Cardiovascular Physiology Flashcards
(168 cards)
1
Q
What are the normal peak LV pressures?
A
120mmHg
2
Q
What are the normal peak RV pressures?
A
25mmHg
3
Q
What pressure does the aortic valve normally open at?
A
80 mmHg
4
Q
What causes the dichrotic notch on the aortic pressure trace?
A
Elastic recoil of the aortic walls
5
Q
What % of volume does atrial contraction contribute to LV filling?
A
30%
6
Q
What does the a wave of the JVP wave represent?
A
Atrial contraction
7
Q
What does the C wave of the JVP wave represent?
A
Tricuspid valve bulge during LV isovolumetric contraction
8
Q
What does the X descent of the JVP wave represent?
A
Atrial relaxation alongside atrial lengthening due to ventricular contraction towards the apex of the heart
9
Q
What does the V wave of the JVP wave represent?
A
Venous return accumulating in the atria whilst TV is closed
10
Q
What does the Y descent of the JVP wave represent?
A
TV opens and blood flows into the LV
11
Q
How does AF affect the JVP wave?
A
Absent a waves
12
Q
How does tricuspid regurgitation affect the JVP wave? (3)
A
1) Giant C waves
2) Loss of X descent
3) Merging of V wave
13
Q
How does AV junction block affect the JVP wave?
A
Regular canon A waves
14
Q
How does complete heart block affect the JVP wave?
A
Irregular cannon A waves
15
Q
What is represented by the area inside the cardiac pressure-volume loop?
A
the stroke’work’
16
Q
What 3 factors influence the pressure-volume loop?
A
1) Preload
2) Contractility
3) Afterload
17
Q
What volume is preload?
A
LV end-diastolic volume
18
Q
How does increasing pre-load affect the cardiac pressure-volume loop?
A
Shifts the loop rightwards and upwards along the slope of elastance
19
Q
What is the equation for the Slope of Arterial Elastance (Ea) on the cardiac pressure-volume loop?
A
Delta P / Delta V
20
Q
How does increasing the contractility of the heart affect the cardiac pressure-volume loop?
A
Increases the gradient of the contractility line (Ees)
21
Q
How does increasing the afterload affect the cardiac pressure-volume loop?
A
Increases the negative gradient of the line joining LVEDV and LVESV (Ea)
= Steeper line
22
Q
What is the normal coronary blood flow of an adult? What is this percentage of the overall cardiac output?
A
200-250ml/min (5% of cardiac output)
23
Q
What is the O2 extractinon within the coronary blood flow compared with the rest of the body?
A
55-60% compare with 25%
24
Q
What does the P wave on an ECG signify?
A
Atrial depolarisation
25
Describe the aortic valve and the mitral valve during isovolumetric contraction?
During isovolumetric contraction both aortic and mitral valve are closed
26
What are the typical systolic and diastolic pressures for the RV and pulmonary artery?
PA = 25/15, RV = 25/8
27
How is SV calculated using the pressure-volume loop?
EDV - ESV
28
Compare coronary blood flow in the right and left coronary vessels during systole?
Blood flow during systole is reduced but continues in the right coronary artery. In the left coronary artery, blood flow stops during systole.
29
How is the heart muscle perfused?
1) Immediate endocardial layer directly absorbs O2 from blood from the cavity
2) Remainder of heart relies on coronary perfusion
30
What pressure is the most significant determinant of coronary blood flow to the left ventricle?
Aortic diastolic pressure
31
What 3 factors contribute to the resting membrane potential of the cardiac cell?
1) Na/K ATPase pump
2) Differential permeability of the membrane to K and Na
3) 'Held' negatively charged molecules inside the cell 'Donnan effect'
32
Describe the action of the Na/K ATPase pump?
3 Na+ ions pumped out, 2 K+ pumped in (net loss of 1 +ve charge per cycle)
33
Describe the differential permeability of the cardiac cell membrane?
Membrane is 100x more permeable to K than to Na. K moves out at much higher rate than Na moves in.
34
The Donnan effect describes the 'held' negatively charged molecules inside the cell - which molecules does this describe?
Proteins and phosphate
35
Which equation calculates the membrane potential for an individual ion at equilibrium?
Nernst equation
36
Which equation calculates the membrane potential taking into account all of the permeable ions?
Goldman equation
37
What is automaticity of a cardiac pacemaker cell?
Lack of a stable resting membrane means it spontaneously decays towards threshold resulting in spontaneous discharge
38
What is the maximum negative potential of cardiac pacemaker cells?
