Cardiovascular Physiology

Question 1

Equation for coronary blood flow

Answer 1

CBF = coronary perfusion pressure (ie Pressure in aortic root minus Pressure in ventricle) divided by coronary vascular resistance

Question 2

What is normal coronary blood flow?

Answer 2

200-250mls per minute
5% of cardiac output
80-160mL per 100g per minute at rest

Question 3

What is the equation for coronary O2 delivery?

Answer 3

Coronary O2 delivery = coronary blood flow x (S02 x ceHb x B02) + (Pa02 X 0.003)

Any O2 delivery determined by its blood flow x its oxygen content

Question 4

What is coronary vascular resistance mediated by?

Answer 4

1. Metabolic activity - e.g. response to ischemia and hypoxia. Adenosine main mediator.
2. Autonomic control - SNS / PNS - alpha receptors vasoconstrict, beta receptors vasodilate
3. Systolic compression
4. Drugs e.g. GTN

Question 5

What is approximate normal coronary O2 delivery?

Answer 5

13 mLs O2 per 100g tissue per minute

Question 6

What is approximate weight of male and female heart?

Answer 6

Male 300 g

Female 250g

Question 7

Which coronary arteries are mainly responsible for altering vascular resistance?

Answer 7

Small endocardial arteries, <1mm in diameter

Question 8

How does coronary blood flow differ between left ventricle and right ventricle?

Answer 8

Right ventricle CBF 50:50 - lower pressures therefore no systolic compression
Left ventricle CBF 75% diastole 25% systole

Question 9

What is the myocardial oxygen consumption during arrest / at rest / at maximal inotropy?

Answer 9

Arrest / cardioplegia: 2mL/100g/min
Resting at HR 60bpm : 8mL/100g/min
Max inotropy: 90mL/100g/min

Question 10

What substrates does the heart metabolise under normal conditions and in what proportion?

Answer 10

65% - Free Fatty Acids 
15% - Glucose 
12% - Lactate and pyruvate 
3% - Amino acids 
5% - Anaerobic glycolysis

Question 11

What is the energy cost of different myocardial activities?

Answer 11

Contraction 60%
Relaxation 15%
Electrical activity 3 - 5%
Basal cell metabolism 20%

Question 12

What are the determinants of myocardia oxygen demand?

Answer 12

MAIN - heart rate
MAJOR - contractility / afterload
MINOR - preload / cost of electrical conduction
Basal cost of cardiac metabolism

Question 13

What is the cardiac output?

Answer 13

The volume of blood ejected by the heart per unit time.
Usually expressed in L/min
Normal value 5.0 L/min

Cardiac index divides CO by surface area of the body

CO = SV x HR

Question 14

What is the normal stroke volume?

Answer 14

Stroke volume is the volume of blood ejected from each ventricle with each cardiac cycle.
It is the EDV minus the ESV.
Normal value 70mLs.

Question 15

What is preload?

Answer 15

• myocardial sarcomere length just prior to contraction
• tension on sarcomeres just prior to contraction
• EDV or EDP
• can also be determined as LV wall stress at end diastole

Question 16

What are the determinants of preload?

Answer 16

1. Pressure filling the ventricle
   - intrathoracic pressure
   - atrial pressure - contractility and rhythm / AV valve competence / ventricular end-systolic volume / ventricular compliance
   - right atrial pressure
   - mean systemic filling pressure - venous compliance / total blood volume
   - cardiac output
2. Compliance of the ventricle
   - pericardial compliance - walls / content
   - ventricular wall compliance - duration of diastole, wall thickness, relaxation, end systolic volume i.e. afterload