High-Yield Physiology for EDAIC Part 1: What You Must Know

Physiology forms the backbone of the EDIAC Part 1 written examination. It underpins every clinical scenario you will face in anaesthesia and intensive care, and the examiners know it. Questions on EDAIC physiology appear across both Paper A (Basic Sciences) and Paper B (Clinical Anaesthesia and Intensive Care), often integrated with pharmacology, equipment or clinical management. The good news: certain topics recur with predictable regularity, and mastering these high-yield areas will earn you marks every sitting.

This article identifies the physiology domains that matter most for the EDAIC Part 1, explains why they are examined so frequently, and offers practical strategies to revise them actively. Whether you are starting your preparation or fine-tuning your knowledge in the final weeks, focusing your effort on these core areas will maximise your return.

Why Physiology Matters for the EDAIC Part 1

The EDAIC basic sciences curriculum emphasises applied physiology — not rote memorisation of textbook facts, but the ability to explain mechanisms, interpret graphs, and apply principles to clinical contexts. Multiple True/False (MTF) questions demand precision: you must judge each of five statements independently as true or false, and vague understanding costs marks. With no negative marking since 2014, you should attempt every statement, but accuracy still depends on solid foundational knowledge.

Physiology questions often test:

• Quantitative relationships: normal values, equations, and the direction of change in pathological states.
• Graphical interpretation: pressure-volume loops, oxygen–haemoglobin dissociation curves, compliance curves.
• Integration across systems: how the respiratory, cardiovascular and renal systems interact to maintain homeostasis.
• Clinical relevance: why a physiological principle matters during anaesthesia, mechanical ventilation or critical illness.

Examiners favour topics that bridge basic science and clinical practice. The high-yield areas below meet that criterion consistently.

Respiratory Physiology: The Oxygen Cascade and Gas Exchange

Respiratory physiology is the single most examined domain in EDAIC physiology. Expect multiple questions every sitting on oxygen transport, carbon dioxide carriage, ventilation–perfusion matching, and the control of breathing.

The Oxygen Cascade

Understand the stepwise fall in partial pressure of oxygen from inspired gas to mitochondria:

• Inspired PO₂ (atmospheric): ~21 kPa at sea level.
• Tracheal PO₂: reduced by water vapour (saturated vapour pressure 6.3 kPa at 37°C).
• Alveolar PO₂ (PAO₂): calculated using the alveolar gas equation; typically ~13–14 kPa on room air.
• Arterial PO₂ (PaO₂): slightly lower than PAO₂ due to physiological shunt and V/Q scatter; normal ~11–13 kPa.
• Mixed venous PO₂ (PvO₂): ~5–6 kPa.
• Mitochondrial PO₂: a few kPa, sufficient for oxidative phosphorylation.

Know the alveolar gas equation and be able to calculate PAO₂ given FiO₂, barometric pressure, PaCO₂ and the respiratory quotient (R, typically 0.8). Questions may ask you to predict the effect of altitude, hypoventilation or changes in FiO₂.

Carbon Dioxide Transport

CO₂ is carried in blood in three forms:

1. Dissolved (~5% of total): obeys Henry's law; contributes to PaCO₂.
2. Bicarbonate (~90%): formed by carbonic anhydrase in red cells; the chloride shift maintains electroneutrality.
3. Carbamino compounds (~5%): CO₂ bound to amino groups on haemoglobin and plasma proteins.

The CO₂ dissociation curve is steeper and more linear than the oxygen dissociation curve, meaning small changes in ventilation produce large changes in PaCO₂. The Haldane effect (deoxygenated blood carries more CO₂) and the Bohr effect (CO₂ and H⁺ shift the oxygen dissociation curve right) are favourite exam topics.

Ventilation–Perfusion (V/Q) Matching

Ideal gas exchange requires matched ventilation and perfusion. In the upright lung:

• Apex: high V/Q (ventilation exceeds perfusion) → high PAO₂, low PACO₂, contributes little to gas exchange.
• Base: low V/Q (perfusion exceeds ventilation) → lower PAO₂, higher PACO₂, but high blood flow means the base contributes most to overall gas exchange.

