1. Interpreting the cardiopulmonary exercise test [CPEX/CPET/Metabolic testing]
Sathish Parasuraman
Cardio-vascular research fellow
University of East Anglia
The primary function of cardiovascular and respiratory systems is to support the cellular respiration. By measuring the oxygen taken in and co2 blown out, you get a good idea of what is happening at the cellular level. This forms the basis of CPEX

2. When to do it
How to do it?
How do you interpret it?
Some examples

3. When to do it?
When you want the whole picture of how a disease is affecting a person Eg. A young sarcoid / young congenital heart disease patient, you want to review annually
2. Patient with exercise limitation ?due to lung ?due to heart
3. Fitness for surgery
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4. Quiz!
When the presenting complaint is exercise limitation, what is the best test to do?
Exercise test
Coronary angiogram
Contrast CT scan of chest
Blood tests
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5. November 8, 2018

6. What can CPEX tell you? Exercise time/ECG/BP/Heart rate
Oxygen consumption at peak exercise
When does the anaerobic metabolism begin?
Oxygen saturations at rest and peak exercise
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7. Terminologies in CPEX Ignore V prefix You know most terms
VE – “minute ventilation” (Litres) = Respiratory frequency * Tidal volume
VO2 – Oxygen uptake (ml/kg/min)
Peak VO2 – Oxygen uptake at peak exercise (ml/kg/min)
VCO2 – Carbon dioxide output (ml/kg/min)
AT – Anaerobic Threshold, when anaerobic metabolism supplements exercise
R – Gas exchange ration = VCO2/VO2
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8. Determinants of exercise capacity
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Determinants of exercise capacity
The ability to perform physical exercise is critically related to the cardiovascular system’s capacity to supply oxygen (O2) to the muscles and the pulmonary system’s ability to clear carbon dioxide (CO2) from the blood via the lungs. Cardio-pulmonary exercise testing allows the clinician to measure simultaneously, the cardio-vascular respiratory responses to exercise.
Pulmonary ventilation-movement of air in and out of lungs
Pulmonary diffusion – across the alveolar capillary membrane
Transport of O2 and CO2 in blood
Capillary gas exchange-o2 and co2 exchange between capillary blood and working muscle
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9. Energy supply during exercise
Hydrolysis of phosphocreatinine
Oxidation of glucose and fatty acids
Anaerobic metabolism
1st minute
2nd to 10th minute
7th to 10th minute
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10. CO2 Production during exercise
Glucose + 10 O CO2+ H2O + Energy
Palmitate + 10 O CO2 + H2O + Energy
Anaerobic Glycolysis Lactate + Energy
CO2

11. oxygen and carbon-dioxide kinetics
Peak VO2 < 85%
Heart Problem
Lung problem
Blood problem
Muscle problem
Deconditioning
CO2
P VO2 O2
O2, CO2
Cardiac output increases by up to 6 times, along with redirection of blood to working muscles + better extraction of tissues
Time
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12. Respiratory Exchange Ratio
RER or simply “R”
Anaerobic Threshold or Lactate Threshold
RER or R=VCO2/VO2
Climbs steadily after AT
At peak exercise it is >1
R greater than 1.1 suggests adequate test, but not an indication to stop the test
Anaerobic threshold occurs at approximately 45-60% of the peak VO2. For athletes this occurs later.
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13. Anaerobic threshold Heart Problem Lung problem Blood problem CO2
Muscle problem
Deconditioning
CO2 O2
O2, CO2
Anaerobic threshold
Anaerobic threshold is expressed as oxygen consumed at that point
Time
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14. VO2 at anaerobic threshold and O2 pulse
Normal AT / Predicted PVO2 >40%
If PVO2 <40% suggests cardiac limitation
O2 pulse = VO2/heart rate
Surrogate for stroke volume
A fall on incremental exercise indicates cardiac pathology
VO2 at AT/pred PVO2
=15.69/38.75
=40%

15. So far.. Low Peak VO2 indicates a pathology
Respiratory Exchange Ratio (CO2/O2) >1.15 suggests maximal test
Anaerobic metabolism sets in early in heart failure (<40% of predicted peak VO2)
Oxygen pulse is a surrogate for stroke volume
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16. Ventilation
Ventilation is a product of tidal volume and respiratory frequency
VE = tidal volume X resp. freq.
During progressive exercise, dead space decreases, tidal volume increases
Respiratory frequency increases, later, but rarely beyond 50 breaths/minute
Resting PFT values are imprecise in predicting gas exchange abnormalities during exercise
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17. Maximum voluntary ventilation & Breathing reserve
Maximum Voluntary Ventilation – The upper
limit of body’s ability to ventilate the lungs
Maximum Voluntary Ventilation(MVV) = FEV1*40
Breathing reserve = MVV - VE (Ventilation) at peak exercise
Heart Problem
Lung problem
Blood problem
Muscle problem
Deconditioning
Breathing reserve<11 L
Even before the start of exercise you can predict the maximal ability of person to ventilate the lungs. In normal people it is the heart that stops them from exercising further.
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18. Desaturation during exercise
Desaturation suggests a lung problem
Oxygen saturations do not fall markedly until the PO2 is <8 kPa
If saturation falls >5%, it suggests abnormal exercise induced hypoxemia
Motion artifact and poor capillary perfusion are recognized sources of error in signals during exercise and tend to cause small underestimates of true oxygen saturation, particularly with use of a fingertip probe. A decrease of >5% in the pulse oximeter estimate of arterial saturation during clinical CPX protocols is suggestive of abnormal exercise-induced hypoxemia,5 and if this is an unexpected finding, confirmation by analysis of arterial blood may be indicated. Some laboratories use oximeter findings of desaturation to less than 80% or 85% as an indication to discontinue exercise tests.
November 8, 2018

