P167: Pulse Pressure Amplification and Augmentation Index Change in Opposite Manner with Arterial Stiffness Independently of Systemic Resistance

Abstract

Background

Pulse Pressure Amplification (PPA) is the increase in Pulse Pressure (PP) from proximal to distal arteries. The Augmentation Index (AIx) is the secondary increase in aortic pressure in systole relative to PP. With aging and increased arterial stiffness the PPA decreases while the AIx increases. Since both depend on the reflection of pressure waves, the finding that PPA and AIx change in opposite ways seems surprising.

Methods

Aortic PPA, AIx and Reflection Magnitude (RM = P_reflected/P_forward) were determined in a multibranched model and during control and Valsalva Maneuver in the human.

Results

During the Valsalva Maneuver reflections decrease: the lower mean arterial pressure results in lower stiffness and Pulse Wave Velocity (PWV) while Systemic Vascular Resistance (SVR) is increased. The model confirms that SVR plays a minimal role in terms of reflections. Reflections result from many reflections sites in the larger arteries. The lower PWV implies shorter wave length and thus artery length/wave length increases. This increase makes the differences in travel times from the many reflection sites to the heart more different resulting in lower total reflection: RM and AIx decrease. The lower PWV, thus the shorter wave length, also implies an increase in travel time over the aorta, and larger amplification. (It has been shown that local reflections change little with changes in stiffness.)

Conclusions

Reflections are mainly determined by travel times of reflected waves of the larger arteries. Mean pressure determines arterial stiffness and the stiffness change, via PWV, results in the opposite changes in RM and PPA.