Blood flow/hemodynamics Flashcards
What are the five functions of the cardiovascular system?
To transport nutrients, waste, oxygen and CO2; to allow mixing of body fluids, pH, ionic composition and osmolarity regulation; to regulate body temperature; to transport hormones; to defend against infection
What volume of fluid is contained in the circulating plasma?
3 L
____ L of fluid is in the cells
30 L
How much fluid is in the interstitial compartment?
12 L
Define: capacitance of blood flow
The amount of blood stored in a location. I.e. the venous side of the circulatory system has a higher capacitance than the arteriole side. It is a reservoir for blood.
Define: VO2
Metabolic needs of a tissue represented as a percentage of oxygen consumption
What percentage of blood is in systemic circulation? In pulmonary circulation? In the heart?
84% systemic
9% pulmonary
7% the heart
Define: systole
When the heart is most contracted. The number on top in blood pressure
Define: diastole
When the heart is most expanded and it fills with blood. The number on the bottom in blood pressure.
What are the requirements for efficient ventricular pumping?
Synchronized, regular, forceful contractions; valves that open fully and do not leak; ventricles that fill adequately
Define: cardiac output. Give the equation as well
The quantity of blood per time pumped into the aorta by the heart.
CO= SV x HR (stroke volume X heart rate)
What is a typical cardiac output for a normal person at rest
5 L/min
What three things determine stroke volume?
Ventricular preload (length of the muscle before contraction), ventricular afterload (tension of the muscle during contraction) and myocardial contractility
Rank these organs from highest to lowest for percent distribution of blood flow in the resting state: brain, liver/GI, skeletal muscle, kidney, skin
Liver/GI (24%), Skeletal muscle (21%), Kidney (20%), Skin (18%), Brain (13%)
What is Starling’s Law of the Heart?
All other things constant, stroke volume (and thus cardiac output) increases as end-diastole filling increases. Collecting more blood means you can pump more blood.
Is the heart a generator of constant pressure or of constant flow?
Constant pressure
Which vessel in systemic circulation has the greatest resistance to flow?
Arterioles
Define: systolic pressure
The peak arterial pressure reached during ejection of blood by the heart. The top number in a blood pressure reading
Define: diastolic pressure
The lowest arterial pressure during diastole. The bottom number in blood pressure
Define: mean arterial pressure. Give the equation too.
The average pressure during the cardiac cycle. To calculate: MAP= diastolic pressure + 1/3 pulse pressure
Define: pulse pressure
The difference between systolic and diastolic pressure
What is an advantage for the auscultatory measurement for blood pressure? A disadvantage?
It is non-invasive but is not as precise as other means
Describe the method of catheterization to measure blood pressure
To measure arterial pressure, pass a catheter in retrograde (opposite the direction of flow) into an artery or the left ventricle. For venous pressure (and RA and RV), pass the catheter in anterograde.
How would you measure the blood pressure of the left atrium or in a pulmonary artery?
Pass a catheter into it with the direction of flow, inflate a balloon and measure the number at which the vascular pressure equilibrates just past the balloon
What two variables affect mean arterial pressure? Give the equation that relates these three things.
Cardiac output and total peripheral resistance. MAP = CO x TPR
How does the body control mean arterial pressure in the short term? In the long term?
Short term- altering peripheral resistance
Long term- altering cardiac output/ blood volume via the kidneys
Define: blood flow
The quantity of blood passing a particular observation point in a given time interval
Define: velocity (for blood flow)
The linear distance displaced by a fluid particle in a given time interval
Blood flow is _____ in the aorta and the pulmonary artery and is ______ in branches of a parallel circuit
The same; additive
How is distribution of flow controlled by the tissues?
Rate of flow is controlled by tissue need which is controlled by adjustment of resistances (sphincters and arterioles) prior to the capillary beds
What is the significance of the parallel architecture of the circulatory system?
