Blood Pressure Flashcards
Blood pressure
The outward (hydrostatic pressure) exerted by blood pressure on the blood vessel walls
Systemic systolic arterial blood pressure
The pressure exerted by blood on the walls of the aorta and systemic arteries when the heart contracts. It should not reach or exceed 140mmHg under resting conditions
Systemic diastolic arterial blood pressure
The pressure exerted by blood on the walls of the aorta when the heart relaxes. Should not reach or exceed 90mHg under resting conditions
Hypertension
Clinical blood pressure of 140/90mmHg or higher and daytime average of 135/85mmHg
Pulse pressure
Difference between systolic and diastolic blood pressures. Should be between 30 and 50mmHg
What clinical items are used to determine blood pressure
Cuff sphygmomanometer and stethoscope
Korotkoff sounds (5)
1 - Peak systolic pressure
2/3 - Intermittent sounds are heard due to turbulent spurts of flow cyclically exceeding cuff pressure
4 - Minimum diastolic pressure, producing a muffled/muted sound
5 - No sound heard due to uninterrupted laminar flow
When are korotkoff sounds heard?
When cuff pressure is between 120-80mmHg
At which korotkoff sound is diastolic pressure measured?
5th korotkoff sound (when sound disappears)
Calculation for pressure gradient
Mean arterial pressure - central venous (right atrial) pressure
Mean arterial blood pressure
The average arterial blood pressure during a single cardiac cycle which involves contraction and relaxation of the heart
Calculations for mean arterial blood pressure (3)
MAP = [(2x diastolic pressure) + systolic pressure] MAP = diastolic blood pressure + 1/3 pulse pressure MAP = cardiac output x systemic vascular resistance
Normal range for mean arterial blood pressure
70-105mmHg
Minimum mean arterial blood pressure required to perfuse vital organs
60mmHg
Why must mean arterial pressure be regulated within a narrow range? (2)
- Pressure is high enough to perfuse internal organs including brain, heart and kidneys)
- Pressure is not too high to ensure that there is no damage to blood vessels or extra strain placed on the heart
Cardiac output
Volume of blood pumped by each ventricle of the heart per minute
Cardiac output calculation
Stroke volume x heart rate
Stroke volume
Volume of pumped by each ventricle of the heart per heart beat
Systemic vascular resistance
Sum of the resistance of all the vasculature in the systemic circulation
Where is systemic vascular resistance greatest?
In the arterioles - major resistance vessels
Control centre for blood pressure
Medulla
Baroreceptors. Where are the following located and what are they innervated by?:
- Carotid baroreceptors
- Aortic baroreceptors
- Carotid baroreceptors - located in the carotid sinus and are innervated by glossopharyngeal nerve (CN IX)
- Aortic baroreceptors - located in the aorta and are innervated by the vagus nerve (CN X)
Postural hypotension
Results from failure of baroreceptor responses to gravitational shifts in blood when moving from horizontal to vertical position
Baroreceptor reflexes in the prevention of postural hypotension
- Venous return decreases as an effect of gravity
- MAP decreases
- Rate of firing of baroreceptors thus reduced
- Vagal tone to heart decreases and sympathetic tone increases, increases HR and SV
- Sympathetic constrictor tone increases, increasing systemic vascular resistance
- Sympathetic constrictor tone to veins increases, increasing venous return and stroke volume
Risk factors for postural hypotension
Age Medication Certain diseases Reduced intravascular volume Prolonged bed rest
How is a positive result of postural hypotension determined?
By a drop, within 3 minutes of standing from lying position, in systolic blood pressure of at least 20mmHg without symptoms or a drop in diastolic blood pressure of 10mmHg with symptoms
What controls blood pressure changes in the short term?
Baroreceptor reflexes
Symptoms of postural hypotension
Dizziness, lightheadedness, blurred vision, faintness, falls
How much of the body fluid is intracellular fluid and how much is extracellular fluid?
Intracellular = 2/3 Extracellular = 1/3
What is extracellular fluid volume?
Plamsa volume + interstitial fluid volume
Interstitial fluid
Fluid that bathes the cells and acts as the go-between the blood and body cells
What happens to control fluid levels if plasma volumes fall?
Compensatory mechanism shifts fluid from interstitial compartment to plasma compartment
2 main factors that influence extracellular fluid volume
Water excess or deficit
Sodium excess or deficit
Hormones which regulate extracellular fluid volume
Renin-angiotensin-aldosterone system
Natriuretic peptides
Antidiuretic hormone
Renin:
- Where is it released from?
- What does it do?
- Granular cells in the juxtaglomerular apparatus in the kidneys
- Stimulates the formation of angiotensin I in the blood from angiotensin produced in the liver
Angiotensin:
- What converts angiotensin I to angiotensin II?
- Functions of angiotensin II
- Angiotensin converting enzyme
- Stimulates the release of aldosterone from the adrenal cortex and causes systemic vasoconstriction, increasing SVR. Also stimulates thirst and ADH release and this contributes to increasing the plasma volume mainly brought about by aldosterone
What is angiotensin converting enzyme mainly produced by?
Pulmonary vascular endothelium
Aldosterone:
- Which type of hormone is it?
- Function
- Steroid hormone
- Acts on the kidneys to increase sodium and water retention thus increasing plasma volume and thus increasing blood pressure
What is the rate limiting step in RAAS system?
Renin secretion