Final answer:
A decrease in preload results in a decrease in cardiac output, as it reduces the heart's stroke volume due to less venous return. Preload should not be confused with afterload or peripheral vascular resistance, which are influenced by different factors.
Step-by-step explanation:
A decrease in preload results in a decrease in cardiac output (B). Preload refers to the initial stretching of the cardiac myocytes prior to contraction, which is related to the volume of blood returning to the heart (venous return). When preload decreases, there is less volume for the heart to pump out, which typically leads to a reduction in stroke volume. Lower stroke volume usually translates into a decreased cardiac output, assuming heart rate remains constant.
Contrary to what might be assumed, a decrease in preload does not necessarily imply a decrease in afterload or peripheral vascular resistance. Afterload is the pressure against which the heart has to pump to eject blood and is largely dependent upon arterial pressure and vascular resistance. Factors that affect afterload include the condition of the aortic valve and the state of systemic vascular resistance, not directly the preload.
Additionally, peripheral vascular resistance would not automatically decrease with a reduced preload; rather, it is influenced by a variety of factors, including autonomic nervous system activity, circulating hormones, and local metabolic activity in the tissues.