Cardiovascular Physiology Flashcards
What are the normal peak LV pressures?
120mmHg
What are the normal peak RV pressures?
25mmHg
What pressure does the aortic valve normally open at?
80 mmHg
What causes the dichrotic notch on the aortic pressure trace?
Elastic recoil of the aortic walls
What % of volume does atrial contraction contribute to LV filling?
30%
What does the a wave of the JVP wave represent?
Atrial contraction
What does the C wave of the JVP wave represent?
Tricuspid valve bulge during LV isovolumetric contraction
What does the X descent of the JVP wave represent?
Atrial relaxation alongside atrial lengthening due to ventricular contraction towards the apex of the heart
What does the V wave of the JVP wave represent?
Venous return accumulating in the atria whilst TV is closed
What does the Y descent of the JVP wave represent?
TV opens and blood flows into the LV
How does AF affect the JVP wave?
Absent a waves
How does tricuspid regurgitation affect the JVP wave? (3)
1) Giant C waves
2) Loss of X descent
3) Merging of V wave
How does AV junction block affect the JVP wave?
Regular canon A waves
How does complete heart block affect the JVP wave?
Irregular cannon A waves
What is represented by the area inside the cardiac pressure-volume loop?
the stroke’work’
What 3 factors influence the pressure-volume loop?
1) Preload
2) Contractility
3) Afterload
What volume is preload?
LV end-diastolic volume
How does increasing pre-load affect the cardiac pressure-volume loop?
Shifts the loop rightwards and upwards along the slope of elastance
What is the equation for the Slope of Arterial Elastance (Ea) on the cardiac pressure-volume loop?
Delta P / Delta V
How does increasing the contractility of the heart affect the cardiac pressure-volume loop?
Increases the gradient of the contractility line (Ees)
How does increasing the afterload affect the cardiac pressure-volume loop?
Increases the negative gradient of the line joining LVEDV and LVESV (Ea)
= Steeper line
What is the normal coronary blood flow of an adult? What is this percentage of the overall cardiac output?
200-250ml/min (5% of cardiac output)
What is the O2 extractinon within the coronary blood flow compared with the rest of the body?
55-60% compare with 25%
What does the P wave on an ECG signify?
Atrial depolarisation
Describe the aortic valve and the mitral valve during isovolumetric contraction?
During isovolumetric contraction both aortic and mitral valve are closed
What are the typical systolic and diastolic pressures for the RV and pulmonary artery?
PA = 25/15, RV = 25/8
How is SV calculated using the pressure-volume loop?
EDV - ESV
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.
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
What pressure is the most significant determinant of coronary blood flow to the left ventricle?
Aortic diastolic pressure
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’
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)
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.
The Donnan effect describes the ‘held’ negatively charged molecules inside the cell - which molecules does this describe?
Proteins and phosphate
Which equation calculates the membrane potential for an individual ion at equilibrium?
Nernst equation
Which equation calculates the membrane potential taking into account all of the permeable ions?
Goldman equation
What is automaticity of a cardiac pacemaker cell?
Lack of a stable resting membrane means it spontaneously decays towards threshold resulting in spontaneous discharge
What is the maximum negative potential of cardiac pacemaker cells?
-60 mV
What is the threshold voltage for cardiac pacemaker cells?
-40 mV
What is the peak positive potential of cardiac pacemaker cells?
+20
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)
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
Explain the depolarisation phase (phase 0) of a cardiac pacemaker cell action potential?
Slow influx of Ca2+ ions
What does the slope of the pre-potential phase of cardiac pacemaker cells determine?
heart rate
Explain the repolarisation phase (phase 3) of a cardiac pacemaker cell action potential?
Inactivation of Ca2+ channels, and increased K+ outflow
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
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.
What is the maximal negative potential of a cardiac muscle cell?
-90 mV
What is the threshold charge of a cardiac muscle cell?
-70 mV
What is the peak positive potential of a cardiac muscle cell?
20 mV
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
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
Explain phase 1 (spike) of a ventricular muscle cell action potential?
Na channel closure so Na no longer moves into cell
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.
What is the purpose of the plateau phase of a ventricular muscle cell?