Each organ (or organ system) receives blood at the expense of another organ. Thus, when you exercise, certain organs receive less blood (the kidneys and GI tract) so others can receive a greater percentage (muscle, skin, the heart)
Cardiac output is equal to the flow through the ________ system
Pulmonary
What is an equation that relates flow (Q), cross-sectional area (A), and velocity (v)?
Q = A x v
Define and give equations for: transit time (t)
The time required for a blood cell to travel between two points. t= Q/Volume or t= length/velocity
What is the transit time for one pass through pulmonary and systemic circulation?
About 60 seconds
Define: viscosity (n)
How much a fluid resists shear forces. How sticky a fluid is
What is the relationship between pressure, resistance and flow?
Q= (change in P)/ R
What is an equation for resistance? Which variable has the greatest effect on it?
R= (8nL)/(pi x r^4)
n= viscosity; L= length
Radius has greatest effect b/c it’s raised to the 4th
What effect does increasing the radius have on pressure? Flow?
Increased radius means decreased resistance. Since flow is constant in the circulatory system, this means change in pressure will decrease too
Total resistance in series is _____. Total resistance in parallel is ______.
Additive (R tot = R1 + R2)
Less than any element in the network (1/R tot = 1/R1 + 1/R2)
What is Poiseuille’s law?
Q= (change in P) x (pi x r^4)/(8nL)
What vessel determines the total resistance for an organ? Why is this?
The arteriole. It has the greatest resistance
Cardiac output is approximately equal to what?
Flow, Q
What real values can you use to calculate MAP?
P (LV)- P (RA)
What units is TPR presented in? What is a normal value? How does it change with exercise? Or in a hypertensive person?
PRU (peripheral resistance units)
1.2 PRU
Exercise lowers, hypertension raises
Define: Reynold’s number
How flow is characterized (as turbulent or laminar). Re = (2rv*rho)/(eta)
3000= turbulent
What is the significance of critical velocity?
It is the point at which flow transitions from laminar to turbulent
What sounds are created by turbulent flow?
Murmurs. They do not normally occur under resting conditions. (Note: auscultatory blood pressure measurement uses turbulent flow too)
What four factors affect blood pressure in circulation?
Gravity, compliance of a vessel, viscous resistance, and inertia
How does gravitational pressure affect blood pressure?
It makes BP seem lower above the heart and higher below it. Gravitational component of BP is (rho x g x h)
How do you calculate total pressure in the circulatory system?
P static + P dynamic
(P lateral + (rho x g x h)) + 1/2 (rho) (v^2)
P lateral= pressure from liquid in a vessel
Why does direction of an open-tip catheter matter in blood pressure measurements?
For arterial BP measurements, the tip should be anterograde to flow to properly measure the P dynamic component of BP (if retrograde, the measurement will be lower than BP actually is)
What is sheer stress? What variables affect it?
It is frictional force produced by blood flow in the direction of flow that acts on the vessel walls. It is directly related to viscosity and flow rate and inversely proportional to the cube of the radius
Describe flow and the amount of sheer stress at the site of an atherosclerotic plaque
Flow is turbulent and sheer stress is low
How does viscosity relate to resistance? Blood flow? Hematocrit?
Increased viscosity-> increased resistance, decreased blood flow (Q= (change in P)/R) Increased hematocrit-> increased viscosity
What is polycythemia?
A disease in which blood hematocrit is about 50% higher than normal and viscosity is double the normal value
What are rouleaux? How do they affect viscosity?
Chain-like aggregates of RBCs that form at low flow rates. They break up as flow increases, decreasing viscosity (and contributing to the anomalous viscosity of blood)
What is plasma skimming? How does it affect viscosity?
Plasma tends to travel on the periphery of blood vessels thus a branch off of a vessel may get more plasma than normal and have a lower hematocrit and viscosity than expected.
What is the function of microcirculation? What vessels make up a microcircuit?
