1. Definition
Preload is the amount of stretch or tension in the ventricular walls at the end of diastole, determined by the volume of blood returning to the heart and filling the ventricles.
2. Influencing Factors
- Venous return – The volume of blood returning to the heart from the veins.
- Blood volume – Higher blood volume increases preload, while dehydration or blood loss reduces it.
- Heart rate – A slower heart rate allows more time for ventricular filling, increasing preload.
- Atrial contraction – Stronger atrial contractions increase preload by pushing more blood into the ventricles.
- Ventricular compliance – More compliant (stretchable) ventricles can accommodate more blood, raising preload.
- Afterload – A reduced afterload can increase venous return and preload indirectly.
- Body position – Supine or leg-elevated positions increase preload by enhancing venous return to the heart.
- Intrathoracic pressure – Decreased pressure during deep inhalation or certain maneuvers increases venous return, raising preload.