Impact of Integrative Cardiopulmonary Exercise Testing (6)

Impact of Integrative Cardiopulmonary Exercise Testing (6)Interpreting Gas Exchange Measurments During Exercise
The responses of the cardiovascular system (heart and systemic circulation), pulmonary system (lungs and pulmonary circulation), and the exercising muscles must be closely coupled during exercise. Thus, there is interaction between the organs requiring increased transport of 02 and C02 and the organ systems responsible for delivery of 02 and C02 to and from the atmosphere. This is conceptualized in Figure 1. From this scheme of interaction between organ systems comes two important considerations. First, an abnormality of any part of a system may have a measurable effect on gas exchange during exercise. Second, there may be characteristic abnormalities in gas exchange that accompany specific disorders of a particular organ system. These two considerations form the basis for interpretation of the integrative cardiopulmonary exercise test. proventil inhaler
Basic measurements and derived measurements are shown in Table 2. Each variable is examined with a specific question about exercise performance and/or organ system dysfunction in mind (Table 3). For example, comparison of measured maximum Vo2 during exercise to the predicted value for that patient addresses the question of whether exercise capacity is abnormally reduced.

Figure-1

Figure 1. Scheme illustrating the interaction between the organ systems required to provide gas exchange between the exercising muscles and the atmosphere. Oxygen (O*) is provided to the mitochondria by coupled transport of 02 from the atmosphere into the lungs, the pulmonary circulation, the heart, and the systemic circulation. During exercise, the increase in 02 flow to the muscles is provided by increased ventilation (increased tidal volume and respiratory frequency) of the lungs, recruitment of the pulmonary circulation, increased cardiac output (increased heart rate and stroke volume), and dilation of the systemic circulation. These increases in (unction also accommodate the increase in C02 production from cellular respiration, resulting in increased elimination of C02 into the atmosphere. 

Table 2—Assessing Function with Physiologic Measurements during Exercise

PhysiologicMeasurement Function Assessed Abnormal Value May Mean
Maximum (peak) 02 uptake Oxygen transport capacity of heart, lungs, circulation Reduced capacity of one or more 02 transport systems
Electrocardiogram Balance between myocardial oxygen supply and demand; cardiac rhythm Myocardial ischemia; conduction defect; cardiac arrhythmia
Arterial blood pressure Increase in myocardial 02 requirement during exercise (SBP x HR); myocardial contractility; degree of peripheral vasodilation Poor myocardial contractility; failure of normal peripheral vasodilatation during exercise
AVo^Awork rate Appropriateness of the quantity of 02 taken up for the amount of work being performed Greater than normal proportion of work supported by anaerobic metabolism (low 02 transport capacity)
Anaerobic threshold Capacity of Oz transport to deliver 02 on a sustained basis (specific for type of work) Reduced 02 transport capacity for sustained work
VOj/heart rate (02 pulse) at maximum work rate Capacity of the heart to deliver 02 per heart beat (product of stroke volume and arterial-venous 02 difference) Low stroke volume or decreased ability of tissues to extract 02 from the blood
Heart rate (HR) reserve (predicted maximum HR — maximum exercise HR) During a symptom-limited exercise test, comparison of cardiac function to theoretical maximum Reduced exercise capacity is likely due to a noncardiac reason (high HR reserve)
Breathing reserve (maximal voluntary ventilation at rest — maximum exercise Ve) During a symptom-limited exercise test, comparison of ventilatory capacity to theoretical maximum Reduced exercise capacity is likely due to reduced ventilatory capacity (low breathing reserve)
Vd/Vt and arterial-end tidal Pco2 difference during exercise Proportion of high Va/Q lung units participating in gas exchange Disorder of lung resulting in maldistribution of high Va/Q type
Pa02 and alveolai^arterial Po2 difference during exercise Contribution of low Va/Q lung units to gas exchange Disorder of lung resulting in maldistribution of low Va/Q type

Table 3—Questions Addressed by Cardiopulmonary Exercise Testing

Question Example of Disorder Markers for Abnormality
1. Is exercise capacity reduced? Any disorder Maximum Vo2
2. Is the metabolic requirement for exercise increased? Obesity Vo2-WR relationship
3. Is exercise limited by impaired 02 flow? Heart; peripheral vascular; pulmonary vascular; anemia; hypoxemia; carboxyhemoglobin ECG; blood pressure; anaerobic threshold; blood lactate; HC03 threshold; AVo/AWR; Vo,/HR; COHb
4. Is exercise limited by reduced ventilatory capacity? Lung; chest wall Breathing reserve; Vd/Vt
5. Is there an abnormal degree of ventilation-periusion mismatching? Lung; pulmonary circulation P(A-a)Oz; P(a-ET)C02; Vd/Vt; Ve/Vco2
6. Is there a muscle oxygen or electron transport chain defect? Muscle mitochondria; muscle phosphorylase Blood lactate
7. Is exercise limited by a behavioral problem? Neurosis Breathing pattern
8. Is work output reduced because of poor effort? Poor effort with secondary gain HRR; BR; peak R; P(A-a)02; P(a-ET)C02
Maximum Vo2 Highest 02 uptake measured BR (breathing reserve) Maximum voluntary ventilation — ventilation at maximum exercise
AVOj/AWR Increase in Vo2 relative to increase in work rate ECG (electrocardiogram)
Vd/Vt Physiologic dead space/tidal volume ratio BP (blood pressure)
P(A-a)02 Alveolar-arterial Po2 difference COHb(carboxyhemoglobin)
P(a-ET)C02 Arterial-end tidal Pco2 difference HRR (heart rate reserve) Predicted maximum heart rate — maximum exercise heart rate
Ve/Vco2 Ventilatory equivalent for COz Peak R (gas exchange ratio) Estimate of subject s effort during exercise test

Category: Pulmonary function

Tags: cardiopulmonary exercise testing, heart failure, lung disease, organ systems