1. (D) Body weight. Maximum oxygen uptake is closely related both to cardiac output, which in turn is related to heart size and blood volume, and the mass of the working muscles. The more work/exercise a patient does, the more oxygen uptake will be needed, and larger people with more muscle mass can perform more work. Age, sex, lean body mass, body weight, and height will thus to some degree each correlate with V̇O_2max, though body weight is generally the most common way of predicting V̇O_2max in pediatric patients. Lean body mass would be more accurate but requires more extensive measurement issues. Postpubertal males tend to have a higher lean body mass than females, which causes differences in V̇O_2max between the sexes, but there is also great variation within each sex, and younger children generally show less male-female difference in V̇O_2max than older children. In children, muscle mass (and V̇O_2max) increases also changes with increasing age (and this is the usual way of referencing V̇O_2max in adults, but V̇O_2max is decreasing rather than increasing with age), though age can be misleading around the age of puberty. Previous studies have revealed an exponent of body length (1.5 to 3.21) has also been unreliable, likely because body mass can vary considerably at any given height.

A caveat is that boys and girls diverge at puberty, with boys becoming taller and gaining muscle mass, whereas height in girls levels off and there is an increase in the weight or adipose tissue. Whereas V̇O_2max is similar in young boys and girls and increases with weight in both sexes, there is generally a plateau in V̇O_2max in girls between ages 12 and 18.

There are a couple of other complexities here. First, V̇O_2max can be expressed in absolute (mL/min) or relative (mL/kg/min) terms. Cardiorespiratory fitness (CRF) is generally rated according to V̇O_2max in mL/kg/min and will correlate well with treadmill performance (where excess weight is not a hindrance), whereas V̇O_2max in mL/min correlates better with cycle performance (where excess weight is not a hindrance since the frame of the cycle bears with height and work is related only to the resistance of turning the pedals). A lean patient will thus outperform a heavier patient on the treadmill, whereas the opposite will occur on the cycle ergometer. To achieve a constancy of V̇O₂ in mL/kg/min versus time on a cycle protocol, workloads will need to be adjusted for weight, whereas this is not necessary for treadmill exercise.

Second, level of physical activity, particularly aerobic training, can markedly affect V̇O_2max, perhaps by as much as 35% to 40%. This means that any indexing of V̇O_2max according to body weight, age, or any other variable will yield only modest correlations since varying levels of activity are so contributory.

2. (D) Cardiorespiratory or aerobic fitness is defined as the highest rate of oxygen consumption, V̇O_2max, achieved during exercise. The highest V̇O_2max that can be achieved depends on the type of work performed and the muscle mass utilized during exercise. One uses more muscle groups when exercising on a treadmill—which requires energy expenditure to bear the patient’s weight—than when using the ergometers listed in the question. On average, values for V̇O_2max in children, like adults are 5% to 15% higher on the treadmill than the cycle ergometer. Aerobic fitness data on children aged 8 years and above show that the absolute values (V̇O₂ in L/min) or peak V̇O₂ increases during childhood and mostly attributable to the increase in muscle mass and strength in both sexes.

3. (C) Stroke volume is dependent on the left ventricular end-diastolic volume and ejection fraction. Stroke volume increases 50% to 100% above baseline during exercise. Stroke volume primarily increases early in exercise (up to an HR of about 130 bpm) due to enhanced venous return and to a less extent, cardiac contractility, but will increase little thereafter as it becomes limited by progressively shorter diastolic filling time.

In comparison, HR increases two- to threefold—even higher for trained athletes who may have resting rates of <50 bpm with peak rates of 200 bpm or higher. Minute ventilation may increase more than 10-fold with exercise—due to a two- to threefold increase in respiratory rate and even larger increases in tidal volume. Oxygen consumption will have the greatest increase of all these physiologic variables, being the product of HR × stroke volume × arteriovenous oxygen difference, producing an overall increase of 10- to 20-fold from rest to peak exercise.

