Assessment of aortic pressure power components and their link to overall elastic and resistive arterial properties

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Abstract

This paper reviews the analytical expressions for in-phase and quadrature aortic power components associated with the real and imaginary parts of aortic input admittance, respectively. It is shown that active power\(\dot W_{act} \), and its steady,\(\dot W_{stdy} \), and pulsatile,\(\dot W_{puls} \), components logically follow from in-phase power. Reactive power follows from quadrature power only for sinusoidal signals. The definition of reactive power indexes for real aortic pressures and flows requires extreme care. The link between overall arterial properties and pressure power components (and indexes) is investigated, making use of a three-element windkessel model and ascending aortic pressure and flow data taken from eight anaesthetised dogs, under basal state and after treatment with a vasoconstrictor (methoxamine). Seven dogs are normotensive in the baseline state (NBA cases, n=7), the average (±SE) of mean pressure being 86.5±5.2 mmHg. The eighth dog has a baseline mean pressure of 134 mmHg and is considered to be hypertensive. The two experimental cases from this dog are grouped with those from the other seven dogs after vasoconstriction, to form the NVC+H group (n=9). On average, fitting the model to the experimental data yields a 100% increase (p<0.05) in total peripheral resistance, a 63% decrease (p<0.01) in total arterial compliance and a 10% decrease (p>0.05) in aortic characteristic impedance, from the NBA group to the NVC+H. Correspondingly, the peak-to-peak amplitude of quadrature power shows a 69% increase (p<0.02).\(\dot W_{act} \),\(\dot W_{stdy} \), and\(\dot W_{puls} \) show a 28% increase (p>0.05), a 40% increase (p<0.02) and a 43% decrease (p>0.05), respectively. Energetic efficiency of the arterial system, Eart=1-(\(\dot W_{puls} /\dot W_{act} \)), increases by 8% (p<0.02). From analysis of the estimates of power components and arterial parameters in relation to lowfrequency phase angles of aortic impedance, it is concluded that the decrease in total arterial compliance with increasing pressure reduces the power lost in pulsation. This happens at the expense of an increase in quadrature power and absolute values of related reactive power indexes.

Keywords

Active power In-phase power Quadrature power Reactive power Three-element windkessel Arterial compliance 
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Copyright information

© IFMBE 1999

Authors and Affiliations

  1. 1.Department of Electronics & AutomaticaUniversity of AnconaAnconaItaly
  2. 2.Department of Veterinary & Comparative Anatomy Pharmacology & PhysiologyWashington State UniversityPullmanUSA

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