factors influencing coronary, cerebral, skeletal muscle and skin ciruculations

Question 1

how do we control coronary circulation

Answer 1

1. coronary perfussion pressure
2. coronary perfussion time
3. vessel diameter
4. vasomoter tone (arteriolar tone)

Question 2

what is a clinical situation/scenario associated with coronary circulation

Answer 2

• patient had a myocardial infraction
  -stent inserted to his critically stenosed right coronary artery
• started on secondary prevention drugs such as beta blockers, ace inhibitors, antiplatelets
• beta blockers and ace inhibitors used to lower blood pressure

Question 3

what is coronary blood flow

Answer 3

60-80ml/100g/min

Question 4

how much of the oxygen is extracted in coronal blood flow

Answer 4

• 70-80% much higher compared to other areas of the body

Question 5

how much does coronal blood flow increase during exercise

Answer 5

5 times

Question 6

what is coronary ischaemia defined as

Answer 6

when o2 demand is greater than supply

Question 7

what is coronary perfusion pressure

Answer 7

the pressure that drives blood to be taken up by myocardial muscle from the coronary arteries

Question 8

what is the equation for coronary perfusion pressure

Answer 8

CPP= diastole aortic pressure - left ventricle end diastole pressure

Question 9

what does a greater Coronary PP mean

Answer 9

• more blood drawn up= increased coronary blood flow= increased o2 delivery

Question 10

when is blood flow greatest in coronary arteries with regards to coronary perfussion pressure

Answer 10

• during diastol- blood can enter coronary arteries
• during systole blood cannot enter coronary arteries

Question 11

what impact does hypertension have on coronary perfussion pressure

Answer 11

• chronic hypertension decreases coronary perfussion pressure as left ventricle pressure increases
• hypertension leads to increased afterload, heart has to work harder this leads to left ventricle hypertrophy
• causes decrease in coronary blood flow
• beta blockers and ace inhibitors can be used to treat hypertension and decrease lv hypertrophy

Question 12

what is coronary perfusion time

Answer 12

• diastole time- the time the heart is in diastole and blood can enter the coronary artereis
• increased coronary perfusion time means increased oxygen delivery to myocardium
• systole is fixed of 0.2 seconds however diastole varies and is dependant on heart rate
• increased heart rate= lower coronary perfusion time= decrease coronary blood flow

Question 13

what mediators have an impact on arteriolar tone

Answer 13

• adenosine
• carbon dioxide
• nitric oxide
  -calcium ions

Question 14

what vasomotor control does large arterioles have

Answer 14

• endothelial control (endothelial control the diameter of blood vessel_
• increased blood flow through large arterioles causes shear stress which leads to NO production and therefore vasodilation

Question 15

what vasomotor control does medium arterioles have

Answer 15

• myogenic control (caused by smooth muscle contracting or relaxing responding changes to bp)
• increased bp causes arteriolar stretch and this activates calcium channels and therefore vasoconstriction

Question 16

what vasometer control does small arterioles have

Answer 16

• metabolic control
• cardiomyocyte produces metabolites such as carbon dioxide and adenosine which causes vasodilation

Question 17

what is autoregulation- in coronary circulation

Answer 17

• part of vasomotor control
• process where blood flow is controlled within the body with changes in pressure
• however at extreme low or high blood pressures blood flow increases/decreases
• autoregulation only takes place in physiological limits

Question 18

what is neurohumoral factors in coronary circulation

Answer 18

• interaction of hormones and nervous system in control physiology in body
• activation of sympathetic nervous system causes release of norepinephrine and epinephrine these hormones bind to beta adrenoreceptor which causes increase hight rate and contractility
• increased myocardial work releases co2, adenosine which causes vasodilation
• alpha adrenoreceptor stimulation can cause vasoconstriction