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Cardio > Physiology > Flashcards

Physiology Flashcards

1
Q

Which side of the heart pumps to the body? To the lungs?

A

Body: left; lungs: right

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2
Q

What is an arterial tree?

A

systemic circulation to carry oxygenated blood, nutrients and hormones to the tissues of the body

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3
Q

What is pulmonary circulation?

A

de-oxygenated blood is pumped to the lungs via the pulmonary artery for gas exchange and oxygenated blood returns to the left heart via 4 pulmonary veins

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4
Q

What is the cardiac cycle?

A 
A. Atrial systole;
B. Isovolumetric contraction;
C. Rapid ventricular ejection;
D. Reduced ventricular ejection;
E. Isovolumetric relaxation;
F. Rapid ventricular filling;
G. Reduced ventricular filling - diastasis
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5
Q

What is venous return?

A

The rate of blood flow back to the RV

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6
Q

What is the pulmonary blood flow?

A

rate of blood flow into the pulmonary artery; equal to right ventricular cardiac output

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7
Q

What is the systemic blood flow?

A

rate of blood flow into the aorta; equal to left ventricular cardiac output

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8
Q

What is the force that causes blood to flow through a vessel or across a valve?

A

the difference in blood pressure (i.e., pressure gradient) across the vessel length or across the valve; the flow of blood is always from high to low pressure; ventricular contraction establishes pressure gradients in the CV system

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9
Q

What is the cardiac output?

A

Rate at which blood is pumped from either ventricle; In the steady state, LV C.O.= RV C.O.; Cardiac output is the total volume of blood ejected per unit of time (normal: approx. 5000mL/min); Cardiac output can remain constant and blood flow is redistributed among organs based on selective alteration of arteriolar resistance; Cardiac output can increase or decrease depending on physiologic conditions

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10
Q

What are the characteristics of arteries?

A

Thick-walled vessels, Carry oxygenated blood to tissues, Blood volume is under high pressure, Branch into smaller arterioles, Arterioles are the site of highest resistance in the CV system, Arteriolar resistance is regulated by a1 and b2 receptors

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11
Q

What are the characteristics of veins?

A

Thin-walled vessels with valves to prevent the backward flow of blood, Carry deoxygenated blood back to the heart, Blood volume is under low pressure, Coalesce into larger veins, Veins contain the highest proportion of blood volume in the CV system, Veno-resistance is regulated by a1 receptors

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12
Q

What is the capillary bed?

A

Thin-walled and consist of a single layer of endothelial cells surrounded by the basal lamina; Site of exchange for diffusible substances between tissue and blood; Site of the highest cross-sectional surface area in the CV system

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13
Q

What is the stressed volume?

A

A small blood volume that is held in the capillaries and in the aorta, arteries, and arterioles

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14
Q

What is the unstressed volume?

A

Greatest volume of blood - it is the blood in the veins and venules

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15
Q

What influences blood flow?

A

cardiac output, vessel diameter and vascular resistance; circulating volume and blood viscosity

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16
Q

How is the velocity of blood flow calculated?

A 
v=Q/A
v=velocity in cm/sec
Q= cardiac output or flow in mL/min
A= cross-sectional area of the vessel;
NOTE: be sure that the units match up!
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17
Q

Where is the velocity of blood flow the highest in the CV System?

A

The Aorta with its small cross-sectional area

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18
Q

Where is the velocity of blood flow the slowest?

A

The Capillary Bed with its large cross-sectional area; this makes sense b/c you have maximum transit time in the vascular bed where gas, nutrient, and metabolite exchange occurs

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19
Q

How can cardiac output be calculated?

A 
Q=deltaP/R
Q= flow or cardiac output in mL/min
deltaP= pressure gradient in mmHg
R= resistance or total peripheral resistance in mmHg/mL/min;
NOTE: can also use: C.O. (L/min) = MAP-RAP/TPR
MAP= Mean Arterial Pressure RAP= Right Atrial Pressure TPR= Total Peripheral Resistance
OR
Cardiac output (CO) = heart rate (HR) x SV
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20
Q

What affects vascular resistance?

A

Vascular resistance increases with increasing muscularity of the vessel wall; If total blood flow is constant at all levels of the CV system, then as resistance increases, downstream pressure must decrease with an increase in deltaP; Pressure drops as blood flows through the vasculature because energy is consumed to overcome frictional resistance

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21
Q

What are the mean pressures in different parts of the heart?

A

Aorta: 100 mmHg; large arteries: 100; arterioles: 50; capillaries: 20; vena cava: 4; right atrium: 0-2; pulmonary artery: 25; pulmonary capillaries: 10; pulmonary vein: 8; left atrium: 2-5

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22
Q

What is the Law of Laplace?

A 
t = Pr/2H
t = tension in vessel wall
P = transmural pressure
r = radius of vessel
H = wall thickness;
in ventricles t = wall stress and r = radius of cavity
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23
Q

What is Poiseuille’s Law?

