CVS Stuff

Question 1

What is afterload?

Answer 1

The load the heart must eject blood against (roughly equivalent to aortic pressure(impedance))

Question 2

What is preload?

Answer 2

Amount the ventricles are stretched in diastole (related to the end diastolic volume or central venous pressure)

Question 3

What is total peripheral resistance?

Answer 3

Also known as systemic vascular resistance

Resistance to blood flow offered by all the systemic vasculature

Question 4

Which blood vessel offers the greatest resistance to blood flow?

Answer 4

Arterioles

Question 5

What effect will constricting arterioles have on resistance?

Answer 5

Increased pressure in arterioles, decreased in capillaries and venules

Question 6

What effect does changing cardiac output or total peripheral resistance have, whilst not changing the other? E.g., increase CO but TPR remains the same

Answer 6

Both of these circumstances follow the same rules:
CO/TPR changes directly correlate to arterial pressure changes
Arterial pressure changes inversely correlate to venous pressure changes
E.g. increased CO means that arterial pressure increases, so the venous pressure falls

Question 7

What is the Ventricular Compliance Curve?

Answer 7

Relationship between LV pressure and volume, related to compliance (how easily the chamber expands)
The higher the venous pressure, the more the heart fills
As heart fills, LV pressure increases
In diseased states compliance can change, eg. decreased compliance means EDV is the same but EDpP will increase and curve will shift to left

Question 8

What is the Frank - Starling Law of the heart?

Answer 8

The more the heart fills, the more the fibres stretch before contracting, so the harder it contracts, so the bigger the SV (up to a limit) (intrinsic control mechanism)
An increase in venous pressure will fill the heart more, and the amount it fills depends on the compliance

Question 9

What is the ‘normal’ operating point at rest of LVEDP and SV?

Answer 9

8 mm Hg

70ml

Question 10

What is the Starling Curve?

Answer 10

LVEDP (filling pressure) against SV
Direct correlation at first (straight line), then curves to a flat line
Increasing venous return leads to increased preload and increased LVEDP, causing an increase in SV so extra blood is pumped out of ventricle

Question 11

How does the length of sarcomeres affect contractile force?

Answer 11

Shorter sarcomeres decrease contractile force, as filament overlap interferes with contraction
As cardiac muscles are stretched, calcium sensitivity increases

Question 12

What is contractility?

Answer 12

Force of contraction for a given fibre length

Can be increased by extrinsic factors such as circulating adrenaline and sympathetic stimulation