Case Study:
CPX Testing for Exercise Prescription in Cardiac Rehabilitation
The patient, a 61-year-old, 78 kg. male, was referred for cardiac rehabilitation
exercise training. The patient's risk factors for coronary artery disease
included an elevated triglyceride value and low HDL cholesterol. He
had a prior history of anterior myocardial infarction followed by 3-vessel
coronary artery bypass surgery. His immediate post-operative course
was complicated by congestive heart failure. Upon resolution of the
acute CHF, his physician felt he could benefit from an organized cardiac
rehabilitation program.
A cardiopulmonary exercise (CPX) test with respiratory gas exchange
measurements was performed on this patient to prescribe a level of exercise
that would be both safe and provide cardiovascular training benefit.
The patient's medications at the time of the CPX test included Aspirin,
Lanoxin, and Lopid.
The patient performed a maximal treadmill CPX test using the Bruce
protocol, with the results below:
| Parameter |
Actual Patient Value |
Normal Value |
| Max Heart Rate |
160 (101% of age-predicted max) |
159 |
| VO2max |
28.1 ml/kg/min (=8.0 METS) |
|
| VO2 max/Pred. VO2 max |
90% |
>85% |
| Max 02 Pulse |
13.7 ml/beat |
15.3 ml/beat |
| VO2 at AT |
21.3 ml/kg/min (=6.0 METS) |
|
| HR at AT |
122 |
|
| Work Rate at AT |
2.5 mph, 12% grade |
|
| VO2 AT/Pred. VO2 max |
69% |
>40% |
| Breathing Reserve |
53% |
>30% |
The patient demonstrated normal maximal aerobic capacity with no evidence
of clinically relevant cardiac or pulmonary limitations to exercise
tolerance. He demonstrated normal BP response to exercise with a resting
BP of 136/90 to a max exercise BP of 152/86. ST-segment changes during
his test could not be interpreted due to Digoxin (Lanoxin) therapy and
a partial left bundle branch block. Target exercise heart rates were
therefore prescribed using respiratory gas exchange measurements as
described below:
- Exercise heart rate: 122 b/min (HR at AT=122)
- Heart rate not to exceed: 144 b/min (HR at onset of terminal hyperventilation)
- MET level for exercise: 6.0 METS
He commenced exercise training with positive benefits and no cardiopulmonary
complications.
Acknowledgement
Neil F. Gordon, MD, PhD; Christopher Scott, MSS, MS, The Heart and
Lung Group of Savannah and The Center for Heart Disease Prevention,
Candler Hospital, Savannah, Georgia.
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