Cardiovascular 3 Flashcards
just read
examiners comment of Compare and contrast the systemic circulation with the pulmonary circulation
As a compare and contrast question this question was well answered by candidates who used a table with relevant headings. Comprehensive answers included: anatomy, blood volume, blood flow, blood pressure, circulatory resistance, circulatory regulation, regional distribution of blood flow, response to hypoxia, gas exchange function, metabolic and synthetic functions, role in acid base homeostasis and filter and reservoir functions. A frequent cause for missing marks was writing about each circulation separately but comparing. For example: many candidates stated ‘hypoxic pulmonary vasoconstriction’, but did not contrast this to ‘hypoxic vasodilation’ for the systemic circulation. Frequently functions of the circulations were limited to gas transport / exchange.
examiners comments 2017 march Q8
What is a normal pulmonary artery pressure from cicm wrecks
25/8 map 15
2017-jan-7, i dont think this is right, should look for another source
litfl
what is pulmonary hypertension numbers
how is this different than aortic stenosis (remember there are multiple criteria)
increase in mean pulmonary arterial pressure (PAPm) ≥25 mmHg at rest as assessed by right heart catheterization (RHC)
Severity of pulmonary hypertension (mPAP)
Mild = 20-40mmHg
Moderate = 41-55mmHg
Severe = > 55mmHg
https://litfl.com/pulmonary-hypertension-echocardiography/
note; really key this is mean pulmonary artery stenosis which has a nroaml range of 9-16
aortic stenosis mean gradient
mild <30
moderate 30-50
severe greater than 50
https://litfl.com/aortic-stenosis-echocardiography/
- Definition of regional blood flow autoregulation:
- Definition of regional blood flow autoregulation:
o “The tendency for blood flow to remain constant despite changes in arterial perfusion pressure” - Johnson, 1986
2014 march 12 deranged
desribe 4 types of Mechanisms which mediate regional autoregulation:
- Mechanisms which mediate regional autoregulation:
o Myogenic mechanisms
o Metabolic mechanisms
o Flow or shear-associated regulation
o Conducted vasomotor responses
2014 march 12 deranged
desribe Myogenic mechanisms
- Mechanisms which mediate regional autoregulation:
o Myogenic mechanisms
This is an intrinsic property of all vascular smooth muscle
Vessel wall stretch produces smooth muscle cell depolarisation
Depolarisation opens voltage-gated calcium channels
Calcium influx produces vasoconstriction by myosin light chain phosphorylation
2014 march 12 deranged
desribe Metabolic mechanisms
o Metabolic mechanisms
Blood flow increases in response to increased tissue demand, eg. in exercising skeletal muscle
This is attributed to the release of metabolic byproducts with vasodilating properties
Potential mediators include potassium, hydrogen peroxide, lactate, hydrogen ions (pH), adenosine, ATP and carbon dioxide
2014 march 12 deranged
desribe Flow or shear-associated regulation
o Flow or shear-associated regulation
This is the phenomenon of proximal vasodilation in response to distal vasodilation.
This shear stress promotes the release of various vasodilatory mediators from the affected endothelium and produces vasodilation of the larger proximal arteriole.
2014 march 12 deranged
desribe Conducted vasomotor responses
o Conducted vasomotor responses
Regional control of one region by the vasomotor events of another neighbouring region.
Mediated by conduction of cell-to-cell signals from a small arteriole upstream to a larger arteriole
2014 march 12 deranged
list the Organ-specific regulatory mechanisms:
o Organ-specific regulatory mechanisms:
Hepatic arterial buffer response:
hepatic arterial flow increases if portal venous flow decreases, and vice versa.
Renal tubuloglomerular feedback
This is a negative feedback loop which decreases renal blood in response to increased sodium delivery to the tubule
The mechanism is mediated by ATP and adenosine secreted by macula densa cells, which cause afferent arterolar vasoconstriction
Maternoplacental blood flow
Blood flow is gradually upregulated over the course of pregnancy by the actions of the trophoblast asit invades the spiral arteries of the uterus
2014 march 12 deranged
definition of Venous return
- Venous return is the rate of blood flow into the heart from the veins.
deranged Question 19 from the first paper of 2020
*At a steady state, X and x are equal.
