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MedSci142 > Lecture 10: Cardiac Output > Flashcards

Lecture 10: Cardiac Output Flashcards

1
Q

What is the Cardiac cycle?

A

The cardiac cycle includes all events associated with ONE heartbeat
The cardiac cycle Forces blood from areas of high pressure to areas of Low pressure (HP–>LP)

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2
Q

What is the need for Cardiac Output?

A

Demand –> Supply
Organ Use –> Oxygen Demand
Tissues, muscles, organs(head,lungs) demand energy and therefore oxygen.
Biochemical processes need energy and circle demand. The heart SUPPLIES THIS DEMAND (Cardiac Output)
The heart generates pressure to Mediate Flow INTO the AORTA
Cardiac Output = heart rate x stroke volume
CO = HR x SV
= can be FASTER, and can increase in VOLUME PER cycle

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3
Q

Why does the heart do during CO and why?

A

Heart Generates Pressure, in order to Mediate Flow into the Aorta

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4
Q

What is cardiac output?

A

“the volume of blood ejected into the aorta (from LV) per min”
units = mLmin-1
The heart generates pressure to Mediate Flow INTO the AORTA
Cardiac Output = heart rate x stroke volume
CO = HR x SV

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5
Q

What is the Cardiac Output at rest?

A

At rest, this cardiac output is between 4-7 mLmin-1 (close to total blood volume)
Venous return of blood = volume of blood returning from the Vasculature to –> the heart every minute
Venous return of blood is linked to CO

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6
Q

What is linked to CO?

A

Venous Return of clod (Blood Vol from Vasculature –> heart, per min)

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7
Q

What is Stroke Volume?

A

the volume of blood ejected by the ventricle during each contraction

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8
Q

What is Heart rate?

A

the number of heartbeats per minute
units = beats per min
Increase in demand of O2 = increase in HR

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9
Q

What is the percentage of the population which dies of Cardiovascular disease?

A

50% of population
high burden = economic cost to county = decrease working = social impact of premature family loss = focus of work and research
CDV= includes heart attacks, strokes, heart failure, renal failure= all cardiovascular disease

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10
Q

What are you feeling from your pulse?

A

Pressure wave, pushing against the artery wall, as the LV traps down and squirts blood into the aorta
pushes blood like a piston
60-80 beats per minute

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11
Q

What is the hearts job?

A

To supply tissues (brain) with oxygen, nutrients into the blood stream
at Rest = demand for O2 is not high

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12
Q

What happens with demand with Exercise?

A

As air began to move muscles, there were receptors in joint which sensed muscle movement, and these receptor provided input into CNS, telling that you are beginning to exercise, therefore your oxygen levels WILL (not have) go up.
therefore Even Before Oxygen deficit, the CNS was signalling the heart to INCREASE HR as DEMAND is going to go up.
Hearts job was to supply O2

“at rest, cardiac output is about 5L/min and during exercise can be lifted up to about 20L/min”

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13
Q

What happens in the car example regarding increased output?

A

Faster put foot on accelerator.
(increases revolutions of engine per minute)
HR of the car increased to increase output power(1L engine max)

But different from the car engine, the heart can pump FASTER (HR) and can pump MORE(SV) per cycle

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14
Q

What does an increase in heart rate lead to?

A

Increase in CO
more volume of blood returning to the heart per minute
after exercise CO= 150 x 130 = 19.5L/min
can effectively Almost Double resting heart rate (4x blood volume pumped per minute)

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15
Q

Why could cardiac output decrease?

A

Cellular Metabolic Need is reduced
therefore the workload of heart decreases
resting CO= 75 x 70 = 5.25L/min

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16
Q

Why could cardiac output increase?

A

Demand for O2 increases

therefore CO increases to compensate

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17
Q

What is the cardiac reserve?

A

Cardiac reserve is the difference between a persons maximum cardiac output and their cardiac output at rest
and average persons cardiac reserve is 4-6 resting volume
Fit person 7-8x cardiac reserve, compared to resting
Severe heart disease has little of no cardiac reserve, as they have breathlessness

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18
Q

What is the cardiac reserve of a fit person?

A

7-8x CR compared to Resting CO

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19
Q

What is the cardiac reserve of someone with severe heart disease?

