Lecture 26: Cardiac Output and its Control

Question 1

Define two intrinsic determinants of cardiac output

Answer 1

• Heart Rate (HR)
  - The number of times the heart beats per minute
  -The average resting heart rate is 70 beats per minute
• Stroke Volume
  - The volume of blood that is pumped per beat
  -The average resting stroke volume is 70ml of blood per beat

TO calculate the average cardiac output
=Average Heart Rate x Average stroke volume

Question 2

Describe the effect of sympathetic and parasympathetic action on the heart, and how these systems impact the cardiac response to changing demands from the body

Answer 2

Sympathetic System
- stimulation via norepinephrine accelerates heart rate by increasing sinoatrial node firing rate; also caused by cardiac contractility(force of contraction of the heart)

Parasympathetic stimulation via acetylcholine decelerates heart rate by decreasing sinoatrial node firing rate; has minimal effect on ventricular contractility

Question 3

Describe the Frank-Starling Law of the Heart and how it changes in heart failure

Answer 3

It is a law that describes the relationship between EDV and SV

During heart failure, the failing heart ejects a lower SV for a given EDV in comparison to a non failing heart

Question 4

Define heart failure and cardiac hypertrophy

Answer 4

Cardiac hypertrophy is when the heart becomes bigger via the hypertrophy(short term compensatory mechanism) of the muscle fibers enabling it to maintain a normal stroke volume.

Heart failure occurs when the heart is unable to pump sufficient blood to meet the metabolic demand of organs and tissues.

Question 5

What is Cardiac Reserve

Answer 5

The difference between the cardiac output at rest and at its peak. ( the max volume of blood that can be pumped by the heart per minute)

Question 6

What is stroke volume determined by?

Answer 6

Venous return - Intrinsic Control
Sympathetic nervous system - Extrinsic Control