Describe how the respiratory system of a newborn differs from that of an adult.
This question required anatomical detail relating to the upper airway and bronchial tree,
which was generally answered well. The functional implications of a highly compliant chest
wall in defending FRC and the relationship of FRC to closing volume was less clearly
explained. Better answers mentioned the high physiological dead space, oxygen
consumption and work of breathing. Additional points were awarded for discussing the
immaturity of the respiratory control centre and propensity for apnoea.
Common omissions included not providing comparative adult data or a written description
of how neonates differed from adults (or the significance of this). Candidates confused chest
wall compliance (increased in newborns) with lung compliance (reduced in newborns but
rapidly approaches normal adult values as “specific compliance”). Increased oxygen
consumption necessitates increased minute ventilation (with tidal volumes equivalent to
adults on a weight basis) via respiratory rate.
Functional Residual Capacity FRC (equivalent to adults) and Closing Capacity (increased
relative to adults) were often confused. Better answers provided responses often in tabular format. Discussion of cardiovascular responses and response to drugs were not requested and gained no marks.