Basics of Cardiopulmonary Exercise Test Interpretation Robert Kempainen, MD Hennepin County Medical Center
None Conflicts of Interest
Objectives Explain what normally limits exercise Summarize basic protocol for CPET List parameters measured in exercise testing. Use combinations of parameters to determine the cause of exercise limitation
A Bit About Normal Exercise Limitation
What Normally Limits Exercise? Fick equation: VO2 = C.O.(CaO2 CvO2) HR x SV (1.34 x [Hb] x O 2 sat) + (0.003 x PaO 2 ) Reflects tissue extraction capillary density mitochondrial density mitochondrial function tissue perfusion tissue diffusion
What Normally Limits Exercise? Multifactorial but primary limiting factor varies with fitness of individual and conditions Healthy and unfit cardiac output > muscle Healthy and fit cardiac output likely primary Endurance athlete cardiac, ventilatory, and muscle likely
Exercise Limitation in Disease Cardiovascular Abnormal cardiac, pulmonary vascular, or systemic vascular function Blood disorder (anemia, CO poisoning) Respiratory Mechanical limitation Gas exchange derangements Peripheral Microvascular, metabolic, neuromuscular disorders
Why Get a Cardiopulmonary Exercise Test?
Reasons to Obtain CPET Unexplained dyspnea Blame the heart vs blame the lungs Exercise-induced bronchoconstriction Preoperative risk assessment Lung resection candidates Monitor patients with severe heart failure Work suitability assessment
Contraindications for cardiopulmonary exercise testing Absolute Acute M.I. (3 5 days) Resting room air sat < 85% Symptomatic, uncontrolled arrhythmias or syncope Thrombosis of lower extremities Active endocarditis, myocarditis, pericarditis Uncontrolled asthma Symptomatic severe aortic stenosis Uncontrolled heart failure Acute P.E. or infarct Pulmonary edema Acute noncardiopulmonary disorder affecting or aggravated by exercise Mental impairment with inability to cooperate Relative Left main coronary stenosis or equivalent Moderate stenotic valvular heart disease Severe arterial hypertension at rest (> 200 sys, > 120 diastolic) Tachyarrhythmias or bradyarrhythmias Orthopedic impairment that compromises exercise performance Hypertrophic cardiomyopathy Significant pulmonary hypertension Advanced or complicated pregnancy Electrolyte abnormalities High-degree AV block
Contraindications for cardiopulmonary exercise testing Absolute Acute M.I. (3 5 days) Resting room air sat < 85% Symptomatic, uncontrolled arrhythmias or syncope Thrombosis of lower extremities Active endocarditis, myocarditis, pericarditis Uncontrolled asthma Symptomatic severe aortic stenosis Uncontrolled heart failure Acute P.E. or infarct Pulmonary edema Acute noncardiopulmonary disorder affecting or aggravated by exercise Mental impairment with inability to cooperate Relative Left main coronary stenosis or equivalent Moderate stenotic valvular heart disease Severe arterial hypertension at rest (> 200 sys, > 120 diastolic) Tachyarrhythmias or bradyarrhythmias Orthopedic impairment that compromises exercise performance Hypertrophic cardiomyopathy Significant pulmonary hypertension Advanced or complicated pregnancy Electrolyte abnormalities High-degree AV block
Familiarization, Borg scale, etc
Cycle Ergometry versus Treadmill Cycle VO 2 max lower higher Work rate measurement yes no Treadmill Blood gas collection easier more difficult Noise and artifacts less more Safety safe less safe? Weight bearing in obese less more More appropriate for: patients active normal subjects
CPET Parameters VO 2 & Work Anaerobic Threshold Cardiac Parameters Ventilatory Parameters
VO 2 and Work Rate Increased work linear increase in VO 2 Chemical potential energy mechanical work Little variation in mechanical efficiency ΔVO 2 / Δwork rate = 8.5 11ml/min/watt Higher if obese, but same linear increase