4. (D) In the normal patient, exercise is associated with an increase in cardiac output, HR, and ejection fraction. A decrease in the total peripheral resistance will occur, and no change occurs in central venous pressure. These changes primarily are due to the large increase in sympathetic activity during exercise. The decreased total peripheral resistance primarily is due to decreased skeletal muscle vascular resistance allowing more blood flow to the muscles. Sympathetic stimulation of the beta fibers in skeletal muscle, heart, and lungs cause dilatation of the arterioles, which more than compensates for the constriction produced by stimulation of alpha fibers in the skin and splanchnic beds. Finally, central venous pressure remains relatively unchanged due to the compensatory mechanisms of the skeletal muscle pump and the respiratory pump that both promote increased venous return without significant change in central venous pressure.

5. (E) Isometric exercise consists of constant muscle length (no change) against a force/tension. Examples include holding a weight in a fixed position, pushing against a door frame, or hand grip exercise. During isometric exercise, systolic and diastolic blood pressure both increase significantly. In isotonic exercise, like cycling or walking/running, however, cardiac output increases while peripheral resistance decreases.

6. (E) During isotonic exercise, systolic blood pressure increases due to increased cardiac output (with more forceful ejection of larger boluses of blood into the aorta). The systolic blood pressure increase during exercise is attenuated, however, by a reduction in total systemic resistance. Diastolic blood pressure normally decreases by at least 10 mm Hg with exercise. (Note: Measurement of diastolic blood pressure during exercise can be challenging, and the laboratory must decide on recording the 4th or 5th Korotkoff phase or both.) Blood pressure changes depend on the patient’s size as well as gender. Larger patients and/or males will have a higher blood pressure at rest and during exercise compared to smaller patients and/or females. Because of greater arterial compliance, exercise blood pressures are generally lower in children than adults. Higher exercise blood pressures are typically seen during cycle ergometry (due to contribution isometric grip on the handlebars) versus the treadmill.

7. (A) There is a linear relationship between HR and V̇O_2max until maximum workload is reached. Every individual has a maximum HR that is achievable, usually ranging between 195 and 215 bpm in adolescents. Normal oxygen consumption (V̇O_2max) is roughly 35 (females) to 45 mL/kg/min (males), though higher V̇O_2max would be seen in athletes. Therefore, an HR of 200 bpm and oxygen consumption of 45 mL/kg/min would be normal for a 15 year old. HR of 145 bpm and oxygen consumption of 1.0 L/min would represent a submaximal exercise test/effort or chronotropic insufficiency.

8. (D) The accepted maximum HR for patients 5 to 20 years of age is roughly 195 to 215 bpm. However, for patients >20 years of age, various HR prediction equations might give estimates of peak HR for a 21-year-old female of 193 to 199 bpm. Therefore, the best estimate of this patient’s maximum HR is 196 bpm. However, there is a large enough standard deviation in peak HR to make (C) 183 bpm a possible, though less probable, peak HR for this woman. Inability to keep up with the treadmill, sweating, and loud, labored breathing might be other signs that exercise was really maximal. These signs with a peak HR of only 123 (A) or 158 (B) might be a cause for further investigation, unless the electrocardiogram showed the abnormality (e.g., AV block). A peak HR of 229 (E) would again prompt close examination of the electrocardiogram, as this is suggestive of some form of supraventricular tachycardia (SVT).

We might also consider why the performance was so limited if the HR of 196 bpm (assuming sinus rhythm) was achieved, indicating a maximal effort. Obviously, severe obesity could be the cause or, conversely, an eating disorder if BMI was extremely low. A young woman of this age might also suffer from anemia, and recent, prolonged illness producing severe deconditioning and postural orthostatic tachycardia syndrome (POTS) could also cause a poor performance despite a good heart rate response.

9. (B) During exercise, minute ventilation increases to provide more oxygen and carbon dioxide exchange with the blood. This occurs by an increase in both ventilation frequency (respiratory rate) and tidal volume. Young children have relatively smaller lungs relative to height versus adults, and the lung volume increases with age, allowing for greater tidal volumes. Oxygen consumption also increases with growth and maturation, as there is a greater muscle mass to perform work and consume oxygen. This is what drives higher exercise ventilation. Tidal volume and ventilation during exercise will continue to increase with increasing age, at least until adult height and torso size are attained. However, the maximum respiratory rate that can be achieved at peak exercise is unchanged or may even decrease slightly. This is a consequence of increasing peak expiratory force with age, on one hand, but larger volumes of air to move, on the other hand.

