Key result
Acoustic double-product breakpoint correlates strongly with anaerobic threshold to estimate aerobic capacity.
Why the study?
There are no simple methods for measuring cardiac metabolic stress during an exercise test, and the double product breakpoint of heart rate and systolic blood pressure coincides with anaerobic threshold.
Does the double product of heart rate and first heart sound amplitude (DP-AHS1) accurately reflect cardiac metabolic stress and anaerobic threshold during graded exercise?
Observational (n=67)
No
Does the double product of heart rate and first heart sound amplitude (DP-AHS1) accurately reflect cardiac metabolic stress and anaerobic threshold during graded exercise?
The double product of heart rate and first heart sound amplitude provides a simple, non-invasive surrogate marker for cardiac metabolic stress and anaerobic threshold during exercise.
BACKGROUND The double product (DP) breakpoint of heart rate (HR) and systolic blood pressure has been identified as coincident with anaerobic threshold (AT), but there are no simple methods for measuring cardiac metabolic stress (CMS) during an exercise test. It was hypothesized that the DP of HR and the amplitude of the first heart sound (AHS1) (DP-AHS1) would reflect CMS, and thus, the breakpoint in the DP-AHS1 (DPBP-AHS1) could be an alternative method for determining AT. METHODS AND RESULTS Subjects (age range, 18-73 years) were recruited to perform a graded exercise test on a cycle ergometer with continuous monitoring of DP-AHS1, with left ventricular pressure (LVP; experiment 1, Ex1), plasma catecholamine and blood lactate (experiment 2, Ex2) and gas exchange (experiment 3, Ex3). Ex1: in all subjects there was a strong correlation between AHS1 and LVdP/dtmax (r=0.94-0.98), and between the DP-AHS1 and the triple product of HR, LVdP/dtmax, and max LVP (r=0.98-0.99). Ex2: DP-AHS1 was strongly correlated with adrenaline (r=0.97-1.00) and lactate (r=0.96-1.00) levels in all subjects. Ex3: there was a strong correlation between DPBP-AHS1, AT and maximum oxygen consumption. CONCLUSIONS The present simple measure of DP-AHS1 can reflect plasma adrenaline and lactate levels during graded exercise testing. Further, DPBP-AHS1 is a surrogate marker of AT and a good index of functional aerobic capacity.
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Tanaka et al. (2013) conducted an observational in Healthy adults undergoing graded exercise (n=67). Measurement of the double product of heart rate and the amplitude of the first heart sound (DP-AHS1) vs. Standard anaerobic threshold (AT) and myocardial oxygen demand indices was evaluated on Correlation between the breakpoint of DP-AHS1 (DPBP-AHS1) and anaerobic threshold (AT) (r=0.86, p=<0.001). The breakpoint in the double product of heart rate and the amplitude of the first heart sound (DPBP-AHS1) during graded exercise is highly correlated with the anaerobic threshold (r=0.86, P<0.001), offering a simple surrogate marker for functional aerobic capacity.
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