How is mean arterial pressure calculated?

Mean arterial pressure (MAP) is an important physiological parameter that provides an average pressure in a person's arteries during one cardiac cycle. It is particularly significant because it accounts for the time the heart spends in diastole and systole, reflecting the perfusion pressure of vital organs more accurately than simple averages of systolic and diastolic pressures.

The correct calculation for MAP is given by the formula: MAP = (2/3 diastolic pressure) + (1/3 systolic pressure). This reflects the fact that the heart spends more time in diastole than systole during the cardiac cycle. In normal physiological conditions, the heart is in diastole about two-thirds of the time and in systole about one-third of the time. Therefore, weighting the diastolic pressure more heavily than the systolic pressure gives a more accurate representation of the average pressure experienced by the arterial system.

This knowledge is crucial for clinicians and medical students as it guides the assessment and management of patients, especially those with cardiovascular disease or those under critical care.

By contrast, the other choices do not accurately represent how MAP is calculated. The first option oversimplifies the calculation without considering the length of time the heart spends in each phase of the cardiac cycle.