Use of Bioimpedance Method to Quantify Changes in Left Ventricular Contractility in Experiments on Anesthetized Rats

Abstract

The impedance method of pre-ejection period (PEP) evaluation had been adapted for a small animal study and validated with a Millar-type pressure sensor inserted into aorta near the aortic valve or in the left ventricle. A strong correlation (r=0.95) was found between the PEP values deter- mined by the impedance and micromanometer methods. The difference between the PEP estimates was about 5 ms. A signif- icant correlation (r=0.75-0.78) was also found between the PEP and invasive indices of left ventricular contractility, dP/dt|max and dP/dt|max/P. It was observed for a variety of the baseline states added with those during dopamine or ketamine injec- tions. The contractility changes induced by a number of sub- stances were evaluated by the invasive and impedance methods, which showed very similar time course of the responses. Mean- while, the diastolic filling of the heart or changes in the arterial pressure during the tilt test or caused by a hypotensive agent may also affect PEP. Our findings suggest that impedance method can provide an accurate estimation of PEP changes in animal experiments. So, it can be a useful tool for quantifying potential inotropic effects of pharmacological agents. However, it should be also taken into consideration the dependency of PEP on the preload and afterload conditions, especially, when vaso- dilation effects persist.