The preload of the ventricle is primarily determined by which factor?

Study for the Paramedic Aandamp;P Exam. Engage with flashcards and multiple choice questions, complete with hints and explanations. Prepare effectively for your exam!

Preload is the amount the ventricle fills with during diastole, reflected by end-diastolic volume and the stretch of the cardiac fibers. The primary determinant is venous return—the volume of blood returning to the heart each minute. When venous return increases, more blood fills the ventricle before contraction, increasing preload and, via the Frank-Starling relationship, the stroke volume. Factors that raise venous return include higher blood volume, increased venous tone, and physiological changes that promote filling (for example, inspiration and the skeletal muscle pump).

Heart rate can influence how long the ventricle has to fill, so it can affect filling time, but preload itself is about how much blood returns, not the rate. Systemic vascular resistance affects afterload—the pressure the ventricle must overcome to eject blood. Ejection fraction is a measure of contractile function and how much of the filled volume is pumped out, not the filling itself.