Final answer:
Systolic blood pressure is measured during the heart's contraction phase called systole and reflects the pressure in the systemic circulation, which is a result of the blood being ejected from the left ventricle.
Step-by-step explanation:
A client who has been diagnosed with hypertension has been instructed to take a daily blood pressure measurement. The systolic blood pressure is the higher value recorded during a blood pressure reading and reflects the pressure resulting from the ejection of blood during the heart's contraction phase, known as systole. The correct answer to this question is: a. left ventricle, as it is the chamber of the heart that ejects blood into the systemic circulation during systole, creating the systolic pressure measured.