Equations of Chemla et al for Estimating Mean Aortic Pressure

The authors studied the total area under the aortic blood pressure curve vs cardiac cycle, and they found that the usual formula for mean arterial pressure shows a bias that underestimates the mean aortic pressure by about 5 mm Hg.

mean aortic pressure in mm Hg =

= (diastolic blood pressure) + ((1/3) * (pulse pressure)) + 5 =

= ((systolic blood pressure) / 3) + (2 * (diastolic blood pressure) / 3) + 5

A second equation was derived with a form factor for use at the aortic root level. This form factor is strongly influenced by the patient's age, aortic pressure, and wave reflection.

mean aortic pressure in mm Hg =

= (diastolic systemic arterial pressure) + ((aortic form factor) * (pulse pressure))

= (diastolic systemic arterial pressure) + (0.45 * (pulse pressure))

Performance:

• The first equation is consistent with mechanical principles in the arterial system. It gives a more precise estimate of the mean aortic pressure in a resting human.

• The bias for the second equation is 0 to +2 mm Hg.