Re-Evaluation of Arteriovenous Cooling of the Blood Supply to Human Brains

1999 ◽  
Author(s):  
Liang Zhu
Keyword(s):  
Heat Conduction ◽  
Heat Exchange ◽  
Carotid Artery ◽  
Body Core Temperature ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Arterial Blood ◽  
Radial Heat ◽  
Body Core ◽  
Vascular Geometry

Abstract The purpose of this work is to evaluate the capacity of the heat loss from the carotid artery in human brain and thus, to provide indirect evidence of the existence of selective brain cooling (SBC) in humans during hyperthermia. A theoretical model is developed to describe the effects of local blood perfusion and vascular geometry on the thermal equilibration in the carotid artery based on the blood flow measurements and the anatomical vascular geometry in the human neck. A theoretical approach is used to estimate the potential for cooling of blood in the carotid artery on its way to the brain by heat exchange with its countercurrent jugular vein and by the radial heat conduction loss to the cool neck surface. It is shown that the cooling of the arterial blood can be as much as 1.3 °C lower than the body core temperature, which is in agreement with previous experimental measurements of the temperature difference between the tympanic and body core temperatures. The model also evaluates the relative contributions of countercurrent heat exchange and radial heat conduction to selective brain cooling. It is found that these mechanisms are comparable with each other. Results of the present study will help provide a better understanding of the thermoregulation during hyperthermia. They can be used to guide the design of future experimental investigations of the mechanism of SBC.

Desaturation of exhaled air in camels

1981 ◽  
Vol 211 (1184) ◽  
pp. 305-319 ◽  
Keyword(s):  
Drinking Water ◽  
Heat Exchange ◽  
Body Temperature ◽  
Water Vapour ◽  
Mechanical Model ◽  
Ambient Air ◽  
Body Core Temperature ◽  
Hygroscopic Properties ◽  
Exhaled Air ◽  
Body Core

We have found that camels can reduce the water loss due to evaporation from the respiratory tract in two ways: (1) by decreasing the temperature of the exhaled air and (2) by removal of water vapour from this air, resulting in the exhalation of air at less than 100% relative humidity (r. h.). Camels were kept under desert conditions and deprived of drinking water. In the daytime the exhaled air was at or near body core temperature, while in the cooler night exhaled air was at or near ambient air temperature. In the daytime the exhaled air was fully saturated, but at night its humidity might fall to approximately 75% r. h. The combination of cooling and desaturation can provide a saving of water of 60% relative to exhalation of saturated air at body temperature. The mechanism responsible for cooling of the exhaled air is a simple heat exchange between the respiratory air and the surfaces of the nasal passageways. On inhalation these surfaces are cooled by the air passing over them, and on exhalation heat from the exhaled air is given off to these cooler surfaces. The mechanism responsible for desaturation of the air appears to depend on the hygroscopic properties of the nasal surfaces when the camel is dehydrated. The surfaces give off water vapour during inhalation and take up water from the respiratory air during exhalation. We have used a simple mechanical model to demonstrate the effectiveness of this mechanism.

Rectal temperature measurement results in artifactual evidence of selective brain cooling

2001 ◽  
Vol 281 (1) ◽  
pp. R108-R114 ◽  
Author(s):  
Shane K. Maloney ◽  
Andrea Fuller ◽  
Graham Mitchell ◽  
Duncan Mitchell
Keyword(s):  
Rectal Temperature ◽  
Brain Temperature ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Blood Temperature ◽  
Arterial Blood ◽  
The Status ◽  
Conscious Sheep ◽  
Surrogate Measures ◽  
Arterial Blood Temperature

Selective brain cooling (SBC) is defined as a brain temperature cooler than the temperature of arterial blood from the trunk. Surrogate measures of arterial blood temperature have been used in many published studies on SBC. The use of a surrogate for arterial blood temperature has the potential to confound proper identification of SBC. We have measured brain, carotid blood, and rectal temperatures in conscious sheep exposed to 40, 22, and 5°C. Rectal temperature was consistently higher than arterial blood temperature. Brain temperature was consistently cooler than rectal temperature during all exposures. Brain temperature only fell below carotid blood temperature during the final few hours of 40°C exposure and not at all during the 5°C exposure. Consequently, using rectal temperature as a surrogate for arterial blood temperature does not provide a reliable indication of the status of the SBC effector. We also show that rapid suppression of SBC can result if the animals are disturbed.

scholarly journals Cranial arterial patterns of the alpaca (Camelidae: Vicugna pacos )

2017 ◽  
Vol 4 (3) ◽  
pp. 160967 ◽  
Author(s):  
Haley D. O'Brien
Keyword(s):  
Carotid Artery ◽  
New World ◽  
Internal Carotid ◽  
Developmental Stages ◽  
Arterial System ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Vicugna Pacos ◽  
Cranial Arteries ◽  
Carotid Arterial

