Abstract
Measuring diameter change in flexible tubular structures embedded in opaque material is challenging. In this article, we present a soft braided coil embedded in an elastomer tube as a method to continuously measure such a change in diameter. By measuring the inductance change in the braided coil, we estimate the instantaneous diameter with a simple inductance model. In applying this method, we demonstrate that diameter waves in a vascular phantom, a model of a radial artery embedded in a viscoelastic wrist structure, can be recorded continuously. Four sensors were made, and their ability to measure physiologically relevant simulated pulse waves was assessed. Several pressure pulse profiles were generated using a precision digital pump. Inductance of the coil was measured simultaneously as the change in diameter was recorded using an optical laser/mirror deflection measurement. One sensor was then embedded in a vascular phantom model of the human wrist. The diameter of the simulated radial artery was recorded via ultrasound and estimated from coil inductance measurements. The diameter estimates from the inductance model corresponded well with the comparator in both experimental setups. We demonstrate that our method is a viable alternative to ultrasound in recording diameter waves in artery models. This opens opportunities in empirical investigations of physiologically interesting fluid-structure interaction. This method can provide new ability to measure diameter changes in tubular systems where access is obstructed.
Highlights
Measuring pressure propagation in soft tubular structures is of interest in the field of arterial mechanics, where pulse wave propagation can be studied to make conclusions about arterial function [1]–[3]
We investigated the flushed and pressurized phantom under ultrasound (Vivid E95, GE Healthcare) to compare the change in diameter of the embedded tube to that estimated from the inductance
The mean absolute error of the inductance estimate compared to the laser measurement ranged from 0.02 to 0.06 mm
Summary
Measuring pressure propagation in soft tubular structures is of interest in the field of arterial mechanics, where pulse wave propagation can be studied to make conclusions about arterial function [1]–[3]. In the case of radial tonometry, a technology that is seeing interest for applications in wearable blood pressure monitoring [7]–[9], the interaction between the vessel wall, the underlying bone, and the tissue between the vessel and skin surface are all important. This can be achieved by placing the vessel model inside tissue-mimicking material, obstructing view of the tube [10]. We propose a soft braided coil cast inside an elastomer tube wall as such a method. The coil is routed back and forth over the length of the tube section, resulting in a weaved braid pattern, as opposed to a sequentially stacked coil (Fig. 1)
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