10. (E) Regular, repetitive aerobic exercise will usually result in improved cardiorespiratory fitness and V̇O_2max fitness. Physiologic changes that occur with increased exercise include higher mass of mitochondria and aerobic enzymes in the trained muscles. This increases oxygen extraction and utilization at the tissue level. Heart volume and weight also increase, and there is an increased blood volume. These changes enhance stroke volume, and there is a secondary increase in vagal tone with decreased resting HR. With intense, prolonged training, there may also be some remodeling of the sodium and potassium channels in cardiac muscle, contributing further to a lower resting HR. Peak HR is generally unchanged, though there are published studies suggesting a small decrease, but heart rate reserve (peak resting heart rate) is significantly increased. This greater increase in HR reserve along with higher stroke volume translates to higher cardiac output.

11. (C) 1 watt = 6.12 kpm/min. Both are measures of power = rate at which work is being performed. 1 MET = 3.5 mL/kg/min. Watts represents power, as does METs, so MET hours measures power × time = work. Body weight does not affect the MET level on a treadmill. Increased body weight translates to more work being performed per time, but METs represents mL/kg/min, so body weight is canceled out of the equation. Arm cycle exercise requires approximately 1.5 times as much V̇O₂ per watt as does leg cycling.

12. (C) Of the answers listed, the only “higher-risk condition” for exercise testing would be primary pulmonary hypertension according to AHA guidelines for pediatric stress testing. An ASD would not be higher risk for exercise testing. A left-to-right shunt would not cause increased hypoxia with exercise. A right-to-left shunt would—though that is not a reason to avoid an exercise test or contribute to significantly increased risk on the test. In some cases, the direction of the shunt changes with exercise—bidirectional shunts become steadily right to left. A VSD will likely decrease V̇O_2max but does not affect patient safety. Regurgitant lesions are graded as lower risk regardless of severity. Repaired tetralogy per se is also not a contraindication to exercise testing. However, a history of any of these conditions, including primary pulmonary hypertension may be an indication for exercise testing to assess symptoms, determine exercise capacity, and adjust therapy, including surgical referral.

13. (E) All of these conditions might potentially result in untoward events during maximal exercise testing except Ebstein anomaly. All regurgitant lesions are considered lower risk regardless of severity. However, for evaluating patients in these categories, the potential benefit of the information gained from the exercise test may exceed the risk of testing in experienced exercise labs with good understanding of the underlying anatomy and physiology of patients with cardiac disease and readily available emergency equipment and code teams that can respond promptly.

14. (A) As one becomes better conditioned, rest HR declines and V̇O_2max increases but HR_max does not change. As one becomes deconditioned, rest HR increases and V̇O_2max decreases but HR_max remains the same. If one fails to reach predicted HR_max, either the effort was submaximal or the patient has chronotropic insufficiency.

15. (E) The VAT refers to a point beyond which both aerobic and anaerobic metabolism contributes to the work done. This is seen as a disproportionate increase in CO₂ production (and minute ventilation) relative to oxygen uptake thought to reflect to the contribution of anaerobic metabolism to energy production. In adults, a disproportionate increase in lactate is also frequently observed. Decompensated acidosis is not synonymous with VAT. Decompensated acidosis occurs later in exercise, after the VAT has occurred. V̇O₂ at VAT less than 40% is abnormal and is indicative of reduced cardiac output or abnormal O₂ delivery to the tissues.

16. (B) The ventilatory equivalent for oxygen is minute ventilation divided by oxygen uptake (V̇_E/V̇O₂). Patients with cyanotic heart disease typically have more hypoxemia at rest and during exercise. The presence of a large right-to-left shunt is a major determinant of this abnormal exercise response. At peak exercise, cyanotic patients increase their minute ventilation (V̇_E) disproportionately to their oxygen uptake (V̇O₂), resulting in a higher ventilatory equivalent for oxygen than acyanotic patients. The blood oxygen saturation and maximum oxygen uptake (V̇O_2max) will be lower, not higher, than for an acyanotic patient. HR and blood pressure should not be systematically affected by the right-to-left shunt.