Anaerobic Threshold VO 2 at which point lactate production sharply increases (sort of) Deficiency of O 2 delivery and/or O 2 metabolism Normally occurs at 40-80% of VO 2 max Low anaerobic threshold non-specific Direct determination of AT Blood lactate or blood bicarbonate
Indirect determination of AT V-slope method VO 2 at which point VCO 2 :VO 2 slope steepens
Cardiac Parameters
Cardiac Parameters: Heart Rate Low intensity exercise: SV & HR increase Higher intensity: CO mostly via in HR Observed vs. predicted max HR For determining maximal effort & limitation Predicted max 220 age tends to underestimate max HR in elderly 210 (age x 0.65) Actual max HR varies by 10 15 beats/min within age groups can be misleading
Cardiac Parameters Heart rate reserve (HRR) Predicted max Observed max Normal is < 15 beats/min Normal max HR > 90% predicted Interpret in light of patients meds
Cardiac Parameters: O 2 Pulse O 2 Pulse = VO 2 /HR Use as a measure of Stroke Volume Assumes O 2 extraction is constant at near maximal/maximal exercise Flat O 2 pulse Cardiac dysfunction (no in SV) O 2 extraction in muscle/deconditioning Ventilatory limitation
Cardiac Parameters: BP Normal response: Increase in systolic BP Diastolic BP stays constant or falls Abnormal responses Excessive increase Known resting hypertension Abnormal regulation if normotensive @ baseline Inadequate increase or fall Cardiovascular disease Defect of sympathetic regulation
Ventilatory Parameters
Ventilatory Parameters: Minute Ventilation (V E ) V E with exercise via V T and RR in V T more important with low intensity V T plateaus at 50 60% of vital capacity in RR more important with high intensity Max RR increases with greater fitness Normal max RR generally under 60 breaths/min Higher RR seen in fibrotic lung disease
Ventilatory Reserve (V E Reserve) Maximum ventilatory capacity 15 second MVV maneuver OR FEV1 x 40 Not reflective of breathing pattern of exercise V E reserve = max vent. capacity - max observed V E Normal V E reserve > 15% of MVV or > 11 L/min With fitness & aging, V E reserve decreases Low V E reserve suggests ventilatory limitation to exercise
Dead Space Ventilation V D /V T normally falls with exercise Resting V D /V T 30%-40% and with age At peak exercise V D /V T < 20% if under 20 y.o. & less than 30% if older than 40 y.o. Need ABG during exercise to accurately measure. Other methods suggestive but less reliable Elevated in COPD, ILD, pulmonary vascular disease
Gauging Effort Max physiologic effort needed Things to go by Normal anaerobic threshold Clear cardiac or ventilatory limitation Observation Respiratory exchange ratio > 1.0 RER = VCO 2 /VO 2 Normal value at rest 0.8. Increases with anaerobic exercise
Suggested normal values for interpretation of CPET Variables VO 2 max or VO 2 peak Anaerobic threshold Criteria of Normality > 84% predicted > 40% VO 2 max predicted normal (40 80%) Heart rate (HR) Heart rate reserve (HRR) HRmax > 90% age predicted HRR < 15 beats/min Blood pressure < 220/90 O 2 pulse (VO 2 /HR) > 80% predicted Ventilatory reserve (VR) MVV - VEmax: > 11 L or VEmax/MVV x 100 < 85%. Wide normal range: 72 ± 15% Respiratory frequency < 60 breaths/min VE/VCO 2 (at AT) < 34 VD/VT PaO 2 P(A a)o 2 < 0.28; < 0.30 for age > 40 years > 80 mm Hg < 35 mm Hg
Normal Case VO 2 max 38 ml/kg/min Max HR 170 bpm Peak O 2 Pulse 12.5 ml/b (90% predicted) (predicted 175 bpm) (90% predicted) V T 1.0 L start 3.0 L peak RR 15/min start 39/min peak Peak V E 90 L/min (MVC 124 L/min) (73%) No oxygenation desaturation
Case 1 46 y.o. sedentary woman with exertional dyspnea and chest pain. History of high BP when on OCP. Seasonal allergies Baseline data FEV1 3.0 L (89% pred), FVC 4.02 (96% pred) 12 lead EKG without ischemic changes MEDS: None. Possible albuterol in past Stopped 2 to both dyspnea and leg fatigue O 2 sat 96% rest, 94% peak exercise
