Effects of temperature and PCO2 on O2 affinity of pigeon blood: implications for brain O2 supply

1985 ◽  
Vol 249 (6) ◽  
pp. R758-R764 ◽  
Author(s):  
B. Pinshow ◽  
M. H. Bernstein ◽  
Z. Arad
Keyword(s):  
Heat Exchangers ◽  
Venous Return ◽  
Brain Temperature ◽  
Columba Livia ◽  
Co2 Exchange ◽  
Arterial Blood ◽  
Effects Of Temperature ◽  
O2 Supply ◽  
The Brain ◽  
And Diffusion

Bird heads contain paired countercurrent heat exchangers, the ophthalmic retia, which function in brain temperature regulation. Blood, cooled by evaporation from the nasal and buccal mucosa and the ocular surfaces, flows to the venous side of each rete and there gains heat from arterial blood flowing countercurrent to it. The cooled arterial blood then flows to the brain. To ascertain whether characteristics of the blood reaching the cooling surfaces and the retia favor O2 and CO2 exchange, as well as heat exchange, we studied blood O2 affinity in relation to temperature (T) and CO2 tension (PCO2) in six pigeons (Columba livia). O2 tension (PO2) at half-saturation (P50, Torr) was measured at various combinations of T and PCO2 from 36 to 44 degrees C and 9 to 33 Torr. pH was uncontrolled. O2 half-saturation of hemoglobin (P50) varied according to P50 = 1.049T + 0.573PCO2–19.444. We propose that shifts in blood O2 affinity, associated with T and PCO2 at the mucosa and eyes and in the retia, would enhance the brain O2 supply by an exchange of O2 and CO2 between air and blood at moist cephalic surfaces, thereby augmenting O2 and reducing CO2 in the venous return to the retia and diffusion of O2 from veins to arteries in the retia. This mechanism might have particular importance at high altitude; we calculate that at 7,000 m above sea level both O2 saturation and PO2 could double in blood flowing from the retia to the brain.

Regulation of brain temperature in pigeons: effects of corneal convection

1982 ◽  
Vol 242 (5) ◽  
pp. R577-R581 ◽  
Author(s):  
B. Pinshow ◽  
M. H. Bernstein ◽  
G. E. Lopez ◽  
S. Kleinhaus
Keyword(s):  
Temperature Difference ◽  
Heat Sink ◽  
Brain Temperature ◽  
Columba Livia ◽  
Venous Flow ◽  
Conductive Heating ◽  
Arterial Blood ◽  
Flow Through ◽  
The Brain ◽  
Domestic Pigeons

The effect of direct ventilation of the eyes on cooling in the brain was investigated in domestic pigeons (Columba livia, mean mass 0.27 kg) with thermocouples chronically implanted in the hypothalamus and anterior eye chamber. During conductive heating in still air body-brain temperature difference (delta T) was 2.6 degrees C. During exclusive ventilation of ocular surfaces, with air flowing at about flight speed, delta T increased to 3.5 degrees C and returned to preventilation values on cessation of ventilation. When the eyes were sealed then ventilated, delta T was not different from that in still air. Administration of phenylephrine caused iridial vasoconstriction and a significant decrease in intraocular temperature, but no changes in brain temperature. This suggests that compensation may occur via other evaporating cranial surfaces. Our findings suggest that the eyes contribute to the control of brain temperature by dissipating heat. Blood cooled while flowing through the ocular vasculature apparently contributes to the venous flow through the ophthalmic rete, serving as a heat sink for arterial blood flowing to the brain.

