B brain; C, carotid; J, jugular tube.

Note that when all parts of the model were rigid but with no extension tube attached, the work of the pump is reduced by about 30% from 890 W to 645 W. When the extension tube was attached, the work of the pump was reduced by another 30% from 645 to 465 V. In all other cases (i.e. when any part of the system is collapsible), whether the valve at P4 is open (O) or closed (C) or whether there was an extension tube attached (+) or not (-), the work of the pump was high and constant at around 900 W.