The Future of Aerobic Exercise Testing in Clinical Practice: Is it the Ultimate Vital Sign?

Ross Arena; Jonathan Myers; Marco Guazzi

Future Cardiol. 2010;6(3):325-342.

Improving the Assessment & Utilization of Aerobic Exercise Testing in Clinical Practice

Aerobic exercise testing is well established and clinically accepted in patients with suspected or confirmed coronary heart disease as well as in patients diagnosed with HF, interstitial lung disease and PAH.^{[13,25,26,111]} Moreover, referral for CPX in patients with unexplained DOE is also an accepted clinical indication that is frequently utilized.^[13] However, with the exception of patients with HF undergoing CPX, there may be an underappreciation of the prognostic value of aerobic capacity. For example, stress testing laboratories generally focus on ECG changes and the results obtained from nuclear imaging studies, but may give little attention to the clinical importance of peak MET level. Other variables with clinical value such as the HR response to exercise and HRR are frequently not considered. While aerobic capacity garners appropriate clinical attention in chronic disease populations such as HF, other important exercise variables, such as ventilatory efficiency (i.e., VE/VCO₂ slope), are often overlooked. Fortunately, these issues are easily overcome through educating clinicians on all aerobic exercise test variables that warrant consideration. As such, aerobic exercise testing already enjoys a strong foundation in clinical practice, particularly in those with suspected or confirmed cardiovascular or pulmonary disease. A larger challenge is making the case for the clinical expansion of aerobic exercise testing in the apparently healthy/asymptomatic population. The available data clearly support the prognostic value of aerobic exercise testing in such individuals, a sentiment reinforced by the American Heart Association's scientific statement on performing this assessment in asymptomatic adults.^[37] What is currently missing however, is evidence demonstrating identification of these individuals at increased risk for adverse events through aerobic exercise testing subsequently improves prognosis and reduces healthcare expenditures. The availability of such evidence would greatly improve the argument for expanding aerobic exercise testing in primary prevention.

The expansion of aerobic exercise testing in clinically appropriate circumstances will likely not occur if physicians are expected to perform or directly supervise this procedure. Fortunately, nonphysician health professionals, such as the exercise physiologist prepared at the masters or doctorate level, are appropriately trained to safely conduct the aerobic exercise test and interpret all relevant data.^[18,112] Using a clinical model where an appropriately trained and experienced exercise physiologist manages the daily operations of an aerobic exercise testing laboratory for a supervising physician, who is readily available if needed, would address the increased personnel requirements for expansion of this valuable assessment procedure.

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Cite this: The Future of Aerobic Exercise Testing in Clinical Practice: Is it the Ultimate Vital Sign? - Medscape - May 01, 2010.

Abstract and Introduction
Key Principles of Aerobic Exercise Testing
Prognostic Applications of Aerobic Exercise Testing
Identifying Risk for the Future Development of Cardiovascular Risk Factors
Diagnostic Applications of Aerobic Exercise Testing
Improving the Assessment & Utilization of Aerobic Exercise Testing in Clinical Practice
Utilization of Aerobic Exercise Testing Data in Clinical Practice
Conclusion
Future Perspective
References
Sidebar

