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MRCEM Primary > Cardiology physiology > Flashcards

Cardiology physiology Flashcards

1
Q

What volume of blood is present in circulation in an average 70kg man?

A

5.5L

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2
Q

How can arteries dampen the pulsatile oscillations in pressure that result from intermittent outflow of blood from the left ventricle?

A

As they are elastic

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3
Q

Smaller arteries and arterioles are the primary vessels involved in what?

A

Regulation of arterial blood pressure and blood flow within organs

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4
Q

Smaller arteries and arterioles are innervated by what?

A

Autonomic nervous system

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5
Q

What are the primary exchange vessels in the body?

A

Capillaries

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6
Q

What are the main differences between arteries and veins?

A

Veins are larger in diameter
Veins provide less resistance
Vein walls are thin and distensible

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7
Q

What percentage of blood volume is contained within veins?

A

70%

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8
Q

Why are veins known as capacitance vessels?

A

Because veins act as a blood volume reservoir

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9
Q

What are the 3 layers of large and medium sized arteries?

A

Tunica intima
Tunica media
Tunica adventitia

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10
Q

What is the tunica intima composed of?

A

Thin layer of endothelial cells
Sub endothelium connective tissue
Elastic lamina

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11
Q

What is the tunica media composed of?

A

Fenestrated elastic membranes
Smooth muscle cells
Collagen

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12
Q

What is the thickest part of arterial walls?

A

Tunia media

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13
Q

What is the tunica adventitia composed of?

A

Thin layer of connective tissue
Lynphatics
Nerves
Vasa Vasorum (blood vessels that supply smooth muscle)

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14
Q

Arteries with a diameter less than what are classed as arterioles?

A

<0.1mm

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15
Q

What are the walls of capillaries made up on?

A

Single endothelial cells

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16
Q

What are the 3 main types of capillary?

A

Continunous
Fenestrated
Sinusoidal

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17
Q

Which vessels are the preferred site of white blood cell migration I inflammation and infection?

A

Veins

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18
Q

What do most vasoconstrictors bind to and cause?

A

Receptors that cause a G-protein mediated rise in intracellular calcium levels = contraction of vascular smooth muscle.

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19
Q

Where does intracellular calcium arise from?

A

Sarcoplasmic reticulum
Entry across sarcolemma through calcium channels

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20
Q

Name some vasoconstrictors.

A

Endothelin-I
Angiotensin-II
Noradrenaline

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21
Q

What do calcium channel blockers do?

A

Prevent or reduce opening of calcium channels = reduction in vasoconstriction.

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22
Q

How do most endogenous vasodilators cause vessel relaxation?

A

By increasing cGMP (E.G. NO) or cAMP (prostacyclin/ beta agonists)

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23
Q

Removal of which ions causes vasodilation?

A

Calcium ions

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24
Q

Which aspect of vessels plays an important role in regulation of vascular tone?

A

Vascular endothelium (as it is a source of important vasoactive mediators)

