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human physiology and exercise > cardiac output and blood pressure > Flashcards

cardiac output and blood pressure Flashcards

1
Q

what is cardiac output?

A
  • volume of blood ejected by the heart per minute
  • measured in ml-min-3
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2
Q

how do you work out cardiac output?

A

cardiac output = stroke volume x heart rate

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3
Q

what is stroke volume?

A
  • volume of blood ejected per beat
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4
Q

what is heart rate?

A
  • beats per minute
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5
Q

describe parasympathetic nervous system

A
  • vagus nerve releases acetylcholine which slows down HR
  • stimulation concentrated to SA and AV nodes
  • causes cell membranes to become more hyperpolarised causing SA node rhythm to slow
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6
Q

describe sympathetic nervous system

A
  • releases norepinephrine which increase heart rate
  • supplies SA and AV nodes so causes cell membrane to depolarise faster
  • shortens AV node delay and speeds up relaxation
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7
Q

what does circulating epinephrine trigger?

A
  • increase in heart rate but lags behind neural stimulation
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8
Q

what opposing factors is stroke volume controlled by?

A
  • force of muscle cell contraction
  • arterial pressure against which they eject blood
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9
Q

what is force of contraction regulated by?

A
  • length- tension properties of cardiac muscle cells
  • effects of hormonal influence on contractility of cardiac muscle
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10
Q

describe length tension properties

A
  • relationship between end diastolic volume and stroke volume
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11
Q

what can length tension properties be known as?

A
  • Starling’s law of the heart
  • more blood returned= more blood pumped out
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12
Q

how can end diastolic volume be increased?

A
  • by greater filling of the heart (venous return) so greater stroke volume because stretching muscle fibres cause them to contract more forcefully
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13
Q

how does training affect the equation?

A

increased stroke volume means increased cardiac output
- increased 02 delivery

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14
Q

describe cardiac hypertrophy

A

increased stroke volume = decreased resting heart rate

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15
Q

what is the effect of diastole?

A
  • greater SV because the cardiac muscle fibres stretching cause them to contract more forcefully
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16
Q

what does sympathetic nerve activity and circulating epinephrine cause?

A
  • increases force of contraction so cardiac muscle will contract more forcefully for a given amount of stretch
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17
Q

when does heart rate and stoke volume increase?

A
  • when vagus nerve activity decreases (removal of parasympathetic)
  • increased sympathetic nerve activity, increased epinephrine and end diastolic volume
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18
Q

what is blood pressure?

A
  • pressure exerted by blood upon walls of blood vessels
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19
Q

on average, what is the normal blood pressure value?

A

120-180 mmHg

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20
Q

what three factors affect blood pressure?

A
  • arteries become stiffer with age due to loss of elasticity
  • pressure is higher in foot and lower in head due to hydrostatic pressure
  • on average women have lower BP than ,men
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21
Q

where is blood pressure highest?

A
  • close to heart
  • declines as blood moves further away
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22
Q

what ensures that blood moves forwards even when heart is relaxed?

A
  • elastic properties of the walls of major arteries
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23
Q

what is blood pressure for ventricles, arteries and arterioles? why?

A
  • pulsatile due to rhythmic contraction of the heart
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24
Q

describe blood pressure in relation to cardiovascular system

A
  • driving force for flow
  • pressure gradient between arteries and veins
  • must be maintained at all times
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25
Q

what is the pressure like in the veins?

A
  • continuous to reflect loss of forward energy mainly due to friction
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26
Q

how is blood pressure measured?

A
  • in systematic arteries
  • varies between a max at peak of ventricular contraction (systole) and minumum at end of ventricular relaxation (diastole)
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27
Q

what happens to blood pressure during dynamic and static exercise?

A

-dynamic = mean blood pressure remains steady
- static= mean blood pressure rises dramatically

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28
Q

how is pressure written?

A
  • millimetres of mercury
  • systolic pressure over diastolic pressure
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29
Q

what is pulse pressure?

A
  • difference between systolic pressure and diastolic pressure
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30
Q

why is MABP used over pulse pressure?

A
  • pulse pressure gives the range within arteries whereas MABP gives a single value and accurate measure of perfusion pressure for tissues and organs
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31
Q

what is mean arterial blood pressure?

A
  • average blood pressure within arteries over one cardiac cycle
  • difference in pressure between arteries and veins
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32
Q

what is the normal mean arterial blood pressure range?

A
  • 70 to 105mmHg
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33
Q

how do you work out mean arterial blood pressure?

A

DP (diastolic) + 1/3 x PP (pulse pressure)

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34
Q

why does the equation multiple pulse pressure by 1/3?

A
  • because 2/3rds of cycle spent in diastole at rest so mean arterial blood pressure is closer to diastolic pressure than systolic
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35
Q

what lasts longer diastole or systole? what is MABP closer to?

