5. General Mechanisms of Exercise Limitation
Pulmonary
Ventilatory
Respiratory muscle
dysfunction
Impaired gas exchange
Cardiovascular
Reduced stroke volume
Abnormal HR response
Circulatory abnormality
Blood abnormality
Peripheral
Inactivity
Atrophy
Neuromuscular
dysfunction
Reduced oxidative
capacity of skeletal muscle
Malnutrition
Perceptual
Motivational
Environmental
6. Learning objectives
1. Indications for CPET;
2. Methodology—equipment, modality, protocols, conduct of the test,
measurements and graphic interrelationships safety, and personnel
issues;
3. Measurements and graphic interrelationships, the physiologic response
to exercise, in “normal” subjects, and the consequences of
pathophysiologic derangements on exercise performance;
4. Normal reference values;
5. Interpretation, including case study analysis; and
6. Future recommendations for research.
7. The Fick equation
Fick equation states that oxygen uptake (VO2) equals cardiac output
times the arterial minus mixed venous oxygen content:
VO2 = (SV x HR) x (CaO2 - CvO2)
Where,
SV is the stroke volume,
HR is the heart rate,
CaO2 is the arterial oxygen content, and
CvO2 is the mixed venous oxygen content.
Oxygen uptake is often normalised for body weight and expressed in
units of ml O2/kg/min.
8. One metabolic equivalent (MET) is the resting oxygen uptake in a
sitting position and equals 3.5 ml/kg/min.
At maximal exercise, the Fick equation is expressed as follows:
VO2max = (SVmax x HRmax) x (CaO2max - CvO2max)
22. Gas exchange measurement: VO2 and VCO2
VO2 = [(Vi . FiO2) - (Ve . FeO2)]/t
Vi is not commonly measured,
N2 is neither absorbed nor discharged from the capillaries
Vi . FiN2 = Ve . FeN2
Vi = Ve . FeN2/FiN2
because FiCO2 in room air is practically zero and may be safely ignored
in the calculation:
Vco2 = [Ve . FeCO2]/t
29. Maximal incremental cycle ergometry protocols
IET protocol
3 minutes of rest, 3 minutes of unloaded pedaling the incremental
phase of exercise every minute (5 to 25 W/minute) until the patient reaches
volitional exhaustion or the test is terminated by the medical monitor
Ramp protocol
increase the work rate continuously, usually every 1 to 2 seconds in a
ramplike fashion
Standardized exponential exercise protocol
work rate is increased exponentially by 15% of the previous workload every
minute
30.
31. Maximal incremental treadmill protocols
Bruce protocol:
the starting point (ie, stage 1) is 1.7 mph at a 10% grade (5 METs).
Stage 2 is 2.5 mph at a 12% grade (7 METs).
Stage 3 is 3.4 mph at a 14% grade (9 METs).
This protocol includes 3-minute periods to allow achievement of a steady
state before workload is increased.
Modified Bruce protocol
2 warmup stages, each lasting 3 minutes.
The first is at 1.7 mph and a 0% grade,
the second is at 1.7 mph and a 5% grade
32. Balke protocol - speed is kept constant at 3.3 mph, and elevation is
increased by 1% every minute
Modified Balke protocol - fixed treadmill speed is chosen and the
treadmill grade is increased by a constant amount each minute
Naughton, Weber, and Asymptomatic Cardiac Ischemia Pilot (ACIP)
study protocols, all of which start with less than 2 METs at 2 mph and
increase in 1- to 1.5-MET increments between stages.
33. Constant work rate protocol
Treadmill or cycle ergometry exercise
at levels approximating the subject’s usual daily activities (e.g., up to 3.0
mph on a treadmill, or up to 50 W on a cycle ergometer).
A constant work rate may be performed about 1 hour after an IET.
This test should involve at least 6 minutes of continuous exercise.
Alternatively, using 50 to 70% of the maximal work rate achieved during
an incremental exercise, a constant work rate test for 5 to 10 minutes
often achieves about 70 to 90% of O2max achieved during IET.
34. Constant work rate protocol
Used:
monitoring response cardiopulmonary rehabilitation, bronchodilators,
LVRS, medical devices
analysis of exercise tidal flow–volume loops and dynamic hyperinflation,
gas exchange kinetics, and validation of pulmonary gas exchange during
incremental exercise testing
35.
36.
37.
38.
39. Patient safety
Relatively safe
0 – 5 / 100000 exercise test (AHA)
Veteran Affairs Health Care System exercise laboratories: an event rate of
1.2 per 10000 tests (MI, VT)