-60 mV
39
What is the threshold voltage for cardiac pacemaker cells?
-40 mV
40
What is the peak positive potential of cardiac pacemaker cells?
+20
41
What are the 3 phases in a cardiac pacemaker cell action potential?
1) Pre-potential (Phase 4)
2) Depolarisation (Phase 0)
3) Repolarisation (Phase 3)
42
Explain the pre-potential phase (phase 4) of a cardiac pacemaker cell action potential?
Slow decrease in membrane permeability to K+, therefore +Ve charge builds up moving RMP from -60 to threshold -40
43
Explain the depolarisation phase (phase 0) of a cardiac pacemaker cell action potential?
Slow influx of Ca2+ ions
44
What does the slope of the pre-potential phase of cardiac pacemaker cells determine?
heart rate
44
Explain the repolarisation phase (phase 3) of a cardiac pacemaker cell action potential?
Inactivation of Ca2+ channels, and increased K+ outflow
45
How is the slope of the pre-potential phase of the cardiac pacemaker cells affected by the sympathetic system?
Sympathetic activation increases the slope of the pre-potential phase increasing heart rate
46
How is the slope of the pre-potential phase of the cardiac pacemaker cells affected by the vagal stimulation?
Increase K+efflux from cell in phase 4, thus delaying the pre-potential reaching threshold. Slope is reduced and so heart rate slowed.
47
What is the maximal negative potential of a cardiac muscle cell?
-90 mV
48
What is the threshold charge of a cardiac muscle cell?
-70 mV
49
What is the peak positive potential of a cardiac muscle cell?
20 mV
50
What are the 5 phases in a ventricular muscle cell action potential?
Phase 0 - Rapid depolarisation
Phase 1- Spike
Phase 2 - Plateau
Phase 3 - Repolarisation
Phase 4 - RMP
51
Explain phase 0 (rapid depolarisation) of a ventricular muscle cell action potential?
Fast Na channels open at threshold of -70mV and so Na+ moves into cell
52
Explain phase 1 (spike) of a ventricular muscle cell action potential?
Na channel closure so Na no longer moves into cell
53
Explain phase 2 (plateau) phase of a ventricular muscle cell action potential?
Balanced influx of Ca2+ through slow-L type Ca channels, alongside efflux of K+. Therefore potential remains positive for plateau phase.
54
What is the purpose of the plateau phase of a ventricular muscle cell?
Creates absolute refractory period preventing tetanic contraction
55
Define the absolute refractory time of a cardiac muscle cell?
The time at which the membrane potential lies above the threshold potential
56
What is the relative refractory time of a cardiac muscle cell?
This period of time follows the absolute refractory period when the membrane potential is between the threshold and RMP - an adequately strong stimulus could cause depolarisation
57
Explain phase 3 (repolarisation) phase of a ventricular muscle cell action potential?
Closure of Ca2+ channels, ongoing efflux of K+ restores potential to RMP
58
Explain how phase 4 (RMP) of a ventricular muscle cell action potential is maintained? (3)
1) 3Na+ out/2K+ in ATP pump
2) Differential permeability of membrane K+ vs Na+ (100:1)
3) Held negatively charged molecules (proteins/phosphate)
59
What is excitation-contraction coupling?
Description of how an electrical impulse (AP) is converted into mechanical force (e.g cardiac muscle contraction)
60
During excitation-contraction coupling of a cardiac muscle cell, depolarisation causes which channels to open?
voltage-gated L type calcium channels
61
During excitation-contraction coupling of a cardiac muscle cell, the influx of calcium through voltage-gated L type channels stimulates which receptors on the surface of the sarcoplasmic reticulum? What does this result in?
Calcium influx stimulates ryanodine receptors on the sarcoplasmic reticulum. This causes calcium to flood out of the SR (calcium-induced calcium release)
62
During excitation-contraction coupling of a cardiac muscle cell, calcium floods out of the cell (CICR) and binds to what?
C-subunit of the troponin molecule
63
What does binding of calcium to the C-subunit of the troponin molecule do?
Causes conformational change in the troponin, which causes tropomyosin (which is bound to troponin via T subunit) to rotate and expose the myosin binding sites on actin molecules
64
What is the result of actin and myosin binding?
Sarcomere shortens and muscular contraction occurs
65
At the end of the plateau phase of the cardiac muscle cell, why do calcium levels fall? (3)
1) reuptake of calcium into sarcoplasmic reticulum through calcium-magnesum pump
2) timed inactivation of l-type calcium channels
3) export of calcium out of call by a sodium-calcium pump
66
Why is diastole an energy consuming phase in relation to the movement of calcium within the cell?