A

Little or no cardiac reserve
as they have breathlessness (symptom of heart failure)
Due to congestion around the lungs
Exercising tissues, demands O2, but with impaired heart function , the Supply of O2 doesn’t math the demand = resulting in breathlessness
Heart failure such that heart doesn’t work efficiently anymore

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20
Q

What is maximum heart rate?

A

220 beats per min

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21
Q

How does the maximum heart rate decrease?

A

Maximum heart rate decreases with age
7yr 150 beats per min
cardiac reserve will decline with age
maximum they can achieve (CO) will also therefore decline with age

22
Q

Where does the heart get information from?

A

Primarily from the Nervous system
+
local factors

23
Q

What happens when the is an increase in stroke volume?

A

More into heart = More out of heart, increasing stroke volume will supply heart with more blood (more venous retum)
this will result in more blood being pumped out per beat

24
Q

What do we regulate to drive up CO?

A

Regulate HR

Regulate SV

25
Q

What are the 3x factors which affect stroke volume?

A
  1. Preload
  2. Contractility (at any given pre-load)
  3. Afterload
26
Q

How does Pre load affect Stroke Volume?

A

more in = more out
The amount of blood flowing to the heart (venous return)
Pressure of the blood returning to the heart (Stretch of the heart wall before ventricular contraction)
Important factor which regulates contractility
Increasing the pressure of major veins as the heart fills up –> Preload goes up –> heart places it under tension and senses preload Stretches more and increases force of contraction

27
Q

How does Contractility affect Stoke Volume?

A
  • contractility at any given preload
    The forcefulness of which the cardio myocytes contract down on the given volume of blood
    Controlled by quantity of blood, hormonal control, # levels of ions(Na, K and Ca) and neural control
    increase in volume coming in –> stretches wall –> muscles sense and respond by increasing the forcefulness of contractility –> increases SV
28
Q

How does Afterload affect Stroke Volume?

A

(effectively blood pressure)
Pressure of blood that the heart needs to work against to pump blood out the aorta (arterial/aortic pressure)
Note: the heart must exceed this pressure for ejection

29
Q

What happens if you have chronically high blood pressure?

A

Initially the heart will compensate by increasing force of contraction
After years of extra contractility, the heart begins to enlarge and you get hypertrophy of the heart
increases force, and stops functioning as well (going into heart failure)

30
Q

What happens to Stroke Volume when there is a Positive Inotropic agent present?

A

SV increases when a positive inotropic agent is present

Often promote Ca2+ inflow during Cardiac AP, which strengthens force of next contraction

31
Q

What happens when there is an increase in pre load?

A

Increase in EDV due to greater stretch, more blood ejected out, therefore more/increased stroke volume

32
Q

What happens when there is an increase in after load?

A

Less blood ejected to ventricles, ESV goes up so decreased stroke volume - more blood at vent at end of systole

33
Q

What happens when there is an increase in contractility?

A

Increased stroke volume as contraction more forceful, more blood goes out, ESV reduced, less left in ventricles

34
Q

Which mechanisms is SV regulated by?

A

Intrinsic regulation

Extrinsic regulation

35
Q

What does the Intrinsic Regulation of SV Mechanism consist of?

A

Intrinsic regulation of the force of contraction

governed by degree of stretch of myocardial fibres at end of diastole

36
Q

What does the Extrinsic Regulation of SV Mechanism consist of?

A

Extrinsic regulation is determined by the activity of the autonomic nervous system and the circulating level of hormones (and ions)

37
Q

What is the Frank Starling Law of the Heart?

A

The more the heart is filled in Diastole(relaxed and filling), the greater the Force of contraction in Systole
- to do with Preload

38
Q

What does the Frank Starling Law of the Heart do?

A

Prevents the damming up of blood(when not balanced)
Balances outflow to match inflow
Equalises Output between Right and Left side of the heart -(heart adjusts output to Match venous Return)
- and is Balanced, both about 5Lmin-1
There energy of contraction of the ventricle is a function of the initial length of the muscle fibres comprising its walls (sarcomere length causes increased force generation)
Even if there is an increase in blood pressure, you heart works against this by increasing after load
Cardiac output is Stable until about 170mmHg or 160 beats/min
from this point, cardiac performance decreases dramatically as the heart rate gets too high due to short term filling –> smaller EDV, preload decrease
Describes phenomenon where heart responds by increasing force of contraction unless it is really high

39
Q

What does EDV stand for?

