In which phase does systolic blood pressure occur?

Systolic blood pressure is measured during the phase of heart contraction, specifically when the ventricles of the heart contract to pump blood out into the arteries. This contraction generates the highest pressure in the arteries, which is what constitutes the systolic value. It reflects the force exerted by the blood against the walls of the arteries while the heart is actively pushing the blood forward.

During heart relaxation, which occurs after contraction, the pressure in the arteries decreases as the heart fills with blood again. This lower pressure is known as diastolic blood pressure. Blood vessel expansion and contraction relate more to the response of the blood vessels to changes in blood flow and pressure but do not directly reflect the moment when the heart generates systolic pressure. Thus, heart contraction is the crucial phase for systolic blood pressure measurement, confirming why this choice is the correct answer.