Temperature Difference Between the Body Core and the Arterial Blood Supplied to the Brain During Hyperthermia or Hypothermia

2001 ◽  
Author(s):  
Liang Zhu ◽  
Maithreyi Bommadevara
Keyword(s):  
Blood Vessel ◽  
Temperature Difference ◽  
Carotid Arteries ◽  
Brain Temperature ◽  
Indirect Evidence ◽  
Blood Perfusion ◽  
The Body ◽  
Arterial Blood ◽  
Body Core ◽  
The Brain

Abstract In this study a theoretical model was developed to evaluate the temperature difference between the body core and the arterial blood supplied to the brain. Several factors including the local blood perfusion rate, blood vessel bifurcation in the neck, and blood vessel pairs on both sides of the neck were considered in the model. The theoretical approach was 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 shows that blood temperature along the common and internal carotid arteries typically decreases up to 0.86°C during hyperthermia. Selectively cooling the neck surface during hypothermia increases the heat loss from the carotid arteries and results in approximately 1.2°C in the carotid arterial temperature. This research could provide indirect evidence of the existence of selective brain cooling (SBC) in humans during hyperthermia. The simulated results can also be used to evaluate the feasibility of lowering brain temperature effectively by selectively cooling the head and neck surface during hypothermia treatment for brain injury or multiple sclerosis.

Heat loss from the human head during exercise

1991 ◽  
Vol 71 (2) ◽  
pp. 590-595 ◽  
Author(s):  
W. Rasch ◽  
P. Samson ◽  
J. Cote ◽  
M. Cabanac
Keyword(s):  
Respiratory Tract ◽  
Heat Loss ◽  
Brain Temperature ◽  
Human Head ◽  
Open Circuit ◽  
Heat Losses ◽  
Arterial Blood ◽  
Head Surface ◽  
The Brain ◽  
Expired Air

Evaporative and convective heat loss from head skin and expired air were measured in four male subjects at rest and during incremental exercise at 5, 15, and 25 degrees C ambient temperature (Ta) to verify whether the head can function as a heat sink for selective brain cooling. The heat losses were measured with an open-circuit method. At rest the heat loss from head skin and expired air decreased with increasing Ta from 69 +/- 5 and 37 +/- 18 (SE) W (5 degrees C) to 44 +/- 25 and 26 +/- 7 W (25 degrees C). At a work load of 150 W the heat loss tended to increase with increasing Ta: 119 +/- 21 (head skin) and 82 +/- 5 W (respiratory tract) at 5 degrees C Ta to 132 +/- 27 and 103 +/- 12 W at 25 degrees C Ta. Heat loss was always higher from the head surface than from the respiratory tract. The heat losses, separately and together (total), were highly correlated to the increasing esophageal temperature at 15 and 25 degrees C Ta. At 5 degrees C Ta on correlation occurred. The results showed that the heat loss from the head was larger than the heat brought to the brain by the arterial blood during hyperthermia, estimated to be 45 W per 1 degree C increase above normal temperature, plus the heat produced by the brain, estimated to be up to 20 W. The total heat to be lost is therefore approximately 65 W during a mild hyperthermia (+1 degrees C) if brain temperature is to remain constant.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Postischemic Canine Cerebral Blood Flow is Coupled to Cerebral Metabolic Rate

1991 ◽  
Vol 11 (4) ◽  
pp. 611-616 ◽  
Author(s):  
John D. Michenfelder ◽  
James H. Milde ◽  
Zvonimir S. Katušić
Keyword(s):  
Brain Temperature ◽  
Energy State ◽  
Reactive Hyperemia ◽  
Low Flow ◽  
Global Cerebral Ischemia ◽  
Flow State ◽  
Arterial Blood ◽  
Cerebral Ischemia And Reperfusion ◽  
Anesthetized Dogs ◽  
The Brain

Following complete global cerebral ischemia and reperfusion, a brief period of reactive hyperemia is followed by a prolonged period of low flow commonly referred to as the delayed postischemic hypoperfusion state. It is generally assumed that this low-flow state may be injurious because of inadequate substrate delivery, thus implying that flow is no longer coupled to metabolic needs. This relationship of CBF to CMRO2 was examined in six anesthetized dogs that were subjected to 12 min of complete ischemia induced either by CSF compression or aortic occlusion. Following reperfusion and onset of the low-flow state, which stabilized at 45 min postischemia, control normothermic (37°C) measurements of CBF and CMRO2 were determined. Thereafter, femoral arterial blood was circulated through a heat exchanger (42.5°C), and brain temperature was increased to 40°C and measurements were repeated. The brain was then cooled back to 37°C for a final set of normothermic measurements. Thereafter, brain biopsies were taken to determine the energy state of the brain. CMRO2 changed ∼6%/°C. CBF paralleled the change in CMRO2. Accordingly, the ratio of CBF to CMRO2 remained constant throughout at a value of 8 to 9, demonstrating maintained coupling. The brain energy state was normal at the end of the study. The authors conclude that postischemic CBF is modulated by the brain's metabolic needs.

