Blood Pressure 1 Flashcards
Degree of constriction
experienced by a blood
vessel relative to…
… its maximally dilated state.
What is vascular smooth muscle?
vascular tone (vascular tonus).
Pre-capillary sphincters + Blood vessel smooth muscle =
major control of blood flow and blood pressure locally
mean diameter and mean wall thickness of artery?
diameter = 4.0 mm
wall thickness = 1.0 mm
mean diameter and mean wall thickness of arterioles?
diameter = 30.0 um
wall thickness = 6.0um
mean diameter and mean wall thickness of capillarys
diameter = 8.0 um
wall thickness = 0.5 um
mean diameter and mean wall thickness of venules?
diameter = 20.0 um
wall thickness = 1.0 um
mean diameter and mean wall thickness of vein?
diameter = 5.0 mm
wall thickness = 0.5 mm
Which units are used to measure blood pressure?
- Bar
- PSI (pound per square inch)
- mm Hg – millimetre of mercury
Define blood pressure?
pressure exerted by circulating blood upon the walls of blood vessels. Force applied to the vessel walls.
What is the flow rate of blood?
volume of blood flowing through a specific vessel – or organ – over a period of time (for example, L/min, mL/s, etc.)
Flow is directly proportional to…
… pressure gradient
Flow is inversely proportional to …
… vascular resistance.
What is vascular resistance?
Frictional force that opposes the flow of a fluid
Increased resistance =
decreased flow rate
decreased resistance =
increased flow rate
How can the body compensate for increased
resistance?
Heart works harder to achieve a larger
pressure gradient
the flow rate of blood through a vessel is…
… the volume of blood passing thorugh per unit of time.
the flow rate of blood thorugh a vessel is directly proportional to…
… the pressure gradient (as the pressure gradient increases, flow rate increases.
the flow rate of blood is inversely proportional to …
… vascular resistance (as resistance increases, flow rate decreases).
flow rate of blood through a vessel =
pressure gradient / resistance of blood vessel.
What causes resistance to blood flow?
- Blood viscosity
- Vessel dimensions
What is blood viscosity?
The ‘thicker’ a liquid, the more viscous it is
What causes resistance to blood flow?
- Vessel dimensions
Length
Radius
Blood ‘rubbing’ - the greater the contact area = the greater the ressitance
‘rubbing against arterial walls.
More blood in contact with the walls of a narrow vessel =
increased resistance - flow decreases.
Less blood in contact with the walls of a wide vessel =
decreased resistance. Flow increases
Slight change in the radius of a vessel =
notable change in flow
Poiseuille law
Flow = pi x pressure gradient x radius^4
/
8 x viscosity x length
Resistance is inversely proportional to…
… the fourth power of the
radius
Doubling the radius reduces resistance to…
1/6th its orginal value
flow is…
… 16 fold
What is pulse pressure?
PP = systolic pressure – diastolic pressure (DP)
in simple terms
Pulse pressure represents…
It represents the force that the heart generates each time it contracts
(Amount of pressure required to create the feeling of a pulse)
MAP = clinically defined as
Perfusion pressure
MAP is normally between…
70 to 110 mmHg
If MAP falls significantly…
organ will not receive enough blood flow -> resulting in ischemia.
cross sectional area is related to…
… velocity
velocity is inversely proportional to …
… cross sectional area.
what is cardiac output?
volume of blood pumped by the heart
Cardiac output (CO) = ?
CO = Heart Rate X Ventricle Stroke Volume = dm3/min, L/min
What is peripheral resistance?
resistance of arteries and
arterioles to blood flow
What results in changes in blood pressure?
Any factor causing a change in cardiac output or peripheral resistance will result in a change in blood pressure.
Factors affecting heart rate?
o2 and co2
Phyiscal activity
Hct
Symp and paraymp activity
body comp
drugs
dehydration
adrenaline adn other hormones
adenosine and caffeine
pH
electrolytes
prostaglandins
Factors affecting heart rate (HR)?
Autonomic innervation
Hormones
fitness levels
age
What factors affect stroke volume?
Heart size
Fitness levels
gender
contratility
duration of contraction
preload (EDV)
Afterload (resistance)
How to calculate stroke volume?
Stroke volume (SV) = EDV - ESV
How to calculate cardiac output?
Cardiac output (CO) = HR x SV
What is vascular compliance?
Ability of a blood vessel wall to expand and contract passively with changes in pressure.
whats vascular compliance?
Ability of a blood vessel wall to expand and contract passively with changes in pressure
What is aortic aneurysm a result of?
of increased total peripheral resistance.
An increase in cardiac output leads to…
…an increase in the volume of blood contained in the aorta and an increase in mean arterial pressure when total peripheral resistance remains the same
a constant cardiac output leads to…
… an increase in the volume of blood contained in the aorta and an increase in mean arterial pressure when total peripheral resistance increases.
aortic aneurysms have a limited…
…vascular compliance
aortic aneurysm affect on aorta?
Enlargement (dilatation) of the
aorta to greater than 1.5 times
normal size.
Aortic aneurysm is often…
…asymptomatic -> high risk of death
what are some occasional symptoms of aneurysms?
Occasionally, abdominal, back, or
leg pain.
Aortic aneurysm most commonly located in…
… abdominal aorta, but can be located in the thoracic aorta.
describe the distribution of blood within the circulation?
the greatest volume found in venous vasculature, where 70-80% of blood is found. FOr this reason, veins are referred to as capacitance vessels. The relative volume of blood between arterial and venous sides of the circulation can vary considerably depending upon total blood volume, intravascular pressures, and vascular compliance.
blood distribution values?
vein = 65%
arteries = 13%
arterioles = 2%
capilleries = 5%
central blood volume = 15%
what is central blood volume (CBV)?
Central blood volume (CBV) = blood in heart cavities + lungs
+ central arterial tree.
CBV increased during …
… sympathetic stimulation
