Sources: Last’s Anatomy, Aneskey.com, Anatomy for anaesthetists

JC 2019

Sources: Last’s Anatomy, Aneskey.com, Anatomy for anaesthetists

JC 2019

2023B 02: 11% of candidates passed this question.
This question expected an outline of the anatomy of the cardiac ventricles. Candidates that broke down the anatomy into subsections with correct and clear descriptions of each component were most successful. A potential structure to approach this question is included below;
– position, orientation, relations and characteristics of the chambers including ventricular interdepence
– internal ventricular structures including muscle type, septum, trabeculae, papillary muscules, infundibulum and moderator band
– valves and valvular rings’ position, structure and attachments
– conduction elements position and divisions
– blood and nerve supply

2019B 16: 27% of candidates passed this question.
The question sought information on the structure (anatomy), function (physiology) and vascular supply of the right and left ventricle. Good answers provided detail in each section e.g. values for ventricular pressure rather than simply stating “high- and low-pressure systems”. Many marks may be gained by a simple anatomical description & labelled PV loop for each ventricle. Many candidates focussed solely on the coronary circulation, to which only a proportion of the marks were allocated.

Regional Supply

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)

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 
• Coronary venous O₂ content = 5 mL/dL
• Coronary sinus SpO₂= 20mmHg

Coronary perfusion pressure (CPP)

• ADP = Ao Diastolic Prssure
  • It is different throughout the cycle and b/w ventricles

Phasic Supply as per diagram.

Determinants of Coro BF

• Physical Factors
  • Extravascular compression (CPP factors)
• Neural and Neurohumoral Factors
  • ↑ SNS tone →
    • α receptor mediated vasoconstriction
    • β receptor mediated vasodialtion 
    • ↑ force and rate of contractions → ↑ vasodialtor metabolite release
    • Overall effect is dilation
  • ↑ PSNS tone → KACh stimulation → mild ↓ Coronary vascular resistance
• Metabolic Factors (main)
  • Vasodilatory
    • ↑ Adenosine, H, K, CO2, Lactate
    • NO → GTP 
    • ↑ O2 demand → ↓ ATP → ↑KATP channel activation → hyperpolarisation → vasodilation
• Myogenic autoregulation (keep CPP 60-180 mmHg)

Gladwin 2016

2023A 15: 66% of candidates passed this question.
For this question a good answer should have encompassed a description of the following components; the arterial supply (epicardial, endocardial supplies), venous supply (major and minor venous drainage), the phasic ventricular blood supply, a description of and the relevance of the high oxygen extraction ratio, an emphasis on metabolic autoregulation whilst including any other mechanisms of physiological regulation.
Most candidates provided reasonable detail surrounding the arterial-circulation and the area of the heart these vessels supply. Less well described were the perforating branches, the capillary network and the venous drainage, these components were often incorrectly described or left out of the candidate answers. Most candidates correctly identified the phasic flow and the difference in flow that occurs between the right and left ventricle. Those candidates that used diagrams to explain this were rewarded when these diagrams were labelled and accurate with respect to their systolic and diastolic distinction. The control of regulation was less well answered with generic statements not specifically identifying the local metabolic controls importance over any other mechanism. Those answers that scored well coupled the metabolic control to the flow dependence highlighting the high oxygen extraction within the coronary circulation.

2021A 19: 62% of candidates passed this question.
Good candidates described normal blood flow to the coronary circulation, including differences between the right and left ventricles. Coronary artery anatomy was outlined, including the regions of the heart supplied and the concept of dominance. In addition to epicardial vessels, strong answers also outlined penetrating arteries, subendocardial supply and venous drainage. Regulation of coronary blood flow required an explanation of flow-dependence of the heart given its high oxygen extraction rate. Metabolic autoregulation and its mediators needed to be described, along with the physical factors driving coronary blood flow. Less important mechanisms such as the role of the autonomic nervous system were also described, with an emphasis on indirect effects over direct effects.

2018A 11: 46% of candidates passed this question.
Some answers suffered from listing things rather than describing things as the question required.
Better answers included a description of metabolic, physical and neuro-humoral factors and the relative importance of each.
Many described detailed anatomy which was not necessary.

