Heart = Pump

Question 1

Amount of liters entering the right and left chambers of the heart total

Answer 1

5L

Question 2

Pumping of the heart is a (?) phenomenon….

External factors (like the ANS) only influence the

Answer 2

1. Intrinsic

2. Pumping rate

Question 3

Propranolol

Answer 3

Drug that is a sympathetic antagonist

Slows heart rate

Question 4

Atropine

Answer 4

Parasympathetic antagonist

Raises heart rate

Question 5

Intrinsic heart rate is around what?

Answer 5

~100bpm

Question 6

General signs/symptoms of heart failure

Answer 6

Difficulty breathing

Severe fatigue

Shortness of breathe, particularly on exertion

Tachycardia, engorged neck veins (increased right atrial pressure)

Ankle edema

Palpable tender liver

Signs of fluid in lungs

Enlargement of heart shadow on CXR

Question 7

What is heart failure

Answer 7

Structural and functional impairment of ventricular filling or ejection of blood

Creates a condition in which the heart cannot pump sufficient O2 blood to meet metabolic demands

OR

Can only do so from an elevated filling pressure

Question 8

Forward heart failure

Answer 8

Reduction in cardiac output due to decreased pumping action

Symptoms:

Fatigue, dizzy, confusion, asthenia

Question 9

Backward heart failure

Answer 9

Congestive state, due to dysfunctional ventricle that does not pump out all the blood it receives

Increase ventricular filling pressure

Results:

Pulmonary edema (congestive within pulmonary vasculature)

Peripheral edema
—> fluid within other tissues like the skin, abdominal cavity

Question 10

Incidence and prevalence of heart failure

Answer 10

5.8 million people have heart failure in the USA

38 billion annually

Most common inpatient diagnosis within this population

Incidence increases with age
—> more common in men from 45-60 years old
—> over 70, risk is equal

Blacks have 25% higher chance

Question 11

Etiology of heart failure

Answer 11

1. Most commonly from impaired myocardial contractility caused by ischemic heart disease or cardiomyopathy

MI = most common cause

2. Systemic hypertension
   —> cardiac valve abnormalities, pericardial diseases, or pulmonary hypertension

Question 12

Stroke volume

Answer 12

Amount of blood ejected of the right or left per contraction

SV = EDV - ESV

Question 13

Cardiac output

Answer 13

Amount of blood ejected out of the heart per unit of TIME

CO = SV * HR

Question 14

Ejection fraction (EF)

Answer 14

Ratio of the volume of blood ejected from the ventricle during systole (SV) to the volume of blood present in the ventricle at the end of the diastole (EDV)

EF = SV/EDV

Question 15

Factors influencing cardiac pump activity

Answer 15

1. Contractile force of ventricular muscle
   —> positive factor dependent on…
   Myocardial fiber length (preload) AND
   Myocardial contractility
2. Pressure in the aorta/pulm artery
   —> negative factor known as AFTERLOAD

Question 16

Preload

Answer 16

= ventricular load at the end of diastole, before the start of contraction

Equates to the amount of stretch on a ventricular fiber just prior to the act of contraction

Initial stretch depends on the volume of blood in the heart during diastole

Larger volume = largery stretch = increased force of the next contraction

PRELOAD = MOST IMPORTANT IN THE DETERMINING STROKE VOLUME (SV)

Question 17

Length-tension (force) relationship

Answer 17

Diastole = lower curve…as length increases, force starts to increase slightly

Systole = upper curve…more drastic increase in force as length increases…but force decreases past optimal length

Question 18

What is a substitute measure for preload, since it is hard to measure?

Answer 18

Right atrial pressure

Question 19

Increased right atrial pressure = ?

Answer 19

Increased stroke volume

Thus, increased preload = increased SV

Question 20

Ventricular function curve (Frank-Sterling relationship)

Answer 20

Relationship between preload (i.e. EDV or myocardial fiber length) and ventricular performance (i.e. SV)

SV is DIRECTLY related to EDV

Relatively linear in the normal range
= SV 60-100mL
= EDV 100-150mL

Force/tension relationship and the physical blood volume contribute to this relationship

Question 21

Indices of myocardial fiber length (preload)

Answer 21

EDV

ED pressure

Ventricular circumference

Venous return/atrial volume

Mean atrial pressure

Question 22

Indices of ventricular performance

Answer 22

SV

CO

Stroke work

Cardiac work

Question 23

Myocardial contractility

Answer 23

= a property of heart muscle accounting for changes in strength of contraction

INDEPENDENT of preload and afterload!! (Intrinsic property)

It influences the relationship between SV and EDV
—> increase contractility, curve shifts upward…and vice versa

NOT THE SAME as increasing contractile force due to increased myocyte tension

Examples:

1. Providing a drug that creates peak contractile force despite less than optimal conditions (such as holding cardiac myocyte fibers at 1/2 their optimal tension)
   —> this change as NOTHING to do with the force-tension relationship, and exhibit intrinsic contractility
2. Patients with heart failure may present with reduced contractile force…despite their cardiac myocyte fibers being at optimal length

Question 24

Effect of NE on contractility

Answer 24

Increases it…

Thereby shifting the curve up and to the left

Exhibits increased contractility = increased SV

Question 25

Digitalis effect on contractility

Answer 25

Increases contractility by increasing the amount of Ca2+ available in heart muscle cells

Often used to treat heart failure

Done by inhibiting Na/K pump, which results in increased intracellular Na

As NA increases…the Na-Ca exchanger stops functioning…keeping Ca inside the cell

Question 26

Afterload in myocardial contraction

Answer 26

= systolic load on a ventricle upon beginning contraction

This is the resistance that musc be overcome by the ventricle in order to eject its contents during contraction

Estimated via:
Aortic pressure
Pulmonary arterial pressure
Peripheral vascular pressure
Systolic ventricular pressure

Increased afterload = decreased SV