A disposable, flexible skin patch for clinical optical perfusion monitoring at multiple depths

Development and validation of quantitative optical index of skin blood content

SIGNIFICANCE

We present an approach to estimate with simple instrumentation the amount of red blood cells in the skin microvasculature, designated as parameter LRBC. Variations of parameter LRBC are shown to reflect local changes in the quantity of skin red blood cells during a venous occlusion challenge.

AIM

To validate a simple algebraic model of light transport in skin using the Monte Carlo method and to develop a measure of the red blood cell content in skin microvessels using the Monte Carlo predictions; to guide the development of an instrument to measure experimentally variations of the amount of red blood cells in the skin.

APPROACH

Monte Carlo simulations were carried out in a multilayer model of the skin to compute remitted light intensities as a function of distance from the illumination locus for different values of the skin blood content. The simulation results were used to compute parameter LRBC and its variations with local skin blood content. An experimental setup was developed to measure parameter LRBC in human volunteers in whom skin blood content of the forearm increased during temporary interruption of the venous outflow.

RESULTS

In the simulations, parameter LRBC was ∼16  μm in baseline conditions, and it increased in near proportion with the blood content of the skin layers. Measuring the diffusely reflected light intensity 0.5 to 1.2 mm away from the illumination locus was optimal to detect appreciable changes of the reflected light intensity as skin blood content was altered. Parameter LRBC measured experimentally on the human forearm was 17  ±  2  μm in baseline conditions it increased at a rate of 4  ±  2  μm  /  min when venous outflow was temporarily interrupted.

CONCLUSION

Parameter LRBC derived experimentally with a two-wavelength diffuse reflectometer can be used to measure local variations of the amount of red blood cells in skin microvessels.

Can Peripheral Skin Perfusion Be Used to Assess Organ Perfusion and Guide Resuscitation Interventions?

Although the definition of septic shock is straightforward, the physiological response to inadequate hemodynamics in patients with septic shock is variable. Therefore, the clinical recognition is limited not only by the patient's response but also by the clinical parameters we can use at the bedside. In this short overview we will argue that the state of the peripheral perfusion can help to identify and to treat patients with septic shock.

Compact dual-mode diffuse optical system for blood perfusion monitoring in a porcine model of microvascular tissue flaps

In reconstructive surgery, the ability to detect blood flow interruptions to grafted tissue represents a critical step in preventing postsurgical complications. We have developed and pilot tested a compact, fiber-based device that combines two complimentary modalities-diffuse correlation spectroscopy (DCS) and diffuse reflectance spectroscopy-to quantitatively monitor blood perfusion. We present a proof-of-concept study on an in vivo porcine model (n=8). With a controllable arterial blood flow supply, occlusion studies (n=4) were performed on surgically isolated free flaps while the device simultaneously monitored blood flow through the supplying artery as well as flap perfusion from three orientations: the distal side of the flap and two transdermal channels. Further studies featuring long-term monitoring, arterial failure simulations, and venous failure simulations were performed on flaps that had undergone an anastomosis procedure (n=4). Additionally, benchtop verification of the DCS system was performed on liquid flow phantoms. Data revealed relationships between diffuse optical measures and state of occlusion as well as the ability to detect arterial and venous compromise. The compact construction of the device, along with its noninvasive and quantitative nature, would make this technology suitable for clinical translation.

Novel diffuse optics system for continuous tissue viability monitoring - extended recovery in vivo testing in a porcine flap model

In reconstructive surgery, tissue perfusion/vessel patency is critical to the success of microvascular free tissue flaps. Early detection of flap failure secondary to compromise of vascular perfusion would significantly increase the chances of flap salvage. We have developed a compact, clinically-compatible monitoring system to enable automated, minimally-invasive, continuous, and quantitative assessment of flap viability/perfusion. We tested the system's continuous monitoring capability during extended non-recovery surgery using an in vivo porcine free flap model. Initial results indicated that the system could assess flap viability/perfusion in a quantitative and continuous manner. With proven performance, the compact form constructed with cost-effective components would make this system suitable for clinical translation.

In vivo preclinical verification of a multimodal diffuse reflectance and correlation spectroscopy system for sensing tissue perfusion

In reconstructive surgery, impeded blood flow in microvascular free flaps due to a compromise in arterial or venous patency secondary to blood clots or vessel spasms can rapidly result in flap failures. Thus, the ability to detect changes in microvascular free flaps is critical. In this paper, we report progress on in vivo pre-clinical testing of a compact, multimodal, fiber-based diffuse correlation and reflectance spectroscopy system designed to quantitatively monitor tissue perfusion in a porcine model's surgically-grafted free flap. We also describe the device's sensitivity to incremental blood flow changes and discuss the prospects for continuous perfusion monitoring in future clinical translational studies.

Design verification of a compact system for detecting tissue perfusion using bimodal diffuse optical technologies

It is essential to monitor tissue perfusion during and after reconstructive surgery, as restricted blood flow can result in graft failures. Current clinical procedures are insufficient to monitor tissue perfusion, as they are intermittent and often subjective. To address this unmet clinical need, a compact, low-cost, multimodal diffuse correlation spectroscopy and diffuse reflectance spectroscopy system was developed. We verified system performance via tissue phantoms and experimental protocols for rigorous bench testing. Quantitative data analysis methods were employed and tested to enable the extraction of tissue perfusion parameters. This design verification study assures data integrity in future in vivo studies.

A compact instrument to measure perfusion of vasculature in transplanted maxillofacial free flaps

The vascularization and resulting perfusion of transferred tissues are critical to the success of grafts in buried free flap transplantations. To enable long-term clinical monitoring of grafted tissue perfusion during neovascularization and endothelialization, we are developing an implantable instrument for the continuous monitoring of perfusion using diffuse correlation spectroscopy (DCS), and augmented with diffuse reflectance spectroscopy (DRS). This work discusses instrument construction, integration, and preliminary results using a porcine graft model.