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Anesthesia > Cardiac Physiology > Flashcards

Cardiac Physiology Flashcards

1
Q

What is an ionotrope?

A

An agent that alters the strength of muscle contraction. Positive inotropes increase contractility Positive inotropes increase cytoplasmic calcium.

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2
Q

What is lusitropy?

A

The strength of myocardial muscle relaxation

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3
Q

What is a surrogate used to measure preload?

A

End diastolic volume

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4
Q

What is afterload?

A

The pressure the heart contracts against and must overcome to eject blood (aortic stenosis)

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5
Q

What is anesthetic-induced cardioprotection?

A

A reduction of myocardial injury that occurs when a volatile anesthetic agent is given prior to or during a cardiac ischemic event

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6
Q

Where are the best locations to auscultate the: 1. Aortic valve 2. Pulmonic valve 3. Tricuspid valve 4. Mitral valve

A
  1. Right 2nd IC space 2. Left 2nd IC space 3. Left 4th-5th IC space near sternum 4. Left 5th IC space mid-clavicular line
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7
Q

What does the ‘a’ wave represent on a Wiggers diagram?

A

Atrial contraction

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8
Q

What does the ‘c’ wave represent on a Wiggers diagram?

A

increase in pressure from the mitral valve bulging into the atrium after closure

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9
Q

What does the ‘v’ wave correspond to on a Wiggers diagram?

A

passive atrial filling

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10
Q

What makes the first heart sounds (S1)?

A

reverberation of blood from the sudden closure of the mitral valve (left A-V valve)

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11
Q

What makes the 2nd heart sound (S2)?

A

reverberation of blood from the sudden closure of the aortic valve.

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12
Q

What is the mechanism of splitting of S2?

A

During inspiration - impedence to pulmonary blood flow is further decreased and the pulmonic valve closes later than the aortic

decreased intrathoracic pressure during inspiration –> increases VR to RA –> increases RV SV and ejection time and prolongs the time until pulmonic valve closure.

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13
Q

What is the mechanism of an S3?

A

normal finding in children and young adults

older adults = underlying cardiac dysfunction (altered ventricular compliance, increased filling pressures, and heart failure)

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14
Q

What is the mechanism of a 4th heart sound (S4)?

A

with atrial contraction in late diastole = a reduced ventricular compliance and diastolic dysfunction

Often from Aortic Stenosis

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15
Q

How does CO relate to pressure and resistance?

A

CO = P / R

Resistance to flow determines the pressure that is produced by CO

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16
Q

What heart sound is expected with an ASD?

A

wide, fixed split S2

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17
Q

Describe ideal anesthetic management for a patient with HOCM.

A

anything that decreases preload or afterload or increases contractility or heart rate may worsen the obstruction

ensure adequate preload

maintenance or augmentation of afterload

avoiding increases in heart rate and contractility.

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18
Q

When does coronary blood flow occur for the right and left ventricles?

A

Right - all the time

Left - diastole only d/t high systolic pressure

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19
Q

What does it mean to have a right dominant heart?

A

Right cornoary artery (RCA) supplied the posterior descending artery - 80% of people

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20
Q

Describe the blood supply to the SA and SV nodes.

A

SA - RCA 55-60%, LCX 40-45%

AV - RCA 80%, LCX 20%

Ischemia from RCA occlusion –> complete heart block –> slow ventricular escape rhythm

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21
Q

What is the main neurotransmitter and receptor for PNS stimulation to the heart?

A

Ach

Vagus nerve –> supraventricular muscarinic receptors (most are M2)

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22
Q

What arteries supply the spinal cord?

A

single anterior spinal artery

two posterior spinal arteries

Artery of Adamkiewicz, which branches from the aorta at T9-T12

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23
Q

What 2 sets of arteries supply the lungs?

A

right heart –> pulmonary arteries –> lungs

left heart –> bronchial arteries –> lungs

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24
Q

What blood vessel carries venous return from the myocardium?

A

Coronary sinus

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25
Q

What would be the most likely physiological effects of phenylephrine in a patient with a heart transplant?

A

After transplant - no vagal innervation = no reflex bradycardia

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26
Q

Where is the vasomotor center located and what is it’s function?

A

Medulla oblongata

Regulates BP via CN IX and X

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27
Q

How are central and peripheral chemoreceptor responses to CO2 different?

A

Central –> stimulates the sympathetic system to vasoconstrict peripheral arterioles

Peripheral –> vasodilation

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28
Q

Where are vasopressin and corticotropin releasing hormone (CRH) synthesized?

A

Paraventricular nucleus of hypothalamus

29
Q

Where are ACTH and ADH synthesized?

A

ACTH - anterior pituitary

ADH - posterior pituitary

30
Q

What is the primary neurotransmitter of the SNS?

A

NE –> alpha & beta adrenergic receptors

31
Q

What is the primary neurotransmitter of the PNS?

A

Ach –> muscarinic receptors

32
Q

What are 2 major classes of adrenergic receptors?

