a unifying explanation of the aortic pulse waveform in humans
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A unifying explanation of the aortic pulse waveform in humans
Dr Justin Davies International Centre for Circulatory HealthImperial College & St Mary’s Hospital
A unifying explanation of the aortic pulse waveform in humans
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
1
23
Systolicupstroke
Inflectionpoint
Elastic recoil of the aortic
windkessel
Arterial Windkessel
Systole
Arterial Windkessel
Systole
Diastole
Morphological features of the arterial pressure wave
1
23
Systolicupstroke
Inflectionpoint
Elastic recoil of the aortic
windkessel
Apparentforwardpressure
Apparentbackwardpressure
Simple separation of pressure waveform
Apparentbackwardpressure
Apparentforwardpressure
Simple separation of pressure waveform
Apparentbackwardpressure
Apparentforwardpressure
Aortic valve closure
When the aortic valve is closed….
Where does forward pressure come from in diastole?
Apparentbackwardpressure
Apparentforwardpressure
Artefacts of simple separation of pressure waveform
Total pressure = Forwards originating + Reflected pressure
Study Aims
Study Aims
1. Use the combined windkessel-separation technique to explain the arterial pressure waveform
Study Aims
1. Use the combined windkessel-separation technique to explain the arterial pressure waveform
2. Assess the relative contributions forward and backward pressure and the arterial windkessel make to augmentation pressure
Study Aims
1. Use the combined windkessel-separation technique to explain the arterial pressure waveform
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
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)
Pres
sure
abo
ve d
iast
olic
(mm
Hg)
Simple wave separation
Pressure separation following windkessel subtraction
Time (ms)
Pres
sure
abo
ve d
iast
olic
(mm
Hg)
Simple wave separation
Time (ms)
Pressureabove diastolic(mmHg)
Effects of windkessel subtraction to pressure separation
Time (ms)
Pressureabove diastolic(mmHg)
Effects of windkessel subtraction to pressure separation
Time (ms)
Pressureabove diastolic(mmHg)
Effects of windkessel subtraction to pressure separation
dPwk (t) = dPwk x dVwk(t) = flowin(t) – flowout(t)
dt dtdVwk(t) C
Time (ms)
Pressureabove diastolic(mmHg)
Effects of windkessel subtraction to pressure separation
dPwk (t) = dPwk x dVwk(t) = flowin(t) – flowout(t)
dt dtdVwk(t) C
Time (ms)
Pressureabove diastolic(mmHg)
Effects of windkessel subtraction to pressure separation
dPwk (t) = dPwk x dVwk(t) = flowin(t) – flowout(t)
dt dtdVwk(t) C
Time (ms)
Pressureabove diastolic(mmHg)
Effects of windkessel subtraction to pressure separation
dPwk (t) = dPwk x dVwk(t) = flowin(t) – flowout(t)
dt dtdVwk(t) C
'd)'(Q
)PP(P)(P'1
0
0
teC
teet RC
tt
t
inRC
t
RCWk
Time (ms)
Pressureabove diastolic(mmHg)
Effects of windkessel subtraction to pressure separation
WindkesselPressure
ExcessPressure
Pressure separation following windkessel subtraction
Time (ms)
Pres
sure
abo
ve d
iast
olic
(mm
Hg)
Simple wave separation Separation after windkessel subtraction
Pressure separation following windkessel subtraction
Time (ms)
Pres
sure
abo
ve d
iast
olic
(mm
Hg)
Time (ms)
Pres
sure
abo
ve d
iast
olic
(mm
Hg)
Simple wave separation Separation after windkessel subtraction
Contributors to augmentation pressure
Augmentationpressure
Contributors to augmentation pressure
Augmentationpressure
Forward pressure wave
Contributors to augmentation pressure
Augmentationpressure
Reflected pressure wave
Forward pressure wave
+
Contributors to augmentation pressure
Augmentationpressure
Reflected pressure wave
+
Windkessel pressure
Forward pressure wave
+
Contributors to augmentation pressure
Contributors to augmentation pressure
windkessel 82%
forward pressure 15%
reflected pressure 3%
Augmentationpressure
Contributors to augmentation pressure
windkessel 82%
forward pressure 15%
reflected pressure 3%
Augmentationpressure
Windkessel: a major determinate of the augmentation pressure
0
20
40
60
80
0 20 40 60 80
Augmentation pressure (mm Hg.s)
Win
dkes
sel p
ress
ure
(mm
Hg.
s)r = 0.98p < 0.001
Windkessel increases with gold standard of arterial compliance
0
20
40
60
0 5 10 15 20
r=0.7p<0.001
Pea
k w
indk
esse
lP
ress
ure
(mm
Hg)
Wave speed (m/s)
Windkessel increases with gold standard of arterial compliance
What accounts for the change in shape of the pressure wave form?
Adolescent Middle-aged Elderly
What accounts for the change in shape of the pressure wave form?
Adolescent Middle-aged Elderly
What accounts for the change in shape of the pressure wave form?
Adolescent Middle-aged Elderly
• Explains shape of pressure wave
What accounts for the change in shape of the pressure wave form?
Adolescent Middle-aged Elderly
• Explains shape of pressure wave
• Biological plausibility
What accounts for the change in shape of the pressure wave form?
Adolescent Middle-aged Elderly
Close correlation between windkessel and pulse wave velocity
0
20
40
60
0 5 10 15 20
r=0.7p<0.001
Peak windkesselPressure (mmHg)
Wave speed (m/s)
What accounts for the change in shape of the pressure wave form?
Adolescent Middle-aged Elderly
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 (%)
31.9
(29.6, 34.2)
25.5
(23.4, 27.7)
6.4
(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)
0.001
PWVCF
(msec-1) 10.7
(10.0, 11.4)
10.2 (9.7, 10.7)
0.5 (-0.2, 1.2)
0.3
Can the result of the Café study be explained by the arterial windkessel?
Peripheral pressure
Derived central pressure
Can the result of the Café study be explained by the arterial windkessel?
Peripheral pressure
Derived central pressure
Can the result of the Café study be explained by the arterial windkessel?
Peripheral pressure
Derived central pressure
Can the result of the Café study be explained by the arterial windkessel?
0 100 200 300 400 500 600 700 800 9000
500
1000
1500
2000
2500
3000
3500
4000
4500
0 100 200 300 400 500 600 700 800 900 10000
500
1000
1500
2000
2500
3000
3500
4000
4500
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)
Pre
ssur
e (P
a)
Measured blood pressure Measured blood pressure
Windkessel
Measured blood pressure
Proximal-originating wave
Distal-originating wave
80
100
120
140
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
Pre
ssur
e(m
mH
g)
Time (ms) Time (ms) Time (ms)
Measured blood pressure Measured blood pressure
Windkessel
Measured blood pressure
Proximal-originating wave
Distal-originating wave
80
100
120
140
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
Pre
ssur
e(m
mH
g)
Time (ms) Time (ms) Time (ms)
Determination of the start of the windkessel inflection point
Start of change of windkessel gradient
What accounts for the change in shape of the pressure wave form?
Adolescent Middle-aged Elderly
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
What accounts for the change in shape of the pressure wave form?
Adolescent Middle-aged Elderly
0
20
40
60
80
0 20 40 60 80
Augmentation pressure (mm Hg.s)
Win
dkes
sel p
ress
ure
(mm
Hg.
s)
r = 0.98p < 0.001
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