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25
Nitrous oxide production is increased by what?
Factors that increase intracellular calcium levels (bradykinin, histamine, serotonin)
26
What is the normal value of cardiac output in an adult?
5-6L/minute at rest More than 35 L/minute for elite athletes during exercise
27
How is cardiac output defined?
Stroke volume x heart rate
28
What is stroke volume?
The amount of blood expelled from the heat with each beat.
29
What is the normal value of stroke volume in an adult?
50-100ml
30
Define mean arterial pressure (MAP).
The average arterial pressure during a single cardiac cycle.
31
What is the normal range for MAP?
65-110 mmHgW=
32
What is the minimum that MAP must be in order for adequate oxygen perfusion to occur?
65mmHg
33
MAP is considered a better indicator of vital organ perfusion that what?
SBP
34
How is MAP calculated?
DBP + 1/3rd pulse pressure OR DBP + ((SBP-DBP)/3)
35
When calculating MAP, who does diastole count for more than systole?
Because 2/3rds of the cardiac output is spent I diastole.
36
What is pulse pressure?
The difference between SBP and DBP,
37
What does pulse pressure measure?
The force generated by the heart each time it contracts.
38
What is the usual resting pulse pressure in healthy adults?
30-40mmHg
39
Name the causes of a narrow pulse pressure.
Reduced CO (blood loss) Aortic stenosis Cardiac tamponade CCF
40
Name the causes of a wide pulse pressure.
Atherosclerosis Aortic regurgitation AV malformation Aortic root aneurysm Aortic dissection Hyperthyroidism
41
Where is central venous pressure recorded?
RA or SVC
42
When should CVP be measured?
With the patient lying flat at the end of expiration.
43
What is CVP a useful indicator of?
Right ventricular preload
44
Name factors that can increase central venous pressure.
Hypervolaemia Forced exhalation Tension pneumothorax Heart failure Pleural effusion Decreased CO Cardiac tamponade Mechanical ventilation Pulmonary hypertension Pulmonary embolism
45
Name factors that can decrease central venous pressure
Hypovolaemia Deep inhalation Distributive shock Negative pressure ventilation
46
What are the 5 components of the CVP waveform?
A wave C wave V wave X descent Y descent
47
Which phase of the cardiac cycle is represented by the A wave?
End diastole
48
Which phase of the cardiac cycle is represented by the C wave?
Early systole
49
Which phase of the cardiac cycle is represented by the V wave?
Late systole
50
Which phase of the cardiac cycle is represented by the X descent?
Mid systole
51
Which phase of the cardiac cycle is represented by the Y descent?
Early diastole
52
What is the mechanical event represented by the A wave?
Atrial contraction
53
What is the mechanical event represented by the C wave?
Closing and bulging of tricuspid valve.
54
What is the mechanical event represented by the V wave?
Systolic filling of the atrium.
55
What is the mechanical event represented by the X descent?
Atrial relaxation.
56
What is the mechanical event represented by the Y descent?
Early ventricular filling.
57
What does Einthoven's law state?
That the voltage in lead II on an ECG is the sum of the voltages in leads I and III.
58
What do the leads of an ECG detect?
Depolarisation as electrical current moves through the heart.
59
Which leads form Einthoven's triangle?
Right arm Left arm Left leg
60
What prevents direct spread of depolarisation from the atria to the ventricles?
Annulus fibrosis
61
Repolarisation is achieved by influx of which ion?
K+
62
What is the Treppe effect?
When an increase in heart rate causes an increase in contractility.
63
Where are baroreceptors located?
Aortic arch and carotid sinus
64
What is the resting membrane potential of SAN cells?
-60 mV
65
Endothelin 1 is stimulated by which substances?
Noradrenaline Angiotesin-II ADH Hypoxia
66
Nitrous oxide production is stimulated by which factors?
Shear stress (increased blood flow) Bradykinin Histamine Serotonin Substance P
67
What causes the plateau phase of the cardiac action potential cycle?
Opening of voltage gated slow L-type Ca2+ channels
68
Where are continuous capillaries found?
Skin Fat Muscle Nervous tissue
69
The Frank-Starling curve shows the relationships between...
Stroke volume and end diastolic volume
70
Where are sinusoidal (discontinuous) capillaries found?
Bone marrow Liver Spleen
71
What are the 5 stages of the cardiac cycle?
Early diastole Atrial systole Isovolumetric ventricular contraction Ventricular ejection Isovolumetric ventricular relaxation
72
What happens during early diastole?
Whole heart relaxed Ventricles filling passively
73
What happens during atrial systole?
Atria contract Final phase of ventricular filling EDV established
74
What happens during isovolumetric ventricular contraction?
Ventricular myocytes begin to contract Ventricular pressure increases Ventricular volume is constant
75
What happens during ventricular ejection?
Ventricles contract fully Aortic pressure increases Ventricular volume at minimum
76
What happens during isovolumetric ventricular relaxation?
Ventricles relax Ventricular volume is constant Atria expand and fill
77
During early diastole, what are the valves doing?
AV valves open SL valves closed
78
During atrial systole, what are the valves doing?
AV valves open SL valves closed
79
