title: Empirical estimates of mean aortic pressure: advantages, drawbacks and implications for pressure redundancy.
abstract: Mean arterial pressure (MAP) is estimated at the brachial artery level by adding a fraction of pulse pressure (form factor; =0.33) to diastolic pressure. We tested the hypothesis that a fixed form factor can also be used at the aortic root level. We recorded systolic aortic pressure (SAP) and diastolic aortic pressure (DAP), and we calculated aortic pulse pressure (PP) and the time-averaged MAP in the aorta of resting adults (n=73; age 43+/-14 years). Wave reflection was quantified using the augmentation index. The aortic form factor (range 0.35-0.53) decreased with age, MAP, PP and augmentation index (each P<0.001). The mean form factor value (0.45) gave a reasonable estimation of MAP (MAP=DAP+0.45PP; bias=0+/-2 mmHg), and the bias increased with MAP (P<0.001). An alternative formula (MAP=DAP+PP/3+5 mmHg) gave a more precise estimation (bias=0+/-1 mmHg), and the bias was not related to MAP. This latter formula was consistent with the previously reported mean pulse wave amplification of 15 mmHg, and with unchanged MAP and diastolic pressure from aorta to periphery. Multiple linear regression showed that 99% of the variability of MAP was explained by the combined influence of DAP and SAP, thus confirming major pressure redundancy. Results were obtained irrespective of whether the marked differences in heart period and extent of wave reflection between subjects were taken into account. In conclusion, the aortic form factor was strongly influenced by age, aortic pressure and wave reflection. An empirical formula (MAP=DAP+PP/3+5 mmHg) that is consistent with mechanical principles in the arterial system gave a more precise estimate of MAP in the aorta of resting humans. Only two distinct pressure-powered functions were carried out in the (SAP, DAP, MAP, PP) four-pressure set.
authors.affiliation: Services de Physiologie Cardio-Respiratoire et d'Anesthésie, CHU de Bicêtre, Université Paris XI, Assistance Publique-Hôpitaux de Paris, UMR 7639 CNRS-Loa-Ensta-Ecole Polytechnique, 94 275 Le Kremlin-Bicêtre, France. denis.chemla@bct.ap-hop-paris.fr
authors.forename: Denis
authors.initials: D
authors.lastname: Chemla
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Hébert
authors.forename: Eduardo
authors.initials: E
authors.lastname: Aptecar
authors.forename: Jean-Xavier
authors.initials: JX
authors.lastname: Mazoit
authors.forename: Karen
authors.initials: K
authors.lastname: Zamani
authors.forename: Robert
authors.initials: R
authors.lastname: Frank
authors.forename: Guy
authors.initials: G
authors.lastname: Fontaine
authors.forename: Alain
authors.initials: A
authors.lastname: Nitenberg
authors.forename: Yves
authors.initials: Y
authors.lastname: Lecarpentier
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D001011:Aorta / Q000502:physiology*; D001794:Blood Pressure; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D011446:Prospective Studies; D011673:Pulsatile Flow / Q000502:physiology; D012016:Reference Values