The complete
experimental set-up including
physiology is shown here. During
free breathing, the diaphragm
rises and falls. During a Valsalva
manoeuver, the diaphragm rises
markedly with high intrathoracic
pressure. During a suction against
resistance manoeuver, the
diaphragm moves downwards
and high underpressure in the
thorax results. These intrathoracic
pressure differences create
markedly different flow
conditions in the SVC and the
IVC. To explain the breathing
manoeuver further, we have
added the two most extreme
manometer positions. Free
breathing, inspiration with apnoea
and expiration with apnoea were
all performed without pressure
control of such a breathing device