lecture 16 Flashcards
(23 cards)
centraldelivery of oxygenated blood
Q = product of heart rate & stroke volume
during exercise, stroke volume increases
- stroke volume &increase in HR increases total O2 delivery to tissues
the cardiovascular system
arteries: carry blood away from heart
arterioles: control blood flow, feed capillaries
capillaries: provide site for nutrient and waste exchange
venules: collect blood from capillaries
veins: carry blood from venules bak to heart
artery —> arteriole —> capillaries —> venule —> vein
arteries and arterioles
- high-pressure tubing that conducts O2-rich blood to tissues:
- connect left ventricle to tissue
- walls contain circular layers of smooth muscle that constrict or relax to regulate peripheral blood flow
- innervated by sympathetic nervous system efferents
- no gas exchange takes place between arterial blood and surrounding tissues - smooth muscle is what controls how open, dilated, or constricted the blood vessel is
- relax = loosen up & made diameter/lumen of the vessel wider
- constrict = make diameter of the vessel smaller
- important for regulating pressure, resistance & flow
- arteries = are more innervated than veins
- i.e. hurts more to get bood taken from arteries - graph:
- arterial circulation = a high pressure circulation
capillaries
- network of microscopic blood vessels so thin they provide room for single red blood cells to squeeze through in single file
- gases, nutrients, and waste products rapidly transfer across thin, porous capillary walls
- velocity progressively decreases as blood moves toward and into capillaries - high pressure
- velocity of blood is fast
- red blood cells fly quickly through aorta
- at the arteries it falls
- slow at capillaries - good for nutrients to occur - rapid fall in velocity of blood as we go from the aorta to arteries
arterial blood flow response to exercise
- arterial blood flow response to double leg knee extension
- measured using ultrasound
- measure total blood flow traveling through the vessel
- can increase resistance in which they had to kick
- ~30 contractions/min - increasing resistance = inreasing O2 demand to muscle
- graph
- as you increase muscle work — arterial muscle flow goes up
- increasing O2 demand will increase O2 delivery
blood flow response to 1-leg exercise
moderate-intensity
heavy-intensity
severe-intensity
- blood flow goes from a low intensity tan rapidly increases to a new, higher steady state
- reaches VO2 plateau at a later time than in the moderate domain
- ampltude is greater, so VO2 demand is greater
- blood flow is increasing in proportion to the O2 demand
- severe
1) VO2 continues to rise upwards & they could not maintain exercise at this intensity
2) matching O2 demand - there is a close relationship between flow of blood to the muscle & metabolic rate of the muscle
basics of Hemodynamics
blood flow is required by all tissues and is dependent on two factors:
- pressure
- force that drives flow
- provided by heart contraction
- blood flow from region of high pressure (LV, arteries) to region of low pressure (veins, RA); if there is no gradient then there is no flow- need a pressure differential for blood flow to occur - pressure is the force that drives flow - this pressure is provided by the heart - blood flow from a region of high pressure to low pressure - flow always goes from the heart (high) to our tissues (low) - resistance
- force that opposes flow
- provided by physical properties of vessels —> cause pressure differential from arterial to venous circulation
- modification of vessel radius is the most important determinant of resistance (i.e. vasoconstriction and vasdilation)
- vasodilation or vasoconstriction is the most important factor of resistance
blood flow (Q)
- from hemodynamic perspective
total volume of blood pumped through a vessel each minute (L of blood per minute)
Q = MAP/TPR (Ohm’s Law)
which equals
blood flow = mean arterial pressure divided by total peripheral resistance
- increase pressure = increase flow
- decrease pressure = decrease flow
- increase resistance = reduce flow
- decrease resistance = increase flow
MAP is P = arterial P - venous P
arterial P is 2/3 DBP (diastolic blood pressure) + 1/3 SBP (systolic blood pressure)
- pressure is not a constant - need to consider how we’re measuring it
- ~1/3 of the time the heart beats, it is contracting (systolic)
- ~2/3 of the time the heart beats, it is relaxing (distolic)
- more time is spent in diastolic than systolic
- this needs to be considered & slight lowers the average
