Define the following terms (40% of marks)
- Saturated Vapour Pressure of Water
- Absolute Humidity
- Relative Humidity
- Latent heat of vaporisation
Briefly outline how the humidity of air is altered during inspiration and expiration by the respiratory tract. (60% of marks)
This question was poorly answered by candidates. Basic aspects, which were critical for a good
answer, such as definitions were often inaccurate. Terms such as ‘amount’ or ‘content’ were
commonly used without provision of units, when mass or pressure was required. The importance
of temperature was often not mentioned. Most candidates identified the importance of the upper
airway in humidification but did not describe details of this process and failed to discuss the events
occurring during expiration.
Syllabus: R2c, S2e, B1k,2d
References: Davis, Basic Physics and Measurement in Anaesthesia, pgs 145-6, Nunn’s respiratory
physiology pgs 12, 19, 166-7
This question is identical to Question 7(p.2) from the second paper of 2009
Inspiratory heating and humidification of the gas mixture
Expiratory reclamation of heat and moisture
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
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Wilkes, Antony, and David Williams. "Measurement of humidity." Anaesthesia & Intensive Care Medicine 19.4 (2018): 198-201.
Thomas, Gary, and Stephen Stamatakis. "Physics of gases." Anaesthesia & Intensive Care Medicine 10.1 (2009): 48-51.
Gupta, Ben. "Gases and Vapours" Anaesthesia 15.2 (2012).
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Dery, R. J. H. M. J. J., et al. "Humidity in anaesthesiology III. Heat and moisture patterns in the respiratory tract during anaesthesia with the semi-closed system." Canadian Anaesthetists’ Society Journal 14.4 (1967): 287-298.
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