Following CICR, calcium re-uptake into the sarcoplasmic reticulum is an ATP dependent process via calcium-magnesium pump
67
Describe the onset and closure of L-type calcium channels in the action potential of a cardiac muscle cell?
Onset = voltage triggered
Closure = timed inactivation
68
How is tetanic contraction prevented within the cardiac muscle cell?
absolute refractory period where membrane potential is above threshold due to plateau phase
69
what is the length of a typical resting sarcomere?
2.2 micrometers
70
Where does calcium bind to tropoin?
Troponin - C
71
Where does actin bind to tropoin?
Troponin - I
72
Where does tropomyosin bind to troponin?
Troponin - T
73
How does beta adrenergic sympathetic stimulation affect calcium flow through L type calcium channels?
Increases calcium flow through L type channels to increase inotropy
74
A positive deflection from the baseline of an ECG means the signal is travelling in which direction in relation to the electrode?
Towards the electrode
75
A negative deflection from the baseline of an ECG means the signal is travelling in which direction in relation to the electrode?
Away from the electrode
76
Describe the 3 ECG limb leads?
I, II, III
Bipolar leads measuring the difference between 2 active electrodes
77
Describe the electrode polarity and degrees of ECG lead I?
RA -ve, LA, +ve
0 degrees
78
Describe the electrode polarity and the degrees of ECG lead II?
RA -ve, LL +ve
+60 degrees
79
Describe the electrode polarity and the degrees of ECG lead III?
LA -ve, LL +ve
+120 degrees
80
What is the name of the triangle made up by the ECG limb leads?
Einthoven's triangle
81
Describe the augmented limb leads?
aVR, aVL, aVR
Unipolar leads measuring the potential difference between one active limb electrode and a 'composite reference' of the average of the other 2 limb leads
82
Describe the electrode polarity and the degrees of ECG limb lead aVR?
RA +ve
-150 degrees
83
Describe the electrode polarity and the degrees of ECG limb lead aVL?
LA +ve
-30 degrees
84
Describe the electrode polarity and the degrees of ECG limb lead aVF?
LL +ve
+90 degrees
85
What plane do the bipolar limb and the augmented unipolar limb leads look at?
Coronal plane
86
Describe the chest leads?
V1- V6
Unipolar leads measuring electrical difference perpendicular to the limb leads
87
What plane do the unipolar chest leads look at?
horizontal plane
88
What area of the heart do ECG leads V1 and V2 look at?
Right ventricle
89
What area of the heart do ecg leads V3 and V4 look at?
Interventricular septum
90
What area of the heart do ECG leads V5 and V6 look at?
Anterolateral aspect of the left ventricle.
91
What is the standard ECG recording speed? (mm/s)
25 mm/s
92
What is the standard ECG calibration? (mV/cm)
1 mV/cm
93
What is the normal cardiac axis?
-30 to 90 degrees
94
What are the inferior territory leads?
II, III, aVF
95
What are the anterior territory leads?
V1 and V2
96
What are the lateral territory leads?
V5, V6, 1, aVL
97
What 3 ECG features indicates posterior territory infarction?
1) V1-V4 ST depression (mirror STe)
2) V1 and V2 R>S wave (mirror Q waves)
3) V1 and V2 upright T waves (TWI)
98
Describe the CM5 ECG position and what it is used for?
C = LL (green) electrode placed clavicle (but can be anywhere
M = RA (red) electrode over manubrium
5 = LA (yellow) electrode in V5 position
CM5 position provides good view of the left ventricle for detecting LV ischaemia
99
What is the most common atrial rate in A Flutter?
Atrial rate 300 bpm
100
What are the common causes of mitral regurgitation? (7)
ACUTE
- Ruptured chordae tendinae
- Post MI
- Trauma
CHRONIC
- MV prolapse
- Rheumatic fever
- Connective tissue disease
- Dilated cardiomyopathy
101
What are the effects of chronic MR on (1) LA (2) LV (3) SV (4) cardiac rhythm?
(1) LA dilatation
(2) LV dilatation
(3) Reduced SV
(4) AF
102
What are the features of mitral regurgitation on cardiac auscultation? (2)
1) pansystolic murmur, max at apex radiating to axilla
2) 3rd HS
103
What are the ECG features you might expect in a patient with mitral regurgitation? (3)
1) P mitrale
2) LVH
3) AF
104
What are the CXR features you might expect in a patient with mitral regurgitation? (3)
1) Cardiac enlargement
2) Straightening of the left heart border
3) Pulmonary oedema
105
In mitral regurgitation, what regurgitant fraction values indicate mild vs severe regurgitation?
