Candidates were expected to present a mechanistic description the neuro-cellular events
following a rise in PaCO2 such as changes in H+ in CSF, stimulation of central and peripheral
chemoreceptors and neural pathways that lead to stimulation of respiratory centre. A
systematic approach to the question with in-depth details of direction and magnitude of
physiologic changes were required. Most candidates presented graphs of cerebral blood
flow and tidal volume changes with increasing PaCO2. Common omissions included other
important points,such as the cardiovascular and respiratory effects of rising CO2 and the
rightward shift of oxygen haemoglobin curve.