17. (C) There is no one “best” exercise protocol. The choice of exercise protocol depends on the complaints and exercise symptoms as well as the fitness of the child being tested. For example, in children with reduced exercise capacity due to chronic conditions, an exercise protocol in which the work rate increases slowly is preferred; otherwise, the test will be prematurely terminated due to fatigue without stressing the cardiopulmonary system adequately. The ramp treadmill protocol is becoming more and more popular due to a somewhat constantly increasing workload (small, frequent increments), especially during cycle ergometry testing. The ramp can be adjusted to have the test last 8 to 12 minutes, which is considered optimal. However, this protocol does not allow assessment of steady-state exercise due to the constant changing workload. The Bruce and modified Bruce treadmill protocols were developed for testing adult patients, but they are often used to also test children—and some normative values have been published, particularly for the standard Bruce protocol. Protocols based on HR response are difficult to implement and are not generally used in clinical practice.

18. (C) At rest, tidal volumes are low and respiratory dead space (in which gas exchange does not occur) maybe be as high as 30% of the tidal volume. With increased work, the ventilatory response includes increased minute ventilation due to increases in both respiratory rate and tidal volume. At the onset of exercise, tidal volume increases predominate while respiratory rate increases only modestly. Hence ventilation becomes more efficient with dead space falling to 10% to 15% of the tidal volume, and V̇_E/V̇CO₂ decreases. At high levels of exercise, above the VAT, tidal volume begins to plateau as expiratory flow limits are reached, so respiratory rate accounts for most of the increase. As a result, V̇_E/V̇CO₂ may increase, indicating less efficient ventilation. Normal patients terminate exercise because cardiac output can no longer increase, even though there typically is still ventilatory reserve available (20% to 30% in healthy individuals with normal heart and lungs). Diffusion limitation is rarely a problem during routine clinical exercise testing, though it can be observed in patients with restrictive lung disease or heart failure.

19. (D) The acetylene-helium rebreathing is an indirect Fick technique used to measure cardiac output noninvasively. It is dependent upon even distribution of the inspired gas throughout the lungs, so it will not be a reliable method for cardiac output measurement in patients with lung disease that involves mismatching of ventilation and perfusion or in the presence of significant intracardiac shunts. Indirect Fick techniques are used because they avoid the arterial puncture and jugular vein catheterization required in direct Fick techniques. The acetylene-helium rebreathing technique is easier to perform during cycle ergometry versus treadmill exercise. The acetylene-helium rebreathing technique is generally better tolerated than the older, CO₂ rebreathing technique, especially in younger children.

20. (E) The sphygmomanometer cuff should have a bladder length that covers at least 80% of the circumference of the upper arm and at least 40% width of the upper arm. Improper cuff size may cause measurement artifacts. Blood pressure increases with age in children and is generally higher in boys than girls, especially after puberty. While an exercise blood pressure of 200 mm Hg is above the median for healthy boys 15 to 17 years of age, it is common enough to be seen on about 8% to 9% of exercise tests and poses no immediate threat of harm to an otherwise normal patient. Athletes may generate higher exercise blood pressure due to higher cardiac output. Blood pressure usually falls in early active recovery due to venous pooling as the muscle pumping action decreases as the speed of the treadmill decreases. This may cause mild lightheadedness. Symptoms will quickly resolve, and blood pressure will increase as active recovery progresses. Abruptly stopping the treadmill at peak exercise without an active recovery may precipitate presyncope or even syncope. Fall in systolic blood pressure and pulse pressure with increasing workload suggests cardiac dysfunction and is an indication for termination of the test.

