WO2014176496A1

WO2014176496A1 - System and apparatus for simulating capillary refill

Info

Publication number: WO2014176496A1
Application number: PCT/US2014/035446
Authority: WO
Inventors: Alan W. EBERHARDT; Robert Clay SHELTON; Claire MCCALL; Mark Haynes; Satyam PATEL; J. Ashlyn MANZELLA; Nancy TOFIL
Original assignee: Uab Research Foundation
Priority date: 2013-04-26
Filing date: 2014-04-25
Publication date: 2014-10-30

Abstract

Provided in accordance with embodiments disclosed herein is a capillary refill simulation device that allows health care professionals to simulate capillary refill in a controlled simulator with life-like color change and temperature, as well as methods of use thereof.

Description

SYSTEM AND APPARATUS FOR SIMULATING CAPILLARY REFILL

STATEMENT OF GOVERNMENT SUPPORT

This invention was made in part with government support under grant number

309872.01.01.2005250.10 awarded by the National Science Foundation. The U.S. Government has certain rights to this invention.

BACKGROUND

Capillary refill is a technique used in the medical field, mainly in pediatrics, to determine the body temperature and current health status of a patient. When pressure is applied anywhere on the body, the blood that runs through the capillaries in that part of the body is expelled from the capillaries. When the pressure is released, there is a visible difference in skin coloration when that area is compared to its surrounding area. In a healthy individual, the blood will return to capillaries within 0.2-2 seconds. If the patient's body temperature is below normal body temperature (98.6° F) or if the patient is in shock, the blood may take up to 8 seconds to return to the capillaries and means that the patient is not experiencing normal blood flow. This indicates that immediate medical action needs to be taken. If the patient's body temperature is above normal body temperature, the blood may return slightly faster than that of a healthy person as long as the patient is not in shock. A capillary refill simulator would increase the realism of medical simulations and aid healthcare personnel training.

Capillary refill may be used to test for shock, dehydration, and proper blood flow to tissue throughout the body. The technique is mainly used in pediatric nursing because there are other techniques that can be used on adults that cannot be used on infants.

There is currently only one patient simulator on the market that can simulate capillary refill. It only uses lights to simulate the effect, so it is not very realistic and does not have the ability for the nurse to detect the temperature of the patient.

SUMMARY

Provided herein is a capillary refill simulation device. In some embodiments, the device includes one or more of : a liquid reservoir; a pump in fluid connection with the reservoir and configured to pump a liquid through a liquid conduit (e.g., tubing); a heating/cooling unit in fluid connection with the reservoir and configured to heat said liquid; a controller configured to control the heating cooling unit and/or pump; and a compressible capillary housing in fluid connection with the liquid conduit.

In some embodiments, the liquid is colored; and at least a portion of said compressible capillary housing is transparent or translucent.

In some embodiments, the device includes a hand or foot model comprising a palm and/or at least one digit having an outer surface and an inner surface, and the compressible capillary housing is attached to said palm and/or inner surface of said at least one digit in a compressible configuration.

In some embodiments, the compressible capillary housing comprises a capillary medium therein. In some embodiments, the capillary medium comprises a foam material. In some embodiments, the foam material is a continuous piece of uncompressed polyurethane memory foam.

In some embodiments, the hand or foot model is a model of a human neonate, infant or juvenile hand or foot.

In some embodiments, the device further comprises a model of a human infant or portion thereof comprising a sternum, said sternum having an inner and outer surface, and said compressible capillary housmg attached to the inner surface of said sternum in a compressible configuration.

In some embodiments, the liquid reservoir comprises a heater configured to heat said liquid to a temperature of from 92 to 102 degrees F.

In some embodiments, the device is a closed-loop system.

In some embodiments, the heater comprises resistors.

In some embodiments, the heating cooling unit comprises a cooler in fluid connection with said reservoir and configured to cool said liquid upon its return from said compressible capillary housing.

In some embodiments, the heating cooling unit comprises a thermoelectric cooler. In some embodiments, the thermoelectric cooler is situated between a first water block and a second water block, said first water block configured to heat the liquid prior to its entry into said compressible capillary housing, and said second water block configured to cool said liquid upon its return from said compressible capillary housing.

In some embodiments, the controller comprises a user interface.

In some embodiments, the device includes a liquid in said reservoir and/or said liquid conduit. Also provided is a capillary refill simulator system comprising a device as taught herein provided in a carrying case.

Further provided is a method for simulating capillary refill time, said method including: providing a device as taught herein, heating a liquid therein to a temperature of from 92 to 102 degrees F, and circulating said liquid through said compressible capillary housing, and then, compressing said capillary housing to at least partially empty the housing of the liquid, then releasing and measuring the refill time of said capillary housing, to thereby simulate capillary refill time.

In some embodiments, the heating comprises inputting a temperature on a user interface, said user interface operatively connected to at least one of the heater(s).

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain principles of the invention. The dimensions and features therein should be understood to be illustrative of approximate and exemplary values, and inclusive of equivalent features performing the same function as would be understood by a person skilled in the art.

Figure 1 presents a schematic of capillary refill simulation device according to some embodiments.

Figure 2A illustrates a capillary medium design having tubes, and Figure 2B illustrates a capillary medium design using a foam mesh.

Figure 3A illustrates a rectangular/square capillary housing design according to some embodiments. Figure 3B illustrates a flattened tube capillary housing design according to some embodiments. Figure 3C illustrates a mold that may be used to create a flattened tube capillary housing design according to some embodiments.

Figure 4 is a model of the capillary refill simulator design according to some embodiments.

Figure 5 presents a schematic of a capillary refill simulator design with a VDC pump.

Figure 6 presents a schematic showing main components of a capillary refill simulator design according to some embodiments.

Figure 7 presents a diagram of the temperature control sub-system that may be implemented according to some embodiments (controller/power supply connections not shown).

Figure 8 presents a schematic representation of the controller system according to some embodiments. Figure 9 provides a detailed view of the user interface used to control the entire temperature-adjusting sub-system according to some embodiments.

Figure 10 presents a schematic implementation of a transistor circuit according to some embodiments.

Figure 11 provides a summarization of the processor duties in the temperature control sub-system.

Figure 12 illustrates a user interface for the simple alternative design for the controller. Figure 13 illustrates an integrated circuit implementation of the alternative design of the controller.

