Figure 2

Computing the second heart sound amplitude variation as a function of heart rate. All the parameters are acquired as instantaneous values at baseline and during stress; mobile mean is utilized to assess baseline value (1 minute recording), at each incremental stress test, at peak test, and during recovery. Left panel: instantaneous S2 amplitude scattering (blue points exercise, red points recovery) depends on the respiratory cycle and thorax expansion; blue and red curves = S2 amplitude mobile mean. Right panel: blue curve = exercise in progress; red curve = recovery.