craig j. hartley, ph.d. department of medicine, program in cv sciences baylor college of medicine,...
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Craig J. Hartley, Ph.D.
Department of Medicine, Program in CV Sciences
Baylor College of Medicine, The Methodist Hospital,
and The DeBakey Heart Center, Houston, TX USA
Measurements and Scaling of Vascular Mechanics in Large and Small Mammals
Professor of Medicine, Program in Cardiovascular SciencesDirector, Instrumentation Development Laboratory
The DeBakey Heart and Vascular CenterBaylor College of Medicine and The Methodist Hospital
Houston, Texas
Ph.D. Electrical Engineering, Univ. of Washington, 1970Post Doctoral Fellow, Bioengineering, Rice Univ. 1970-72Faculty at Baylor College of Medicine 1973 - PresentAdjunct Professor of BME at Rice and Univ. of Houston
Craig J. Hartley, Ph.D.
Dissertation: "Ultrasonic properties of artery walls."
About 15 years ago we started using mice in our research, and we wondered if we could adapt what we had developed for use in patients and larger animals for use in mice.
“Have a nice day at the lab, dear?”
And could we do it noninvasively so our patients don't go home like this.
Why use mice?
Genomicsor
geneticengineering
Allows us to study human cardiovascular diseases and conditions such as: cardiac hypertrophy, atherosclerosis, hypertension, aging, and many others. But… How similar are the cardiovascular systems?
Comparison of Heart sizesDog
Rat
Mouse
Are mice good models for human diseases?
Does the size difference matter?
What are the similarities and differences?
Mice are much smaller and shorter lived, but Their cardiovascular systems appear similar.
Scaling in mammals from elephants to mice
Y = a BW b Relationship to BW(kg)* BW=25gHeart weight BW1 4.3 BW 112 mgLV volume BW1 2.25 BW 56 lStroke volume BW1 0.95 BW 24 lHeart rate BW-1/4 170 BW-1/4 427 bpmCardiac output BW3/4 224 BW3/4 14 ml/minAortic diameter BW3/8 3.6 BW3/8 0.9 mmAortic length BW1/4 13 BW1/4 5.2 cmArterial pressure BW0 100 100 mmHgAortic velocity BW0 100 100 cm/sPW velocity BW0 500 500 cm/sEntrance length BW3/4 20 BW3/4 1 mmLife span BW1/4 7.5 BW1/4 3 years
*T.H. Dawson, “Engineering design of the cardiovascular system of mammals” , Prentice Hall, 1991.
Based on cell metabolism, diffusion distances and times, and energy transport
How to these theoretically derived relationships compare with reality?
Log-log plots of heat production, oxygen consumption, and heart rate versus body weight
3/4 powerOxygen consumption
Heart rate-1/4 power
Heat production3/4 power
• Blood Pressure• Flow & Velocity• Dimensions• Cardiac Function• Impedance• Reflections• Stiffness
Cardiovascular parameters of interest
Challenge is to be noninvasive with high spatial and temporal resolution
mousemouseaortaaorta
All are functionsof time, so we need waveforms
• Fluid-filled catheters
• Micromanometers
• Tonometry
• Tail cuff
• Ultrasonic transit-time
• Ultrasonic Doppler
• Sonomicrometry
• M-mode echo & Doppler
intravascular
Intravascular
extravascular
noninvasive
extravascular
noninvasive
extravascular
noninvasive
Methods to measure pressure,flow, and dimensions in mice
Set-up for noninvasive DopplerSet-up for noninvasive Dopplermeasurements in micemeasurements in mice
10 MHzpulsed
Doppler
ECG
Cardiac Doppler measurements in mice
+90
+60
+30cm/s-0
-30
-60
Aortic
Mitral
A----
mo|
mc|
|ao
------P
Accel
| 380 ms |
------E
|ao
|ac
+12-
+8-
+4-kHz
0-
-4-
-8- R|
ECG
systolic and diastolic function and timing
ProbeProbe
Velocity and waveforms are simliar to man
20 MHzDopplerProbe
mm
Mouse carotid Dopper signal processing
Indus
ECG
256 point FFT125 k-samples/speak Doppler shift
f = 2 fo(V/c)cosθV (cm/s) = 3.75 f (kHz)
Doppler probemm
Carotid arteriesSample volume
HumanCarotid
-60
-40
-20cm/s-0
|— 1 sec —|
What aboutother vessels?