DETAILED DESCRIPTION OF EMBODIMENTS

In some embodiments, a self-contained, cost-effective, interchangeable device is provided that allows health care professionals to simulate capillary refill in a controlled simulator (e.g., neonate, infant, juvenile, young adult, and adult simulation models) with life-like color and temperature.

In some embodiments, the design uses a model hand or foot, for example, a modified Laerdal Sleeve, with liquid pump to simulate blood flow, and a liquid reservoir with a heater (e.g., a resistor system) to heat the liquid. The heated liquid also serves to heat the model hand or foot.

In some embodiments, the system serves to simulate the life-like mechanism of capillary refill with a variance in temperature, color, and/or rate of refill, and may be used to practice diagnosing medical conditions based on capillary refill time (CRT).

In some embodiments, the device simulates capillary refill on a medical training dummy. In some embodiments, the device is a fmger sleeve, however attaching the device to the palm of the hand or the sole of the foot would also be useful. In some embodiments, the device is removably attached to the dummy and has a lifelike appearance. When the "skin" is squeezed, it goes from pinkish/reddish to white and then back to flesh colored when the skin is released.

In some embodiments, capillary refill simulation includes multiple sites, e.g., the palm of the hand, as well as the thumb and middle finger on a hand dummy.

In some embodiments, the capillary housing may contain foam/mesh as a capillary medium that is selected based on durameter values similar to human skin and/or fingernail.

"Capillary refill time" or "CRT" is the rate at which blood refills empty capillaries. One way to measure CRT in a human is to hold a hand or foot higher than heart-level and press the soft pad of a finger, toe, etc., or a nail bed, until it turns white, and then measuring the time needed for the color to return once the pressure is released. See also U.S. Patent No. 8,802,017 to Messerget et al., and U.S. Application 2013/0018241 to Bezzerides et al., which are incorporated by reference herein in their entireties.

In newborn infants, CRT can be measured by pressing on the sternum and measuring the time to color return. Normal refill time is less than two seconds, or up to 3 seconds, though the test can be variable between different patients. In non-human animals such as dogs or cats, CRT can be assessed by pressing on gum tissue. Thus, though exemplary systems are shown with a hand simulator, simulators or models of other areas of the body may also be used with the system as taught herein.

In some embodiments, the device has a capillary housing that is attached to a simulated hand, foot, sternum, etc., in a compressible configuration, such that when the housing is squeezed or compressed, the liquid can be squeezed out and allowed to return upon release of the pressure, e.g., against an opposite side, or rigid core, or rigid piece of the simulated or modeled body part.

A "thermoelectric cooler" or "TEC" is a solid state device that creates a heat flux between two different materials on opposing sides of the device, resulting in a "hot" side and a "cold" side.

A "water block" is a type of heatsink that may be used to heat or cool a liquid.

The disclosures of all United States patent references cited herein are hereby incorporated by reference to the extent they are consistent with the disclosure set forth herein. As used herein in the description of the invention and the appended claims, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, the terms "about" and "approximately" as used herein when referring to a measurable value such as an amount of a compound, dose, time, temperature, and the like, is meant to encompass variations of 20%, 10%, 5%, 1%, 0.5%, or even 0.1% of the specified amount. Also, as used herein, "and/or" or "/" refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative ("or").

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the relevant art. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and/or clarity.

The capillary refill simulator may fit dummies ranging in size from preemie to adult. In some embodiments, the device fits dummies ranging in size from 1 to 10 years old.

In some embodiments, the device is configured to simulate capillary refill times of 0.2s-

8s with skin temperatures of 92°F-105°F. In some embodiments, the temperature has a range at the low end of 83-90 °F, a range at the high end of 92-99 °F, and a resting temperature of 91 °F. In some embodiments, the temperature may be in a range of about 70, 7₅ or 80, to 100, 105, or 110 °F.

In some embodiments, the flow system has one or more liquid flow control valves, such as pressure valves and/or volume valves that control the pressure and/or volume in the system and thus the rate of capillary refill modeled. A pressure detector and/or controller may be used, if desired. In some embodiments, the pressure detector and/or controller may detect the pressure and or volume and adjust the liquid input/output accordingly, to form a closed-loop system.

In some embodiments, the pressure may be applied at about 2.94* 104 Pa, or 4.26 psi.

The liquid may be any suitable liquid, and preferably is colored (e.g., red, orange, yellow, green, blue, indigo, violet, or some combination thereof). For example, the liquid may be red or pink-red in color. In some embodiments the liquid is automotive transmission fluid, which is red. In some embodiments, at least a portion of the tubing in which the colored liquid is flowing is transparent or translucent.

In some embodiments, the capillary refill time may be from 1 to 7 seconds.

As illustrated in Figure 1, provided herein according to some embodiments is a device for simulating capillary refill time (CRT), including: a liquid reservoir (10), and a reservoir heater (12) configured to heat a liquid (11) in said reservoir (10); a pump (20) in fluid connection with said liquid reservoir (10) and configured to pump the liquid through the device; at least two flow control valves (30) (e.g., pressure valve, volume valve, etc.), each of said valves in fluid communication with at least one of said pump (20) or said liquid reservoir (10), wherein said flow control valves (30) are connected with a liquid conduit (50), and wherein said flow control valves (30) are configured to regulate the liquid pressure and/or volume between them and in said liquid conduit (50).

As illustrated in Figures 2A and 2B, in some embodiments the medium could be a series of small silicon tubes paralleled together (58) (see Figure 2A), or a low to medium density foam (see Figure 2B), which could be white to simulate the whiteness of the finger when the skin is depressed. Either of these mediums would absorb and hold the liquid (11) flowing therethrough, but they would also allow the liquid (11) to drain out of the medium (56) when it is depressed, in some embodiments exposing a white base (57). When the pressure is released, the medium (56) would begin to absorb more of the liquid (1 1), in some embodiments returning to its original pinkish-reddish color.

As illustrated in Figures 3A and 3B, a capillary housing (55) is provided to enclose the capillary medium and direct the liquid flow into and out of the medium at an inlet (51) and outlet (52), respectively, and may be provided in a variety of shapes. It will be understood that the capillary housing (55) may contain multiple inlets (51) and outlets (52), and these may not necessarily be on opposite sides of the capillary housing (55) as illustrated. Figure 3A illustrates a substantially rectangular design, and Figure 3B shows an alternative flattened tube design that may be used according to some embodiments. The alternative capillary housing fabrication method is less complicated, and fabrication can be accomplished using only a mold (Figure 3C), a heat gun and a length of tubing such as plasticized PVC tubing.

