Hemodynamics Flashcards
(36 cards)
Name three types of pressure that drive blood flow through vessels
- Pressure diff btw arterial and venous blood
- Transmural- pressure difference across wall of vessel
- gravitational pressure
Which vessels are known as resistance vessels?
Arterioles
Which vessels are known as capacitance vessels?
veins- hold largest volume of blood
Flow equation and what are the assumptions of this equation
Flow (Q) = ΔP/R
P= pressure
R=resistance
Assumptions: constant pressure, constant resistance, straight rigid tube, laminar flow, non-pulsatile flow
Velocity equation
v= Q/A
Where A is cross sectional area, and Q is flow
Cardiac output equation and average CO
(mean arterial pressure- venous pressure)/ Total peripheral resistance (TPR)
Avg CO= 5L/min
Poiseuilles Equation
Q= ∆P x [(pi r^4)/ (8nl)] Q=flow r=radius l=length P= pressure n= viscosity of blood Note: only valid for single vessels
Describe flow through CV system
Flow is constant b/c CV system is closed loop . Total flow is Cardiac output. Flow in must equal flow out
Resistance equation- parallel vessels
1/Rt = 1/R1 + 1/R2 + 1/R3 Rt= total resistance
Resistance equation - vessels in series
Rt= R1+ R2+ R3 Rt= total resistance
Compare resistance in parallel vs in series vessels
Parallel: Total resistance is lower than the resistance of a single lowest resistance vessel in the system. In each vessel, pressure is the same but flow can be different
In series: Total resistance of a series of vessels is higher than the resistance of any individual vessel. Flow is constant but pressure decreases through the series
What is laminar flow
- smooth, streamlined, and most efficient
* velocity slowest at edge of tube, fastest in center
What is turbulent flow?
- irregular, with eddies & vortices (less efficient)
* requires more pressure for same average velocity compared to laminar flow
What increases turbulent flow?
large diameter, high velocity, low viscosity, abrupt changes in diameter, irregularities on tube walls.
What is shearing force?
Turbulent flow causes viscous drag of fluid flowing through tube, which exerts force on the walls. Shear forces can damage vascular endothelium, which promotes formation of thrombi and embolisms
What is pulsatile flow?
Heart pumps intermittently, creating pulsatile flow in the aorta — arterial pressure is not constant.
What is systolic and diastolic pressure?
• Systolic pressure = peak aortic (~arterial) pressure; Diastolic pressure = minimum aortic pressure
o Systole = contraction phase of cardiac cycle; Diastole = relaxation phase
Pulse pressure = ?
systolic – diastolic = 120 – 80 = 40 mmHg
Explain how the pulsatile flow of blood produced by the heart is converted to steady flow in the capillary beds.
in capillary beds, no pulse variation, pressure (and thus flow) is continuous. Pulse pressure, mean pressure and velocity all decrease from aorta to capillaries. Compliance of arteries absorbs energy, transforms pulsatile flow to continuous flow
Define vascular compliance.
C= ∆V/∆P
V=volume in ml
P= pressure mmHg
Compliance represents the elastic properties of vessels. Determined by relative amounts of elastin vs smooth muscle and collagen
What is LaPlace’s law?
T= (∆P r)/ u T=tension (wall stress) ∆P= transmural pressure r= radius u= wall thickness
What is Fick’s principle?
How much of a substance is used by a tissue x(used)= Q([x]i - [x]o) x(used)= amount used Q= flow Xi= initial amount Xo= final amount
What is starlings equation?
Flux = k[(Pc-Pi) – (πc – πi)] Flux = net movement across capillary wall k = constant Pc = capillary hydrostatic pressure Pi = interstitial hydrostatic pressure πc = capillary oncotic pressure πi = interstitial oncotic pressure
What is Mean arterial pressure?
diastolic pressure + 1/3(systolic – diastolic)
-Diastole is longer than systole at rest