A

End Diastolic Volume

It the blood left in the heart at the end of filling - venous return - duration of ventricular diastole

40
Q

What is the relationship between Preload and EDV

A

The greater the End Diastolic Volume (EDV) the greater the Force of the next contraction

41
Q

What is the Ejection fraction?

A

What proportion of volume is being ejected into the Aorta, from the amount which comes in
Wants to increase the contractile force of the LV
Stroke volume / EDV
e.g. 80/120 = 66% = 66mL of blood out, for 1L of blood in
normal = 60-70% at rest
= 60-70% of the blood that is pumped into the LV will be pumped out during the cardiac cycle
There lower the Ejection fraction value, the greater the proportion of blood left in the ventricle (ESV)
Ejection fraction decreases in diseased heart
Cardiac Echoes (using ultrasound) are used to calculate E.F. in patients
Tool which is used to quickly plot and easily interpret the performance of the heart

42
Q

What is the Pressure Volume Loop?

A

Volume in LV doesn’t go to 0 (never pumps all blood in it)
Starts at A:
Mitral valve opens, Pressure Low, Volume Low, with the Suction Effects of Relaxing muscle
Between points A-B: 0.55s
Stoke volume = 80mL
Ventricle is filling (Passive Filling)
Pressure falls at first due to suction effects of relaxing muscles
later is starts to rise passively as volume increases
Point B:
EDV, 120 mL, Preload
Mitral valve closes
Begins to contract
Between point B-C: 0.05s
Pressure rises steeply, but as aortic valve is closed, there is no change in volume –> isovolumetric contraction
Systole –> 80mmHg
Point C:
at 80mmHg (Diastolic pressure) and 120 mL
Aortic valve opens as the Pressure in the LV greater > than pressure in the aorta
Blood is ejected from the ventricle
Between points C - D:0.25s blood is ejected into the aorta whilst continuing to contract on the volume of blood in the LV. This increase in force = increase in pressure
Point D:
Systolic Pressure= 120mmHg
aortic valve closes
ESV
haven’t been able to eject all the blood out (80mL successfully)
Pressure starts to decrease again
Point D-A:0.15s
Isovolumetric Relaxation
Diastole

43
Q

What can you measure from a Pressure Volume relationship?

A

Stroke Volume
Volume at different points of the Cardiac cycle
Assessment of heart performance (esp. LV(part of the heart which does all the work)
The amount of blood pumped in relative to the amount of blood pumped out

44
Q

What doe the Area of the Pressure-Volume relationship resemble?

A

Area= change in Pressure x Change in Volume

= Totally work earned out by ventricle in single cardiac cycle = stroke work by myocardium

45
Q

Which ventricle is the most important?

A

LV
Heart failure is almost always affecting the performance of the Left side of the heart
generates the pressure/driving force, to eject blood into the Aorta

46
Q

What doe the Pressure - Volume relationship look like in Mitral Regurgitation?

A

Some blood flows back to LA, so the volume of blood ejected is less
Some blood is regurgitated at iso-volumetric Ventricular Contraction, and some at Ventricular Ejection

47
Q

How do you find the stroke volume on a Pressure Volume curve?

A

SV = b/w points A-B = what we pumped in

48
Q

How can you measure contractility of Pressure-Volume graph?

A

Measure forcefulness of contraction

Ejection Fraction

49
Q

What can lead to a difference in Ejection fraction?

A

Age
Sex
Exercise status (increased demand)

50
Q

What do Cardiac Echoes measure?

A 
Change in volume
and pressure
and change in size of chamber 
- valves working effectively
-measures ejection Fraction
51
Q

What happens if you go into heart failure?

A

Ejection fraction decrease (more than natural age decrease)
IF EF is less the 50% = breathless most of the time, even with light exercise
means only 50% of blood pumped in is being pumped back out
the remaining just sits in the veins, and is Dammed
Supply of blood is still there, but the heart isn’t pumping it appropriately
The medication will be trying (atlas intiially) Increase the Forcefulness of the Contraction (SV)
If you are below 30% you will be on O2 supplementation chronically
below 25% , won’t have long to live, will need Heart transplantation.

52
Q

What is an important point to remember with arterial pressure?

A

That it DOESNT go to zero
and it Matches very closely the pressure generated by the heart
As the heart generates its contractile force we can feel the pressure wave moving through our arterial system

MedSci142 (20 decks)

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