Describe the physiological consequences of decreasing Functional Residual Capacity (FRC) by
one litre in an adult.
This is core knowledge and it was expected candidates would describe physiological
consequences accurately. Good answers included a definition of FRC and correct value. A number
of candidates omitted this. It was also expected that candidates mention that as FRC falls,
alveolar closure occurs, lung compliance decreases and airway resistance increases work of
breathing increases, pulmonary vascular resistance, and thus right ventricular afterload increases.
Many candidates described alveolar closure as causing increased dead space ventilation rather
than altered V/Q.
References: Nunn’s respiratory physiology, pages 51-56
This question is identical to Question 8 from the first paper of 2017; the second time it came up the pass rate was much better
A short answer would probably have these points:
Effects of decreased FRC on lung mechanics
Effect of decreased FRC on gas exchange
Effects of decreased FRC on the pulmonary circulation
Wanger, J., et al. "Standardisation of the measurement of lung volumes." European respiratory journal 26.3 (2005): 511-522.
Lutfi, Mohamed Faisal. "The physiological basis and clinical significance of lung volume measurements." Multidisciplinary respiratory medicine 12.1 (2017): 3.
Hopkins, Erin, and Sandeep Sharma. "Physiology, Functional Residual Capacity." StatPearls [Internet]. StatPearls Publishing, 2019.