Figure 4. Beat-to-beat variability of CL: percent changes.

The same protocol described in Figure 2 was performed on another cell. A₁: 10-beats sequences recorded in the three perfusion conditions. A₂: superimposed shortest (NT) and longest (treated) CLs, referenced to the preceding beat, taken from each sequence. A₃: time course of CL over the corresponding 10 beats. Percent values are CV_CL of each 10 beats sequence. B₁: Seven cells underwent the entire protocol; the average CV_CL measured on this sample is reported in the histogram. B₂: On a larger number of cells we only succeeded in applying NT and ivabradine; mean CV_CL is reported in the histogram for this larger sample. C₁: all seven 10-beats CL sequences for the 3 perfusion conditions, each one normalized for the corresponding average value of CL, are pooled together in the 15-bins frequency histograms. All frequency distributions were well fitted by Gaussian curves, which are reported in Panel C₂ with the corresponding correlation coefficients. Statistics: paired t-test p<0.05 (*).