AVACEN embodies heat transfer research conducted at Stanford University by Dr. Craig Heller, Chair of Biological Sciences, and Dr. Dennis Grahn, Senior Research Scientist from the late 1990s to the present. The following highlight relevant research.
AVACEN restores normal core (central) body temperature in humans that are hypothermic or hyperthermic. It uses patented and tested technology that noninvasively heats or cools blood by influencing a unique set of subcutaneous vascular structures (arteriovenous anastomoses and venous plexuses) located in the glabrous areas of the body, primarily the palms of the hands. These vascular structures enable large volumes of blood to flow through the subcutaneous space. These structures provide a pathway for blood to flow directly from the heart (via arterial outflow) to the body surface and back to the heart (via venous return).
This radiator-like structure enables a thermal load to be transferred primarily to the blood rather than to the skin, muscle, and bone in other areas of the body. The limiting factor for heat transfer is vasomotor tone; vasocontriction shuts down heat transfer.
Citations
Insulation reduces heat exchange between a body and the environment. Glabrous (nonhairy) skin surfaces (palms of the hands, soles of the feet, face, and ears) constitute a small percentage of total body surface area but contain specialized vascular structures that facilitate heat loss. We have previously reported that cooling the glabrous skin surfaces is effective in alleviating heat stress and that the application of local subatmospheric pressure enhances the effect. In this paper, we compare the effects of cooling multiple glabrous skin surfaces with and without vacuum on thermal recovery in heavily insulated heat-stressed individuals...
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Grahn DA, Dillon JL, Heller HC. J Biomech Eng. 2009 Jul;131(7):071005.
PubMed PMID: 19640130.
Many individuals afflicted with multiple sclerosis (MS) experience a transient worsening of symptoms when body temperature increases due to ambient conditions or physical activity. Resulting symptom exacerbations can limit performance. We hypothesized that extraction of heat from the body through the subcutaneous retia venosa that underlie the palmar surfaces of the hands would reduce exercise-related heat stress and thereby increase the physical performance capacity of heat-sensitive individuals with MS. METHODS: Ten ambulatory MS patients completed one or more randomized paired trials of walking on a treadmill in a temperate environment with and without cooling...
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Grahn DA, Murray JV, Heller HC.BMC Neurol. 2008 May 12;8:14.
PubMed PMID: 18474113; PubMed Central PMCID: PMC2396661.
In situations where the accumulation of internal heat limits physical performance, enhanced heat extraction from the body should improve performance capacity. The combined application of local subatmospheric pressure (35-45 mmHg) to an entire hand (to increase blood volume) and a heat sink (18-22 degrees C) to the palmar surface were used to draw heat out of the circulating blood. Subjects walked uphill (5.63 km/h) on a treadmill in a 40 degree C environment...
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Grahn DA, Cao VH, Heller HC. J Appl Physiol. 2005 Sep;99(3):972-8. Epub 2005 May 5.
PubMed PMID: 15879169.
The combined application of subatmospheric pressure and heat to a forearm and hand has been previously reported to be an effective method for restoring normothermia in hypothermic postoperative patients. The objective of this study was to determine whether this technique also could be useful for the treatment of accidental hypothermia. Four otherwise healthy cold-stressed soldiers (core temperature <36.0 degrees C) were studied. In all four cases, application of the subatmospheric pressure induced an immediate local distention of the subcutaneous vasculature of the hand and fingers. Tympanic temperature reached a plateau in a normothermic range within 15 min in all subjects. The subjects also noted rapid elimination of shivering and improvement in subjective assessment of thermal comfort. These results are encouraging and warrant further investigation of the technique.
Grahn DA, Heller, HC. ITACCS Critical Care Monograph, Spring 2004.
The combined application of subatmospheric pressure and heat to a forearm and hand has been previously reported to be an effective method for restoring normothermia in hypothermic postoperative patients. The objective of this study was to determine whether this technique also could be useful for the treatment of accidental hypothermia. Four otherwise healthy cold-stressed soldiers (core temperature <36.0 degrees C) were studied. In all four cases, application of the subatmospheric pressure induced an immediate local distention of the subcutaneous vasculature of the hand and fingers. Tympanic temperature reached a plateau in a normothermic range within 15 min in all subjects. The subjects also noted rapid elimination of shivering and improvement in subjective assessment of thermal comfort. These results are encouraging and warrant further investigation of the technique.
Soreide E, Grahn DA, Brock-Utne JG, Rosen L.
J Emerg Med. 1999 Jul-Aug;17(4):725-30.
PubMed PMID: 10431966.
Peripheral vasoconstriction decreases thermal conductance of hypothermic individuals, making it difficult to transfer externally applied heat to the body core. We hypothesized that increasing blood flow to the skin of a hypothermic individual would enhance the transfer of exogenous heat to the body core, thereby increasing the rate of rewarming...
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Grahn D, Brock-Utne JG, Watenpaugh DE, Heller HC. J Appl Physiol. 1998 Nov;85(5):1643-8.
PubMed PMID: 9804564.
Tremors are common in mammals emerging from anesthesia. To determine whether appropriate thermal manipulations immediately before emergence from anesthesia are sufficient to eliminate these tremors, electroencephalographic (EEG) and electromyographic (EMG) activities, hypothalamic temperature (Thy), and O2 consumption were monitored in 12 rats recovering from halothane anesthesia under three thermal regimes. EEG and EMG activities were recorded throughout anesthesia and served as feedback signals for controlling anesthetic depth...
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Grahn DA, Heller MC, Larkin JE, Heller HC. J Appl Physiol. 1996 Dec;81(6):2547-54.
PubMed PMID: 9018505.
Patents
Grahn; Dennis A., Heller; H. Craig, inventors; The Board of Trustees of the Leland Stanford Junior University, assignee; Methods and devices for manipulating the thermoregulatory status of a mammal.
United States patent US 7,182,776. 2007 Feb 27.
Grahn; Dennis A., Heller; H. Craig, inventors; The Board of Trustees of the Leland Stanford Junior University, assignee; Methods and devices for prevention of hypothermia in a mammal during prolonged exposure to extreme cold.
United States patent US 6,673,099. 2004 Jan 6.
Grahn; Dennis A., Heller; H. Craig, inventors; The Board of Trustees of the Leland Stanford Junior University, assignee; Methods and devices for manipulating the themoregulatory status of a mammal.
United States patent US 6,602,277. 2003 Aug 5.
Grahn; Dennis A., Heller; H. Craig, inventors; The Board of Trustees of the Leland Stanford Junior University, assignee; Methods and devices for extracting thermal energy from the body core of a mammal.
United States patent US 6,656,208. 2003 Dec 2.
Grahn; Dennis A., Heller; H. Craig, inventors; The Board of Trustees of the Leland Stanford Junior University, assignee; Methods and devices for extracting thermal energy from the body core of a mammal.
United States patent US 6,974,442. 2005 Dec 13.
Grahn; Dennis A., Heller; H. Craig, inventors; The Board of Trustees of the Leland Stanford Junior University, assignee; Methods and devices for prevention of hypothermia in a mammal during prolonged exposure to extreme cold.
United States patent US 6,966,922. 2005 Nov 22.
Grahn; Dennis A., Heller; H. Craig, inventors; The Board of Trustees of the Leland Stanford Junior University, assignee; Controlled heat transfer with mammalian bodies.
United States patent US 7,122,047. 2006 Oct 17.
