[Cold tremor in unanesthetized, chronically spinalized rabbits as compared with cold shivering in intact animals]

Bioheat Transfer Basis of Human Thermoregulation: Principles and Applications

Thermoregulation is a process that is essential to the maintenance of life for all warm-blooded mammalian and avian species. It sustains a constant core body temperature in the face of a wide array of environmental thermal conditions and intensity of physical activities that generate internal heat. A primary component of thermoregulatory function is the movement of heat between the body core and the surface via the circulation of blood. The peripheral vasculature acts as a forced convection heat exchanger between blood and local peripheral tissues throughout the body enabling heat to be convected to the skin surface where is may be transferred to and from the environment via conduction, convection, radiation, and/or evaporation of water as local conditions dictate. Humans have evolved a particular vascular structure in glabrous (hairless) skin that is especially well suited for heat exchange. These vessels are called arteriovenous anastomoses (AVAs) and can vasodilate to large diameters and accommodate high flow rates. We report herein a new technology based on a physiological principle that enables simple and safe access to the thermoregulatory control system to allow manipulation of thermoregulatory function. The technology operates by applying a small amount of heating local to control tissue on the body surface overlying the cerebral spine that upregulates AVA perfusion. Under this action, heat exchangers can be applied to glabrous skin, preferably on the palms and soles, to alter the temperature of elevated blood flow prior to its return to the core. Therapeutic and prophylactic applications are discussed.

From Nanowarming to Thermoregulation: New Multiscale Applications of Bioheat Transfer

This review explores bioheat transfer applications at multiple scales from nanoparticle (NP) heating to whole-body thermoregulation. For instance, iron oxide nanoparticles are being used for nanowarming, which uniformly and quickly rewarms 50-80-mL (≤5-cm-diameter) vitrified systems by coupling with radio-frequency (RF) fields where standard convective warming fails. A modification of this approach can also be used to successfully rewarm cryopreserved fish embryos (∼0.8 mm diameter) by heating previously injected gold nanoparticles with millisecond pulsed laser irradiation where standard convective warming fails. Finally, laser-induced heating of gold nanoparticles can improve the sensitivity of lateral flow assays (LFAs) so that they are competitive with laboratory tests such as the enzyme-linked immunosorbent assay. This approach addresses the main weakness of LFAs, which are otherwise the cheapest, easiest, and fastest to use point-of-care diagnostic tests in the world. Body core temperature manipulation has now become possible through selective thermal stimulation (STS) approaches. For instance, simple and safe heating of selected areas of the skin surface can open arteriovenous anastomosis flow in glabrous skin when it is not already established, thereby creating a convenient and effective pathway to induce heat flow between the body core and environment. This has led to new applications of STS to increase or decrease core temperatures in humans and animals to assist in surgery (perioperative warming), to aid ischemic stress recovery (cooling), and even to enhance the quality of sleep. Together, these multiscale applications of nanoparticle heating and thermoregulation point to dramatic opportunities for translation and impact in these prophylactic, preservative, diagnostic, and therapeutic applications of bioheat transfer.

From Nanowarming to Thermoregulation: New Multiscale Applications of Bioheat Transfer

This review explores bioheat transfer applications at multiple scales from nanoparticle (NP) heating to whole-body thermoregulation. For instance, iron oxide nanoparticles are being used for nanowarming, which uniformly and quickly rewarms 50-80-mL (≤5-cm-diameter) vitrified systems by coupling with radio-frequency (RF) fields where standard convective warming fails. A modification of this approach can also be used to successfully rewarm cryopreserved fish embryos (∼0.8 mm diameter) by heating previously injected gold nanoparticles with millisecond pulsed laser irradiation where standard convective warming fails. Finally, laser-induced heating of gold nanoparticles can improve the sensitivity of lateral flow assays (LFAs) so that they are competitive with laboratory tests such as the enzyme-linked immunosorbent assay. This approach addresses the main weakness of LFAs, which are otherwise the cheapest, easiest, and fastest to use point-of-care diagnostic tests in the world. Body core temperature manipulation has now become possible through selective thermal stimulation (STS) approaches. For instance, simple and safe heating of selected areas of the skin surface can open arteriovenous anastomosis flow in glabrous skin when it is not already established, thereby creating a convenient and effective pathway to induce heat flow between the body core and environment. This has led to new applications of STS to increase or decrease core temperatures in humans and animals to assist in surgery (perioperative warming), to aid ischemic stress recovery (cooling), and even to enhance the quality of sleep. Together, these multiscale applications of nanoparticle heating and thermoregulation point to dramatic opportunities for translation and impact in these prophylactic, preservative, diagnostic, and therapeutic applications of bioheat transfer.

