the Vascular System
Pressure and flow waveforms do not necessarily contain the exact
significant harmonics. When the flow harmonic becomes very
small, the ratio of pressure to flow or the impedance modulus for that
harmonic component obtained can be erroneous.
Input impedance of the systemic arterial tree have been obtained in
the systemic pulmonary and coronary arterial circulations.
impedances have been measured in man, dog and other mammalian
gives an example of the modulus and phase of the
vascular impedance measured at the ascending aorta or the input
impedance of the systemic arterial tree in normal adults.
Modulus and phase
the impedance measured at the ascending aorta or input
the systemic arterial tree in a normal adult
and the average obtained
indicates characteristic impedance
the proximal aorta. From
Nichols and O’Rourke
Input impedance shows
large decrease in magnitude at very
Hz), then oscillates, exhibiting maxima and minima, and
somewhat constant level-low compared to
value, at higher frequencies
approaches the characteristic impedance
proximal aorta at these high frequencies. The phase of the impedance is
initially negative, becoming progressively more positive and crossing
zero at about
Hz, and remains positive but close to zero thereafter.