Which of the following decreases stroke volume?

Decreasing intracellular sodium can lead to a reduction in stroke volume through its effect on cardiac contractility. Intracellular sodium levels are crucial for maintaining the sodium-calcium exchanger's function, which regulates calcium influx into cardiac myocytes during contraction. When intracellular sodium decreases, it can hinder this exchange, resulting in lower intracellular calcium concentrations. Since calcium plays a vital role in the strength and effectiveness of cardiac muscle contraction, a reduction in calcium leads to a decrease in contractility and, consequently, stroke volume.

Understanding these ionic influences is essential in cardiovascular physiology, as they highlight how electrolyte imbalances can profoundly affect heart function. Other factors like an increase in intracellular calcium or sympathetic stimulation typically enhance contractility and stroke volume, while changes in extracellular sodium would not have a direct effect on stroke volume in the same manner.