21. (B) With improved fitness, a patient can complete more work; thus, a higher maximum V̇O₂ is achieved. Choice (E) also shows a lower V̇O_2max, but values this high would be characteristic of athletes in endurance sports, not large, muscular American football players. Maximum minute ventilation is a product of tidal volume and respiratory rate (V̇_E = Vt × RR). Minute ventilation at rest is roughly 9 L/min. The rule of nine states that for every 25 watts increase the minute ventilation increases by 9 L/min. Maximum minute ventilation (V̇_E) also increases with improved fitness and might thus decrease with deconditioning, but these values are much too low for a large 20-year-old male. An athlete’s ability to reach maximum HR will not be limited by deconditioning, assuming his injury was fully healed such that he was not limited by musculoskeletal factors on the test. The oxygen saturation during an exercise test should not decrease as a result of deconditioning. A value of 98% at peak exercise is normal for a team sport athlete, though extremely well-trained endurance athletes may show mild desaturation because their cardiac outputs become too high for blood to be fully oxygenated in the lungs (which, unlike the heart, do not increase in size with training).

22. (C) MVV is obtained at rest and difficult to perform correctly and does not compare well to the actual breathing during exercise. Owing to the dependence on the patient’s effort, MVV must cautiously be used for suggesting pulmonary limitation. The ATS/ACCP statements on CPET testing recommend the use of FEV₁ × 35 or FEV₁ × 40 as the predicted MVV. At the point of exercise termination in a normal patient, minute ventilation (V̇_E) is 60% to 80% of MVV. Patients with lung disease and pulmonary limitation will achieve V̇_E >70% by tapping into the ventilatory reserve. Tidal flow-volume loops are a more accurate method of assessing pulmonary limitation to exercise than MVV. Tidal flow-volume loops also have the advantage of assessing vocal cord dysfunction, which is an increasingly common cause for exertional dyspnea.

23. (D) African-American children have a higher blood pressure response to exercise than Caucasian children. The same holds true for larger-sized children when compared to smaller-sized children. Of similar-sized patients, boys have a greater blood pressure response than girls, especially after puberty. During exercise, contractility improves resulting in lower end-systolic volume. During treadmill or cycle ergometer exercise, the diastolic pressure generally decreases (though diastolic blood pressure increases during isometric exercise). Blood pressure increases during exercise predominately occur by increased cardiac output. The total systemic resistance generally decreases during exercise.

24. (C) Acetylene-helium rebreathing technique, which is dependent on even distribution of the inspired gas throughout the lungs, is used to measure cardiac output indirectly by measuring effective pulmonary blood flow in the absence of significant intracardiac shunts. It will not be a reliable method of cardiac output measurement in patients with lung disease that involves mismatching of ventilation and perfusion or those patients with significant intracardiac or intrapulmonary shunts. Therefore, the only patient with an insignificant intracardiac shunt of those listed would be the 14-year-old boy with a patent foramen ovale with trivial left-to-right shunt.

25. (E) Acetylene-helium rebreathing technique is noninvasive, and it is usually well tolerated by children. This method directly measures the effective pulmonary blood flow in the absence of significant intrapulmonary or intracardiac shunts. This allows for an effective method to estimate cardiac output. Acetylene diffuses from the alveolus into the pulmonary capillary blood, and thus the acetylene concentration declines relative to the volume of effective pulmonary blood flow. This technique depends on an even distribution throughout the lungs.

26. (B) In the normal, healthy child, the cardiovascular system will be the limiting factor to exercise—assuming an appropriate exercise protocol that does not exceed a young child’s capacity for work from a muscular standpoint. Maximum cardiac output will be achieved when the maximum HR limits ventricular filling during diastole and in turn stroke volume. The pulmonary system in a normal, healthy child will not limit exercise capacity. Minute ventilation (V̇_E) and work have a linear relationship until the ventilatory anaerobic threshold (VAT) is achieved. At this point, there is a disproportionate increase in V̇_E relative to V̇O₂. At the point of exhaustion, V̇_E is generally 60% to 80% of the maximum ventilatory volume. This percentage increases with aerobic fitness.

27. (A) A few equations for exercise are needed to calculate the total work accomplished as well as the total power achieved. Work is defined by force multiplied by distance or, in other words, the force needed to move a mass a given distance. The unit for work is the Newton-meter or joule (J). Force is mass × acceleration. Power is the work performed per unit time. The other equations listed are not correct. On exercise testing, power is the quantity usually expressed. For cycle ergometry, it can be kilopond meters/min or watts (1 watt = 6.12 kilopond meters/min). Watts can be converted to METs, which is an expression of power based on rate of oxygen consumption (1 MET = 3.5 mL of O₂ consumed/kg of body weight/min).

