Figure 12.20 shows the effects of intravenous adrenaline and noradrenaline infusions on some cardiovascular variables. For each event or trace a–e below, select the best option from the following list

a.  Event A: Option 5 Period of adrenaline infusion. This corresponds to a period of increased heart rate and widening of the pulse pressure with a fall in diastolic pressure, whereas at the second event heart rate decreased and both systolic and diastolic pressure increased, indicating that noradrenaline was infused during periodB.

b. Trace C: Option 2 Heart rate. Adrenaline accelerates the heart but noradrenaline causes reflex slowing produced by the steep rise in mean arterial pressure. This is the only scale giving an initial value (around 80) corresponding to a normal (slightly apprehensive) heart rate.

c. Trace D: Option 1 Arterial pressure. Adrenaline lowers the diastolic pressure but noradrenaline raises it. This is the only dual trace corresponding to systolic and diastolic pressures; the initial value 130/80 corresponds to normal blood pressure.

d. Trace E: Option 3 Cardiac output. Adrenaline raises cardiac output but noradrena-line reduces it because of the reflex depression of cardiac activity. Again the scale corresponds to an initially normal/slightly raised cardiac output around 6–7 litres/minute.

e. Trace F: Option 4 Peripheral resistance. Noradrenaline raises total peripheral resis-tance because of its predominant effect on alpha adrenoceptors which mediate vasocon-striction; adrenaline lowers it because of its predominant effect on beta adrenergic receptors which mediate vasodilation. These units are appropriate for peripheral resistance: from the equation Mean arterial pressure=Cardiac output  x Peripheral resistance we can derive that Peripheral resistanceMean arterial pressure/Cardiac output For the initial state this equals approximately 100/7=14–15 as in F (the units are mmHg/litre/minute).

Note that for this question it was necessary to consider all aspects of the diagram together, rather than consecutively.