A

Alpha (1, 2)

Beta (1, 2, 3) - stimulate chronotropy, inotropy, lusitropy, and dromotropy

33
Q

What is the major muscarinic AchR in the myocardium and what are the effects of its stimulation?

A

M2

reduces SA node activity

slows atrioventricular (AV) conduction

decreases atrial contractile force

inhibition of contractility

34
Q

What is the Bainbridge reflex?

A

stretch receptors in RA wall & cavoatrial junction

increase in right-sided filling pressure –> vagal signals to the VMC in the medulla –> inhibit parasympathetic activity –> INC HR

Spinal/epidural –> vasodilation –> dec atrial stretch –> dec HR

35
Q

What is the Bezold-Jarisch reflex?

A

vagal reflex - unmyelinated vagal afferent type C fibers as a response to noxious ventricular stimuli

Stimuli sensed by chemoreceptors and mechanoreceptors in LV wall –> hypotension, bradycardia, and coronary artery dilatation

Thought to be the response in MI, thrombosis, revascularization and syncope.

36
Q

What is the oculocardiac reflex?

A

pressure applied directly to the globe or traction on its surrounding structures

Stretch receptors EOMs –> afferent signals through the short and long ciliary nerves –> merge –> CN V-1 at the ciliary ganglion –> Gasserian ganglion.

efferent signal via vagus nerve –> increased parasympathetic tone and bradycardia

glycopyrrolate or atropine, reduces the incidence of bradycardia during eye surgery

“Five and dime” reflex

37
Q

What is the baroreceptor reflex?

A

responsible for maintaining blood pressure stability

BP changes monitored by stretch receptors (>170mmHg) in the carotid sinus and aortic arch –> CN IX, X –> nucleus solitarius, in the VMC of the medulla

Response –> decreased sympathetic activity, decreased cardiac contractility, lower HR, and lower vascular tone

The opposite effects are elicited with the onset of hypotension

38
Q

Where are the body’s chemreceptor cells located and what do they do?

A

carotid bodies and the aortic body

respond to arterial pH changes (acidosis) and oxygen tension alterations (PaO2 <50mmHg) –> send impulses along sinus nerve of Hering (a branch of CN IX) and CN X –> chemosensitive area of the medulla

Response –> stimulating respiratory centers –> increasing ventilatory drive + activation of PNS –> Dec HR, contractility.

persistent hypoxia, however, –> direct CNS stim–> increase in sympathetic activity, overriding PNS effects

39
Q

What is a mixed venous oxygen saturation (SvO2)?

A

O2 saturation in the blood returning to the lungs from the right ventricle = ave. amount of O2 remaining after all tissues have removed O2 from the Hb.

Ideally drawn from the distal tip of a pulmonary artery catheter

***can determine whether the cardiac output and oxygen delivery is adequate to meet metabolic needs

40
Q

What are major causes of low SvO2?

A

Normal = 60-80%

Hypoxemia

low CO

anemia

increased oxygen consumption

41
Q

What thinkgs can increase SvO2?

A

decreased oxygen consumption (e.g. cyanide toxicity)

elevation in CO

normalization of hemoglobin

improvement in oxygenation

42
Q

Located on vascular PRE-junctional nerve terminals, this receptor type inhibits the release of NE through negative feedback.

A

Alpha-2

43
Q

Define preload.

A

ventricular load at the end of diastole (LVEDV)

Preload is dependent on volume status, ventricular relaxation, and venous capacitance

44
Q

Define afterload.

A

load on the left ventricle (LV) after contraction has begun (systole)

Afterload is dependent on blood pressure, which is proportional to systemic vascular resistance (SVR)

SVR depends on the compliance of the peripheral and central vasculature.

45
Q

Define contractility.

A

work performed by cardiac muscle at any given end-diastolic fiber length

As the left ventricle fills with increasing volumes of blood, a linear relationship exists –> force of cardiac contractions increases

46
Q

How does stretching of muscle fibers (inc preload) alter muscle contraction?

A

increases the affinity of troponin C for calcium –> increases the number of actin-myosin cross-bridges within the muscle fibers

Frank-Starling mechanism

47
Q

What factors increase contractility?

A

exercise, adrenergic stimulation, digitalis

48
Q

What factors decrease contractility?

A

acidosis, hypothermia, beta-blockers

49
Q

What are the 4 phases of diastole?

A

(1) Isovolumetric relaxation = energy dependent.
(2) The rapid filling phase (i.e., the LV chamber filling at variable LV pressure) = most of the filling
(3) Slow filling, or diastasis.
(4) Final filling during atrial systole.

50
Q

What happens to VR, MAP, HR during valsalva maneuver?

A

increase in intrathoracic pressure –> decreases venous return –> decrease in blood pressure

decreased pressure is sensed by baroreceptors –> activate the baroreceptor reflex –> increase in heart rate and contractility SNS stimulation

51
Q

What is the Cushing reflex?