>0.3 = mild
>0.6 = severe
106
How do you optimise your anaesthetic management of the cardiovascular system to optimise cardiac output in a patient with mitral regurgitation? (3)
MR likes FAST and LOOSE
1) Avoid bradycardia
2) Avoid vasoconstrictors - want a dilated peripheral circulation
3) Avoid large increases in preload
107
What are the main causes of aortic stenosis? (3)
CONGENITAL
1) Bicuspid or unicuspid valve
ACQUIRED
2) Rheumatic heart disease
3) Degenerative calcification
108
What acquired comorbities are associated with calcification of the aortic valve? (4)
Hypertension
Diabetes
High cholesterol
Smoking
109
How does aortic stenosis effect the LV?
LV hypertrophy, reduced compliance and diastolic dysfunction
110
Why do patients with aortic stenosis have more reliance on the 'atrial kick'?
Reduced compliance means reduced passive LV filling, so atrial kick plays bigger contribution
111
Why does aortic stenosis reduce blood flow through the coronary arteries?
High LV diastolic pressures - reduces the coronary perfusion gradient
112
Why are exercise induced symptoms classical in patients with aortic stenosis?
Heart unable to adequately increase its cardiac output due to outflow obstruction
113
What clinical signs would you expect to find in a patient with aortic stenosis? (cardiac auscultation and BP - 3)
1) Ejection systolic murmur - max over aortic area radiating to carotids
2) Quiet S2
3) Narrowed pulse pressure
114
What CXR findings would you expect in a patient with aortic stenosis? (2)
1) Cardiac enlargement
2) AV calcification
115
What ECG findings would you expect in a patient with aortic stenosis? (4)
1) LVH
2) LAD (assoc with LVH)
3) Prolonged QRS (assoc with LVH)
4) 1st or 2nd degree heart block (if calcification extends to conduction system)
116
What is the ECG voltage criteria for LVH?
R wave in either V5 or V6 > 25mm
OR
Tallest R wave in V5 or V6 plus deepest S wave in V1 or V2 >35mm
117
What indicates a 'strain' pattern with LVH
TWI in lateral leads (V5, V6, 1, aVL) +/- ST depression
118
What is the healthy adult aortic valve area?
2.5 to 3.5mm
119
Why are aortic valve areas more reliable than mean gradients in detecting aortic stenosis?
If AS is associated with significant LVSD, the transvalvular gradient may be low despite severe stenosis
120
How do you optimise your anaesthetic management of the cardiovascular system to optimise cardiac output in a patient with aortic stenosis? (4)
AS likes SLOW and TIGHT
1) Avoid tachycardia (which can reduce diastolic time for coronary blood flow)
2) Avoid vasodilatation and maintain SVR to maintain aortic diastolic pressure for coronary filling
3) Maintain preload
4) Maintain SR for atrial kick
121
In what conditions are J waves seen on an ECG? (4)
1) Hypothermia
2) Hypercalcaemia
3) Head injury
4) SAH
122
What are the triad of symptoms seen in aortic stenosis?
Angina
Heart failure
Syncope
123
Which area of the heart is most susceptible to reduced coronary perfusion pressure as a result of aortic stenosis and LVH?
Sub-endocardium
124
Where are baroreceptors located? (3)
Carotid sinus
Aorta
Heart
125
What happens to baroreceptors in response to chronic hypertension?
Reference range resets
126
What branch of which cranial nerve carries the afferent pathway of carotid sinus baroreceptors to the CNS vs Aorta and Heart baroreceptors?
Hering branch of glossopharyngeal (carotid sinus), CN X (heart/aorta)
127
Where is the pressor vasomotor ventre located?
ventrolateral medulla
128
Where is the depressor ventre located?
Caudal and medial to the pressor centre, in the medulla
129
What is the name of the sensory nucleus for CN IX and X?
Nucleus tractus solitarius
130
What reflex is caused by direct response of the pressor centre cells in the ventrolateral medulla to ischaemia?
Cushings reflex
131
What neurotransmitters are released from sympathetic pre-ganglionic nerves?
ACh
132
What neurotransmitters are released from sympathetic post-ganglionic nerves going towards the heart and vessels? (2)
Noradrenaline and Dopamine
133
What neurotransmitters are released from sympathetic post-ganglionic nerves foing towards sweat glands and vessels?