A
  • diastole lasts almost twice as long as systole
  • MABP closer to diastolic blood pressure value
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36
Q

what is a direct measurement of MABP?

A
  • catheter into artery connected to a pressure gauge
  • pressure measured as height of fluid it pushes up against gravity
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37
Q

what is the disadvantages of direct measurements?

A
  • invasive
  • inconvenient
  • impractical
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38
Q

what are the two types of indirect measurements?

A
  • stethoscope
  • sphygmomanometer
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39
Q

describe systolic pressure using a cuff

A
  • cuff placed on upper arm and inflated to stop blood flow from brachial artery to arm
  • when pressure in cuff exceeds pressure in artery, blood flow is occluded and no pulse felt below cuff
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40
Q

what happens as you release the cuff? what sound is heard?

A
  • pressure begins to decrease and when it reaches peak systolic pressure artery opens a little but flow is turbulent
  • disorganised flow generates tapping sounds called Korotkoff sounds
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41
Q

describe using a cuff to measure diastolic blood pressure

A
  • as cuff pressure continues to decrease, the artery regains its normal diameter so flow becomes laminar
42
Q

what sound is heard in diastolic blood pressure?

A
  • sound is more muffled and eventually disappears so cuff pressure recorded at point of muffling
43
Q

why do we regulate blood pressure?

A
  • tissues need nutrient and can’t accumulate by products
  • flow rate proportional to pressure gradient along vessel
44
Q

what is flow rate ?

A
  • volume of blood which passes along a blood vessel per unit of time
45
Q

what is flow velocity?

A
  • distance travelled by an object relative to time (m/s)
46
Q

how do you work out flow (Q)

A

Q= V x A
flow = velocity x area

47
Q

what shows the flow in the cardiovascular system? why can this be used

A
  • cardiac output as any blood that leaves the heart will be returned as system is closed
48
Q

how do you work out cardiac output?

A

CO= HR x SV ; volume of blood leaving heart per minute

49
Q

how do veins make up for slower velocity of blood flow compared to arteries?

A
  • veins contain more blood volume
  • net effect is the same volume of blood returns to heart as was ejected
50
Q

what happens to blood pressure from aorta to vena cava?

A
  • decreases due to resistance to blood flow in cardiovascular system
51
Q

how do you work out resistance ?

A

resistance = pressure gradient/ flow rate

52
Q

if streamlined non- turbulent flow, what factors can determine resistance?

A
  • viscosity of blood
  • radius of blood vessel
53
Q

what’s the equation for resistance in streamlined object?

A

resistance= 8nl (liquid viscosity, length of vessel) / pie r (radius of vessel) ^4

54
Q

what has the biggest influence on resistance and why?

A
  • radius of vessel as when liquid is flowing through a tube, the outermost layer in contract with the wall moves slowly than layer inside so every layer is slower than layer inside it
55
Q

where is the flow fastest?

A
  • in the middle layer
56
Q

what is blood flow sensitive to? what does this mean?

A
  • sensitive to changes in blood vessel radius
  • the greater the cross sectional area means the slower the blood will flow
57
Q

what vessel has the slowest blood flow?

A
  • capillaries due to the fact they have largest cross sectional area
  • allows sufficient time for diffusion of nutrients and waste between blood and tissue
58
Q

what is the total peripheral resistance?

A
  • combined resistance of all vessels in systematic circulation
59
Q

how do you work out total peripheral resistance?

A

total peripheral resistance = pressure gradient / flow rate

60
Q

what is flow rate equal to and what is pressure gradient equal to?

A
  • flow rate equal to cardiac output
  • pressure gradient equal to mean arterial blood pressure
61
Q

how do you work out mean arterial blood pressure linking other factors together?

A

MABP= cardiac output x total peripheral resistance

62
Q

what vessel is most suited to regulate blood flow in systematic circulation ? why?

A
  • arterioles due to layer of smooth muscle that allows them to alter their radius and hence resistance
63
Q

what does contraction of smooth muscle cause?

A
  • vasoconstriction
  • contraction in arteriolar wall decreases radius which increases resistance and decreases flow
64
Q

what does relaxation of smooth muscle cause?

A
  • vasodilation
  • increases radius which decreases resistance and increases flow
65
Q

what do arterioles provide to capillaries?

A
  • fine control of blood flow as can divert blood to and from capillary beds
66
Q

is blood flow pulsatile in systemic circulation?

A
  • no as it is non- pulsatile within capillary and venous vasculature
67
Q

why is right ventricular wall thinner?

A
  • pressure required within pulmonary circulation is not as great as that required within systemic circulation
68
Q

what is autoregulation?

A
  • some organs are intrinsically able to prevent and reduce changes in local blood flow (if pressure decreases) and revert it back to normal within minutes
69
Q

what does autoregulation occur without and what does it link?