With reference to Figure 4, in some embodiments, the liquid (11) (e.g., dyed water or other colored liquid) may be kept in a heated and insulated liquid reservoir (12) (e.g. , at about 92 °F) for use in the system. A pump (20) (e.g., centrifugal pump) will pump the liquid (11) from the reservoir (12) into a water block that is connected to the hot end of a thermoelectric cooler (TEC) in a TEC/waterblock sandwich (19), where, if needed, it will be heated past the reservoir temperature to the desired temperature set by the user. After being heated inside of the water block, it will be pumped into the capillary housing (55) where the simulation may be performed.

As illustrated in Figure 3B, the capillary housing (55) may be provided in some embodiments as a deformed, flexible PVC tube. In some embodiments, the capillary housing (55) may lined with open-cell polyurethane foam (PUR) as the capillary medium. The open cells allow for flexibility of the PUR as well as the ability for the PUR to absorb the liquid as it is pumped in; however, PUR does not absorb dyes after it has been manufactured, so a liquid having dye should not stain the PUR. With reference to Figure 5, after exiting the capillary housing (55), the liquid may travel into a second water block (16b) that is connected to the cold end of the TEC (15). where some of the heat left in the liquid will be regenerated back into the hot side of the TEC (15).

Because in some embodiments the foam can cause very low flow rates, which prevents the heated reservoir water from making it to the capillary mechanism, a bypass tube and valve (not shown) may be installed to keep the liquid (11) flowing. The liquid (11) is then pumped back into the reservoir (1₀), where the process repeats. In some embodiments, the pump speed may be controlled by a rheostat, and the TEC may be controlled by a microprocessor controller.

In some embodiments, the capillary refill speed would be controlled by a potentiometer. The temperature of the system could be controlled by using a thermoelectric cooler (TEC) (15) to both heat and cool the liquid very quickly and efficiently deliver the temperature differences. To heat the liquid, the thermoelectric cooler (15) can be connected with reverse polarity, and connected correctly to cool the liquid.

In some embodiments, as illustrated in Figure 5, the device has one or more controllers (60) that control the temperature and capillary refill time. The various controllers may be consolidated in a single unit or circuitry, or provided as two or more separate units or circuitries, or any other suitable architecture. In some embodiments, the device uses the pump (20), which may be a positive displacement or a centrifugal pump, to generate a higher pressure on one side of the system. The higher-pressure liquid would then flow through the tubing into a capillary medium to represent the very fine capillaries in the finger.

In some embodiments, red liquid in the liquid reservoir (10) is heated to about 88, 90, 92 or 94 °F. See Point 1 on Figure 5. The liquid is then pumped past temperature sensors (13) and through a resistance heater (14) where the temperature increases. See Points 2 and 3 on Figure S. At Point 4 on Figure 5, the warm liquid flows past additional temperature sensors (not shown) and through a water block (16a) that is attached to a thermoelectric cooler (TEC) (15). When necessary, the TEC (15) gives a final temperature adjustment. Then the liquid is at the desired temperature for the simulation (e.g., from 92-105 degrees F) and flows into the capillary housing (55), which in some embodiments may contain a foam or fiber mesh as a capillary medium (56). See Points 6 and 7 on Figure 5. After Point 7 on Figure 5, the liquid flows into a second water block (16b) which is attached to the other side of the TEC (15). This water block (16b) acts as the heat sink for the TEC (15) (see Point 8 on Figure 5) and the liquid flowing through it absorbs heat from the TEC (15). The liquid then returns to the reservoir (10) at Point 9 on Figure 5.

The controller (60), TEC (15), resistance heater (14) and pump (20) may be powered by a DC power supply (40) as denoted by the arrows on Figure 5. The controller (60) may be connected to the pump (20), TEC (15), resistance heater (14) and power supply (40) as denoted by the arrows on Figure 5. The controller (6Ό) in some embodiments contains a temperature controller, a capillary refill rate controller, and a power switch. In some embodiments, the temperature is programmed to deliver the requested temperature for a given simulation. In some embodiments, the capillary refill rate may be changed by using variable position switch to adjust the amount of power that the pump (20) receives. If an AC pump (20) is used, the only change to Figure 5 is that the DC power supply (40) is no longer used to power the pump (20).

Capillary Refill Sub-Systems

In some embodiments, the capillary refill simulator design may be represented by five interconnected sub-systems. The five sub-systems are outlined in Figure 6, and the components of each system are outlined in Table 1. Some components may be shared by several subsystems. For example, the liquid reservoir (10) and water blocks (16a, 16b) may be shared by both the pump and non-capillary tubing system and the heating and cooling system.

Table 1. Capillary refill simulator sub-system components.

Sub-Systems Pump and Non-Capillary Tubing System (100)

Components of this sub-system may include the pump (20), water blocks (16a, 16b), reservoir (10), and reservoir heater (12). Preferably, the pump (20) will be a water pump with a low maximum pressure, steady flow rate, and variable volumetric flow rate. For embodiments in which the capillary refill housing (55) will be attached to a patient simulator (70) lying on a hospital bed (80) (see Figure 4), the pump (20) may be capable of pumping liquid up at least 37 inches. In some embodiments, the pump (20) may be a centrifugal pump or a positive displacement pump. Pressure can be varied by changing the amount of power supplied to the centrifugal pump, while positive displacement bypass pumps operate at a set pressure. The type of pump power source may also be a factor in the pump selection process. A potential advantage of using a pump (20) that runs on direct current voltage (VDC) is that the voltage needed to run a VDC pump is lower than the voltage needed to run a pump that uses alternating current voltage (VAC). This implies that a VDC pump may be safer to use, especially when used around water. A potential advantage to using a VAC pump is that it may lower the cost of the simulator by allowing the use of a lower VDC power supply. Thus, in some embodiments a centrifugal VDC pump is used.

Low cost and high thermal conductivity may be considered when selecting the water blocks (16a, 16b). Only copper and aluminum water blocks are commercially available. In some embodiments, copper water blocks are used since copper alloys have thermal conductivity coefficients between 160-390 W/m. °C (Limited, G. D. (2012). CES Edupack 2012. Cambridge, United Kingdom). However, copper water blocks are expensive and choosing them would increase the cost of the simulator. Aluminum alloys have thermal conductivity coefficients between 76-235 W/m. °C (Limited, 2012), which is lower than the thermal conductivity coefficients of copper alloys. Aluminum alloys are also approximately one-third the cost of copper alloys, so using aluminum alloy water blocks would minimize the cost of the simulator.

