Blood Pressure Flashcards
How many litres of blood in the body?
4-6L
What is the pulmonary circuit?
Lungs
What is the systemic circuit?
Rest of the body - not lungs
What is the cardiac output?
5L/min
Define maxima
Systolic pressure
Define minima
Diastolic pressure
What is the incisura/dicrotic notch?
Brief drop caused by back flow which closes atrioventricular valves
How do you calculate mean arterial pressure?
Diastolic + 1/3 pulse pressure
How you calculate pulse pressure?
Systolic - diastolic
Measuring blood pressure
1) Cuff at heart level on brachial artery
2) Inflate above expected systolic pressure
3) Release pressure (arterial pressure > cuff pressure) - Korotoff sound
4) Record systolic pressure
5) Release pressure. Sound: tapping –> muting –> pounding –> muffling –> silence
6) Muffle (UK) or silence (US) is diastolic pressure
What are the two main determinants of systolic pressure?
- Ejection velocity
- Stroke volume
What are the two main determinants of diastolic pressure?
- Total peripheral resistance
- Blood flow: arterial –> venous
Define orthostasis
Standing up
What occurs during orthostasis?
Raise MABP as fall in bp is detected by baroreceptors
Increase sympathetic input to the heart
Increase sympathetic flow to vessels (constriction)
Decrease parasympathetic flow to heart
How can drugs affect blood pressure?
As MABP = CO x TPR, any drugs that affect either cardiac output or total peripheral resistance will affect the mean arterial blood pressure
Give some examples of drugs that affect total peripheral resistance
- Angiotensin II
- Sympathetic agonist at α1 receptors
- Sympathetic antagonist at α1 receptors
Effect on total peripheral resistance by angiotensin II
Increase total peripheral resistance by vasoconstriction
Give an example of a sympathetic agonist at α1 receptors which will increase TPR by vasoconstriction
Phenylephrine
Give an example of a sympathetic antagonist at α1 receptors which will decrease TPR by vasodilation
Prazosin
Give examples of drugs that affect cardiac output
- Sympathetic agonists at ß1 receptors
- Digitalis/Digoxin
- Sympathetic antagonists at ß1 receptors
- Ca2+ channel blockers
Give an example of a sympathetic agonist at ß1 receptors which will increase CO by increasing HR or stroke volume
Dobutamin
Give an example of a sympathetic antagonist at ß1 receptors which will decrease CO by decreasing HR or stroke volume
Atenolol
Which part of the body always receives the same volume of blood?
The brain
