EDAIC Clinical Measurement and Physics 5

Question 1

What is the significance of the 'isobestic point' at approximately 805 nm in oximetry?

Accepted Answer

It is the wavelength at which oxyhemoglobin and deoxyhemoglobin absorb light equally, used as a reference

Answer

At the isobestic point (~805 nm), HbO₂ and Hb have identical molar extinction coefficients, so absorbance is independent of saturation and can serve as a reference for total hemoglobin.

Question 2

The Joule-Thomson effect describes the temperature change when a gas expands through a valve. Clinically, this is most relevant when:

Accepted Answer

Oxygen from a high-pressure cylinder cools as it passes through the reducing valve

Answer

Real gases (including oxygen) cool on isenthalpic expansion through a regulator; this Joule-Thomson cooling can cause frost on cylinder valves during rapid discharge.

Question 3

Which type of spirometry measurement is most useful for detecting early small airways disease in an EDAIC candidate?

Accepted Answer

Forced expiratory flow between 25% and 75% of FVC (FEF 25–75%)

Answer

FEF 25–75% reflects mid-expiratory flow predominantly from small airways and is the most sensitive spirometric index for early obstructive disease in peripheral airways.

Question 4

In neuromuscular monitoring, post-tetanic count (PTC) is used when:

Accepted Answer

Deep block is present and TOF gives zero twitches, allowing estimation of depth via post-tetanic facilitation

Answer

PTC uses 5-second 50 Hz tetanus followed by 1 Hz single twitches; counting facilitated post-tetanic twitches quantifies the degree of intense neuromuscular block when TOF = 0.

Question 5

Infrared absorption spectroscopy in anaesthetic gas analysers is based on the principle that:

Accepted Answer

Polyatomic molecules absorb infrared radiation at characteristic wavelengths corresponding to vibrational modes

Answer

Heteronuclear polyatomic molecules (CO₂, N₂O, volatile agents) have dipole moment changes during vibration, allowing them to absorb IR at specific wavelengths used for identification and quantification.

EDAIC - European Diploma in Anesthesiology and Intensive Care Practice Test

EDAIC - European Diploma in Anesthesiology and Intensive Care Practice Test

EDAIC Clinical Measurement and Physics 5