When selecting a liquid reservoir (10), the reservoir's cost, ability to retain heat, and capability to hold liquid at 92°F-105°F may be considered. Preferably the reservoir (10) would be made of a material with a low thermal conductivity and/or with a thick cross-section to ensure that the liquid will retain its heat without having to constantly heat it. High-density polyethylene (HDPE) plastic buckets are very low-cost and have low thermal conductivity coefficients between 0.403-0.435 W/m.°C, which means they are good insulators, but they have a thin cross- section (Limited, 2012). This means that the reservoir (10) heat loss would be 173.7 W. This heat loss is undesirable because the chosen reservoir heater (12) would need to have a higher wattage to compensate for this loss, which would increase the cost of the reservoir heater (12). To address this problem, the reservoir (10) may include a small container, such as a bucket, placed inside of a larger container to increase thickness, and the area between the containers may be filled with and insulator, such as DAP® KWIK FOAM® Polyurethane Insulating Foam Sealant (spray foam insulation), to increase the insulation of the liquid. The thermal conductivity coefficient of polyurethane is 0.235-0.244 W/m. °C, which should reduce the reservoir (10) heat loss to 3.4W (Limited, 2012). Sub-Systems Capillary System (200)

Main components of the capillary sub-system (200) according to some embodiments are the capillary medium (56), and the capillary housing (55). Thickness, flexibility, and the ability to withstand pressure without deforming are preferred when selecting the capillary system components. Since the pump (20) in the system can cause comparatively high pressures inside of the liquid conduit (50) and housing (55), in some embodiments the components are designed to yield or leak before breaking. The thickness of these components in some embodiments is large enough to contain the internal pressures, but small enough to minimize costs.

In the case of capillary tubing as the capillary medium (56), the small diameter tubes inside of the housing (55) would be under the largest pressure, and wall thickness of these tubes may be adjusted, accordingly. The tubes should be thick enough not to rupture from the high internal pressures, but their flexibility must remain intact so that they can be easily squeezed by a human to expel the liquid from them during the simulation. The flow rate should also be controlled to ensure that the liquid (11) comes back into the tubes at the correct speed.

In the case of a foam or mesh as the capillary medium (56), the housing (55) would be under the most pressure, so the thickness of the medium (56) may need to be adjusted, accordingly. The housing (55) should be able to contain the high internal pressure without rupturing, but the housing (55) should also be able to be pressed by a human hand to expel the liquid from the capillary medium (56) inside of the housing (55). Similar to the capillary tubing form of capillary medium (56), the flow rate of the liquid should be controlled to prevent the liquid from refilling too quickly or too slowly.

Sob-Systems Heating and Cooling System (300)

The heating and cooling system (300) according to some embodiments includes the reservoir heater (12), resistance heater (14), thermoelectric cooler (15), and two water blocks (16a, 16b). In some embodiments, the heating system involves the use of a resistive heater (12) to maintain the reservoir (10) temperature at a constant 80, 85, 90, 92 or 94 °F, which would be the lowest temperature that would be expected out of the heating system. When higher temperatures are demanded from the system, a resistance heater (14) provides the extra energy required. A thermoelectric cooler (15) installed in line before the capillary system is used to make final temperature adjustments as needed. Having a method of cooling the system enables the user to change to liquid temperature during a simulation or to run multiple simulations in quick succession without overheating the liquid. In some embodiments, the thermal efficiency of the thermoelectric cooler (15) may be increased by sending the liquid (11) exiting the capillary system through a water block attached to the cold side of the thermoelectric cooler. The cold side of the thermoelectric cooler (15) would then absorb energy from the exiting liquid which would reduce the temperature difference between the hot and cold sides of the thermoelectric cooler. This prevents some of the energy bleeding from the hot side, through the thermoelectric cooler (15), and into the cool side. Thus, the efficiency of the thermoelectric cooler would increase.

Sub-Systems Controls (400)

In some embodiments, a temperature control system is integrated into the capillary refill simulator. This temperature-control sub-system would allow the user to accurately adjust the temperature at the test region of the capillary refill simulation. Preferably, the temperature of the test region should be adjustable from approximately 92°F (33.3°C) to 103°F (39°C).

According to some embodiments, as seen in Figure 7, an approach to address this integration involves adjusting the temperature of the test region by adjusting the temperature of the working liquid (11). In order to have the temperature of this liquid change accurately, a series of heating elements may be used. In total, the system may include a water reservoir (10), reservoir heater (12), and possibly the resistance heater (14). Use of these components may provide a system that can adjust the temperature of the working liquid (11) effectively and with the highest precision. In some embodiments, the entire system may calibrated to an accompanying control box (60) which works as a simple user interface to control the system.

Liquid Reservoir (10)

One of the main potential issues of the liquid temperature-adjusting design was that a large amount of time may needed to make significant temperature changes. In order to minimize the amount of temperature change needed to reach the input temperature, the liquid reservoir (10) and reservoir heater (12) therein may be used.

By using a reservoir heater (12), the liquid (11) returning from the system is able to be reheated to a minimum temperature. By adding this step to the heating process, a smaller amount of energy is required to be added to the system in order to achieve the desired temperature.

Another aspect of this part of the design is the liquid reservoir (10) itself. Although the temperature of the liquid (11) is changing, in some embodiments there is a relatively small amount of liquid (11) running through the system. In some embodiments, most of the volume of the liquid (11) is within the reservoir (10). The reservoir (10) that holds the liquid temperature may protect against extreme temperature fluctuations and achieve and maintain the overall equilibrium of the system in a more efficient manner.

Heating/Cooling Unit (18)

The heating cooling unit (18) provided according to some embodiments is a component of the heating and cooling sub-system (300), and may include a thermoelectric cooler (TEC) (15) sandwiched between two water blocks (16a, 16b), as seen in Figure 7 (e.g., the TEC/waterblock sandwich (19) in Figure 4). The tubing (17a, 17b) within the water blocks (16a, 16b) may be made of metal such as copper if an increase in heat transfer at these regions is desired (otherwise made of other materials, such as normal silicone tubing).

In some embodiments, the liquid (11) entering the heating/cooling unit (18) during use will have a temperature of 80, 85, 90, 92 or 94 °F because the reservoir (10) holds this temperature. Thus, the TEC (15) will only need to heat the liquid entering the inlet water block. The amount of current required to accurately adjust for heat loss in order to achieve the user inputted temperature may be determined through a standard calibration process.