A

Poiseuille’s Law states that the resistance to flow depends on the dimension of the tube and the characteristics of the fluid; The principal determinant of resistance to blood flow through any vessel is its caliber (radius)
R= 8hl/(pi)r(to the 4th)
h= viscosity of blood
l = length of blood vessel
r4 = radius of blood vessel raised to the 4th power

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24
Q

How do blood vessels in series affect blood flow?

A

For blood vessels in series, a RBC that flows from an upstream vessel will flow to the downstream vessel during a circuit through the body; Total resistance of vessels in a series arrangement is equal to the sum of its individual resistances; Reflects the arrangement of blood vessels within an organ; Rt = R1 + R2 + R3 + R4 + R5; Arteriolar resistance contributes the greatest to the total resistance; Pressure decreases progressively as blood flows through sequential vessels

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25
Q

How do blood vessels in parallel affect blood flow?

A

For blood vessels in parallel, a RBC will flow through one vessel and not another during a circuit through the body; Total resistance of vessels in a parallel arrangement is less than any of the individual resistances; Reflects the arrangement of the major arteries in the CV system; 1/(Rt) = (1/R1) + (1/R2) + (1/R3)…

26
Q

What is laminar flow?

A

In laminar flow, all elements in the blood move in streamlines that are parallel to the axis of the vessel; blood flow in normal vessels is laminar

27
Q

What is turbulent flow?

A

In turbulent flow, blood moves axially and radially and requires more energy to drive flow; Turbulent blood flow can be audible with a stethoscope as a murmur

28
Q

What is Reynold’s number?

A 
N = pdv/n
N = Reynold’s number
p= density of blood
d = diameter of blood vessel
V= velocity of blood
n= viscosity of blood
29
Q

How does Reynold’s number predict type of blood flow?

A

If N is less than 2000, then flow usually laminar; If N is more than 3000, then flow is usually turbulent; Large vessel diameters, high velocities and low viscosity predispose to turbulence

30
Q

What is the capacitance of blood vessels?

A 
Describes the volume of blood a vessel can hold at a given pressure; Capacitance is greater for veins than arteries; Arterial capacitance decreases with age
C = V/P
C= capacitance/compliance
V= volume in mL
P= pressure in mm Hg
31
Q

How is circulating blood distributed to the different regions of the body under different stresses?

A

Modulation of vascular resistance determines the distribution of cardiac output

32
Q

How does normal exercise affect the vascular system?

A

When you run, you need to increase blood flow the exercising skeletal muscle; Your cardiac output increases by increasing heart rate, myocardial contractility and stroke volume; Arteriolar vascular resistance drops in the skeletal muscle, promoting preferential blood flow; Arteriolar resistance increases in non-exercising vascular beds; Venous return increases because of venoconstriction and increased skeletal muscle tone

33
Q

How can cardiac output be measured with catheterization?

A

Fick Equation, Thermodilution

34
Q

What is the Fick Equation?

A

Fick Principle is based on the conservation of O2 utilization by the body; O2 consumption can be estimated; O2 content can be measured directly by removing blood from the circulation
CO= O2 Consumption
[O2]PV - [O2]PA
CO= cardiac output in L/min
O2 Consumption= O2 use by body in mL O2/min, typically 250 mL/min
[O2]PV = O2 content in pulmonary vein mL O2/ mL blood
[O2]PA = O2 content in pulmonary artery mL O2/ mL blood

35
Q

How do you convert from mmHg min/L (Wood units) to dyne sec/cm5?

A

Multiply by 80

36
Q

Which blood flow is pulsatile? Non-pulsatile?

A

Blood flow in the aorta and larger arteries is pulsatile; Blood flow in the capillaries is essentially non-pulsatile; Pulsatile blood flow is dampened by the distensibility of the larger arteries and the resistance of the arterioles

37
Q

How does blood flow change in the cardiac cycle?

A

Each cardiac cycle consists of the ventricle pumping blood in systole and filling with blood during diastole; When blood is pumped out of the heart into the aorta, a substantial fraction of the blood is stored in the stretched arterial walls during ventricular systole.; During ventricular diastole, the previously stretched arteries recoil. The volume of blood that is displaced by the vascular recoil provides for continuous capillary flow when the heart is not beating.

38
Q

What is systolic pressure?

A

Systolic pressure is the highest measured pressure after blood is ejected into the aorta

39
Q

What is diastolic pressure?

A

Diastolic pressure is the lowest measured pressure when the aortic valve is closed and no blood is flowing into the aorta

40
Q

What is pulse pressure?

A

Pulse pressure is the difference between systolic and diastolic blood pressure and reflects the volume of blood ejected with each heart beat (stroke volume)

41
Q

What is mean arterial pressure?

A 
Mean arterial pressure is the driving force for blood flow in the arteries and is influenced more by diastolic blood pressure than systolic blood pressure
Calculating MAP
= (SBP+2DBP)/3 or
= DBP +1/3 PP or
= DBP + 1/3(SBP-DBP)
42
Q

What occurs in atrial systole?