Acetylcholine
134
Which gland do sympathetic pre-ganglionic nerve fibres synapse directly at?
Adrenal glands
135
Describe the volume loss for the 4 classes of shock?
Class 1: up to 15%
Class 2 15-30%
Class 3: 30-40%
Class 4: >40%
136
How much fluid can be reabsorbed from interstitium to plasma during major haemorrhage?
0.25ml/kg/min
137
What hormone is released from the pituitary gland in response to fall in stimulation from atrial stretch receptors?
ADH
138
Give 3 actions of ADH?
1) Increase thirst
2) Renal conservation of water (reduced urine production)
3) Vasoconstriction
139
Where in kidneys does ADH work?
Collecting ducts
140
What 2 compartments make up the extracellular fluid compartment? Describe the percentrages?
Intravascular fluid (25%) and interstitial fluid (75%)
141
Compared the precentage of intracellular to extracellular fluid?
66% ICF, 33% ECF
142
How much intrathoracic pressure does a valasalva maneouvre generate?
40mmHg
142
Describe a valsalva maneouvre?
Forced expiration against a closed glottis
143
Describe the BP and HR in phase 1 of a valsalva maneouvre?
BP rise
HR remains steady
144
Why does BP rise in phase 1 of valsalva maneouvre? (2)
1) Squeeze on intrapulmonary vessels leading to increased return of blood to LA
Increased preload therefore increased SV
2) Direct itransmission of intra-thoracic pressure into aorta
145
Describe the BP and HR in phase 2 of valsalva?
BP steadily falls
HR steadily increases
146
Why does the BP fall and HR increase in phase 2 of a valsalva maneouvre?
Persistent intra-thoracic pressure leads to reduced venous return with resultant reduced CO and BP
Baroreceptors sense reduced BP and sympathetic compensation increases HR /vasoconstriction
147
Describe the BP and HR in phase 3 of valsalva maneouvre (release of strain)?
BP falls further
HR steady
148
Why does phase 3 of valsalva maneouvre (release of strain) lead to further fall in BP but steady HR?
Loss of squeeze on intra-pulmonary vessels temporarily reducing return of blood to the heart
Too brief for compensatory change in heart rate
149
Describe BP and HR in phase 4 of valsalva maneouvre?
Overshooting increase in BP
HR falls
150
Why does phase 4 of valsalva lead to high BP and low HR?
Venous return to left atrium normalises and so CO is delivered into highly vasocontricted peripheral circulation
Reflex vagal bradycardia via carotid sinus baroreceptors
151
Which phase of the valsalva maneouvre is useful for cardioversio of SVTs?
Phase 4 - vagal reflex bradycardia
152
The valsalva maneouvre decreases the loudness of all heart murmurs except? (2)
Mitral valve prolapse
HOCM murmurs
153
How do you calculate the valsalva ratio? (2)
1) Max HR in phase 2/ Min HR in phase 4
2) Longest R-R interval in phase 4 / Shortest R-R interval in phase 2
154
What is the use of calculating a valsalva ratio?
Ratio >1.5 indicates competent functioning of the autonomic cardiac control?
155
Describe pre-ganglionic sympathetic fibres in terms of length and myelin sheath?
Short and myelinated (B fibres)
156
Describe post-ganglionic sympathetic nerve fibres in terms of length and myelin sheath?
Long and unmyelinated
157
What neurotransmitter is used by both sympathetic and parasympathetic pre-ganglionic nerve fibres? And what receptors does this act on?
Acetyl choline on nicotinic receptors
158
What does standing from supine do to the renal perfusion pressure and thus the release of renin?
Increases release of renin due to fall in renal perfusion pressure
159
What organs act as reservoirs of circulating volume for change of posture/haemorrhage? (3)
Lungs, liver, muscle beds
160
Where are volureceptors located? (2)
Right atrium
Great veins
161
Where is renin secreted from
Juxta-glomerular apparatus
162
What does aldosterone do to to N/H2O/K in the kidneys?
Promotes renal retention of Na (and thus water) at the expense of K excretion
163
Does vasoconstriction or venoconstriction mobilise blood held in reservoirs in the lungs/liver/muscle beds into the circulation?
VENOconstriction
164
What is the % threshold change for volureceptor stimulation?
8-10%
165
What is the % threshold change for osmoreceptor activation?
1-2%
166
Where is ADH secreted?
posterior pituitary
