A unifying explanation of the aortic pulse waveform in humans

Dr Justin Davies International Centre for Circulatory HealthImperial College & St Mary’s Hospital

Dr Justin Davies International Centre for Circulatory HealthImperial College & St Mary’s Hospital

No conflicts of interest to declare

Adolescent Middle-aged Elderly

What accounts for the change in shape of the pressure wave form?

McDonald’s Blood Flow in Arteries,4th Edition (1998), Arnold.

Morphological features of the arterial pressure wave

Systolicupstroke

Inflectionpoint

Elastic recoil of the aortic

windkessel

Arterial Windkessel

Systole

Arterial Windkessel

Systole

Diastole

Morphological features of the arterial pressure wave

Systolicupstroke

Inflectionpoint

Elastic recoil of the aortic

windkessel

Apparentforwardpressure

Apparentbackwardpressure

Simple separation of pressure waveform

Aortic valve closure

When the aortic valve is closed….

Where does forward pressure come from in diastole?

Artefacts of simple separation of pressure waveform

Total pressure = Forwards originating + Reflected pressure

Study Aims

1. Use the combined windkessel-separation technique to explain the arterial pressure waveform

Study Aims

2. Assess the relative contributions forward and backward pressure and the arterial windkessel make to augmentation pressure

Study Aims

2. Assess the relative contributions forward and backward pressure and the arterial windkessel make to augmentation pressure

3. Assess how the arterial windkessel relates to pulse wave velocity

Study Design

Subjects undergoing diagnostic coronary angiography

Study Design

Subjects undergoing diagnostic coronary angiography

Simultaneous haemodynamic measurements were made at aortic root

Doppler Flow wire(Flowire, Volcano Therapeutics)

Pressure wire(Wavewire, Volcano Therapeutics)

Patient demographics

• 19 subjects

• 54 ±13 years old

• 9 Female

• 145/80 mmHg

Pressure separation following windkessel subtraction

Time (ms)

Simple wave separation

Time (ms)

Simple wave separation

Time (ms)

Pressureabove diastolic(mmHg)

Effects of windkessel subtraction to pressure separation

Time (ms)

dPwk (t) = dPwk x dVwk(t) = flowin(t) – flowout(t)

dt dtdVwk(t) C

Time (ms)

dt dtdVwk(t) C

Time (ms)

dt dtdVwk(t) C

Time (ms)

dt dtdVwk(t) C

'd)'(Q

)PP(P)(P'1

teet RC

Time (ms)

WindkesselPressure

ExcessPressure

Time (ms)

Simple wave separation Separation after windkessel subtraction

Time (ms)

Simple wave separation Separation after windkessel subtraction

Contributors to augmentation pressure

Augmentationpressure

Forward pressure wave

Reflected pressure wave

Windkessel pressure

windkessel 82%

forward pressure 15%

reflected pressure 3%

windkessel 82%

forward pressure 15%

reflected pressure 3%

Windkessel: a major determinate of the augmentation pressure

0 20 40 60 80

Augmentation pressure (mm Hg.s)

s)r = 0.98p < 0.001

Windkessel increases with gold standard of arterial compliance

0 5 10 15 20

r=0.7p<0.001

Wave speed (m/s)

Windkessel increases with gold standard of arterial compliance

• Explains shape of pressure wave

• Biological plausibility

Close correlation between windkessel and pulse wave velocity

0 5 10 15 20

r=0.7p<0.001

Peak windkesselPressure (mmHg)

Wave speed (m/s)

Dr Jamil Mayet Prof Alun Hughes

British HeartFoundation

CoronaryFlowTrust

Key Findings

• Waves and windkessel make up pressure waveform• Windkessel greatest contributor to augmentation

pressure • Windkessel highly correlated with PWV

Dr Darrel Francis Prof Kim Parker

Can the result of the Café study be explained by the arterial windkessel?

Parameter Atenolol Amlodipine Difference

(Atenolol-Amlodipine)

Statistics t-test (p)

Augmentation

Index (%)

(29.6, 34.2)

(23.4, 27.7)

(4.1, 8.7)

<0.001

Augmentation (mmHG)

16.1 (14.4, 17.7)

12.4 (10.9, 13.9)

3.7 (2.0, 5.3)

(msec-1) 10.7

(10.0, 11.4)

10.2 (9.7, 10.7)

0.5 (-0.2, 1.2)

Peripheral pressure

Derived central pressure

Peripheral pressure

0 100 200 300 400 500 600 700 800 9000

0 100 200 300 400 500 600 700 800 900 10000

Wave Intensity Analysis

Separation of forward pressure wave using wave intensity analysis and Fourier methods gives identical results

Fourier technique

Start with p(t) and u(t) Differentiate to get dp(t) and du(t) Forward pressure(t) = (1/2)dp(t) + (1/2)rho c du(t) Integrate it to get pplus(t)

Start with p(t) and u(t) Fourier transform to get P(f) and U(f) Forward pressure) = (1/2) P(f) + (1/2) rho c U(f) Reverse Fourier transform to getpplus(t)

Time (ms)

Measured blood pressure Measured blood pressure

Windkessel

Measured blood pressure

Proximal-originating wave

Distal-originating wave

0 200 400 600 800 10000 200 400 600 800 1000 0 200 400 600 800 10000 200 400 600 800 1000 0 200 400 600 800 10000 200 400 600 800 1000

Time (ms) Time (ms) Time (ms)

Measured blood pressure Measured blood pressure

Windkessel

Measured blood pressure

Proximal-originating wave

Distal-originating wave

0 200 400 600 800 10000 200 400 600 800 1000 0 200 400 600 800 10000 200 400 600 800 1000 0 200 400 600 800 10000 200 400 600 800 1000

Time (ms) Time (ms) Time (ms)

Determination of the start of the windkessel inflection point

Start of change of windkessel gradient

Windkessel 82% of augmentation pressure

Shape of pressure waveform determined by timing and magnitude of forward and backward waves and windkessel

Windkessel

Forward Pressure

Reflected Pressure

Video to show the effect of windkessel subtraction on pressure separation

Total pressure

0 20 40 60 80

Augmentation pressure (mm Hg.s)

r = 0.98p < 0.001

A unifying explanation of the aortic pulse waveform in humans

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