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Where to B in dZ/dt


  • We thank Yunju Chen for assistance. This research was supported in part by grants from the NHLBI to G.G.B. (HL54428) and C.F.E. (HL068956), a NIMH grant (MH058767) to B.D.M., and by Grant M01-RR00034 from the National Center of Research Resources of the NIH to the General Clinical Research Center, Ohio State University.

Address reprint requests to: Gary G. Berntson, Ohio State University, 1835 Neil Avenue, Columbus, OH 43210. E-mail:


The B point on the impedance cardiograph waveform corresponds to the opening of the aortic valve and is an important parameter for calculating systolic time intervals, stroke volume, and cardiac output. Identifying the location of the B point is sometimes problematic because the characteristic upstroke that serves as a marker of this point is not always apparent. Here is presented a reliable method for B point identification, based on the consistent relationship between the R to B interval (RB) and the interval between the R-wave and the peak of the dZ/dt function (RZ). The polynomial function relating RB to RZ (RB=1.233RZ−0.0032RZ2−31.59) accounts for 90%–95% of the variance in the B point location across ages and gender and across baseline and stress conditions. This relation affords a rapid approximation to B point measurement that, in noisy or degraded signals, is superior to visual B point identification and to a derivative-based estimate.