Creates absolute refractory period preventing tetanic contraction
Define the absolute refractory time of a cardiac muscle cell?
The time at which the membrane potential lies above the threshold potential
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
Explain phase 3 (repolarisation) phase of a ventricular muscle cell action potential?
Closure of Ca2+ channels, ongoing efflux of K+ restores potential to RMP
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)
What is excitation-contraction coupling?
Description of how an electrical impulse (AP) is converted into mechanical force (e.g cardiac muscle contraction)
During excitation-contraction coupling of a cardiac muscle cell, depolarisation causes which channels to open?
voltage-gated L type calcium channels
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)
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
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
What is the result of actin and myosin binding?
Sarcomere shortens and muscular contraction occurs
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
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
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
How is tetanic contraction prevented within the cardiac muscle cell?
absolute refractory period where membrane potential is above threshold due to plateau phase
what is the length of a typical resting sarcomere?
2.2 micrometers
Where does calcium bind to tropoin?
Troponin - C
Where does actin bind to tropoin?
Troponin - I
Where does tropomyosin bind to troponin?
Troponin - T
How does beta adrenergic sympathetic stimulation affect calcium flow through L type calcium channels?
Increases calcium flow through L type channels to increase inotropy
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
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
Describe the 3 ECG limb leads?
I, II, III
Bipolar leads measuring the difference between 2 active electrodes
Describe the electrode polarity and degrees of ECG lead I?
RA -ve, LA, +ve
0 degrees
Describe the electrode polarity and the degrees of ECG lead II?
RA -ve, LL +ve
+60 degrees
Describe the electrode polarity and the degrees of ECG lead III?
LA -ve, LL +ve
+120 degrees
What is the name of the triangle made up by the ECG limb leads?
Einthoven’s triangle
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
Describe the electrode polarity and the degrees of ECG limb lead aVR?
RA +ve
-150 degrees
Describe the electrode polarity and the degrees of ECG limb lead aVL?
LA +ve
-30 degrees
Describe the electrode polarity and the degrees of ECG limb lead aVF?
LL +ve
+90 degrees
What plane do the bipolar limb and the augmented unipolar limb leads look at?
Coronal plane
Describe the chest leads?
V1- V6
Unipolar leads measuring electrical difference perpendicular to the limb leads
What plane do the unipolar chest leads look at?
horizontal plane
What area of the heart do ECG leads V1 and V2 look at?
Right ventricle
What area of the heart do ecg leads V3 and V4 look at?
Interventricular septum
What area of the heart do ECG leads V5 and V6 look at?
Anterolateral aspect of the left ventricle.
What is the standard ECG recording speed? (mm/s)
25 mm/s
What is the standard ECG calibration? (mV/cm)
1 mV/cm
What is the normal cardiac axis?
-30 to 90 degrees
What are the inferior territory leads?
II, III, aVF
What are the anterior territory leads?
V1 and V2
What are the lateral territory leads?
V5, V6, 1, aVL
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)
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
What is the most common atrial rate in A Flutter?
Atrial rate 300 bpm
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
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
What are the features of mitral regurgitation on cardiac auscultation? (2)
1) pansystolic murmur, max at apex radiating to axilla
2) 3rd HS
What are the ECG features you might expect in a patient with mitral regurgitation? (3)
1) P mitrale
2) LVH
3) AF
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
In mitral regurgitation, what regurgitant fraction values indicate mild vs severe regurgitation?
> 0.3 = mild
0.6 = severe
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
What are the main causes of aortic stenosis? (3)
CONGENITAL
1) Bicuspid or unicuspid valve
ACQUIRED
2) Rheumatic heart disease
3) Degenerative calcification
What acquired comorbities are associated with calcification of the aortic valve? (4)
Hypertension
Diabetes
High cholesterol
Smoking
How does aortic stenosis effect the LV?
LV hypertrophy, reduced compliance and diastolic dysfunction
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
Why does aortic stenosis reduce blood flow through the coronary arteries?
High LV diastolic pressures - reduces the coronary perfusion gradient
Why are exercise induced symptoms classical in patients with aortic stenosis?