Hypothermia due to an ascending impairment of shivering in hyperacute experimental allergic encephalomyelitis in the Lewis rat

Severe hypothermia and an ascending impairment of shivering are previously undescribed clinical signs in hyperacute experimental allergic encephalomyelitis (EAE) in the Lewis rat. These occurred in hyperacute EAE induced by inoculation with guinea pig spinal cord homogenate and heat-killed Bordetella pertussis. Hypothermia was first detected on day 6-7 post-inoculation, within 12-24 h of the onset of neurological signs, and became more severe as the disease progressed. Rectal temperatures less than or equal to 30 degrees C were common at ambient temperatures of 19-22 degrees C. Shivering was assessed by palpation and by cold tremor electromyography. Shivering was absent in the tail by day 6-7 post-inoculation. The impairment then progressed to affect the hindlimbs, thorax and occasionally the forelimbs. Shivering was absent in hindlimbs with only mild or moderate weakness. Histological studies revealed perivascular inflammation with polymorphonuclear and mononuclear cells, oedema, fibrin deposition, haemorrhage, primary demyelination and axonal degeneration in the spinal cord, dorsal root ganglia and spinal roots. The brainstem was also involved but the cerebral hemispheres, including the hypothalamus, were spared. The close relationship between the severity of hypothermia and the extent of shivering impairment indicates that reduced shivering is an important cause of hypothermia in hyperacute EAE. It is concluded that this impairment of shivering is due not to hypothalamic damage but to lesions elsewhere in the central and peripheral nervous systems.

Spectral analysis of tremorine and cold tremor electromyograms in animal species of different size

In 14 mice (36.2 +/- 5.4 g), 17 rats (425 +/- 46.4 g), and 11 rabbits (3,200 +/- 340 g) a comparative electromyographic analysis of tremorine tremor and cold tremor was performed in gastrocnemius and tibialis anterior muscles using spectral analysis. The mean frequency of cold tremor decreased with increasing body weight (mice: 40.2 +/- 4.5 Hz; rats: 31.3 +/- 4.9 Hz; rabbits: 16.4 +/- 3.2 Hz). With tremorine tremor no such allometric correlation was found for tremor frequency and body weight (mice: 17.7 +/- 3.6 Hz; rats: 19.6 +/- 5.1 Hz; rabbits: 15.9 +/- 2.1 Hz). Cross spectral analysis revealed that during cold tremor the flexor muscle (tibialis anterior) and the extensor muscle (gastrocnemius) of rabbits are activated alternately. The mean phase shift between the activation of flexor and extensor muscle was -155.5 degrees. Stronger activation was observed in the flexor muscle. Tremorine tremor was characterized by synchronous activation of flexor and extensor muscles with a mean phase angle of 3.0 degrees and a predominance of the extensor muscle. The results suggest that the nervous mechanisms for the generation of tremorine tremor and cold tremor are different.

Initiation of muscle activity in spinalized pigeons during spinal cord cooling and warming

1. The effect of spinal cord temperature changes on muscle activity was investigated in unanaesthetized intact and chronically spinalized pigeons and in acutely spinalized pigeons which were artifically respirated and lightly anaesthetized with ether. 2. Spinal cord cooling regularly produced an increase in muscle activity and visible muscle tremor in intact and spinalized pigeons. This motor cold defence reaction was less intensive in spinalized animals, but was qualitatively identical in all groups with regard to spindle shaped firing patterns and grouped discharges. 3. Intravenous injection of 60-100 mg/kg L-Dopa enhanced the motor response to spinal cord cooling in acutely spinalized pigeons. It is suggested that L-Dopa may act on dopaminergic or noradrenergic neurones in the spinal cord. 4. The results demonstrate that the generation of the motor cold defence response to cooling of the spinal cord in pigeons is basically independent from supra-spinal nervous mechanisms. The decreased intensity of cold induced muscle activity in spinalized animals may be attributed to the loss of excitatory or disinhibitory descending inputs to the spinal cord. 5. Spinal cord warming above normal body temperature (41.5 degrees C) produced an increase in muscle activity and slow muscle movements. The pattern was qualitatively different from that of the cold induced tremor.

Patterns of differentiation in various sympathetic efferents induced by hypoxic and by central thermal stimulation in decerebrated rabbits

The patterns of regional changes of sympathetic efferent activity evoked by thermal stimulation of the spinal cord and by arterial and primary tissue hypoxia were investigated in decerebrated, anesthetized and immobilized rabbits. Decerebration was performed either at the mid- or infracollicular level. The responses of the decerebrated rabbits evoked by spinal thermal stimulation were the same as those of intact rabbits, i.e., splanchnic and cardiac sympathetic activity increased and cutaneous sympathetic activity decreased during warming, while the reverse response was elicited by cooling. It is concluded that the typical thermoregulatory response pattern of the sympathetic nervous system can be produced also after the loss of hypothalamic integration, i.e., by integrative mechanisms in the lower brain stem and the spinal cord. In contrast, the responses of decerebrated rabbits to arterial and primary tissue hypoxia differed from those of intact rabbits in that they consisted in an overall activation in all investigated sympathetic branches. It is confirmed by this result that suprabulbar integration is essential for the generation of the inhibitory components in the differential sympathetic responses to hypoxia, which typically consist in cutaneous and cardiac sympathetic inhibition with splanchnic activation during arterial hypoxia and in cutaneous sympathetic inhibition with cardiac and splanchnic sympathetic activation during primary tissue hypoxia.