Bifurcations in the Impedance Cardiograms of Apparently Healthy Men and Women

Abstract

We have compared data from apparently healthy subjects who produced an impedance cardiogram (ZCG) having a bifurcation in the dZ/dt wave with data from other subjects to determine whether data from the bifurcated waveform should be extrapolated to the general population. Thirty men and 30 women, 21-59 years, participated. The 8 men and 5 women with bifurcations in their ZCGs were shorter, with more ponderous builds and larger chests and abdominal circumferences, and they had lower respiratory flow rates than subjects with normal ZCGs. They also had several differences in cardiovascular function at rest and in response to postural change that were measured independently of the ZCG waveform. Furthermore, the men with bifurcated ZCGs had lesser changes in stroke volume as determined from the ZCG when they changed posture than the men with normal ZCGs. We cannot explain these waveform differences by the physics of impedance or by pathology. The possibility exists that these waveforms indicate something other than 'normal'. Thus, we recommend that cardiovascular data derived from impedance cardiograms with bifurcated dZ/dt waveforms not be extrapolated to the general population until we understand the etiology of the waveform.