- At a steady state, venous return and cardiac output are equal.
deranged Question 19 from the first paper of 2020
Equation for Venous return
- Venous return can be expressed as VR = (MSFP - RAP) / VR = HR × SV
where MSFP is mean systemic filling pressure, RAP is right atrial pressure and VR is the venous resistance
note; I would not put VR as two variables
deranged Question 19 from the first paper of 2020
Factors which influence venous return include:
- Factors which influence venous return include:
1 Factors which affect cardiac output
o Afterload
o Contractility
2 Factors which affect mean systemic filling pressure
o Total venous blood volume
o Venous smooth muscle tone (which affects the size of the “stressed volume”
3 Factors which affect right atrial pressure
o Intrathoracic pressure (spontaneous vs. positive pressure ventilation)
o Pericardial compliance (eg. tamponade, open chest)
o Right atrial compliance (eg. infarct, dilatation)
o Right atrial contractility (i.e. AF vs sinus rhythm)
o Tricuspid valvular competence and resistance
4 Factors which affect venous resistance
o Mechanical factors
Posture
Intraabdominal pressure
Skeletal muscle pump
Obstruction to venous flow (eg. pregnancy, SVC obstruction)
Hyperviscosity (polycythemia, hyperproteinaemia)
o Neuroendocrine factors
Autonomic tone
Vasoactive drugs (eg. noradrenaline, GTN)
deranged Question 19 from the first paper of 2020
note; easy if you remember that VR=CO and that CO equals stroke volume x heart rate and stroke volume relies on preload, contractility, afterload, and venous return is in an equation with RAP, MSFP and vascular resistance
What is MSFP
mean systolic filling pressure
deranged Question 19 from the first paper of 2020
what is normal MSFP
7mmHg
cicmwrecks Question 19 from the first paper of 2020
What is a Cardiac reflexes?
Cardiac reflexes are fast-acting reflex loops between the heart and central nervous system that contribute to regulation of cardiac function and maintenance of physiologic homeostasis.
2013 aug examiner comment question two cardiac reflex
just read
2013 aug examiner comment question two cardiac reflex
It was expected candidates would include within their answer a mention of the stimulus and how it is sensed, the reflex arc and the resultant effect.
2013 aug examiner comment question two cardiac reflex
List all the cardiac reflexes?
Thus candidates could have mentioned the Baroreceptor Reflex/Carotid Sinus Reflex, Chemoreceptor, Bainbridge, Cushing, Oculocardiac and Bezold-Jarisch (involves response to ventricular stimuli, sensed by receptors within the LV wall that trigger vagal afferent type C fibers and the resultant triad of hypotension, bradycardia, and coronary artery dilatation) reflexes.
2013 aug examiner comment question two cardiac reflex
Bainbridge (elicited by stretch receptors located in the right atrial wall and the cavoatrial junction), Cushing (result of cerebral medullary vasomotor centre ischemia), oculocardic (provoked by pressure applied to the globe of the eye or traction on the surrounding structures), Bezold-Jarisch (responds to noxious ventricular stimuli sensed by chemoreceptors and mechanoreceptors within the LV wall) reflexes be mentioned and described. 2010
Describe this cardiac reflex
* Baroreceptor reflex
- Baroreceptor reflex
o Sensors: pressure (carotid sinus and aortic arch)
o Afferent: vagus and glossopharyngeal nerves
o Processor: nucleus of the solitary tract and nucleus ambiguus
o Efferent: vagus nerve and sympathetic chain
o Effect: increased HR and BP in response to a fall in BP
deranged 2013 Q2
Describe this cardiac reflex
Bainbridge reflex
Bainbridge reflex
Afferent: vagus (atrial stretch)
Processor: nucleus of the solitary tract and the caudal ventral medulla
Efferent: vagus nerve and sympathetic chain
Effect: increased RA pressure produces an increased heart rate;
deranged 2013 Q2
Describe this cardiac reflex
* Chemoreceptor reflex
- Chemoreceptor reflex
o Afferent: carotid / aortic chemoreceptors (low PaO2 and/or high PaCO2)
o Processor: nucleus of the solitary tract and nucleus ambiguus
o Efferent: vagus nerve and sympathetic chain
o Effect: bradycardia and hypertension in response to hypoxia
(also secondary tachycardia from Bainbridge and Hering-Breuer reflexes)
deranged 2013 Q2
Describe this cardiac reflex
* Cushing reflex
- Cushing reflex
o Afferent: mechanosensors in the rostral medulla?
