Central Augmentation Index (CAI)

Patient examination: Determination of the central pressure waveform, either directly or noninvasively from a peripheral artery.

Parameters:

(1) systolic blood pressure in mm Hg

(2) diastolic blood pressure in mm Hg

(3) pressure at the first inflection point (peak or shoulder) in the central pressure waveform in mm Hg.

(4) pressure at the second inflection poin in the central pressure waveform in mm Hg

The non-systolic inflection point is the merging point of an incident and a reflected wave. In a healthy young adult the first inflection point is the systolic pressure peak and the second inflection point is seen on the downslope of the pulse waveform. In an older adult the first inflection point precedes the systolic inflection point.

pulse pressure =

= (systolic blood pressure) - (diastolic blood pressure)

augmentation pressure =

= (pressure at the second inflection point) - (pressure at the first inflection point)

augmentation index =

= (augmentation pressure) / (pulse pressure)

Interpretation:

• The augmentation index is typically negative in a healthy young adult and tends to increase with age.

• The greater the augmentation index the greater the arterial stiffness.

• The greater the augmentation index the greater the patient's risk for coronary artery disease, stroke and other vascular diseases.