19. Ventilatory efficiency
Ventilatory efficiency of elimination CO2
Measured from the beginning of exercise to anaerobic threshold
High VE/VCO2 slope indicates ventilation- perfusion mismatch
Slope 63
Heart Problem
Lung problem
Blood problem
Muscle problem
Deconditioning
Slope 34
Slope 23
VE-VCO2 slope <30 degrees
The most widely studied index is minute ventilation0CO2 output relationship
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20. So far… Desaturation indicates lung problem
Low breathing reserve indicates lung problem
High VE-VCO2 slope indicates ventilation-perfusion mismatch
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21. Truly limited Lung limitation V/Q mismatch and early anaerobic met.
Not the lungs
Lung limitation
V/Q mismatch and early anaerobic met.
High VE/VCO2 slope
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22. General considerations
A protocol is chosen, so patient lasts no more than 8-12 minutes
Reason for stopping could give a clue
Leg fatigue- cardiac
Leg pain-peripheral vascular disease
Chest pain-angina
Breathlessness-lung

23. 64 m
Recent diagnosis of prostrate Ca, receiving local radiation
Feels tired and breathless
Inconclusive treadmill ETT
VO2 at AT/Pred PVO2
= 18.27/24.8
= 74%

24. Borderline breathing reserve No desaturation during exercise
Report
Normal PVO2
Normal VO2 at AT
Normal VE/VCO2 slope
Borderline breathing reserve
No desaturation during exercise
Abrupt flattening of VO2, VO2 pulse towards peak exercise, with unexpected raise on recovery
Imp
Coronary ischemia
64 m
Recent diagnosis of prostrate Ca, receiving local radiation
Feels tired and breathless
Inconclusive treadmill ETT
Sensitivity of normal ETT ranges from 40% for single vessel disease to 90% in 3 vessel disease. It is well known that in the cascade of events following myocardial ischaemia, angina pectoris and ECG ST segment changes are more delayed than regional myocardial dysfunction due to perfusion abnormalities. As compared with standard ECG stress testing, CPET had higher sensitivity (87%), specificity (74%), and also positive and negative predictive values (positive predictive value: 88%; negative predictive value: 72%).
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25. Coronary ischemia
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26. FH of HOCM IVS of 13 mm Fit & well man
FH of HOCM. Normal ECG, septum of 12 mm. Fit and well. Each hospital has its own machine, so just pic what you want

27. FH of HOCM IVS of 12 mm Asymptomatic Report Normal PVO2
Normal VO2 at AT
Normal spirometry, breathing reserve & saturations
Normal VE-VCO2 slope
Imp
No exercise limitation
Most of the graphs you have seen before..

28. A difficult case 67 year old man, breathlessX1 year Clubbed
CT chest- ground glass opacification, normal LV systolic function
Ex- smoker X 40 PY
Abnormal spirometry with reduced DLCO
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29. A difficult case
Treadmill CPEX for 7 minutes, stopped due to breathlessness
PVO2 of 82% of predicted
R of 1.29
VO2 at AT is 53% of predicted PVO2
VE/VCO2 slope is RCP
Breathing reserve is 6, maximal respiratory frequency was 40

30. Oxygen saturation Increased on exercise!
suspect this is primary lung issue
coexisting ischemia
Why the PaO2 increases on exercise?
Potential right to left shunt which decreased during exercise
ie-pulmonary shunt
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31. HT, DM, congenital blindness
43 m, Breathless
HT, DM, congenital blindness
Mild LV hypertrophy, normal angiogram, Normal spirometry
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33. Likely mitochondrial myopathy
Report
Likely mitochondrial myopathy
10 mins recovery Ph 7.21
20 mins recovery
7.27
November 8, 2018
PH 7.19

34. Another difficult case
19 Female
Being investigated for breathlessness/tiredness
Normal haemoglobin, echocardiogram
Normal FEV1, FVC, reduced DLCO (65%)
Normal CT (plain) chest

35. 19 f, breathless. Slightly reduced DLCO, normal echo & plain CT
Low PVO2
Low VO2 at AT
Normal breathing reserve
What other value would you like…?
November 8, 2018

36. Saturations at peak exercise unclear Very high respiratory frequency
Report
Low PVO2
Low VO2 at AT
Normal VE-VCO2
Saturations at peak exercise unclear
Very high respiratory frequency
Imp/DD
Mitochondrial myopathy
Left to right shunt
In mitochondrial myopathy the patient is unable to perform aerobic metabolism and instead lactic acid accumulates early.
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37. Evidence base for CPEX
Heart failure patients with PVO2 < 12 ml/kg/min indicate poor prognosis and are candidates for heart transplantation
In lung cancer- a PVO2 of <15 ml/kg/min predicts high perioperative risk
In major abdominal and vascular surgeries, VO2 at AT of <11ml/kg/min predicts high cardiovascular risk and poor survival
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38. Thank you!
November 8, 2018