Along with using the generated temperature change from the TEC (15) to heat the inlet liquid, a regenerative effect also occurs from the tubing at the cold side (17b) to the tubing at the hot side (17a). The outlet water block (16b) is colder than the liquid (11) returning. Thus, there is a heat transfer effect that occurs from the liquid to the cold side of the TEC (15). Due to the nature of the TEC (15), this additional heat gain is pushed from the cold side to the hot side. This regenerative effect in turn improves the efficiency of the TEC (15). Another benefit is that heat is drawn from the liquid (1 1) before returning to the liquid reservoir (10). Therefore, the temperature of the returning liquid (11) should be less than or equal to the temperature of the liquid in the reservoir before entering the reservoir (10). This also may obviate a need to have a cooling mechanism of the liquid in the reservoir.

Major Heating Unit (14)

The resistance heater (14) provided according to some embodiments may include tubing (141), e.g., a metal tubing such as copper, or polymeric tubing such as silicone. The tubing (141) may be wrapped in resistive wire (142), such as nickel chromium resistive wire. A heat sink (143) and a fan (144) may also be included (Figure 7). A purpose of the major heating unit (14) is to heat the liquid (11) as quickly as possible. For situations where large temperature differences are required, the resistive wire (142) is activated by running a current through the wire (142). When active, the wire (142) begins to produce heat. The produced heat is then carried through the thermally conducting copper and absorbed by the flowing liquid (11). In the case where the user inputs a low temperature and the liquid is already heated to a high temperature, a heat sink (143) and fan (144) may be included to help reduce the temperature of the copper tubes (141). In some embodiments, during times where heat is added to the copper tubes (141), the fan (144) will not be on to maximize efficiency. Finally, the tubing (141) may be oriented in a zigzag pattern to allow for a larger surface area and an efficient way to cool the tubing (141).

Controller (60)

A purpose of the controller (60) is to efficiently adjust the temperature of the liquid (11) at the testing region(s), control the flow speed of the liquid (1 1) , and/or power the entire system on or off. A schematic design of the controller (60) according to some embodiments is outlined in Figure 8.

An exemplary user interface (61) that may be used according to some embodiments is shown in Figure 9. The controller (60) may include a user interface (61). In some embodiments, the controller (60) includes all of the integrated circuits used to control the temperature subsystem, which may include a microcontroller used to accurately control and hold the user inputted temperature at the test region(s). Flow Speed and Main Power

The flow speed of the liquid (11) in some embodiments may be controlled by a flow speed controller (611). Any suitable flow speed controller may be used. For example, the flow speed controller (611) may make use of a slider switch (Figure 9) which linearly changes to deliver a magnitude of current to the pump (10) and corresponds with the calibrated flow speed. Alternatively the flow speed controller (611) may make use of a rheostat (not shown). The flow speed controller (611) may be configured to adjust the current to the pump (10) linearly, meaning that a variable mediator unit (i.e., microcontroller) is not needed in order to carry out the task. In some embodiments, the maximum and minimum flow speeds may be set to 8.0s and 0.2s, respectively.

The main power switch (610) to the system is connected to the power supply (40) and is able to turn it on and off. In some embodiments, the power supply (40) powers the pump (10) (i.e., flow speed), the thermoelectric cooler (15), and the resistance heater (14), if used. In some embodiments, the only element not influenced by the main power switch (610) is the reservoir heater (12) within the liquid reservoir (10). By leaving a separate power switch (not shown) for the reservoir heater (12), the user can choose whether or not to leave the heater (12) on at all times without stressing the temperature control system to heat the liquid (11) from room temperature. This option allows for a more efficient use of energy and also a time-saving option to using the simulator.

Input Temperature

The input temperature interface (612) according to some embodiments is built up of a series of LED lights and switches. In some embodiments, as illustrated in Figure 9, there are two switches that control increasing the input temperature and two switches that control whether the input is in Celsius or Fahrenheit. There are sixteen LEDs that display the input temperature in digital form, and one LED that turns on when the test region has reached the input temperature. Because the input temperature and the switching elements are constantly changing the current input to the thermoelectric cooler (15), a microcontroller may be needed to control this type of interface. The input temperature display may also need to be controlled and interpreted by a microprocessor in order to function.

The microcontroller may be integrated into the system by comparing the temperature values of the input and the test region(s). Temperature sensors (not shown) record the values of test region temperature and relay them back to the microcontroller. The test region temperature is subtracted from the input temperature and the value of the difference determines the value of the current to be applied to the thermoelectric cooler (15). Due to the innovative design of the thermoelectric cooler and the principle of the regeneration of heat, the cold side of the TEC will reduce the temperature of the liquid inlet to the reservoir to less than or equal to the initial liquid reservoir temperature. Thus, in some embodiments the TEC (15) will always be adding heat to the system (through input current and regeneration).

Ultimately, the microcontroller will decode the input temperature f om input LED display and determine the test region temperature using the temperature sensor which is placed in the test region. The difference between these values determines the magnitude of change value. The magnitude change value is cross-referenced with a corresponding current input (which may be pre-defined during the calibration process), and this current input value is applied to the TEC (15). When the difference between the test region and the input temperature is close to zero (e.g., within one degree Fahrenheit), the "system ready" light (615) turns on, and the system is ready to be used (Figure 9). Finally, in order to maintain this temperature, in some embodiments the processor repeatedly runs the algorithm every 0.1 seconds and is able to adjust the current applied, if necessary. This microcontroller algorithm should be applied to an integrated circuit. The microcontroller code may be applied by using transistors, resistors and a variable switch. In some embodiments, as the microcontroller indicates the required current input, a non-changing step current is applied to the corresponding transistor by the processor. This action causes the transistor to close the circuit loop containing a voltage source (i.e., power supply) and a resistor. This activated circuit outputs the desired current to the TEC (15). If the applied current is needed to be changed, the microcontroller switches the transistor input, and the same process occurs again.

Microcontroller

A purpose of the microcontroller is to collect all the inputs (e.g., both analog and digital) and determine a suitable output (e.g., digital). The major inputs to the system are the user input temperature from the LED display and the temperature of the liquid at the capillary refill mechanism recorded by the thermistor. The microcontroller also allows information to be stored and accessed. This function is particularly useful for the LED display implementation because the microcontroller may be able to count up and down correctly, store initial values, and convert from Celsius to Fahrenheit and vice versa.