Shunt (V/Q = 0) and dead space (V/Q = ∞) are extreme forms of mismatch. Know how to calculate shunt fraction using the shunt equation and how to interpret the A–a gradient. Questions often ask which interventions improve V/Q matching (e.g. PEEP, prone positioning) and which do not (e.g. increasing FiO₂ has little effect on true shunt).

Exam tip: Draw the oxygen–haemoglobin dissociation curve from memory, label the P₅₀ (~3.5–3.6 kPa), and list the factors that shift it left (alkalosis, hypothermia, fetal haemoglobin, low 2,3-DPG, carbon monoxide) and right (acidosis, hyperthermia, increased 2,3-DPG). This curve appears in some form almost every sitting.

Cardiovascular Physiology: The Cardiac Cycle and Pressure–Volume Relationships

Cardiovascular physiology questions focus on the cardiac cycle, determinants of cardiac output, pressure–volume loops, and the regulation of blood pressure.

The Cardiac Cycle

Know the seven phases and the corresponding valve movements, pressure changes and ECG events:

1. Atrial systole
2. Isovolumetric contraction
3. Rapid ejection
4. Reduced ejection
5. Isovolumetric relaxation
6. Rapid ventricular filling
7. Reduced filling (diastasis)

Be able to identify each phase on a left ventricular pressure–volume loop and explain how preload, afterload and contractility alter the loop's shape. Examiners love to present a loop and ask which intervention (fluid bolus, vasodilator, inotrope) produced the change.

Determinants of Cardiac Output

Cardiac output (CO) = stroke volume (SV) × heart rate (HR). Stroke volume depends on:

• Preload (end-diastolic volume): Frank–Starling mechanism.
• Afterload (systemic vascular resistance): increased afterload reduces SV.
• Contractility (inotropy): intrinsic myocardial performance, independent of loading conditions.

Know the difference between contractility and the Frank–Starling relationship (the latter is load-dependent, the former is not). Understand how to estimate cardiac output using the Fick principle and thermodilution, and the assumptions and limitations of each method.

Pressure–Volume Loops

The left ventricular pressure–volume loop is a graphical representation of the cardiac cycle:

• Width (end-diastolic volume minus end-systolic volume) = stroke volume.
• Area enclosed = stroke work.
• Slope of the end-systolic pressure–volume relationship (ESPVR) = contractility.
• Slope of the end-diastolic pressure–volume relationship (EDPVR) = diastolic compliance.

Questions may show loops under different conditions (hypovolaemia, aortic stenosis, mitral regurgitation, positive-pressure ventilation) and ask you to identify the pathology or predict the haemodynamic effect of an intervention.

Key point: The area of the loop represents external stroke work. Increased afterload (e.g. aortic stenosis) increases the pressure the ventricle must generate, shifting the loop upward and leftward, reducing stroke volume unless contractility increases to compensate.

Renal Physiology: Filtration, Reabsorption and Acid–Base

Renal physiology questions test your understanding of glomerular filtration, tubular function, and the kidney's role in acid–base balance and fluid regulation.

Glomerular Filtration Rate (GFR)

GFR is determined by the balance of Starling forces across the glomerular capillary:

• Favours filtration: glomerular capillary hydrostatic pressure (~45 mmHg).
• Opposes filtration: Bowman's capsule hydrostatic pressure (~10–15 mmHg) and plasma oncotic pressure (~25 mmHg).

Net filtration pressure ≈ 10 mmHg. GFR is also influenced by the filtration coefficient (surface area × permeability). Know how afferent and efferent arteriolar tone affect GFR and renal blood flow (afferent constriction reduces both; efferent constriction increases filtration fraction).

Tubular Reabsorption and Secretion

The proximal tubule reabsorbs ~65% of filtered sodium and water isosmotically. The loop of Henle establishes the medullary osmotic gradient via countercurrent multiplication. The distal tubule and collecting duct fine-tune sodium, potassium and water balance under hormonal control (aldosterone, ADH).