28. (C) For patients between the ages of 5 and 20, the HR_max reported in several large cohorts ranges from 195 to 215 bpm with little consistent impact of age or sex on HR. For patients >20 years of age, however, the maximum HR will decrease with increasing age. The most commonly used equation to determine a patient’s maximum HR is a simple HR_max = 220 – age, though other formulas with larger datasets have been published, including HR_max = 210 – 0.65 × age. Some studies have produced different equations for women (210 – 0.8 × age) versus men, reflecting perhaps different hormonal changes with age. The reason for this decline in HR_max is decreased nerve conduction; during aging, a gradual shift toward higher sympathetic versus parasympathetic balance attenuates the decline in HR with age. Stroke volume increases early in exercise with little change thereafter, except in highly trained endurance athletes. The HR increases, then accounts for increasing cardiac output. With exercise, the total systemic vascular resistance declines. Systolic blood pressure will increase with isotonic exercise while the diastolic blood pressure remains relatively unchanged. With isometric exercise, both systolic and diastolic blood pressures rise.

29. (B) Maximal V̇O₂ achieved is dependent on age, sex, hemoglobin level, and type of work completed. As age increases in childhood, the maximal V̇O₂ achievable also increases. Between the sexes, the maximal V̇O₂ achievable is relatively the same before puberty (about 35 mL/kg/min at age 11), but thereafter, males have a higher V̇O_2max (45-50 vs. 35-40 mL/kg/min at age 17). Anemic patients have a lower achievable V̇O_2max than patients with normal hemoglobin; hemoglobin of 10 g/dL would lower V̇O_2max by about 15% to 20%. By age 17, V̇O_2max would have largely reached adult levels, so the added 2 years of age in the anemic patient versus the normal 17-year-old boy would not be expected to matter significantly. Finally, achievable V̇O_2max depends on the type of work completed; the more muscle groups involved, the higher the V̇O₂ achieved. Therefore, a higher V̇O_2max is achieved with treadmill ergometry > cycle ergometry > arm crank ergometry > hand grip ergometry. Therefore, the older, nonanemic male would likely achieve the highest V̇O_2max during cycle exercise testing. The arm ergometer test might be expected to produce a V̇O_2max of 65% to 75% of the leg cycle ergometer test. Caveat: level of physical activity and degree of exercise training can greatly impact V̇O_2max. A 17-year-old girl on the cross-country team could certainly achieve a higher V̇O_2max than her sedentary 17-year-old male classmate; even the 11-year-old boy could have the highest V̇O_2max of the group based on level of physical activity—and degree of adiposity (if the 17-year old children were obese), which is another important contributor to V̇O_2max.

30. (D) In a well-trained athlete higher blood volume and lower resting HR will result in increased end-diastolic volume—producing a higher stroke volume at rest (and during exercise). A decreased left ventricular end-systolic dimension volume during exercise will also occur as a result of greater contractility.

31. (C) Bicuspid aortic valve with mild AR should not affect cardiac output and V̇O_2max during exercise. Though the heart has normal macrostructure in LTQS type 1, the beta blocker will reduce peak HR and V̇O_2max. The patient with ccTGA has a systemic right ventricle with likely a significant reduction in cardiac output. Ebstein anomaly to varying degrees reduces forward RV stroke volume resulting in decreased blood flow to the lung. Anomalous pulmonary veins in Scimitar syndrome recycle oxygenated blood back to the inferior vena cava, reducing LV filling and decreasing A-V̇O₂ difference in mixed venous blood.

32. (A) Of the answers listed, the only condition not considered as higher risk to exercise testing in pediatric patients is second-degree AV block. Mostly likely, a type 1 seconddegree block will resolve with exercise, whereas a type 2 will not—and ultimately limit exercise, but not constitute a risk of sudden death. Severe aortic stenosis with clear symptoms or an ejection fraction <50% would be an indication for surgery; exercise testing is not required or recommended. Known exercise-induced arrhythmias can be higher-risk conditions; however, exercise testing is a useful provocative test in the diagnosis of CPVT and long QT syndrome—or to determine adequacy of antiarrhythmic therapy and confirm that defibrillator settings are appropriate. Therefore, exercise testing can be carried out in these patients. Finally, anomalous origin of a coronary artery might be a higher-risk condition, especially if it is a left coronary anomaly or a single coronary artery, but exercise testing is needed to help determine the necessity for operative repair.