During isovolumetric ventricular contraction, what are the valves doing?
Both valve pairs closed
80
During ventricular ejection, what are the valves doing?
AV valves closed SL valves open
81
During isovolumetric ventricular relaxation, what are the valves doing?
Both valve pairs closed
82
What creates S1?
Closure of mitral and tricuspid valves
83
What creates S2?
Closure of aortic and pulmonary valves
84
When can S3 occur?
Early diastole
85
What are the causes of an S3 being present?
Heart failure **Can occur in children + young adults
86
When does S4 occur?
Late diastolic filling
87
What are the causes of S4?
Increased resistance to filling (stiff ventricular wall)
88
What conditions can an S4 heart sound be associated with?
Ventricular hypertrophy Aortic stenosis Post-MI ventricular fibrosis Hypertrophic cardiomyopathy Restrictive cardiomyopathy
89
On an ECG, what is early diastole represented by?
Iso-electric line
90
On an ECG, what is atrial systole represented by?
P wave + PR interval
91
On an ECG, what is isovolumetric ventricular contraction represented by?
QRS complex
92
On an ECG, what is ventricular ejection represented by?
ST segment
93
On an ECG, what is isovolumetric ventricular relaxation represented by?
Iso-electric line
94
S1 occurs during which stage of the cardiac cycle?
Isovolumetric ventricular contraction
95
S2 occurs during which stage of the cardiac systole?
Isovolumetric ventricular relaxation
96
S3 can occur during which phase of the cardiac cycle?
Early diastole
97
S4 can occur during which phase of the cardiac cycle?
Atrial systole
98
Define cardiac output.
The volume of blood pumped by the heart in 1 minute.
99
How is cardiac output calculated?
CO = SV x HR
100
Define stroke volume.
The amount of blood pumped from the left ventricle per beat.
101
How is stroke volume calculated?
Volume at end of diastole - volume at end of systole.
102
What is central venous pressure?
The blood pressure in the vena cava in close proximity to the right atrium.
103
What does Starling's law represent?
The relationship between stroke volume and end diastolic volume.
104
What does Starling's law state?
The stroke volume of the heart increases in response to an increase in end diastolic volume, before the contraction when all other factors remain constant. The greater the end diastolic volume, the greater the strength of the muscle fibre (sarcomere) length, the grater the contractility.
105
What does a decrease in inotropy do to the starling curve?
Shifts it down and to the right = smaller SV.
106
What does an increase in inotropy do to the starling curve?
Shifts it up and to the left = larger SV.
107
What is the most important consequence of starling's law?
That the stroke volumes of the right and left ventricles are matched.
108
According to starling's law, if output from the RV was greater than output from the LV, what would happen?
Bloods would accumulate in the lungs = pulmonary blood pressure would rise = pulmonary oedema.
109
Which 3 factors influence stroke volume?
Preload Contractility of the heart Afterload
110
What is preload?
The amount of stretch of the myocardium at the end of diastole.
111
What is after load?
The pressure against which the heart has to pump.
112
How are inotropic effects normally achieved?
Through alteration of free calcium ion concentration.
113
Give an example of a negative inotrope.
Acidosis (raised H+ concentration competes with Ca2+ for intracellular binding sites).
114
Give 2 examples of positive inotropes.
Cardiac glycosides Sympathetic stimulation
115
What is the effect of an increased after load on the starling curve?
Shifts it down and to the right.
116
What is the effect of a decreased after load on the starling curve?
Shifts it up and to the left.
117
Which receptors detect CVP upon standing?
Baroreceptors
118
What is the point of origin of electrical impulses in the heart?
SAN
119
Where is the SAN?
Right atrium at junction with SVC.
120
At what rate does the SAN generate electrical impulses under normal conditions?
60-100 times per minute.
121
Where is the AVN located?
Right atrium at posteroinferior area of intratrial septum.
122
What slows down the electrical impulse between the atria and the ventricles?
Annulus fibrosis
123
How often does the AVN generate impulses?
40-60 times per minute.
124
How often do the purkinje fibres generate impulses?
20-40 times per minute.
125
How many phases are there in the cardiac action potential?
5 (0-4)
126
What is phase 0 of the cardiac action potential?
Rapid depolarisation phase
127
What is phase 1 of the cardiac action potential?
Early depolarisation phase
128
What is phase 2 of the cardiac action potential?
Plateau phase
129
What is phase 3 of the cardiac action potential?
Rapid depolarisation phase
130
What is phase 4 of the cardiac action potential?
Resting phase
131
When is a cardiac action potential triggered?
When the membrane potential reaches -70mV
132
What is the main movement of ions responsible for the rapid depolarisation?
Rapid influx of Na+ through fast Na+ channels.
133
When do L-type Ca2+ channels open?
Phase 0 (rapid depolarisation phase)
134
When does phase 1 (early depolarisation phase) begin?
Once Na+ channels inactivate.
135
What is the mainstay of ion movement in phase 1 (early depolarisation phase).
Efflux of K+ and Cl- ions
136