venous P is CVP
so MAP is P = arterial P - venous P, which is 2/3 DBP + 1/3 SBP - CVP
- average pressure difference between aortic pressure when blood leaves the heart and venous pressure when blood returns to the heart
resting MAP = (0.66 x 75mmHg + 0.33 x 120mmHg) - 5 mmHg = 85mmHg
MAP at VO2max = (0.66 x 75mmHg + 0.33 x 200mmHg) - 5mmHg = 110mmHg
- ~9mL of mercury — average mean arterial pressure
- during exercise, systolic pressure increases consistently
- more pressure in ehart = increase cardiac output
- an extra ~25mL of flow to drive blod flow through body
- dastolic (venous) pressure does not change much
arterial blood pressure
systolic pressure (SBP)
- highest pressure in artery (during systole)
- top number, ~110 to 120mmHg (rest)
diastolic pressure (DBP)
- lowest pressure in artery (during diastole)
- bottome number, ~70 - 80mmHg
mean arterial pressure (MAP)
- average pressure on the arterial vessel walls over an entire cardiac cycle
- MAP = ~ 2/3 DBP + 1/3 SBP
- diastole
- when we completely relax our left ventricle — the pressure goes to almost 0
- the pressure drops and increases - in large arteries
- the systolic is almost the same
- the diastolic is different
- our arteries are much more stiff
- more resistance during the arteries
- always flow, exerting a pressure
- will never be 0 - arterioles
- in the arterioles, pressure falls
- this isbecause - you’re further away from the pressure
- i.e. if measuring pressure wave from in the finger — it is a far distance from the heart
- also is due to arterioles having a larger surface area - systolic pressure = peak pressure within the artery (~200)
- diastolic pressure = lowest pressure during diatole — do not hear any sounds
- the pressure the artery is generating is greater than the pressure the cuff is generating to block it off
- learge veins = pressure is quite low
- low on venous side in the right atrium
- increases again when you get back to left ventricle (or rigt???)
venous blood pressure
central venous pressure (CVP)
- blood pressure taken in the vena cava or right atrium pressure
- reflects amount of blood returning to the heart and ability of the right heart to pump blood into pulmonary circulation
- normal ranges from 0 - 8mmHg
blood flow response to 1-leg exercise
- mean arterial pressure increases more & more from moderate-intensity to severe-intensity
- pressure is increasing because flow is increasing
TPR
total peripheral resistance to flow
resistance = n x L / r4
which is resistance = viscosity of blood times length of vessel divided by vessel radius^4
- resistance of any fluid = (viscosity of fluid + the length of tube the fluid runs through)/ radius ^4
- viscosity of blood…
- is largely determined by how many red blood cells you have
- they stay relatively the same & if changes occurs it happens slowly - radius^4
- radius is powerful at controlling resistance
- if we reduce radius, it greatly increases resistance - high resistance to flow = reduces flow
- low resistance to flow = increases flow
total peripheral resistance (TRP)
- resistance to cardiac output offered by all of the systemic vasculature, excluding pulmonary vasculature
- three factors determine resistance to cardiac output:
- poiseuille’s law
1. viscosity (blood thickness)
2. length of conducting tube
3. radius of blood vessel (vasoconstriction)- we can only acutely change #3 - vasoconstriction (VC) — narrowing of blood vessels —> increase TPR - vasodilation (VD) — widening of blood vessels —> decrease TPR - diversion of blood to regions most in need - arterioles “resistance vessels” - control total peripheral resistance - site of most potent VC and VD - responsible for 70-80% of pressure drop from the left ventricle to the right atrium - TPR = MAP / Q (mmHg x min per mL) - can be calculated this way but is not determined by either of these variables! - increase total peripheral resistance
- vasodilate…
- widen blood vessels
- icnreases radius
- reduces resistance - almost 90% of resistance to flow in our body is contrlled in the arteral circulation
cardiac output (Q)
- from hemodynmic perspective
total volume of blood pumped by the ventricle each minute (L of blood per minute)
Q = MAP / TPR (ohm’s law)
cardiac outflow is determined by the driving pressure generated byt the heart and the total systemic resistance to flow:
- increase MAP; decrease TPR —> increase Q
but where does that Q go? if Q increases dring exercise, how do we direct the flow of oxygenated blood to where it is needed?