A
  • occurs without neural or hormonal input
  • links perfusion pressure, blood flow and resistance
70
Q

what happens to resistance if pressure drops?

A
  • resistance decreases to maintain blood flow
71
Q

what are the three primary mechanisms of autoregulation ?

A
  • endothelial, metabolic and myogenic
72
Q

describe endothelial mechanism

A
  • endothelium produces specific vasodilating factors like prostacyclin and nitric oxide
73
Q

describe metabolic mechanism

A
  • when blood flow is reduced, resultant hypoxia causes localised release of vasodilating factors from tissue surrounding blood vessels
74
Q

describe myogenic mechanism

A
  • blood vessels that contain smooth muscle are able to alter their diameter in response to stretch or compression of blood vessel
75
Q

what does percentage of total blood volume in each group of vasculature depend on?

A

-combined cross- sectional area
- vessel length

76
Q

how much blood found in aorta/ arteries, systematic arterioles, capillaries and venules?

A

-aorta/ arteries= 11%
- systematic arterioles= 3%
- capillaries = 6%
- veins= 64%

77
Q

where is the remainder of blood volume found?

A
  • heart= 7%
  • pulmonary circulation= 9%
78
Q

what is an important determinant of volume of blood?

A
  • change in radius alters blood resistance
  • radius changes during contraction or relaxation of vascular smooth muscle
79
Q

what does compliance mean?

A
  • how much a blood vessel’s volume changes with a given pressure change
80
Q

what is the compliance of a vessel that easily expands at low pressure?

A
  • high compliance
81
Q

describe low compliance

A
  • more pressure is required for the vessel to accommodate at given volume
82
Q

why do veins store most blood?

A
  • cross sectional area isn’t static as vessels can change shape
  • described as distensible as swell due to pressure from inside
83
Q

what name have veins been given?

A
  • capacitance vessels as they have the ability to rapidly increase its volume at lower pressures
84
Q

what happens as vessel expands?

A
  • elastic tension generate which increases pressure inside vessel
85
Q

what determines amount of tension generated?

A
  • elastic properties of vessel wall
86
Q

how much larger is compliance of veins compared to arteries at lower pressure? how is this shown?

A
  • 10-20 times larger
  • shown by steeper slope as vein’s cross sectional shape is elliptical at low volumes and circular at higher volumes
87
Q

can vessels keep expanding?

A
  • vessels can only expand to a certain size
  • indicated by flat slope at top of curve
88
Q

what happens to gravity when we lay down?

A
  • gravity is evenly distributed across our blood
89
Q

what is the expected thing to happen when we stand up? but why doesn’t this occur?

A
  • gravity should act to pull blood towards fit
  • but cardiovascular system is closed and effects of gravity on arterial and venous compartments will be the same
90
Q

what is enough to distend the veins when we stand?

A
  • hydrostatic pressure as veins are compliant
91
Q

what happens to blood when we stand up? what does this do to venous return?

A
  • blood pools in lower extremities
  • venous return decreased initially as if more blood pools in one area then less is available to return to the heart
92
Q

what are the 5 mechanisms that pump the pooled blood back to the heart?

A
  • nerves
  • valves
  • skeletal muscle
  • diaphragm
  • heart
93
Q

describe nerve mechanism

A
  • regulate smooth muscle in walls of veins to constrict them and hence decrease their volume and increase pressure to facilitate return of blood
94
Q

describe valves mechanism

A
  • prevents blood flowing backwards
  • half- moon shaped and close passively when blood flow reverses
95
Q

describe skeletal muscle mechanism

A
  • helps squeeze veins; becomes more pronounced during exercises that utilise lower limb e.g. cycling
96
Q

describe diaphragm mechanism

A
  • during expiration> diaphragm ascends which ^ intrathoracic pressure and lowers abdominal pressure to help blood to vena cava
  • during inspiration> decrease in intrathoracic pressure but ^ abdominal pressure to help blood move to thorax
97
Q

describe heart mechanism

A
  • movements of heart during ventricular systole increases volume of right atrium thus decreasing right atrial pressure > suction effect so blood from VC to right atrium
98
Q

what is stroke volume dependent on?

A
  • volume of blood in ventricles at end of diastole= end diastolic pressure
  • EDV dependent on adequate venous return
99
Q

describe starling’s law of the heart

A
  • states that up to a point the heart will pump whatever volume it receives out
100
Q

what happens if blood flow to the brain is reduced?

A
  • lose consciousness and fall
101
Q

how is stroke volume increased and decreased?

A
  • increased by vasoconstriction of veins
  • decreased by decrease in circulating blood volume, decrease in venous return, dehydration and haemorrhage

human physiology and exercise (18 decks)

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