A

The cardiac cycle begins with depolarization and contraction of the atria. Atrial systole is atrial contraction and is preceded by the P wave on the EKG. Contraction of the left atrium causes an increase in left atrial pressure and causes the a wave on the venous pulse. This is the end of diastole. There is a slight increase in ventricular volume as blood is actively ejected from the left atrium into the left ventricle.

43
Q

What is isovolumetric contraction?

A

Isovolumetric contraction begins during the QRS complex which represents electrical activation of the ventricles. As soon as the LV contracts, LV pressure begins to rise. As soon as LV pressure exceed LA pressure, the MV closes. On the right side, the TV closes. Closure of the AV valves generates the first heart sound S1. Ventricular pressure increases dramatically but ventricular volume remains constant because all of the valves are closed.

44
Q

What is rapid ventricular ejection?

A

The ventricle continues to contract. Ventricular pressure reaches it highest value and when ventricular pressure exceeds aortic pressure, the aortic valve opens. Blood is rapidly ejected into the aorta, driven by the pressure gradient between the left ventricle and the aorta. Most of the stroke volume is ejected during rapid ejection. Aortic pressure will increase because of the rapid increase of blood in the aorta.

45
Q

What is reduced ventricular ejection?

A

The ventricles begin to depolarize, marked by the T wave on the EKG. Ventricular pressure falls. Ejection of blood continues but at a reduced rate. Blood is running off of the arterial tree, causing aortic pressure to fall.

46
Q

What is isovolumetric relaxation?

A

Isovolumetric relaxation begins after the ventricles are fully repolarized, marked by the end of the T wave. LV pressure falls dramatically. When LV pressure falls below aortic pressure, the aortic valve closes. The pulmonic valve also closes. Closure of the aortic valve and pulmonic valve generates S2, the second heart sound. Since all valves are closed, ventricular volume remains constant.

47
Q

What is rapid ventricular filling?

A

When ventricular pressure falls to its lowest level (and slightly below left atrial pressure, the mitral valve opens. The ventricle begin to fill with blood from the left atrium, and ventricular volume increases. Ventricular pressure remains low because the ventricle is relaxed and compliant. The rapid flow of blood from the atria to the ventricles produces a third heart sound S3 which is normal in children but not in normal adults. Aortic pressure decreases as blood runs off from the aorta to the arterial tree.

48
Q

What is reduced ventricular filling?

A

Reduced ventricular filling or diastasis is the longest phase of the cardiac cycle at a normal heart rate and includes the final portion of ventricular filling which is at a slower rate than in the initial phase. The end of diastasis marks the end of diastole. The ventricular volume is the end diastolic volume.

49
Q

How do changes in heart rate affect diastasis?

A

Changes in heart rate alter the time available for diastasis.
If diastasis is reduced by an increase in heart rate, ventricular filling is compromised, end-diastolic volume will be reduced, and stroke volume will be reduced (via the Frank-Starling mechanism).

50
Q

What is the Frank-Starling relationship?

A

The volume of blood ejected by the ventricle depends on the volume present in the ventricle at end of diastole.; Stroke volume increases as preload increases (to a point); NOTE: Shifts in the Frank-Starling curves are non-specific and can reflect changes in contractility or afterload.

51
Q

Why cannot we just keep increasing preload to increase cardiac output?

A

As LV end diastolic volume (and LV end diastolic pressure) increases, the pulmonary venous pressure rises.; As pulmonary venous pressure rises, fluid leaks out of the capillaries into the interstitum and alveoli, impairing gas exchange

52
Q

What is preload?

A

The load on the ventricle at the end of diastole - Clinically important measures of preload include end-diastolic volume, end-diastolic pressure, end-diastolic wall stress

53
Q

What is afterload?

A

The load on the ventricle during ejection and is determined by the arterial system - Clinically important measures of afterload are aortic pressure, total peripheral resistance, ejection wall stress

54
Q

How can stroke volume be calculated?

A

Stroke volume (SV) = end-diastolic volume (EDV)- end-systolic volume (ESV)

55
Q

How can the ejection fraction be calculated?

A

Ejection fraction (EF) = SV/ EDV

56
Q

What affects myocardial contractility?

A

an alteration of calcium release to the myofilaments; an alteration in affinity of the myofilaments for calcium; An alteration in the number of myofilaments available for contraction; NOTE: Slope of the ESPVR is a measure of contractility

57
Q

What meds increase contractility?

A

Positive inotropes
Examples:
Dobutamine
Milrinone

58
Q

Why are patients in hypovolemic shock hypotensive?

A 
–Decreased blood volume
–Decreased venous return
–Decreased preload
–Decreased cardiac output
–Decreased MAP
59
Q

Why are patients in hypovolemic shock tachycardic?

A

To try to maintain cardiac output

remember: C.O. = SV x HR

60
Q

How do you treat hypovolemic shock?

A

–Stop the bleeding
–Administer IV fluids or blood transfusion
–May need drugs to maintain BP

Cardio (9 decks)

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