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Research Papers: Max Jakob Award Paper

Heat Transfer in Health and Healing1

[+] Author and Article Information
Kenneth R. Diller

Department of Biomedical Engineering,
The University of Texas at Austin,
107 West Dean Keeton Street,
BME 4.202A,
Austin, TX 78712-1084
e-mail: kdiller@mail.utexas.edu

Max Jakob Award paper.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received November 21, 2014; final manuscript received April 1, 2015; published online June 2, 2015. Assoc. Editor: Terry Simon.

J. Heat Transfer 137(10), 103001 (Oct 01, 2015) (12 pages) Paper No: HT-14-1759; doi: 10.1115/1.4030424 History: Received November 21, 2014; Revised April 01, 2015; Online June 02, 2015

Our bodies depend on an exquisitely sensitive and refined temperature control system to maintain a state of health and homeostasis. The exceptionally broad range of physical activities that humans engage in and the diverse array of environmental conditions we face require remarkable strategies and mechanisms for regulating internal and external heat transfer processes. On the occasions for which the body suffers trauma, therapeutic temperature modulation is often the approach of choice for reversing injury and inflammation and launching a cascade of healing. The focus of human thermoregulation is maintenance of the body core temperature within a tight range of values, even as internal rates of energy generation may vary over an order of magnitude, environmental convection, and radiation heat loads may undergo large changes in the absence of any significant personal control, surface insulation may be added or removed, all occurring while the body's internal thermostat follows a diurnal circadian cycle that may be altered by illness and anesthetic agents. An advanced level of understanding of the complex physiological function and control of the human body may be combined with skill in heat transfer analysis and design to develop life-saving and injury-healing medical devices. This paper will describe some of the challenges and conquests the author has experienced related to the practice of heat transfer for maintenance of health and enhancement of healing processes.

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Figures

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Fig. 1

A pictorial representation of the skin areas involved in STS along the cervical spine and GSHT at the palms and plantar surfaces. An important feature is that STS and GSHT occupy only minor fractions of the total body surface area, providing minimal interference with other simultaneous medical procedures.

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Fig. 2

Temperatures on the skin overlying the cervical spine and the fourth finger pad and concurrent blood perfusion values in the middle index finger (glabrous skin) and the matching medial aspect of the forearm (nonglabrous skin) during a neck heating trial to stimulate GSBF. Temperatures are in the upper pane and blood flow in the lower pane.

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Fig. 3

Initial and stimulated finger pad CVC data as a function of application of neck heating stimulation for subjects exposed to room air at 22 °C. Open squares are for controls with no stimulation. Filled circles are for stimulation. Straight lines are linear least squares fits to the two data sets.

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Fig. 4

Time rate of change of finger pad CVC (TI) as a function of application of neck heating stimulation for subjects exposed to room air at 22 °C. Open squares are for controls with no stimulation. Filled circles are for stimulation.

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Fig. 5

Graphical representation of the connectedness among elements for the Wissler human thermoregulation finite difference model. The classic model has four additional elements for two hands and two feet [57].

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Fig. 6

Graphical representation of the control algorithm for blood flow to AVAs as a function of core and mean skin temperatures. Vasoconstriction occurs progressively below 28 °C mean skin temperature and 36 °C core temperature. Vasodilation occurs progressively above 38 °C core temperature. Normothermic perfusion exists for the plateau of states between these thresholds [57].

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Fig. 7

Effect on modulation of core temperature as a function of the magnitude of GSBF as a percent of CO to both hands and both feet with surface cooling at 22 °C [57]

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Fig. 8

Anesthesia-modified AVA perfusion control algorithm. Dashed line depicts the normal function. Vasodilation is elevated at normothermia and persists to lower core temperatures. Hysteresis occurs in transitions to normothermia. The mean skin temperature threshold states are unchanged [60].

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Fig. 9

Change in core temperature in response to forced air heating at 38 °C during spinal surgery with Propofol anesthesia [61]. Data points are from the clinical study without (lower) and with (upper) preheating. Solid lines are simulations for no external heating (bottom), interoperative heating (next higher), preheating + interoperative heating (next higher), and glabrous skin + interoperative heating (top) [60].

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Fig. 10

Data for a cryotherapy trial with a circulating ice water CTU applied to the shin area of the lower leg. The protocol consisted of 15 min of baseline data followed by active cooling for 40 min and passive rewarming for 90 min. The upper panel shows temperature histories measured at two locations on the skin under the water perfusion bladder. The lower panel shows two superficial (lower and upper) and one deep (middle) perfusion histories under the cooling bladder [76].

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Fig. 11

Hysteresis in local skin blood flow responding to falling and rising skin temperatures during cryotherapy for trials with two different devices and subjects (open circle and star symbols). Left data points are for cooling and right for warming. Owing to experimental time limitations, the cryotherapy cooling and heating cycles did not accommodate a complete return of perfusion to its baseline value during rewarming [76].

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Fig. 12

Temperature and blood perfusion histories for cyclic cooling and heating applied to the knee with a circulating ice water CTU and electric heater attached to the surface of the bladder. Following an initial period of baseline data collection, the protocol consisted of cycles of 30 min of active cooling and 10 min of active heating. The data show blood perfusions and temperatures at two locations on the skin beneath the bladder.

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Fig. 13

Finite difference simulation of heat penetration away from and into tissue during cyclic cooling and heating of the skin surface. Temperature histories are plotted at depth increments of 0.1 mm from the surface to 10.7 mm (outlined in red). The initial temperature is 34 °C followed by stepwise changes in the surface temperature between 15 °C and 40 °C.

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