may be seen in the spirometry of a mild asthmatic patient. Deep inspirations may cause progressive bronchodilation with improving FEV₁ and FEV₁/FVC. This is a beneficial compensatory mechanism and is likely similar to the asthmatic athlete who is able to “run through” his or her asthma with bronchodilation during exercise. After exercise, tidal volumes decrease, airway temperature changes, and bronchoconstriction may be provoked.

Airway Malacia

Unusual flow-volume curves may be very helpful in providing clues to the location of fixed or variable obstruction. One scenario common in pediatrics is tracheal and/or bronchial malacia. Malacia refers to an airway (or more than one airway) that is soft and pliable because of a lack of supportive connective or cartilaginous tissue. Depending on the location (intrathoracic, extrathoracic, or both), these airways may collapse during inspiration or be compressed during exhalation. Tracheal or bronchomalacia in infants may produce significant stridor and “noisy breathing,” especially when the baby is excited or crying. With time and growth, the airways stiffen and are less prone to collapse.

For older children, airway malacia may produce some bizarre-shaped F-V curves. Refer to Figure 8-14. These F-V loops are from a 12-year-old child with a malaciac left main stem bronchus. Trial 1 represents a forced exhalation that is normal in shape. Trial 2 is from the same patient during the same testing session. Notice the rapid drop in flow rate, followed by a “flattening” or shelf-like appearance in the curve. Blowing harder caused critical compression at the malaciac segment and resulted in a sudden decrease in flow rate, or flow transient. Note the reduction in FEV₁, as well as FEF_25%–75%, from Trial 1 to Trial 2. This represents another example of the inadequacy of looking solely at one or two parameters instead of considering the entire picture. The shape of the curve in Trial 2 is characteristic of two lungs emptying at different time constants. One lung empties normally during forced exhalation, whereas the other lung takes considerably longer to empty because of the central intrathoracic obstruction present. Obtaining repeatable and acceptable F-V loops in the face of airway malacia can be challenging. Although not always successful, taking extra time with the child to try different breathing techniques or different mouthpieces may result in a more normal expiratory loop.

Inhalation Challenges

The most common type of inhalation challenge performed is the methacholine challenge. The child inhales methacholine chloride in succeedingly higher doses of medication. One popular dosing regimen involves a ten dose schedule beginning at a low dose (0.031 mg/mL), doubling each successive dose to a maximal dose of 16 mg/mL. A second recommended regimen with five levels of dosing starts at 0.0625 mg/mL and increases to 16 mg/mL. The drug can be administered either with a dosimeter that delivers a very specific dose with each breath or via the 2-minute tidal breathing method. Details of these two methods are discussed in Chapter 9 and both methods are generally considered to be equivocal. The 1999 ATS Guidelines provide specific recommendations for choosing the appropriate method, dosing regimens for methacholine chloride and modifications as necessary, and many other considerations for labs undertaking bronchoprovocation studies. As mentioned earlier, it is necessary to establish a consistent and repeatable spirometric flow-volume loop at baseline before the administration of the methacholine. Obtaining not only repeatable expiratory loops, but also maximal inspiratory loops, can be very helpful in considering possible vocal cord dysfunction. Serial spirometry is obtained at approximately 30-60 seconds after the administration of methacholine and again at 90 seconds. Because the half life of methacholine chloride is very short, further spirometry trials may not reflect the action of the methacholine. However, caution is advised if the child’s spirometry worsens with repeated blows, and a third trial of spirometry may be warranted. Additionally, if symptoms such as cough, wheezing, or shortness of breath begin during trials, bronchoconstriction may also be worsening, and this child should not be given an increased dose of methacholine until his or her spirometry stabilizes. A drop of 20% or more in the FEV₁ is considered the stopping point for the challenge. Most often, the computer software is able to calculate the provocative concentration that would produce a fall in FEV₁ of exactly 20% (PC₂₀), Laboratories that use dosimeters often report the provocative dose (PD₂₀), or the dose of methacholine that correlates with an exact drop of 20% in FEV₁. Pediatric patients should always be given a bronchodilator, such as albuterol, to reverse any possible bronchospasm that has occurred from the administration of the methacholine. This is true even if the challenge is considered negative. The bronchodilator may produce a significant response in FEV₁ above the child’s baseline spirometry, and that information may be relevant to the physician.