A microcontroller unit that may be used for this design is an Arduino Uno control board that includes 14 digital inputs and outputs (6 of which are pulse with modulation or PWM), 6 analog Inputs, and an ATmega32 microprocessor which has a clock speed of 16MHz. The board has an input of 7-12 VDC and will most likely draw 12VDC (Arduino). Since the DC pump will also be drawing this same voltage, the calibration of the mass flow rate of the system will be greatly simplified by inputting 12VDC across the board.

Many different microcontroller setups may be used, from a standalone RAM and microprocessor setups to other control boards. A design may include a PSOC board programmed using a C code to measure and set temperature for a high temperature oven (Random Canadian (2011). Precision Temperature Controller). A similar approach could be adapted to this system by adjusting voltage across the TEC instead of supplying voltage across a resistive heater.

The Arduino board may provide a simpler way to program a controller subsystem and is programmed using a high-level proprietary code (similar to C++) rather than C. Also, since the PSOC board was programmed for high temperature range measurements rather than high accuracy, the temperature calculations would have to be redone in the supplied C code which would increase the difficulty of the problem. The Arduino is preferred in some embodiments because it is the simplest microcontroller board that can achieve the same results as other boards. Thermistor (3-pin analog)

Any suitable temperature sensor may be used, for example, a thermistor resistor. A purpose of the thermistor is to accurately read the temperature at the capillary refill mechanism and relay that information back to the microcontroller. According to some embodiments, this device must relay the temperature data back to the controller roughly ten times faster than the propagation of the microcontroller.

An element selected to build the temperature sensor may be the L 35DT NOPB thermistor manufactured by Texas Instruments. The thermistor reads temperatures from 2 degrees Celsius to 150 degrees Celsius which is a large range for this capillary refill mechanism. However, with an approximate accuracy of 0.5 degrees Celsius per measurement (Texas Instruments, 2011. LM35 Datasheet. Literature Number:SNIS159B), the readings taken are still valid for a smaller range in temperatures. Thus, this thermistor is a reasonable choice for the capillary refill mechanism.

Some of the main selection criteria for the device according to some embodiments were accuracy, relay time, durability, and cost. Although devices like thermocouples also read temperature, these devices may not be ideal due to a high cost-to-accuracy ratio. In order to improve response time and durability, the thermistor may be attached to the bottom surface of the capillary refill mechanism (which has same temperature as the top surface) using a laser cut acrylic support and contact cement. These materials will protect the thermistor from external damage. By fixing the thermistor, the overall temperature reading accuracy is also maintained.

LED Displaver (3-pin digital)

In order for the 7-segment LED display to count correctly and display the desired temperature output, a master and slave chip setup may be used. The slave chip may be a MAX721 CNG with a 4-wire serial interface, and may be connected to a 4-digit, 7-segment LED display (the master chip may be the ATmega32 on the Arduino board) (Maxim, July 2003. Serially Interfaced, 8-Digit LED Display Drivers. 19-4452). This master-slave design may be particularly useful in embodiments having the complexity of the LED display in accordance with the up arrow, down arrow and also the Celsius to Fahrenheit converter switch. This design separates the display from the rest of the processor calculations and reduces the complexity of the main program. Although there are expected to be propagation delays, these delays will be undetectable for the purposes of this device. Another benefit to using a master-slave design is that multiple LED displays can be added later if needed without adjusting the main code. Thus, up to 8 7-segment displays can be supported by just adding a few lines of code. Transistor Circuit

The purpose of the transistor circuit is to work as a switch based on an on or off signal from the microcontroller. This circuit is made up of a transistor (switching element) and a driver to accurately and efficiently control the transistor element. Because the maximum input current of the TEC is 30A, the transistor must also be able to withstand this current.

Suitable design choices, particularly considering the cost, include the LT1910 High side MOSFET driver and the CSD16321Q5 N-channel MOS power transistor (Figure 10) (Linear Technology Corporation (2009). Protected High Side MOSFET Driver. LT0409 RevA) (Texas Instruments, May 2010. N-channel NexFET Power MOSFET. SLPS220B). These allow for a high current output without damaging the Arduino controller.

Flow Speed and Main Power

The flow speed of the liquid may be controlled by a rheostat, which linearly adjusts the magnitude of voltage to the pump which corresponds with the calibrated flow speed. The flow speed controller adjusts the voltage to the pump linearly, meaning that a variable mediator unit (i.e., microprocessor) is not needed in order to carry out the task. In some embodiments, the maximum and minimum flow speeds are 8.0s and 0.2s, respectively.

The main power switch to the system is connected to the power supply and is able to turn the power supply on or off. The power supply may be connected to power the pump (i.e., flow speed) and/or the thermoelectric cooler. In some embodiments, the only element that cannot be influenced by the main power switch is the water heater within the water reservoir. This separation may be desirable because the reservoir water would take a long time to heat to 92°F from room temperature. By leaving a separate power switch for the reservoir heater, the user can choose whether or not to leave the heater on at all times without stressing the temperature control system. This option allows for a more efficient use of energy and also a time-saving option to using the simulator. Input Temperature

Any suitable user interface may be used to receive an input temperature. For example, the input temperature interface may be built up of a series of LED lights and switches, with two switches that control increasing the input temperature and two switches that control whether the input is in Celsius or Fahrenheit. There may be sixteen LEDs that display the input temperature in digital form and one LED that turns on when the test region has reached the input temperature. Because the input temperature and the switching elements are constantly changing the current input to the thermoelectric cooler, a microprocessor may be needed to control this type of interface. The input temperature display may also need to be controlled and interpreted by the microprocessor.

The microcontroller may be integrated into the system by comparing the temperature values of the input and the capillary refill mechanism. The thermistor records the value of the capillary refill mechanism temperature and relays them back to the microcontroller. The capillary refill mechanism temperature is subtracted from the input temperature and the value of the difference determines the duty cycle of the transistor circuit in order to heat the working liquid accordingly. Due to the innovative design of the thermoelectric cooler and the principle of the regeneration of heat, the cold side of the thermoelectric cooler will reduce the temperature of the liquid inlet to the reservoir to <92°F. Thus, the thermoelectric cooler will always be adding heat to the system (through input current and regeneration).

