Vascular resistance quantification in high flow resistance areas using the Doppler method

Abstract

The objective of the present study is to define and validate on an animal model (ewe) a new Doppler parameter for the assessment and monitoring of the vascular resistances in high resistance to flow areas (lower limbs, placenta with vascular disease). The high resistance index (HRI) was derived from the transmission line theory and defined as: HRI = D S with S the amplitude of the systolic peak and D that of the diastolic reverse flow. Validation of the HRI was performed on adult ewes. Distal lower limb vascular resistances were evaluated from the Doppler femoral waveform (HRI) and compared with the classic vascular resistances ( Rν), calculated from pressure and flow (mmHg/mL/min). The femoral flow variations were measured by duplex (echo-Doppler) method and the mean pressure through an arterial catheter inserted into the abdominal aorta. Two tests were used in this study: (1) A calibrated venous compression of the lower limbs extremity: The femoral flow dropped by 29%, the pressure and heart rate did not change, the HRI increased by 37% ( p < 0.01), and the vascular resistances ( Rν) by 46% ( p < 0.01). (2) The intravenous injection of 1 mg adrenaline: The arterial pressure increased by 70% ( p < 0.001), the heart rate and femoral flow dropped by 50% ( p < 0.001), and 35% ( p < 0.001), the HRI increased by 70% ( p < 0.01) and the vascular resistances ( Rν) by 140% ( p < 0.01). During the two tests, the HRI changed in proportion with the “classic” vascular resistances. Comparison of the absolute values of HRI and Rν showed a good correlation in the two tests ( r = 0.82). The present animal experiment and other human experiments have demonstrated the high sensitivity of the HRI for the assessment of vascular resistance changes.