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

· Waveforms

· Aetiology

· Difference by location

· Difference with ageing

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