Ultimately, the microcontroller will determine the input temperature from input LED display and determine the capillary refill mechanism temperature using the temperature sensor which is placed in the capillary refill mechanism. The difference between these values determines the magnitude of change value. The magnitude change value is cross-referenced with a corresponding duty cycle (pre-defined during the calibration process) and is applied to the thermoelectric cooler. When the difference between the capillary refill mechanism and the input temperature is close to zero {e.g., within one degree Fahrenheit), the "system ready" light turns on and the system is ready to be used (Figure 11). Finally, in order to maintain this temperature, the processor repeatedly runs the algorithm, e.g., every 0.1 second. Alternative Design

An alternative design of the user interface (61) is shown in Figure 12. Although the LED display design is aesthetic and highly functional, the simple objectives can be met by creating a manually-controlled input temperature interface (612). In some embodiments it includes at least five different output temperatures, which can be met by delivering different currents to the TEC (15) (as further discussed above). However, because the LED screen and the temperature sensor are not included in this design, the microprocessor is not needed for this to be functional. The currents are passed by a manually-controlled switch and varying resistive circuits (Figure 13). Sub-Systems: Power System (500)

In some embodiments, the power system (S00) is a 12V DC power supply (40) that may power both the pump (20) and the thermoelectric cooler (IS). The power supply (40) may also have a 5V DC output as well as a 3.3V DC output that can be used for the controller (60). In some embodiments, the power supply (40) chosen may be equipped with an overload safety such that, if a short circuit were to occur, all power would be removed from the pump (20), thermoelectric cooler (1₅), and controller (60). The present invention is further illustrated by the following non-limiting examples.

EXAMPLES

Example 1

A capillary refill simulator was made by modifying an existing mannequin hand (Laerdal) to allow CRT to be performed on two fingers and temperature to be sensed on the palm of the hand. The engineering design was divided into two subsystems: capillary refill and heating components. The capillary refill subsystem was created by using a submersible pump, tubing, and two fingernail cavities: one in the middle finger to represent normal/healthy and one in the thumb to provide shock CRT. In each finger there is a pacifier tip which serves as the refill cavity. Sponges were used to provide life-like feel to the cavities. A less absorbent sponge was added to the shock cavity to decrease the fill rate and thus slow the refill time. The "blood" is represented by transmission fluid, which was chosen for its high flash point to prevent potential electrical flammability, thermal conductivity to heat the sleeve adequately, and appropriate color. The heating component is a resistor-switch system wrapped in heat transfer tape and electrical tape and then secured to palm of the hand. There are two bundles of 8 resistors located in the palm of the hand that are attached to two switches connected to a rechargeable 3 V battery pack. Shock or cold temperature is modeled when the heating system is off. When one switch is on, it represents normal/healthy skin temperature of approximately 91°F. Two switches on provides heat to represent fever skin temperature of 99°F.

A bucket holding approximately 48 ounces of transmission fluid and a submersible aquarium pump as well as the battery pack were placed in a toolbox for ease of use. Two barb and 1 busing connectors were used to connect 5/8" tubing from the pump output to the ¼" tubing. The tubing runs to a nylon T-valve which allows the tubing to branch off into two differing fingers in the hand. The fluid returns through ¼" tubing from the fingers to a second nylon T-valve which allows one tube to return to the reservoir. Approximately six foot of tubing and wire allow the user to use the device at the foot or head of the model patient's bed. The entire refill system is stored in a toolbox. Illustrations and pictures of the system are shown in Figure 1.

Recognized limitations of the prototype include bulkiness of the liquid container, pump strength, durability of the heating component, time delay required for heating, and spilling of liquid.

Example 2

Fabrication of Capillary Housing

The first step of the construction phase was to create the capillary housing. Two versions of the capillary refill mechanism were fabricated during the build phase of this project. The first version of the capillary housing was made from a piece of PVC tubing. The housing consisted of a piece of 1 " inner diameter tubing that was flattened in the middle. The capillary medium would be inserted into the flattened section of the capillary housing. In order to flatten the tubing, a mold was created. (See Figure 3C) This would allow permanent shaping of the material when heat was applied and eliminated the need for any structures to maintain the desired shape. With these structures eliminated, it was hoped that the act of squeezing the housing and medium assembly would be easier and more lifelike.

Wooden molds with 0.020" stock left for finishing by sanding was machined. The molds were then sanded to size where the circumference at any given point was equal to the circumference of the inner diameter of the tubing. This prevented any stretching and unwanted deformation in the tubing and allowed the tubing to maintain its strength. The molds were then be inserted into the tubing and the shape verified. The tubing was then heated to its glass transition temperature (Tg) (approximately 85°C) and allowed to set. Heating to the T_g softened the polymer and allowed it to become leathery and pliable. The tubing was then cooled which allowed the new shape to become permanent. The molds were then removed.

After removing the molds, the ease at which the housing could be squeezed was observed. It was decided that the housing was not as easy to squeeze as hoped. The difficulty in squeezing the housing was attributed to the l/8in wall thickness of the tubing. Some extremely flexible 0.5in ID PVC tubing with a l/16in wall thickness had been purchased to run lines from the reservoir to the TEC/waterblock assembly. Because this tubing was very easy to squeeze, it was decided that the capillary refill mechanism housing should be made from apiece of this tubing. Reservoir Assembly

The reservoir consists of a ₅ gallon bucket and a large 18 gallon plastic bin. A large hole was drilled through both the bucket and the bin to allow tubing to be run through them. The bucket was then placed into the bin and insulating foam was sprayed into the open space of the bin to help keep heat inside the reservoir.

TEC Waterblock Assembly

A set of aluminum waterblocks and a Thermal Electric Device (TEC) were attached together by first cleaning the surface of the waterblocks using isopropyl alcohol and a non-lint cloth to remove any dust or grease from their surfaces. Thermal epoxy was then mixed and spread onto one side of the TEC, and a waterblock was placed on top of the paste. This procedure was done on the other side of the TEC with the second waterblock. Clamps were then placed around the assembly to hold it together, and it was also placed in front of a heater to allow the epoxy to harden and cure. After the epoxy was fully cured, the clamps were removed.

Capillary Mechanism Assembly

Assembling the capillary mechanism was a simple process. Pieces of foam were put inside the capillary refill mechanism housing. A one-way flow valve was connected to the capillary refill housing to prevent liquid from flowing back into the capillary mechanism. A short piece of tubing was connected after the flow valve. The inlet of the capillary refill mechanism tubing was connected to the barbed outlet of the hot side of the TEC/waterblock assembly. The outlet of the capillary refill mechanism tubing was connected to the barbed inlet of the cold side of the TEC/waterblock assembly. To decrease the likelihood that the connections would leak, all connections were clamped and sealed with silicone sealant.

