Peripheral Augmentation Index Defines the Relationship Between Central and Peripheral Pulse Pressure

Peripheral systolic blood pressure is amplified above central aortic systolic pressure, but the late systolic shoulder of the peripheral pulse may approximate central systolic pressure. Because late systolic pressure also determines the peripheral augmentation index, a measure of pressure wave reflection within the systemic circulation, this implies a direct relationship between amplification and augmentation. We compared the late systolic shoulder of the peripheral pressure waveform with estimates of central systolic pressure obtained using a transfer function in 391 subjects undergoing diagnostic coronary angiography and/or elective angioplasty (30% with insignificant coronary artery disease). In a subset (n=12) we compared the late systolic shoulder of the peripheral pulse with central pressure obtained with a catheter placed in the aortic root. Measurements were made at baseline, during atrial pacing, and during administration of nitroglycerin. Late systolic shoulder pressure closely approximated transfer function estimates of central pressure (R=0.96; P<0.0001; mean difference+/-SD: 0.5+/-5.2 mm Hg). Despite changes in waveform morphology induced by pacing and nitroglycerin (reducing mean values+/-SE of the augmentation index from 76+/-3.8% to 66+/-4.6% and 60+/-3.3%, respectively), there was close agreement between the late systolic shoulder of the peripheral pulse and measured values of central pressure (R=0.96; P<0.001; mean difference: 1.7+/-4.8 mm Hg). In conclusion, the late systolic shoulder of the peripheral pulse closely approximates central systolic pressure and peripheral augmentation index, the ratio of central:peripheral pulse pressure. Interventions to lower augmentation index and peripheral vascular resistance will have multiplicative effects in lowering central blood pressure.