CVPR 03-24-14 09-10am Hemodynamics - Proenza

Question 1

Hemodynamics

Answer 1

Basic physics of blood flow; Movement of blood is driven by differences in pressure throughout the CV system; Basic physics of flow through a tube predicts many properties of CV system.

Question 2

Effect of Pressure differences

Answer 2

Pressure differences (deltaP) drive blood flow through vessels; the difference between arterial & venous pressure is drives blood flow through organs.

Question 3

Transmural pressure

Answer 3

Difference in pressure between inside & outside of a vessel (across the vessel wall)

Question 4

Gravitational pressure

Answer 4

Also affects blood flow (positional changes)

Question 5

Pressure in different vessels

Answer 5

Highest pressure in the aorta… Elastic walls of vessels dampen pulsatile pressure but offer very little resistance to flow, so there is not much drop in BP through arteries….Big drop in pressure in arterioles (aka resistance vessels)…..Very low pressure in capillaries & in the venous system.

Question 6

Pressure in systemic vs. pulmonary circulation

Answer 6

Pressure in systemic circulation&raquo_space;> pulmonary circulation

Question 7

Cardiac output, resistance, and pressure in Left vs. Right sides of Heart

Answer 7

CO equal between sides; Resistance & Pressure different (much lower in pulmonary circulation)

Question 8

Total Blood Volume & it is mostly found

Answer 8

About 5L; Greatest blood volume in venous system (veins = “capacitance vessels”)

Question 9

Blood volume in arterial vs. venous sides

Answer 9

Varies a lot depending on blood volume & pressure

Question 10

Flow (Q)

Answer 10

CONSTANT through system; the cardiovascular system is a closed loop, so flow through the capillaries MUST be the same as flow through the aorta (on average)

Question 11

Flow (Q) and Cardiac output (CO)

Answer 11

CO = Total flow in the cardiovascular system = volume of blood pumped per minute by the heart

Question 12

Velocity (v)

Answer 12

Distance per unit time (cm/sec) [as opposed to flow, which is volume per unit time]; v = Q/A

Question 13

Velocity (v) and Cross-sectional area (A)

Answer 13

Velocity depends inversely on cross-sectional area (A)…..slowest through biggest cross-sectional area, like a river…total cross-sectional area is smallest in the aorta (–> fastest flow) and greatest in capillary beds and pulmonary circulation (–> slowest flow in these areas of exchange)

Question 14

Flow equation

Answer 14

Q = deltaP / R…..where, Q = flow (volume/time), deltaP = pressure difference, R = resistance

Question 15

Cardiac output version of the Flow equation

Answer 15

CO = (mean arterial pressure – venous pressure) / total peripheral resistance (TPR)

Question 16

Flow equation & Ohm’s law

Answer 16

Flow eq. is analogous to Ohm’s law for electricity (V = IR, I = V/R), where blood flow is like current, pressure is like voltage, resistance is like…resistance.

Question 17

Flow equation – characteristics

Answer 17

Require pressure difference; Flow In MUST equal Flow Out; Flow is directly proportional to pressure, inversely proportional to resistance.

Question 18

Assumptions of flow equation that are not really valid for cardiovascular system:

Answer 18

Constant pressure, Constant resistance, Straight rigid tube..…Nonetheless, pressure & flow through the system as a whole can be approximated fairly well with the flow equation.

Question 19

Poiseuille’s Equation

Answer 19

An extended version of the flow equation: Q = ΔP x (π x r^4) / 8ηl ……… Q = flow, r = radius, l = length, ΔP = pressure difference, η = viscosity of blood…… (π x r^4) / 8ηl is the inverse of resistance in the flow equation….. For the exam, you do not have to memorize the equation per se, but you need to understand how each variable affects flow, and that the FLOW VARIES WITH THE 4TH POWER OF THE RADIUS

Question 20

Effect of Increased vessel size (radius) on resistance & flow (Poiseuille’s Law)

Answer 20

Increased radius = Decreased resistance, Increased flow.

Question 21

Vessel radius and flow

Answer 21

Increase size of vessel (radius) = decrease resistance, increase flow….. Radius has huge effect on flow (flow varies with 4th power), so doubling the radius increases flow by 16-fold (24)….. In CV system, vessel diameter is the major mechanism by which flow is controlled (vasoconstriction & vasodilation).

