ABSTRACT
Analytical solutions were developed based on the Green's function method to describe heat transfer in tissue including the effects of blood perfusion. These one-dimensional transient solutions were used with a simple parameter estimation technique and experimental measurements of temperature and heat flux at the surface of simulated tissue. It was demonstrated how such surface measurements can be used during step changes in the surface thermal conditions to estimate the value of three important parameters: blood perfusion (w(b)), thermal contact resistance (R"), and core temperature of the tissue (T(core)). The new models were tested against finite-difference solutions of thermal events on the surface to show the validity of the analytical solution. Simulated data was used to demonstrate the response of the model in predicting optimal parameters from noisy temperature and heat flux measurements. Finally, the analytical model and simple parameter estimation routine were used with actual experimental data from perfusion in phantom tissue. The model was shown to provide a very good match with the data curves. This demonstrated the first time that all three of these important parameters (w(b), R", and T(core)) have simultaneously been estimated from a single set of thermal measurements at the surface of tissue.
Subject(s)
Blood Circulation , Models, Biological , TemperatureABSTRACT
A new thermal perfusion probe operates by imposing a thermal event on the tissue surface and directly measuring the temperature and heat flux response of the tissue with a small sensor. The thermal event is created by convectively cooling the surface with a small group of impinging jets using room temperature air. The hypothesis of this research is that this sensor can be used to provide practical burn characterization of depth and severity by determining the thickness of non-perfused tissue. The measurement system was tested with a phantom tissue that simulates the blood perfusion of tissue. Different thicknesses of plastic were used at the surface to mimic layers of dead tissue. The sensor uses a parameter estimation procedure with analytical solutions of the Pennes bio-heat equation to determine effective values of blood perfusion, core temperature, and thermal contact resistance. Twelve different thicknesses of plastic were used along with three different flow rates of perfusate to simulate burned skin in the phantom perfusion system. The resulting values of thermal contact resistance for the complete set of measurements correlate well with the layer thickness. The values are also nearly independent of the flow rate of the perfusate, which shows that the parameter estimation can successfully separate these parameters. These results with simulated burns show the value of this minimally invasive technique to predict the burn depth in tissue.
ABSTRACT
This article discusses the data collection tool developed to investigate how patient flow is affected by the delivery of different types of care within Perioperative Services. To better understand the Perioperative Services processes, this study tracked staff members as they perform their activities. A challenging aspect of documenting the processes observed while tracking the Perioperative Services staff is to record the specific times and order in which the activities took place. The Perioperative Services is a fast-paced, dynamic environment where the staff members often perform multiple tasks that may also be interrupted, and each staff member may perform these tasks in their own sequence. To meet the needs of accurate data gathering, an iPhone/iPod Touch application was developed. It provides several advantages over the traditional paper/pencil method: (1) time stamps are instantaneous and consistent among the data collectors, (2) activities are entered via swipe-and-click capability, (3) multiple active tasks and interruptions can be tracked, and (4) collected data can be output to Microsoft Excel or Access for analysis. The "app" has proven to be useful in capturing data for our study. This technology can be customized and applied to similar settings at other hospitals.
