Transcript VO2
Cardiopulmonary Stress Testing
Danielle Rowe BS RRT, RPFT Senior Clinical Sales Specialist Carefusion
WHAT IS THE PURPOSE OF CPX TESTING?
It is an assessment of a subject’s functional (work) capacity under stress.
We judge this functional capacity by primarily evaluating peak VO2.
After functional capacity is established, we then are provided with insight on cause of limitations if they exist.
Possible limitations to Exercise
Ventilation Gas Exchange Circulation (inc. ECG) Metabolism metabolism
O 2 CO 2
Peripheral Gas Exchange Pulmonary Gas Exchange
Indications For Cardiopulmonary Exercise Testing
Evaluation of exercise tolerance Evaluation of undiagnosed exercise intolerance Evaluation of patients with cardiac disease Evaluation of patients with Respiratory disease Specific Clinical Applications Preop assessment on certain populations, rehab evaluations, disability, transplantation etc.
From ATS/ACCP
Max or Submax Testing
For Cardiopulmonary diagnostic purposes, MAXIMAL testing is performed.
We aim to stress the cardio-respiratory system until we identify the factor which limits exercise capacity.
Sub max test are more common in athletics training, rehabilitation etc.
Exercise Protocols
Cycle Ergometry
Ramp, typically increases of 5 -30 W/minute Aim to have exercise portion of testing lasting approx. 10 minutes 1-3 minutes resting data 1-3 minutes unloaded pedaling
Treadmill
Speed constant and grade increased (Balke Protocol). 2 mph, 0% grade and then the grade is increased 2-3% every minute.
Speed and grade are both increased ( Bruce Protocol). 1.7 mph, 10% grade and then increased by .8 mph and 2% grade every 3 minutes.
Bike vs Treadmill
VO2 Max Work Rate Meas.
Blood gas collection Noise and artifacts Safety Wt. bearing in obese Leg muscle fatigue
Bike
lower Yes easier less safer less often
Treadmill
higher No harder more less safe?
more less
Bike vs. Treadmill cont.
Bike
All things considered, bike is considered the most appropriate for patients. This is due to ability to accurately quantify work and the minimizing of test artifacts.
Just remember vigorous encouragement is often needed near peak of exercise test to help overcome and push through leg muscle fatigue.
Treadmill
VO2 max is often 5-10% higher Most appropriate for athletes and patients in whom abnormalities may occur only with the highest demand ( cardiac ischemia).
5 Watts/min 10 Watts/min 15 Watts/min 20 Watts/min 25 Watts/min 30 Watts/min 40 Watts/min
Selecting the Work Rate
Severe impairment (e.g. patient who is confined to home or walks only short distances) Moderate impairment (e.g. patient who walks one or two city blocks before symptoms) Mild impairment or sedentary older patient Sedentary younger patient Active younger patient physical exercise) (regular sports, Athletic and fit (competitive sports) Extremely fit (highly competitive) Chris Cooper, MD.. Harbor UCLA Medical
Was it a Good Test ?
How can we tell ?
Most common problem seen is sub-maximal performance.
Patients are supposed to “suffer” - that is the whole idea of the test - to put them under stress.
Don’t stop when the patient hits Max Predicted Heart Rate - carry on until the patient stops.
Often the best Indicator..
RER
“Although no one RER value defines maximal effort, values greater than 1.15 are more likely to be associated with near maximal or maximal effort.”
From ATS/ACCP Statement
RER (or RQ) = VCO2/VO2
At Baseline, RER < 0.8
If it isn’t, check for hyperventilation If no hyperventilation, something is wrong Many patients hyperventilate in the baseline state
At end of test, RER > 1.15
Indicates maximal exercise effort and therefore a good test
Indications for Exercise Termination
Chest pain suggestive of ischemia Ischemic ECG changes Complex ectopy Second or third degree heart block Fall in systolic pressure >20 mmHg from the highest value during the test.
