Wave transmission and reflection of waves “The myth is in their use”

Arterial input impedance, as complete description of the arterial system, is explained by waves and wave reflection. Without wave reflections input impedance would equal aortic characteristic impedance and pressure and flow wave shapes would be similar. Waves reflect at many locations, causing input impedance to deviate from aortic characteristic impedance. For low harmonics (frequencies) reflections add, causing a large composite reflected (backward) wave, high harmonics return randomly giving small total refection. Non-pulsatile parts of pressure and flow (means) are related through peripheral resistance. Raised resistance increases mean pressure but leaves wave reflections and wave shape almost unaffected. Stiffer arteries increase impedance at low harmonics, therefore reflection increases with stiffening. Pressure alone, depends on heart and load, thus systolic, diastolic, pulse pressure and augmentation index, cannot give accurate information about the arterial system. The myth of waves is that wave travel and reflection could give information on arterial function. Waves do not apply to mean pressure, and resistance cannot be derived. Characteristic impedance is used in separation. Due to many reflection sites the return time of the reflected wave, inflection and shoulder points all differ and cannot give accurate information on stiffness. Reflection Magnitude (Pbackw/Pforw) increases nonlinearly by 50%, when total arterial stiffness increases by a factor 4, (Pulse Wave Velocity, PWV 6 to 12 m/s), but changes hardly when aortic stiffness alone is increased by this factor. PWV is a surrogate of (aortic) stiffness, but aortic length and average diameter are required. Thus waves give limited information of arterial stiffness.