The relationship between heart rate and oxygen consumption in heart transplant recipients during a cardiopulmonary exercise test: heart rate dynamic during exercise test.

Background: In healthy subjects, the percentage of heart rate reserve (%HRR) versus the percentage of oxygen consumption reserve (%VO(2)R) is the closest relationship between heart rate and VO(2) and it seems also to be true to heart failure patients only if they are under optimized beta-blocker therapy.
Aim: To evaluate the closest relationship between heart rate and VO(2) (%peak heart rate versus %peak VO(2); %HRR versus %VO(2)R or absolute heart rate versus absolute VO(2)) in heart transplant recipients during a treadmill cardiopulmonary exercise test.
Methods: A total of 19 sedentary heart transplant recipients (5.4 ± 3.3 years after transplant) in a stable condition (for, at least, 3 months), were recruited to perform a cardiopulmonary exercise test. The relationship between %HRR-%VO(2)R, %peak heart rate versus %peak VO(2) and absolute heart rate versus absolute VO(2) were tested.
Results: The strongest relationship was found between %HRR-%VO(2)R (r = 0.95, p<0.0001), followed by %peak heart rate versus %peak VO(2) (r = 0.91, p<0.0001) and absolute heart rate versus absolute VO(2) (r = 0.67, p<0.0001). The mean regression line did not coincide with the line of identity in any group (p<0.0001 for all groups).
Conclusion: The %HRR versus %VO(2)R showed the closest relationship followed by %peak heart rate versus %peak VO(2) and absolute heart rate versus absolute VO(2). Despite this, the perfect reliability of the heart rate versus VO(2) was not found.
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