Aortic input impedance during hypovolemic shock and after hyperosmotic solution infusion

ABSTRACT

Aortic input impedance (Zin) was determined in 7 chloralose-urethane-anesthetized dogs. Flow and pressure were recorded in the ascending aorta during randon cardiac pacing. These signals were processed on a spectrum analyzer utilization the Fast tansform. Measurements were made 1) under control conditions; 2) every 5 min throughout 1 h of hypovolemic shock; 3) every 5 min for 5 min for 30 min after ending infusions of hypersosmotic solution (7.5%) NaCl, 4.5 ml/Kg body weight). We conclude that the determination of characteristics impedance (Zc) (average value of Zin from 4 to 10 Hz) can be useful for determining the initial phase of vascular decompensation in hypovolemic shock. After hyperosmotic solution infusion we observed a reduction in peripheral resistance, Zin, Zc, frequency of minimal Zin and frequency of phase crossover. These datea strongly suggest a decrease in arterial vascular tonus