2014B 10: 65% of candidates passed this question.
This question was generally well answered. Some candidates did not mention the factors which are peculiar to the coronary circulation and answered in a generic manner, as if for any vascular bed. The coronary circulation has a high O2-ER and flow-dependence. Many candidates seemed to lack a perspective that metabolic demand dominates control of the coronary arterial flow. The phasic nature of flow was best shown with a diagram and whilst “publication-level” graphs are not expected, the graph drawn must be factually correct and convey the principal similarities and differences. While this topic is covered in both Guyton and Ganong, additional detail can be found in the Mosby physiology monograph series: Cardiovascular Physiology, 10th Edition by Pappano and Wier,( the replacement of Berne and Levy).

2008B 11: 2 (40%) candidates passed this question
This question required the candidate to provide some detail why a given dose of intravenous anaesthetic administered for the purpose of induction may result in a variable response between individuals. A logical division into pharmacokinetic and pharmacodynamic factors pertaining to the drug and how these are impacted by patient physiology, citing appropriate examples, was expected. Extremes of age, pregnancy, low and high cardiac output states, sympathetic tone, body habitus and factors impacting on drug redistribution and elimination should have been addressed. Extra marks were awarded for relevant discussion of pharmacogenetics. Discussion of the “bolus effect” versus slow infusion of an induction drug, relative to these factors should have been included. Mention of drug interactions, idiosyncratic reactions and relevant pathophysiology impairing organ function reserve was appropriate. The consequences of variability in drug response in terms of over- / underdosing, haemodynamic compromise, respiratory depression, delayed recovery and allergic reactions needed emphasis to demonstrate understanding of the significance of predisposing factors.
Effective answers to this question utilised either clear headings, or a tabular format, dividing what is a large topic into discrete areas. The lack of a structured approach to this question was invariably unsuccessful.
Syllabus Ref: G2a 2.c,d,e,f,g
Suggested Reading: Pharmacology and Physiology in Anaesthetic Practice / R K Stoelting – 4th ed – 2006. Chapters 4,6.

Foetal Circulation

• Placenta
  • Supplied by paired umbilical artery and drains to single umbilical vein
  • Capillary networks in parallel à high flow, low resistance system, decreases overall systemic vascular resistance.
  • Oxygenated blood (SpO₂ 80% PO₂ 35mmHg) from placenta returns to foetus via umbilical vein
  • 60% of blood from umbilical vein bypasses liver via ductus venosus into IVC
    • Blood in IVC from systemic circulation is hypoxaemic (SpO₂ 30%)
• Heart
  • Blood from IVC enters right atrium and oxygenated blood, directed via the Eustachian valve, preferentially flows across foramen ovale to left ventricle à supplies ascending aorta (SpO₂ 65%, PaO₂ 25mmHg)
    • This allows most oxygenated blood to supply the brain and coronary arteries
  • Blood from SVC enters right atrium and continues to right ventricle and pulmonary arteries → flows into aorta via ductus arteriosus and predominantly supplies descending aorta (SpO₂ 60%, PaO₂ 20mmHg) and organs
• Lungs
  • High pulmonary vascular resistance due to;
    • Unexpanded lungs
    • Hypoxic pulmonary vasoconstriction
  • Therefore blood in pulmonary artery preferentially perfuses systemic circulation via ductus arteriosus
  • Only approx 12% of pulmonary arterial blood enters the pulmonary circulation

Changes at birth

• Placenta
  • Vasoconstriction occurs due to longitudinal stretch of umbelical vessels and increase in PaO₂
  • Augemented by clamping of vessels
  • Loss of placenta increases systemic vascular resistance
  • Increased left heart pressures
• Lungs
  • After first breath…
    • Hypoxic pulmonary vasoconstriction is relieved,
    • Lung expands
      • Recruitment of collapsed parallel capillary networks
      • Dilation of existing vasculature
    • Pulmonary blood flow increases 10-fold and pulmonary vascular resistance decreases
  • Combined with decreased venous return (from placenta), decreases right heart pressures
• Heart
  • Foramen ovale
    • Equilibration of right and left heart pressures closes flap of foramen ovale (occurs within minutes to hours)
    • Pulmonary arterial blood flow further increases
  • Ductus arteriosus
    • The ductus arteriosus shunt become bi-directional
    • Closure
      • Due vasospasm caused by increased PO₂
      • Also, loss of PGE₂ produced by placenta causes loss of vasodilation
      • Occurs within 96 hours

Sakurai 2016

2015A 02: 55 % of candidates passed this question.
This topic is well covered in standard texts and has been asked previously. Better answers displayed knowledge of the key concepts, such as the parallel circulations in the foetus and preferential flow of better oxygenated blood to the brain and upper limbs. Some candidates spent time on the maternal and placental circulations which were not required to answer the question asked.