Artiodactyl cranial arterial patterns deviate significantly from the standard mammalian pattern, most notably in the possession of a structure called the carotid rete (CR)—a subdural arterial meshwork that is housed within the cavernous venous sinus, replacing the internal carotid artery (ICA). This relationship between the CR and the cavernous sinus facilitates a suite of unique physiologies, including selective brain cooling. The CR has been studied in a number of artiodactyls; however, to my knowledge, only a single study to date documents a subset of the cranial arteries of New World camelids (llamas, alpacas, vicugñas and guanacoes). This study is the first complete description of the cranial arteries of a New World camelid species, the alpaca ( Vicugna pacos ), and the first description of near-parturition cranial arterial morphology within New World camelids. This study finds that the carotid arterial system is conserved between developmental stages in the alpaca, and differs significantly from the pattern emphasized in other long-necked ruminant artiodactyls in that a patent, homologous ICA persists through the animal's life.

scholarly journals In Cold Blood: Intraarteral Cold Infusions for Selective Brain Cooling in Stroke

2014 ◽  
Vol 34 (5) ◽  
pp. 743-752 ◽  
Author(s):  
Elga Esposito ◽  
Matthias Ebner ◽  
Ulf Ziemann ◽  
Sven Poli
Keyword(s):  
Side Effects ◽  
Brain Temperature ◽  
Therapeutic Option ◽  
The Body ◽  
Global Cerebral Ischemia ◽  
Body Core Temperature ◽  
Whole Body ◽  
Brain Cooling ◽  
Stroke Patients ◽  
Selective Brain Cooling

Hypothermia is a promising therapeutic option for stroke patients and an established neuroprotective treatment for global cerebral ischemia after cardiac arrest. While whole body cooling is a feasible approach in intubated and sedated patients, its application in awake stroke patients is limited by severe side effects: Strong shivering rewarms the body and potentially worsens ischemic conditions because of increased O2 consumption. Drugs used for shivering control frequently cause sedation that increases the risk of aspiration and pneumonia. Selective brain cooling by intraarterial cold infusions (IACIs) has been proposed as an alternative strategy for patients suffering from acute ischemic stroke. Preclinical studies and early clinical experience indicate that IACI induce a highly selective brain temperature decrease within minutes and reach targeted hypothermia 10 to 30 times faster than conventional cooling methods. At the same time, body core temperature remains largely unaffected, thus systemic side effects are potentially diminished. This review critically discusses the limitations and side effects of current cooling techniques for neuroprotection from ischemic brain damage and summarizes the available evidence regarding advantages and potential risks of IACI.

Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep

2007 ◽  
Vol 293 (1) ◽  
pp. R438-R446 ◽  
Author(s):  
Andrea Fuller ◽  
Leith C. R. Meyer ◽  
Duncan Mitchell ◽  
Shane K. Maloney
Keyword(s):  
Drinking Water ◽  
Brain Temperature ◽  
Heat Exposure ◽  
Plasma Osmolality ◽  
Threshold Temperature ◽  
Evaporative Heat Loss ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Blood Temperature ◽  
Arterial Blood

By cooling the hypothalamus during hyperthermia, selective brain cooling reduces the drive on evaporative heat loss effectors, in so doing saving body water. To investigate whether selective brain cooling was increased in dehydrated sheep, we measured brain and carotid arterial blood temperatures at 5-min intervals in nine female Dorper sheep (41 ± 3 kg, means ± SD). The animals, housed in a climatic chamber at 23°C, were exposed for nine days to a cyclic protocol with daytime heat (40°C for 6 h). Drinking water was removed on the 3rd day and returned 5 days later. After 4 days of water deprivation, sheep had lost 16 ± 4% of body mass, and plasma osmolality had increased from 290 ± 8 to 323 ± 9 mmol/kg ( P < 0.0001). Although carotid blood temperature increased during heat exposure to similar levels during euhydration and dehydration, selective brain cooling was significantly greater in dehydration (0.38 ± 0.18°C) than in euhydration (−0.05 ± 0.14°C, P = 0.0008). The threshold temperature for selective brain cooling was not significantly different during euhydration (39.27°C) and dehydration (39.14°C, P = 0.62). However, the mean slope of lines of regression of brain temperature on carotid blood temperature above the threshold was significantly lower in dehydrated animals (0.40 ± 0.31) than in euhydrated animals (0.87 ± 0.11, P = 0.003). Return of drinking water at 39°C led to rapid cessation of selective brain cooling, and brain temperature exceeded carotid blood temperature throughout heat exposure on the following day. We conclude that for any given carotid blood temperature, dehydrated sheep exposed to heat exhibit selective brain cooling up to threefold greater than that when euhydrated.