left carotid aortic arch
celiac
left renal abdominal aorta
right carotid
ascending aorta
right renal
-100
-50cm/s-0
| 250 ms |
descending aorta
Stop
20 MHz Doppler Probe
mm
20 MHz Doppler signals fromperipheral arteries in a mouse
Velocities are similar in magnitude and shape to those from humans
Pulse-wave velocity measurements in mice
20 MHzDoppler
40 mmSampleVolume
((((
(((
c = PWV = 40/12 = 3.3 mm/ms
ECG12 ms
Probe
c2 = Eh/d
PWV is similar in man
Normal, n=19 αSMA-/-, n=10 Matrix GLA-/-, n=3
0
300
600
900
1200
PWV
cm/s
Pulse-wave velocity in knockout mice
*p<0.05 vs normal
465 360 1037* *
Control
Phenylephrine
**990 432
*
**p<0.05 vs control
and responses to phenylephrine
What happens if you administer a vasoconstrictor?Again, the values are similar to those from humans.
Arterial Tonometry in MiceMillar 1.4F micromanometer
0.45 mm diameter
ECG
Pressurewaveform
MouseAorta
50 ms/div
-100
-50
0
50
100
800 900 1000 1100 1200 1300 14000 msec 100 200 300 400 500 600
mmHgor cm/s
ECG, Doppler velocity, tonometric pressure,and derivatives from a mouse carotid artery
Velocity
Pressure
dP/dt
dV/dt
ECG
Can we generate a pressure waveform noninvasively?
Real-time 2-D image of a mouse carotid artery takenwith a 30 MHz state-of-the-art VisualSonics scanner
Can we measure the waveform of the diameter pulsations during the cardiac cycle?
Vessel walls generate well-defined moving echoes.
0
30
60
90
120
600 700 800 900
-30
0
30
60
90
| 200 ms |
Diameter change=near-far
Near-wall motion1
gate 1 gate 2 gate 3
cm/sor m
- 90
- 60
- 30
- 0
Far-wall motion 3
Blood Velocity d2/dt
DopplerProbe
carotid artery
skin
((((sound beam
Blood velocity and wall motion measured in a mousecarotid artery
couplinggel
wall motion
wall motion
~500 mSV
SV3
SV1
SV2
xmit samples xmit
time Multigate 20 MHz
Pulsed Doppler
bloodvelocity
How do we stabilize the probe?
Anesthetized mouse showing Doppler probein clip holder at 60o to the right carotid artery
0
40
80
120
160
400 500 600 700
Noninvasive displacement signals from the carotidartery, abdominal aorta, and iliac artery of a mouse
40m
Abdominal aorta (~110m)
Carotid (~50m)
Iliac (~20m)
0 msec 100 200 300
R-wave
Diameters pulsate about 10%Waveforms damp with distanceResemble pressure waves
0
50
100
150
200
10 110 210 310
50mSMA (100 m)
Old (55 m)
WT (45 m)
ApoE (14 m)
0 msec 100 200 300
Carotid artery diameter signals fromdifferent types and strains of mice
Resemble pressure wavesHow good is the resolution?
-20
-19
-18
-17
-16
-15
-14
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
150 200 250 300 3500 ms 50 100 150 200
1 m
Carotid artery wall motionin an ApoE-KO mouse
demonstrating high spatialand temporal resolution
Mousered cell
What about the inflections?
0
30
60
90
120
150
600 700 800 900
-25
5
35
65
95
125
30-
cm/s0-
__
30m__
net diameterchange
blood velocity
0 msec 100 200 300
wall velocity
3-
mm/s0-
infmax
min
local minimum
Vessel diameter and velocity showing how theaugmentation index is calculated from strain
AI = max-infAI = max-inf max-minmax-min
D = max-minD = max-min
In humans,AI increaseswith age andvasc disease
0.3
AI
0.2
0.1
0.00 m 20 40 60 80 100
Diameter change
WTApoESMAOld
0
0.1
0.2
0.3
0 20 40 60 80 100
WT
ApoE
aSMA
Old
Carotid artery augmentation index versus diameterpulsations for several types and strains of mice
Aorta Carotid artery
Velocity
Pressure
ECG
Why do the velocity waveforms look different? Pulse transmission and reflection in a compliant tube
PWV = c = (Eh/d)1/2
•PWV is a function of stiffness and geometry and is faster in hard vessels and slower in floppy ones.
•The interaction of the forward and backward waves generate the shape of the measured pressure and flow waves at each site.
