Principles of Blood Flow Flashcards
State the units of blood pressure
A person’s blood pressure is usually expressed in terms of the systolic pressure over diastolic pressure and is measured in millimetres of mercury (mmHg), for example 120/80 (normal).
Describe the change in blood pressure around the circulation
The blood pressure drops more gradually along the length of large arteries, more rapidly along the length of small arterioles and capillaries, and then gradually along the length of the veins.
Describe how parallel architecture of the circulatory system mediates redistribution of blood flow and response to physiological change
In order to avoid hypoxia, the flow of oxygen in the arteries to the tissues must be equal to or greater than the rate of oxygen consumption by the tissues. In the parallel architecture of the cardiovascular system, the flow of oxygen is distributed to each tissue at rest in accordance with the metabolic activity of each tissue.
During exercise, blood flow & allocation increases dramatically. During exercise the fraction of cardiac output, and hence the allocation of oxygen delivery, to the various tissues changes. Note the dramatic increases in blood flow to the skin, muscles and heart during exercise as the venous reserve is mobilized.
given data, calculate the vascular resistances of vessels in parallel or series networks
Rseries = R1 + R2 + R3 + Rn
Rparallel = 1/R1 + 1/R2 + 1/R3 + Rn
State the relationship between blood flow, velocity and vessel diameter; State the units for flow and velocity; given two values, calculate the unknown quantity
Flow = cross sectional area x velocity or Q = A x v
So Q is proportional to A & V, But A & V are inversley proportional
A is in cm^2, A = pi*r^2 & r = d/2 –(d = diameter)
V = cm/sec
Q = cm3/sec
If Q1 =Q2, then: v1 x A1 =v2 x A2
Therefore, for a given flow, the ratio of velocities in two parts of the system depends only on the ratio of total cross-sectional areas.
Flow in a series (1 tube flows into another) of tubes is
Constant
Q=Q1=Q2=Q3=Qn
*Objective: given data, be able to calculate the vascular flow in vessels in parallel or series networks
Flow expressed mathematically in parallel circuits
It is additive among the branches of a parallel circuit (as seen when arteries branch off to the organs).
Q = Q1 + Q2 + Qn
*Objective: given data, be able to calculate the vascular flow in vessels in parallel or series networks
Define blood flow
Blood flow, volume/time, Q (L/min) is the quantity of blood passing a particular observation point in a given time interval.
1 L = ? cm^3
1 L = 1000 cm^3
since 1 cm^3 = 1ml
Transit time; given two values, calculate the unknown quantity
The time, t (sec), required for a blood cell to travel between two points in the system.
May be estimated either from the velocity (cm/sec) and tube length, l (cm), or from the flow Q (cm3/sec) and volume V (cm3), of fluid in the vessel.
t = l/v (x=vt) or t = V/Q.
The total time for a blood cell to pass through the entire systemic and pulmonary circulations is about 60 sec.
Relationship between blood flow, resistance, & pressure
dP=QR
Change in pressure (mmHg) = flow rate (ml/min) x resistance (mmHg/ml/min)
What contributes to resistance?
Resistance to flow comes from the walls of the vessel (which are not moving) and also from viscosity of the blood.
resistance is directly proportional to length of tube & inversely proportional (to 4th power) to the radius or just normal cross sectional area. Changes in vasoconstriction or vasodialation are a big deal in resistance.
R = L/A^2
Temperature is inversely related to the viscosity of most fluids, including water and blood.
The higher the pressure drop, the higher the
resistance
This is important to note because pressure changes in response to resistance, not flow so much. P = QR since flow = CO
Capillaries have the largest ___ in the body.
Capillaries have the highest total cross-sectional area & surface area in the body.
The velocity of blood flow in the large arteries is ___ than in the capillaries
The velocity of blood flow in the large arteries is from 100 to 500 times faster than in the capillaries. This attributable to the greater total cross-sectional area of the capillaries (1800 cm2 vs. 4 cm2). Q = A x v.