scholarly journals Selective cooling of the brain in reindeer

1987 ◽  
Vol 253 (6) ◽  
pp. R848-R853 ◽  
Author(s):  
H. K. Johnsen ◽  
A. S. Blix ◽  
J. B. Mercer ◽  
K. D. Bolz
Keyword(s):  
Heat Stress ◽  
Nasal Mucosa ◽  
Venous Return ◽  
Brain Temperature ◽  
Open Mouth ◽  
Heating And Cooling ◽  
Stressed Animal ◽  
Facial Vein ◽  
Selective Cooling ◽  
The Brain

Cineangiographic examination of reindeer exposed to local (hypothalamic) or general heating and cooling revealed that the angular oculi veins are constricted during cold stress but dilated during heat stress. Moreover, during heat stress a segment of the facial vein appeared to be occluded, causing the cold venous return from the nasal mucosa to be routed directly to the cavernous sinus for selective cooling of the brain. Histological examination of the vasoactive segment of the facial vein showed unusually thick longitudinal and circular layers of smooth muscle cells. Obstruction of angular oculi blood flow by clamping of the veins in the heat-stressed animal resulted in an immediate rise in brain temperature. When reindeer under heat stress shift from closed- to open-mouth panting, only the expiratory phase of the respiratory cycle takes place through the mouth, whereas inspiration through the nose is continued. In this way, cooling of the nasal mucosa and, hence, cooling of the brain, is maintained.

The contribution of carotid rete variability to brain temperature variability in sheep in a thermoneutral environment

2007 ◽  
Vol 292 (3) ◽  
pp. R1298-R1305 ◽  
Author(s):  
Shane K. Maloney ◽  
Duncan Mitchell ◽  
Dominique Blache
Keyword(s):  
Blood Flow ◽  
Temperature Difference ◽  
Heat Production ◽  
Brain Temperature ◽  
Brain Blood Flow ◽  
Tight Coupling ◽  
Hypothalamic Temperature ◽  
Arterial Blood ◽  
Carotid Arterial ◽  
The Brain

The degree of variability in the temperature difference between the brain and carotid arterial blood is greater than expected from the presumed tight coupling between brain heat production and brain blood flow. In animals with a carotid rete, some of that variability arises in the rete. Using thermometric data loggers in five sheep, we have measured the temperature of arterial blood before it enters the carotid rete and after it has perfused the carotid rete, as well as hypothalamic temperature, every 2 min for between 6 and 12 days. The sheep were conscious, unrestrained, and maintained at an ambient temperature of 20–22°C. On average, carotid arterial blood and brain temperatures were the same, with a decrease in blood temperature of 0.35°C across the rete and then an increase in temperature of the same magnitude between blood leaving the rete and the brain. Rete cooling of arterial blood took place at temperatures below the threshold for selective brain cooling. All of the variability in the temperature difference between carotid artery and brain was attributable statistically to variability in the temperature difference across the rete. The temperature difference between arterial blood leaving the rete and the brain varied from −0.1 to 0.9°C. Some of this variability was related to a thermal inertia of the brain, but the majority we attribute to instability in the relationship between brain blood flow and brain heat production.

scholarly journals Guttural pouches, brain temperature and exercise in horses

2006 ◽  
Vol 2 (3) ◽  
pp. 475-477 ◽  
Author(s):  
Graham Mitchell ◽  
Andrea Fuller ◽  
Shane K Maloney ◽  
Nicola Rump ◽  
Duncan Mitchell
Keyword(s):  
Brain Temperature ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Free Living ◽  
Heat Injury ◽  
Blood Temperature ◽  
Arterial Blood ◽  
Exchange Function ◽  
The Brain ◽  
Arterial Blood Temperature