Selective regulation of brain and body temperatures in the squirrel monkey

1983 ◽  
Vol 245 (2) ◽  
pp. R293-R297 ◽  
Author(s):  
C. A. Fuller ◽  
M. A. Baker
Keyword(s):  
Squirrel Monkey ◽  
Brain Temperature ◽  
Human Subjects ◽  
Venous Blood ◽  
The Body ◽  
Body Core Temperature ◽  
Saimiri Sciureus ◽  
Brain Cooling ◽  
The Face ◽  
Body Core

Many panting mammals can cool the brain below body core temperature during heat stress. Studies on human subjects suggest that primates may also be able selectively to regulate brain temperature. We examined this possibility by measuring hypothalamic (Thy) and colonic (Tco) temperatures of unanesthetized squirrel monkeys (Saimiri sciureus) in two different experiments. First, Thy and Tco were examined at four different ambient temperatures (Ta) between 20 and 36 degrees C. Over this range of Ta, Thy was regulated within a narrower range than Tco. In the cold Ta, Tco was lower than Thy; whereas in warm Ta, Tco was higher than Thy. Second, monkeys maintained at 35 degrees C Ta were acutely exposed to cool air blown on the face or abdomen. Air directed at the face cooled Thy more and faster than Tco, whereas air directed at the abdomen cooled Tco and Thy at the same rate. The second experiment was repeated in anesthetized animals with a thermocouple in the right atrium, and the results showed that this brain cooling was not produced by cooling of blood in the body core. These data demonstrate that the squirrel monkey is capable of selectively regulating Thy. Further the results suggest that venous blood returning from the face may be involved in selective brain cooling in warm environments.

scholarly journals Baroreceptor modulation of active cutaneous vasodilation during dynamic exercise in humans

2001 ◽  
Vol 90 (4) ◽  
pp. 1464-1473 ◽  
Author(s):  
Gary W. Mack ◽  
Doug Cordero ◽  
Jochen Peters
Keyword(s):  
Lower Body Negative Pressure ◽  
Human Subjects ◽  
Dynamic Exercise ◽  
Body Core Temperature ◽  
Arterial Blood ◽  
Cutaneous Vasodilation ◽  
Vasodilator Activity ◽  
Forearm Skin ◽  
Body Core ◽  
Cutaneous Vascular Conductance

The hypothesis that baroreceptor unloading during dynamic limits cutaneous vasodilation by withdrawal of active vasodilator activity was tested in seven human subjects. Increases in forearm skin blood flow (laser-Doppler velocimetry) at skin sites with (control) and without α-adrenergic vasoconstrictor activity (vasodilator only) and in arterial blood pressure (noninvasive) were measured and used to calculate cutaneous vascular conductance (CVC). Subjects performed two similar dynamic exercise (119 ± 8 W) protocols with and without baroreceptor unloading induced by application of −40 mmHg lower body negative pressure (LBNP). The LBNP condition was reversed (i.e., either removed or applied) after 15 min while exercise continued for an additional 15 min. During exercise without LBNP, the increase in body core temperature (esophageal temperature) required to elicit active cutaneous vasodilation averaged 0.25 ± 0.08 and 0.31 ± 0.10°C (SE) at control and vasodilator-only skin sites, respectively, and increased to 0.44 ± 0.10 and 0.50 ± 0.10°C ( P < 0.05 compared with without LBNP) during exercise with LBNP. During exercise baroreceptor unloading delayed the onset of cutaneous vasodilation and limited peak CVC at vasodilator-only skin sites. These data support the hypothesis that during exercise baroreceptor unloading modulates active cutaneous vasodilation.

Extracorporeal femoral to carotid artery perfusion in selective brain cooling for a giant aneurysm

2004 ◽  
Vol 100 (2) ◽  
pp. 343-347 ◽  
Author(s):  
Stephen P. Lownie ◽  
Alan H. Menkis ◽  
Rosemary A. Craen ◽  
Bernard Mezon ◽  
James MacDonald ◽  
...  
Keyword(s):  
Carotid Artery ◽  
Giant Aneurysm ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Artery Perfusion

Thermal signals in control of selective brain cooling

1994 ◽  
Vol 267 (2) ◽  
pp. R355-R359 ◽  
Author(s):  
G. Kuhnen ◽  
C. Jessen
Keyword(s):  
Body Temperature ◽  
Temperature Difference ◽  
Arteriovenous Shunt ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Whole Brain ◽  
Arterial Blood ◽  
The Brain ◽  
Internal Body

In species with a carotid rete, the arterial blood destined for the brain can be cooled on its passage through the rete. The temperature difference between the blood before the rete and the brain is termed selective brain cooling (SBC). The onset and degree of cooling depend on internal body temperature. The aim of this study was to determine the brain sites where the temperature signals driving SBC are generated. Thirty-six experiments were performed in three conscious goats, which were prepared with an arteriovenous shunt, carotid loops, and hypothalamic thermodes to manipulate the temperatures of the trunk (Ttr), the hypothalamus (Thyp), the extrahypothalamic brain (Texh), or the whole brain (Tbr). In all experiments, Ttr was clamped at 39.5 degrees C. The increase of SBC was 2.1 degrees C per 1 degree C increase of Tbr (gain = 2.1). The rise of Thyp at constant Texh yielded a gain of 1.6, whereas the gain of Texh at constant Thyp was 0.7. It is concluded that onset and degree of SBC are predominantly determined by temperature signals generated in the hypothalamus itself.

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