Methacholine chloride has also been shown to provoke vocal cord dysfunction. It is not known whether the medication itself causes the vocal cords to behave abnormally, or if the child experiences enough stress performing the multiple trials to unmask the vocal cord dysfunction. Examination of the flow-volume loops throughout the entire challenge can be very helpful in identifying flow abnormalities in both the inspiratory and expiratory loops. Refer to the previous discussion of flow-volume loops. An important point worth repeating: One of the hallmarks of vocal cord dysfunction is the variability in the clipping or truncation of the inspiratory loops. Because the child is required to perform multiple trials, it is possible to examine many flow-volume loops.

Most recently, the use of mannitol as a provocative inhalational agent has been proposed by many pulmonary laboratories. The advantage of mannitol over methacholine chloride is the method of delivery and the cost of medication. Mannitol can be delivered as a dry powder inhalant; therefore nebulization of medication is unnecessary. The mannitol capsules are much cheaper to produce and do not require the pharmacy making dilutions on a regular basis. An added bonus is that the sensitivity and specificity are very similar to methacholine. A disadvantage of mannitol is the dosing regimen that has been proposed. The number of doses currently recommended is eight, plus a placebo baseline. For young children, use of a dry powder inhaler may be difficult. The number of spirometry trials and the time necessary to do the testing are also extended, therefore limiting the use of mannitol challenges in the pediatric laboratory.

Pulmonary Exercise Stress Testing

Pulmonary function laboratories are asked to perform exercise stress tests for two main reasons: (1) to provoke bronchoreactivity and (2) to assess level of fitness. Protocols for exercise are as varied as protocols for inhalation challenges. The protocol used is often geared toward answering a specific question, such as, “Does this child have exercise-induced bronchospasm or asthma (EIB or EIA)?” An example of a protocol to evoke EIB includes pre-exercise spirometry as the first step. ECG leads are placed on the chest for heart rate assessment, and pulse oximetry is used to follow oxygen saturation. The patient performs a “free run” on a treadmill, with noseclips in place, but without a mouthpiece. Jogging on a treadmill is the most “asthmagenic” exercise because it mimics natural exercise and uses many muscle groups. This protocol also permits the technologist to watch and listen to the child without a mouthpiece in place. Evaluation of hyperventilation and/or stridorous respirations can be made. Several of the symptoms manifested (i.e., intense shortness of breath and sternal chest pain) should also be noted. The speed and elevation of the treadmill are increased every minute to increase the patient’s heart rate to approximately 85% of the maximal HR and sustained at this level for 6-8 minutes. This equates to a HR of 170-180 for at least 6 minutes. The entire exercise study should take no more than 8-10 minutes and should end abruptly without a cool-down period. Following exercise, the airways cool rapidly, and it is felt that the rapid change in temperature and/or humidity causes an inflammatory response that further elicits a bronchospasm. Post-exercise spirometry is performed every 3-5 minutes until 20-30 minutes after exercise. Laboratories differ as to the parameter and percent decrease needed to signify EIB. A decrease in the FEV₁ of 15%, often associated with a decreased FEV₁/FVC, is considered diagnostic of EIB. Some laboratories consider a drop of 10% or greater in the FEV₁ as a significant decrease. Maximal bronchoconstriction most often occurs 6-12 minutes after exercise. Cough, desaturation, and worsening shortness of breath usually accompany changes in pulmonary function. Researchers now question whether repeated exposure in cold weather sports, ice rinks, chlorinated pools, and high pollution climates causes chronic airway inflammation and eventual remodeling of the airways. This may be particularly relevant in elite endurance athletes, as well as in children whose lungs are still growing and developing. Clinicians should be mindful, however, of effort-related problems after exercise. A proportionate decrease in flows and volumes immediately after exercise is suspect for poor patient effort or technique-related problems.