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