Cardiopulmonary Exercise Testing Flashcards
CPET definition
-Non-invasive, simultaneous measurement of the cardiovascular and respiratory system
-during exercise to assess a patient’s exercise capacity
Rationale for CPET
-Exercise intolerance is the hallmark of pulmonary and cardiac diseases
-Measurements at rest are poorly predictive of the degree of exercise intolerance
-Necessary to directly assess an individual’s exercise intolerance and where possible, establish its causes
Coupling of external ventilation and cellular metabolism
Mechanisms of exercise limitation
Pulmonary
-ventilatory
-respiratory muscle dysfunction
-impaired gas exchange
Cardiovascular
-Reduced SV
-Abnormal HR response
-Circulatory abnormality
Peripheral
-Inactivity
-Atrophy
-Neuromuscular dysfunction
-Perceptual
-Motivational
-Environmental
What is CPET?
-Symptom-limited exercise test
-Measure airflow, SpO2, expired oxygen and CO2
-Allows calculation of peak oxygen consumption, anaerobic threshold
ETT vs CPET
-ETT uses non-uniform increments (Bruce) which are too difficult for pulmonary patients
-ETT terminated at arbitrary end point (85% predicted max heart rate) does not provide peak VO2 or reserve capacities
-Gas exchange provides additional cardiac/circulatory information non-invasively
Advantages of bike over treadmill
-cheaper
-safer
-direct power calculation
-little training needed
-easier bp recording
-less space/noise
Advantages of treadmill over bike
-Attain higher VO2
-More functional
What is the modified Borg scale?
-Measure of exertion
1 - nothing
10 - maximal
Indications for CPET
-Pre-op evaluation
-Assess response to therapy
-Prognosis of life expectancy
-Disability determination
-Pulmonary rehabilitation - response to participation
-Evaluation of dyspnoea - cardiac vs pulmonary vs peripheral limitation
Absolute contraindications of CPET
-Acute MI
-Unstable angina
-Uncontrolled arrhythmias causing symptoms
-Syncope
-Active endocarditis/myocarditis/pericarditis
Relative contraindications of CPET
-Left main coronary stenosis
-Moderate stenotic valvular heart disease
-Severe arterial hypertension at rest (200/120)
-Tachyarrhythmias/Bradyarrhythmias
-High degree AV block
Steps before carrying out CPET
-Ensure all equipment is serviceable and calibrated
-Take history, cardiac medication (beta blockers?)
-Gain verbal/written consent
-Take height and weight
-12 lead ECG - abrade and alcohol
-Perform spirometry - patient sat down
-Remind patient of end-point criteria
Increment vs Ramp protocol
-Ramp is better
-8-12 minute duration
-Long enough to see peak VO2
-Not so long that it demotivates
How to calculate work rate?
Selecting work rate for different levels of fitness
Indications for exercise termination
-Patient request
-Dizziness/faintness/confusion
-Ischemic ECG changes (>2mm ST)
-2nd or 3rd degree heart block
-Fall in BP >20mmHg
Slow twitch vs Fast twitch muscle fibres
Red/slow twitch/type 1
-sustained activity
-high mitochondrial density
-metabolise glucose aerobically
-rapid recovery
White/fast twitch/type 2
-rapid burst exercise
-few mitochondria
-metabolise glucose anaerobically
slow recovery
Lactic acid
-Product of anaerobic respiration
-Build up of hydrogen ions causes muscle fatigue
Resting blood lactate = 1mM
AT = 4mM
VO2 max = 8mM
Top athletes = 25mM
What is RER?
Respiratory Exchange Ratio
RER=CO2 produced/O2 consumed
RER closer to 0.7 - fats being used
RER closer to 1.0 - carbs being used
What are ventilatory equivalents?
-Litres of ventilation to eliminate 1 litre of CO2
-Litres of ventilation to uptake 1 litre of O2
-Ratio between these
Ventilatory equivalents at rest and exercise
Rest: 6-10 litres/min
Exercise: 100-170 litres/min
How does VE increase with VO2?
-Increases linearly with VO2 and workload until 60% of maximum
-Beyond this, it increases at a faster rate due to AT: more CO2, blood is more acidic, breathing rate increases
What is average anaerobic threshold?
50-60% of VO2 max
-AT can be estimated using ventilatory response to exercise
Relationship of AT to RER
Method 1 of determining AT
V slope method
Method 2 of determining AT
Ventilatory equivalent plot
-At AT, VE increases at a higher rate than O2 consumption, so VE/VO2 begins to increase
-Point at which VE/VO2 and VE/VCO2 lines cross
VO2 max definition
-Maximum ability of cardiovascular system to deliver oxygen to exercising skeletal muscle
-and exercising skeletal muscle to extract oxygen from the blood
Fick equation for VO2
HR x SV x A-VO2 difference
Average of 3.5ml/kg/min at rest
VO2 max vs VO2 peak
VO2 max = max in theory
VO2 peak = max in reality
Formula for maximum HR
220-age
What is heart rate reserve?
(1-actual/predicted) x 100
Normal < 15%
Low HRR = Heart disease
High HRR = Lung disease
What is breathing reserve
(1-actual/predicted) x 100
Normal = 10-40%
Low BR = Lung disease
High BR = Heart disease
Cardiac vs Pulmonary limitation
Heart disease
BR > 40%
HRR < 15%
Lung disease
BR < 40%
HRR >15%
