William G. Kubicek

Physiological correlates of the cardiac thoracic impedance waveform

Abstract A high frequency, constant sinusoidal current can be passed through the chest by a noninvasive technique and pulsatile changes in the thoracic impedance recorded. These pulsations are related to the beating of the heart. Three major components are present. One component shows an increase in impedance, is associated with atrial contraction, and consistently follows the P wave of the electrocardiogram. The other two waves show a decrease in impedance. The first is associated with ventricular systole, and corresponds in time with the QRS complex of the ECG. The systolic wave is then followed by the third component, which also shows a decrease in impedance, but occurs in diastole. In instances of arrhythmias the deflection associated with the P wave occurs independently of the other two deflections. The impedance change waveform is similar to the pattern of blood flow in the venae cavae and the pulmonary veins. It is possible that the impedance changes are related to the flow of blood in these venous circuits, and the heart.

Effects of Betahistine HCl, Nicotinic Acid, and Histamine on Basilar Blood Flow in Anesthetized Dogs

An intermandibular-transclival approach to the posterior cranial fossa has been developed which allows exposure of the basilar artery for attachment of a small electromagnetic blood flow transducer. The results of single intravenous injections of betahistine hydrochloride indicated a mean increase in basilar artery blood flow of 54% and a simultaneous decrease in systemic arterial blood pressure of a duration of action of approximately one minute. Histamine phosphate yielded results similar to betahistine hydrochloride, while nicotinic acid produced only slight increases in blood flow in the basilar artery.

The effect of atrial rhythm on the thoracic impedance cardiogram.

We have observed that the thoracic impedance waveform is altered when there is a change in atrial rhythm. In order to investigate this, we selected for review impedance cardiograms of patients with various atrial rhythms. The study showed that the thoracic impedance waveform displays characteristic deflections that are specifically associated with different atrial rhythms and are analogous to those seen on the electrocardiogram. The finding that the waveform was sensitive even to the small atrial movements discernible during the rhythm of coarse atrial fibrillation was consistent with the possibility that blood flow within the vena cave-right atrial and/or the pulmonary venous-left atrial systems may be important in the genesis of the cardiac thoracic impedance waveform.