VO 2 max 28.6 ml/kg/min Anaerobic threshold Max HR 156 bpm Peak O 2 Pulse 13.7 ml/b Case 1: CPET 75% predicted 60% of VO2 max predicted 180 bpm 90% predicted BP 132/68 186/83 predicted < 220/90 V T 0.6L 1.7 L 1.5 L RR 14/min 47/min Max V E L/min 70 L/min predicted < 60/min predicted 104 L/min Good effort based on appearance, anaerobic threshold, RER > 1.1
Case 1 Continued Pre-exercise Post-exercise
Exercise-induced Bronchoconstriction - Look for 10% - 15% drop in FEV1 - FEV1 back to baseline post-albuterol - Separate protocols to test for EIB - e.g. maintain patient at 80 to 90% maximal heart rate for 6 to 8 minutes partway through study - Normal study does not rule out EIB
Case 2 59 y.o. woman with COPD and lung cancer undergoes pre-operative CPET Baseline data Height 64 inches, Weight 110 lbs FEV1 1.0 L (38% predicted) Baseline EKG without ischemic changes Meds: Inhalers, prednisone, nicotine patch Stopped 2 to leg fatigue 95% sat at rest, nadir of 91%
Case 2: CPET Observed Predicted % Pred VO 2 max 9.9 ml/kg/min 27 37 Max HR 130 bpm 161 81 Max O 2 Pulse 9 ml/b 12.5 72 BP 130/80 180/85 < 220/90 AT Indeterminant V T 0.5L 0.9 L RR 16/min 38/min Max V E 34 L/min 35 L/min 97
Case 2: Ventilatory Limitation AT often indeterminate in COPD patients Decreased ventilatory reserve Heart rate reserve as COPD severity Look for signs of increased dead space In this patient, VO 2 max < 10 ml/kg/min = high risk of perioperative complications with lung resection
Case 3 59 y.o. man with hypertension, possible pulmonary asbestosis, and alcohol abuse has CPET for dyspnea evaluation Baseline data FEV1 2.6 L (75% pred), FVC 3.1 L (70% pred) EKG within normal limits Carvediolol, aspirin Stopped due to leg fatigue O 2 sat 96% at rest and at peak exercise
Case 3: CPET Observed Predicted % Pred VO 2 max 25 ml/kg/min 42 60 Max HR 157 bpm 182 bpm 86 Max O 2 Pulse 9.0 ml/b 14.1 ml/b 64 BP 130/80 180/85 < 220/90 AT 10.1 ml/kg/min > 10 ml/kg/min V T 0.6L 1.7 L RR 16/min 38/min Max V E 64.6 L/min 104 L/min 62
Case 3: Cardiac Limitation Normal or large ventilatory reserve Reduced O 2 pulse May see increased heart rate reserve Early anaerobic threshold Deconditioning and mild CHF look similar on CPET
Case 4 39 y.o. man with obesity, HTN and DM has CPET for eval of exertional dyspnea Baseline data Height 70 inches, weight 250 lbs, BMI 35.9 FEV1 4.5 L (82%) FVC 5.5 L (82%) 12-lead EKG with no ischemic change, LVH Meds: diltiazem, rosiglitazone Stopped 2 leg fatigue O 2 sat 92% start, 96% at peak exercise
Observed Case 4: CPET Predicted % Pred VO 2 max 3.2 L/min 3.4 94 VO 2 max 28.2 ml/kg/min 46.6 58 Max work 100 watts 150 67 Max HR 178 bpm 181 98 Max O 2 Pulse 12.3 ml/b 12.5 ml/b 98 BP 130/80 180/85 < 220/90 AT 1.6 L/min > 18.6 ml/kg/min V T 0.8L 2.3 L RR 16/min 45/min Max V 103 L/min 157 L/min 66
Obesity Exercise Limitation Normal VO 2 max in L/min but low normalized value Elevated VO 2 /work and low peak watts Normal peak O 2 pulse, AT, gas exchange Potential co-contributors to limitation Diastolic dysfunction Respiratory impairment Breathing at low lung volumes inspiratory load
Case 5 27 y.o. male with dyspnea with vigorous exertion Baseline data Height: 72 inches, Weight 147 lbs FEV1 5.5 L (114%) FVC 6.9 L (118%) Normal EKG No meds Stopped 2 dyspnea O 2 sat 99% start, 92% peak
Case 5: CPET Observed VO 2 max 5.3 L/min VO 2 max 79 ml/kg/min Max HR 188 bpm Max O 2 Pulse 29 ml/b BP 130/80 140/85 AT 4.6 L (88% VO 2 max) V T 1.8L 3.1 L RR 21/min 60/min Max V E 187 L/min Predicted 3.4 L/min 192 bpm 15.5 ml/b < 220/90 40 80% of VO 2 max 192 L/min
References ATS/ACCP Statement on Cardiopulmonary Exercise Testing American Journal of Respiratory and Critical Care Medicine Vol 167. pp. 211-277, (2003) Weisman IM, Zeballos RJ. Clinical exercise testing. Clin Chest Med 2001;22:679-701