- if we increase MAP or reduce TPR — we will reduce cardiac output
- at maximal exercise, cardiac output can go up to 20-25%
blood flow distribution and exercise
- where does cardiac output go during exercise at different intensities…
- total height of the columns = total cardiac output
- rest = ~5L/min
- maximal exercise = as high as ~25L/min - when we exercise — the biggest consumer of our O2 is muscles
- muscles = % of bar with stripes on it
- muscles:
- rest = 1L/min of CO goes to muscle
- L/min increases with increasing exercise intensity
- during severe exercise, muscles can reflect ~80-85% of cardiac output - total amount of cardiac output (or blood flow) going to the other tissues is falling as exercise intensity increases
- cardiac muscle must work harder with increasing intensities
- heart is working hearder so it receives more blood flow
- blood flow of the heart is increasing as intensity increases - brain = always needs adequate O2
- does not really change as exercise intensity increases
- at rest = same blood flow as maximal intensity exercise - lowering blood flow to other areas of the body that aren’t required for exercise so we can get more flow to the muscles/tissues required for exercise (allow for muscle movement)
- divert blood flow to the muscle duing exercise - kidneys reduce flow during exercise (by ~5 - 8X)
- stomach/gut/intestines/bladder/colon = require less flow during exercise
- also, skin & other organs in the body that demand less CO can also redirect blood flow
- pressure is not changing in these differet circulations — the only thing that can change is resistance
distribution of blood flow
- blood flows to sites where most needed
- often, regions of increased metabolism —> increase blood flow (i.e. muscle)
- other examples: after eating (splanchnic region), in the heat (skin) - at rest (Q = 5L/min)
- liver, kidneys receive 50% of Q
- skeletal msucle receives ~20% of Q - heavy exercise (Q = 25L/min)
- exercising muscles receive 80% of Q via VD
- flow to liver, kidneys decreases via VC - one flow goes up & the other flow goes down
- due to dilation & constriction
- muscle dilates & th other organs constrict - dilate
- lower resistance = increase flow
- increase resistane = redue flow
relationship between Q and muscle blood flow
resting
- cardiac output = 10L/min
- leg blood flow = 4L/min
leg blood flow = 40% of cardiac output
exercise
- cardiac output = 25L/min
- leg blood flow = 20L/min
leg blood flow = 80% of cardiac output
- total proportion of flow is increasing to the actie muscle
- active muscles are increasing resistance
- in-active tissue is decreasing resistance to redirect flow towards the muscle
muscle blood flow
Q = P / TPR (ohm’s law)
Muscle BF = P (pie) r^4 / 8 n L (poiseuille’s law)
most of the increase in local blood flow to any tissue is determined by the calibre of resistance vessels (i.e. exten to which they are constricted or dilated)
- biggest change is due to resistance
-if we change resistance — we can change flow - the radius in the resistance formula is what most affects the resistance in the muscle
- resistance is the most powerful tool we have to increase & redirect muscle flow
arterioles adn smooth muscle
- arterioles have a strong muscular wall of smooth muscle
- during contraction, smooth muscle cells shorten narroing vessel lumen diameter
- smooth muscle use crossbrdge cycling between actn and myosin to develop force tension and Ca2+ serve t initiate contraction
- increase intramuscular Ca2+ = contraction
- decrease intramuscular Ca2+ = relaxation
- smooth muscle is innervated by sympathetic nerve efferents
- smooh muscle conrtacile state is controlled by hormones and other local chemical signals within the vessel and from surrounding tissues (e.g. skeletal muscle) - endothelial wall
- smooth muscle narrows — wor just like skeletal muscle (crossbridge formation)
- smooth muscle have actin & myosin
- contract due to Ca+
- decrease Ca+ = reduce contraction - SNS constricts the blood vessels
- can be done through innervation or through the release of hormones (catecholamines - Epi + NE) released through the adrenal gland
factors that change vasomotor tone
resistance through arterioles (and thus flow) is mostly determinedby the diameter of the vessel (i.e. the degree to which the vessel is dilated vs. constricted)
normal arteriole —> BF = P (pie) r^4 / 8 n L
vasoconstriction —> narrowing of blood vessel
- caused by smooth muscle cell contraction
- lumen becomes smaller (decrease radius)
vasodilation —> widening of blood vessel
- caused by smooth muscle cell relaxation
- lumen becomes larger (increase radius)
blood flow response to exercise
- mean arterial pressure / cardiac output = Q
- resistance is progressively falling as exercise intensity increases
- so, increase in flow is driven by heart contraction & the pressure it generates, as well as a vasodilation mechanism
- one mechanism from the heart & one from circulation
blood flow response to 1-leg exercise
vascular conductance (VC) = inverse of resistance
VC = 1 / TPR
Q = MAP x VC
- both pressure & resistance that allows us to match O2 devlievery to O2 demand
- bottom row = opposite of resistance (conductace)
training reduces peripheral resistance
- this facilitates greater muscle blood flow
Q = MAP / TPR
study looked at sedentary rats vs. rats performing high intensity sprint training
- hind limb flow:
- higher in sprint training rats vs. sedentary rats
- no difference between their MAP
- same pressure but different flows
- there had to be a difference in their resistance
- resistance of trained rats = lower tan sedentary rats