Nutrient source/waste removal + filtration in kidneys + thermoregulation in skin
Arterioles, capillaries, venules and maybe metarterioles
What is the significance of metarterioles? Of precapillary sphincters?
Metarterioles provide a shunt to bypass capillaries
Precapillary sphincters control local flow in the capillary network
What are the three different types of capillaries? Describe a general property of each type and where it is found
Continuous- small diameter, small pores. Everywhere in the body
Fenestrated- small diameter, large pores maybe with diaphragms. Exocrine glands
Discontinuous/sinusoidal- large diameter, fenestrations and large gaps in endothelium. Liver sinusoids
Define: convective transport. What two factors can affect it?
Transport with the flow of blood. Flow rate and concentration
What is the Fick principle? How do you know if a tissue is using or producing a substance.
Tissue rate of utilization/production of a substance = Q x (arterial concentration- venous concentration).
If (-)-> tissue is producing, if (+) -> tissue is using
What is Fick’s law of diffusion? What four factors affect the diffusion rate of a substance b/wn blood and interstitial fluid (if)?
J (flux) = D (diffusion constant) x A (cross-sectional area) x [cp-ci (conc in plasma - conc in if)]/[l (thickness of membrane0]
Concentration gradient, surface area, diffusion distance (membrane thickness), permeability of the wall (diffusion constant)
Define: hydrostatic pressure. Define: osmotic pressure. How are they related?
Hydrostatic- pressure exerted by fluid on walls
Osmotic- pressure required to prevent flow of water across a semi-permeable membrane (osmosis)
Hydrostatic pressure opposes osmotic pressure
What is the normal osmotic pressure of plasma? Why?
About 5000 mm Hg. B/c of proteins like albumin
What four pressures influence capillary fluid balance? What equation relates them?
P net = (Pc- Pif)- (Pi c- Pi if)
Pc= capillary hydrostatic pressure
Pif= interstitial fluid hydrostatic pressure
Pi c= capillary osmotic pressure
Pi if= interstitial fluid osmotic pressure
What does a positive Pnet mean? A negative Pnet? What about a positive change in P? Positive change in pi?
+ Pnet= net filtration (fluid out of the capillaries)
- Pnet= net absorption (fluid into capillaries)
+ change in P (positive hydrostatic pressure difference)= net filtration
+ change in pi (positive osmotic pressure difference)= net absorption
How does hydrostatic pressure change along the length of a capillary? What is the significance of this?
It falls from about 35 mm Hg to about 15 mm Hg. This favors filtration initially and reabsorption at the venous end.
What equation relates capillary pressure (Pc), arteriolar pressure (Pa), venous pressure (Pv)?
Which is capillary pressure normally closer to?
Pc= [(Resistance post/Resistance pre)Pa + Pv]/[1+ (Resistance post/Resistance pre)]
Resistances refer to before and after the capillary
Pc is normally closer to Pa
What changes cause increased capillary pressure? Decreased capillary pressure?
Increased- arteriolar dilation or venule constriction
Decreased- arteriolar constriction or venule dilation
What does an increased Pc favor? An increased Pif? An increased Pi c? An increased Pi if?
Increased Pc= filtration
Increased Pif= Absorption
Increased Pi c= absorption
Increased Pi if= filtration
What is the approximate volume of total capillary filtration in a day? Total absorption? Total lymph flow?
Capillary filtration- 20 L/day
Capillary absorption- 16-18L/day
Lymph flow- 2-4L/day
What is edema? What can cause it?
Excess salt and water in interstitial space.
Left or Right heart failure, pulmonary hypertension, lymphatic blockage, hypoalbuminemia, too much ADH
How does temperature affect viscosity?
Increased temperature decreases viscosity
What factors influence compliance of a vessel? What equations relate them?
More volume, less pressure = more compliance
C= (change in volume/(change in pressure)
C is approximately equal to SV/PP
How do total pressure and pulse pressure change across a vessel?
Total pressure decreases, pulse pressure increases
Where is the largest PP in the body?
The LV