A

ICP increases to a critical level –> dec brain perfusion –> ischemia

Ischemia at medullary vasomotor center –> SNS –> increase in heart rate, blood pressure, and myocardial contractility to improve cerebral perfusion

Increased BP –> reflex bradycardia via baroreceptors

Brainstem ischemia –> irregular breathing

52
Q

What are the “big 3” determinants of myocardial oxygen demand?

A

cardiac wall tension (preload & afterload)

contractility

heart rate

53
Q

Describe each phase of the ventricular action potential

A

Phase 0 (Rapid Upstroke): Massive Na+ inflow. Activated by -65 mV membrane threshold.

Phase 1 (Early Repolarization): K+ efflux and cessation of Na+ inflow.

Phase 2 (Plateau): Diminution of most current flows.

Phase 3 (Late Repolarization): Inactivation of Ca2+ flows and reactivation of K+ efflux.

Phase 4 (Diastolic Depolarization).

54
Q

What is the formula for MAP?

A

MAP = (1/3 x SBP) + (2/3 x DBP)

55
Q

What is the formula for Cerebral Prefusion Pressure?

A

CPP = MAP - (greater of ICP or CVP)

56
Q

What is the forumla for cornoary perfusion pressure?

A

CPP = DBP - LVEDP

57
Q

What are normal intracardiac pressures for:

Right atrium

Right venticle

Left atrium

Left ventricle

A

Right Atrium: 3-8 mmHg

Right Ventricle: 15-30 / 3-8 mmHg

Left Atrium: 4-10 mmHg

Left Ventricle: 100-120 / 3-12 mmHg

58
Q

What is the normal pulmonary artery pressure?

A

15-30 / 4-12 mmHg

increased in conditions w/ elevated pulmonary vascular resistance or in conditions w/ elevated left atrial pressure.

59
Q

What is a normal venous pressure?

A

(0-5 mmHg), as veins comprise a high-capacitance, low-pressure system.

Measurement of venous pressure will therefore be more dependent on gravity and location than arterial pressure.

60
Q

What is the formula for SVR and what contibutes to SVR?

A

SVR = (MAP - CVP) / CO

Principal contributor to SVR = small arterioles. Vasoconstriction –> raise SVR

Blood viscosity also contributes to SVR

61
Q

What factors contribute to blood viscosity?

A

flow rate, hematocrit, plasma viscosity, temperature, and red blood cell deformability

increased: sickle cell anemia or polycythemia vera abnormal perfusion (e.g., non-pulsatile cardiopulmonary bypass)

62
Q

What is the formula for pulmonary vascular resistance?

A

PVR = (PAmean – Left Atrial Pressure) / CO

Pulmonary vasoconstriction, PE, extremes of alveolar ventilation (atelectasis or hyperinflation) —> raise PVR

Hyperventilation –> DEC PVR

63
Q

Systolic blood pressure is largly depednent on what two factors?

A
  1. Pressure generated by the left ventricle
  2. Elasticity of large arteries.
64
Q

Describe the relationship between flow, pressure and resistance and what Poiseuille’s Law is.

A

Flow = Pressure/Resistance

Poiseuille’s Law = relationship b/w flow of a fluid in a long narrow tube, viscosity of the fluid and the radius of the tube:

Flow = (Pi x r4) / (8 x η x L) x ∆P

∆P = pressure difference between two ends of the tube (vessel)

η = viscosity

r = radius of lumen

L = length of the tube (vessel)

65
Q

Describe axial streaming and its effect on viscosity.

A

Axial streaming = blood cells flow down the central axis of the blood vessel –> small area along the wall of the blood vessel without cells –> less friction along the wall –> decreasing the viscosity.

Explains why we see a reduction in blood viscosity as the diameter of the vessel decreases. The cell-free zone = constant 5 μm width. In the small vessels, this 5 μm layer = much greater % of the overall diameter of the vessel = greater effect on the viscosity of blood.

66
Q

What effect will low Po2 and increasing precapillary resistance (pressor) have on blood flow and filtration?

A

A low PO2 –> decrease the precapillary resistance, –> more blood to flow through the capillaries

Inc precapillary resistance –> dec capillary hydrostatic pressure –> dec filtration

67
Q

What are the three primary factors that control venous return?

A
  1. Mean systemic filling pressure.
  2. Right atrial pressure (central venous pressure).
  3. Blood flow resistance (between the peripheral veins and the right atrium).

VR = (MSFP - RAP) / Resistance to VR

68
Q

Define mean systemic filling pressure. What things increase and decrease MSFPs?

A

pressure throughout the systemic circulation

reflects the degree the systemic circulation is filled (i.e. volume of blood in the circulatory system)

Increased by: IVFs and/or vasoconstrictors to —> increase in venous return (and CO).

Decreased by: Increased capacitance (i.e. vasodilation) —> dec mean systemic filling pressure —> dec VR

69
Q

Describe the relationship b/w intrathoracic pressure and VR

A

Inverse relationship

Inc intrahtoracic pressure - expiration, valsalva –> DEC VR

Anesthesia (25 decks)

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