Cardiac Output

Question 1

Contractility

Answer 1

The intrinsic ability of cardiac muscle to develop force for a given muscle length.

Question 2

Preload

Answer 2

The muscle length prior to contractility, and it is dependent of ventricular filling (or end-diastolic volume)

The value is related to right atrial pressure.

The most important determining factor for preload is venous return.

Question 3

Afterload

Answer 3

The tension (or the arterial pressure) against which the ventricle must contract.

If arterial pressure increases, afterload also increases.

Afterload for the left ventricle is determined by aortic pressure.

Afterload for the right ventricle is determined by pulmonary artery pressure.

Question 4

Cardiac Output

Answer 4

The volume (liters) of blood pumped each minute and is expressed by CO= SV x HR

Question 5

Heart rate is proportional to ______?

Heart rate is modified by what 3 factors?

An increase in parasympathetic activity will ____ HR?

An increase in sympathetic activity will ____ HR?

Answer 5

Cardiac Output

Autonomic, immune and local.

P- decrease (M2 cholinergic receptors)

S- increase (B1 and B2 adrenergic receptors)

Question 6

Stroke Volume

End diastolic volume

End systolic volume

Answer 6

SV= EDV (amount of blood collected in a ventricle during diastole)- ESV (amount of blood remaining in a ventricle after contraction)
Determined by preload, afterload and contractility.

Question 7

Cardiac Reserve

Answer 7

The difference between resting and maximal cardiac output.

Question 8

Frank Starling Principle

Answer 8

The relationship between cardiac output and left ventricular end diastolic volume (or the relationship between stroke volume and right atrial pressure).

Based on length-tension relationship within the ventricle.

If ventricular EDV (preload) is increased then the ventricular fiber length is also increased, resulting in an increased ‘tension’ of the muscle.

The contraction and therefore stroke volume in response to changes in venous return is called the Frank-Starling mechanism or Starling’s Law of the Heart.

Question 9

Autonomic Nervous System and HR Regulation

-Three baroreceptors and where they maintain BP

Answer 9

SNS stimulation is activated by stress, anxiety, excitement or exercise.

PNS stimulation is mediated by acetylcholine and opposes the SNS slowing HR

Carotid sinus reflex- brain
Bainbridge reflex- heart
Aortic sinus reflex- aorta

Question 10

Bainbridge Reflex

Answer 10

A sympathetic reflex initiated by increased blood in the atria. Causes stimulation of the SA node. Stimulated baroreceptors in the atria, causing increased SNS stimulation.

Question 11

Chemical Regulation of the Heart

Answer 11

Epinephrine and thyroxine (T4) increase HR

Hormonal regulation

• Renin
• ADH
• Aldosterone

Intra and extracellular ion concentrations must be maintained for normal heart function

Question 12

Homeostatic Imbalances

• Hypocalcemia
• Hypercalcemia
• Hypernatremia
• Hyperkalemia

Answer 12

Hypocalcemia- reduced ionic calcium depresses the heart

Hypercalcemia- dramatically increases the heart irritability and leads to spastic contractions

Hypernatremia- blocks heart contraction by inhibiting ionic calcium transport

Hyperkalemia- leads to heart block and cardiac arrest

Question 13

Congestive Heart Failure is caused by: (4)

Answer 13

1. Coronary atherosclerosis
2. Increased blood pressure in the aorta
3. Successive myocardial infarcts
4. Dilatred cardiomyopathy