What happens in phase 2 (plateau phase) of the cardiac action potential.
Slow influx of Ca2+ via L-type Ca2+ channels that opened in phase 0. AND Efflux of K+ ions via delayed rectifier channels.
137
How is the plateau in phase 2 of the cardiac action potential sustained?
A balance between movement of calcium ions in and potassium ions out of the myocytes.
138
When do L-type Ca2+ channels close?
Phase 3 (rapid depolarisation)
139
What happens during phase 3 (rapid depolarisation) of the cardiac action potential?
Further efflux of K+ via already open K+ channels.
140
What happens in phase 4 (resting phase) of the cardiac action potential?
Resting potential is restored by Na+/K+ ATPase and Na+/ Ca2+ exchanger
141
What is the resting potential of the cardiac membrane?
-90mV
142
About how long does the cardiac action potential last?
~200ms
143
What does an ECG 'lead' show?
A view of the heart's electrical activity from a particular angle across the body.
144
Which ECG leads view the heart from a horizontal place?
Chest leads
145
Which ECG leads view the heart from a vertical plane?
Limb leads
146
Which ECG leads look at the right ventricle?
V1-V2
147
Which ECG leads look at the septum?
V3-V4
148
Which ECG leads look at the anterior and lateral walls of the left ventricle?
V5-V6
149
How much time is represented by 1 small square on an ECG?
0.04 seconds
150
How much time is represented by a large square on an ECG?
0.2 seconds (5 small squares)
151
What does the p wave on an ECG correspond to?
Atrial depolarisation
152
What does the QRS complex on an ECG correspond to?
Ventricular depolarisation
153
What does the T wave on an ECG correspond to?
Ventricular depolarisation
154
How long is the QRS complex under normal conditions?
0.12 seconds (3 small squares)
155
If the QRS complex is <0.12 seconds, where does the rhythm originate from?
Above the bifurcation of the BoH (the rhythm is supra ventricular and originates from the SAN, AVN or atria).
156
If the QRS complex is >0.12 in length then where does the rhythm originate from?
Ventricular myocardium or supraventricular with aberrant conduction
157
What is the normal QRS axis?
Between -30 and +90 degrees
158
What are the deflections of lead I and aVF in a normal axis?
Both positive
159
What are the deflections of lead I and aVF in a left axis deviation?
Lead I = positive aVF = negative
160
What are the deflections of lead I and aVF in a right axis deviation?
Lead I = negative aVF = positive
161
What are the deflections of lead I and aVF in extreme axis deviation?
Both negative
162
What are the causes of LAD?
Normal (physiological axis deviation) LVH LBBB Inferior MI WPW syndrome
163
What are the causes of RAD?
Right heart strain (PE) RVH RBBB Lateral wall MI WPW syndrome
164
What duration should a normal p wave last for?
<120ms (3 small squares)
165
In which leads is it normal for aa t wave to be inverted?
V1 aVR Lead II
166
What does the PR interval represent?
Conduction from AVN to bundle branches and purkinje fibres
167
How long should the normal PR interval be?
0.12 - 0.2 seconds (3-5 small squares)
168
How long should a normal QT interval be?
<440ms
169
Name metabolic disorders that can cause a prolonged QT interval.
Hypothyroidism Hypocalcaemia Hypokalaemia Hypomagnesaemia Hypothermia
170
Name drugs which can cause a prolonged QT interval.
Erythromycin Quinidine Amiodarone TCAs Terfenadine Sotalol Methadone Procainamide
171
Name structural heart problems that can cause a prolonged QT interval.
IHD Mitral valve prolapse Rheumatic carditis
172
Which systems exhibit good auto regulation?
Renal Coronary Cerebral
173
Which 2 mechanisms contribute to auto regulation?
Myogenic stretch response Locally produced vasodilation factors
174
How does the myogenic stretch response work?
Increase blood flow or pressure = myocytes stretch = membrane depolarisation = L-type calcium channels activated = influx of calcium = vasoconstriction.
175
What are the most potent vasodilators in skeletal muscle?
K+ Adenosine
176
What are the most potent vasodilators in cerebral circulation?
CO2 and K+
177
Does hypoxia cause vasodilation or vasoconstriction?
Vasodilation
178
What is the earliest measurable sign of shock?
Tachycardia
179
Define the blood loss for the 4 categories of haemorrhage.
1 = Up to 750 2 = 750 - 1500 3 = 1500 - 2000 4 = >2000
180
Define the pulse rate for the 4 categories of haemorrhage.
1 = <100 2 = 100-120 3 = 120-240 4 = >140
181
Define the respiratory for the 4 categories of haemorrhage.
1 = 14-20 2 = 20-30 3 = 30-40 4 = >40
182
Define the SBP for the 4 categories of haemorrhage.
1 = normal 2 = normal 3 = decreased 4 = decreased
183
Which ion channels are not present in the SAN?
Fast Na+ channels
184
What causes depolarisation in the SAN?
Ca2+ influx via slow calcium channels
185
What permits the spread of depolarisation across the atria?
Gap junctions
186
What drives the self-generated automaticity of pacemaker cells?
The pacemaker potential
187
What determines the timing of the next action potential and the HR in cardiac myocytes?
The rate of decay of the pacemaker potential.
188
What does a u wave on an ECG represent?
Depolarisation of the inter ventricular septum.
189
Where does calcium originate from in myocytes?
Sarcoplasmic reticulum
190

MRCEM Primary (39 decks)

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