Background: In a given individual, a consistent relationship exists between oxygen uptake (V˙O2) and heart rate (HR) during exercise. The quotient of V˙O2 and HR (V˙O2/HR) is called the oxygen pulse (O2 pulse), and its value is dependent on stroke volume (SV). However, it is difficult to believe that the O2 pulse would indicate the SV when HR has been modified as with the use of beta-adrenergic receptor blockers (BB). Until now, the effect of BB on peak O2 pulse has not been precisely studied. We tried to clarify the effect of BB on the relationship between O2 pulse and SV.
Methods: Of 699 consecutive heart disease subjects who performed cardiopulmonary exercise tests (CPX) from 2012 to 2014, we enrolled 430 subjects who had sinus rhythm and could perform CPX until exhaustion. One hundred and fifty-seven subjects were taking BB. SV was evaluated during CPX using impedance cardiography, and we compared the peak O2 pulse with peak SV between patients without BB (Group A) and with BB (Group B).
Results: The HRs at rest and peak exercise in Group A were greater than those in Group B (74.4±13.0/min vs. 71.8±11.3/min, p<0.01, 134.9±21.7/min vs. 124.9±23.6/min, p<0.01, respectively). The regression line of the peak O2 pulse against the peak SV was steeper in Group B than in Group A. When we divided the patients into two groups according to the average values of the peak SV and peak V˙O2, O2 pulse/SV ratio in Group B above the average was greater than that in Group A, whereas it was similar in the two groups that were below average.
Conclusion: We found that the increase in the O2 pulse was disproportionately greater than the SV that was measured by impedance cardiography when a BB was used in patients with preserved SV and exercise tolerance.
Keywords: Beta-adrenergic receptor blocker; Cardiopulmonary exercise test; Oxygen pulse; Stroke volume.
Copyright © 2016. Published by Elsevier Ltd.