A small piece of tubing with a valve was connected to the system on both sides of the capillary housing. This piece of tubing allows for controlled flow of the water in the system to help keep the water circulating throughout the system since the flow rate through the capillary housing is so low. Additionally, the extra flow rate allows for easier calibration of the capillary refill mechanism.

Assembly Details

The pump and the heater were placed inside of the reservoir. The pump's tubing and all of the wiring was run through the holes that were drilled in the reservoir and its insulated bin. The pump's tube, which is the only tube in the assembly with a different diameter than the rest, was connected to smaller diameter tubing. This smaller diameter tubing is 25 feet long and was connected to the 'entrance' of the hot side of the waterblock apparatus. The 'exit' of the hot waterblock was connected to the 'entrance' of the cold waterblock with the capillary housing connected in the middle of this tube. The 'exit' of the cold waterblock was connected back to the reservoir using another 25 feet of the small diameter tubing.

Changes Made to the Design During Construction

Two versions of the capillary refill mechanism have been fabricated during the build phase of this project. The first version of the capillary refill mechanism was fabricated by putting a mold inside of a 8in piece of lin ID plasticized PVC tubing and then heating it in a furnace until the material's temperature approached the material's glass transition temperature (approximately 85 °C). The group decided that this tubing was a little stiffer than desired, so this housing was scrapped. In its place, the group used a small portion of the highly plasticized tubing used throughout the rest of the design as the capillary housing.

Water was not circulating throughout the system due to the low flow rate caused by the foam in the capillary housing. A small piece of tubing with a valve on it was connected to the system on both sides of the capillary housing as a way to get controlled circulation throughout the system. This valve will remain locked in its calibrated position to keep the refill rates and water temperatures at their desired values.

It was found that if the water was left stagnant in the reservoir for too long, mold started to grow within the reservoir. Since the waterblocks are made of 6061 aluminum, it was decided that using a halogen (i.e., chlorine, iodine, bromine) would be a poor choice to keep the water clean because they would cause corrosive pitting in the waterblocks. Instead, it was decided that borax would be dissolved into the water to inhibit this unwanted growth. The system may also be flushed periodically with fresh water.

Testing and Revision

Testing was conducted in the polishing lab on the third floor of the BEC. While the controller was being built and tested, calibration was performed on the flow rates of the capillary housing. The system was filled with heated, dyed water from the reservoir using the pump and TEC. Polyurethane foams of different densities were placed inside the capillary housing, and the flow rates were tested to see how fast or slow the foam absorbed water at different pumping speeds. The foams were sometimes shoved into the housing, which left them in a compressed state, and other times they were inserted uncompressed. The foam was also tested using multiple pieces of foam compared with one large piece of foam to see how the refill rates reacted. After many hours of testing, it was decided that a large, continuous piece of uncompressed PUR memory foam gave the best refill rates.

Safety

Since water and electricity will be used so close together in this project, safety is a concern. To keep the water safely confined to the tubing, two clamps were placed at every junction point of the device to keep the water from leaking out. These junction points will also be sealed with a silicon coating, and the all of the tubing will be coated with insulating foam to help keep the heat and water in the system.

Some of the parts in the system can get extremely hot to the touch, so an acrylic box has been fashioned to house the power supply and some of the controller units to prevent burns. The fan on the power supply will be used in conjunction with a heat sink to help keep the transistor and other parts from overheating, which should also help prevent any heat related accidents from occurring.

With some tweaking to the control panel code, a "human pulse" can be created using the bilge pump by turning it on and off rather than having a continuous flow.

The foregoing is illustrative of the present invention, and is not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims

What Is claimed is;

1. A capillary refill simulation device, comprising:

a liquid reservoir;

a pump in fluid connection with, said reservoir and configured to pump a liquid through a liquid conduit;

a ^'heating/cooling unit in fluid connection with said reservoir and configured to heat said liquid:

a controller configured to control said heating/cooling unit and pump; and

a compressible capillary housing in fluid connection with said liquid conduit,

2. The device of claim 1 , wherein said liquid is colored; and at least a portion of said compressible capillary housing is transparent or translucent.

3. The device of claim 1 or claim 2, further comprising a hand or foot mode! comprising a palm and/or at least one digit having an outer surface and an inner surface, and said compressible capillary housing is attached to said palm and/or inner surface of said at least one digit in a compressible configuration.

4. The device of any of claims 1-3 , wherein the compressible capillary housing comprises a capillary medium therein,

5. The device of claim 4_? wherein said capillary medium comprises a foam material,

6. The device of claim 5_S wherein said foam material is a continuous piece of uncompressed poly rethane memory foam.

7. The device of any of claims 3-6. wherein said hand or foot model is a model of a human neonate, infant or juvenile hand or toot,

8. The device of any of claims 1-7. wherein the device further comprises a model of a human- infant or portion thereof comprising a sternum, said sternum having an inner and outer surface, and said compressible capillary housing attached to the inner surface of said sternum in a compressible configuration.

9. The device of any preceding claim, wherein said liquid reservoir comprises a heater configured to heat said liquid to a temperature of from 92 to 102 degrees F.

10. The device of any preceding claim, wherein said device is a closed-loop system, .11. The device of any preceding claim, wherein said heater comprises resistors.

12, The device of any. preceding claim, wherein said heating/cooling unit comprises a cooler in fluid connection with said reservoir and configured to cool said liquid upon its return from said compressible capillary housing.

13, The device of any preceding claim, wherein said heating cooling- nit comprises a thermoelectric cooler.

14, The device of claim 13, wherein said thermoelectric cooler is situated between a first water block and a second water block, said first water block configured to heat the liquid prior to its entry into said compressible capillary housing, and said second water block configured to cool said liquid upon its return from said compressible capillary housing.

15, The device of any preceding claim, wherein said controller comprises a user interface.

16, The device of any preceding claim, further comprising a liquid in said reservoir and/or said liquid conduit.

17, A capillary refill simulator system comprising the device of any of claims 1-36 provided in a carrying case.

18, A -method for simulating capillary refill time comprising:

providing a device- of any one of claims 1-17..

heating a liquid therein to a temperature of from 92 to 102 degrees F, and

circulating said Liquid through said compressible capillary housing, and then,

compressing said capillary housing to at least partially empty the ^'housing of the liquid, then releasing and measuring the refill time of said capillary housing,

to thereby simulate capillary refill time,

1 . The method of claim 18, wherein said heating comprises inputting a temperature on a user interface, said user interface operatively connected .to at least one heater.