In-silico and in-vitro investigation of a photonic monitor for intestinal perfusion and oxygenation

Abstract

Abstract:The quantification of visceral organ oxygenation after trauma-related systemic hypovolemia and shock is critical to enable effective resuscitation. In this work, a photoplethysmography-based (PPG) sensor was specifically designed for probing the perfusion and oxygenation condition of intestinal tissue with the ultimate goal to monitor patients post trauma to guide resuscitation. Through Monte Carlo modeling, suitable optofluidic phantoms were determined, the wavelength and separation distance for the sensor was optimized, and sensor performance for the quantification of tissue perfusion and oxygenation was tested on the in-vitro phantom. In particular, the Monte Carlo simulated both a standard block three-layer model and a more realistic model including villi. Measurements were collected on the designed three layer optofluidic phantom and the results taken with the small form factor PPG device showed a marked improvement when using shorter visible wavelengths over the more conventional longer visible wavelengths. Overall, in this work a Monte Carlo model was developed, an optofluidic phantom was built, and a small form factor PPG sensor was developed and characterized using the phantom for perfusion and oxygenation over the visible wavelength range. The results show promise that this small form factor PPG sensor could be used as a future guide to shock-related resuscitation.

In vivo performance of a visible wavelength optical sensor for monitoring intestinal perfusion and oxygenation

“…The sensor boards utilized were modified ADPD103Z boards from Analog Devices. 26 As mentioned above, conventional optical perfusion and oxygenation measurements utilize long visible and NIR wavelengths, which enable increased penetration depth for dense tissues. For the thin intestinal tissues, the photon penetration is too deep at these long wavelengths, resulting in high background signals and motion artifact.…”

“…The decrease in nonpulsatile signal intensity for the red signal results from the decrease in blood velocity, reducing both the alignment of the orientation of the red blood cells that increase reflected light as well as the expansion of the vessels. The effects seen with wavelength in vivo were also validated using the previously described optofluidic phantom 26 by altering the scattering properties of the blood phantom used. Comparing the blood phantom to the same phantom with the addition of aluminum oxide particles with an increasing flow rate yielded the signals in Fig.…”

“…To confirm that higher absorbance of blood at short wavelengths drives the signal generation, comparison of the flow in the vasculature was performed with the optofluidic phantom system, which mimics the flow through the small intestine. 26 While a comparison of the flow velocity through the cranial mesenteric artery to the optical signals would be ideal, it is difficult to correctly match pulses between the artery and the sensor, given the unknown vascular path length between the two points. The use of the in vitro system provided a defined path of fluid flow and a more reliable comparison of the flow to Fig.…”

“…Taking advantage of visible wavelengths and short source-todetector separations, a photoplethysmographic sensor has been designed, built, and validated in vitro to separate perfusion and oxygenation information acquired from the intestinal wall. 22,26 The use of visible wavelengths, with the increased scattering associated with shorter wavelengths and the increased absorbance of hemoglobin, confines photons within the perfused tissue and increases the hemoglobin signature in the collected optical signal. It is hypothesized that this sensor may be used to directly inform the physician on the resuscitation status via intestinal perfusion and oxygenation.…”