Hemodynamics
description
Transcript of Hemodynamics
![Page 1: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/1.jpg)
Hemodynamics
Purpose of control mechanisms of blood flow?
Maintain homeostasisPurpose of blood flow?
Nutrient and waste exchange
Blood flow to brain and heart must be maintained
Insufficient blood volume to perfuse all tissuesimultaneously
Blood flow must match metabolic needs of tissue
AJ Davidoff
![Page 2: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/2.jpg)
MAP = CO x TPR
Important to maintainadequate perfusion pressure in order to control blood flow
Sherwood Fig 10-1
HR x SV
MAP = mean arterial pressureTPR = total peripheral resistanceCO = cardiac output
![Page 3: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/3.jpg)
Sherwood
Capillary exchange is the sole purpose of the circulatory system
Blood flow depends on pressure gradients and vascular resistance
![Page 4: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/4.jpg)
Relationship between blood flow, pressure and resistance
Ohm's Law: V = I*R or I = V/R
V = voltage (potential difference)I = currentR = resistance
Blood Flow: P = Q*R or Q = P/R
Q = flow (mL/min) P = pressure gradient (mm Hg)R = resistance (mm Hg/mL/min)
The major mechanism for changing blood flow is by changing arterial resistance (e.g., TPR or in a single
organ)
![Page 5: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/5.jpg)
Pressure gradients
Pressure difference affects flownot absolute pressure
Sherwood Fig 10-3
![Page 6: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/6.jpg)
Resistance to Blood Flow
Poiseuille equationR = 8L r4
R = resistance = viscosity of bloodL = length of blood vesselr4 = radius of blood vessel raised to the fourth power
If radius decreases by one half, resistance increases by 16-fold (= 24)!!!
(r4 = area)
![Page 7: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/7.jpg)
Radius profoundly affects blood flow
Sherwood Fig 10-4
R~ 1/r4
Q = P/R
Flow ~ r4
![Page 8: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/8.jpg)
Costanzo Fig 4-5
Q = P/R
Total resistance equals the sum of the individual resistances
Total flow is the same at each level, but pressure decreases progressively
(93 mm Hg) (4 mm Hg)
Why?
Series Resistance
![Page 9: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/9.jpg)
Parallel Resistance
Flow in aorta is equal to the flow in the vena cave (steady state)Flow to each organ is a fraction of the total blood flowTotal resistance is less then any of the individual resistances,therefore no significant loss of arterial pressure to each organ
5 L/min 5 L/min
Needs work
![Page 10: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/10.jpg)
Velocity of Blood Flowv = Q/A
v = velocity of flow (cm/sec)Q = flow (ml/sec)A = cross-sectional area (cm2)Costanzo Fig 4-4
![Page 11: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/11.jpg)
Costanzo Fig 4-3
Total cross sectional area of systemic blood vessels
v = Q/A
![Page 12: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/12.jpg)
Laminar flow and Turbulence
Laminar flow is parabolic, highest velocity in center (least resistance), lowest adjacent to vessel walls
Turbulent flow is disoriented, no longer parabolic, energy wasted, thus more pressure required to drive blood flow.
quiet
noisy
Costanzo Fig 4-6
![Page 13: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/13.jpg)
Ganong Fig 30-8
Turbulence is velocity of blood flowdiameter of blood vessel1/ viscosity of blood
Mohrman and Heller Fig 6-6
![Page 14: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/14.jpg)
Bernouilles Principle (in a single vessel)Total energy = distending pressure (PD) + kinetic energy (KE)
Higher velocity through a constrictionPDKE
Bad for plaque regionsWhy?
Total energy is actually not conserved completely because of heat loss
![Page 15: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/15.jpg)
Bad for aneurysmsWhy?
KE
PD
Bernouilles Principle
![Page 16: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/16.jpg)
Cardiovascular Physiology Conceptshttp://www.cvphysiology.com/Blood%20Pressure/BP004.htm
Compliance of blood vessels
C = compliance (mL/mm Hg)V = volume (mL)P = pressure (mm Hg)
C = V/ P
• Compliance is a slope
• At low pressures, veins have a greater compliance than arteries
• At high pressures, compliance is similar in veins and arteries (but volume is much greater in veins)
![Page 17: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/17.jpg)
Compliance changes related to vasocontraction or aging
With vasocontraction:• Venous volume
decreases and pressure increases
• Venous compliance decreases
Similar effects in arteries with aging
![Page 18: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/18.jpg)
Martini Fig 21-2
ArteriesConduits
BloodVessels
![Page 19: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/19.jpg)
Pressure reservoir
Sherwood Fig 10-6 & -7
Elastic recoil continues to drive blood toward arterioles during diastole
![Page 20: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/20.jpg)
B&B Fig 17-11
![Page 21: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/21.jpg)
MAP = diastolic pressure + 1/3 pulse pressure(at rest)
2/3 time in diastole1/3 time in systole
80 mph for 40 min120 mph for 20 min
Sherwood Fig 10-7
![Page 22: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/22.jpg)
G&H Fig 15-6
Dampening pulse pressures
Arterial pulse pressureinfluenced by:
elasticityrigidityresistance
resistance, pulse pressure
![Page 23: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/23.jpg)
What does systolic pressure tell you?What does diastolic pressure tell you?
CO & TPRTPR
Cardiac Output (CO) = MAP TPR
Sherwood Fig 10-9
![Page 24: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/24.jpg)
G&H Fig 15-4 and B&B
Aortic pressure changes
rigid
![Page 25: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/25.jpg)
G&H Fig 15-4
Aortic pressure changes
![Page 26: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/26.jpg)
G&H Fig 23-4
![Page 27: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/27.jpg)
Mean arterial pressure (MAP) is the main driving force for blood flow through capillaries
G&H Fig 14-2
![Page 28: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/28.jpg)
Basis of auscultatory method for measuring BP(Sounds of Korotkoff)
Mohrman and Heller Fig 6-9Turbulent flow is noisy
![Page 29: Hemodynamics](https://reader036.fdocuments.in/reader036/viewer/2022062400/56813a8e550346895da288af/html5/thumbnails/29.jpg)
Why should cuff be placed at heart level?
What effects on BP measurement wouldthe presence of obesity cause?