Basic Hemodynamic Elements
The impedance of the three basic hemodynamic elements  is shown in the right hand side of the Figure in the box. For the resistance, the pressure drop and flow are in phase and their amplitude ratio gives the value of the resistance. For the compliance, the sine wave of flow precedes the pressure drop, and they are −90° out of phase, i.e., a quarter of the whole sine wave for all frequencies. The modulus of the impedance, |Z(ω)| equals 1/ω ⋅ C, with C compliance and ω the circular frequency, ω = 2π ⋅ f, f being the frequency in Hz (cycles per second). Increasing frequency implies decreasing impedance modulus. For the inertance the impedance modulus equals |Z(ω)| = ω ⋅ L= 2π ⋅ f ⋅ L, the impedance increases with frequency, and the phase angle is +90° for all frequencies.
KeywordsPressure Drop Aortic Valve Phase Angle Sine Wave Systemic Vascular Resistance
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