•Because the waves distort and meet at different times, the shape of the measured pressure and flow waves is a function of position.
•In arteries, the speed is fast enough and ejection takes long enough that reflections start to arrive at the heart before the end of cardiac ejection.
Wave transmission and reflection in the aorta
Heart Aorta
Forward wave
Backward wave
Time
Measured wave
Wave transmission and reflection in the aorta
Measured wave
Flow wave
Heart Aorta
Forward wave
Backward wave
Time
Pf
Pb
Pm
Qm
Pressure, diameter, flow, and velocity start up at the same time and have similar shapes until the reflected wave arrives.
Qf = Pf/Zc
Qb = -Pb/Zc
Pm = Pf + Pb
Qm = (Pf - Pb)/Zc
Pf = (Pm + ZcQm)/2Pb = (Pm - ZcQm)/2
Zc = dPs/dQs
-150
-100
-50
0
50
100
150
400 500 600 700
0
10
20
30
40
50
60Velocity, Diameter, and calculated forward and backward waves in a mouse carotid artery
Velocity Diameter
Forward
Backward
D = Df + Db
v = (Df - Db)/Zc
Df = (D + Zcv)/2Db = (D - Zcv)/2
Zc = dDs/dvs (=c)
(f) = Db/Df = || ej
Z(f) = |D/v| ej0 msec 100 200 300
50
40-
30-
20-
10-
cm/s0-
Pressure ~ Diameter Flow ~ Velocity
Why are there 2 peaks in Df? Does this happen in man?
0
20
40
60
80
100
120
140
700 900 1100 1300 1500 1700 1900 2100 2300 2500 2700
-20
0
20
40
60
80
100
120140-Press
120-
100-
80-
60-
40-
20-mmHg
0-
-80Velocity-60
-40
-20cm/s-0
0 Seconds 1 2
Human carotid pressure and velocity signals
Tonometric Pressure
Doppler Velocity
Forward
Backward
Body Worlds 3 - Gunther von Hagen
Can we measure coronary blood
flow in mice?
Cast of Coronary Arteries
What happensto coronary flow?
Doppler catheters can be used to sense flow in man. However, because of compensation, resting flow is often normal even with a severe coronary stenosis. What is limited is maximum flow.
H/B = 3.0
In humans, the physiological significance of coronary artery disease is often assessed by the ratio of peak hyperemic velocity (after administration of a vasodilator) to resting baseline coronary velocity (H/B). A form of stress test.
----Hyperemic
-----Baseline
Injection of contrast agent
1 sec timer
raw phasic velocity
filtered mean velocity
fast | slow paper speed
3
HB
2
1
Can we do this in mice?
Cole & Hartley, Circulation, 1977
Problems:
Coronary arteries are small, ~200m
They are close to many other vessels
Everything around them moves
It seemed impossible to measure flow .... until we tried.
Coronary Blood Flow in Mice?
20 MHz Doppler Probe((((((
Method to sense coronary blood flow noninvasively in mice
-50cm/s-50cm/s
Is this coronary flow?
Left main coronary flow
Common carotid flow
Aortic flow
ECG HR = 550
Velocity in 3 mouse vessels showing relative timing-50
cm/s-0
-50
cm/s-0-100
-50
cm/s-0
---maximum
This give us baseline velocity, but, how can we measure hyperemic velocity and coronary reserve noninvasively?
--80--
--60--
--40--
--20--cm/s---0---
ECG
| 800 ms |
Noninvasive coronary Doppler signals from a mouse
Vmean
HR = 398 b/min
low =1.0% high = 2.5%
H/B = Vhigh/Vlow = 2.2
HR = 412 b/min
anesthetized at low and high levels of isoflurane gas
Vmax
What about old and ApoE mice?
0
20
40
60
80
100
120
140
6 wk 3 mo 2 yr ApoE
140-
120-
100-
80-
60-
40-
20-cm/s
0-
H/B-4
-3
-2
-1
-06 wk 3 mo 2 yr 2 yr ApoE-/-
B
H
H/B
B - Baseline Peak Diastolic Velocity (1.0 % Isofl) H - Hyperemic Peak Diastolic Velocity (2.5 % Isofl)
Mean +/- SE
35 84 2.4 30 84 3.0 25 87 3.6 52 120 2.5
Coronary flow velocity reserve (H/B) in miceas a function of age and atherosclerosis
What about non-coronary forms of heart and vascular disease?