Hypertension ( >250 mmHg sys; >120 mmHg diastolic) Severe desaturation: SpO2 ≤ 80% when accompanied by symptoms and signs of severe hypoxemia Sudden pallor Loss of confusion Dizziness or faintness Signs of respiratory failure From ATS/ACCP Statement
VO2 Peak/Max
Maximal Oxygen Uptake (VO2 max) Represents the highest VO2 that can be reached as evidenced by a failure for VO2 to increase further despite and increase in work rate.
Peak Oxygen Uptake ( VO2 peak) Represents the highest VO2 reached during the test where a presumed maximal effort was given.
These Terms are often used interchangeably.
Oxygen Consumption
The amount of oxygen used per minute.
250 mL/min at rest (3.5 mL/min/kg) 5,000 mL/min at strenuous exercise (>70 mL/min/kg) AGE 20-29 yrs 30-39 yrs 40-49 yrs 50-59 yrs 60-69 yrs Men <25 <23 <20 <18 <16
Low
Women <24 <20 <17 <15 <13
Average
Men 34 - 42 31 – 38 27 – 35 25 – 33 23 – 30 Women 31 - 37 28 - 33 24 -30 21 - 27 18 - 23 Expected Vo2 mL/min/kg values from American Heart Association
Weber- Janicki Classification in heart failure
Severity
None to Mild Mild to Moderate Moderate to Severe Severe Very Severe
Class
D E A B C
Peak Vo2 mL/kg/min
>20 16 – 20 10 – 16 6 -10 <6
Peak VO2 Cont.
Peak VO2 is often used in the course of treating heart failure and in selecting heart transplant candidates:
Typically these subjects that test with a peak VO2 <14 ml/min/kg are strongly considered for
transplantation.
Peak Vo2 is often considered with major surgery especially abdominal surgery in elderly or sick patients.
>20 ml/min/kg good prognosis
<15 ml/min/kg high risk
VO2- Work relationship
•
VO2/Work slope = Normal is right around 10/ml/min/watt with relatively small range of normal reported in many studies. Typically (8.5- 11) considered normal.
•
Shallower slope, so a value < 8.5- 8.7 ml/min/watt point to a problem of O2 flow or O2 utilization.
Anaerobic Threshold (AT)
Lactacte Threshold, Lactic Acid Threshold, Gas Exchange threshold, Ventilatory threshold etc..
The highest level of metabolic acidosis.
oxygen consumption that can be sustained without developing
The point at which anaerobic
metabolism starts to contribute.
AT cont.
Normally occurs at about 50-60% of Vo2 max predicted however there is a wide range of normal reported (35 80%).
40% is the generally accepted lower limit of normal used clinically.
Detecting AT Invasive determination
Arterial Lactate measurements. AT is graphically determined by plotting lactate concentration vs. Vo2.
AT by V-Slope Method
AT by Dual Criteria Method
AT summary
Athletes can do more activity aerobically so AT is increased.
In diseases ( most cardiovascular) that affect O2 supply to exercising muscles , the AT is often found to be early. This can also occur in more rare conditions with mitochondrial myopathies. In clinical CPX testing you are searching for an early AT. If it is not early, then it really does not matter precisely where it occurred.
Cardiac Parameters
Heart Rate and HR reserve BP <220/90 O2 pulse ECG HR –VO2 relationship
Heart Rate and HR reserve
Many formulas exist for predicting max HR.
220- age 210- (age × 0.65) HR reserve is the difference between the predicted max and the achieved max.
Normally there is very little to no reserve in normal subjects giving maximal effort.
Often a HRR < 15 beats/min is normal.
HR- VO2 Relationship
200 -
Predicted Maximum Heart Rate
HRR = 0
HR (b/min)
0 0
VO2
| Max Predicted HR/VO2 normal = 3-4 beats/ml/min/kg
O2 pulse
VO2/HR Amount of O2 uptake per each beat of heart.
Dependent on stroke volume and O2 uptake.
O2 pulse = SV × C(a-v)O2 O2 pulse normally increases with incremental exercise due to increases in both SV and O2 extraction. When O2 content and C(a-v)O2 are maximal and assumed to be normal ( approx. 15 ml/dl), stroke volume can be estimated: SV= O2 pulse/15 *100
Ventilatory Parameters
VE RR Tidal volume Breathing reserve Inspiratory capacity trending ( Ex. FVL) Capacity, reserve assessment
VE and Breathing reserve
Measure Spirometry and MVV prior to exercise test. Then decide which to use as predictor of maximal ventilation. Quality of these baseline measurements is key….be careful!