Table 1. Key exercise testing variables.
	Relevance	Units	Normal exercise response	Population(s) where variable should be assessed
Exercise HR	Insight into cardiac exercise response: cardiac output = heart rate × stroke volume; lower at a given submaximal workload in fitter individuals and those without cardiac dysfunction secondary to better stroke volume	Beats per min	No β-blocking agent: linear response to progressive exercise test; ~10 beats/MET; achieve at least 80% of predicted maximal heart rate with good effort	All populations
HRR	Difference between maximal and recovery HR; insight into the speed of parasympathetic reactivation	Beats per min	Should be more than 12 beats during 1 min	All populations
Exercise BP	Insight into cardiac response to exercise and left ventricular afterload	mmHg	Progressive increase in systolic blood pressure with increasing workloads; 10 mmHg/MET (both male and female); ~210 mmHg and ~190 mmHg expected upper range for males and females, respectively; diastolic blood pressure remains same or slightly decreases	All populations
Electrocardiography	Insight into cardiac rhythm; allows for identification of rhythm or waveform abnormalities during exercise	Seconds for interval and millivolts for amplitude calculations	P wave: amplitude increase in inferior leads; PR segment: shortens and slopes downwards in inferior leads; decrease in R-wave amplitude of lateral leads at maximal exercise and first minute of recovery paralleled by increase in S-wave; J-point depression and increase in ST-segment slope; increase in T-wave amplitude; no deviation from normal sinus rhythm	All populations
Pulse oximetry	Indirect assessment of arterial oxygen saturation	Percentage	≥95% at rest and throughout exercise	Individuals with unexplained exertional dyspnea, interstitial lung disease, suspected or confirmed pulmonary arterial hypertension
Subjective symptoms	Quantifies perception of exercise test response; exertion, dyspnea and angina assessed by different numeric scales with unique verbal anchors	None	Perceived exertion progressively increases with increasing workload; dyspnea and angina not normal perceived limitations to exercise	All populations
METs	Primary measure obtained from exercise testing; method for expressing VO₂; 1 MET = 3.5 ml O₂·kg⁻¹·min⁻¹; used when estimating VO₂ from workload; higher MET level reflects better cardiac function and health, specifically, progressively higher MET levels reflect better cardiac function as described by modification of the Fick equation (VO₂ = Q × a-VO₂ difference)	None	Dependent on age and sex	All populations
VO₂	Primary measure obtained from exercise testing; expression of VO₂ when measured by ventilatory expired gas; maximal designation used in apparently healthy populations, implies a plateau in VO₂; peak designation typically used in patient populations and implies no plateau; higher peak VO₂ reflects better cardiac function and health, specifically, progressively higher MET levels reflect better cardiac function as described by modification of the Fick equation (VO₂ = Q × a-VO₂ difference)	mlO₂·kg⁻¹·min⁻¹	Dependent on age and sex	All populations
Percent-predicted aerobic capacity	Expression of peak/maximal METs or VO₂ in relation to predicted values	Percentage	≥100% predicted	All populations
VO₂ at ventilatory threshold	Submaximal workload where theoretically oxygen demand for aerobic energy production begins to outpace oxygen supply to working skeletal muscle; detectable with ventilatory expired gas analysis and is estimate of anaerobic threshold	mlO₂·kg⁻¹·min⁻¹	~47–64% of maximal aerobic capacity; influenced by exercise habits and genetic predisposition	All populations
Peak respiratory exchange ratio	Ratio of VCO₂/VO₂ measured by ventilatory expired gas analysis Best indicator of subject effort during exercise	No units	Value of ≥1.10 indicates excellent subject effort	All populations
Ventilatory efficiency (VE/VCO₂)	Insight into the coupling of pulmonary ventilation and perfusion; expressed as a slope using all exercise data or a ratio at ventilatory threshold/peak exercise; measured by ventilatory expired gas analysis	No units	<30	Individuals with unexplained exertional dyspnea, interstitial lung disease, suspected or confirmed pulmonary arterial hypertension
P_ETCO₂	Insight into the coupling of pulmonary ventilation and perfusion and augmentation of cardiac output during exercise; measured by ventilatory expired gas analysis	mmHg	36–42 mmHg at rest; increases by 3–8 mmHg during exercise at mild-to-moderate workloads; decreases at maximal exercise	Individuals with unexplained exertional dyspnea, interstitial lung disease, suspected or confirmed pulmonary arterial hypertension
Pulmonary function testing	Battery of variables including forced vital capacity, forced expiratory volume in 1 s, forced expiratory flow during the middle half of expiration and peak expiratory flow; majority of ventilatory expired gas analysis systems capable of performing pulmonary function testing	Liters or liters per second	Normal values influenced by age, sex and body habitus	Individuals with unexplained exertional dyspnea
VE/MVV	Normal maximal exercise response typically does not elicit MVV; measured by ventilatory expired gas analysis system	No units	≤80%	Individuals with unexplained exertional dyspnea

BP: Blood pressure; HR: Heart rate; HRR: Heart rate recovery; MET: Metabolic equivalent; P_ETCO₂: Partial pressure of end-tidal carbon dioxide; VE/MVV: Minute ventilation/maximal voluntary ventilation; VO₂: Peak/maximal oxygen consumption.
Data adapted from.^{[19,20,25,26,28–30]}

Table 2. Conditions, physiologic mechanisms and key cardiopulmonary exercise testing variables in the assessment of patients with unexplained dyspnea on exertion ^†.
Condition	Physiologic mechanism	Ventilatory efficiency	Pulmonary function testing	Pulse oximetry	Hemodynamics
Condition	Physiologic mechanism	CPX Variables
Exercise-induced bronchospasm	Exertion triggers constriction of large airways	VE/VCO₂ and P_ETCO₂ normal	Development of obstructive pattern following exercise compared with baseline values; VE/MVV abnormally high; ≥15% decrease in forced expiratory volume in 1 s or peak expiratory flow following exercise is diagnostic criteria for exercise-induced bronchospasm (see Figure 2)	Normal	Normal response
Pulmonary gas exchange abnormalities	Two mechanisms: – Interstitial lung disease resulting in respiratory muscle fatigue and ventilation–perfusion abnormalities – Pulmonary arterial hypertension resulting in ventilation–perfusion abnormalities	VE/VCO₂ may be abnormally elevated and P_ETCO₂ may be abnormally decreased with both mechanisms; level of abnormality reflects disease severity	Abnormal at baseline with interstitial lung disease (obstructive or restrictive pattern) and no change post-exercise; VE/MVV abnormally high; normal at baseline and no change post-exercise with pulmonary arterial hypertension; VE/MVV normal	May drop with exercise; reflective of increasing disease severity	Normal response
Hypertensive response to exercise	Excessive increase in blood pressure with physical exertion raises afterload to levels that left ventricular output cannot match; increasing pulmonary pressure	VE/VCO₂ and P_ETCO₂ typically normal; may become abnormal if test continues for longer period as excessive increase in blood pressure continues to rise	Normal at baseline and no change post-exercise; VE/MVV normal	Normal	Abnormally high systolic and possibly diastolic blood pressure response
Hypotensive response to exercise	Acute decline in left ventricular performance secondary to valvular (i.e., aortic stenosis) or contractile (myocardial ischemia) abnormalities	VE/VCO₂ and P_ETCO₂ typically normal; may become abnormal if test continues for a longer period as drop in blood pressure continues	Normal at baseline and no change post-exercise; VE/MVV normal	Normal	Acute drop in systolic blood pressure

^†See Table 1 for normal exercise values.
P_ETCO₂: Partial pressure of end-tidal carbon dioxide; VE: Minute ventilation; VE/MVV: Minute ventilation/maximal voluntary ventilation; VCO₂: Maximal carbon dioxide consumption.

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The Future of Aerobic Exercise Testing in Clinical Practice: Is it the Ultimate Vital Sign?

Improving the Assessment & Utilization of Aerobic Exercise Testing in Clinical Practice

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