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Overview :
Chemla et al developed 2 equations for estimating the mean
aortic blood pressure based on the measurement of systolic and diastolic
pressures. The authors are from Universite Paris XI, CHU Henri Mondor (Creteil),
Hopital Jean-Rostand (Ivry-sur-Seine) and CHU Xavier Bichat (Paris) in
France.
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.
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