33. (E) Neither treadmill nor cycle ergometry is superior to the other. Even children as young as 10 years can be tested using the child cycle ergometer or treadmill. However, there are advantages and disadvantages to each type. Small children generally cannot reach the pedals of a cycle ergometer designed for adult testing, but the availability of a child cycle ergometer circumvents this, and they may also need a lower front handrail on the treadmill for safety concerns. Treadmill ergometry will allow a patient to derive a higher V̇O_2max and HR due to the use of more muscle groups during exercise. However, the treadmill is potentially more dangerous due to the potential of the patient falling, especially if syncope is a potential concern or the patient has neurologic issues; and there is more noise and artifact while running when compared to stationary cycling. A more accurate and controlled measurement of work can be obtained with cycle ergometry. The patient is not moving as much back and forth and up and down as grade increases. And work/power changes are more closely tied to V̇O₂—especially with an electronically braked cycle ergometer when compared to a treadmill—where degree of handrail support and familiarity with treadmill walking may affect V̇O₂. Continuous video laryngoscopy, where a flexible laryngoscope is passed trans nasally to determine movements of the laryngeal structures during exercise to evaluate for vocal cord dysfunction/exercise-induced laryngeal obstruction can be safely done with the child in a seated position on a cycle ergometer.

34. (E) Exercise testing in AS patients can be helpful in the assessment of mild-to-moderate stenosis for significant ST segment changes with exercise as well as distinguishing between chest wall pain and more significant causes of chest pain. However, severe, symptomatic AS or severe AS with LVEF <50% is a contraindication to exercise testing; surgery is indicated for these patients. In AS, there is an inverse relationship between the total cardiac work performed and transaortic pressure gradient. Also, patients with more severe AS (i.e., higher transaortic gradient) have a lower increase in their blood pressure response during exercise than less severe AS patients. The higher the transaortic gradient, the more likely that ST segment changes occur. VT may also occur in the setting of AS. Dyspnea on exertion, poor blood pressure response, ST changes, limited exercise capacity, and VT are all considered to indicate poor prognosis in AS. Not surprisingly, it has been shown that patients with more severe AS achieve a lower V̇O_2max, though few patients with even moderate AS achieve a normal V̇O_2max, since many are treated with beta blockers limiting maximal HR. Several papers have demonstrated that survival in AS is impaired when V̇O_2max is <80% predicted. An important caveat is that transaortic pressure gradient is not the sole driver of exercise capacity in AS patients. The usual factors—amount of beta blockade, degree of adiposity, level of physical activity, and the presence of other diseases like coronary artery disease or COPD also influence exercise performance and V̇O_2max. Finally, there is a class of patients with low transaortic gradients despite severe AS according to valve area (<1.0 cm²) and valve area index (<0.6 cm²/m² of body surface area) who are at very high risk. A second caveat is that these data have been derived by studying outcomes in adults with mostly acquired AS, not pediatric patients with congenital AS. AS in pediatric patients is often part of a larger set of cardiac abnormalities requiring early surgical intervention even when AS is not severe enough to consider surgical intervention by itself.

35. (D) Unrepaired single ventricle patients will have reduced maximum aerobic power and excessive ventilation relative to V̇O₂ and V̇CO₂. Specifically, unrepaired patients with pulmonary atresia with VSD have exercise performance and maximum oxygen uptake when compared to first stage repaired or complete repaired patients as well as normal patients. Blood oxygen saturation levels in unrepaired and first-stage repaired patients are lower at rest than normal patients and decrease significantly with exercise. After complete repair, patients will have a relatively normal resting blood oxygen saturation level but may have a small decrease with exercise. Exercise capacity and peak V̇O₂ in repaired single ventricle patients normally does not improve to 100% or greater of normal for age and sex.

