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Module 04 · Anaesthesia Blueprints

Physics and clinical measurement: exam notes and MCQs

Prepare physics and clinical measurement for postgraduate anaesthesia examinations with structured notes, exam-style questions and referenced explanations from standard textbooks and current guidelines.

Practise all 48 Physics and clinical measurement questions free →

Exam notes in this module

Gas laws, flow and pressure
The physical principles behind cylinders, vaporisers, flowmeters and airway resistance.
Clinical measurement — temperature, gas analysis and electrical safety
Principles of common FRCA measurement topics with their clinical pitfalls.
Statistics for anaesthetists
Data types, distributions, hypothesis testing, errors, diagnostic tests and effect measures.
Ultrasound physics and needle guidance
Sound waves, probes, image optimisation, artefacts, Doppler and safe needling.

Sample questions

Q1. The Reynolds number, which predicts turbulent flow, is proportional to:

  1. Viscosity / (density × velocity × diameter)
  2. (Density × velocity × diameter) / viscosity
  3. Pressure × radius⁴
  4. Velocity² / diameter
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Answer B: (Density × velocity × diameter) / viscosity

Re = ρvd/η. Values above ≈ 2000 favour turbulence. Turbulent flow depends on density (hence heliox — low-density helium — reduces resistance through narrowed airways), whereas laminar flow depends on viscosity (Hagen–Poiseuille).

Exam style: AIIMS INI-SS

Q2. Under laminar flow conditions, halving the internal radius of an IV cannula reduces flow by a factor of about:

  1. 2
  2. 4
  3. 8
  4. 16
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Answer D: 16

Hagen–Poiseuille: Q = πPr⁴ / 8ηl. Flow is proportional to the fourth power of the radius, so halving the radius reduces flow 16-fold; doubling length only halves flow. Hence short, wide cannulae (and rapid infusers) for massive haemorrhage.

Exam style: NEET-SS Anaesthesia

Q3. Body plethysmography measures thoracic gas volume using which physical principle?

  1. Charles's law
  2. Boyle's law
  3. Dalton's law
  4. Henry's law
Show answer

Answer B: Boyle's law

At constant temperature, P × V is constant (Boyle). The subject pants against a closed shutter in a sealed box; changes in mouth pressure and box pressure allow calculation of the compressible gas volume in the thorax — including gas trapped behind closed airways, which helium dilution misses.

Exam style: NEET-SS Anaesthesia

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