2017A10 Draw both aortic root and radial artery pressure waveforms on the same axes. Explain the differences between them.

Aortic wave

·   Due to change in intra-aortic volume and pressure across the cardiac cycle

Radial wave

·   Due to transmission of the waveform

·   Not due to blood flow (but a small amount of forward flow is required for propagation of the waveform)

Pressure wave propagation

·   Wave has fast moving (10m/s) and slow moving (0.5m/s components)

·   Role of resistance:

o Some forward flow required to distend the vessel and propagate the wavefront

o Pressure drop ∝ arterial resistance

·   Role of compliance:

o Arterial compliance ∝ volume increment ∝ 1/speed

Radial waveform (cf. aortic)

Reason

Delayed start 0.06 seconds

·   Time taken for wave front to travel (note much faster than blood flow)

Narrower and higher systolic component

Steeper upstroke = ↑dp/dt max

·   Less elastic tissue

·   Relatively more muscular tissue

·   ↓ compliance (δv/δp)

Lower diastolic component

·   Less elastic tissue

·   Less Windkessel effect (storage and release of energy)

Slightly lower mean

·   Above factors

Widened pulse pressure

·   Above factors

Disappearance of high freq components

·   Damping affects high > low freq

·   Damping ∝ frictional tissue interactions per length or time

Appearance of dicrotic notch

·   Reflection and resonance.

↓Large artery elasticity

·   ↓Compliance

·   ↓Elastic return and Windkessel effect

·   ↓Waveform variation (aortic similar to radial)

·   ↑Waveform propagation velocity