o Processor: rostral ventrolateral medulla
o Efferent: sympathetic fibres to the heart and peripheral smooth muscle
o Effect: hypertension and baroreflex-mediated bradycardia
deranged 2013 Q2
Describe this cardiac reflex
Bezold-Jarisch reflex
Bezold-Jarisch reflex
Afferent: vagus (mechanical/chemical sttimuli to the cardiac chambers)
Processor: nucleus of the solitary tract
Efferent: vagus nerve and sympathetic chain
Effect: hypotension and bradycardia in response to atrial stimulation
deranged 2013 Q2
Describe this cardiac reflex
Oculocardiac reflex
Oculocardiac reflex
Afferent: trigeminal nerve (pressure to the globe of the eye)
Processor: sensory nucleus of CN V; nucleus of the solitary tract
Efferent: vagus nerve and sympathetic chain
Effect: vagal bradycardia, systemic vasoconstriction, cerebral vasodilation
deranged 2013 Q2
Describe this cardiac reflex
Diving reflex
Diving reflex
Afferent: trigeminal nerve (cold temperature; pressure of immersion)
Processor: sensory nucleus of CN V; nucleus of the solitary tract
Efferent: vagus nerve and sympathetic chain
Effect: vagal bradycardia, systemic vasoconstriction, cerebral vasodilation
deranged 2013 Q2
Describe this cardiac reflex
Barcroft-Edholm
Barcroft-Edholm (vasovagal) reflex
Afferent: emotional distress, hypovolaemia
Processor: unknown
Efferent: vagus nerve and sympathetic chain
Effect: bradycardia, systemic vasodilation, hypotension
deranged 2013 Q2
Describe this cardiac reflex
Respiratory sinus arrhythmia
Respiratory sinus arrhythmia
Afferent: central respiratory pacemaker
Processor: nucleus ambiguus
Efferent: vagus nerve, via the cardiac ganglion
Effect: cyclical increase of heart rate during inspiration
deranged 2013 Q2
Tell me the coronary artery circulation
Arteries:
* LCA to
- LCx to
- OM1
- OM2
- LAD has branches
- ## Diagonal 1 or 2
- RCA
- Right Ventricular
- Acute Marginal
- Posterior descending
2021 march Q19 cicm wrecks
CONCEPT OF Cardiac DOMINANCE:
The dominance of coronary circulation is determined by the artery that supplies the posterior descending artery (PDA). Approximately 60% are right-dominant, 25% are co-dominant, and 15% are left-dominant
2021 march Q19 cicm wrecks
Describe Cardiac veins
Veins:
*Great, small, middle
*Drain into the thebesian veins → ventricles directly
*Empty into the coronary sinus on the posterior wall or the RV
2021 march Q19 cicm wrecks
Describe normal coronary artery blood flow
Normal Coronary Blood Flow
* 80 mL/min/100 g
* or 200-250 mL/min
* 5% of CO at rest
* Can increase by 3-4 times (up to 400mL/min/100g)
2021 march Q19 cicm wrecks
note; in another slide it says oxygen extraction ratio cannot increase by much so of course coronary blood flow must be able to increase
What is cardiac extraction ratio/
High Extraction Ratio High at rest (55-65%) body average of 25%
* Extraction ratio can only rise by factor of < 2 to 90%
* AV Δ O₂ = 11 mL/dL (I don’t even know what this means)
* Coronary venous O₂ content = 5 mL/dL (I don’t even know what this means)
* Coronary sinus SpO₂= 20mmHg OR coronary sinus SpO2 <30%
2021 march Q19 cicm wrecks
note; so in another slide it says blood flow can increase 3-4 times, which makes sense since extranactin cannot increase by that much
Determinants of Coronary artery Blood flow
Determinants of Coronary artery Blood flow
1 Physical Factors
* Extravascular compression (CPP factors)
2 Neural and Neurohumoral Factors
* ↑ SNS tone →
* α receptor mediated vasoconstriction
* β receptor mediated vasodilator
* ↑ force and rate of contractions → ↑ asodilator metabolite release
* Overall effect is dilation
* ↑ PSNS tone → KACh stimulation → mild ↓ Coronary vascular resistance
3Metabolic Factors (main)
* Vasodilatory
* ↑ Adenosine, H, K, CO2, Lactate , /prostaglandins/
* NO → GTP
* ↑ O2 demand → ↓ ATP → ↑atp sensitive K channel activation → hyperpolarisation → vasodilation
4 Myogenic autoregulation (keep CPP 60-180 mmHg)
2021 march Q19 cicm wrecks
just read
highlights of examiners comments
HIGH OXYGEN EXTRACTION, coronary sinus SpO2 <30%
Diastolic aortic pressure
FLOW DEPENDENCE (graph below)
Metabolic autoregulation dependent on:
The phasic nature of flow GRAPH
Better answers included a description of metabolic, physical and neuro-humoral factors and the relative importance of each
2021 march Q19 cicm wrecks
Outline the physiological responses to anaemia (The specific physiological responses to hypovolaemia are NOT required)
2013 aug and 2007 aug
Define Anaemia
Definition:
- Anaemia is a decrease in circulating red blood cells due to increased destruction, blood loss or reduced production.
