Benchtop venous flow model to investigate mechanical factors influencing noninvasive venous waveform analysis (NIVA)

Abstract

Excessive IV fluid administration creates a hypervolemic state where fluid accumulates in the extravascular tissue, which adversely affects patient outcomes. GDFT has proven to reduce complications, but is still hamstrung by inadequate methods to guide fluid administration. NIVA is a noninvasive venous waveform analysis methodology that reveals elevated expression of higher pulse harmonics (f3-f8) in volume overloaded patients. We hypothesize that the changes in higher pulse harmonics captured by NIVA are a result of the intrinsic changes to the extravascular tissue in an edematous state. This study utilized porcine myocutaneous (PMF) flaps and artificial vessels to simulate a vein embedded in tissue. A physiological and a synthetic flow waveform were programmed into a pump to simulate venous flow. The PMF was subjected to a saline bath to simulate hypervolemia. Waveform capture on the pre-/post- bath PMF model showed an increase of 4.6% (p < 0.0001, n=15) in the relative power of higher pulse harmonics. The model also demonstrated that NIVA score and the power of f0 increases with flow rate (p < 0.0001, n = 5). The increase in %HF not only confirms that the extravascular tissue is a key factor in the generation of the higher pulse harmonics themselves, but also that volume status influences the amplification of the higher pulse harmonics. Additionally, the benchtop model showed that venous flow rate is one of the contributing factors to NIVA score. The benchtop model described in this study is further confirmation that NIVA can provide extravascular volume assessment.