Know which substances are reabsorbed where, which are secreted (e.g. creatinine, PAH, potassium in the distal nephron), and the maximum transport capacities (Tm) for glucose and amino acids. Questions often ask about renal handling of specific drugs or the effect of diuretics on different nephron segments.

Renal Regulation of Acid–Base

The kidneys regulate acid–base balance by:

• Reabsorbing filtered bicarbonate (mainly in the proximal tubule).
• Generating new bicarbonate via titratable acid (phosphate) and ammonium excretion in the distal nephron.

In metabolic acidosis, the kidneys increase ammonium excretion (takes days). In metabolic alkalosis, bicarbonate reabsorption is reduced. Understand the role of carbonic anhydrase and how acetazolamide (a carbonic anhydrase inhibitor) causes a normal anion-gap metabolic acidosis.

Neurophysiology: Action Potentials, Synaptic Transmission and Autonomic Function

Neurophysiology questions focus on the generation and propagation of action potentials, neuromuscular transmission, and autonomic nervous system pharmacology.

The Action Potential

Know the ionic basis:

• Resting potential (~−70 mV): maintained by the Na⁺/K⁺-ATPase and selective permeability to K⁺.
• Depolarisation: voltage-gated Na⁺ channels open; threshold ~−55 mV.
• Repolarisation: Na⁺ channels inactivate, voltage-gated K⁺ channels open.
• Hyperpolarisation (undershoot): delayed closure of K⁺ channels.

Conduction velocity increases with axon diameter and myelination. Understand saltatory conduction and why local anaesthetics preferentially block small, unmyelinated fibres (C fibres for pain) before large, myelinated fibres (Aα motor fibres).

Neuromuscular Transmission

The neuromuscular junction is a chemical synapse:

1. Action potential reaches the presynaptic terminal.
2. Voltage-gated Ca²⁺ channels open.
3. Acetylcholine (ACh) vesicles fuse with the membrane and release ACh.
4. ACh binds to nicotinic receptors on the motor end-plate.
5. Na⁺ influx depolarises the muscle fibre.
6. Acetylcholinesterase hydrolyses ACh.

Know the differences between depolarising and non-depolarising neuromuscular blockers, the mechanism of fade and post-tetanic potentiation, and how to reverse non-depolarising block (neostigmine inhibits acetylcholinesterase; sugammadex encapsulates rocuronium/vecuronium).

Autonomic Nervous System

Understand the anatomy (sympathetic: thoracolumbar outflow, short preganglionic fibres; parasympathetic: craniosacral outflow, long preganglionic fibres) and the receptor subtypes:

• Sympathetic: α₁, α₂, β₁, β₂, β₃ adrenoceptors; noradrenaline is the postganglionic neurotransmitter (except sweat glands, which are cholinergic).
• Parasympathetic: muscarinic (M₁–M₅) receptors; ACh is the postganglionic neurotransmitter.

Questions often link autonomic physiology to drug actions (e.g. why glycopyrrolate causes tachycardia, why β-blockers reduce myocardial oxygen demand).

Acid–Base Physiology: Buffers, Compensation and Interpretation

Acid–base questions appear in almost every EDAIC Part 1 sitting. You must be able to interpret arterial blood gases rapidly and explain the underlying physiology.

The Henderson–Hasselbalch Equation

pH = pKa + log([HCO₃⁻] / [CO₂])

For the bicarbonate buffer system, pKa ≈ 6.1. At physiological pH (~7.4), the ratio [HCO₃⁻]:[CO₂] is ~20:1. This equation explains why the bicarbonate buffer is effective despite its pKa being far from physiological pH: the system is open (CO₂ can be exhaled), and both components can be regulated (CO₂ by ventilation, HCO₃⁻ by the kidneys).

Respiratory and Metabolic Disturbances

Know the primary disturbance and expected compensation:

Calculate the anion gap (Na⁺ − [Cl⁻ + HCO₃⁻]; normal ~12 mmol/L) to distinguish high anion-gap (lactic acidosis, ketoacidosis, toxins, renal failure) from normal anion-gap (diarrhoea, renal tubular acidosis, acetazolamide) metabolic acidosis.