- Hb concentration below < 2 standard deviations below mean of normal population
- WHO Hb levels Men < 13 g/dL Women < 12 g/dL
- Chronic > 3 months
- produces reduced O2 content in blood -> increased extraction of O2 by the tissues and peripheral vascular dilatation to increase tissue blood flow. Compensation: Kidney 90% (and liver 10%) sense decreased tissue oxygenation release EPO which increases RBC production
Outline the physiological responses to anaemia (The specific physiological responses to hypovolaemia are NOT required)
2013 aug and 2007 aug
note; does it need to be chronic??
What is the blood oxygen delivery equation
and the oxygen content equation
Total blood oxygen delivery (DO2) = CO × CaO2,
and CaO2 = (sO2 × ceHb × BO2 ) + (PaO2 × 0.03)
where:
* ceHb = the effective haemoglobin concentration
* CO = cardiac output
* PaO2 = the partial pressure of oxygen in arterial gas
* 0.03 = the content, in ml/L/mmHg, of dissolved oxygen in blood
* BO2 = the maximum amount of Hb-bound O2 per unit volume of blood (normally 1.39)
* sO2 = oxygen saturation
deranged 2013 aug 24
- Cardiovascular effects of acute isovolaemic anaemia are:
- Cardiovascular effects of acute isovolaemic anaemia are:
o Tachycardia
o Increased stroke volume
o Increased cardiac output
o Decreased peripheral vascular resistance
deranged 2013 aug 24
just read
isovolaemic anaemia are Mechanisms of these cardiovascular effects:
o Vagally mediated tachycardia is partly due to direct aortic arch chemoreceptor activity and partly due to baroreflex activation
Baroreflex activation is due to systemic vasodilation
o Decreased peripheral vascular resistance is due to:
Systemic vasodilation which is mediated by nitric oxide, as the result of decreased oxygen delivery to the tissues (a part of the normal metabolic autoregulation of regional blood flow)
Decreased blood viscosity, as viscosity is an important determinant of peripheral vascular resistance
* Long term effects are related to chronic vasodilation, and include:
o Salt retention (mediated by aldosterone)
o Body water volume expansion (mediated by vasopressin and aldosterone)
o Angiogenesis (to increase the number of capillaries and therefore decrease the diffusion distance between capillaries and cells)
deranged 2013 aug 24
just read
isovolaemic anaemia are Mechanisms of these cardiovascular effects:
2013 aug and 2007 aug
2013 aug 24. Outline the physiological responses to anaemia. (The specific physiological responses to hypovolaemia are NOT required.) It was expected candidates would expand on the central role haemoglobin has in oxygen delivery and that in the presence of reduced haemoglobin there are various efforts aimed at maintaining oxygen delivery. Cardiac output is increased, systemic vascular resistance is reduced, modifications are seen in regional circulations and as tissue oxygenation begins to falter then the end products of anaerobic metabolism provide a further stimulus to enhance cardiac out and tissue oxygen delivery. Better answers also included a mention of additional factors that enhance tolerance of chronic anaemia (e.g. angiogenesis).
deranged 2013 aug 24
Candidates were expected to base their answer around the variables involved in the equations that describe oxygen content in blood and oxygen delivery. Although most candidates mentioned changes in haemoglobin that increase oxygen carriage, a more complete discussion of the changes that influence cardiac output and the peripheral circulation was often omitted