Often MVV may not be the best indicator of capacity as breathing pattern of the 12-15 sec effort is not typically a pattern subject adopts during exercise. FEV1 × 35 or 40 is often used to estimate MVV or capacity.
Things to consider: Effort and quality of baseline spirometry and MVV. Can I use either?
It may be better to use actual MVV in cases of upper airway obstruction or neuromuscular weakness.
Breathing reserve= (MVV-VE max/ MVV)× 100 Normal = 20-30 %. Typically < 15% considered low.
Breathing pattern
The rise in VE during exercise is associated with an increase in both depth and frequency of breathing.
Tidal Volume - Vt typically increases until it reaches about 50-60% of VC or 70% of IC.
Further increases in VE are accomplished by respiratory rate .
Typically the rate does not normally exceed around 55 bpm.
Exercise Tidal FVL tracings
Normal
What happens here?
Ventilatory Equivalents
How many liters of air we need to breath to exchange 1 L of gas.
VEVO2 VECO2 Indicators of efficiency of ventilation.
Increases in ventilatory equivalents: Often found in diseases in which pulmonary blood flow is abnormally reduced to ventilated gas exchange units.
Ventilatory Equivalents
(Efficiency of ventilation)
VE/CO2 VE/VO2 40 20 AT RC NORMAL VALUES:
Ref: Wasserman
0 VE/VO2 @ AT: 26.5 (22.1 – 30.9) VE/VCO2 @ AT: 29.1 (24.8 – 33.4)
Arterial Blood Sampling
Sometimes….
Do we need it?
When the adequacy of pulmonary gas exchange is in question up front. Typically in diseases like ILD, pulmonary vascular disease, COPD with low DLCO etc.
When concern over increased dead space is and issue. You want real VD/VT measurements.
When patients have an abnormal initial CPET maybe showing increased VE/VCO2 but no specific reason. Was it hyperventilation or due to increased VD.
If you do it, do it right! Use and Arterial line. No single samples at peak exercise.
Additional pieces of information when blood gas sampling is done
Information about ability to exchange oxygen.
PaO2- normally >80 mmHg and should not decrease with exercise.
P (A-a)O2- should be <35 mmHg at peak.
SaO2
ABG cont..
VD/VT = (PaCO2 – PECO2)/PaCO2 Fraction of each breath “wasted” on ventilating anatomic and physiologic dead space.
You need PaCO2 to get a true VD/VT. You cannot accurately estimate!
The estimated VD/VT that is often reported uses end-tidal PCO2 in place of PaCO2 which can be misleading.
Normally PetCo2 is a little less than PaCO2 at rest but becomes greater than PaCO2 with exercise leading to an overestimation of VD/VT.
With lung disease PetCO2 may remain below PaCO2 even with exercise causing an underestimation of dead space.
VD/VT
Normal at rest is 30-40%.
Should fall with exercise due to increasing tidal volume.
Typically at peak exercise we should see values less than 28% in subjects < 40 yrs. Values less than 30% normal in subjects >40 yrs.
Putting it all together
Was it a good test?
Can subject achieve normal VO2 and do normal amount of “work”?
Is there a premature metabolic acidosis? Low AT Is there a cardiovascular limitation?
Is there a ventilatory (mechanics) limitation?
Does pulmonary gas exchange contribute to exercise limitation?
Obesity
High O2 cost to perform work.
Peak VO2/kg is low when expressed per kg of actual wt but normal when expressed per kg of ideal wt.
Low PaO2 that often normalizes with exercise.
Failure to develop normal ventilatory compensation for metabolic acidosis.
Cardiovascular disease
Low VO2 Early AT Reduced maximal O2 pulse Steep HR/VO2 relationship Peak HR variable- may be normal or reduced.
Often increased ventilatory reserve
Ventilatory limitation
Low VO2 High VD/VT Low breathing reserve High heart rate reserve AT normal or not reached Failure to develop respiratory compensation for metabolic acidosis.