Heart unable to adequately increase its cardiac output due to outflow obstruction
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
What CXR findings would you expect in a patient with aortic stenosis? (2)
1) Cardiac enlargement
2) AV calcification
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)
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
What indicates a ‘strain’ pattern with LVH
TWI in lateral leads (V5, V6, 1, aVL) +/- ST depression
What is the healthy adult aortic valve area?
2.5 to 3.5mm
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
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
In what conditions are J waves seen on an ECG? (4)
1) Hypothermia
2) Hypercalcaemia
3) Head injury
4) SAH
What are the triad of symptoms seen in aortic stenosis?
Angina
Heart failure
Syncope
Which area of the heart is most susceptible to reduced coronary perfusion pressure as a result of aortic stenosis and LVH?
Sub-endocardium
Where are baroreceptors located? (3)
Carotid sinus
Aorta
Heart
What happens to baroreceptors in response to chronic hypertension?
Reference range resets
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)
Where is the pressor vasomotor ventre located?
ventrolateral medulla
Where is the depressor ventre located?
Caudal and medial to the pressor centre, in the medulla
What is the name of the sensory nucleus for CN IX and X?
Nucleus tractus solitarius
What reflex is caused by direct response of the pressor centre cells in the ventrolateral medulla to ischaemia?
Cushings reflex
What neurotransmitters are released from sympathetic pre-ganglionic nerves?
ACh
What neurotransmitters are released from sympathetic post-ganglionic nerves going towards the heart and vessels? (2)
Noradrenaline and Dopamine
What neurotransmitters are released from sympathetic post-ganglionic nerves foing towards sweat glands and vessels?
Acetylcholine
Which gland do sympathetic pre-ganglionic nerve fibres synapse directly at?
Adrenal glands
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%
How much fluid can be reabsorbed from interstitium to plasma during major haemorrhage?
0.25ml/kg/min
What hormone is released from the pituitary gland in response to fall in stimulation from atrial stretch receptors?
ADH
Give 3 actions of ADH?
1) Increase thirst
2) Renal conservation of water (reduced urine production)
3) Vasoconstriction
Where in kidneys does ADH work?
Collecting ducts
What 2 compartments make up the extracellular fluid compartment? Describe the percentrages?
Intravascular fluid (25%) and interstitial fluid (75%)
Compared the precentage of intracellular to extracellular fluid?
66% ICF, 33% ECF
How much intrathoracic pressure does a valasalva maneouvre generate?
40mmHg
Describe a valsalva maneouvre?
Forced expiration against a closed glottis
Describe the BP and HR in phase 1 of a valsalva maneouvre?
BP rise
HR remains steady
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
Describe the BP and HR in phase 2 of valsalva?
BP steadily falls
HR steadily increases
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
Describe the BP and HR in phase 3 of valsalva maneouvre (release of strain)?
BP falls further
HR steady
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
Describe BP and HR in phase 4 of valsalva maneouvre?
Overshooting increase in BP
HR falls
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
Which phase of the valsalva maneouvre is useful for cardioversio of SVTs?
Phase 4 - vagal reflex bradycardia
The valsalva maneouvre decreases the loudness of all heart murmurs except? (2)
Mitral valve prolapse
HOCM murmurs
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
What is the use of calculating a valsalva ratio?
Ratio >1.5 indicates competent functioning of the autonomic cardiac control?
Describe pre-ganglionic sympathetic fibres in terms of length and myelin sheath?
Short and myelinated (B fibres)
Describe post-ganglionic sympathetic nerve fibres in terms of length and myelin sheath?
Long and unmyelinated
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
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
What organs act as reservoirs of circulating volume for change of posture/haemorrhage? (3)
Lungs, liver, muscle beds
Where are volureceptors located? (2)
Right atrium
Great veins
Where is renin secreted from
Juxta-glomerular apparatus
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
Does vasoconstriction or venoconstriction mobilise blood held in reservoirs in the lungs/liver/muscle beds into the circulation?
VENOconstriction
What is the % threshold change for volureceptor stimulation?
8-10%
What is the % threshold change for osmoreceptor activation?
1-2%
Where is ADH secreted?
posterior pituitary
