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physiology and anatomy > week 5: cardiac physiology: cardiac output, blood pressure and flow > Flashcards

week 5: cardiac physiology: cardiac output, blood pressure and flow Flashcards

1
Q

cardiac output

A

volume of blood pumped out by each ventricle per unit time
most common unit: litres per min

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2
Q

cardiac output (CO)=

A

heart rate (HR) x stroke volume (SV)

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3
Q

stroke volume depends on

A

body size

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4
Q

cardiac index

A

normalises SV to body surface area

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5
Q

normal resting cardiac index

A

3.2 Lmin-1 m-2

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6
Q

SA node innervated by both

A

sympathetic and parasympathetic branches of the autonomic nervous system

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7
Q

noradrenaline

A

transmitter released by postganglionic S fibres

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8
Q

what transmitters do P fibers release

A

acetylcholine (ACh)

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9
Q

noradrenaline and acetylcholine action

A

act to change and regulate heart rate

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10
Q

sympathetic effects are mediated via

A

B1 adrenoceptors

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11
Q

Parasympathetic effects are mediated via

A

muscarine receptors

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12
Q

increase in sympathetic nerve firing

A

increase in heart rate
tachycardia

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13
Q

increase in parasympathetic nerve firing

A

decrease in heart rate
bradycardia

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14
Q

dominant tone in resting state

A

parasympathetic

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15
Q

intrinsic firing rate on SA node and therefore intrinsic frequency of a de-innervated heart

A

100 bpm

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16
Q

what is heart rate determined by

A

pacemaker potential of the SA node cells

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17
Q

stroke volume

A

vol of blood ejected out each ventricle per heartbeat
vol of blood in ventricle at end of diastole - volume og blood remaining at end of systole
end-diastolic vol - end systolic vol

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18
Q

ejection fraction

A

fraction of the EDV ejected during the subsequent ventricular contraction
EF= SV/ EDV
(end-diastolic vol)
referred to as the pre-load

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19
Q

end-systolic volume determined by

A

contractility of the ventricular muscle and the diastolic aortic blood pressure

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20
Q

diastolic aortic blood pressure termed

A

afterload- resistance to blood ejection

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21
Q

at the cellular level, strength of contraction depends on

A

initial sarcomere length and overlap of actin and myosin filaments

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22
Q

The Frank Sterling law

A

strength of contraction depends on the initial degree of stretch: within the physiological range, stretching ventricular muscle leads to an increased force in contraction

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23
Q

what does initial stretch depend on

A

end-diastolic volume (pre-load)

24
Q

determinants of end-diastolic volume

A

venous return

25
Q

what does venous return depend on

A

pressure in the large veins returning blood to the heart, the central venous pressure (CVP)

26
Q

central venous pressure can be influenced by

A
  1. blood volume increased blood volume= increased CVP)
  2. postural changes
  3. respiratory and skeletal muscle pumps ( aid venous return and increase CVP)
  4. vasoconstriction ( via increased sympathetic activity)
27
Q

extrinsic regulation of stroke volume comes from

A

autonomic nervous system

28
Q

what control is autonomic regulation of SV under

A

sympathetic:
little parasympathetic innervation of the ventricular myocardium

29
Q

during action potential, B1 adrenoreceptors

A

increase level of cytosolic Ca2+ in ventricular myocytes
(EC coupling)

30
Q

increasing levels of Ca2+ in ventricular myocytes

A

increases contractility of myocardium at any given length
(starling curve shifted up)
resulting in greater stroke volume from any given end diastolic volume

31
Q

blood flows down

A

pressure gradient

32
Q

pressure results

A

when flow is opposed by resistance

33
Q

steepest drop in pressure

A

occurs across arterioles, where the greatest resistance to blood flow occurs

34
Q

dicrotic notch (after phase 1)

A

closure of the aortic semilunar valve

35
Q

phase 1

A

diastole
no blood enters aorta from left ventricle
aortic vol and pressure decline to minimum

36
Q

typical systolic blood pressure (left)

A

120mmHg
highest arterial pressure corresponds to the systolic phase of the cardiac cycle

37
Q

typical diastolic pressure (left)

A

80 mmHg
lowest arterial pressure, corresponds to the diastolic phase of the cardiac cycle

38
Q

pulse pressure

A

40 mmHg
systolic pressure- diastolic pressure

39
Q

mean arterial pressure

A

diastolic + (pulse pressure/3)
typical 93mmHg

40
Q

Darcys law

A

in the steady state, fluid flow between 2 points is equal to the difference in pressure between the 2 points divided by resistance to flow
flow=(p1-p2)/R
analogous to OHms law for electrical current I=V/R

41
Q

Relating systemic circulation to Darcys law

A

flow= left ventricular output (ie CO)
P1-P2= aortic pressure- right atrial pressure (effectively the MAP)
R= The total resistance to flow imposed by all the blood vessels in the systemic circulation ( the total peripheral resistance, TPR, or systemic vascular resistance, SVR)
hence CO=MAP/TPR can be rearranged

42
Q

what determines total peripheral resistance

A

resistance to a steady flow along a straight cylindrical tube is proportional to tube length and fluid viscosity and inversely proportional to tube radius ^4

the smaller the radius, the greater the resistance

43
Q

poiseuille’s Law

A

combing P definition of resistance with Darcy’s law of flow
derive expression for flow throughout blood vessel
flow=(P1-P2) X pi xr^4/ 8n xL

44
Q

arteriolar walls contain

A

high proportion of circularly arranged smooth muscle

45
Q

arteriolar radius under the influence of

A

sympathetic nervous system
metabolic and myogenic autoregulatory influences

46
Q

what does metabolic autoregulation during exercise lead to

A

vasodilation in vascular beds of active skeletal muscle and heart
leads to large increase in blood flow to skeletal muscle

47
Q

what is vasoconstriction mediated by

A

sympathetic nervous system

48
Q

what does vasoconstriction lead to

A

decrease in blood flow to the splanchnic and renal vasular beds

49
Q

active hyperaemia

A

diversion of blood to active muscles

50
Q

baroreceptors

A

receptors that are sensitive to changes in pressure

51
Q

what do arterial baroreceptors detect

A

degree of stretch in blood vessel wall
mechano-receptor

52
Q

arterial baroreceptors are

A

sprays of non-encapsulated nerve endings in the adventitial layer of the arterial walls in the carotid sinus and the aortic arch

53
Q

baroreceptor afferents nerve fibers project to the

A

medulla oblongata
main CV control centre

54
Q

increase in baroreceptor discharge firing rate leads to

A

increase in parasympathetic signalling
decrease in sympathetic stimulation
of heart

decreased sympathetic stimulation of systemic arterioles and veins

55
Q
A

physiology and anatomy (31 decks)

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