CFR = H/B
n = 10 n = 10 n = 10 n = 20
and carotidremodeling
Right Left
27gauge
Aortic banding in mice
Before After
mm
Produces cardiac hypertrophy-pressure overload
Carotid Flows?
-500
cm/s-0
-20-0-160
cm/s-0
ECG
Aortic Arch Jet Velocity - 10 MHz Doppler
Left Carotid Artery Velocity - 20 MHz Doppler
Right Carotid Artery Velocity - 20 MHz Doppler
AorticBand
left maincoronary
artery
msec
P~75 mmHg
mm scale
Simultaneous Doppler signals from a banded mouse
What happens to coronary flow?
21Days
H/B = 0.9
| 400 ms |
1 Day
H/B = 1.7
-100
-50
cm/s-0
Coronary blood velocityin a banded mouse
PreBand
1% isoflurane
2.5% isofluraneH/B = 2.0
0
1
2
3
4
Pre 1 d 7 d 14d 21d
4-
3-
2-
1-
0-Pre 1 day 7 day 14 day 21 day
Hyperemic/Baseline Velocity
H/B Heart Rate
Response of coronary velocity and heart rate to isoflurane in 10 banded mice during remodeling
(CFR)
(Little change)
3.2 2.2 1.7 1.4 1.1
0.0
0.2
0.4
0.6
0.8
1.0
Pre 1 d 7 d 14d 21d
1.0-
0.8-
0.6-
0.4-
0.2-
0.0-Pre 1 day 7 day 14 day 21 day
S/D Baseline
S/D Hyperemic
Systolic/Diastolic coronary velocity area ratio before and after banding in mice
S S DD
.17 .23 .29 .50 .67 .81 .83 .88 .92 .86
Differences in timing between left and right coronary flow velocity in a patient
200
100mmHg
0
8
4kHz
0
ECG
Pressure
DopplerShift
Left coronary artery Right coronary artery
Systole
Heart weight BW1 Capillary diameter BW1/12
LV volume BW1 Capillary length BW5/24
Stroke volume BW1 Capillary number BW5/8
Blood volume BW1 Capillary velocity BW-1/24
Heart Rate BW-1/4 Cell number BW5/8
Heart Period BW1/4 Cell length BW1/8
Circulation time BW1/4 Cell volume BW3/8
Life span BW1/4 Elastic modulus BW0
Artery length BW1/4 Blood viscosity BW0
Artery diameter BW3/8 Arterial pressure BW0
Wall shear stress BW-3/8 Blood velocity BW0
Cardiac output BW3/4 PW velocity BW0
Entrance length BW3/4 Diameter pulsation BW0
Acceleration, dP/dt BW-1/4 Coronary reserve BW0
*T.H. Dawson, “Engineering design of the cardiovascular system of mammals” , Prentice Hall, 1991.
Scaling in mammals from elephants to mice Y = a BW b
Parameter Power RatioHeart & blood volume 1 2800Cardiac output, flow 3/4 385Cell number 5/8 143Vessel diameter 3/8 20 Linear dimension 1/3 14Vessel length, periods 1/4 7Cell length 1/8 2.7Capillary diameter 1/12 2Blood pressure & vel. 0 1Capillary velocity -1/24 0.7Heart rate, Accel. -1/4 0.14
Human/mouse scale factorsAllometricEquation
Y = a BWb
Human/mouse70kg / 25g
Conclusions - (Measurements)
•Blood velocity signals from the heart and most arteries of mice can be obtained noninvasively
•High-fidelity arterial displacement signals can also be obtained noninvasively at the same time
•Pulse wave velocity, augmentation index, percent diameter change, and coronary reserve can be determined from velocity and displacement signals and their responses to vasoactive agents
Conclusions - (Scaling)
•Blood velocity, blood pressure, pulse wave velocity, and percent wall displacement in mice and humans are similar in both magnitude and shape.
•The arterial time constants are scaled to heart period such that reflections return to the heart at similar times during the cardiac cycle. Waveforms
•Most of the things we can measure in mice and man are altered by age and disease in similar ways.
Anil Reddy Lloyd MichaelMark Entman George TaffetYi-Heng LiDirar KhourySridhar Madala (Indus)Y-X (Jim) Wang (Berlex)
Faculty Collaborators TechniciansFaculty Collaborators Technicians
Thuy PhamJennifer Pocius
Jim BrooksRoss HartleyAlex Tumang
CreditsCredits