Cardiac Output

What is the term for amount of blood ejected by each ventricle in 1 minute?

Cardiac output

What is the formula for cardiac output?

CO = HR x SV

What is the difference between a person's maximum and resting CO?

Cardiac reserve

What can cause tachycardia?

stress, anxiety, drugs, heart disease, fever, loss of blood, damage to myocardium

What can cause bradycardia?

sleep, low body temperature, endurance-trained athletes

What does a positive chronotropic agent do?

Raise HR

What does a negative chronotropic agent do?

Lower HR

Cardiac centers in __ initiate autonomic output to the heart.

Reticular formation of medulla oblongata

What is the cardiostimulatory/cardioaccelerator effect?

neurons of cardiac center transmit signals to heart by way of sympathetic pathways

What is the cardioinhibitory effect?

others transmit parasympathetic signals by way of the vagus nerve

What are sympathetic postganglionic fibers?

Adrenergic - release NE

Sympathetic postganglionic fibers lead to opening of what channels?

Ca2+ channels, lead to depolarization of SA node
Leads to increase of HR

What is the result of an excessively high heart rate?

Stroke volume and cardiac output are reduced

What effect does parasympathetic vagus nerves have on the SA and AV nodes?

Cholinergic and inhibitory effect

How does parasympathetic innervation affect HR?

Ach binds to muscarinic receptors
K+ gates open in nodal cells
K+ leaves cells and they become hyperpolarized, firing less often
HR slows

T/F: Without influence from cardiac centers, the SA node has an intrinsic firing rate of 100 bpm.

True

What does vagal tone do to HR?

Decreases from 100 to 70-80 bpm

What effect does nicotine and caffeine have on HR?

Positive chronotropic effect

What electrolyte has the greatest chronotropic effect?

Potassium

What chronotropic effect does hyperkalemia have?

Negative

What chronotropic effect does hypokalemia have?

Positive - Abnormal rhythm

What chronotropic effect does hypercalcemia have?

Negative

What chronotropic effect does hypocalcemia have?

Positive

What 3 variables govern stroke volume?

Preload
Contractility
Afterload

What does increased preload or contractility do to SV?

Increases stroke volume

What does increased afterload do to SV?

decrease stroke volume

What is the amount of tension in ventricular myocardium immediately before it begins to contract?

Preload

What does increased preload cause?

Increased force of contraction

What is the Frank-Starling mechanism?

Force of heart contraction is proportional to initial length of muscle fiber
Increasing strength of ventricular muscle increases contraction strength

Describe the Frank Starling law of the heart.

Stroke volume is proportional to the end diastolic volume.

What does a positive inotropic agent do?

Increase contractility

What does a negative inotropic agent do?

Decrease contractility

What are some positive inotropic agents?

Hypercalcemia
Catecholamines
Glucagon
Digitalis

What is a negative inotropic agent example?

Hypocalcemia

What is the largest part of the afterload?

Blood pressure in aorta and pulmonary trunk

What is afterload?

Sum of all forces opposing ejection of blood from ventricle
Opposes opening of semilunar valves
Limit stroke volume

How does hypertension affect afterload?

Increase afterload
Oppose ventricular ejection

What conditions can contribute to a higher afterload?

Hypertension
Lung diseases
Cor pulmonale
Emphysema
Chronic bronchitis
Black lung disease

How does exercise affect cardiac output?

Increase cardiac output