36. (B) A complete 12-lead ECG should be obtained at least once at rest, at each workload, and several times after completion. A typical recording includes at rest sitting, supine, and standing; then at each workload and peak exercise, as well as each minute (1 to 5 or 6) of recovery. At least three standard surface ECG leads should be continuously displayed and recorded during the exercise study as well as for 5 to 10 minutes after the study is completed. For fitness tests performed on healthy subjects where the ECG is primarily used to measure heart rate, sometimes only one surface lead is monitored, but this is inappropriate for testing patients with known or suspected cardiac disease, as the ECG provides more information than just HR response. Operators should have the option of switching between various combinations of those leads (i.e., inferior leads, anterior right, anterior left). Appropriate ECG electrode and lead placement should be used in all types of ergometry to limit artifact. Placing the electrode above bone rather than on muscle or adipose tissue usually improves the stability of the tracing and limits random motion artifact. Good skin cleansing with alcohol and abrading a small area with sand-paper to remove dead skin is important. Securing the ECG lead cables with an elastic band or knit shirt may be helpful, especially if the patient is obese or sweats profusely, and if treadmill running is expected. Vigorous exercise itself often produces ECG artifact even with good skin preparation, so obtaining a 12-lead ECG in the first 15 to 30 seconds of active recovery when the HR is still near the peak level attained during exercise is helpful in more accurately interpreting ST-T response. Owing to the typical noise artifact with treadmill exercise testing, the Korotkoff sounds, especially diastolic, can be very difficult to measure accurately. There is some variance as to whether diastolic pressure during exercise should be taken as the 4th or the 5th Korotkoff sound (the 5th phase sound can sometimes be heard down to 0 mm Hg), and some laboratories record both. Published data are mixed as to whether diastolic blood pressure provides any important and independent prognostic information. Direct blood pressure measurement through arterial access in the peripheral arteries will overestimate the central aortic pressure due to peripheral pulse amplification. Aortic puncture for the purpose of blood pressure measurement during exercise is seldom justified.

37. (B) Because of the right-to-left shunt and resultant increase in dead space, cyanotic patients hyperventilate in order to remove additional CO₂. Hence ventilation is disproportionately high relative to V̇CO₂ (and V̇O₂). Exercise capacity is reduced in cyanotic patients, but peak exercise HR is not likely affected. Because of reduced oxygen uptake relative to cardiac output, submaximal heart rates will likely be higher in the cyanotic patient. There is no clear indication of how diastolic blood pressure would be affected, though peak systolic blood pressure would likely be lower as less work could be performed and reduced pO₂ might be expected to promote lower vascular resistance at the level of autoregulation in the active muscles.

38. (E) The CO₂ rebreathing technique is one of the two most frequently used techniques (other being acetylene-helium rebreathing technique) for measuring cardiac output noninvasively. The CO₂ rebreathing technique is based on the Fick principle for CO₂ {Cardiac output = VEcontent} needs to be directly measured from systemic arterial blood pCO₂ or, noninvasively, by estimating this by using the Bohr equation. This is accomplished by solving for PaCO₂ (systemic arterial pCO₂): Vd/Vt = (PaCO₂ – PeCO₂)/PaCO₂. This technique is not well tolerated by all, especially children, because rebreathing CO₂ can cause dyspnea, an unpleasant taste, and a transient headache. This technique involves a few areas of potential error. These include the need to adjust CO₂ concentration used for the patient’s size and exercise intensity as well as taking into account dead space (mouthpiece, etc.).

39. (C) These heart rate changes are characteristic of pacemaker Wenckebach. The upper rate was likely set at 180 bpm. An atrial rate above 180 cannot be followed 1-to-1 by the ventricular lead, so it begins to drop beats. If the patient is not an athlete and is not reporting any limitations to physical activity, nothing may need to be done; otherwise the upper rate limit can be increased. Anomalous origin of the RCA may sometimes produce ischemia if there is a slit-like ostium and/or a long intramural course. SA node ischemia would manifest as a gradual slowing of the sinus rate, not dropped beats. An example of pacemaker Wenckebach with corresponding drop in V̇O₂ in a patient with repaired Shone complex is shown in Figure 7.14.

Figure 7.15 shows the low HR point at peak exercise and the return to 1:1 pacing in active recovery 2 minutes later.