Stewart's Approach

Some questions reference the Stewart (strong ion difference) approach to acid–base. Know that pH is determined by three independent variables:

1. PaCO₂
2. Strong ion difference (SID) = [Na⁺ + K⁺] − [Cl⁻]
3. Total weak acids (mainly albumin and phosphate)

This approach explains why hyperchloraemic acidosis occurs (reduced SID) and why hypoalbuminaemia causes alkalosis (fewer weak acids to donate H⁺). You do not need to master Stewart's equations in detail, but understand the concept and how it complements the traditional Henderson–Hasselbalch framework.

Exam tip: Practice interpreting blood gases daily. Use a systematic approach (pH, PaCO₂, HCO₃⁻, anion gap, compensation) and explain the physiology aloud. This active recall cements the concepts far better than passive reading.

How to Revise EDAIC Physiology Actively

Passive reading will not prepare you for MTF questions. High-yield revision strategies include:

• Draw diagrams from memory: oxygen cascade, cardiac cycle, nephron, action potential. If you cannot draw it, you do not know it well enough.
• Teach a colleague: explaining a concept aloud reveals gaps in your understanding.
• Work through past questions: focus on why each statement is true or false, not just the answer. If you got it right by guessing, that is a gap to fill.
• Use question banks: platforms that mirror the MTF format train you to judge statements independently and manage time.
• Create summary tables: normal values, equations, factors that increase/decrease a variable. Condense information for rapid review.
• Link physiology to clinical scenarios: why does PEEP improve oxygenation in ARDS? Why does aortic stenosis cause syncope on exertion? Why does hypokalaemia cause metabolic alkalosis? Every physiological principle has a clinical application.

Consistent, spaced repetition over weeks beats last-minute cramming. Aim to revise each high-yield topic multiple times, each pass adding depth and clinical context.

Frequently Asked Questions

What are the most important physiology topics for EDAIC Part 1?

Respiratory physiology (oxygen cascade, V/Q matching, CO₂ transport), cardiovascular physiology (cardiac cycle, pressure–volume loops, determinants of cardiac output), renal physiology (GFR, tubular function, acid–base regulation), neurophysiology (action potentials, neuromuscular transmission, autonomic nervous system), and acid–base interpretation. These domains appear consistently across both Paper A and Paper B.

How much detail do I need to know for EDAIC physiology questions?

You need applied, exam-level detail: normal values, key equations, the direction of physiological changes, and the ability to interpret graphs and clinical scenarios. Rote memorisation of obscure facts is less useful than understanding mechanisms and being able to reason through MTF statements. Focus on breadth across high-yield topics rather than excessive depth in niche areas.

Should I use the same physiology textbook for EDAIC as for undergraduate study?

Standard postgraduate anaesthesia physiology texts are more appropriate than undergraduate resources. They provide the depth and clinical focus the EDAIC demands. Supplement textbook reading with question banks and practice papers to ensure your knowledge translates into exam performance. Active revision — drawing, teaching, question practice — is more effective than passive reading alone.

How does EDAIC physiology differ from FRCA Primary physiology?

The EDAIC and FRCA Primary cover similar core physiology, but the EDAIC integrates basic sciences more explicitly with clinical anaesthesia and intensive care across both papers. The MTF question format and the absence of negative marking also shape how you prepare: precision and the ability to judge each statement independently are critical. Both examinations demand a high standard, and candidates often use overlapping resources when preparing.

Final Thoughts

Mastering EDAIC physiology is not about memorising every page of a textbook. It is about identifying the high-yield topics that recur in every sitting, understanding the underlying mechanisms, and practising active recall until you can explain, draw and apply the concepts under exam conditions. Respiratory, cardiovascular, renal, neurophysiology and acid–base are the pillars. Build your revision around them, link them to clinical practice, and test yourself relentlessly with MTF questions.

The EDAIC Part 1 written examination rewards candidates who combine breadth of knowledge with precision and the ability to reason through complex statements. Physiology is the foundation. Get it right, and you will earn marks in both Paper A and Paper B — and, more importantly, you will carry that understanding into every clinical decision you make as an anaesthetist.

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