Selective brain cooling (SBC) is defined as the lowering of brain temperature below arterial blood temperature. Artiodactyls employ a carotid rete, an anatomical heat exchanger, to cool arterial blood shortly before it enters the brain. The survival advantage of this anatomy traditionally is believed to be a protection of brain tissue from heat injury, especially during exercise. Perissodactyls such as horses do not possess a carotid rete, and it has been proposed that their guttural pouches serve the heat-exchange function of the carotid rete by cooling the blood that traverses them, thus protecting the brain from heat injury. We have tested this proposal by measuring brain and carotid artery temperature simultaneously in free-living horses. We found that despite evidence of cranial cooling, brain temperature increased by about 2.5 °C during exercise, and consistently exceeded carotid temperature by 0.2–0.5 °C. We conclude that cerebral blood flow removes heat from the brain by convection, but since SBC does not occur in horses, the guttural pouches are not surrogate carotid retes.

Regional blood flow in the brain and spinal cord of hypothermic rats

1989 ◽  
Vol 257 (3) ◽  
pp. H785-H790
Author(s):  
T. Sakamoto ◽  
W. W. Monafo
Keyword(s):  
Spinal Cord ◽  
Blood Flow ◽  
Brain Stem ◽  
Regional Blood Flow ◽  
Experimental Conditions ◽  
Pentobarbital Sodium ◽  
Arterial Blood ◽  
Group A ◽  
Group B ◽  
The Brain

[14C]butanol tissue uptake was used to measure simultaneously regional blood flow in three regions of the brain (cerebral and cerebellar hemispheres and brain stem) and in five levels of the spinal cord in 10 normothermic rats (group A) and in 10 rats in which rectal temperature had been lowered to 27.7 +/- 0.3 degrees C by applying ice to the torso (group B). Pentobarbital sodium anesthesia was used. Mean arterial blood pressure varied minimally between groups as did arterial pH, PO2, and PCO2. In group A, regional spinal cord blood flow (rSCBF) varied from 49.7 +/- 1.6 to 62.6 +/- 2.1 ml.min-1.100 g-1; in brain, regional blood flow (rBBF) averaged 74.4 +/- 2.3 ml.min-1.100 g-1 in the whole brain and was highest in the brain stem. rSCBF in group B was elevated in all levels of the cord by 21-34% (P less than 0.05). rBBF, however, was lowered by 21% in the cerebral hemispheres (P less than 0.001) and by 14% in the brain as a whole (P less than 0.05). The changes in calculated vascular resistance tended to be inversely related to blood flow in all tissues. We conclude that rBBF is depressed in acutely hypothermic pentobarbital sodium-anesthetized rats, as has been noted before, but that rSCBF rises under these experimental conditions. The elevation of rSCBF in hypothermic rats confirms our previous observations.

Analysis of Whey Proteins Solubility at High Temperatures

2012 ◽  
Vol 8 (3) ◽  
Author(s):  
Daniela Helena Guimarães Pelegrine ◽  
Maria Thereza Moraes Santos Gomes
Keyword(s):  
Heat Exchangers ◽  
Protein Unfolding ◽  
Protein Solubility ◽  
Whey Proteins ◽  
Protein Isolate ◽  
Cow Milk ◽  
Ph Conditions ◽  
Effects Of Temperature ◽  
Ph Range ◽  
Integrated Study

Abstract This work showed the whey proteins solubility curves, according with temperature and pH conditions. The product constituted of a whey protein isolate obtained from cow milk (ALACENTM 895), acquired by New Zeland Milk Products Ltd. There is a straight analogy between fouling and protein unfolding when milk derived fluids are processed in equipments of heat exchangers, where whey proteins are unfolded in an irreversible way, exposing hidrophobic groups, and they become insoluble and form aggregates. An integrated study was conducted on the effects of temperature and pH on the solubility of whey proteins. The solubility was determined experimentally in the temperature range of 40-90 °C, and pH range of 5.0 - 6.8. The results showed that, both the temperature and pH influenced in the protein solubility; besides, the solubility values were minimum at the pH 4.0 for all temperature values. It was also observed that solubility decreased with temperature increased.

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