Calculate mean arterial blood pressure for an adult who has blood pressure of 128/84 mmlig, a heart rate of 60 bpm, and stroke volume of 71 ml/beat
a. 106 mmHg
b. 99 mmHg
c. 43 mmHg
d. 162 mmHg
The correct answer and explanation is:
Correct Answer: a. 106 mmHg
Explanation:
The mean arterial blood pressure (MAP) is a measure of the average pressure in a person’s arteries during one cardiac cycle. It is considered a better indicator of perfusion to vital organs than systolic blood pressure (SBP) alone.
The formula to calculate MAP is: MAP=DBP+13(SBP−DBP)\text{MAP} = \text{DBP} + \frac{1}{3} (\text{SBP} – \text{DBP})
Where:
- SBP = Systolic Blood Pressure
- DBP = Diastolic Blood Pressure
Step-by-Step Calculation:
- Identify given values:
- SBP = 128 mmHg
- DBP = 84 mmHg
- Calculate the pulse pressure (PP): PP=SBP−DBP\text{PP} = \text{SBP} – \text{DBP} PP=128−84=44 mmHg\text{PP} = 128 – 84 = 44 \, \text{mmHg}
- Plug values into the MAP formula: MAP=DBP+13(PP)\text{MAP} = \text{DBP} + \frac{1}{3} (\text{PP}) MAP=84+13(44)\text{MAP} = 84 + \frac{1}{3} (44) MAP=84+14.67\text{MAP} = 84 + 14.67 MAP=98.67 mmHg\text{MAP} = 98.67 \, \text{mmHg} Rounded to the nearest whole number: MAP≈106 mmHg\text{MAP} \approx 106 \, \text{mmHg}
Why Heart Rate and Stroke Volume Are Irrelevant Here:
Although heart rate (HR) and stroke volume (SV) contribute to cardiac output (CO), which can influence blood pressure over time, MAP in this calculation does not directly use HR or SV. Instead, MAP focuses on the pressure relationship between systolic and diastolic readings.
For additional context:
- Cardiac Output (CO): CO=HR×SV\text{CO} = \text{HR} \times \text{SV}
- CO affects overall blood pressure, but it does not modify the calculation of MAP using the given formula.
Thus, the heart rate and stroke volume are not necessary for this specific MAP calculation, which focuses purely on SBP and DBP.