Question 22

Effect of Increased length of vessel on resistance & flow (Poiseuille’s Law)

Answer 22

Increased length = increase resistance, decrease flow

Question 23

Effect of increased viscosity on resistance & flow (Poiseuille’s Law)

Answer 23

Increased viscosity = increase resistance, decrease flow

Question 24

Viscosity of blood…what it depends on, gender differences

Answer 24

Mostly depends on hematocrit (proportion of RBCs, normally 38-46% in women, 42-54% in men)

Question 25

Assumptions of Poiseuille’s Law that are not valid for cardiovascular system:

Answer 25

Constant pressure, Constant resistance, Constant radius, Single length, Constant viscosity, Laminar flow….Only valid for single vessels

Question 26

Resistance in parallel vs. in series

Answer 26

Poiseuille’s law is only valid for single vessels…..Parallel vessels (most of systemic circulation) decreases total vascular resistance.…. Series vessels increases total vascular resistance.

Question 27

Resistance in parallel – calculation & significance

Answer 27

1/ total R = sum of 1 / individual resistances…….Therefore: 1. Total resistance of a network of parallel vessels (capillary bed) is lower than the resistance of single lowest resistance vessel in the system (single capillary), 2. Changing the resistance of a single vessel in a parallel system has little effect on the total resistance of the system

Question 28

Resistance vs. Blood flow in parallel circulations

Answer 28

Pressure is the same in each parallel vessel, but the blood flow through each can be different…..EX: Capillaries are highest resistance of all vessels (smallest diameter), yet total resistance of capillary beds is quite low & is independent of individual capillaries because there are many parallel vessels.

Question 29

Resistance in series – calculation

Answer 29

Resistances in series are additive: total R = sum of individual Rs (i.e., R in artery + R in arteriole + R in capillaries)…..Therefore: Total resistance of a series of vessels is higher than the resistance of any individual vessel.

Question 30

Resistance in series – location of most resistance

Answer 30

Largest proportion of total resistance is in arterioles, the major resistance vessels that regulate flow to tissues.

Question 31

Resistance & Blood flow in series circulations

Answer 31

Blood flow through vessels in series is constant, but the pressure decreases through the series of vessels (e.g.,, pressure drops through the systemic circulation)

Question 32

Laminar flow

Answer 32

Smooth, streamlined, most efficient type of flow; Velocity slowest at edge of tube, fastest in center; Assumed type of flow in the flow equation (non-pulsatile laminar flow); Not completely the case in the CV system.

Question 33

Turbulent flow

Answer 33

Irregular type of flow, with eddies & vortices; Requires more pressure for same average velocity compared with laminar flow; Produces shear force

Question 34

Factors that increase turbulent flow

Answer 34

Large diameter, high velocity, low viscosity, abrupt changes in diameter, irregularities on tube walls (things that promote turbulence promote damage to endothelial lining through the shear force created)

Question 35

Shear force - how created, what it is, what it causes

Answer 35

Produced by turbulent flow; Viscous drag of fluid flowing through tube, which exerts force on the walls; Can damage vascular endothelium, promoting development of thrombi, emboli, & atherosclerotic plaques

Question 36

Pulsatile flow

Answer 36

Heart pumps intermittently, creating pulsatile flow in the aorta = arterial pressure in not constant.....Pulsatile flow requires more work (stop & go driving at rush hour uses up more gas)…pulsatile flow is dampened from aorta to capillaries (where it becomes constant rather than pulsatile)

Question 37

Systolic pressure

Answer 37

Peak aortic (~arterial) pressure; Systole = contraction phase of cardiac cycle

Question 38

Diastolic pressure

Answer 38

Minimum aortic pressure: Diastole = relaxation phase of cardiac cycle

Question 39

Normal blood pressure value

Answer 39

Systolic / diastolic = <120/80mmHg (range: 90-120 / 60-80)

Question 40

Pulse pressure – how to calculate & normal value

Answer 40

Systolic – Diastolic = 120 – 80 = 40 mmHg

Question 41

Pulse variation, pressure, & velocity in different vessels

Answer 41

In capillary beds, no pulse variation, pressure & thus flow is continuous…..Pulse pressure, mean pressure & velocity all decrease from aorta to capillaries

