Expansion
Venous return, venous tone, blood volume, atrial contraction, heart rate and compliance
Expansion
Anything that alters ventricular end-diastolic volume:
- Blood volume - haemorrhage lowers it, transfusion raises it
- Venous tone - venoconstriction shifts blood from the unstressed to the stressed volume
- Body position and muscle pump - standing pools blood in the legs
- Intrathoracic pressure - positive pressure ventilation and PEEP reduce venous return
- Atrial contraction - the atrial kick adds 10 to 20 per cent, lost in atrial fibrillation
- Heart rate - tachycardia shortens diastole and reduces filling time
- Ventricular compliance - a stiff ventricle fills less for the same pressure
The last point is the trap in clinical measurement: filling pressure is used as a surrogate for filling volume, but in a stiff ventricle a high pressure can coexist with a low volume.