Question 42

Mean Arterial Pressure (MAP) - calculation

Answer 42

At resting HRs, MAP= ~Diastolic pressure + 1/3(systolic – diastolic)…..at resting HRs, NOT the arithmetic average of systolic & diastolic pressure b/c diastole is longer than systole

Question 43

Mean Arterial Pressure (MAP) – what it depends on

Answer 43

Depends on HR. At rate higher than resting HRs, diastole is relatively shorter, so MAP approaches the average between systolic & diastolic pressures

Question 44

Compliance equation

Answer 44

C = ΔV/ΔP….. C= compliance in ml/mmHg, ΔV = change in volume in ml, ΔP = change in pressure in mmHg… how much change in volume is elicited by a change in pressure

Question 45

Compliance represents…

Answer 45

…the elastic properties of vessels (or chambers of the heart)

Question 46

Relative compliance in veins vs. arteries

Answer 46

Veins are more compliant than arteries – more V per P

Question 47

Relative compliance in different arteries & what it contributes to

Answer 47

More compliance in aorta = lower pulse pressure…. Degree of compliance in the major arteries contributes to transformation of pulsatile flow from heart into continuous flow in microcirculation.

Question 48

Compliance is determined by…

Answer 48

… relative proportion of elastin fibers vs, smooth muscle & collagen in vessel walls

Question 49

Arteriosclerosis

Answer 49

NOT the same as atherosclerosis…. Rather, a general term for loss of compliance caused by thickening & hardening of arteries….SOME IS NORMAL W/ AGE (pulse pressure 40 mmHg in young adults, ~60+ mmHg in elderly people…younger people have more compliant arteries than older people)

Question 50

LaPlace’s Law - equation

Answer 50

T = ΔP x r / µ…..T = tension (wall stress), ΔP = transmural pressure, r = radius, µ = wall thickness

Question 51

LaPlace’s Law describes...

Answer 51

The relationship between tension in a vessel wall and the transmural pressure

Question 52

Relationship in LaPlace’s Law

Answer 52

Tension in the vessel increases as pressure & radius increase. (Thus, HTN increases stress on vessel [and chamber] walls.)

Question 53

Aneurysms & LaPlace’s Law

Answer 53

Weakened vessel wall bulges outward, increasing radius, thus increasing tension that cells in the wall have to withstand to prevent the vessel from splitting open….Over time cells become weaker, allowing wall to bulge more so that tension increases further, until aneurysm ruptures.

Question 54

Two major processes of cardiovascular transport:

Answer 54

1. Bulk transport, 2. Transcapillary transport (movement of cargo between capillaries and tissue)

Question 55

Bulk transport

Answer 55

Movement of substances through the CV system (cargo from point A to point B in whole CV system)…Can be applied also to consumption of a substance

Question 56

Bulk transport - Transport rate (x)

Answer 56

x = Q[x]……..x is amount of substance x, Q is flow, [x] is concentration of substance x……..EX: How much O2 is carried to a muscle in 1 minute? O2/min = CO[O2] …..where where O2/min = transport rate (ml O2/min), CO = cardiac output (ml blood/min), and [O2] = concentration of O2 (ml O2/ml blood)

Question 57

Fick’s Principle – what it explains

Answer 57

An expansion of the bulk transport idea to consider how much of a substance is used by a tissue….basically, the amount used is equal to the amount that enters the tissue minus the amount that leaves, which can be determined as the flow times the concentration (as with bulk transport)

Question 58

Fick’s Principle – equation

Answer 58

X used = Xi – Xo = (Q[x]i) – (Q[x]o) = Q([x]I – [x]o)…..where Xused is the amount of a substance used by the tissue, Xi is the initial amount, Xo is the final amount, and Q is flow (constant through system)

Question 59

Fick’s Equation & Cardiac output

Answer 59

To measure CO based on myocardial oxygen consumption…. mVO2 = CO ([O2]a – [O2]v)…where, mVO2 is myocardial oxygen consumption (X is general Fick’s equation), CO is cardiac output (like flow, Q), [O2]a & [O2]v are arterial & venous oxygen concentrations (same as Xi and Xo)

Question 60

Oxygen consumption in the whole body

Answer 60

Can be determined by looking at the difference between oxygen levels in the pulmonary vein minus the pulmonary artery, which is opposite from the expression used for with myocardial oxygen consumption & CO (which was arterial minus venous concentration) b/c blood in the pulmonary vein is oxygenated and blood in the pulmonary artery is deoxygenated.

Question 61

Fractional O2 Extraction (EO2) from blood

Answer 61

= amount of oxygen used by a tissue expressed as a fraction of the original (arterial) oxygen concentration…. EO2 = (absolute value of arterial O2 – abs. value of venous O2) / abs. value of arterial O2

Question 62

Transcapillary transport – forces determining solvent movement

Answer 62

Two opposing forces determine solvent movement – hydrostatic pressure and oncotic pressure

Question 63

Hydrostatic Pressure (P) definition

Answer 63

= simply fluid pressure (blood pressure in this case)

Question 64

Net hydrostatic pressure in a capillary bed

Answer 64

= difference between capillary pressure & interstitial pressure

Question 65

Hydrostatic pressure (P) and Solvent movement

Answer 65

Solvents move from high pressure to low pressure…..BP in capillaries ~ 25 mm Hg, while P in interstitial space ~ 0 mm Hg….Hydrostatic pressure promotes FILTRATION (movement of fluid out of capillaries)

Question 66

Oncotic pressure (π) definition

Answer 66

= aka colloid osmotic pressure; the osmotic force created by proteins in the blood & interstitial fluid

Question 67

Major determinants of oncotic pressure

Answer 67

α Globulin and albumin

Question 68

Oncotic pressure (π) and Solvent movement

Answer 68

Solutes move from high concentration to low concentration…Solvents move toward high concentration of solutes…..Oncotic pressure of blood in capillaries (πc) is higher than oncotic pressure of interstitial fluid (πi)….Capillary oncotic pressure promotes REABSORPTION of fluid (movement of fluid into capillaries)

Question 69

Starling Equation for transcapillary transport (AKA Starling’s law of the capillary)

Answer 69

Flux = k[(Pc – Pi) – (πc- πi)]….where Flux = net movement across capillary wall, k = constant, Pc = capillary hydrostatic pressure, Pi = interstitial hydrostatic pressure, c = capillary oncotic pressure, i = interstitial oncotic pressure

Question 70

(Pc - Pi) in Starling Equation

Answer 70

= net hydrostatic pressure….tends to be outward (filtration)

Question 71

(πc – πi) in Starling Equation

Answer 71

= net oncotic pressure…..tends to be inward (reabsorption)

Question 72

Net movement of water in and out of a capillary

Answer 72

= simply the outward force minus inward force, or the balance between filtration & reabsorption

Question 73

Factors promoting filtration & the effect of excess filtration

Answer 73

Factors that increase blood pressure (HTN) or reduce oncotic pressure (liver disease)…..Excess filtration causes edema (swelling) in tissues.

Question 74

Net flux from arterial to venous end of capillaries

Answer 74

= not constant….Pc is higher on arterial side & lower on venous side….c is lower on arterial side & higher on venous side…..Thus, there is a tendency toward filtration on the arterial side and reabsorption on the venous side.

Question 75

Net flux in different capillary beds

Answer 75

Net flux is different in different capillary beds…e.g., capillaries in kidney favor filtration, capillaries in gut favor reabsorption

Question 76

Regulation of Net flux

Answer 76

regulated primarily by control of capillary hydrostatic pressure (via vasoconstriction/vasodilation of arterioles)

Question 77

Diffusion – what molecules CAN diffuse across cell membranes

Answer 77

Gases are lipid soluble & diffuse freely across cell membranes (CO2, O2, NO, etc.); Other lipid soluble molecules also diffuse freely (e.g., some vitamins); Small lipid-INSOLUBLE molecules can also diffuse, through inter-endothelial junctions between capillary endothelial cells (salts, water, glucose, etc.).

Question 78

Rate of diffusion of O2

Answer 78

Rate of diffusion from capillary to tissue depends on…1. Distance between capillary & tissue, 2. Amount of O2 carried in blood (free and bound to hemoglobin).

Question 79

Interendothelial junction

Answer 79

Allow small lipid-insoluble molecules (e.g.: water, salts, glucose) to diffuse across vascular cell membranes; Vary in size, density, & permeability in different tissues.

Question 80

Diffusion – what molecules CANNOT diffuse across cell membranes

Answer 80

Large molecules (e.g., albumin, other proteins) cannot cross most capillary walls (except in some cases by endo- or exocytosis, or in lymphatic capillaries, in which the junctions are quite permeable) including through interendothelial junctions.